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Vitamin A

Vitamin A

Retinol, the dietary form of vitamin A, is a fat-soluble, antioxidant vitamin important in vision and bone growth. It belongs to the family of chemical compounds known as retinoids. Retinol is ingested in a precursor form; animal sources (milk and eggs) contain retinyl esters, whereas plants (carrots, spinach) contain carotenoids. Tissue cells convert these precursors to retinol, and then to either retinal or retinoic acid.

Chemical structure and function

Many different geometric isomers of retinol, retinal and retinoic acid are possible as a result of either a trans or cis configuration of the four double bonds found in the polyene chain. The cis isomers are less stable and can readily convert to the all-trans configuration (as seen in the structure of all-trans-retinol shown here). Nevertheless, some cis isomers are found naturally and carry out essential functions. For example, the 11-cis-retinal isomer is the chromophore of rhodopsin, the vertebrate photoreceptor molecule. Rhodopsin is comprised of the 11-cis-retinal covalently linked via a Schiff base to the opsin protein (either rod opsin or blue, red or green cone opsins). The process of vision relies on the light-induced isomerisation of the chromophore from 11-cis to all-trans resulting in a change of the conformation and activation of the photoreceptor molecule. One of the earliest signs of vitamin A deficiency is night-blindness followed by decreased visual acuity. retinoic acid functional group. The first full synthesis route for the compound was found by David Adriaan van Dorp and Jozef Ferdinand Arens in 1947.]] George Wald won the 1967 Nobel Prize in Physiology or Medicine for his work with retina pigments (also called visual pigments), which led to the understanding of the role of vitamin A in vision. Many of the non-visual functions of vitamin A are mediated by retinoic acid, which regulates gene expression by activating intracellular retinoic acid receptors. The non-visual functions of vitamin A are essential in the immunological function, reproduction and embryonic development of vertebrates as evidenced by the impaired growth, susceptibility to infection and birth defects observed in populations receiving suboptimal vitamin A in their diet. Retinol can also be used in the treatment of acne in a topical cream. A form of retinoic acid, all-trans retinoic acid (ATRA) is currently used as chemotherapy for acute promyelocytic leukemia, a subtype of acute myelogenous leukemia. This is because this transformed cells of this subtype respond in most cases to agonists of the retinoic acid receptor (RAR).

Dietary intake

During the absorption process in the intestines, retinol is incorporated into chylomicrons as the ester form, and it is these particles that mediate transport to the liver. Liver cells (hepatocytes) store vitamin A as the ester, and when retinol is needed in other tissues, it is de-esterifed and released into the blood as the alcohol. Retinol then attaches to a serum carrier, retinol binding protein, for transport to target tissues. A binding protein inside cells, cellular retinoic acid binding protein, serves to store and move retinoic acid intracellularly. Carotenoid bioavailability ranges between 1/5 to 1/10 of retinol's. Carotenoids are better absorbed when ingested as part of a fatty meal.

Topical use

All forms of vitamin A are used in cosmetic and medical applications applied to the skin. Retinoic acid, retinyl palmitate, isotretinoin, tretinoin and retinol are all used medicinally as a topical treatment for acne and keratosis pilaris. In cosmetics, vitamin A derivatives are used as so-called antiaging chemicals- vitamin A is absorbed through the skin and increases the rate of skin turnover, and gives a temporary increase in collagen giving a more youthful appearance.

Vitamin A deficiency

collagen] Vitamin A deficiency is common in developing countries but rarely seen in developed countries. Approximately 250,000 to 500,000 malnourished children in the developing world go blind each year from a deficiency of vitamin A. Night blindness is one of the first signs of vitamin A deficiency. Vitamin A deficiency contributes to blindness by making the cornea very dry and damaging the retina and cornea. Vitamin A deficiency diminishes the ability to fight infections. In countries where children aren't immunized, infectious disease like measles have relatively higher fatality rates. Subclinical deficiency can also be a problem as it may increase children's risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness. Iron deficiency can also affect vitamin A uptake. Excess alcohol consumption can deplete vitamin A, however a stressed liver may be more susceptible to vitamin A toxicity. People that consume large amounts of alcohol should seek medical advice before taking vitamin A supplements.

Vitamin A overdose

Too much vitamin A can be harmful or fatal. The body converts the dimerized form, carotene, into vitamin A as it is needed, therefore high levels of carotene are not toxic compared to the ester (animal) forms. The livers of certain animals, especially those adapted to polar environments, often contain amounts of vitamin A that would be toxic to humans. The first documented death due to vitamin A poisoning was Xavier Mertz, a Swiss scientist who died in January 1913 on an Antarctic expedition that had lost its food supplies and fell to eating its sled dogs. Mertz consumed lethal amounts of vitamin A by eating the dogs' livers. The liver of the polar bear also has enough vitamin A to kill a human being, or enough to make even sled dogs very ill. Excess vitamin A has also been suspected to be a contributor to osteoporosis. The carotenoid beta carotene was interestingly associated with an increase in lung cancer when it was studied in a lung cancer prevention trial in male smokers.

Closely related chemicals

- Isotretinoin (Tradename: Accutane)
- Retinyl palmitate (aka. "pro-vitamin A")
- All-trans retinoic acid

Genetically engineered vitamin A enriched rice

Due to the high prevalence of vitamin A deficiency in rice-eating societies, there are efforts to produce genetically modified rice rich in beta carotene. The golden rice project is one such effort, and is already undergoing trials.

External links

- [http://ods.od.nih.gov/factsheets/cc/vita.html NIH Office of Dietary Supplements - Vitamin A]
- [http://www.talkwellness.org/vitamina.html Vitamin A information]
- [http://www.biochemj.org/bj/348/0481/bj3480481.htm Retinol binding protein]
- [http://www.merck.com/mrkshared/mmanual/section1/chapter3/3b.jsp Merck Manual of Diagnosis and Therapy: Vitamin A Deficiency]
- [http://www.who.int/nut/vad.htm World Health Organization, Combating vitamin A deficiency]
- [http://www.westonaprice.org/men/vitaminabodybuilding.html Weston A. Price Foundation - Vitamin A: The Forgotten Bodybuilding Nutrient] Category:Vitamins Category:Alcohols ko:비타민 A ja:ビタミンA

Vitamin

A Vitamin is an organic molecule required by a living organism in minute amounts for proper health. An organism deprived of all sources of a particular vitamin will eventually suffer from disease symptoms specific to that vitamin. Vitamins can be classified as either water soluble, which means they dissolve easily in water, or fat soluble, which means they are absorbed through the intestinal tract with the help of lipids. In general, an organism must obtain vitamins or their metabolic precursors from outside the body, most often from the organism's diet. Examples of vitamins that the human body can derive from precursors include vitamin A, which can be produced from beta carotene; niacin from the amino acid tryptophan; and vitamin D through exposure of skin to ultraviolet light. The term, vitamin, does not encompass other essential nutrients such as dietary minerals, essential fatty acids or essential amino acids, nor is it used for the large number of other nutrients that are merely health promoting, but not strictly essential. The word vitamin was coined by the Polish biochemist Casimir Funk in 1912. Vita in Latin is life and the -amin suffix is short for amine; at the time it was thought that all vitamins were amines. Though this is now known to be incorrect, the name has stuck.

History

The value of eating certain foods to maintain health was recognized long before vitamins were identified. The ancient Egyptians knew that feeding a patient liver would help cure night blindness, now known to be caused by a vitamin A deficiency. In 1747, the Scottish surgeon James Lind discovered that citrus foods helped prevent scurvy, a particularly deadly disease in which collagen is not properly formed, and characterized by poor wound healing, bleeding of the gums, and severe pain. In 1753, Lind published his Treatise on the Scurvy. His discovery, however, was not widely accepted. In the Royal Navy's Arctic expeditions in the 19th century, for example, it was widely believed that scurvy was prevented by good hygiene on board ship, regular exercise, and maintaining the morale of the crew, rather than by a diet of fresh food, so that Navy expeditions continued to be plagued by scurvy. At the time Robert Falcon Scott made his two expeditions to the Antarctic in the early 20th century, the prevailing medical theory was that scurvy was caused by "tainted" canned food. In 1881, Russian surgeon Nikolai Lunin fed mice upon an artificial mixture of all the separate constituents of milk known at that time, namely the proteins, fats, carbohydrates, and salts. They died, while the mice fed by milk itself developed normally. He made a conclusion that "a natural food such as milk must therefore contain besides these known principal ingredients small quantities of unknown substances essential to life" [http://nobelprize.org/medicine/laureates/1929/hopkins-lecture.html] However, his conclusion was rejected by other researchers who were unable to reproduces his results. One difference was that he used table sugar (sucrose), while other researchers used milk sugar (lactose) which still contained small amounts of vitamin B. In 1905, William Fletcher discovered that eating unpolished rice instead of polished helped prevent the disease beriberi. The following year, Frederick Hopkins postulated that foods contained "accessory factors"—in addition to proteins, carbohydrates, fats, etc.—that are necessary to the human body. When Casimir Funk isolated the water-soluble complex of micronutrients whose bioactivity Fletcher had identified, he proposed that it be named "Vitamine". The name soon became synonymous with Hopkins' "accessory factors", and by the time it was shown that not all vitamins were amines, the word was already ubiquitous. In 1920, Jack Cecil Drummond proposed that the final "e" be dropped, to deemphasize the "amine" reference, after the discovery that vitamin C had no amine component, and the name has been "vitamin" ever since. Throughout the early 1900s, scientists were able to isolate and identify a number of vitamins by depriving animals of them. Initially, lipid from fish oil was used to cure rickets in rats, and the fat-soluble nutrient was called "antirachitic A". The irony here is that the first "vitamin" bioactivity ever isolated, which cured rickets, was initially called vitamine A, this bioactivity is now called vitamin D, which is subject to the semantic debate that vitamin D is not truly a vitamin because it is a steroid derivative. What we now call "vitamin A" was identified in fish oil because it was inactivated by ultraviolet light. Most of what we now recognize as the water-soluble organic micronutrients were initially referred to as just one entity, "vitamin B".

Human vitamins

In humans, there are thirteen vitamins, divided into two groups, the four fat soluble vitamins (A, D, E and K) and the nine water soluble vitamins (eight B vitamins and vitamin C). Some of the vitamins are known by other names in older literature. Vitamin B₂ is also referred to as Vitamin G. Vitamin B₇, or Biotin is also referred to as Vitamin H. Vitamin B₉, or Folic Acid is also referred to as Vitamin M. Vitamin B₃ is also referred to as "Vitamin PP", a name derived from the obsolete term "pellagra-preventing factor". Many other essential dietary substances were originally called vitamins and are now classified differently.

Vitamin deficiency and excess

An organism can survive for some time without vitamins, although prolonged vitamin deficit results in a disease state, often painful and potentially deadly. Body stores for different vitamins can vary widely; an adult may be deficient in Vitamins A or B₁₂ for a year or more before developing a deficiency condition, while Vitamin B₁ stores may only last a couple of weeks. Fat-soluble vitamins may be stored in the body and can cause toxicity when taken in excess. Water-soluble vitamins are not stored in the body, with the exception of Vitamin B₁₂, which is stored in the liver.

Pseudo-vitamins

- Vitamin F was the designation originally given to essential fatty acids that the body cannot manufacture. They were "de-vitaminized" because they are fatty acids. Fatty acids are a major component of fats which, like water, are needed by the body in large quantities and thus do not fit the definition of vitamins which are needed only in trace amounts.
- Although there is no Vitamin S, the suggestion has been made that salicylic acid may qualify for the criteria needed to be defined as a vitamin, and that in this case the designation "Vitamin S" could be used to describe it.
- Herbalists and naturopaths have named various herbs and chemicals "vitamins", even though they are not, including Vitamin T and Vitamin U.
- Some authorities say that Ubiquinone, also called Coenzyme Q₁₀, is a vitamin. Ubiquinone is manufactured in small amounts by the body, like Vitamin D.
- Pangamic acid and the related substance dimethylglycine are sometimes referred to as Vitamin B₁₅.
- Laetrile is sometimes referred to as Vitamin B₁₇. Both pangamic acid and laetrile were first proposed as vitamins by Ernst T. Krebs; neither are recognized by the medical community as vitamins.
- Flavonoids are sometimes called Vitamin P.
- A few substances were once thought to be B-complex vitamins and are referred to as B-vitamins in older literature, including B₄ (Adenine) and B₈, but are no longer recognized as such.

Colloquial usage of the term

- Likewise, Vitamin A and Vitamin C are sometimes used as slang terms for alcoholic beverages and caffeine, respectively.
- Biotin is sometimes referred to as Vitamin H.
- Vitamin I is a colloquialism for ibuprofen.
- Vitamin J has been used to refer to Jägermeister, which is a herbal liquor exported from Germany.
- The sedative Ketamine is often called Vitamin K when used as a recreational drug.
- Vitamin Love is mentioned in the Patti Page song, "I Don't Care if the Sun Don't Shine", referring to love itself.
- Vitamin W is a colloquialism for water.
- Vitamin V is a colloquialism for Viagra, Vitamin Z for Zoloft, and Vitamin R for Ritalin, especially when implying that these drugs are overprescribed (or, as a hyperbole, taken as commonly as vitamins).
- Colloquially, the word vitamin is often used to refer to vitamin supplements, products, often in pill form, that contain one or more purified vitamins which are used to supplement the vitamin content of a diet.

Non-human vitamins

Different organisms need different trace organic substances. Most mammals need, with few exceptions, the same vitamins as humans. One notable exception is Vitamin C (ascorbic acid); most mammals can synthesize this. The less related a species is to mammals, the more different the organisms' requirements become. For example, some bacteria need adenine. Pyrroloquinoline quinone (PQQ) was reported as a vitamin for mice in 2003. Housecats require the nutrient taurine; this makes it a vitamin for them, but not for humans as they can manufacture their own taurine, although like any internally formed nutrient, taking it directly usually has no harmful effects if done within reason.

References

- STEDMAN'S MEDICAL DICTIONARY. Ed. Maureen Barlow Pugh et.al. 27th ed. Baltimore: Lippincott Williams & Wilkins, 2000.
- Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005.
- Funk, C. and H. E. Dubin. The Vitamines. Baltimore: Williams and Wilkins Company, 1922.
- [http://www.cyber-north.com/vitamins/history.html The History of Vitamin Discovery]. Retrieved 1 Feb 2005.
- Bellis, Mary. [http://inventors.about.com/library/inventors/bl_vitamins.htm History of Vitamins]. Retrieved 1 Feb 2005.
- Challem, Jack (1997). [http://www.thenutritionreporter.com/history_of_vitamins.html The Past, Present and Future of Vitamins]. Retrieved 1 Feb 2005.
- Leonhardt, David (2004). [http://www.theallineed.com/health/04111401.htm Vitamin A - The Glow in the Dark Vitamin]. Retrieved 1 Feb 2005.

External links

- [http://www.nal.usda.gov/fnic/dga/rda.pdf USDA RDA chart in PDF format]
- [http://www.brain.riken.go.jp/labs/mdmd/pqq/index-e.html The lab which discovered the enzyme associated with PQQ]
- [http://faculty.washington.edu/ely/JOM5.html A Brief Update on Ubiquinone (Coenzyme Q10), Journal of Orthomolecular Medicine 2000; 15(2):63-68.]
- [http://www.vitaminsdiary.com/vitamins.htm#vitamins-chart Vitamins Chart]
- [http://www.best-home-remedies.com/vitamins/index.htm Vitamins (Co- Enzymes)]
- [http://www.vitaminstuff.com News and information on vitamins]
- [http://www.vitamins-minerals-supplements.org Vitamins, minerals and supplements ]
- [http://www.hc-sc.gc.ca/fn-an/nutrition/reference/table/ref_vitam_tbl_e.html Health Canada Dietary Reference Intakes Reference Chart for Vitamins] Category:Essential nutrients Category:Nutrition ko:비타민 ja:ビタミン th:วิตามิน

Antioxidant

An antioxidant is a chemical that prevents the oxidation of other chemicals. In biological systems, the normal processes of oxidation (plus a minor contribution from ionizing radiation) produce highly reactive free radicals. These can readily react with and damage other molecules: in some cases the body uses this to fight infection. In other cases, the damage may be to the body's own cells. The presence of extremely easily oxidisable compounds in the system can "mop up" free radicals before they damage other essential molecules. Food produces free radicals (oxidants) when metabolized, and virtually all studies of mammals have concluded that a restricted calorie diet extends the lifespan of mammals by as much as 100%. This remarkable finding suggests that food is actually more damaging than smoking which takes on average 25% of a person's lifespan. Antioxidant-rich diets are thought to stave off the effects of aging significantly better than calorie rich, vitamin poor diets. The following vitamins have shown positive antioxidant effects:
- Vitamin A (Retinol or beta-carotene) protects dark green, yellow and orange vegetables and fruits from solar radiation damage, and is thought to play a similar role in the human body. Carrots, squash, broccoli, sweet potatoes, tomatoes, kale, collards, cantaloupe, peaches and apricots are particularly rich sources of beta-carotene.
- Vitamin C (Ascorbic acid) is a water-soluble compound that fulfills several roles in living systems. Important sources include citrus fruits (such as oranges, sweet lime, etc.), green peppers, broccoli, green leafy vegetables, strawberries, raw cabbage and tomatoes. Linus Pauling was a major advocate for its use.
- Vitamin E, including Tocotrienol and Tocopherol, is fat soluble and protects lipids. Sources include wheat germ, nuts, seeds, whole grains, green leafy vegetables, vegetable oil, and fish-liver oil. Recent studies showed that some tocotrienol isomers have wonderful anti-oxidant properties.
- Selenium must be taken in measured amounts because large doses of the element can be toxic. Good food sources include fish, shellfish, red meat, grains, eggs, sunflower seeds, chicken, garlic, and brazil nuts. Vegetables can also be a good source if they are grown in selenium-rich soils. Some nutritional supplements contain beneficial amounts of Selenium, but the total intake must be regulated to avoid toxicity. Workers in Integrated Circuit fabrication have been known to develop toxic levels of Selenium through contact with chemicals used in industrial processes.
- Omega 3 fatty acids prevent the formation of atherosclerosis when they are taken in conjunction with antioxidants to prevent themselves being oxidised. It should also be noted that many dark berries, including pomegranate, noni, blueberries and blackberries have high concentrations of antioxidants, as do some types of tea, especially green tea. The FDA has recently suggested that Americans increase their natural antioxidant intake to 7000 ORAC units daily, which is nearly 12 servings of high ORAC value fruit, to help curb the cancer epidemic. In the absence of consumption of large amounts of antioxidant fruits, nutritional supplements can be used.(Editor's Note: I don't know how you could get this much ORAC value from eating fruit; you would almost certainly have to use nutritional supplementation.) Several food additives, including pectin, ascorbic acid (vitamin C) and tocopherol-derived compounds are used as antioxidants to help guard against food deterioration. Some enzymes are antioxidants, including glutathione peroxidase, superoxide dismutase and catalase. Free radical damage in living cells mitochondria is a byproduct of oxidative phosphorylation. Superoxide radicals are generated, which can damage mitochodrial DNA and mitochondrial membranes. Unlike DNA in the cell nucleus, mitochondrial DNA has only a few DNA-repair enzymes and the DNA is not protected by histones. Many antioxidants, however (including vitamin C and vitamin E) can't get into mitochondria for various reasons (e.g. because too hydrophilic to cross mitochondrial membranes or too hydrophobic to cross the cytoplasm). A group of scientists in Russia (led by V. Skulachev) have created a custom antioxidant (a Skulachev ion forms the point of the molecule and penetrates the mitochondrial membrane; the antioxidising part is attached behind it) that can enter the mitochondria and stays there due to the membrane potential gradient; preventing damage to DNA. Tests dating back to the 1950's have indicated that nutritional supplementation of trace amounts of the mineral Selenium is highly beneficial in reducing the actual occurrence, as well as prevention of male prostate cancer. Recent studies conducted using modern statistical methods by the China national health system have verified these earlier studies. Although there is little doubt that antioxidants are a necessary component for good health, there is considerable doubt as to the most beneficial antioxidant and as to the optimal amount for results. A study of lung cancer patients found that those given antioxidant supplements had worse prognoses. This is believed to be due to antioxidant interference with the body's normal use of localised free radicals e.g. Nitric oxide for cell signalling. Due to the complex nature of the interactions of antioxidants with the body, it is difficult to interpret the results of many experiments designed to test such things. In vitro testing (outside the body) has shown many natural antioxidants, in specific concentration, can halt the growth of or even kill cancerous cells. For example, recent studies are suggesting that at high levels, synthetic antioxidant vitamins such as A, E and C may prove to have pro-oxidant effects: increasing the formation of free radicals. The fact that natural antioxidants are always ingested together with a wide variety of flavonoids and other phytochemicals also likely plays a part. Many supplement manufacturers supply more expensive tablets containing these. Newer liquid nutritional supplements using plant ionic compounds are believed to be more readily absorbed in the human body. The benefits of antioxidants were examined during the Age-Related Eye Disease Study.

The Industry

Many nutraceutical and health food companies have, in light of scientific studies, produced products that supplement the diet with such antioxidants. Large companies such as the Nutraceutical Corporation and Natrol have products that are explicitly composed of derivatives that contain antioxidants, like resveratrol in grape seeds. Other companies, such as Canprev, Vemma and Natural Health, produce supplements that contain a combination of antioxidants, like their Immunotality formula. The green tea industry, with makers like Japanese Green Tea and Arizona (for iced) have benefitted tremendously from recent articles on antioxidants in green tea delaying onset of AMD.

References

- Halliwell B. 1999. Antioxidant defence mechanisms: from the beginning to the end (of the beginning). Free Radical Research 31:261-72.

External links

- [http://www.thedoctorslounge.net/medlounge/articles/antioxidants/ Antioxidants: Introduction, Biochemistry & Classification]
- [http://www.ext.colostate.edu/pubs/columnnn/nn000322.html Foods that are rich in antioxidants]
- [http://www.benbest.com/nutrceut/AntiOxidants.html General Anti-Oxidant Actions]
- [http://nanoaging.com/nanoagingforum Supplements (Antioxidant) Forum]
- Category:Physiology

Visual system

The visual system is the part of the nervous system which allows organisms to see. It interprets the information from visible light to build a representation of the world surrounding the body. Note that different species are be able to see different part of the light spectrum; for example, some can see into the ultraviolet, while others can see into the infrared. This article mostly describes the visual system of mammals, although other "higher" animals have similar visual systems. In this case, the visual system consists of:
- The eye, especially the retina
- The optic nerve
- The optic chiasm
- The optic tract
- The lateral geniculate nucleus
- The optic radiations
- The visual cortex

visual cortex
Light is inverted by the lens and projected onto the retina; blue-attuned cone cells will be most strongly stimulated by blue light, while yellow/red-attuned cone cells will not be.

Eye

The eye is a complex biological device. The functioning of a CCD camera makes an apt metaphor for the workings of the eye, which takes visible light and converts it into a stream of information that can be transmitted via nerves. nerveian Retina, 1900]] Light entering the eye is refracted as it passes through the cornea. It then passes through the pupil (controlled by the iris) and is further refracted by the lens. The lens inverts the light and projects an image onto the retina. The retina consists of a large number of photoreceptor cells which contain a particular protein molecule: the photopigment called rhodopsin. When rhodopsin is struck by a photon (a particle of light) it transmits a signal to the cell; the more photons strike the cell, the stronger the signal will be. In some animals, like humans, cone cells contain cone opsin molecules attuned to specific wavelengths of light; i.e., a blue cone cell contains opsin most attuned to blue-wavelength light and will most strongly be stimulated by blue-wavelength light, while a yellow-red cone cell will only be weakly stimulated by blue-wavelength light. This gives the ability to distinguish color.

Optic nerve

colora, joining left and right eye information in the optic tract, and layering left and right visual stimuli in the lateral geniculate nucleus. V1 in red at bottom of image. (1543 image from Andreas Vesalius' Fabrica)]] Following some rudimentary processing (mostly involving color boundaries), the information about the image received by the eye is transmitted to the brain via the optic nerve. In humans, the optic nerve is the only sensory system that is connected directly to the brain and does not connect through the medulla, due to the necessity of processing the complex visual information quickly.

Optic chiasm

The optic nerves from both eyes meet and cross at the optic chiasm, at the base of the frontal lobe of the brain. At this point the information from both eyes is combined and split according to the field of view. The corresponding halves of the field of view (right and left) are sent to the left and right halves of the brain, respectively (the brain is cross-wired), to be processed. That is, though we might expect the right brain to be responsible for the image from the left eye, and the left brain for the image from the right eye, in fact, the right brain deals with the left half of the field of view, and similarly for the left brain. (Note that the right eye actually perceives part of the left field of view, and vice versa).

Optic tract

brain Information from the right visual field (now on the left side of the brain) travels in the left optic tract. Information from the left visual field travels in the right optic tract. Each optic tract terminates in the lateral geniculate nucleus (LGN) in the thalamus.

Lateral geniculate nucleus

The lateral geniculate nucleus (LGN) is a sensory relay nucleus in the thalamus of the brain. The LGN consists of six layers in humans and some other primates such as macaques. Layers 1, 4, and 6 correspond to information from one eye; layers 2, 3, and 5 correspond to information from the other eye. Layer one (1) contains M cells, which correspond to the M (magnocellular) cells of the optic nerve of the opposite eye. Layers four and six (4 & 6) of the LGN also connect to the opposite eye, but to the P cells of the optic nerve. By contrast, layers two, three and five (2, 3, & 5) of the LGN connect to the M cells and P (parvocellular) cells of the optic nerve for the same side of the brain as its respective LGN. The six layers of the LGN are the area of a credit card, but about three times the thickness of a credit card, rolled up into two ellipsoids about the size and shape of two small birds eggs. The neurons of the LGN then relay the visual image to the primary visual cortex (V1) which is located at the back of the brain (caudal end).

Optic radiations

caudal end The optic radiations carry information from the midbrain lateral geniculate nucleus to layer 4 of the visual cortex. The P layer neurons of the LGN relay to V1 layer 4C β. The M layer neurons relay to V1 layer 4C α. There is a direct correspondence from an angular position in the field of view of the eye, all the way through the optic tract to a nerve position in V1. At this juncture in V1, the image path ceases to be straightforward; there is more cross-connection within the visual cortex.

Visual cortex

The visual cortex is the most massive system in the human brain and is responsible for higher-level processing of the visual image. It lies at the rear of the brain (highlighted in the image), above the cerebellum. The interconnections between layers of the cortex, the thalamus, the cerebellum, the hippocampus and the remainder of the areas of the brain are under active investigation. Currently, much of what is known stems from patients with damage to known areas of the brain, with a corresponding study of the cognitive functions which have been spared. hippocampus (red).]] [http://cercor.oxfordjournals.org/cgi/content/abstract/10/12/1211"Lesions Affecting the Parahippocampal Cortex Yield Spatial Memory Deficits in Humans", Cerebral Cortex, Vol. 10, No. 12, 1211-1216, December 2000] Zeineh et al., "Dynamics of the Hippocampus During Encoding and Retrieval of Face-Name Pairs", Science 2003 299: 577-580. See also:Hippocampus#Role in spatial memory and navigation, and the Fusiform gyrus in the temporal lobe of the cortex.

References

- David H. Hubel (1989), Eye, Brain and Vision. New York: Scientific American Library.
- David Marr (1982), Vision: A Computational Investigation into the Human Representation and Processing of Visual Information. San Francisco: W. H. Freeman.
- R.W. Rodiek (1988). "The Primate Retina". Comparative Primate Biology Vol. 4 of Neurosciences. (H.D. Steklis and J. Erwin, editors.) pp. 203-278. New York: A.R. Liss.
- [http://webvision.med.utah.edu/VisualCortex.html Matthew Schmolesky, The Primary Visual Cortex]
- Martin J. Tovée (1996), An introduction to the visual system. Cambridge University Press, ISBN 0521483395 (References, pp.180-198. Index, pp.199-202. 202 pages.)
- Andreas Vesalius (1543) De Humanis Corporis Fabrica (On the Workings of the Human Body)
- Torsten Wiesel and David H. Hubel (1963), "The effects of visual deprivation on the morphology and physiology of cell's lateral geniculate body". Journal of Neurophysiology 26, 978-993. Category:Visual system

Retinoid

The Retinoids are a class of chemical compounds that are related chemically to vitamin A. Retinoids are used in medicine, primarily due to the way they regulate epithelial cell growth. Research is also being done into their ability to treat epithelial cancers.

Milk

:For other senses of this word, see milk (disambiguation). milk (disambiguation) Milk most often means the nutrient fluid produced by the mammary glands of female mammals. It provides the primary source of nutrition for newborns before they are able to digest more diverse foods. It is also processed into dairy products such as cream, butter, yoghurt, ice-cream, gelato, cheese, casein, whey protein, lactose, condensed milk, powdered milk, and many other food-additive and industrial products. It can also be used to mean
- the white juice and the processed meat of the coconut in, more or less, liquid form, used especially in Thai, Indian (Kerala), and Polynesian cuisine.
- a non-animal substitute such as soya milk, rice milk, and almond milk. Human milk is fed to infants through breastfeeding, either directly or by the female expressing her milk to be saved and fed later. The early lactation milk is known as colostrum, and carries the mother's antibodies to the baby. It can reduce the risk of many diseases in both mother and baby.

Composition and nutrition

The composition of milk differs widely from species to species and a little within species. Factors such as the lactose content, the proportion of and size of the butterfat globule, and the strength of the curd (formed by the human enzymes digesting the milk) can differ from breed to breed and mammal to mammal. For example:
- Human breast milk is thin and high in lactose, its primary sugar.
- Cow's milk is lower in sugar and higher in protein, and is composed of about 3.5% to 6.5% milkfat, 4% to 8.5% milk solids and about 88% water. Its main protein (80%) is casein, while whey proteins make up most of the rest. The nutritional makeup of cow's milk is much different from human milk. One cup of human milk has 70% less protein, 38% more fat, and 47% more carbohydrates than cow's milk. Vitamin C, folic acid, sodium, iron and calcium levels also differ significantly. Lactose in milk is digested with the help of the enzyme lactase produced by the bodies of infants. In humans, production of lactase falls off towards adulthood, leading to an inability to digest milk; this is known as lactose intolerance. Some human populations (most notably Europeans) retain the ability to digest lactose into adulthood. Whole cow's milk has approximately 634 Calories (2650kJ) per litre.

Cow's milk

In the western world cow's milk is most often extracted on an industrial scale for human consumption and industrial uses. It is the most commonly consumed form of milk. Dairy farming has become such a large business that in many countries the process is highly automated; with farmers using machines that attach directly to the teats of the cow's udder to speed milking, and breeds of cattle, such as Holstein, specially bred for increased milk production.

Commercial processing of milk

Holstein In North America a dairy facility processes milk and products obtained from milk (dairy products), such as cream, butter, cheese, and so on. Most dairies are local companies, as opposed to large or nationwide companies found in the southern hemisphere. Upon standing, fresh milk has a tendency to separate into a high-fat cream layer on top of a larger, skim-milk layer. The cream is often sold as a separate product with its own uses. In the United States, a blended mixture of half cream and half milk is often sold in smaller quantities and is called half and half. Half and half is used for creaming coffee and similar uses. Milk produced for commercial consumption usually undergoes several processes. Pasteurization kills many harmful micro-organisms by heating the milk for a short time and then cooling it for storage and transportation. Pasteurized milk is still perishable and must be stored cold by both suppliers and consumers. Dairies print expiration dates on each container, after which stores will remove any unsold milk from their shelves. In many countries it is illegal to sell milk that is not pasteurized. A complementary process for commercial milk is homogenization, which produces milk in a single phase (or layer). This is accomplished by mechanically reducing the fat globules to a size that stabilizes them in solution. Milk, sold commercially in countries where the cattle (and often the people) live indoors, commonly has vitamin D added to it to make up for lack of exposure to UVB radiation. Milk often has flavoring added to it for better taste or as a means of improving sales. Chocolate-flavored milk has been sold for many years, followed recently by other flavors of milk and cream. South Australia has the highest consumption of flavoured milk per person, where Farmers Union Iced Coffee outsells Coca-Cola, a success shared only by Inca Kola in Peru and Irn-Bru in Scotland.

Support

Cow's milk is a generally healthy source of protein and calcium in human diets. It is also a good source of a number of vitamins. A serving (1 cup or 250 ml) of 2%-fat milk contains 285 mg of calcium, which represents 22% to 29% of the daily recommended intake (DRI) of calcium for an adult, depending on the age, 8 grams of protein, and a number of other nutrients (either naturally or through fortification):
- Vitamins D and K - essential for bone health
- Iodine - a mineral essential for thyroid function
- Vitamin B12 and Riboflavin - necessary for cardiovascular health and energy production
- Biotin and Pantothenic Acid - B vitamins important for energy production
- Vitamin A - critical for immune function
- Potassium and Magnesium - for cardiovascular health
- Selenium - cancer-preventive trace mineral
- Thiamin - B-vitamin important for cognitive function, especially memory
- Conjugated Linoleic Acid - beneficial fatty acid that inhibits several types of cancer in mice, has been shown to kill human skin cancer, colorectal cancer and breast cancer cells in in vitro studies, and may help lower cholesterol and prevent atherosclerosis; only available in milk from grass-fed cows Milk supporters point out that studies show possible links between low-fat milk consumption and reduced risk of arterial hypertension, coronary heart disease, and obesity. Overweight individuals who drink milk may benefit from decreased risk of insulin resistance and type 2 diabetes. [http://www.nationaldairycouncil.org/NationalDairyCouncil/Nutrition/Reducing/DairysRoleManagingBP.htm]

Criticism

Cow's milk is also argued to be unhealthy primarily due to its fat and cholesterol content, as well as the toxicity of its protein. The following studies are used to support this position:
- The pasteurization process for raw milk kills most, if not all, resident micro-organisms (including beneficial ones that aid in its digestion and metabolization) and many nutritional constituents. The resulting pasteurized product causes digestive problems, is less nutritional and turns rancid (as opposed to souring) when aging. [http://www.realmilk.com/rawvpasteur.html Raw Milk Versus Pasteurized Milk]
- Some milk is rich in saturated fat, which studies have linked to increased risk of atherosclerosis and coronary heart disease. Low-fat and non-fat forms of milk may mitigate any such risk.
- Up to 70% of humans have an incomplete ability to digest milk, lactose intolerance. For those individuals, milk may induce symptoms such as cramping, bloating, gas, and diarrhoea. Certain ethnic groups may be more susceptible to these effects.
- Critics dispute the claim that drinking large amounts of milk can reduce the risk of bone fractures, especially in the elderly. Studies have failed to associate high calcium intakes with lower risk of hip and forearm fractures in men[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9278560] or women[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9224182].
- Critics of milk claim that plant-based sources of calcium are preferable, on the grounds that animal proteins in milk causes leaching or excretion of calcium from bones.[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=8198060] Such critics refute the claim that milk prevents osteoporosis and make the counterclaim that milk, in fact, contributes to that disease.
- A study published in June 2005 suggests that consumption of milk by 9- to 14-year-old children is associated with weight gain, although the researchers identify that excessive calorie intake is the cause rather than dairy specific factors. Researchers were surprised by their conclusion that weight gain was associated with dietary calcium and low-fat or skim milk, but not dairy fat.[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15939853]
- A February 2005 study found a positive association between acne and the consumption of whole milk, skim milk, and other dairy products in high-school-age women.[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15692464].
- Critics also make the claim that the protein content of cow’s milk can act to block the absorption of calcium and cause the human body to produce antibodies that are believed to damage the pancreas, leading to the development of type 1 diabetes.
- In children, cow’s milk consumption has allegedly been linked to anemia, colic, allergies, and asthma. In adults, cow's milk consumption has been related to breast cancer.
- Two studies show a correlation between high galactose consumption, and high rates of ovarian cancer. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=2510499][http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=2567871]
- A study suggests a correlation between high calcium intake and prostate cancer.[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=9458087]. There is no evidence that any such problem is specific to milk. A review published by the World Cancer Research Fund and the American Institute for Cancer Research states that at least 11 human population studies have linked dairy product consumption and prostate cancer.
- Scientific evidence has also been unable to support the claim that the consumption of cow’s milk as a source of calcium reduces the risk of osteoporosis. On the contrary, epidemiological research has linked the countries with the highest dairy consumption rates (for example, the United States, Sweden and Finland) to the incidence of osteoporosis. But no studies have shown the same in New Zealand, which has the highest per capita consumption.
- The A1 β-casein in cow's milk has been reportedly linked to ischaemic heart disease, type I diabetes, and to a lesser extent, schizophrenia and autism. Some milk contains higher levels of the A2 β-casein, which has been claimed to not lead to these diseases. Milk with the "A2 milk" trademark has been tested to be high in the A2 β-casein.

Distribution

A2 milk A2 milk milk]] Because of the perishable nature of milk, expeditious distribution is desirable. Milk used to be delivered to households daily, but this is no longer economically feasible. People buy it chilled at grocery or convenience stores or similar retail outlets. Prior to the widespread use of plastics, milk was often distributed to consumers in glass bottles, and before that in bulk that was ladled into the customer's container. In the UK, milk can be delivered daily by a milk man who travels his local milk round (route) using a battery-powered milk float, although this is becoming less popular as a result of supermarkets selling milk at cheaper prices. New Zealand was possibly the last country to distribute milk in glass bottles. As of November 30, 2005, New Zealand Dairy Foods will cease to produce bottled milk at their Christchurch factory. In the United States bottles were replaced with milk cartons, tall boxes with a square cross-section and a peaked top that can folded outward upon opening to form a spout. Now milk is increasingly sold in plastic bottles. First the gallon and half-gallon sizes were sold in plastic jugs while the smaller sizes were sold in milk cartons. Recently milk has been sold in smaller bottles made to fit in automobile cup holders. The half-pint milk carton is the traditional unit as a component of school lunches. Pictures of missing children were printed on milk cartons as a public service until it was determined that this was disturbing children. Milk preserved by the UHT process is sold in boxes often called a "brick" that lack the peak of the traditional milk carton. Glass containers are rare these days. Most people purchase milk in plastic jugs or bags or in waxed-paper cartons. Ultraviolet light from fluorescent lighting can destroy some of the proteins in milk so many companies, that once distributed milk in transparent or highly translucent containers, are using thicker materials that block the harmful rays. Many people feel that such "UV protected" milk tastes better. In the United States, milk is commonly sold in gallon, half-gallon and quart containers (U.S. customary units) of rigid plastic or waxed cardboard. The US single-serving size is usually the half-pint (about 500 ml). In Canada, a 1 1/3 litre plastic bag (sold as 4 litres in 3 bags) is the most common, while 2 litre, 1 litre, 500 millilitre, and 250 millilitre cartons are also available. In Europe, sizes of 500 millilitres, 1 litre (the most common), 2 litres and 3 litres are commonplace (in the UK, some stores still stock the equivalents of old Imperial sizes: 568 ml (1 pint), 1.136 l (2 pints), 2.273 l (4 pints) or, rarely, a combination including both metric and imperial sizes). In Australia and New Zealand a 250 ml cardboard container of flavoured milk is marketed as a common breakfast meal. For refrigerator use milk comes in 1, 2 and 3 litre plastic screw-top bottles. Most UHT-milk is packed in 1 litre paper containers with a sealed plastic spout. Condensed milk is distributed in metal cans, 250 and 125 ml paper containers and 100 and 200 ml squeeze tubes, and powdered milk (skim and whole) is distributed in boxes or bags.

Varieties and brands

Cow's milk is generally available in several varieties. In some countries these are:
- full cream (or "whole" in North America, about 3.25% fat)
- semi-skimmed ("reduced fat" or "low fat", about 1.5-1.8% fat)
- skimmed (about 0.1% fat) Milk in the U.S. and Canada is sold as
- "whole" varieties
- "2 percent" (reduced fat)
- "1 percent" (low fat)
- "1/2 percent" (low fat)
- "skim" (very low fat) Note: In Canada "whole" milk refers to unhomogenized milk. "Homogenized" milk (or "Homo milk" in short) refers to milk which is 3.25% butterfat. Generally all store-bought milk in Canada has been homogenized, yet the term is also used as a name to describe butterfat content for a specific variety of milk. Modern commercial dairy processing techniques involve first removing all of the butterfat, and then adding back the appropriate amount depending on which product is being produced on that particular line. In Britain, it is possible to get Channel Island milk, which is 5.5% fat. In the United States, skim milk is also known as "fat free" milk, due to USDA regulations stating that any food with less than 1/2 gram of fat per serving can be labeled "fat free". Full cream, or whole milk, has the full milk fat content (about 3-4% if Friesian- or Holstein-breed are the source). For skimmed or semi-skimmed milk, all of the fat content is removed and then some (in the case of semi-skimmed milk) is returned. The best-selling variety of milk is semi-skimmed; in some countries full-cream (whole) milk is generally seen as less healthy and skimmed milk is often thought to lack taste. Whole milk is recommended to provide sufficient fat for developing toddlers who have graduated from breast milk or infant formula.

Other milk animals

In addition to cows, the following animals provide milk for dairy products:
- Humans
- Sheep
- Goats
- Horses
- Donkeys
- Camels (Including the South American camelids)
- Yaks
- Water buffalo
- Reindeer In Russia and Sweden, small moose dairies also exist [http://www.cnn.com/2004/WORLD/europe/06/23/sweden.moosecheese.ap/index.html]. Donkey and horse milk have the lowest fat content, while the milk of seals contains more than 50% fat. [http://www.havemilk.com/article.asp?id=1485#contentbyspecies]

Curdling

When raw milk is left standing for a while, it turns sour. This is the result of fermentation: lactic acid bacteria turning the milk sugar into lactic acid. This fermentation process is exploited in the production of various dairy products such as cheese and yogurt. Pasteurized cow's milk, on the other hand, spoils in a way that makes it unsuitable for consumption, causing it to assume an unpleasant odor and pose a high danger of food poisoning if ingested. The naturally-occurring lactic acid bacteria in raw milk, under suitable conditions, quickly produce large amounts of lactic acid. The ensuing acidity in turn prevents other germs from growing, or slows their growth significantly. Through pasteurization, however, these lactic acid bacteria are mostly destroyed, which means that other germs can grow unfettered and thus cause decomposition. In order to prevent spoilage, milk can be kept refrigerated and stored between 1 and 4 degrees Celsius. Most milk is Pasteurized by heating briefly and then refrigerated to allow transport from factory farms to local markets. The spoilage of milk can be forestalled by using ultra-high temperature (UHT) treatment; milk so treated can be stored unrefrigerated for several months until opened. Sterilized milk, which is heated for a much longer period of time, will last even longer, but also lose more nutrients and assume a still different taste. Condensed Milk, made by removing most of the water, can be stored for many months, unrefrigerated. The most durable form of milk is milk powder which is produced from milk by removing almost all water.

External links

- [http://www.pukeariki.com/en/stories/farming/milkingintheearlydays.asp Milking in the early days]
- [http://www.pukeariki.com/en/stories/farming/elthamfirsts.asp Advances in processing milk]
- [http://www.attra.org/attra-pub/gbdairy.html Year-round grazing of dairy cows in the United States]
- [http://www.milkismilk.com Milk is Milk Web site and blog]
- [http://www.ars.usda.gov/is/AR/archive/mar03/osteo0303.htm Boning Up on Osteoporosis]
- [http://www.drafthorsejournal.com/features/horsemilk/horsemilk.htm Horse milk]
- [http://www.hsph.harvard.edu/nutritionsource/calcium.html Harvard School of Public Health: Calcium and Milk]: describes claims of milk supporters and critics
- [http://www.nal.usda.gov/fnic/foodcomp/Data/SR17/wtrank/sr17w301.pdf USDA National Nutrient Database, Calcium contents of selected foods]
- [http://www.iom.edu/Object.File/Master/7/294/0.pdf USDA Dietary Reference Intakes: Elements]
- [http://www.straightdope.com/columns/030321.html Is cow's milk "the worst beverage on earth?"] - straightdope.com response to anti-milk websites.
- [http://beauty.about.com/od/bathmilk/ Bath Milk] (About.com), milk used for bathing
- [http://www.milksucks.com MilkSucks.Com] - a site run by PETA extolling the benefits of going Dairy-free Category:Beverages Category:Non-alcoholic drink Category:Dairy products
- Category:Materials involved in Hinduism ko:우유 ia:Lacte] [[id:Susu]] [[io:Lakto ja:乳 simple:Milk th:นม

Egg (food)

:This article is about bird eggs as food. For the edible eggs of sea animals, see roe and caviar. caviar caviar Bird eggs are a common food source. The most commonly used bird eggs are those from the chicken, duck, and goose, but smaller eggs such as quail eggs are occasionally used as a gourmet ingredient, as are the largest bird eggs, from ostriches. The eggs of turtles are sometimes used for food also. Eggs are frequently used in both sweet and savoury dishes as a source of protein and/or to bind the other ingredients in a recipe together. Sometimes the egg yolk is used separately from the egg white (or albumen). The egg yolk is suspended in the egg white by one or two spiral bands of tissue called the chalaza (Greek word from "khalaza" meaning hailstone, or hard lump.)

Nutrition of chicken eggs

Chicken eggs are the most commonly eaten egg. They are highly nutritious. Eggs are high in complete protein and provide significant amounts of several vitamins and minerals (Vitamin A, Riboflavin, Folic Acid, Vitamin B6 and Vitamin B12, and Iron). Eggs are among the cheapest single-food source of complete protein available, which is essential to health and well being. Iron All of the egg's vitamin A, D and E are in the yolk. They are one of the few foods naturally containing vitamin D (though this nutrient is naturally produced in the human body with exposure to sunlight). A large egg yolk contains approximately 60 calories (250 kilojoules); the egg white contains about 15 calories (60 kilojoules). A large yolk contains more than two-thirds of the recommended daily limit of 300 mg of cholesterol. The yolk makes up about 33% of the liquid weight of the egg. It contains all of the fat in the egg and almost half of the protein. Recently chicken eggs that are especially high in Omega 3 fatty acids have come on the market. These eggs are made by feeding laying hens a diet containing polyunsaturated fats and kelp meal. Two brands available in the UK are Columbus Eggs[http://www.columbuseggs.com] and The Hearty Egg[http://www.theheartyegg.com]. Nutrition information on the packaging is different for each of the brands.

Health issues of eating chicken eggs

Cholesterol and fat

Chicken egg yolks contain a small amount of fat. People on a low-cholesterol diet may feel the need to cut down on egg consumption, although most of the fat in egg is unsaturated fat and may not be harmful. The egg white consists primarily of water (87%) and protein (13%) and contains no cholesterol and little if any fat. Some people try to avoid eggs in their diet because they are high in cholesterol which is concentrated in the yolk. This issue is sometimes addressed by removing some or all of the eggs' yolks. People sometimes do this themselves, or may use prepared egg substitutes such as Egg Beaters. In addition, the United States egg industry launched its continuing "Incredible Edible Egg" campaign, which touts eggs as a healthy part of a balanced diet. The American Egg Board publicizes modern research which shows that dietary cholesterol has less effect on blood cholesterol than previously thought. Eggs are an excellent component of a low-carbohydrate diet

Contamination

A health issue associated with eggs is contamination by pathogenic bacteria like Salmonella. Eggs exit a female bird via the cloaca, so care must be taken to avoid the eggs being contaminated with fecal matter. In commercial practice, eggs are quickly washed with a sanitizing solution within minutes of being laid. Most health experts advise people to cook their eggs thoroughly before eating them, as the heat is necessary to kill any infectious micro-organisms that may be present. Raw and undercooked eggs have been associated with salmonella infection. As with meat, ready-to-eat food should not come in contact with containers and surfaces that have been used to process raw eggs. The risk of infection from raw or undercooked eggs is dependent in part upon the sanitary conditions under which the hens are kept. Some smaller egg producers make a point of keeping their hens in cleaner (and, in their view more humane) conditions, and observe few or no cases of salmonella in the birds themselves.

Ethical issues

Many who practice vegetarianism feel it is acceptable to eat eggs as the bird is not killed and the eggs remain unfertilised. People concerned about animal welfare (especially vegans) are reluctant to eat mass-produced eggs as factory farming is considered cruel. Even free-range eggs are sometimes unacceptable to those who are concerned about animal welfare as it is felt that alleged free-range birds may not be much better off than confined birds. Many vegans believe it is inaccurate that eating eggs does not cause an animal to be killed since most farms (both free-range and factory farms) kill the chickens once their egg production declines. Most farms also buy the chicks from hatcheries where the male chicks are killed at birth. From a religious standpoint some vegetarians such as certain practitioners of Buddhism feel that eggs are the same as "liquid meat" and thus unacceptable for consumption.

Cooking and preparation

The primary cooking techniques for eggs are:
- baking
- boiling
- poaching
- frying Some common egg dishes are
- fried eggs
- omelettes
- scrambled eggs
- soufflé
- quiche
- egg salad
- century egg Eggs, particularly their yolks, are important as binding agents in many preparations in European cooking due to the emulsifying action of lecithin. This property is crucial for sauces such as mayonnaise and Hollandaise, custards such as crème anglaise, crème brûlée, flan and lemon custard, and meat dishes such as sausages and pâté. Eggs may also be pickled, hard-boiled and refrigerated, or eaten raw, though the latter is not recommended for people who may be susceptible to salmonella, such as the old, the infirm, or pregnant women. If an egg is overcooked a greenish ring sometimes appears around egg yolk, this is the result of iron and sulfur compounds in the egg. It can also occur when there is much iron in the cooking water. The green ring affects neither taste nor nutrition. When eggs become rotten, the yolk will turn green and the egg will emit a sulfurous smell when broken. Although deemed offensive by most Western palates, fermented eggs are considered a delicacy by some in China, when prepared using a special method which includes letting them sit for three months to age (or rot, depending on one's interpretation).

Egg substitutes for baking

For those who choose not to or are unable to consume eggs, alternatives used in baking include other rising agents, such as Ener-G egg replacer, or binding materials, such as ground flax seeds. Tofu can also act as a partial binding agent, since it is high in lecithin due to its soy content. Extracted soybean lecithin, in turn, is often used in packaged foods as a cheap substitute for egg-derived lecithin.

Egg characteristics

The shape of an egg is approximately an oblate ellipsoid, but, while keeping cylindrical symmetry, there is typically not quite symmetry in a plane perpendicular to the long axis. See also oval (geometry).

Shell color

Different breeds of chicken can lay eggs with shells varying from whites through to brown and rarer colours such as speckled green. Although there are absolutely no nutritional differences, there is often a cultural preference for one colour over another. For example, in most regions of the United States eggs are generally white, while in the northeast of that country, and in the United Kingdom eggs are generally light-brown. These habits may be associated with perceptions of greater purity in white-shelled eggs or greater wholesomeness in brown-shelled eggs.

Yolk color

United Kingdom Yolk colour depends on the diet of the hen, if the diet contains yellow/orange plant pigments known as xanthophylls, then they are deposited in the yolk, colouring it. A colourless diet, can produce an almost colourless yolk. Farmers may add natural pigments to enhance yolk colour, but artificial colours are banned.

Abnormalities

Some hens will lay double-yolked eggs as the result of unsynchronized production cycles, although heredity causes some hens to have a higher propensity to lay double-yolked eggs. Double-yolked eggs only rarely, and even then only with human intervention, lead to the successful development of two embryos [http://www.abc.net.au/science/k2/moments/s409538.htm]. It is also possible for a young hen to produce an egg with no yolk at all.

Trivia

- If a raw egg is spun, abruptly stopped and then quickly released, it will start to spin again as the liquid inside continues to rotate. This technique can be used to reliably determine whether an egg is raw or already boiled – a solid egg will remain stationary once halted. Additionally, if a cooked egg and a raw egg are spun with the same force, the cooked egg will spin much faster.
- It is difficult (some say impossible) to break a chicken egg by squeezing it from end-to-end on its long axis.
- An ostrich egg can make omelets for ten people and takes forty-five minutes of boiling to harden through.
- An egg that floats in water is likely to have been spoiled by bacteria that entered through the pores in the shell and created gas inside it. The increased pressure due to the gas production may push some of the white through the shell, which may also signify a bad egg.
- There is an urban legend which states that an egg can only be stood on end on one of the two equinoxes.[http://www.snopes.com/science/equinox.htm]

Pop culture

- There is a famous nursery rhyme about an anthropomorphic egg named Humpty Dumpty. When he fell off a wall, all the King's horses and men could not fix him.
- In The Neverending Story, the Old Man of Wandering Mountain lives in a giant egg at the summit of a wandering mountain. This is where he eternally writes the Neverending Story, as it happens.
- Billy Hatcher and the Giant Egg is a video game about a boy in a chicken outfit pushing around giant eggs in order to defeat his enemies. Occasionally, the eggs hatch into helpful animals.
- In the video game The Legend of Zelda: Link's Awakening, a giant egg atop a mountain is central to the plot.
- There is a Pokémon known as Exeggcute which consists of a group of egg-like beings. Pokémon also reproduce by laying eggs under certain conditions, these conditions are nearly always at a daycare centre, if you have a female and a male pokémon that are friendly with each other they will give birth to one of the parenting pokémon, sometimes baby form, new baby pokémon have been introduced, these are what the eggs hatch into.
- In RahXephon, a giant egg is central to the plot.
- A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs (usually by dyeing). Occasionally, adults hide the eggs for children to find, an activity known as an Easter egg hunt. See Egg decorating and Easter eggs.

Egg Attacks

Although a food, they have been used to throw at people or things such as houses or cars, a minor criminal offence. On Halloween for example, if you do not give trick or treaters anything, they have been known to throw eggs at property or people. John Major, a former British prime minister had an egg thrown at him in protest by a student. Current deputy prime minister John Prescott also had an egg thrown at him by a protester (in addition to this he has also been attacked with iced water and even been punched).

External links

- [http://www.EggCruelty.com/ cruelty investigations at egg factory farms]
- [http://www.eggscam.com/ criticism of the "Animal Care Certified" logo found on most eggs in the United States] Category:Egg Category:Breakfast foods

Carrot

The carrot is a root vegetable, typically orange or white in colour with a woody texture. The edible part of a carrot is a taproot.

Uses

Carrots can be eaten raw, whole, chopped or shaved into salads for colour, and are also often chopped and cooked in soups and stews. A well known dish is Carrots Julienne. One can also make carrot cake and carrot pudding. The greens are edible as a leaf vegetable, but are rarely eaten. Together with onion and celery, carrots are one of the primary vegetables used in a mirepoix to make various broths. Since the late 1980s, baby carrots or mini carrots, carrots that have been chopped and peeled into uniform 5 cm (2 inch) cylinders, have been a popular ready-to-eat snack food in many supermarkets. Beta carotene, a dimer of Vitamin A, is abundant in the carrot and gives this vegetable its characteristic orange colour. Furthermore, carrots are rich in dietary fiber, antioxidants, and minerals and are an alkaline food. Carrot juice is also widely marketed.

History

Carrot juice The wild ancestors of the carrot are likely to have come from Afghanistan which remains the centre of diversity of D. carota. The familiar wild plant wild carrot, often called "Queen Anne's lace", is a relative of the garden carrot; garden carrots that run to seed soon revert to their wild prototype, with a forking carroty-smelling, edible root that quickly becomes too woody and bitter to eat. The Parsnip is a close relative of the carrot.

Cultivars

Carrot cultivars can be grouped into two broad classes, eastern carrots and western carrots.

Eastern carrots

Eastern carrots were domesticated in Central Asia, probably in modern-day Afghanistan in the 10th century or possibly earlier. Those of the eastern carrot that survive to the present day are commonly purple or yellow in colour, and often have branched roots. The purple colour common in these carrots comes from anthocyanin pigments.

Western carrots

The Western carrot emerged in the Netherlands in the 15th or 16th century, its orange colour making it popular in those countries as an emblem of the House of Orange and the struggle for Dutch independence. The orange colour results from abundant carotenes in these cultivars. While orange carrots are nearly ubiquitous in the West, other colours do exist, including white, yellow, red, and purple. These other colours of carrot are raised primarily as novelty crops. The Vegetable Improvement Center at Texas A&M University has developed a purple-skinned, orange-fleshed carrot, the BetaSweet, with substances to prevent cancer, which has recently entered commercial distribution. Western carrot cultivars are commonly classified by their root shape:
- Imperator carrots are the carrots most commonly sold whole in U.S. supermarkets; their roots are longer than other cultivars of carrot, and taper to a point at the tip.
- Nantes carrots are nearly cylindrical in shape, and are blunt and rounded at both the top and tip. Nantes cultivars are often sweeter than other carrots.
- Danvers carrots have a conical shape, having well-defined shoulders and tapering to a point at the tip. They are somewhat shorter than Imperator cultivars, but more tolerant of heavy soil. Danvers cultivars are often pureed as baby food.
- Chantenay carrots are shorter than other cultivars, but have greater girth, sometimes growing up to 8 cm (3 inches) in diameter. Shapewise, they have broad shoulders and taper towards a blunt, rounded tip. They are most commonly diced for use in canned or prepared foods. While any carrot can be harvested before reaching its full size as a more tender "baby" carrot, some fast-maturing cultivars have been bred to produce smaller roots ordinarily. The most extreme examples produce round roots about 2.5 cm (1 inch) in diameter. These small cultivars are also more tolerant of heavy or stony soil than long-rooted cultivars such as 'Nantes' or 'Imperator'. The "baby carrots" sold ready-to-eat in supermarkets, are however often not from a smaller cultivar of carrot, but are simply full-sized carrots that have been sliced and peeled to make carrot sticks of a uniform shape and size. Carrots are used as food plants by the larvae of some Lepidoptera species including Common Swift, Garden Dart, Ghost Moth, Large Yellow Underwing and Setaceous Hebrew Character.

Trivia

In 2005, a poll of 2,000 people revealed that the carrot was Britain's 3rd favourite culinary vegetable. For the purposes of the European Union's "Council Directive 2001/113/EC of 20 December 2001 relating to fruit jams, jellies and marmalades and sweetened chestnut purée intended for human consumption" carrots can be defined as a fruit as well as a vegetable. This is because carrot jam is a Portuguese delicacy. A common urban legend is that carrots help with a persons night vision. It is believed that it was disinformation introducted in 1940 by John "Cat's Eyes" Cunningham during the Battle of Britain as an attempt to cover up the discovery and use of radar technologies (see Snopes investigation in the external links). It reinforced existing German folklore and helped to encourage children to eat the vegetable. The world's largest carrot was grown in Palmer, Alaska by John Evans in 1998. It weighed 18.99 pounds (8.614 kg)! Carrots are also traditionally used as noses when building snowmen. There is a large statue of a carrot in Ohakune, New Zealand.

External links

- [http://www.nutritiondata.com/foods-carrot011000000000000000000.html Complete nutritional info.]
- [http://vic.tamu.edu/main/VFICIndex/Web%20pages/f&vresearchpgs/betasweetnews/newmightmaroon.htm BetaSweet purple carrot at Texas A&M]
- [http://dmoz.org/Home/Cooking/Fruits_and_Vegetables/Carrots/ Recipes with carrots]
- [http://www.carrotmuseum.com World Carrot Museum]
- [http://growingtaste.com/vegetables/carrot.shtml Carrots for the home gardener]
- [http://www.nsac.ns.ca/pas/instind/pcrp/index.htm Processing Carrot Research Program, Nova Scotia Agricultural College]
- [http://www.snopes.com/food/ingredient/carrots.asp The claim that eating carrots results in improved vision is false] (from Snopes.com)
- [http://www.abc.net.au/science/k2/moments/s1392430.htm Carrots improve night vision is a myth] Category:Root vegetables Category:Apiaceae ms:Lobak ja:ニンジン

Carotenoid

Carotenoids are organic pigments that are naturally occurring in plants and some other photosynthetic organisms like algae, some types of fungus and some bacteria. Carotenoids are split into two classes;xanthophylls and carotenes.

Properties

Carotenoids are characterized by a large (35-40 carbon atoms) polyene chain, sometimes terminated by rings. Carotenoids where some of the double bonds have been oxidized such as lutein and zeaxanthin, are known as xanthophylls; the un-oxidized carotenoids such as alpha-carotene, beta-carotene and lycopene are known as carotenes. Probably the most well-known carotenoid is the one that gives this group its name, carotene, found in carrots and responsible for their bright orange colour. Their color, ranging from pale yellow, through bright orange, to deep red, is directly linked to their structure: The double carbon-carbon bonds interact with each other in a process called conjugation. As the number of double bonds increases, the wavelength of the absorbed light increases, giving the compound an increasingly red appearance.

Physiological effects

In photosynthetic organisms, carotenoids play a vital role in the photosynthetic reaction centre. They either participate in the energy-transfer process, or protect the reaction center from auto-oxidation. In non-photosynthetic organisms, carotenoids have been linked to oxidation-preventing mechanisms. Carotenoids have many physiological functions. Given their structure (above) carotenoids are efficient free-radical scavengers, and they enhance the vertebrate immune system. Consequently, epidemiological studies have shown that people with high beta-carotene intake and high plasma levels of beta-carotene have a significantly reduced risk of lung cancer. But studies of supplementation with large doses of beta-carotene in smokers have shown an increase in cancer risk (possibly because excessive beta-carotene results in breakdown products that reduce plasma Vitamin A and worsen the lung cell proliferation induced by smoke). Similar results have been found in other animals. Animals are incapable of synthesizing carotenoids, and must obtain them through their diet, yet they are common and often in ornamental features. For example, the pink colour of flamingos and salmon, and the red colouring of lobsters are caused by carotenoids. Carotenoids are used in ornamental traits because, given their physioloigcal and chemical properties, they can be used as honest indicators of individual health, and hence they can be used by animals when selecting potential mates.

Aroma chemicals

Products ofcarotenoid degradation such as ionones, damascones, and damascenones are also important fragrance chemicals that are used extensively in the perfumes and fragrance industry. Both beta-Damascenone and beta-Ionone although low in concentration in rose distillates are the key odor contributing compounds to flower. In fact, the sweet floral smells present in black tea, aged tobacco, grape, and many fruits are due to the aromatics compounds resulting from carotenoid breakdown.

External links

- [http://www.carotenoidsociety.org/ http://www.carotenoidsociety.org/ ]
- [http://www.benbest.com/nutrceut/phytochemicals.html#carotenoids Carotenoid Terpenoids]
- [http://leffingwell.com/caroten.htm Carotenoids as Flavor and Fragrance Precursors] Category:Pigments Category:Photosynthesis ja:カロテノイド

Retinal

The Retinenes (Retinene₁ and Retinene₂) are chemical derivatives of the dietary supplement vitamin A (see retinol) formed through oxidation reactions. Retinene₁ is better known as retinaldehyde or simply retinal and is fundamental in the transduction of light into visual signals in the photoreceptor level of the retina. Retinene₂ is more formally known as dehydroretinaldehyde. The energy of impinging photons will convert retinaldehyde from an 11-cis isomer into an all-trans form. In the retina, this conversion induces a conformational change in the surrounding photopsin protein pigment, leading to signaling through the G protein transducin. Retinaldehyde also forms a part of bacteriorhodopsin, a light-induced proton pump found in some archaea. Experimentally, it is possible to replace 11-cis retinaldehyde by perfusing retinal tissue preparations with retinaldehyde derivatives. Selective modification of the retinaldehyde structure, particularly the density of electrons in the π-orbitals, can lead to insights into the interaction between the retinaldehyde moiety and the surrounding pigment protein.

David Adriaan van Dorp

David 'Davy' Adriaan van Dorp (Amsterdam April 27 1915 - Vlaardingen February 19 1995) was a Dutch chemist. Van Dorp was born as the son of Hendrik van Dorp and Maria van Dorp, and studied chemistry in Amsterdam where he received a PhD for his thesis Aneurine en gistphosphatase in 1941. In 1946, while employed by the Dutch Organon company in Oss, Van Dorp and Jozef Ferdinand Arens ('Coco') published the synthesis for vitamin A acid in the scientific journal Nature. In 1947, they completed the first full synthesis for the complex compound vitamin A, by taking the final step and turning the acid in an alcohol. Their synthesis was not to be used for commercial production, as an alternative route that was published soon after by Otto Isler and co-workers (Hoffmann-La Roche) turned out to be much more suited for upscaling. Van Dorp joined the Unilever Research Laboratory in Vlaardingen in 1959, and was a key person in the studies regarding the role of arachidonic acid in the metabolic pathway to prostaglandin E2, in close cooperation with Sune K. Bergström who would later receive a Nobel prize for his work on prostaglandins.

References

- J.F. Arens, D.A. van Dorp, Nature 157, 190-191 (1946)
- D.A. van Dorp, J.F. Arens, Nature 160, 189 (1947)
- O. Isler, W. Huber, A. Ronco, M. Kofler, Helv. Chim. Acta 30, 1911-1927 (1947)
- D.A. van Dorp, R.K. Beerthuis, D.H. Nugteren, H. Vonkeman, Biochim. Biophys. Acta 90, 204-207 (1964)
- S. Bergström, H. Danielsson, B. Samuelsson, Biochim. Biophys. Acta 90, 207-210 (1964)

External links

- [http://nobelprize.org/medicine/laureates/1982/bergstrom-lecture.pdf Bergströms scientific biography] Dorp, David Adriaan van Dorp, David Adriaan van Dorp, David Adriaan van

George Wald

George Wald (November 18, 1906 – April 12, 1997) was an American scientist who is best known for his work with pigments in the retina. He won a share of the 1967 Nobel Prize in Physiology or Medicine with Haldan Keffer Hartline and Ragnar Granit.

Research

Ragnar Granit As a postdoctoral researcher, Wald discovered