Vitamin A is a component of rhodopsin that feels weak light in visual cells. Rhodopsin is composed of opsin and 1 1- cis retinoic acid, which is related to dark vision.
Lack of vitamin A in human body can lead to dry skin, desquamation, hair loss and other symptoms.
physiological function
1, maintain normal visual function.
The photoreceptors of the eye are rod cells and cone cells in the retina. Both of these cells have photosensitive pigments, namely rhodopsin sensitive to weak light and rhodopsin sensitive to strong light. Both rhodopsin and rhodopsin are composed of retinol and retinaldehyde. After rhodopsin is irradiated by light, 1 1- cis-retinoic acid forms trans-retinoic acid, which is separated from opsin and loses its color. This process is called bleaching. If you enter the darkness, you can't see because the rhodopsin sensitive to low light disappears.
The separated retinoic acid is reduced to all-trans retinoic acid, which is further converted into trans retinoic acid ester (or cis isomer) and stored in pigment epithelium. Retinyl ester is converted into trans-retinol by retinyl ester hydrolase, and oxidative isomerization forms 1 1- cis retinoic acid. It recombines with protein to become rhodopsin, which restores its sensitivity to weak light, so that it can see clearly in the dark under certain illumination. This process is called "dark adaptation". Retinol released from the liver binds to retinol binding protein (RBP), and then binds to prealbumin in plasma, which is transported to the retina to participate in the photochemical reaction of the retina. If vitamin A is sufficient, rhodopsin can regenerate quickly and completely, so the recovery time of dark adaptation is short. If vitamin A is insufficient, the regeneration of rhodopsin is slow and incomplete, so the recovery time of dark adaptation is prolonged, and in severe cases, night blindness may occur.
2. Maintain the health of epithelial cells and promote the synthesis of immunoglobulin.
Vitamin A can participate in the synthesis of glycoprotein, which is very important for the normal formation, development and maintenance of epithelium. When vitamin A is insufficient or deficient, it can lead to abnormal glycoprotein synthesis intermediates, accumulation of low molecular weight polysaccharides and lipids, proliferation and thickening of epithelial basal layer, accelerated cell division, increased myofibril synthesis, and flat, irregular and dry surface cells. Endometrial keratinization of respiratory tract, gastrointestinal tract and urogenital system, such as nose, pharynx and larynx, weakens the natural barrier (structure) to prevent bacterial invasion and is easy to be infected. In children, it is easy to be complicated with respiratory tract infection and diarrhea. Some kidney calculi is also related to keratinization of urinary tract. Excessive intake of vitamin A does not increase the resistance to epithelial infection with dose.
Immunoglobulin is a glycoprotein, so vitamin A can promote the synthesis of this protein, which has an important impact on the immune function of the body. When it is deficient, cellular immunity will decline.
3. Maintain the normal growth and development of bones.
Vitamin A promotes the biosynthesis and differentiation of bone cells in protein. When it is deficient, the balance between osteoblasts and osteoclasts is destroyed, or due to the enhancement of osteogenic activity, the bone proliferates excessively, or the formed bone is not absorbed. If pregnant women lack vitamin A, it will directly affect fetal development and even stillbirth.
4. Promote growth and reproduction
Vitamin A contributes to cell proliferation and growth. When animals are deficient in vitamin A, growth stagnation appears obviously, which may be related to the decrease of animal appetite and protein utilization rate. Vitamin A deficiency affects spermatocyte production of sperm epithelium in male animals, periodic changes of vaginal epithelium in female animals, placental epithelium and embryo formation. Vitamin A deficiency will also reduce the activity of enzymes needed to catalyze the formation of progesterone precursors and reduce the production of steroids in adrenal gland, gonad and placenta, which may be the reason for affecting reproductive function.
5, inhibit tumor growth
Clinical trials show that retinoic acid can delay or prevent precancerous lesions and prevent chemical carcinogens, especially for epithelial tumors, and has achieved good results as an adjuvant treatment in clinic. β -carotene has been reported as an antioxidant in recent years. It is an effective antioxidant to capture active oxygen, which is of great significance to prevent lipid peroxidation, cardiovascular diseases and tumors and delay aging.
6, nutritional supplements
It can be used as a nutritional additive in cosmetics to prevent rough skin and promote normal growth and development, and can be used in cream emulsion.
Although vitamin A has the above points, it has more beneficial effects on the human body, but like other nutrients, the extremes meet. Excessive intake can cause headache, nausea and diarrhea, hepatosplenomegaly and so on. So you need to take it in moderation.
function
1. has the functions of regulating the metabolism of epidermis and stratum corneum, resisting aging and removing wrinkles.
2. Reduce sebum overflow, make skin elastic, fade spots and soften skin at the same time.
3. Helps to protect epidermis and mucosa from bacteria, healthy skin and prevent skin cancer.
4. Prevent night blindness and vision loss, treat various eye diseases, and make women bright and ignorant.
5. Promote bone growth and help teeth grow and regenerate.
6. Effectively prevent obesity and keep women slim.
7. It can help prevent and treat hair loss. [2]
efficiency
1. Prevent night blindness and vision loss, and contribute to the treatment of various eye diseases (vitamin A can promote the formation of ocular photosensitive pigments);
2. Anti-respiratory infection;
3. Help the immune system to function normally;
4. Get well as soon as possible if you are sick;
5. It can keep the surface of tissues or organs healthy;
6. Helps to remove age spots;
7. Promote development, strengthen bones and keep skin, hair, teeth and gums healthy;
8. External use helps to treat acne, pustules, furuncles, skin surface ulcers and other diseases;
9. Conducive to the treatment of emphysema and hyperthyroidism.
10. Helps to treat alopecia.
Pharmacological reaction
This product is easily absorbed after oral administration and mainly stored in the liver. Almost all of them are metabolized in the body. β -carotene is the precursor of vitamin A, which can be converted into active vitamin A in animal intestinal mucosa. It is mainly excreted through urine and feces, and only a small amount is excreted through milk.
Beta carotene is also a fat-soluble antioxidant. The research of Facklman (1990) shows that β -carotene can prevent and treat many senile diseases, such as obstructive atherosclerosis, coronary heart disease and stroke. They believe that β -carotene can prevent low-density lipoprotein from being oxidized to form oxidized low-density lipoprotein, and toxic oxidized low-density lipoprotein will cause damage to vascular epithelial cells, thus accelerating the deposition of lipids in injured parts to form plaques, and even blocking blood vessels, leading to obstructive atherosclerosis and other diseases.
Vitamin A can treat dry eye, keratomalacia, xeroderma and night blindness. In addition, it is also effective for burns, frostbite and ulcers.
Vitamin A can increase the amount of PFC in sheep red blood cells or spleen of protein immunized mice, and enhance the antibody production caused by non-T cell-dependent antigen. It can also enhance the response of human peripheral blood lymphocytes to PHA and NK cell activity, improve macrophage activity, and stimulate T cell proliferation and IL 2 production.