vitamin A (redirected from vitamin A A excess)

vitamin A

n.

A fat-soluble vitamin or a mixture of vitamins, especially vitamin A₁ or a mixture of vitamins A₁ and A₂, occurring principally in fish-liver oils, milk, and some yellow and dark green vegetables, and functioning in normal cell growth and development with deficiencies causing hardening and roughening of the skin, night blindness, and degeneration of mucous membranes. Also called retinol.

---

vitamin A,

n a fat-soluble vitamin found in dark-colored vegetables and fruits, meats, dairy products, and whole eggs. Has been used to treat deficiencies, viral infections, and skin disorders. Contraindicated for pregnant women (beta-carotene is recommended instead), especially those taking valproic acid and for patients taking warfarin or isotretinoin. Also called
retinol.

---

vitamin A

a fat-soluble, organic alcohol formed in animal tissues from carotenoids found in plants. Called also retinol. It is formed from carotenoids, principally carotene, in the intestinal epithelium, except by cats, and stored in the liver. It is essential for the proper growth and maintenance of surface epithelium, for the accurate sculpting and proper growth of bones, and for the maintenance of light-sensitive pigments in the eye.

Nutritional deficiency due to lack of carotene in the diet in herbivores and to lack of carotene and preformed vitamin A in the diet in omnivores and carnivores causes hypovitaminosis A. The resulting clinical syndrome varies with species and age. In young animals there is compression of the brain and spinal cord caused by faulty bone growth and characterized by convulsions, blindness and posterior paralysis. In other animals there is night blindness, corneal keratinization, pityriasis, hoof defects, infertility and possibly congenital defects.

Hypovitaminosis in birds is manifested by poor egg production, ocular discharge at first watery then thick and caseous, a nasal discharge and pustular lesions and accumulations of caseous material in the mouth, pharynx, esophagus and trachea.

---

vitamin A A₂

called also dehydroretinol and found in fish livers. Has the same effects and efficiency as retinol; it is absorbed unchanged and is immediately metabolically active.

vitamin A A excess

see hypervitaminosis A.

vitamin A A poisoning

see hypervitaminosis A.

vitamin A A-responsive dermatosis

seborrhea, particularly in Cocker spaniels, is sometimes found to be responsive to vitamin A.

teratogenic vitamin A A

causes abnormalities in closure of the neural tube in the developing fetus causing defects in the brain, eye and heart.