Ascorbic Acid Deficiency (Vitamin C) PDF

## Ascorbic Acid (Vitamin C) ### Ascorbic Acid Deficiency Weakens Collagen Fibers Throughout the Body - Ascorbic acid is essential for activating the enzyme prolyl hydroxylase. - This enzyme promotes the hydroxylation step in the formation of hydroxyproline. - Hydroxyproline is an integral constit...

## Ascorbic Acid (Vitamin C) ### Ascorbic Acid Deficiency Weakens Collagen Fibers Throughout the Body - Ascorbic acid is essential for activating the enzyme prolyl hydroxylase. - This enzyme promotes the hydroxylation step in the formation of hydroxyproline. - Hydroxyproline is an integral constituent of collagen. - Without ascorbic acid, the collagen fibers are defective and weak. - This vitamin is essential for the growth and strength of the fibers in subcutaneous tissue, cartilage, bone, and teeth. ### Ascorbic Acid Deficiency Causes Scurvy - Deficiency of ascorbic acid for 20 to 30 weeks causes scurvy. - One of the most important effects of scurvy is failure of wounds to heal. - This is caused by failure of the cells to deposit collagen fibrils and intercellular cement substances. - Healing of a wound may require several months instead of the several days ordinarily necessary. - Lack of ascorbic acid also causes cessation of bone growth. - The cells of the growing epiphyses continue to proliferate but no new collagen is laid down between the cells. - The bones fracture easily at the point of growth because of failure to ossify.. - When an already ossified bone fractures in a person with ascorbic acid deficiency, the osteoblasts cannot form new bone matrix. - Consequently, the fractured bone does not heal. ### The Blood Vessel Walls Become Extremely Fragile in Scurvy - The blood vessel walls become extremely fragile in scurvy because of (1) failure of the endothelial cells to be cemented together properly and (2) failure to form the collagen fibrils normally present in vessel walls. - The capillaries are especially likely to rupture. - Many small petechial hemorrhages occur throughout the body. - The hemorrhages beneath the skin cause purpuric blotches, sometimes over the entire body. - To test for ascorbic acid deficiency, one can produce such petechial hemorrhages by inflating a blood pressure cuff over the upper arm. - This occludes the venous return of blood, the capillary pressure rises, and red blotches occur on the forearm if the ascorbic acid deficiency is sufficiently severe. ### In Extreme Scurvy - The muscle cells sometimes fragment. - Lesions of the gums occur, with loosening of the teeth. - Infections of the mouth develop. - Vomiting of blood, bloody stools, and cerebral hemorrhage can all occur. - Finally, high fever often develops before death. ## Vitamin D - Vitamin D increases calcium absorption from the gastrointestinal tract and helps control calcium deposition in the bone. - The mechanism by which vitamin D increases calcium absorption is mainly to promote active transport of calcium through the epithelium of the ileum. - It increases the formation of a calcium binding protein in the intestinal epithelial cells that aids in calcium absorption. - The specific functions of vitamin D in relation to overall body calcium metabolism and bone formation are presented in Chapter 79. ## Vitamin E - Several related compounds exhibit so-called vitamin E activity. - Only rare instances of proved vitamin E deficiency have occurred in human beings. - In experimental animals, lack of vitamin E can cause degeneration of the germinal epithelium in the testis and, therefore, can cause male sterility. - Lack of vitamin E can also cause resorption of a fetus after conception in the female. - Because of these effects of vitamin E deficiency, vitamin E is sometimes called the "antisterility vitamin." - Deficiency of vitamin E prevents normal growth and sometimes causes degeneration of the renal tubular cells and the muscle cells. - Vitamin E is believed to play a protective role in the prevention of oxidation of unsaturated fats. - In the absence of vitamin E, the quantity of unsaturated fats in the cells becomes diminished, causing abnormal structure and function of such cellular organelles as the mitochondria, the lysosomes, and even the cell membrane.