CELLULAR BIOCHEMISTRY AND METABOLISM (CLS 331) Dr. Samah Kotb Nasr Eldeen Dr. Samah Kotb Nasr Eldeen 1 Dr Samah Kotb Lecturer of Biochemistry

Dr Samah Kotb 2 DIGESTION&ABSORPTIONOF VITAMINS & MINERALS DIGESTION&ABSORPTIONOF

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Vitamins are organic nutrients that are required in small quantities for a variety of biochemical functions and which generally cannot be synthesized in the body and must be supplied by the diet

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6  Vitamins and minerals are released from food during digestion.

Dr Samah Kotb 7  The fat-soluble vitamins are absorbed in the lipid micelles that result from fat digestion.  Water-soluble vitamins and most mineral salts are absorbed from the small intestine either by active transport or by carrier- mediated diffusion.

Dr Samah Kotb 8  Vitamin B12 absorption requires a specific transport protein, intrinsic factor.  Calcium absorption is dependent on vitamin D.  Zinc absorption probably requires a zinc-binding ligand secreted by the exocrine pancreas.

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10  Vitamin D regulates calcium homeostasis and is required for the intestinal absorption of calcium.

Dr Samah Kotb 11  Synthesis of the intracellular calcium binding protein, calbindin, required for calcium absorption, is induced by vitamin D, which also affects the permeability of the mucosal cells to calcium, an effect that is rapid and independent of protein synthesis.

Dr Samah Kotb 12 Phytic acid (inositol hexaphosphate) in cereals binds calcium in the intestinal lumen, preventing its absorption.

Dr Samah Kotb 13  Other minerals, including zinc, are also chelated by phytate.

Dr Samah Kotb 14  High concentrations of fatty acids in the intestinal lumen as a result of impaired fat absorption can also reduce calcium absorption by forming insoluble calcium salts; a high intake of oxalate can sometimes cause deficiency.

IRON ABSORPTION Dr Samah Kotb 15

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Dr Samah Kotb 17  It is limited & strictly controlled but is enhanced by vitamin C.  Inorganic iron is accumulated in intestinal mucosal cells bound to an intracellular protein, ferritin. Once the ferritin in the cell is saturated with iron, no more can enter. Iron Absorption

Dr Samah Kotb 18  The most effective compound is vitamin C, and while intakes of 40–60 mg of vitamin C per day are more than adequate to meet requirements.

Dr Samah Kotb 19  An intake of 25–50 mg of vitamin C per meal will enhance iron absorption, especially when iron salts are used to treat iron deficiency anemia.  Ethanol and fructose also enhance iron absorption.

Dr Samah Kotb 20  Heme iron from meat is absorbed separately and is considerably more available than inorganic iron.  However, the absorption of both inorganic and heme iron is impaired by calcium a glass of milk with a meal significantly reduces availability.

Dr Samah Kotb 21 The body mass index, defined as weight in kilograms divided by height in meters squared, is commonly used as a way of expressing relative obesity to height.

Dr Samah Kotb 22 Basal metabolic rate (BMR) is the energy expenditure by the body when at rest, but not asleep, under controlled conditions of thermal neutrality, measured at about 12 hours after the last meal, and depends on weight, age, and gender.

Dr Samah Kotb 23  Body weight affects BMR because there is a greater amount of active tissue in a larger body.

Dr Samah Kotb 24  The decrease in BMR with increasing age, even when body weight remains constant, is due to muscle tissue replacement by adipose tissue, which is metabolically much less active.

Dr Samah Kotb 25  Similarly, women have a significantly lower BMR than do men of the same body weight because women’s bodies have proportionately more adipose tissue than men.

Dr Samah Kotb 26  Undernutrition occurs in two extreme forms: marasmus- a form of severe malnutrition characterized by energy deficiency in adults and children and kwashiorkor is a form of severe protein -energy malnutrition characterized by edema in children.

Dr Samah Kotb 27 Overnutrition from excess energy intake is associated with diseases such as obesity, type 2 diabetes mellitus, atherosclerosis, cancer, and hypertension.

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