Digestion and Absorbtion of vitamins Dr. Samah Kotb Lecturer of Biochemistry 2015 Cellular Biochemistry and metabolism 1 CLS 331

Dr Samah Kotb2 DIGESTION&ABSORPTIONOF VITAMINS & MINERALS DIGESTION&ABSORPTIONOF

Dr Samah Kotb3

Objectives In the end of the lecture, you should know 1.Definition of vitamins. 2.Digestion and absorption of vitamins and minerals. 3.Some important definitions in metabolism

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

DIGESTION & ABSORPTION OF VITAMINS & MINERALS Dr Samah Kotb6

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

Dr Samah Kotb8  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 Kotb9  Vitamin B 12 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.

Dr Samah Kotb10

Dr Samah Kotb11  Vitamin D regulates calcium homeostasis and is required for the intestinal absorption of calcium.

Dr Samah Kotb12  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 Kotb13 Phytic acid (inositol hexaphosphate) in cereals binds calcium in the intestinal lumen, preventing its absorption.

Dr Samah Kotb14  Other minerals, including zinc, are also chelated by phytate.

Dr Samah Kotb15  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 Kotb16

Dr Samah Kotb17

Dr Samah Kotb18  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 Kotb19  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. Iron Absorption

Dr Samah Kotb20  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.  fructose also enhance iron absorption. Iron Absorption

Dr Samah Kotb 21  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. Iron Absorption

Dr Samah Kotb23 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. body mass index (BMI)

Dr Samah Kotb24 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. Basal metabolic rate (BMR)

Dr Samah Kotb25  Body weight affects BMR because there is a greater amount of active tissue in a larger body. Basal metabolic rate (BMR)

Dr Samah Kotb26  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. Basal metabolic rate (BMR)

Dr Samah Kotb27  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. Basal metabolic rate (BMR)

Dr Samah Kotb28  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. Basal metabolic rate (BMR)

Dr Samah Kotb29 Overnutrition from excess energy intake is associated with diseases such as obesity, type 2 diabetes mellitus, atherosclerosis, cancer, and hypertension. Basal metabolic rate (BMR)

Dr Samah Kotb30