Absorption of Water, Ions, Vitamins April 5, 2019 Absorption of Vitamins

Water & Electrolytes Colon 1.35 litr reabsorbed April 5, 2019 1.5 – 2.5 L/d ingested 8 – 10 L/d intestinal secretion 9.5 – 12.5 8 –10 litr reabsorbed in small intestine 1.5 Colon 1.35 litr reabsorbed 150 ml appears in stool April 5, 2019 Absorption of Vitamins

Absorption of Water Water absorption Dependent on solute absorption Passive Diffusion Dependent on solute absorption Trans-cellular Intercellular Lumen H2O H2O K+ Na+ Na+ H2O K+ H2O H2O ECF Na+ April 5, 2019 Absorption of Vitamins

Sodium 5 to 8 gm of Na+ ingested Additional 20 to 30 gm secreted by intestines Small intestine must absorb 25 to 35 gm Lumen 5 – 8 gm 20 – 30 gm Na+ Na+ 25 – 35 gm April 5, 2019 Absorption of Vitamins

Sodium 5% of intestinal sodium Lost in feces Lumen April 5, 2019 5 – 8 gm 20 – 30 gm Na+ Na+ 25 – 35 gm April 5, 2019 Absorption of Vitamins

Chloride, Bicarbonate Ions In the upper part of intestines Chloride ions Absorbed by passive diffusion Along electrical gradient Created by active absorption of Na+ April 5, 2019 Absorption of Vitamins

Bicarbonate In the duodenum & jejunum Bicarbonate ions Absorbed indirectly Active absorption of Na+ in exchange of H+ Na+ Na+ H+ H+ HCO3 - HCO3 - HCO3 - H2CO3 H2CO3 CO2 + H2O H2O + CO2 April 5, 2019 Absorption of Vitamins

Bicarbonate In the lumen The CO2 diffuse into the enterocytes H+ + HCO3-  H2CO3 H2CO3  H2O + CO2 The CO2 diffuse into the enterocytes Formation of carbonic acid Dissociates to form H+ HCO3- Na+ Na+ H+ H+ HCO3 - HCO3 - HCO3 - H2CO3 H2CO3 CO2 + H2O H2O + CO2 April 5, 2019 Absorption of Vitamins

Calcium Calcium plays important roles It is essential for Many physiological functions It is essential for Bone formation Contraction of muscles Transmission of nerve impulses Secretory process Absorptive process April 5, 2019 Absorption of Vitamins

Calcium Source In order to be absorbed Milk & milk products Cheese Digestive juices In order to be absorbed Must be in solution and ionized April 5, 2019 Absorption of Vitamins

Calcium Bound calcium must be freed At pH 5.0 to 7.0 Calcium phosphate & bicarbonate Solubilized At pH 5.0 to 7.0 Maximum amount of calcium is in the absorbable form Site of absorption Can occur throughout intestine Rate is most rapid in duodenum April 5, 2019 Absorption of Vitamins

Calcium Calcium is absorbed by active process Both the Mucosal carrier Basal layer mechanisms Require parathyroid hormone action Diet Ca++ Ca++ Ca++ Ca++ Ca++ + Prot Carrier protein April 5, 2019 Absorption of Vitamins

Fat Soluble Vitamins A D E K Require bile salt for solubilization (micelle) Absorbed with other lipids April 5, 2019 Absorption of Vitamins

Water Soluble Vitamins B Vitamins Nicotinic acid, biotin, pantothenate, pyridoxine, riboflavin, thiamin Vitamin C Absorbed by carriers that are Na+ cotransporters April 5, 2019 Absorption of Vitamins

Folic acid Folic acid composed In liver occurs Para-amino benzoic acid Glutamic acid Para-amino benzoic acid Pteridine In liver occurs Pentaglutamate (5 glutamic acid molecules) Para-amino benzoic acid Glutamic Acid Pteridine April 5, 2019 Absorption of Vitamins

Folic Acid In intestines Monoglutamate Polyglutamate hydrolysed to Monoglutamate by Intestinal conjugase enzyme Monoglutamate Absorbed into plasma April 5, 2019 Absorption of Vitamins

lumen Enterocyte Blood Folic acid Polyglutamate Monoglutamate April 5, 2019 Absorption of Vitamins

Vitamin B12 (Cyanocobalmin) Synthesized by bacteria in gut of ruminants Source Meat and sea food Stored in liver 50 – 100 μg/100gm Enough stores to last up to 3 yrs Dietary B12 bound to R-protein April 5, 2019 Absorption of Vitamins

B12 Absorption Dietary B12 is attached to protein by peptide bond R-protein B12 Dietary B12 is attached to protein by peptide bond Pepsin hydrolyses this bond B12 is then bound to Intrinsic factor Peptide bond Hydrolysed Intrinsic Factor B12 B12 April 5, 2019 Absorption of Vitamins

Vitamin B12 In Intestine In the Ileum B12 – Intrinsic factor Protect B12 from Hydrolysis In the Ileum Intrinsic factor – B12 complex Bind to receptors Vitamin B12 is then absorbed April 5, 2019 Absorption of Vitamins

Enterocyte lumen Blood IF B12 B12 Endocytosis Transcobalmin II April 5, 2019 Absorption of Vitamins

Vitamin B12 In the absence of Intrinsic factor Minimal amount can be absorbed by diffusion Require massive doses April 5, 2019 Absorption of Vitamins