HMP200/UPC203/VMP200/DEC/2019
DIGESTION AND
ABSORPTION OF
VITAMINS
WHAT ARE VITAMINS?
Organic dietary micronutrients
Vital physiological/Biochemical roles
Critical for human nutrition
Cannot be synthesized endogenously
Intermediary metabolism
Organ systems specific metabolism
No direct supply of energy
Necessary for Life, health, & growth
FAT-SOLUBLE VITAMINS
A
D
E
K
Ingested as esters
Cholesterol esterase
Fat intake necessary for their absorption by
enterocytes
FAT-SOLUBLE VITAMINS
Incorporated into micelles
Malabsorption
Lack of pancreatic lipolytic enzymes
Obstruction of bile duct
Obstructive jaundice
Exocrine pancreatic disorders
VITAMIN A (RETINOL)
(Yellow veg & fruits)
Constituent of visual pigments
Retinal pigment
Necessary for fetal development
Necessary for cell development throughout life
DEFICIENCY SYMPTOMS:
Follicular hyperkeratosis
Night blindness
Dry skin
VITAMIN D (1, 25-CHOLECALCIFEROL)
(Fish, liver)
Increased intestinal absorption of calcium &
phosphate
Hormonal control of calcium & phosphate
metabolism
Physiology of bone
DEFICIENCY SYMPTOMS
Rickets, bone demineralization & resorption
VITAMIN E (α-TOCOPHEROL)
(Milk, eggs, meat, leafy veg)
Antioxidants & Cofactors
DEFICIENCY SYMPTOMS
Peripheral neuropathy
Ataxia
Spinalcerebellar dysfunction
VITAMIN K
(Leafy Green Veg)
Blood clotting
Necessary for synthesis of prothrombin &
factors VII, IX, & X
DEFICIENCY SYMPTOMS
Hemorrhagic diseases
ADEK-DIGESTION & ABSORPTION
Gastric Acidity & proteolysis release ADEK from
association with proteins
Pancreatic & brush border membrane carboxyl ester
hydrolases liberate free ADEK from their esters
Incorporated into emulsion droplets, multilamella &
unilamella vesicles & mixed micelles
INSIDE THE ENTEROCYTES
Free ADEK or attached to carrier proteins diffuse to
SER
ADEK are associate with lipid droplets that form
chylomicrons & VLDLs
Translocation through Golgi & secretory vesicles for
exocytosis into lymph
From systemic blood circulation ADEK enters liver by
receptor-mediated endocytosis of chylomicrons
MALABSORPTION OF ADEK MAY BE CAUSED BY:
Malabsorptive surgery
Drugs that impair TAG hydrolysis (Orlistat)
Drugs that bind to bile acids (Cholestyramine)
Impaired hepatobiliary function (reduction of bile
acids)
Unabsorbable dietary fat substitutes
Impaired hepatic function
WATER SOLUBLE VITAMINS
VITAMIN B12 (CYANOCOBALAMIN/COBALAMIN)
(Liver, meat, eggs, milk)
RECOMMENDED DIETARY ALLOWANCE (RDA)- 2 µg
Coenzyme in in amino acid metabolism
Stimulates erythropoiesis
DEFICIENCY SYMPTOMS
Pernicious anemia (megaloblastic anemia)
VITAMIN B1 (THIAMINE)
(Liver, unrefined cereal grains)
Cofactor in decarboxylation of pyruvate & α-keto acids
DEFICIENCY SYMPTOMS
BERIBERI
NEURITIS
VITAMIN B2 (RIBOFLAVIN)
(Liver, milk)
Constituent of flavoproteins
DEFICIENCY SYMPTOMS
Hyperemia of nasopharyngeal mucosa
Normocytic anemia
Glossitis
Cheilosis
VITAMIN B3 NIACIN (NICOTINIC ACID)
(Yeast, lean meat, liver)
Constituent of nicotinamide adenine dinucleotide
(NAD+) & nicotinamide adenine dinucleotide phosphate
(NADP+)
DEFICIENCY SYMPTOMS
PELLAGRA (skin, GI tract, & brain)
VITAMIN B6 (PYRIDOXINE)
(Yeast, wheat, corn, liver)
Coenzyme in transamination for synthesis of amino acids
DEFICIENCY SYMPTOMS
STOMATITIS
GLOSSITIS
NORMOCYTIC ANEMIA
CONVULSIONS
HYPERIRRITABILITY
VITAMIN C (ASCORBIC ACID)
(Citrus fruits, leafy green veg)
Coenzyme in formation of hydroxyproline used in collagen
Maintains prosthetic metal ions in their reduced form
Scavenges free radicals
DEFICIENCY SYMPTOMS
SCURVY
FOLATE (FOLIC ACID)
(Leafy green veg)
(RDA)- 180 to 200 µg
PREGNANCY: 400 µg
Used to synthesize purines and thymine
Coenzyme for “1-carbon” transfer
Involved in methylating reactions
DEFICIENCY SYMPTOMS
MEGALOBLASTIC ANEMIA
SPRUE
NEURAL TUBE DEFECTS IN CHILDREN BORN TO
FOLATE-DEFICIENT WOMEN
BIOTIN
(Egg yolk, liver, tomatoes)
Coenzyme in carboxylation reactions
DEFICIENCY SYMPTOMS
NEUROLOGIC CHANGES
DEMATITIS
ENTERITIS
PANTOTHENIC ACID
(Eggs, liver, yeast)
Constituent of CoA
Necessary for carbohydrate metabolism
Necessary fat metabolism involving acetyl-coA
Necessary for amino acid synthesis
DEFICIENCY SYMPTOMS
ABDOMINAL PAIN, VOMITING, NEUROLOGIC SIGNS
DEMATITIS
ENTERITIS
ALOPECIA
ADRENAL INSUFFICIENCY
VITAMINS B12
(CYANOCOBALAMIN/COBALAMIN)
MEAT, FISH, SHELLFISH, EGGS, MILK
LARGE BODY STORES ~ 5 mg
DAILY ADULT REQUIREMENT - 2 µg (micrograms)
DELIVERED THROUGHOUT THE BODY
EXCESS SECRETED BY LIVER INTO BILE
ENTEROHEPATIC CIRCULATION
PRIMARY FUNCTION OF VIT B12
SERVE AS A COENZYME FOR
HOMOCYSTEINE:METHIONINE METHYLTRANSFERASE
TRANSFERS METHYL GROUP FROM
METHYLTETRAFORATE TO HOMOCYSTEINE FORMING:
METHIONINE &
TETRAHYDROFOLATE
PRIMARY FUNCTION OF VIT B12
COENZYME IN REDUCTION OF RIBONUCLEOTIDES TO
DEOXYRIBONUCLEOTIDES
PROMOTION OF FORMATION OF ERYTHROCYTES,
PROMOTION OF FORMATION MYELIN
DEFICIENCY SYMPTOMS
PERNICIOUS ANEMIA (MEGALOBLASTIC ANEMIA)
NEUROLOGICAL DYSFUNCTION
PSYCHOLOGICAL ABNORMALITIES
8 STEPS SHOWING THE PROCESS OF ABSORPTION OF VIT
B12
1. Cobalamin (CBL) bound to protein in food
2. Gastric acid & pepsin release from dietary protein
3. Gastric glands secrete haptocorrin, which then binds to CBL
4. Gastric parietal cells secrete intrinsic factor (IF)
VIT B12 IN THE STOMACH
BOUND TO PROTEINS
PEPSINS
LOW GASTRIC pH
VIT B12 COMPLEX WITH HAPTOCORRIN
VIT B12 CAN’T COMPLEX WITH IF
8 STEPS SHOWING THE PROCESS OF OBSORPTION OF VIT
B12
5. The pancreas secretes proteases & HCO3- - (alkaline secretion)
6. CBL is released after the proteolytic degradation of haptocorrin
7. The IF-CBL complex forms
8. Ileal enterocytes absorbs IF-CBL complex
VIT B12 IN THE PROXIMAL SMALL INTESTINE
HAPTOCORRIN DEGRADED BY PANCREATIC
PROTEASES
VIT B12 COMPLEX WITH IF
HIGHLY RESISTANT TO ENZYME DEGRADATION
ABSORPTION OF VIT B12 BY ENTEROCYTES IN THE ILEUM
SPECIFIC RECEPTORS
BINDS ONLY VIT B12-IF COMPLEX
SELECTIVE/SPECIFIC RAPID BINDING
REQUIRES Ca2+
NOT ENERGY DEPENDENT
INSIDE THE TERMINAL ILEUM ENTEROCYTES
Uses energy to absorb CBL-IF complex across the apical
membrane
CBL-IF dissociates
CBL-Transcobalamin II (CBL-TCII)
Portal circulation
Storage or secretion into the bile
CAUSES OF VIT B12 DEFICIENCY
STRICT VEGETARIAN DIET
NO GASTRIC PARIETAL CELLS
NO HCL & IF
POOR ABSORPTION OF VIT B12
CAUSES OF VIT B12 DEFICIENCY
BACTERIAL OVERGROWTH
BACTERIAL BINDING & METABOLISM OF VIT B12
CROHN DISEASE-AFFECTING ILEUM
ILEAL RESECTION
PERNICIOUS ANEMIA/MEGALOBLASTIC ANEMIA
Atrophy of gastric mucosa
Autoimmunity against parietal cells
Absence of parietal cells
Lack of HCI & IF
Elevated plasma gastrin levels
Deficiency of CBL
PERNICIOUS ANEMIA/MEGALOBLASTIC ANEMIA
Enlarged circulating RBCs
Peripheral neuropathy
Memory impairment, demetia, depression
Impaired senses of touch, vibrations. Temperature
Weakness, ataxia
PARENTERAL ADMINISTRATION OF CBL
Thank you
