Human Digestive system (HDS) – Digestion and absorption of food
Digestion • Proteins, lipids and carbohydrates in food must be hydrolyzed into their monomers before they can be utilized. • Teeth, muscles, enzymes and water all play important roles in the digestion.
Carbohydrate digestion • Carbohydrates in food are in the form of • Glucose • Galactose Monosaccharides • Fructose • Sucrose • Maltose Disaccharides • Lactose • Starch • Cellulose Polysaccharides • Glycogen
Carbohydrate digestion in mouth • The digestion of carbohydrates starts here. • Starch is degraded to maltose by the activity of the enzyme amylase. • Cellulose can not be digested by humans, since no enzyme exists to digest it. • Microorganisms in the digestive system are capable of digesting cellulose. • The enzymes that digest carbohydrates are called carbohydrases.
Carbohydrate digestion in small intestine • Digestion completes in small intestine • Products of starch and ingested sucrose, lactose and maltose are broken down into their monomers (small particles) by the enzymes secreted by the intestinal mucosa.
Protein • Protein is a big molecule which is composed of aminoacids • Aminoacids build up peptides
Digestion of proteins in stomach • They are digested in the stomach and small intestine. • Gastric juice includes inactive pepsinogen which, in the presence of HCI, is converted to active pepsin. • It is an enzyme which hydrolyzes protein molecules to peptides.
Digestion of proteins in small intestine • Pancreatic secretion contains enzyme trypsinogen • Trypsinogen is converted by enterokinase into active trypsin, which hydrolyzes peptides to amino acids.
Lipid+Lipase+Bile+H 2 O → Fatty acids+Glycerol Digestion of Lipids • Digestion takes place only in the small intestine. • Bile salts breaks large masses of fat into smaller droplets. • As a result enzyme lipase breaks down smaller droplets into glycerol and fatty acids
Absorption in small intestine • Absorption occurs in small intestine • Villi play important role in absorption • Microvilli contains capillaries and lymph vessels, which transport nutrients
Absorption in small intestine • The venules from the villi flow into the hepatic portal vein, which transports all absorbed nutrients from the small intestine to the liver. • Blood leaves the liver by the hepatic vein and flows into the inferior vena cava, and finally enters the right atrium of the heart.
Absorption in large intestine • Absorption of excess water and electolytes • Microorganisms of the large intestine synthesize vitamins K.
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