Transcript lec---22
Physiology 3-Digestion • Digestion: is the mechanical and chemical breaking down of food into smaller components, to a form that can be absorbed. Digestion is a form of catabolism that means break down of macro-food molecules to smaller one. a)- Extracellular digestion : In mammals, food enters the mouth, being chewed by teeth, and broken down by the saliva اfrom the salivary glands. Then it travels down the esophagus into the stomach , where acid begins physical break down of some food. The food go through the small intestine, through the large intestine, and are excreted outside. b)- Intracellular digestion : Some other unicellular organisms use different mechanisms to digest food inside the cell. Digestive system The main stages of food processing 1- Ingestion : is the act of eating 2- Digestion :is break down of food into small molecules enough for the body to absorb. 3- Absorption : the animal cell take up small molecules such as amino acid and simple sugar. 4- Elimination : when undigested material passes out of the digestive system. Mammalian digestive system Organ specialized for food processing : 1- Mouth: ingestion and first stages of digestion occur in The mouth as teeth cut and grind food Salivary gland released saliva which contain amylase enzyme That hydrolyzes starch into small disaccharide Saliva has protective function. 2- Pharynx 3- Esophagus : waves of muscular contraction move bolus to the stomach 4- stomach Stomach secretes gastric juice that mixed with digestive food to form chyme. Components of gastric juice • Hydrochloric acid converts pepsinogen to pepsin which begin chemical digestion of proteins. • Hcl also kill most bacteria. 5-Small intestine Most enzymatic hydrolysis of macromolecules from food occurs in the small intestine . Hormonal control digestion 1- gastrin stimulate production of gastric juice 2- secretin :stimulates the pancreas to release sodium carbonate which neutralize chyme. Pancreatic enzyme are trysine and chymotrypsin. . 6- Large intestine: • Its function is to absorb water from the remaining indigestible food matter, and then to pass useless waste material from the body . Absorption in small intestine The nutrient must cross lining of alimentary canal to reach blood stream Most of this absorption occurs in small intestine which has huge surface area . Transport across epithelial cell: 1-Sugar like fructose move by facilitate diffusion. 2- Amino acid, vitamins and most glucose molecules are pumped against concentration gradient . 3- Triglycerides are incorporated into water-soluable called chylomicrons which are too large to pass through capillaries. They are transported into lacteals which are part of lymphatic system. Functions of liver 1- Production of bile . 2- Detoxification. • Bile plays an important role in the destruction of red blood cells which results in formation of bile pigments. • Bile pigment eliminated from the body with feces. Bile production by the liver: Digestion of fat and lipids begin in small intestine due to production of bile By the liver. Bile contain salts which aid indigestion and absorption of lipids. Bile store and concentrated in gallbladder Enzymes and their function Enzymes Function organ Amylase (Saliva) Converts starch to soluble sugars (disaccharides maltose) mouth stomach Pepsin Breaks protein into peptones Gastric amylase Degradation of starch pancreas stomach Rennin Conversion of liquid milk to solid particles Pancreas Gastric lipase Degradation of butter fat Sucrase Converts sucrose to disaccharides and monosaccharides Maltase Converts maltose to glucose Lactase Converts lactose to glucose and galactose Small Intestine Small Intestine Small Intestine The Summary