digestion in man

digestion in man

• In the buccal cavity, saliva is secreted from the salivary glands into the mouth cavity.
• Saliva contains salts such as NaOH, NaHCO₃, Ca²⁺ and K⁺ which provides the right pH for the action of enzyme,
• Mucus in saliva Contains lysozyme, a lytic enzyme which kills bacteria that might have come in with food
• Salivary amylase in saliva begins the hydrolysis of starch to maltose
• In the stomach, the parietal or oxyntic cells secrete dilute HCl while the chief zymogen cells secrete the inactive enzyme pepsinogen and prorenin from the stomach wall into the stomach.
• HCl renders the pH of the stomach contents acidic which is the pH ideal for optimum activity of stomach enzymes.
• It helps to kill any bacteria present in the food we might have come in from the mouth.
• It losses the fibrous and cellular components of food facilitating digestion.
• It activates pepsinogen to pepsin and prorenin to rennin.
• Pepsin breaks down proteins to smaller polypeptides
• Rennin coagulates the soluble milk protein caseinogen into insoluble casein which is then digested by pepsin.
• In the duodenum, bile is released from the gall bladder through eh bile duct and pancreatic juice is secreted into the duodenum from the pancreases.
• Bile is produced in the liver and temporarily stored in the gall bladder. It contains bile salts such as NaHCO3 which neutralizes acidic chyme from the stomach creating an optimum pH for pancreatic enzymes.
• Bile salt emulsify fats reducing their surface tension by breaking them into small droplets, increasing surface area for the action of lipase.
• Pancreatic juice contains pancreatic amylase which breaks down starch to maltose
• Pancreatic lipase which breaks down lipids to fatty acids and glycerol
• Trypsinogen activated to trypsin by the hormone enterokinase with hydrolyses proteins to smaller polypeptides
• Peptides which break down peptides to amino acids
• Nucleases which break down nucleic acids into nucleotides.
• In the ileum, Brunner glands in the intestinal wall secret fluids into numerous microscopic pits called crypts of Lieberkühn which then secret intestinal juice into the intestinal lumen which contains enzymes that complete the process of digestion.
• Maltase breaks down maltose to two glucose molecules
• Lactase breaks down lactose to juice and galactose
• Sucrase breaks down sucrose to glucose and fructose
• Nucleosidases break down nucleotides into pentose sugar, an organic and a phosphate group
• Peptidase breaks down peptides into amino acids
• Lipase breaks down lipids to fatty acids and glycerol