Bio 20IB- Digestion

• saliva contains amylase enzymes, which break down starches
• saliva also lubricates so you can swallow food and drinks more easily
• we detect flavor when food particles dissolved in saliva penetrate cells of taste buds
• the esophagus is the path from the mouth to the stomach
• a bolus of food stretches the esophagus, causing rhythmic contractions, called peristalsis, which helps move food down
• the stomach contains 3 layers of muscle in opposite directions to churn food
• 2 sphincters regulate what enters and exits stomach: lower esophageal sphincter (LES), and the phyloric sphincter
• the lower esophageal sphincter allows food to enter stomach
• pyloric sphincter allows food to leave stomach into the small intestine
• cells secrete stomach fluid called gastric fluid which aids digestion
• gastric fluids contain mucus, hydrochloric acid, and pepsinogen
• hydrochloric acid in gastric fluid kills harmful substances and converts pepsinogen into pepsin
• pepsinogen in gastric fluids, when converted to pepsin, is a digestive enzyme that breaks proteins into smaller peptides
• the stomach has a PH level between 2 and 3, so the mucus layer protects the stomach lining
• the duodenum is the first 25-30cm of the small intestine
• villi line the small intestine to increase surface area. the lining of each villus has microvilli, to further increase surface area
• each villus is supplied with capillary networks, which are intertwined with lymph vessels called lacteals that transport material
• capillary networks absorb monosaccharides and amino acids
• lacteals absorb fats
• capillary: blood vessel that connects arteries and veins; the site of fluid and gas exchange
• lacteal: small vessel that transports the products of fat digestion to the circulatory system
• when acids enter the small intestine, a chemical called prosecretin is converted to secretin, where it is absorbed into the bloodstream and carried to the pancreas. This signals the release of bicarbonate ions which raise the PH level in the small intestine to 8-9 and inactivates pepsin
• pancreatic secretions contain enzymes that help the breakdown of proteins, carbs and lipids. The enzymes include tripsinogen, erepsin, amylase, and lipases
• trypsinogen: a protein digesting enzyme. when it enters the small intestine, an enzyme called enterokinase converts inactive trypsinogen to trypsin, which breaks down long-chain polypeptides
• erepsin: released from the pancreas and small intestine. it breaks down short chain polypeptides into its amino acids
• amylase: released from the pancreas and continues the digestion of carbohydrates. They are broken down into disaccharides and another enzyme called disaccharidases complete the digestion
• Lipases: break down lipids. Pancreatic lipase breaks down fat into glycerol and fatty acids. Phospholipase acts on phospholipids
• bile salts: produced by the liver and stored in the gall bladder. they emulsify fats so that lipases can act more efficiently
• when fats are in the small intestine, a hormone called cholecystokinen is released, which travels through blood to the gallbladder, triggering it to release bile salts
• liver stores glycogen and vitamins A, B12, and D
• the liver detoxifies harmful substances. It makes substances more soluble so it can be released in urine
• gallstones: crystals of bile salts that form in the gallbladder
• jaundice: yellowish discolouration of skin and tissues brough about by the collection of bile pigments in the blood
• cirrhosis: chronic inflammation of the liver tissue, characterized by the growth of nonfunctioning fibrous tissue
• the colon is the largest part of the large intestine. it stores waste, and absorbs water which contains vitamins and minerals
• the large intestine stores bacteria essential to life. it synthesizes vitamins B and K
• cellulose reaches the large intestine undigested. it provides bulk. when waste builds up in the large intestine, receptors in the wall sends signals to the nervous system, prompting bowel movement
• gastric secretions are released when smelling or seeing food, not just when you are eating
• when food enters stomach, nerves in the stomach will cause muscles to contract and gastric fluids to be secreted
• eating a large meal activates more receptors, which causes more forceful contractions so the stomach empties faster