control of digestion

• Digestive glands


  Secrete digestive juices in response to the presence of food in the digestive tract
• Hormones


  • Used to control the secretion of digestive glands
• Gastrin release


  1. Sensory cells in the stomach detect the presence of food

  2. Other cells detect stomach distension

  3. These trigger stomach cells to release gastrin into the blood
• Gastrin release


  Stimulates the cells in the stomach that produce gastric juice to release more
• The process of gastrin release takes about 1 minute
• Secretin release


  1. Acidic chyme enters the duodenum

  2. Secretin is produced by the small intestine

  3. Secretin stimulates the pancreas to release bicarbonate to neutralize the acid
• CCK release


  1. Presence of fats or fatty acids in the duodenum

  2. CCK is released

  3. CCK stimulates the release of digestive enzymes from the pancreas and bile from the gallbladder
• Enterogastrone (GIP)


  • Also known as gastric inhibitory peptide
  • Released by the small intestine when it detects acidic chyme
  • GIP then works to inhibit stomach acid production, slowing the digestion process to allow more time for fat digestion
• Esophagus


  The tube that stretches between the pharynx and the stomach
• Esophagus


  • The inner surface is lined with mucous membranes
  • The outer layer is surrounded by smooth muscle
• Food movement through the esophagus

  Circular and longitudinal muscles help move the food down
• Stomach


  A thick walled J-shaped organ that can stretch to hold about 1-2 litres of material
• Stomach


  • Food is further digested mechanically by muscular churning
  • Food is also chemically digested by gastric juices
• Gastric glands


  Produce pepsinogen and HCl
• Pepsinogen


  When activated by HCl, it forms pepsin enzyme that breaks down proteins
• HCl


  Gives the stomach an approximate pH of 2, helping to break down food and kill bacteria
• Chyme


  The acidic semi-liquid mass that the food is converted into in the stomach
• Food movement from stomach

  Pyloric sphincter opens to release chyme to the small intestine
• Digestion


  The mechanical and chemical breakdown of ingested food into their respective monomers
• Absorption


  Transporting the digested nutrients from the gut into the blood or lymph to be distributed
• Elimination


  Expulsion of indigestible food from the body
• Digestion in the mouth

  Food is broken down mechanically by the teeth and chemically by saliva
• Saliva


  Contains water, mucus and salivary amylase which breaks down starch
• Salivary glands

  • Parotid
  • Sublingual
  • Submandibular
• Bolus


  The ball of chewed food formed by the tongue and passed to the back of the mouth
• Pharynx


  The passageway between the mouth and esophagus where the food is swallowed
• Swallowing


  A reflex action that causes the epiglottis to cover the trachea
• Small intestine


  Where most of the digestion and absorption occurs, divided into duodenum, jejunum and ileum
• Small intestine


  • Receives secretions from the liver and pancreas to further digest the food
  • Contains villi to increase the surface area for absorption
• Bile


  A thick green liquid produced by the liver that helps break down fats
• Pancreatic juice


  Contains enzymes like amylase, trypsin, lipase and nuclease to further digest food
• Intestinal enzymes


  Peptidase, maltase, lactase and nuclease to break down food into monomers
• Lacteal


  Part of the lymphatic system that absorbs fat products
• Capillaries


  Part of the circulatory system that absorb glucose, amino acids and nucleotides
• Colon


  The large intestine that reabsorbs water and houses gut bacteria
• Rectum


  The last section of the colon where feces is stored before elimination
• Appendix


  A small finger-like extension at the beginning of the colon, now a vestigial structure