digestion system

• What is the main function of the stomach and give the adaptations of muscle layer and the adaptations of submucosa

  - The main function: temproray food store; musclar churning mixes and breaks up food and contains enzymes the kills microorganisms in food some digestion

  - Adaptations of muscle layer: three layers run in different directions as the layers contracts and relaxes

  - adaptations of submucosa: seperates musclar and glandular layer
• What is the main function of the oesophagus and give the adaptations of muscle layer and the adaptations of submucosa

  - the main function: to push food to the stomach

  - adaptations of muscle layer: two thick layers force solid food along by peristalsis

  - adaptations of submucosa: elastic to allow expansion as food passes. Glands secrete mucus to lubricate passage of food
• What is the main function of the duodenum and give the adaptations of muscle layer and the adaptations of submucosa

  Duodenum is the first 25cm of small intestine

  - main function: neutralisation of stomach acid. Point of entry for pancreatic juice and bile. Digestion and some absorption

  - adaptations of muscle layer: two layers for peristalsis

  - adaptations for submucosa: contains Brunner's glands that secrete alkaline mucus which helps to neutralise stomach acid.
• What is the main function of the Ileum and give the adaptations of muscle layer and the adaptations of submucosa

  Ileum is the lower part of small intestine

  - main function: completion of digestion. Absorption of products of digestion.

  - adaptations of muscle layer: two layers for peristalsis

  - adaptations of submucosa: contains many blood and lymph vessels that take up absorbed foods and transport them around the body
• Name the enzyme secreted due to the sight, smell, and taste of food; and what is it function?

  Saliva contains the enzyme, salivary amylase with water, mucus and chloride ions. Amylase hydrolyses starch into maltose
• What is the gastric juice


  The digestive secretion produced by the stomach lining, it consists of pepsinogen, HCl, and mucus
• HCl has three main functions:

  - kills some of the bacteria present in the food

  - provides an optimum PH (1-2) for the enzyme pepsin

  - activates pepsin
• What is the pancreatic juice

  An alkaline fluid, containing sodium hydrogen carbonate, amylase, lipase, trypsin, exopeptidases
• What is the function of lipases


  Hydrolyses lipids into fatty acids and glycerol
• What is the function of trypsin (endopeptidase)


  Hydrolyses specific internal peptide bonds, breaking down larger polypeptides into smaller polypeptides
• What is the function of exopeptidases

  Hydrolyse the terminal peptide bonds at the ends of polypeptide chains releasing individual amino acids
• What is bile?


  This is an alkaline fluid containing sodium hydrogen carbonate and bile salts. It is produced in the liver and stored in the gall bladder, entering the duodenum by the bile duct
• What is the function of the bile?

  It neutralises the acidic chyme and provides a slightly alkaline optimum PH for the pancreatic enzymes. The bile salts emulsify lipids causing them to form small droplets, increasing their surface area to speed up hydrolysis by pancreatic lipase.
• What is the pancreatic juice and what does it contain?

  It's an alkaline fluid containing sodium hydrogen carbonate and several enzymes including: amylase (carbohydrates) / lipase / trypsin (endopeptidase) / exopeptidase
• What is amylase?


  An enzyme that works with carbohydrates, completes the hydrolysis of starch into maltose
• What is lipase?


  Hydrolyses lipids into fatty acids and glycerol
• What is trypsin?


  An enzyme that works with endopeptidase - hydrolyses specific internal peptide bonds, breaking down larger polypeptides into smaller polypeptides. Trypsin is stored and secreted in an inactive form and is activated in the duodenum
• What is maltase?


  Hydrolyse maltose (disaccharide) to two glucose molecules
• What is exopeptidase?


  Hydrolyse the terminal peptide bonds at the ends of polypeptide chains releasing individual amino acids. These exopeptidase continue to remove these terminal amino acids until a dipeptide is produced
• What is dipeptidase


  These hydrolyse the dipeptides to produce individual amino acids
• Why are the products of the enzyme production in the duodenum are close to the epithelial cell surface?

  To allow transport by specific carrier proteins
• Adaptations of the ilium:

  - large surface area due to its long length and the presence of vili and microvilli

  -short diffusion pathway for absorption die to wall of villi consisting of a single layer of epithelial cells
• How does the ileum maintain a high diffusion gradient?

  - Villi contain blood capillaries which absorb monosaccharides and amino acids maintaining high diffusion gradient for further absorption

  - the lacteals (lymph vessels) in the villi absorb digested lipids maintaining a high diffusion gradient
• How simple sugars are absorbed into the blood capillaries?

  By vacillated diffusion and co transport using specific carrier proteins
• How amino acids are absorbed?

  Enter the blood capillaries by facilitated diffusion and activate transport through carrier proteins specific for amino acids
• Absorption in ileum related to lipids

  - Monoglycerides, fatty acids and glycerol can enter the columnar epithelial cells of the

  villi by simple diffusion (without the use of carriers due to their lipid solubility) and are

  reconverted into triglycerides inside the cells.

  - These lipids are coated by protein to form chylomicrons (very small lipid droplets).

  - The chylomicrons are transported to the lacteal in the villi. The lymph eventually drains into the blood stream at the subclavian vein and the chylomicrons are then transported around the body.
• What is co-transport of glucose?

  Used to absorb the glucose against a concentration gradient and it involves glucose being taken into the epithelial cells along with sodium ions Na+
• What is the mechanism of Co-transport of glucose?

  1) sodium ions in epithelial cells transported into blood strewn by co-transport (when 1 sodium ion enters blood stream, 1 potassium ion enter the epithelial cell)

  2) now we have more sodium ions in the lumen (where the food is) than in the epithelium, so the NA+ will enter the epithelium with glucose

  3- glucose diffuses from epithelium into the blood via a carrier protein
• What is symbiotic bacteria?

  Bacteria that is good for us in our guts producing vitamins and breaking down fibres / helps with digestion
• Adaptations of the large intestine (colon)

  - contain simple columnar epithelium

  - goblet cells (mucus production)
• The digestive secretion produced by the stomach is

  Gastric juice
• The secretion of gastric juice is stimulated by a number of factor, these include:

  Cephalic phase and gastric phase
• Describe the cephalic phase in the secretion of gastric juice

  During chewing of food in the mouth, nerve impulses are transmitted along parasympathetic nerve to the stomach lining, stimulating the release of gastric juice
• Describe the gastric phase in the secretion of gastric juice

  The presence of food in the stomach 1) causes distension of the stomach 2) produces peptide digestion;

  Which stimulates the release of the hormone gastric from the stomach lining. Gastrin travels in the blood to the gastric glands in the stomach lining, also stimulating the release of gastric juices.
• What stimulates the release of cholecystokinin and secretin in the duodenum?

  As the acidic chyme hits the mucosa of the duodenum it stimulates the release of these two hormones
• Compare cholecystokinin and secretin

  1) cholecystokinin: travels in the blood to the gall bladder secreting bile and to the pancreas stimulating it to secrete the enzymic components of pancreatic juice, which enter the duodenum

  2) secretin: travels in the blood to the pancreas stimulating the secretion of the non-enzymic component of pancreatic juice - sodium hydrogen carbonate. This enters the duodenum with the pancreatic enzymes, secretin also stimulates the release of bile by hepatic (liver) cells

  Both hormones also inhabit the secretion of gastric juice