Lecture 4

Cards (15)

  • Stomach
    • Mechanical breakdown of food continues, this includes the churning of food across the rugae (lines in the wall (muscles) of the stomach)
    • Gastric juices are released (HCl, mucus, pepsinogen)
    • HCl chemically breaks down food and kills foreign substances (eg. bacteria), HCl converts pepsinogen into active form pepsin. 
    • Pepsin breaks down proteins into shorter chains
    • The food becomes a semi-liquid called chyme
    • Mucus protects stomach from being digested by HCl
  • The Pyloric Sphincter 
    • Controls the movement of food into the small intestine. Moves like a drawstring on a bag. 
    • At this point the food is semi liquid and 5% digested
    • The undigested matter is known as chyme. 
  • More on the stomach…
    • The innermost mucosa of the stomach is folded into deep pits called GASTRIC PITS.
    • These pits are lined with specialized cells that secrete various substances that aid in digestion. Collectively, all of these secretions are called Gastric JUICES.
  • The GASTRIC JUICES are composed of:
    • Hydrochloric Acid (HCl) - kills bacteria entering with food and converts inactive pepsinogen to active pepsin.
    • Water & Salts
    • Pepsin active form of the enzyme pepsinogen, that initiate the digestion of protein
    • Mucus - secreted by mucosa cells and a THICK layer of mucus protects the stomach’s inner layer (wall) from HCl and pepsin → as both can degrade the protein in the cell membranes of the stomach cells 
  • More on the Pepsin..
    • PEPSIN breaks down PROTEINS and/or LARGE POLYPEPTIDES into SMALLER POLYPEPTIDES
    • Pepsinogen is the inactive form of PEPSIN (active form) 
    • This activation only occurs in an acidic environment (low pH_ of HCl in the stomach.
    • Protein digestion begins in the stomach, but it is not complete
    • The small polypeptides, produced after the action of pepsin, will undergo further chemical digestion in the SMALL INTESTINES, to be broken down into their amino acids subunits…
  • Small Intestine
    • About 2.5 cm wide, 7 m long
    • Coiled Loop
    • There is Gastric Juice here as well to help with chemical digestion of chyme
  • Three parts of the small intestine:
    1. Duodenum: first 25 cm where the majority of digestion occurs
    2. Jejunum: 3m long
    3. Ileum: 4 m long 
  • Small Intestine - Duodenum
    • Chemical digestion of food
    • Has tubes (ducts) leading from liver and pancreas
    • Bile and digestive enzymes enter from the ducts and are mixed with the chyme 
    • Disaccharidases (sucrase, maltase, lactase) are released to further break down carbs 
  • Small Intestine - Jejunum & Ileum 
    • Responsible for nutrient absorption 
    • Molecules of fat, protein and carbohydrates get absorbed into the bloodstream and then are transported to liver 
    • Pushes undigested material into large intestine
  • Absorption in Small Intestine
    • The interior of the small intestine is covered in finger-like tube extensions called villi (singular = villus)
    • villi greatly increase the surface area of the small intestine thus increased absorption 
    • Each villus has hair like extensions called microvilli (singular = microvillus)
    • These will also increase the surface area of the interior small intestine and thus increase absorption
  • Characteristics of Villi
    1 - Project into the SI, and are bathed in the digested nutrient molecules 
    2 - one cell layer thick (thin enough for absorption of nutrient molecules EASILY)
    3 - contain blood vessels (capillaries) and a lymph vessel 
    • (lacteal) inside of them to absorb the nutrient molecules 
  • Label this
    A) Large Intestine
    B) Transverse Colon
    C) Ascending Colon
    D) Appendix / Cecum
    E) Anus
    F) Rectum
    G) Descending Colon
  • Large Intestine - Colon
    water and dissolved minerals are absorbed from undigested food
    bacteria break food down further and produce vitamins (B12, K) and amino acids
    • forms and expels feces
  • Large Intestine - Rectum
    • acts as temporary storage area for feces
  • Large Intestine - Anus
    • egestion of wastes by peristalsis
    • sphincters control the release of feces