TEST 7

• How long is the Large intestine

  1.5 M in length, but 6.5 cm in Diameter
• What are the 4 major regions of the Large intestine?

  Cecum, Colon, Rectum, and ileum
• What are the 4 major regions of the colon - which ones are retroperitoneal

  Ascending colon (R), Transverse colon, Descending colon (R), Sigmoid colon
• Rectum


  leads to the anal canal, connects to the external portion of the anus

  - 15 cm

  - made of simple columnar epithelium
• What guards the ileum and what does it do?

  The ileocecal sphincter- - controls chyme
• What are the two sharp turns in the large intestine called?

  The Right and Left Colic Fixture
• Teniae coli


  three bands of longitudinal smooth muscle in muscularis
• haustra


  pouches that form in the large intestine when the longitudinal muscles are shorter than the colon
• omental appendices


  Lobules of fat hanging off external surface of haustra; attached to the teniae coli
• Vermiform appendix


  plays a role in immune responses as it is attached to the cecum, may repopulate the microbes
• Anal Canal -what type ofcell

  2-3 cm of the GI tract - protective effect of mucus layer- stratified squamous cell
• Internal anal sphincter


  smooth muscle, involuntary, controlled by ANS
• External Anal sphincter


  skeletal muscle, voluntary
• hemmoroids


  swollen blood vessels in and around the anus and lower rectum, stretched and inflammed
• Anal columns


  folds in mucous membrane- arteries and veins
• Which layer is much more thicker in the large intestine than it is in the other regions of the digestive system

  the muscular layer
• What is the Muscularis layer in the large intesine?

  Longitudinal, Myenteric plexus, Circular Layer of Muscle
• What is in the submucosa layer of the large intestine?

  Arterioles, venules, and lymphatic vessels
• What is in the Mucosa layer of the large intestine?

  Muscularis Mucosae, Lymphatic nodule, Lamina propria, Glands, Goblet Cells, Absorptive Cells
• What structure in the Large intestine create the pores?

  The Lamina propria
• What is the difference between the absorptive cells in the small intestine compared to the large intestine?

  The Large intestine absorptive cells mainly absorbs water rather than carbs, fats, and proteins
• Gastroileal reflex


  When the stomach is full, gastrin hormone from the G cells relaxes the ileocecal sphincter to make room in the small intestine
• Haustral Churning


  haustrum fills, once distended, contracts to move contents to next haustrum
• Peristaltic waves


  3 to 12 contraction/minute
• Mass peristalsis


  Strong peristaltic wave from transverse colon - pushed contents into the rectum
• Gastrocolic reflex


  initiates mass peristalsis - food moves from transverse colon to rectum when the stomach is full
• What does bacteria do in the Large intestine?

  Undigested Carbs (methane, CO2) to produce the gas

  Digestion of amino acids (indoles and skatoles to produce smell)

  Decompose of bilirubin to produce color

  Produce vitamins K and B in the colon,

  Maintain homeostasis
• What is feces


  dead epithelial cell, undigested foods such as cellulose, bacteria, metaboli by-products
• Defecation Reflex


  Initiated by the gastrocolic reflex,

  - stretch receptors signal the PNS within the sacral region

  - the descending and sigmoid colon

  - increases the pressure as the anal rectum length decreases
• what are the phases of digestion

  cephalic, gastric, intestinal
• Cephalic phase of digestion

  Before, or just as food is eaten -

  - gastric secretion and motility

  - Use of sensory receptors + neural centres in the cerebral cortex + hypothalamus and brain stem
• Which cranial nerves are activated during the cephalic phse

  nerves 7 + 9 signal the salivary glands to increase salivation

  Vagus Nerve - stimulates gastric glands to release gastric juice into stomach
• Gastric phase


  Increase secretion of gastric juices to liquify food into chyme

  - Neural Rg. & Hormonal Rg.
• What happens neurally during the gastric phase

  1. Stretch receptors and chemoreceptors are activated in the stomach by the distension and increase in pH

  2. Submucosal plexus signals the parasympathetic and ENS

  3. Begins the peristaltic wave and continues the secretion of gastric juice
• How is gastric secretion reversed?

  as chyme leaves, the pH and distension decrease --> less gastric juice secretion
• What is happening hormonally in the Gastric phase?

  Gastrin released from G cells into the blood when stomach is distended or an increase in the pH
• What does gastrin do?

  increased release of gastric juice, increased constriction of lower esophageal sphincter, increased motility in the stomach by stimulating peristaltic waves, relaxing pyloric sphincter

  
  

  - pushes chyme into the large intestine
• How do we reverse gastrin release

  pH decreases
• What occurs in the intestinal phase?

  once chyme enters the small intestine - this promotes the digestion by limiting its speed

  - inhibition of gastric emptying to allow full digestion & absorption
• What happens to the intestine neurally during the intestinal phase?

  Stretch receptors in duodenum sense some level of distension using theenterogastric reflex(inhibits PNS and increase SNS through medulla oblongata)

  - Gastric motility inhibited and an increase in contraction of pyloric sphincter (so less chyme leaves)