Digestion

Digestive Anatomy

  • digestive system is a tube connecting external orifice of mouth to external orifice of anus

    • as material passes along the tube it is broken down and absorbed into the bloodstream

  • digestion: relies on mechanical & chemical means of breaking down large foodstuffs into small enough molecules to be absorbed

  • absorption: occurs in various organs of GI tract

  • motility: movement through GI tract is provided by peristalsis (contractions propelling of food to next area) & segmentation (contractions keeping food in place to increase exposure to absorptive tissue)

  • Esophagus: where peristalsis starts

  • Stomach: where chemical breakdown begins, and where food can be stored w/in body

  • Small intestine: where most chemical breakdown is & where most absorption occurs. Presence of vili and microvili

  • Large intestine: extracts as much water as possible

Grissy’s Lecture: Glucose Regulation

Why Glucose is Important

  • glucose = primary fuel = high energy yield, essential for survival

  • Pancreatic B cells: sense increase in glucose

  • Pancreatic A cells: sense decrease in glucose

  • brain can also sense glucose

  • integrated hormonal + neural response

How glucose enters the B-cell

  • facilitated diffusion

  • GLUT glucose transporters

  • independent of insulin

Glucose Metabolism

Once glucose is in the B-cell:

  1. glucose metabolized

  2. ATP/ADP increase

  3. ATP closes k+ channels

  4. Membrane depolarization from Ca influx

  5. insulin secretion

Gluconeogenesis

  • creation of new glucose in liver/kidneys using:

    • lactate

    • amino acids

    • glycerol

Glycogenolysis

  • breakdown of glycogen → glucose

  • occurs in liver

  • rapid response, short term supply

Glycolysis

  • breakdown of glucose for energy

  • all cells

  • makes ATP

Homeostatic Framework

Insulin

  • hormone from pancreatic B cells

  • released after eating to lower blood glucose

  • makes muscle, liver, and fat store glucose for energy

  • “key” allowing glucose to enter cell

Glucagon

  • hormone released by pancreatic A cells

  • released when blood glucose is low

  • gets glucose into the bloodstream by having liver cells perform glycogenolysis