physiology lab: glucose absorption

mechanical digestion

physical force breaks down large pieces into smaller particles

major organs of digestive system

oral cavity, salivary glands, esophagus, liver, stomach, gall bladder, pancreas, small intestine, large intestine

GI tract organs

oral cavity, esophagus, stomach, small intestine, large intestine

stomach

reservoir that controls the rate at which food enters the responsible for rhythmic contractions such as propulsion, retropulsion, and grinding (churning in the antrum)

monosaccharides

glucose, fructose, galactose

disaccharides

lactose and maltose

polysaccharides

cellulose and starch

sucrose, maltose, and starch products

one glucose and one fructose, two glucose, multiple glucose

fiber

found in sources of simple carbs like raw fruits and veggies

main site of monosaccharide absorption

small intestine

SGLT1

cotransporter that moves glucose against its concentration gradient, along with Na+, from the lumen into the epithelial

GLUT2

transporter that pumps glucose from the intestinal epithelia into the neighboring capillaries

protein digestion

amino acids, di-, and tri-peptides can be absorbed

protein absorption

H+/di/tripeptide symporter brings peptides from the small intestine into the epithelial layer, where proteases cut peptides into amino acids.

amino acids are then distributed to the capillaries

lipid digestion

begins via lipases in the acidic, churning environment of the stomach and then takes place in the small intestine once lipids have bene morphed into micelles

micelle

a phospholipid-wrapped-salted unit that allows the free fatty acids inside to be digested and fully absorbed.

micelle formation

delayed gastric emptying allows lipid movement into SI be simultaneous with release of bile salts from the gall bladder, which act as the “shell” for the emulsified chunks of lipids

lipid absorption

some free fatty acids from micelles are reassembled into triglycerides by the smooth ER and packaged as chylomicrons by the golgi apparatus before being sent into the lymph vessel → subclavian vein → bloodstream. small fatty acids are absorbed into intestinal capillaries.

factors that control rate of digestion

volume (more food, more contraction)

liquid vs solid (solids must undergo retropulsion)

osmolarity

brain energy source

glucose: it is the only substrate that can bypass the BBB

glucagon

hormone released by alpha pancreatic cells when blood glucose levels decrease

insulin

secreted by beta pancreatic cells:

• increases GLUT4 expression (glucose import into cells)

• prompts glucose storage as glycogen or triglycerides

• tells other systems to use glucose as primary substrate

glycogenesis vs glycogenolysis vs gluconeogenesis

• glycogen synthesis from glucose (insulin function)

  • typically accompanied by glucose uptake

• release of glucose from glycogen (glucagon function)

• synthesis of glucose from non-glycogen substrates

all occur in the liver

acute stress response

epinephrine and norepinephrine activate adrenergic receptors → glucagon functions unfold to release glucose for rapid response (gluconeogenesis, glycogenolysis, lipolysis)

growth hormone (GH)

promotes tissue growth/repair, releases and synthesizes glucose from skeletal muscle and the liver, liberates fatty acids and glycerol (energy sources!), and stimulates immune system

synergistic with glucagon and is functionally the opposite of insulin

glycosuria in diabetes mellitus

glucose is found in patient’s urine because the glucose that is filtered in the nephron tubules overpowers the capacity of reabsorption into interstitial tubules

energy STORES

where energy sits until it is needed: glycogen, proteins, and triglycerides

energy SUBSTRATES

ingredients for immediate energy usage: glycerol, fatty acids, amino acids, and glucose

which of the following does NOT metabolize glucose?

a) gut epithelium cells

b) brain and RBCs

c) skeletal muscle

d) liver cells (hepatocytes)

gut epithelium cells! these are the middle men for glucose absorption from the GI tract to the bloodstream