GI Physio

Question 1

Small Intestine Absorption

Answer 1

-Carbs: starch, disaccharides, monosaccharides (SI only absorbs MONO)-Fats: Present as TAGS (MONOglycerides/FA absorbed by GI)-Proteins: Vary in size (Single, di & tri peptides absorbed by SI)

Question 2

Digestion (absorption)

Answer 2

• Majority happens @ SI/LI- Churning & Propulsion @ SI facilitates with absorption-Enzymes for digestion are released from Stomach, SI, Mouth, pancreas

Question 3

Enteric Nervous System (Intrinsic sympathetic/parasympathetic)

Answer 3

-DIvision of ANS regulates/controls GI- Located within GI tissue = Intrinsic - Brain/ANS NO input- AcH is primary NT @ Pre & post- Regulates secretory & muscle activity- VIP (vasoactive intestinal peptide): Inhibits muscle contractility, stim fluid/electrolyte secretion-Lesser NT: NO, somatostatin, serotonin, Sub. P

Question 4

Submucosal Plexus (Meissner’s)

Answer 4

-Found in submucosal layer of SI/LI-Part of Enteric NS-Controls secretion/blood flow

Question 5

Myenteric Plexus (Auerbach’s Plexus)

Answer 5

-Found between Circular & longitudinal muscle layers of GI tract (esophagus to rectum)-Controls motility

Question 6

Extrinsic Neural regulation (Parasympathetic)

Answer 6

• Has more regulation over GI then Sympathetic- Vagus: esophagus, Stomach, Pancreas, Upper LI- Vasovagal reflexes = afferent/efferent vagus- Pelvic nerve: lower LI, rectum, anus

Question 7

Extrinsic Neural regulation (Sympathetic)

Answer 7

-Post. fibers can synapse DIRECTLY to target cell/organ-Usually inhibitory

Question 8

Immune system of GI

Answer 8

-Mast cells: located in lamina propria (mucosa contains ducts/capillaries)-Sensitive to NTs-Release histamines in response to foreign antigens-INCREASES gastric H+ secretion

Question 9

GI motility (3 Classes)

Answer 9

-Rhythmic & Tonic-Churning: NON propulsive = Mixing-Propulsion: Peristaltic contractions = one way progressive way of relax–>contraction-Reservoir action: “hollow organs” (stomach/LI) HOLD contents further digestion & absorption. Possible DUE to sphincters

Question 10

Sphincters & Locations

Answer 10

-Barriers = (+) resting pressure in low pressure system, changes in pressure with smooth muscle contractions-Upper eso: Striated muscle/highest resting pressure)-Lower middle eso: Unique muscle grouping (smooth/striated)-Pyloric: Stomach/Duodenum -ileocecal: ileum/cecum-Internal anal: longitudinal/circular-External anal: striated

Question 11

Small Intestine Motility (Churning)

Answer 11

-Segmented, non propulsive -Mixes pancreatic, biliary and SI secretions-Serves to expose more digested material to SI for absorption-Result of circular contracting flanked by relaxation

Question 12

Small Intestine Motility (Propulsion)

Answer 12

-Contraction of circular & relaxation of longitudinal muscles upstream -Results in caudate (tailend) movement for absorption by distal portions of SI/LI or excretion

Question 13

Small Intestine Motility (MMC)

Answer 13

-Migrating motor complex rhythmic contractions (SI ONLY)-Fasting state only!-Purpose to clear any remnants in Stomach (up to 2mm) and SI

Question 14

Large Intestine Motility (proximal colon)

Answer 14

-Propulsion/reservoir function-Proximal colon: nonpropulsive segmentation (mixing) mass peristalsis -Produced by slow wave circular contraction-Churns-Allows contents to stay in LI longer for better absorption (fluids/electrolyte)-1 to 3 times a day initiated by eating

Question 15

Large Intestine Motility (distal colon)

Answer 15

-Primary segmental contractions-Final desiccation (drying out) propels it to rectum-Occasional mass peristalsis propels contents to rectum

Question 16

The Rectum

Answer 16

-Filled by distal end of colon-Filling triggers reflexes internal/external sphincters-“Rectosphincteric reflex”: relaxing of internal sphincter-Defecation = voluntary/involuntary action of external sphincter -Delay in defecation occurs by voluntary external rectal muscles to override rectal distention (aka potty training)

Question 17

GI hormones (Gastrin)

Answer 17

• All activity confined to 4 C-terminal AA
  1. Little Gastrin: 17 AA secreted in response to a meal
  2. Big Gastrin: 34 AA NOT a dimer of little

Question 18

GI hormones (CCK-Gastrin) Actions

Answer 18

-33 AA, homologous to gastrin
Actions: stimulates contraction of gallbladder and relaxation of sphincter of oddi (valve for ampulla of Vater)
-up pancreatic enzyme & bicarb secretion
-up growth of exocrine pancreas/gallbladder
-Inhibits gastric emptying (meals w/high fat content=more time for intestinal digestion/absorption)

Question 19

GI hormones (Gastrin-CCK) Actions

Answer 19

-increases H+ secretion in parietal cells (stomach), stimulates growth of gastric mucosa stim. RNA (tumors=overgrowth)

Question 20

GI hormones (Gastrin-CCK) Stimulate/Inhibition

Answer 20

• Stimulated: secreted from G cells (antrum of stomach) in response to meal w/small peptides & AA (MOST potent is phenylalanine/Tryptophan), distention of stomach, Vagal stimulation mediated by GRP
• Inhibition: H+ in Lumen negative feedback & Somatostatin (hypothalamus)

Question 21

GI hormones (CCK-Gastrin) Stimulus

Answer 21

• Released from I cells of duodenal/jejunal mucosa–>small peptides/AA & FA & monoglycerides (TAGs NO stim CANNOT cross intestinal cell membranes)
• Inhibition: Same as Gastrin

Question 22

GI hormones (Secretin)

Answer 22

• 27 AA
• homologous to glucagon
• All of it’s AA required for activity

Question 23

GI hormones (Secretin) Actions

Answer 23

• S cells of Duodenum
• Up pancreatic bicarb (neutralize H+)
• Up biliary bicarb (up bile production through Liver)
• Down gastric H+ (inhibit parietal cells in stomach)

Question 24

GI hormones (Secretin) Stimulus

Answer 24

-Stimulate: Response to H+ in lumen of duodenum & FA in lumen of duodenum

Question 25

GI hormones (GIP)

Answer 25

• 42 AA

- homologous to secretin/glucagon

Question 26

GI hormones (GIP) Actions

Answer 26

• Insulin release in presence of oral glucose

- Inhibits H+ secretion by parietal cells

Question 27

GI hormones (GIP) Stimulus

Answer 27

• Secreted by duodenum/Jejunum

- ONLY hormone released in response to fat, protein, and carbs. (oral glucose only)