Gut Structure and Function Overview

Question 1

Diffusion

Answer 1

J = (gradient)(solubility)(SA)/distaince

Can change by increased SA, gradient, or thin membrane

Question 2

Fxns of GI tract

Answer 2

Motility - divided into propulsion and mxing
Secretion
Digestion
Absorption

Question 3

Ingestion
Mastication
Deglutition
Peristalsis

Answer 3

Food into mouth

Chew and mixing

Swallonwing

Move through GI tract

Question 4

Antral-pyloric pumping
Segmentation
Peristalsis
Haustrations
Mass mvmtn

Answer 4

Stomach…also has retropulsion

Mixing movement in small intestine

Starlings law of intestine - upward contraction and downstream relaxsation

Haustrations- colon

Massmovement - coordinated constraction

Question 5

Muscles in GI tract dividion

Answer 5

Skeletal - tongue/mastication, upper esophagus, UES, extenral anal sphincter - striated

Rest is smooth

Question 6

Secretion

Answer 6

Includes both exocrine - from duct

and endocrine - from cell directly

Question 7

Layers

Answer 7

Mucosa
Submucosa
Muscular externa
Serosa

Question 8

Mucosa

Answer 8

Lines the lumen with simple columnar epithelium

Lamina prorpia - thin layer of conn tisue with lymph nodes

Muscularis mucosae - thin layer of smooth muscle responsible for folds

Goblet cells secrete mucus

Question 9

Submucosa

Answer 9

Thick and huighly vasculairzed

Absorbed molecules enter blood and lymph vessels

Submucosal glands

Submucosal plexus - mostly sensory…provide autonomic nerve supply to muscularis mucosae

Question 10

Muscularis externa

Answer 10

Responsbile for segmental contractions and peristalsis

Inner circular layers and outer long layer

Myenteric plexus between 2 layers is major nerve supply to GI tract

Question 11

Serosa

Answer 11

Binding and protective outer layer

Conn tissue covered with ismple squamous epithelium

Contigu woith omentum and mesentery

Question 12

Transit rate
pH
Pressures

Answer 12

Transit rate high til stomach then drops til rectum

pH acidic until end of stomachthen slightly alkaline

Negative pressurei n the esopagus…higher pressures at sphincters

Question 13

Sphincters

Answer 13

UES - striated with voluntary and involuntary
LES
Pyloric
SO
Ileocecal - regulates absorption
IAS - tonically contracted 
EAS - striated and normally relaxed

Question 14

Extrinsic innervaton

Answer 14

Somatic - only a few

PS - vagus and spinal nerves inc motility and secrtetions

symp - postganglionic that pass through submucosal anmd myenteric plexi to innervate GI tract

Question 15

Intrinsic innervation

Answer 15

Enteric nervous system - submucosal and myenteric plexi

Paracrine scretion

Homronal secretion

Question 16

General secretion

Answer 16

Intake + secretion = reabsorption + excretion

Question 17

Purposes of secretions in GI

Answer 17

Lubrication and protection of mucosa

Enzymatic fxn
Acidification and neutralixation

Question 18

Important electrolyte concentrations

Answer 18

Na - 140
K - 4
Cl - 100
HCO3 - 27

Most secretions end up being alklaine and isotonic

Question 19

Regulation of secreitons

Answer 19

Local myenteric reflexes stimulated by various things
PNS and SNS
Hormones

MOSTLY through regulation of blood flow

SNS and PNS cna release local casoactive usbstances