Chapter 21 - The digestive system Flashcards
What is chyme?
The mixture of ingested food, mixed with secretions from the salivary glands, the liver, pancreas, and gallbladder
What is the function of the small intestine? Which sections does the small intestine have?
In the small intestine the majority of digestion occurs. Nutrients and fluids are absorbed
The sections of the small intestine are the duodenum, the jejunum, and the ileum
What are the four layers of the gut from inside to outside?
- mucosa
- submucosa
- muscularis externa
- serosa
What are the three layers of the mucosa?
- mucosal epithelium facing the lumen
- lamina propria, subepithelial connective tissue holding the connective tissue in place
- muscularis mucosae, a thin layer of smooth muscle
What are peyer’s patches?
Collections of lymphoid tissue adjoining the epithelium in the mucosa that play an important immunological function
What is the submucosal plexus?
It is a nerve network innervating cells in the epithelial layer
What is the muscularis externa and what two layers of smooth muscle does it have?
The muscularis externa is the outer muscular wall of the GI tract. It consists of an inner circular layer and an outer longitudinal layer
What is the myenteric plexus?
It innervates the muscularis externa, controlling it and coordinating its motor activity
What is the serosa?
The outer connective tissue covering of the digestive tract
What are the four basic processes of the digestive system? WHat happens in those processes
- Digestion, chemical and mechanical breakdown of foods into smaller units
- Absorption, the movement of substances from the lumen of the GI to the ECF
- Secretion, movement of water and ions from the ECF to the GI tract, and the release of substances from the Gi into the lumen or ECF
- Motility, the movement of material in the GI tract as a result of muscle contraction
What are the three main challenges the digestive tract faces?
- avoiding autodigestion
- mass balance, matching fluid input with output
- protecting the body from foreign invaders
What does the GI tract manufacture?
- digestive enzymes, HCl (stomach acid) intrinisic factor mucus vitamin K
What is the GALT and its function?
THe gut-associated-lymphoid tissue is a collection of lymphoid tissue in the gut that helps with foreign invaders
What is the function of the M cells in the GALT?
M cells sample gut contents and present antigens to the cells of the GALT
What are the two main functions of motility?
- to move the food from mouth to anus
- to mechanically mix food
What are the two functions of the mucus in the GI tract?
To form a protective coating over the GI mucosa cells
To lubricate the contents of the gut
What are slow wave potentials and where are they made?
Slow wave potentials are cycles of depolarization & repolarization in the smooth muscle. The originate from the interstitial cells of cajal
What are tonic contractions and where do they occur in the GI tract?
contractions that are sustained for minutes or hours occuring in the smooth mucle sphincters and the anterior part of the stomach
What are phasic contractions? Where in the GI tract do they occur?
Contraction-relaxation cycles lasting only a few seconds occuring in the posterior stomach region and the small intestine
What are peristaltic contractions?
Progressive waves of contraction responsible for forward movement
What are segmental contractions?
Mixing contraction in which segments contract alternatingly, there is no forward movement
How is GI motility mediated?
By the enteric nervous system, modulated by hormones, paracrine signals, or neuropeptides
What is the migrating motor complex?
It is a function of the GI that sweeps food remnants and bacteria out of the upper GI tract and into the large intestine
What is peristalis?
Progressive wave of contraction that move from one section of the GI tract to the next
