Chapter 21 - The digestive system

Question 1

What is chyme?

Answer 1

The mixture of ingested food, mixed with secretions from the salivary glands, the liver, pancreas, and gallbladder

Question 2

What is the function of the small intestine? Which sections does the small intestine have?

Answer 2

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

Question 3

What are the four layers of the gut from inside to outside?

Answer 3

• mucosa
• submucosa
• muscularis externa
• serosa

Question 4

What are the three layers of the mucosa?

Answer 4

• mucosal epithelium facing the lumen
• lamina propria, subepithelial connective tissue holding the connective tissue in place
• muscularis mucosae, a thin layer of smooth muscle

Question 5

What are peyer’s patches?

Answer 5

Collections of lymphoid tissue adjoining the epithelium in the mucosa that play an important immunological function

Question 6

What is the submucosal plexus?

Answer 6

It is a nerve network innervating cells in the epithelial layer

Question 7

What is the muscularis externa and what two layers of smooth muscle does it have?

Answer 7

The muscularis externa is the outer muscular wall of the GI tract. It consists of an inner circular layer and an outer longitudinal layer

Question 8

What is the myenteric plexus?

Answer 8

It innervates the muscularis externa, controlling it and coordinating its motor activity

Question 9

What is the serosa?

Answer 9

The outer connective tissue covering of the digestive tract

Question 10

What are the four basic processes of the digestive system? WHat happens in those processes

Answer 10

• 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

Question 11

What are the three main challenges the digestive tract faces?

Answer 11

• avoiding autodigestion
• mass balance, matching fluid input with output
• protecting the body from foreign invaders

Question 12

What does the GI tract manufacture?

Answer 12

- digestive enzymes, 
HCl (stomach acid) 
intrinisic factor
mucus
vitamin K

Question 13

What is the GALT and its function?

Answer 13

THe gut-associated-lymphoid tissue is a collection of lymphoid tissue in the gut that helps with foreign invaders

Question 14

What is the function of the M cells in the GALT?

Answer 14

M cells sample gut contents and present antigens to the cells of the GALT

Question 15

What are the two main functions of motility?

Answer 15

• to move the food from mouth to anus

- to mechanically mix food

Question 16

What are the two functions of the mucus in the GI tract?

Answer 16

To form a protective coating over the GI mucosa cells

To lubricate the contents of the gut

Question 17

What are slow wave potentials and where are they made?

Answer 17

Slow wave potentials are cycles of depolarization & repolarization in the smooth muscle. The originate from the interstitial cells of cajal

Question 18

What are tonic contractions and where do they occur in the GI tract?

Answer 18

contractions that are sustained for minutes or hours occuring in the smooth mucle sphincters and the anterior part of the stomach

Question 19

What are phasic contractions? Where in the GI tract do they occur?

Answer 19

Contraction-relaxation cycles lasting only a few seconds occuring in the posterior stomach region and the small intestine

Question 20

What are peristaltic contractions?

Answer 20

Progressive waves of contraction responsible for forward movement

Question 21

What are segmental contractions?

Answer 21

Mixing contraction in which segments contract alternatingly, there is no forward movement

Question 22

How is GI motility mediated?

Answer 22

By the enteric nervous system, modulated by hormones, paracrine signals, or neuropeptides

Question 23

What is the migrating motor complex?

Answer 23

It is a function of the GI that sweeps food remnants and bacteria out of the upper GI tract and into the large intestine

Question 24

What is peristalis?

Answer 24

Progressive wave of contraction that move from one section of the GI tract to the next

Question 25

What happens in segmental contractions to mix the food?

Answer 25

Segments of the intestine alternately contract and relax. The circular muscles contract while longtitudinal muscles relax in the contracting segment. The alternating segmental contractions mix the food and keep it in contact with the absorptive epithelium of the gut

Question 26

Under which gut peptides is fluid secretion regulated?

Answer 26

Uroguanylin and guanylin