Intro to functions and control of ailmentary tract

Question 1

Name 2 areas of the digestive tract that have storage functions

Answer 1

fundus

colon/rectum

Question 2

Name 1 paracrine secretion of the digestive tract and its function

Answer 2

Somatostatin – inhibits gastrin-mediated acid secretion

Question 3

Name 3 endocrine secretions of the digestive tract

Answer 3

Gastrin; secretin, CCK

Question 4

Name 1 lymphoid tissue within the digestive tract

Answer 4

Peyer’s patches

Question 5

Name 2 processes by which food is moved along the digestive tract

Answer 5

Peristalsis, segmentation, mass movement, migrating motor complex (Phase III)

Question 6

Name 1 process important in the receptive relaxation of the stomach and name 2 substances important in this relaxation

Answer 6

Neural control/vago-vagal reflex/ parasympathetic stimulation; and then NO & VIP

Question 7

List 2 effects of acetylcholine on the gastrointestinal tract

Answer 7

Acid secretion (histamine mediated effect) and gut motility

Question 8

Name the cells that mediate the gastrin release from antrum

Answer 8

G cells

Question 9

What is the effect of gastrin on parietal cells? – cell types it acts on and the mediator (ECL; histamine)

Answer 9

Acid secretion (histamine-mediated effects, direct effects on parietal cells and also effects on chief cells)

Question 10

Name 2 parts of the stomach

Answer 10

Antrum and fundus

Question 11

Two nerve fibres are important in the local control of the functions of the gastrointestinal tract. Name these and state their functions

Answer 11

Submucosal plexus (Meissner’s plexus): Intestinal secretion and local movement (has only PS gibres)
Myenteric plexus (Auerbach’s plexus): motor function, tone and velocity of movement of GIT (has both PS and S input)

connected to CNS by PS and S fibres but can function autonomously without these connections

Question 12

State how fast/slow the following foods are emptied from the stomach:

Rice
Some cubes of rump steak
Fatty bacon cooked in pure lard

Answer 12

Rice: fast
Some cubes of rump steak: slow
Fatty bacon cooked in pure lard: slower than the rate of emptying of rump of steak

(fatty acids in the duodenum - decrease gastric emptying by increasing contractility of the pyloric sphincter)

Question 13

The gastrointestinal tract is often taught to have a “little brain” of its own that can regulate its functions without input from the higher centres. What is the name of this “little brain”?

Answer 13

Enteric Nervous System

Question 14

Explain the process of gastrin mediated effects

Answer 14

Neuron stimulation causes release of GRP
GRP acts on G cells which release ghrelin
ghrelin binds directly to parietal and ECL cells, causing histamine release (from ECL cells)
Acid secretion from parietal cells
ACh also causes direct acid secretion

Question 15

What is the difference between the way hormones (endocrine) and paracrine agents go to their target tissues?

Answer 15

hormones go through blood

paracrine agents via interstitial fluid

Question 16

Explain the vago-vagal reflex

Answer 16

where both afferent and efferent axons are in the vagus nerve trunk
reflex circuit within the GIT
Pathway is via the brain stem (medulla) - describes reflex control of responses to gut stimuli via the NTS and DMVN

Active during receptive relaxation of stomach in response to swallowing

• reflex goes from stomach to brain and then back to stomach
• -> active relaxation of smooth muscles of stomach
• also promotes motility and acid secretion

Question 17

What is NTS?

Answer 17

Nucleus tractus solitarius - main site of termination of vagal afferents

Question 18

What is DMVN?

Answer 18

dorsal motor vagal nucleus - main site of origin of vagal efferents supplying the gut

Question 19

Describe the vago-vagal reflex pathway

Answer 19

brainstem- vagal motor nucleus –> pre-ganglionic vagal efferent –> releases ACh –> post ganglionic (short) –> releases ACh (usually) to target tissue –>

1. secertion
2. motility (contraction) by peristalsis

Question 20

What are the neurotransmitters of the enteric nervous system?

Answer 20

ACh, NO, NA, 5-HT, GABA, ATP

Question 21

Where are the Auerbach’s and Meisnner’s plexuses located and what do they lead to?

Answer 21

In wall of colon
PS activity (cholinergic innervation) - increases contraction of proximal colon
S activity (adrenergic innervation) - decreases colon movement
(colo-colonic reflex)