Intro to Control of Alim Tract

Question 1

Features of sympathetic innervation of the gut

Answer 1

Thoraco-lumbar, sympathetic ganglia -> inhibit digestive activity and stimulate glucose release by liver

Question 2

Features of parasympathetic innervation of the gut

Answer 2

Cervical-sacral -> stimulate digestive activity, stimulate gallbladder and relax rectum

Question 3

Describe peristalsis and how it is regulated

Answer 3

Wave of propulsive contractions moving contents of gut towards anus. Initiated by distension - vagal inhibitory and excitatory fibres control movement.

Quicker in SI than LI.

Reg the ‘enteric brain’ - smooth muscle cells with receptors for transmitters modulate it.

Motor signals sent:
- Ach/SubP -> ascending contraction of gut

• VIP/NO -> descending relaxation of gut

Question 4

How does the ANS enable movement of food into the duodenum?

Answer 4

• Ripples of contraction move food towards antrum
• Pyloric sphincter often relaxed but closes upon arrival of peristaltic wave
• Repulsion of chyme -> Opening of pyloric sphincter
• Small partially digested material is squirted through the pyloric sphincter into duodenum
• Repulsion of antral contents backwards towards body allows mixing

Question 5

What type of hormones are produced from the gut?

Answer 5

ALL are peptides

Question 6

What is the relevance of the fundus within control?

Answer 6

• Pacemaker zone
• Spontaneous depolarisation
• BER + Peristalsis

Question 7

Describe the role of gastrin, where it’s released from and where it acts

Answer 7

Endo hormone, produced by G-cells in ANTRUM and act on BODY.

Specifically, gastrin acts on ECL cells (-> hist) and parietal cells (-> HCl) -> ACID production!

Gastrin stimulated by GRP (neurocrine).

Question 8

What else stimulates parietal cells apart from gastrin and histamine?

Answer 8

Ach (vagal), also acts on ECL cells to promote acid secretion (and contraction!)

Question 9

Discuss an example of paracrine control within GI

Answer 9

Somatostatin released by D cells inhibits G cells to prevent gastrin release. Occurs in the ANTRAL LUMEN.

(D-Cells are stimulated by H+)

Question 10

Discuss neural control of GI

Answer 10

The major extrinsic pathways:

• Vagal afferents/efferents = para
• Spinal aff/efferents = symp

Question 11

What is the vago-vagal reflex?

Answer 11

A reflex in which both the afferent and efferent axons are in the vagus nerve trunk

Question 12

Describe the vago-vagal reflex pathway

Answer 12

Pathway is via brain stem (medulla).
Vagal afferents -> NTS -> Dorsal Motor Vagal Nucleus -> pre-ganglionic vagal efferent (long) -> Ach -> post-ganglionic (short) -> Ach -> Target tissue -> Secretion or motility

Question 13

What two nerve fibres are intrinsic to the gut and their functions? (ENS)

Answer 13

1. Myenteric: motor function

2. Submucosal: intestinal secretions

Question 14

How does the ENS function?

Answer 14

Connected to CNS by para and symp fibres but can function autonomously. Local reflex mediated entirely by ENS (100 mill neurones).

Question 15

Name some ENS/Local reflex neurotransmitters

Answer 15

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

Question 16

Describe the most prominent of the two plexuses

Answer 16

Myenteric/Auberbach’s

• Cholinergic increases motility/secretion (para)
• Adrenergic decreases motility/secretion (symp)

Question 17

Describe the colo-colonic reflex

Answer 17

Both plexuses are in wall of colon.

Para activity -> increases contraction of proximal colon

Symp activity -> decreases colonic movement

Question 18

In terms of metabolic control, what link do types of food have with RATE of emptying?

Answer 18

Dependent upon material’s ability to be absorbed:

• Carbs emptied quickly
• Proteins slower emptying
• Fatty are slowest, they decrease gastric emptying by increasing the contractility of the pyloric sphincter