Intro to GI physiology

Question 1

How long are the pharynx, oesophagus and stomach?

Answer 1

1m

Question 2

How long is the small bowel?

Answer 2

6m

Question 3

How long is the large bowel?

Answer 3

1.5m

Question 4

What are the functions of the GI tract?

Answer 4

Ingestion
Occurs when materials enter digestive tract via the mouth

Mechanical processing
Crushing and shearing, wetting and softening
Makes materials easier to propel along digestive tract

Digestion
The chemical breakdown of food into small organic fragments for absorption by digestive epithelium
Secretion
Is the release of water, acids, enzymes, buffers, and salts
By epithelium of digestive tract
By glandular organs

Absorption
Movement of organic substrates, electrolytes, vitamins, and water across digestive epithelium into interstitial fluid of digestive tract

Excretion
Removal of indigestible material, and waste products from body fluids

Question 5

What are the features of the peritoneum?

Answer 5

lines the abdominal cavity (parietal peritoneum)

Covers organs (visceral peritoneum)

Forms mesenteries, which suspend the organs, support them, and keep them from tangling

Secretes peritoneal fluid, which provides lubrication, and permits organs to move against each other without friction.

Question 6

What are the features of the mesenteries?

Answer 6

Mesenteries suspend the organs, and stop the loops of gut getting tangled around each other.

Also carry blood vessels, nerves, and lymphatics.

Fat pads cushion and protect organs.

Question 7

Name the three branches of the aorta that supply the GI tract.

Answer 7

Coeliac artery - foregut
Superior mesenteric artery - midgut
Inferior mesenteric artery - hindgut

Question 8

Into which vein does most of the blood from the GI tract drain?

Answer 8

Hepatic portal vein.

Question 9

What are the four histological layers of the GI tract, starting with the luminal surface?

Answer 9

Mucosa
Submucosa
Muscularis externa
Serosa

Question 10

Describe the role of tight junctions.

Answer 10

• Is an occluding junction

- Seals the gap between epithlial cells at the apical surface

Question 11

Describe the role of adherens junctions.

Answer 11

• Connects actin filament bundle with in one cell with that in the next cell.
• One of the cell-cell anchoring junctions

Question 12

Describe the role of desmosomes.

Answer 12

Connects intermediate filaments between cells.

Question 13

Describe the role of gap junctions.

Answer 13

Allows the passage of small water soluble molecules between cells (ie ions).

Question 14

Describe the role of hemidesmosomes.

Answer 14

Anchor intermediate filaments in cells to the ECM.

Question 15

What is the equation for calculating net flux of fluid across a membrane?

Answer 15

Net flux (Jnet) = J(abs)-J(sec)

Question 16

Describe the transcellular route of absorption.

Answer 16

Via the cells in which case, two barriers (apical and basolateral membranes) must be traversed

Question 17

Describe the paracellular route of absorption.

Answer 17

Absorption that takes place between cells.

Question 18

Describe the various modes of transport across cell membranes.

Answer 18

1. Passive:

Non coupled - solute moves down its electrochemical gradient.
Can occur via pores or channels e.g. diffusion of ions, H2O
Transporters – facilitate diffusion of small non electrolytes

2. Active Transport:

Primary:
Energy to drive transport comes directly from ATP
Substrate moves against an electrochemical gradient

Secondary:
Energy to drive active transport comes from electrochemical gradient for one substrate (set up by primary active transport)
Second substrate moves against its electrochemical gradient

Question 19

From where does the main sensory and motor input of the GI tract come from?

Answer 19

The parasympathetic system.

Question 20

Which parts of the gut are controlled by the vagus?

Answer 20

Foregut

Midgut

Question 21

What controls the hindgut?

Answer 21

Pelvic splanchnic nerves.

Question 22

What is the ‘third division of the ANS’?

Answer 22

The enteric nervous system. The ANS contacts neurones from the ENS. The ENS can control much of the gut motility autonomously.

Question 23

What are the two divisions of the ENS?

Answer 23

Myenteric plexus

Submucosal plexus

Question 24

What are the interstitial cells of Cajal?

Answer 24

Mediators of the slow waves of membrane potential oscillation (3-12min). Have connections with other smooth muscle cells.