Introduction to the control of the GIT

Question 1

Where do the vagus and splanchnic nerves go to? Where does the enteric nervous system go to?

Answer 1

They go into the CNS and send efferents to the enteric nervous system. The enteric system then goes to the gut.

Question 2

What does the ANS enable?

What nerve fibres does this use?

What are the 3 types of relaxation used to regulate the gastric reservoir? What occurs in these relaxations?

How do these relaxations occur?

LOOK AT DIAGRAM!

Answer 2

• It enables food storage in the stomach.
• Parasympathetic nerves and Vagus Inhibitory fibres
• 1. Receptive relaxation - presence of food in pharynx gets the stomach ready to receive it.
     
     2. Adaptive relaxation - occurs when food is already in the stomach.
     3. Feedback relaxation - can also occur, sending signals from the duodenum.
• Vagus Inhibitory fibres release ACh to activate the enteric pathway to release NO, VIP etc. = Distension of stomach

Question 3

How does the food/chyme to move into the duodenum?

Answer 3

1. Waves of contraction moves the food to the antrum - thicker muscle layer.
2. The pyloric sphincter, which is often relaxed, closes when the peristaltic wave reaches it.
3. Repulsion of chyme causes the pyloric sphincter to open slightly.
4. Small, partially digested material goes through the sphincter to enter duodenum.
5. Repulsion of antral contents allows mixing and grinding to occur.

Question 4

Where is Gastrin released from?

Where does Gastrin act?

How does depolarisation occur in the stomach?

Answer 4

• G cells of pyloric antrum
• In the body of the stomach
• Fundus has Pacemaker cells that can create electrical activity = Spontaneous depolarisation

Question 5

What are the types of control that occurs in the stomach?

What is endocrine control?

What is paracrine control?

Answer 5

Endocrine, Paracrine, Neural, Metabolic control.

• Hormones travel in blood and act on their target tissue receptors
• Hormones travel in interstitial fluid and act on adjacent cells

Question 6

What is the Vago-vagal reflex?

What is the reflex in response to?

What does it control?

Where in the medulla do the afferent and efferent fibres enter and exit?

Answer 6

• A reflex circuit in the GIT. Both the afferent and efferent axons are in the vagus nerve trunk as the pathway is via the medulla.
• Gut stimuli
• It controls the accommodation of food in the gut and the coordination of contraction/relaxation along the gut.
• In the NTS, and out from the DMVN.

Question 7

ENTERIC NERVOUS SYSTEM:
What are the 2 nerve fibres intrinsic to the gut? What are they involved in?

Where are both plexi found?

How are the fibres connected to the CNS?

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Answer 7

• 1. Myenteric (AuErbach’s) Plexus - motor function
     
     2. Submucosal (MeiSSner’s) Plexus - intestinal secretions
• In the walls of the colon
• By parasympathetic and sympathetic fibres

Question 8

What is peristalsis?

What initiates its contraction?

What controls the contraction/relaxation of the gut smooth muscle?

Compare the peristalsis in the large intestine with that in the small intestine

Answer 8

• Wave of propulsive contractions that move gut contents towards the anus
• Distension
• Vagal inhibitory and excitatory fibres
• Its much slower in the large intestine

Question 9

GET PICTURE SHOWING INNERVATIONS OF THE GUT!

Answer 9

GET PICTURE SHOWING INNERVATIONS OF THE GUT!