General Principle of GI System

Question 1

What are the different layers of GIT?

Answer 1

From outside to inside:

• serosa
• muscularis externa (longitudinal muscle layer. circular muscle layer)
• submucosa
• mucosa

Question 2

Describe the neural control of GI function

Answer 2

• ENS and ANS
• ENS consists of submucosal plexus (secretions) and myenteric plexus (movements).
• ANS consists of sympathetic and parasympathetic. Sympathetic arises from thoracolumbar segments of spinal cord ‘T5to L2’. Parasympathetic arises from S32-S3 segments of spinal cord.
• Functions of parasympathetic stimulation:
  a) increases secretion
  b) increases motility
  c) decreases constriction of sphincter
  d) increases blood flow
• Functions of sympathetic is the opposite of parasympathetic

Question 3

Describe the hormonal control of GI function

Answer 3

1. When we ingest food, gastrin hormone is secretin the stomach
2. Gastrin hormone stimulates muscle contraction and gastric acid production in stomach
   3, Partially digested food (chyme) moves from stomach to small intestine. CCK and secretin hormone are secreted into blood
3. CCK and secretin stimulate the secretion of digestive enzymes and bicarbonate ions from the pancreas into the small intestine
4. CCK also stimulates secretion of bile from gall bladder into small intestine

Question 4

What are the functions of GI system?

Answer 4

a) Motility
b) Secretion
c) Digestion
d) Absorption

Question 5

State the differences between Myenteric (Auerbach’s) plexus and Submucosal (Meissner’s) plexus.

Answer 5

a) Layer (myenteric plexus is muscularis external and submucosal is submucosa)
b) Location (myenteric is found between the longitudinal and circular muscle layers @ outer plexus; submucosal is found in the inner plexus)
c) Controls (myenteric controls movements; submucosal controls secretions, absorption and local blood flow)
d) Inhibitory neurons (present in myenteric; absent in submucosal)
e) Type of control (myenteric increases tone, rate, intensity and velocity of rhythmic contraction; submucosal controls segmental contraction)