Physiology 1 - functional anatomy

Question 1

1. What is the porpoise of the GI?

Answer 1

Provide the body with nutrients and water

Question 2

2. What allows the GI to perform its function?

Answer 2

• Movement of food in the GI tract
• exocrine secretion
• absorption
• particular blood circulation
• nervous and hormones control

Question 3

3. What does the enteric system consist of?

Answer 3

Myenteric (Auerbach) nerve plexus - deals with muscle movement

Submucosal (Messner) nerve plexus - deal with secretions

Question 4

4. What is the myenteric system?

Answer 4

Myenteric (Auerbach) nerve plexus - deals with muscle movement

Question 5

5. What is the Submucosal nerve plexus?

Answer 5

Submucosal (Messner) nerve plexus - deal with secretions

Question 6

6. What are the layers of the GI?

Answer 6

1. Seriosa
2. Longitudinal muscle
3. Circular muscle
4. 5 Myenteric nerve plexus
5. Submucosa
6. 5 Meissner’s nerve plexus
7. Mucosa
8. Epithelial lining
9. Mucosal gland
10. Submucosal gland

Question 7

7. Describe the muscles of the GI tract.

Answer 7

Skeletal muscles: in the mouth, upper third of the esophagus, external anal sphincter - voluntary control

Smooth muscles: the lower 2/3 of the esophagus till the colon

The muscles are connected through gap junctions to form syncytial

Question 8

8. Describe the electrical activity of the GI muscles?

Answer 8

• At rest:
  1. the Vm is -60-(-50) with a slow wave pattern (probably by interstitial cells of Cajal interactions with the smooth muscle),
  2. Like pacemaker
  3. Voltage change made by Na pumps
  4. NO AP so this is not the reason for contraction (except from the stomach)
• Depolarization:
  1. When Vm > -40 -> AP
  But can be depo/hyperpolarized by stretch, ACh, ParasymNS
  2. The result is spikes pattern (higher Vm, higher frequency)
  3. Smooth muscle contraction is based on Ca entering the smooth muscle cells
• Hyperploarization:
  By norepinephrine and the SymNS

Question 9

9. What are the functions of the GI tract?

Answer 9

Digestion and absorption, are not regulated

Motility and secretions, are regulated (ANS)

Question 10

10. Describe the neural control of the GI?

Answer 10

We have the ENS (submucosal & myenteric plexus)

1. It is mainly autonomous but it can be modulated by short reflexes from afferent neu.s from the GI or by long reflexes involving the CNS.
2. Receptors in the epithelium of the GI can be stimulated by mechanical/chemical/osmolarity and send it to the ENS/CNS
3. It is also modulated by the Para/SymNS

Question 11

11. What are the main stimuli in the GI?

Answer 11

1. Products of digestion
2. HCl
3. Stretching
4. Smell & sight

Question 12

12. Describe the reflexes?

Answer 12

Short reflexes:

• involving the ENS, give autonomy to the GI
• local and short
• activated by local stimuli
• affecting the 2 plexuses

Long reflexes:

• involving the CNS
• stimuli can be local or external
• para\symNS are involved (inhibit\excites)

Question 13

13. What are the reflexes?

Answer 13

1. Gastrocolic reflex- stomach on the colon, cause evacuation of the colon (especially active in babies)
2. Enterogastric reflex- colon on the stomach, inhibit emptying of the stomach when its full
3. Colonoileal reflex- the colon inhibits the emptying of the ileal
4. Pain reflex
5. Defection reflex

Question 14

14. What are the hormones that are involved in GI regulation

Answer 14

Gastrin
Cholecystokinin (CCK)
Secretin
Gastric Inhibition Peptide
Motilin

Question 15

15. Describe the hormonal control of Gastrin

Answer 15

Stimulus: proteins (products of protein breakage), distention, ParasymNS
* acid inhibits release

Site of secretion: G cells, small intestine

Action: gastric acid secretion stimulation, mucosal growth

Question 16

16. Describe the hormonal control of Cholecystokinin (CCK)

Answer 16

Stimulus: protein, fat (especially), acid

Site of secretion: I cells in the duodenum, jejunum and ilium

Action: Gallbladder contraction, inhibition of gastric emptying, stimulation of bicarbonate, pancreatic enzymes production, growth of exocrine pancreas

Question 17

17. Describe the hormonal control of Secretin

Answer 17

Stimulus: low pH + Fat

Site of secretion: S cells in the duodenum, jejunum and ilium

Action: stimulation of pancreatic biliary+bicarbonate production (buffer), inhibition of acid secretion in stomach, growth of exocrine pancreas, pepsin secretion

Question 18

18. Describe the hormonal control of Gastric Inhibition Peptide

Answer 18

Stimulus: protein, fat, carbohydrates

Site of secretion: k- cells in the duodenum, jejunum and ilium

Action: inhibition of acid secretion in stomach, insulin release

Question 19

19. Describe the hormonal control of Motilin

Answer 19

Stimulus: fat, low pH, parasymNS

Site of secretion: M cells in the duodenum, jejunum

Action: inverse stomach and intestine motility

Question 20

20. What are G/I/S/K/M cells secrete?

Answer 20

G- Gastrin
I- CCK
S- Secretin
K- Gastrin inhibition peptide
M- Motilin

Question 21

21. Describe the blood circulation of the GI tract?

Answer 21

1. Splanchnic circulation
2. 25% of the blood outputs goes to the GI and can also increase specifically on the sites that are activated
3. Blood coming from gut has nutrients and bacteria, but it goes to the liver that assign the metabolites and kill the bacteria by the portal vein
4. The villus is the structure that absorb the nutrients, filled with capillaries and has a lacteral vessel where the fat goes to