Physiology: motility and organs

Question 1

In the muscular layer of the GIT, what are the 2 layers? What is the effect of contraction on each layer?

Answer 1

Outer longitudinal layer - contraction shortens
Inner circular layer - contraction narrows

Question 2

Oesophagus
- Describe the skeletal muscle:SMC composition down the oesophagus

Answer 2

Top 1/3: skeletal muscle
Middle 1/3: mixed skeletal and smooth muscle
Bottom 1/3: smooth muscle

Question 3

Oesophagus:
- Describe the contraction of the circular and longitudinal layers, as a bolus of food passes down the oesophagus.

Answer 3

Above the bolus, the circular muscle contracts - to push the bolus forwards. (Below - relaxes)
Below the bolus, the longitudinal muscle contracts - to shorten (above - relaxes)
The circular muscle forces the bolus forwards.

Question 4

Oesophageal manometry testing
- Normal results?
- Specifically, what is unique at the lower oesophageal sphincter? Why do we see this?

Answer 4

Drop in pressure after swallowing - as the lower oesophageal sphincter relaxes (as a reflex). Contacts (and pressure normalises) after bolus has passed.

Question 5

Stomach: what reflex is responsible for the receptive relaxation of the stomach?

Answer 5

The vagovagal reflex

Question 6

Describe how the vagovagal reflex enables receptive relaxation of the stomach?

Answer 6

Food enters the stomach
Activates sensory receptors in stomach
Sent via vagal afferents to the stomach.
Vagus nerve sends efferents to myenteric plexus
- Releases NO and VIP to relax the stomach

Question 7

Stomach
- Do peristaltic contractions occur? Does it mix food with gastric secretions?
- Why are hunger pains caused?
- What is the name of the substance formed in the stomach?
- What is the name of the sphincter connecting the stomach to the SI?

Answer 7

Yes, yes
Peristaltic contractions of an empty stomach
Chyme
Pyloric sphincter

Question 8

Small intestine
- Describe the further digestion that occurs in the small intestine
- Does chemical digestion complete in the small intestine?
- Most _________ absorption occurs in the small intestine

Answer 8

Chyme is mixed with digestive enzymes and juices
Yes
Nutrient

Question 9

In the small intestine, activity differs in the fed and fasted states.
- What 2 types of contractions occur in the fed state?
- In the fasting state?

Answer 9

Mixing/segmentation contractions + peristaltic contractions
Migrating myoelectric motor complexes (MMMCs)

Question 10

Mixing/segmentation contractions
- Only one layer is involved in contractions. Which one is it?
- Does it advance contents along the intestinal wall?
- What is its function?

Answer 10

The circular muscle
No
Mixes chye, brings it into contract with the intestinal wall –> enabling absorption

Question 11

Migrating myoelectric motor complexes
- Are they propulsive?
- Where does it start
- Where does it end
- How long does a whole MMMC take
- When does it end
- Can it be modulated by hormones, ANS, ENS?

Answer 11

Yes
Lower portion of stomach
Distal ileum
~2 hours
When feeding occurs
Yes

Question 12

Migrating myoelectric motor complex:
What are its functions?

Answer 12

Clears the intestine of residual content/undigested food, bacteria, desquamated cells
Prevents bacterial overgrowth

Question 13

Large intestine
- It absorbs _______ and _______________ .
- It doesn’t have as large of a role in absorbing nutrients - but what role does it have?

Answer 13

Water and electrolytes
Absorption of nutrients created by chemical digestion by enteric bacteria

Question 14

Large intestine:
- What are the 2 main types of contractions?

Answer 14

Mixing/segmentation contractions
Peristaltic contractions

Question 15

Large intestines
- In mixing contractions, what muscle layers are involved?
- What is the name of the bulges of unstimulated regions formed?

Answer 15

Both circular and longitudinal (teniae coli) contract
Forms haustrations

Question 16

Large intestines
- What is another name for peristaltic contractions here?
- How many are normal in a day?
- What happens to haustra?
- What are peristaltic contractions stimulated by?

Answer 16

Mass movements
3-4
They are lost (since muscles contract)
Stretch of stomach and duodenum (via ANS)

Question 17

Sphincters of the GIT:
- 2 sphincters of the oesophagus?
- Stomach –> SI sphincter?
- Bile duct –> duodenum sphincter?
- Ileum –> cecum sphincter?
- Anal sphincters?

• Which ones of these are skeletal muscle?

Answer 17

Upper and lower oesophageal
Pylorid
Oddi
Ileocecal
Internal and external

Upper oesophageal, external anal

Question 18

SMC sphincters
- Are they usually contracted or relaxed? Why?
- How are the SMC sphincters relaxed?

Answer 18

Contracted - to prevent passage of luminal contents between adjacent compartments
Inhibitory nerves of the myenteric plexus, parasympathetic nerves

Question 19

Defecation reflex:
- Mass movements of feces into the rectum activate _____________ _________
- These send signals via sensory nerve fibres in the spinal cord

Answer 19

Stretch receptors

Question 20

Defecation reflex:
- Describe the 2 involuntary components of the defecation reflex

Answer 20

Spinal cord nerves synapse with parasympathetic nerves which
- Contract sigmoid colon and rectum
- Relax internal anal sphincter

Distension activates ENS - relaxation of internal anal sphincter

Question 21

Defecation reflex:
- Describe the volunary component of the defecation reflex

Answer 21

Somatic nerves cause relaxation of the external anal sphincter