Physiology: motility and organs Flashcards
In the muscular layer of the GIT, what are the 2 layers? What is the effect of contraction on each layer?
Outer longitudinal layer - contraction shortens
Inner circular layer - contraction narrows
Oesophagus
- Describe the skeletal muscle:SMC composition down the oesophagus
Top 1/3: skeletal muscle
Middle 1/3: mixed skeletal and smooth muscle
Bottom 1/3: smooth muscle
Oesophagus:
- Describe the contraction of the circular and longitudinal layers, as a bolus of food passes down the oesophagus.
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.
Oesophageal manometry testing
- Normal results?
- Specifically, what is unique at the lower oesophageal sphincter? Why do we see this?
Drop in pressure after swallowing - as the lower oesophageal sphincter relaxes (as a reflex). Contacts (and pressure normalises) after bolus has passed.
Stomach: what reflex is responsible for the receptive relaxation of the stomach?
The vagovagal reflex
Describe how the vagovagal reflex enables receptive relaxation of the stomach?
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
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?
Yes, yes
Peristaltic contractions of an empty stomach
Chyme
Pyloric sphincter
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
Chyme is mixed with digestive enzymes and juices
Yes
Nutrient
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?
Mixing/segmentation contractions + peristaltic contractions
Migrating myoelectric motor complexes (MMMCs)
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?
The circular muscle
No
Mixes chye, brings it into contract with the intestinal wall –> enabling absorption
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?
Yes
Lower portion of stomach
Distal ileum
~2 hours
When feeding occurs
Yes
Migrating myoelectric motor complex:
What are its functions?
Clears the intestine of residual content/undigested food, bacteria, desquamated cells
Prevents bacterial overgrowth
Large intestine
- It absorbs _______ and _______________ .
- It doesn’t have as large of a role in absorbing nutrients - but what role does it have?
Water and electrolytes
Absorption of nutrients created by chemical digestion by enteric bacteria
Large intestine:
- What are the 2 main types of contractions?
Mixing/segmentation contractions
Peristaltic contractions
Large intestines
- In mixing contractions, what muscle layers are involved?
- What is the name of the bulges of unstimulated regions formed?
Both circular and longitudinal (teniae coli) contract
Forms haustrations
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?
Mass movements
3-4
They are lost (since muscles contract)
Stretch of stomach and duodenum (via ANS)
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?
Upper and lower oesophageal
Pylorid
Oddi
Ileocecal
Internal and external
Upper oesophageal, external anal
SMC sphincters
- Are they usually contracted or relaxed? Why?
- How are the SMC sphincters relaxed?
Contracted - to prevent passage of luminal contents between adjacent compartments
Inhibitory nerves of the myenteric plexus, parasympathetic nerves
Defecation reflex:
- Mass movements of feces into the rectum activate _____________ _________
- These send signals via sensory nerve fibres in the spinal cord
Stretch receptors
Defecation reflex:
- Describe the 2 involuntary components of the defecation reflex
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
Defecation reflex:
- Describe the volunary component of the defecation reflex
Somatic nerves cause relaxation of the external anal sphincter
