GI physiology 4 (small + large intestine)

Question 1

Why are muscle contractions important?

Answer 1

They mix the stomach content, ensure the luminal content is in contact with epithelial cells and transport chyme

Question 2

What are the two types of contraction in the small intestine?

Answer 2

Segmentation and Peristalsis

Question 3

What is the function of segmentation?

Answer 3

To mix content in the intestine

Question 4

What is the migrating motility complex?

Answer 4

Propulsive movements that ‘sweep’ the intestine clean between meals- it removes bacteria and sloughed off epithelial cells

Question 5

How is the contraction in the small intestine controlled?

Answer 5

via pacemaker cells

Question 6

What are pacemaker cells?

Answer 6

Specialised neurones that can generate slow waves that then contract the smooth muscle

Question 7

What else is released that effects the membrane potential of the smooth muscle?

Answer 7

peptides and other neurotransmitters

Question 8

Where are most carbohydrates and proteins broken down?

Answer 8

The small intestine

Question 9

What are some adaptations of the small intestine?

Answer 9

Folds in the inner surface (mucosa), villi with microvilli (all to increase surface area)

Question 10

What is the structure of enterocytes?

Answer 10

They contain an apical membrane that is in contact with the intestinal lumen, Tight junctions that connect adjacent enterocytes and a basolateral membrane that acts as extracellular space

Question 11

How does absorption work in the small intestine?

Answer 11

Nutrients are transferred from the lumen, across the apical membrane (if they are organic)

Question 12

Transcellular absorption

Answer 12

absorption through the cell through the enterocytes (organic nutrients)

Question 13

Paracellular absorption

Answer 13

Inorganic ions and water diffusing through tight junctions that connect the enterocytes

Question 14

What are the two phases of digestion?

Answer 14

Luminal and membranous, they are both catalysed by enzymes

Question 15

Where and how are carbohydrates digested?

Answer 15

By amylase, in the proximal part of the stomach

Question 16

Where does the final degradation of proteins into amino acids occur?

Answer 16

In the membrane of the stomach

Question 17

How are fats broken down in the small intestine?

Answer 17

Fats are emulsified by bile produced from the pancreas, FFA’s and monoglycerides then diffuse into the epithelial cell where they become chylomicrons and enter the lymph vessel

Question 18

Levels of Absorption of calcium in the small intestine

Answer 18

It is essential that the level of calcium within cells remains low so calcium is bound to a protein during its transport from the apical membrane to the basolateral

Question 19

What is the function of calcitrol?

Answer 19

Increases the number of channels in the apical membrane and increases synthesis of the transporter proteins so more calcium is taken up

Question 20

Absorption of sodium

Answer 20

All sodium is re-absorbed, co-transported with glucose

Question 21

Absorption of potassium

Answer 21

Mostly absorbed via diffusion through the apical membrane in the gut

Question 22

Where does microbial digestion occur?

Answer 22

In the large intestine, it is most of benefit to simple stomached herbivores (e.g horses/ rabbits)

Question 23

What occurs to Carbohydrates in the large intestine?

Answer 23

they are degraded to VFA’s by microorganisms, these can then be absorbed by the epithelium

Question 24

What happens with the excess acid after VFA production in horses? (too many VFA’S produced)

Answer 24

large amounts of HCO3- produced in the pancreas and ileum are transferred to the LI to neutralise the acids

Question 25

What are the 4 types of contraction in the large intestine

Answer 25

Segmentation, Peristalsis, Antiperistalsis and Mass Movements

Question 26

What is the most common form of contraction in the large intestine?

Answer 26

Segmentation, it forms ‘Haustra’ over several minutes, it is a movement of content slowly back and forth and occurs in horses and pigs

Question 27

What are the two contractions found in the caecum?

Answer 27

segmentation and mass movements

Question 28

What is the purpose of segmentation in the caecum?

Answer 28

maintains high microbial activity for degradation of
food and absorption of water and ions

Question 29

What is the purpose of mass movements in the caecum?

Answer 29

replace segmentation at intervals, pushing
content forward into the colon

Question 30

What is the most important function of contractions in the colon?

Answer 30

ensure the luminal content is well mixed and
exposed to epithelial surfaces for maximum absorption of water, ions and
VFA

Question 31

What is the function of the pelvic flexure?

Answer 31

• critical for transport of
  content
• functions similarly to a
  sphincter
• larger particles cannot
  pass through, so
  retained until they are
  broken down further

Question 32

How is faeces produced?

Answer 32

Mass movements,

Question 33

How does the proximal colon receive faeces?

Answer 33

In a fluid-like consistency it is then mixed in the ascending and transverse colon

Question 34

What happens when faeces enters the rectum?

Answer 34

there is reflexive relaxation of the internal anal sphincter known as the rectosphincteric reflex which causes fedecation

Question 35

Malabsorptive diarrhoea

Answer 35

occurs when absorption is inadequate to recover a sufficient portion of
secreted water
- Can be caused by viral or bacterial infection

Question 36

Hypersecretory diarrhoea

Answer 36

occurs when rate of intestinal secretion increases and overwhelms absorptive
capacity
- E. coli and salmonella will cause this

Question 37

How does Hypersecretory diarrhoea occur?

Answer 37

Produces enterotoxins
- These bind to epithelium and stimulate cAMP activity, causing
opening of chloride channels
- This causes water and electrolytes to be secreted from the crypt epithelium

Question 38

What is absorbed across the tight junctions?

Answer 38

water and ions

Question 39

What is absorbed across the extracellular space?

Answer 39

water and ions