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S + F 2 > 11. GIT - physiology 4 > Flashcards

11. GIT - physiology 4 Flashcards

1
Q

Why are muscle contractions important in the small intestine?

A

Mixing content

Ensures luminal content contracts with epithelial cells

Transport chyme along the tract

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2
Q

What are the 2 types of contractions in the small intestine?

A

Segmentation (mixing movements)

Peristalsis (propulsive movements)

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3
Q

What is the function of the migrating motility complex during the interdigestive period?

A
  • “sweeps” the intestine clean between meals
  • between periods of peristaltic contractions
  • gets rid of bacteria and sloughed off epithelial cells
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4
Q

What is another name for pacemaker cells?

A

Interstitial cells of cajal (ICC)

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5
Q

what are pacemaker cells?

A

modified smooth muscle cells

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6
Q

how do propulsive movements happen?

A

the longitudinal muscle relaxes, circular muscle contracts which move the chyme. Then they swap

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7
Q

What are the pacemaker cells of the small intestine?

A
  • Insterstitial Cells of Cajal (ICCs)
  • Modified smooth muscle cells
  • Form an interconnected lattice of cells that
    surround circular + longitudinal muscle in SI
  • Create the slow-wave potential which runs constantly over the smooth muscle in the GIT.
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8
Q

How does the smooth muscle in the GIT contract?

A
  • Needs to be enough membrane polarisation to cause action potentials
  • slow wave frequency = not enough
  • Muscle contractions = same or lesser frequency than slow wave potential
  • ENS releases peptides + neurotransmitters
    affects membrane potential, when depolarised - action potential.
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9
Q

When are the pacemaker cells activated?

A

When chyme enters the small intestine.

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10
Q

Where is the frequency of slow waves the highest?

A

Proximal small intestine

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11
Q

What nervous activity increases or decreases contraction strength?

A

Increased parasympathetic vagal fibre activity increase contraction strength

Increased sympathetic activity decreases contraction strength

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12
Q

Which nervous system primarily regulates strength of peristaltic and segmentation contractions?

A

Enteric nervous system

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13
Q

Which nervous system primarily regulates strength of peristaltic and segmentation contractions?

A

Enteric nervous system

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14
Q

What does the ENS release that affects membrane potential in the small intestine?

A

Peptides and neurotransmitters in the vicinity of smooth muscle cells

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15
Q

What does the ENS release that affects membrane potential in the small intestine?

A

Peptides and neurotransmitters in the vicinity of smooth muscle cells

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16
Q

Where does most of the digestion and absorption occur in non-ruminants?

What happens to the rest?

A

mall intestine

Carbohydrates and protein are digested in the small intestine

If not digested there, they are moved to the large intestine for microbial digestion

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17
Q

Which 3 structures increase the surface area of the small intestine?

A

Folds in the inner surface of small intestine (mucosa)

Inner surface covered with villi

Villi have microvilli

18
Q

what us the structure of an enterocyte?

A
  • apical membrane: contact with intestinal lumen
  • tight junctions: connect adjacent enterocytes
  • basolateral membrane: extracellular space ( EC fluid)
19
Q

what are the 2 mechanisms of absorption?

A
  • transcelluar
  • paracellular
20
Q

what is transcellular absorption?

A

organic nutrients are transported from intestinal lumen to the interstitial fluid across the enterocyte

21
Q

what is paracellular absorption?

A

inorganic ions and water can diffuse through tight junctions connecting enterocytes

22
Q

what is absorption?

A

transfer of substances from the lumen of the GIT to blood/lymph capillaries

23
Q

what are the 3 transport mechanisms across the intestine?

A

Simple Diffusion:
cell membrane = barrier
allows water + lipid soluble substances
water can diffuse rapidly because of aquaporins in the membrane

Carrier Proteins:
Large water-soluble nutrients can go via protein pumps

Exocytosis/endocytosis:
vesicle forms around nutrient + transports to cell.

24
Q

what are the 2 phases of digestion?

A
  • luminal
  • membranous
25
Q

How is starch digested + absorbed?

A

Degraded by amylase in proximal portion of stomach
Pancreatic juice in simple stomached animals (EXCEPT HORSES) have lots of amylase
Final step = occurs across membrane of microvilli

26
Q

What is maltose digested into?

A

Glucose

27
Q

What is sucrose digested into?

A

Glucose and fructose

28
Q

What is lactose digested into?

A

Glucose and galactose

29
Q

What is glucose absorption linked to?

A

Sodium absorption via Na-K-ATPase pump

30
Q

What is glucose absorption linked to?

A

Sodium absorption via Na-K-ATPase pump

31
Q

What happens to monosaccarides after absorption?

A

Transported to liver via portal vein + stored as glycogen.

32
Q

How is protein digested?

A
  • Pepsin in the stomach/SI creates peptides
  • Peptides are broken down into short-chain peptides in SI
  • Final degradation to AAs = membrane of epithelial cells.
32
Q

How is protein digested?

A
  • Pepsin in the stomach/SI creates peptides
  • Peptides are broken down into short-chain peptides in SI
  • Final degradation to AAs = membrane of epithelial cells.
33
Q

How are amino acids absorbed?

A
  • Active transport (linked to Na uptake)
  • Mostly transported into cells as tri-/di- peptides
  • Transported to liver via portal vein.
34
Q

How are triglycerides broken down during non-microbial degradation?

A

Broken down into x2 FAs and 1 mono-glyceride.

35
Q

Why are bile salts important for fat digestion?

A
  • Lipase = water soluble
    can only be used at the water/fat interface
  • Bile salts needed to emulsify fats
    *increases SA for lipase enzymes
  • Bile salts form micelles which are water soluble and act as transporters of digested products
  • Lipid-soluble vitamins (A/D/E/K) absorbed at same time.
36
Q

How is water absorbed?

A
  • Mucosa = freely permeable
  • aquaporins
  • Water lost from intestine = replaced w/ blood’s water
  • 12 L absorbed by small intestine
  • Simple stomached herbivores = lots of water needed in Large intestine for fermentation
36
Q

How is water absorbed?

A
  • Mucosa = freely permeable
  • aquaporins
  • Water lost from intestine = replaced w/ blood’s water
  • 12 L absorbed by small intestine
  • Simple stomached herbivores = lots of water needed in Large intestine for fermentation
37
Q

Where does water absorption occur?

A

villi

38
Q

Where does water secretion into the intestinal lumen occur?

A

Crypts

39
Q

Where does water secretion into the intestinal lumen occur?

A

Crypts

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