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HUBS192 > Lecture 27 GI physio Absorption > Flashcards

Lecture 27 GI physio Absorption Flashcards

1
Q

whats the process of absorption?

A

net passage of substances from lumen across lining of intestine into the interstitial fluid and then into the blood or lymph

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2
Q

wheres the main site of absorption?

A

Small intestine
90% water and sodium
All nutrients

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3
Q

what are the sites of absorption?

A

Mouth, esophagus and stomach
Small intestine
Large intestine

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4
Q

whats the absorption of Mouth, esophagus and stomach?

A

Minimal

Lipid soluble substances

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5
Q

whats the absorption of Small intestine?

A

Main site
90% water and sodium
All nutrients

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6
Q

whats the absorption of Large intestine?

A

9% of water and sodium

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7
Q

what factors affect absorption?

A

motility
SA
transport
removal

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8
Q

what do you need for motility?

A

correct rate of propulsion for digestion and absorption

exposure to absorptive surfaces

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9
Q

what do you need for available SA?

A

Rate of absorption proportional to SA

Anatomical adaptations maximise SA (villi, epithelial cells, microvilli)

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10
Q

whats the problem of transport of molecule across epithelium?

A

intestinal epithelium is a barrier to absorption

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11
Q

what are the 2 pathways for transport of molecules across epithelium?

A

Paracellular (between cells)

Transcellular (across cell membranes, through cytoplasm)

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12
Q

whats the paracellular pathway?

A 
Passive (requires gradient)
non selective (need to be small enough)

solutes dont cross cell membranes
only barrier is tight junction that binds cells together

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13
Q

whats the transcellular pathway?

A

solutes must cross 2 cell membranes lipid bilayer (solutes not lipid soluble need transport proteins)

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14
Q

whats transport proteins?

A

selective

allow active transport

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15
Q

how do you Maximise absorption across epithelium?

A

Reduction in size
- Chemical digestion

Specific transport proteins
- Selective absorption

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16
Q

how do you remove substances from interstitial space?

A

Large blood flow
arrangement of vessels in villi
position of lacteal

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17
Q

what are the specific substances absorbed?

A
  1. Water
  2. Na
  3. Bile salts
  4. Vitamins
  5. Carbs
  6. Proteins
  7. Lipids
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18
Q

How much water has to be absorbed?

A

Drink ≈ 1.5 L day-1

Total water delivered to SI ≈ 9-10 L/day

19
Q

whats the mechanism of water absorption?

A

osmosis
passive

movement of water from lumen into blood

20
Q

what sets up osmotic gradient?

A

absorption of salts and nutrients

21
Q

whats the mechanism for Na absorption?

A

passive via paracellular pathway

active vis transcellular

22
Q

whats the Transport mechanisms for active absorption of Na+?

A

Na+ transport alone
Na+ absorption coupled to glucose
Na+ absorption coupled to amino acids

23
Q

Na will move INTO cells (high to low concentration) but how does Na get OUT of cells?

A

uses energy (ATP) i.e. ACTIVE

24
Q

whats the 2 mechanisms for carbohydrate absorption (products of carb digestion)?

A

passive or active absorption

25
Q

whats the passive absorption of carbs?

A

monosaccharides - glucose, galactose, fructose

diffuse down gradient via paracellular pathway

26
Q

whats the active absorption of carbs?

A

cotransport with Na+

monosaccharides glucose and galactose

via transcellular pathway

Na+ coupled absorption of products of carbohydrate digestion

27
Q

whats the 2 mechanisms for protein absorption (products of protein digestion)?

A

passive or active absorption

28
Q

whats the passive absorption of proteins?

A

amino acids

diffuse down gradient via paracellular pathway

29
Q

whats the active absorption of proteins?

A

co transport with Na+
Amino acids coupled to Na+
via transcellular pathway

similar process that occurs for glucose

30
Q

Products of fat digestion are lipid soluble. whats the absorption of lipids?

A

FFA and monoglycerides diffuse across cell membrane into cell
Dont need a transporter
Delivered to brush border via micelles

31
Q

absorption of products of lipid digestion. is the whole micelle absorbed?

A

no

fatty acids and monoglycerides diffuse into cell

32
Q

absorption of products of lipid digestion

what happens to FFA and monoglycerides in the cell?

A

synthesized into triglycerides
packaged into chylomicrons
chylomicrons exit cell via exocytosis, enter lacteals.

33
Q

How do chylomicrons exit cell?

A

via exocytosis, enter lacteals.

34
Q

where does Bile salt absorption occur?

A

distal portions of small intestine to promote fat absorption.

35
Q

Is the Majority of secreted bile salts reabsorbed?

A

yes

36
Q

whats bile sale salt absorption?

A

Active transport in terminal ileum.
- Apical Na+-dependent bile acid transporter.

Passive absorption in jejunum.

37
Q

where does Passive absorption of bile salt occur?

A

jejunem

38
Q

where does Active transport of bile salt absorption occur?

A

terminal ileum.

- Apical Na+-dependent bile acid transporter.

39
Q

what are fat soluble vitamins and hows it absorbed?

A

Vitamins A, D, E & K

Absorbed with fats

40
Q

what are water soluble vitamins and hows it absorbed?

A

Vitamin C and B12

Na+ dependent absorption

41
Q

Hows Vitamin B12 absorbed?

A

distal ileum

Would be digested as passes through duodenum/jejunum so needs Intrinsic Factor (produced in stomach) bound to it to prevent digestion.

42
Q

whats elimination?

A

dont absorb it all

Expulsion of residues of digestion
eg faeces

43
Q

wheres faeces formed and hows it eliminated?

A

LI

Transferred to rectum via peristaltic contractions

Faeces eliminated from the body via defecation reflex.

44
Q

vitamin B12 would be digested as it passes through duodenum/jejunum, what does it need to prevent digestion?

A

Intrinsic Factor (produced in stomach) bound to it

HUBS192 (36 decks)

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