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HUBS192 2022 > lecture 27 - absorption > Flashcards

lecture 27 - absorption Flashcards

1
Q

What is GI absorption?

A

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

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2
Q

What absorption occurs in the mouth, oesophagus and stomach?

A

minimal absorption - lipid soluble substances

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3
Q

What absorption occurs in the small intestine?

A

All nutrients, and 90% of water and sodium

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4
Q

What absorption occurs in the large intestine?

A

9% of water and sodium - no nutrients

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5
Q

What part of the GI tract does the majority of absorption occur in?

A

Small intestine

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6
Q

What are the 4 factors affecting GI absorption?

A

Motility, surface area, transport across epithelium, removal from interstitial fluid

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7
Q

How does motility affect absorption in the GI tract?

A

The correct rate of propulsion needs to ensure sufficient time for digestion. Segmentation allows products of digestion to be exposed to the absorptive surfaces

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8
Q

What are the 2 types of transport across epithelium in absportion in the GI tract?

A

Paracellular and transcellular pathways

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9
Q

What is required to efficiently remove the products of digestion from interstitial fluid after absorption across the epithelium?

A

A large blood supply with villi arranged with blood vessels and lacteals

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10
Q

What is the mechanism of water absorption?

A

Osmosis - the passive movement of water from lumen into the blood - from low solute to high solute concentration.

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11
Q

What creates the osmotic gradient that allows for water to absorbed in the intestines?

A

The absorption of salts and nutrients generates a high solute concentration within the blood

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12
Q

What are the 2 possible pathways for sodium absorption?

A

Passive movement via the paracellular pathway or active transport via cells

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13
Q

What are the 3 transcellular mechanisms in sodium absorption from the lumen to the epithelial cells and then out in the SI/LI?

A

Na+ transporters alone, Na+ transport coupled to monosaccharides, Na+ transport coupled to amino acids

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14
Q

How is Na+ absorbed (on its own) from the lumen into epithelial cells of the SI, as part of a transcellular pathway ?

A

Na+ moves down its concentration gradient into cells via transport proteins such as the Na+ channel and Na+/H+ exchanger

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15
Q

How is Na+ released from SI epithelial cells into the interstitial fluid in a transcellular absorption pathway?

A

Uses active transport to go from low to high concentration via Na+,K+-ATPase, which pumps Na+ out of the cell while bringing K+ in.

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16
Q

What are the 2 absorption mechanisms for carbohydrates?

A

Passive via paracellular pathways, and actively via transcellular pathways

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17
Q

What carbohydrate molecules can be passively absorbed via the paracellular pathway in the SI?

A

Monosaccharides - glucose, galactose and fructose - which diffuse down their concentration gradient

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18
Q

What monosaccharides can be passively absorbed in the paracellular pathway in the SI?

A

glucose, galactose, fructose

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19
Q

What transcellular mechanism is used for carbohydrate absorption in the SI?

A

Co-transport with Na+

20
Q

What monosaccharides are absorbed in the SI via the transcellular pathway?

A

Glucose, galactose

21
Q

What cotransporter is required to absorb monosaccharides from the lumen into the SI epithelial cells?

A

Na+ monosaccharide contrasporter, which brings Na+ and a monosaccharide into the cell, with Na+ down its concentration gradient

22
Q

What transporter is used to release monosaccharides from an SI epithelial into the interstitial fluid?

A

Monosaccharide carrier - passive diffusion

23
Q

What is used to ensure that there is a Na+ concentration gradient across the apical membrane so that the Na+ monosaccharide cotransporter has a driving force?

A

A Na+,K+ - ATPase into the serosal membrane pumps Na+ from the interstitial fluid to maintain a low concentration of sodium within the cell.

24
Q

What are the 2 mechanisms of SI absorption of amino acids (protein digestion products)?

A

passive via paracellular pathway, and active via transcellular pathway

25
Q

What cotransporter is required to absorb amino acids from the lumen into the SI epithelial cells?

A

Na+ amino acid contransporter

26
Q

What transporter is used to release absorbed amino acids from an SI epithelial cell into the interstitial fluid?

A

Amino acid carrier - passive diffusion

27
Q

What is used to ensure that there is a Na+ concentration gradient across the apical membrane so that the Na+ amino acid cotransporter has a driving force?

A

A Na+,K+ - ATPase into the serosal membrane pumps Na+ from the interstitial fluid to maintain a low concentration of sodium within the cell.

28
Q

What is the mechanism of absorption of larger products of protein digestion - di and tri peptides?

A

Active transcellular absorption via contransport with H+

29
Q

What cotransporter is required to absorb di and tri peptides from the lumen into the SI epithelial cells?

A

H+ peptide cotransporter on the apical membrane

30
Q

What is used to break di and tri peptides down into amino acids when they have been absorbed into SI epithelial cells?

A

Intracellular peptidases - the amino acids can then be transported to the interstitial fluid via amino acid carriers in the basolateral membrane

31
Q

How are fats absorbed across the SI epithelial apical membrane into the epithelial cells?

A

Bile salts dissociate from free fatty acids and monoglycerides so they are no longer bound in a micelles and can pass though apical membrane by simple diffusion.

32
Q

What happens to fats when they have diffused into SI epithelial cells?

A

The are transported to the endoplasmic reticulum where they are resynthesised to triglycerides to maintain a gradient for apical diffusion. They are secreted from the Golgi as chylomicrons that target the basolateral membrane for exocytosis.

33
Q

What aids in the resynthesis of monoglycerides and free fatty acids in SI epithelial cells?

A

Triglyceride synthetic enzymes in the Endoplasmic Reticulum

34
Q

Why must free fatty acids and monoglycerides be resynthesised to triglycerides once absorbed into SI epithelial cells?

A

To maintain a concentration gradient for further absorption from the apical membrane, and so that they can be packaged into chylomicrons

35
Q

In what form are triglycerides exocytosed from SI epithelial cells?

A

Chylomicrons

36
Q

Where do chylomicrons enter after being exocytosed from SI epithelial cells?

A

Enter lymph via lacteals of villi

37
Q

When does bile salt reabsorption occur?

A

After fat absorption is complete

38
Q

Where does bile salt reabsorption occur?

A

In the ileum and then in the colon

39
Q

What is the mechanism of bile salt reabsorption in the ileum?

A

Active transport using apical Na+ dependent bile acid cotransporters.

40
Q

What is the mechanism of bile salt reabsorption in the colon?

A

Passive absorption

41
Q

What are the 2 types of vitamin?

A

Fat soluble vitamins and water soluble vitamins

42
Q

How are fat soluble vitamins absorbed?

A

With fats

43
Q

How are water soluble vitamins absorbed?

A

Via Na+ dependent absorption

44
Q

What is the key water soluble vitamin?

A

Vitamin C

45
Q

How is Vitamin B12 absorbed?

A

In the ileum by binding to intrinsic factor and being absorbed via a specific cotransporter.

46
Q

What is the condition caused by a lack of intrinsic factor?

A

Pernicious anemia

HUBS192 2022 (38 decks)

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