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Digestion and Excretion > Digestion and Absorption > Flashcards

Digestion and Absorption Flashcards

1
Q

What is paracellular transport?

A

Substances diffuse between adjacent cells of the epithelium
Quite restrictive - tight junctions

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2
Q

What is transcellular transport?

A

Substances move into an epithelial cell across either the luminal or basolateral surface, diffuse through the cytosol and exit across opposite membrane

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3
Q

What is glucose?

A

Aldose containing 5 carbon sugar

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4
Q

How do carbohydrates form chains?

A

Via alpha or beta linked OH groups

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5
Q

What is the type of linkage determined by?

A

Presence of an alpha or beta carbon on one monosaccharide and position of disaccharide bond on the adjacent monosaccharide

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6
Q

How is starch broken down?

A

By salivary and pancreatic enzymes
1:4 alpha linkages broken down by glucoamalyse
1:6 alpha linkages broken down by alpha limit dextrinase

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7
Q

Why must carbohydrates be digested in their simplest form?

A

Only monosaccharides can cross epithelial barrier

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8
Q

What are some carbohydrate digestion disorders?

A

Lactose malabsorption syndrome
Congenital lactose intolerance
Isomaltose deficiency
galactose malabsorption syndrome

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9
Q

What are sodium gradients crucial for?

A

Absorption of glucose
Generated by Na+/K+-ATPase

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10
Q

Where is the Na+/K+ ATPase pumps located?

A

Basolateral membrane of intestinal epithelial cells

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11
Q

What does the sodium bind to on the apical membrane?

A

SLGT1 transporter
Only works if glucose and sodium are both present
Glucose coupled to sodium gradient (secondary active transport)

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12
Q

What transporter does glucose use on the basolateral membrane?

A

GLUT2 - facilitated diffusion

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13
Q

What sugar has a separate transporter?

A

Fructose - on proximal tubule S3 segment

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14
Q

How does the sodium gradient affect water?

A

Causes water to pass from lumen of the gut by osmosis

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15
Q

What substances digest peptides?

A

Pancreatic, brush border and intracellular proteases

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16
Q

What are large polypeptides absorbed by?

A

They can’t except in neonatal receptor mediated endocytosis

17
Q

How are dipeptides, tripeptides and amino acids absorbed?

A

Across brush border
stereospecific -high affinity for L-type amino acids

18
Q

How do amino acids and small peptides cross the epithelia?

A

Sodium gradient
Neutral AA coupled to sodium channel SNAT

19
Q

How do AA cross the basolateral membrane?

A

By facilitated absorption

20
Q

What are the 3 lipases involved in lipid digestion?

A

Triacylglycerol hydrolase
Cholesterol ester hydrolase
Phospholipase

21
Q

What do bile salts facilitate?

A

Micelle formation at the epithelial surface

22
Q

What are the 6 steps of fat emulsification?

A
  1. Large fat globule
  2. Smaller emulsion droplets
  3. Micelle formation
  4. Passive Diffusion across epithelial
  5. Re-synthesis of lipids in ER
  6. Chylomicron formation and transport
23
Q

What must be added to bile to emulsify lipids?

A

lecithin
2- monoglycerides

24
Q

What are bile salts?

A

Flat molecules with a polar face and a non-polar face

25
Q

Where are hydrophobic molecules digested?

A

Interior of the micelle of the bile salt

26
Q

What is the significance of the critical micelle concentration?

A

Any concentration below critical micelle formation, micelle formation will not occur

27
Q

Where are lipids reformed?

A

Smooth Endoplasmic Reticulum

28
Q

What happens to reformed lipids?

A

Packaged into chylomicrons coated with beta-lipoproteins and exocytosed into lacteal system

29
Q

Where are short free fatty acids absorbed?

A

Directly into portal vein

30
Q

What do micelles transport?

A

Monoglycerides, cholesterol and fat soluble vitmains

31
Q

Where are bile salts recycled?

A

Terminal ileum by enterohepatic circulation

32
Q

What is ASBT?

A

Apical sodium dependent bile salt transporter

33
Q

What is OSTa/b?

A

Basolateral sodium independent bile acid transporter

34
Q

Do dietary lipids enter the faeces?

A

no

35
Q

What can lead to increased fat in the faeces?

A

Removal of the gall bladder

36
Q

Where are remanent chylomicrons processed/

A

In the liver where new liposomes are formed

37
Q

How are triglycerides processed?

A

Delivered to adipose tissue via chlyomicrons from the GIT

Digestion and Excretion (22 decks)

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