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GI -S > Physiology - Nutrient Digestion and Absorption 1 > Flashcards

Physiology - Nutrient Digestion and Absorption 1 Flashcards

1
Q

Name the 3 dietary constituents

A

Carbohydrate
Protein
Fat

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2
Q

In addition to the 3 principle dietary constituents what other dietary constituents are required?

A

Vitamins
Minerals
Water

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3
Q

Vitamin is short for what?

A

Vital Amine

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4
Q

Why can the bodies ability to absorb water through the skin be clinically significant?

A

If someone is vomiting and can’t take in fluids this can be another way to replace lost fluids. Can be useful in children with fevers

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5
Q

What form of carbohydrates are absorbed?

A

Monosacharides

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6
Q

Name the 3 hexose sugars

A

Glucose
Galactose
Fructose

All have 6 carbons

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7
Q

Why does nature package monosaccharides into complex carbohydrates?

A

Osmolarity depends on the number of molecules in solution.

By packaging a large amount of monosaccharides into a single complex carbohydrate the storage of carbs has virtually no effect on osmolarity and so the movement of water.

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8
Q

What are disaccharides?

A

Two monomers linked together by glycosidic bonds.

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9
Q

What are the three disaccharides, what makes them up and what enzymes break them down?

A

Lactose = glucose + galactose (lactase)

Sucrose = glucose + fructose (sucrase)

Maltose = glucose + glucose (maltase)

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10
Q

How are disaccharides broken down?

A

Broken down to constituent monomers by brush border enzymes in small intestine.

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11
Q

Explain lactose intolerance

A

Failure to express lactase.
Lactose doesn’t get broken down and so sits in the lumen.
This has an effect on the tonicity of the lumen and water flows in.
Watery diarrhoea results

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12
Q

List the three polysaccharides

A

Starch
Cellulose
Glycogen

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13
Q

Explain the structure of starch.

A

Plant storage of glucose.

Made up of: a-amylose (glucose linked in straight chains) and amylopectin (glucose chains highly breached)

Glucose monomers are linked by an a-1,4 glycosidic bonds.

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14
Q

What enzymes hydrolyse a-1,4 glycosidic bonds?

A

Amylases:

  • salivary amylase
  • pancreatic amylase
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15
Q

Explain the structure of cellulose.

A

Unbranched, linear chains of glucose monomers linked by b-1,4 glycosidic bonds.

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16
Q

What role does cellulose play in the diet?

A

Cellulase is not produced by vertebrates. Can only be broken down by bacteria.

Cellulase therefore acts as dietary fibre.

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17
Q

What is glycogen?

A

Glycogen is the animal form of storage. Basically the animal form of starch.

Glucose in the blood is offloaded in the liver and converted to glycogen

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18
Q

What is the structure of glycogen?

A

Glycogen is formed by glucose monomers linked by a-1,4 glycosidic bonds (highly branched)

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19
Q

What polymers can a-amylase breakdown?

A

Starch and glycogen

Can only hydrolyse a-1,4 glycosidic bonds.

Cannot breakdown the b-1,4 glycosidic bonds in cellulase

20
Q

How does the small intestines structure create a great surface for absorption?

A

Villi about 0.5mm long increase the surface area of the small intestine.

Monolayer of columnar epithelial cells provide the shortest distance for diffusion.

Apical surface of epithelial cells have microvilli further increasing surface area.

21
Q

What are the two surfaces of the epithelial cells that glucose must pass through to be absorbed?

A

Apical membrane

Basolateral membrane.

22
Q

What junctions fix the epithelial cells together in the monolayer?

A

Tight junctions

23
Q

What are the two modes of transport in absorption?

A

Transcellular route = passes through the apical and basolateral membrane

Pancellular route = passes between the cells (tight junctions make this hard and so the molecules must be small (Smaller than Glucose))

24
Q

What is glucose galactose malabsorption?

A

Genetic condition where cells lining the intestine cannot take in glucose or galactose.

SGLT-1 transporter is not expressed on the apical surface (protein fails to be placed at surface much the same as CF).

This causes much the same effect as lactose intolerance.

25
Q

What part of the golgi apparatus decides where expressed proteins are transported to within the cell?

A

The trans face of the golgi apparatus.

26
Q

What chemicals does the SGLT-1 transporter uptake into epithelial cells?

A

The sodium glucose linked transporter number 1 (SGLT-1) Moves both glucose and sodium into small intestine epithelial cells from the lumen.

The energy required to do this is required by the sodium electrochemical gradient set up by the sodium potassium pump on the basolateral surface.

A deficit of sodium is created inside the cell so sodium along with glucose is pulled in.

27
Q

The movement of sodium from the lumen to blood along with glucose causes what chemical movement?

A

Water moves pancellularly into the blood.

Having salt and sugars in your drink will drive water uptake from the gut. This is the idea behind sports drinks

28
Q

The gradient created by the sodium potassium pump drives the uptake of glucose. What name is the pump therefore given in this process?

A

Primary active transporter.

29
Q

What happens to glucose once it is absorbed into the small intestine epithelium?

A

The glucose accumulates in the cell.

Once it reaches 5mmol its second transporter (GLUT-2) opens and it moves into the blood

30
Q

What other sugar is absorbed by the same way as glucose?

A

Galactose

31
Q

How is fructose transported?

A

Fructose is taken into the epithelial cells by the GLUT-5 transporter.

It then is moved into the blood by the GLUT-2 transporter

32
Q

How is fructose stored in the body?

A

It isn’t. Fructose isn’t stored inside the body and so is metabolised immediately.

33
Q

What basolateral transporter moves all sugars from small intestine epithelium to the blood?

A

GLUT-2

34
Q

What bond links amino acids together to form polymers?

A

Peptide bonds

C double bond O, N-H

35
Q

How do different proteins vary?

A

Different proteins have large variations in chain length and shape

36
Q

What post-translational modifications can proteins undergo?

A

Addition of CHO = glycoprotein

Addition of lipid = lipoprotein

37
Q

What is the difference between a protein and a peptide?

A

A peptide is a small protein of about 3-10 amino acids in length.

A protein is often much larger (>10 amino acids in length)

38
Q

What are the enzymes called which hydrolyse peptide bonds and reduce proteins or peptides to amino acids?

A

Proteases = for larger proteins

Peptidases for smaller proteins

(No difference really)

39
Q

What is an endopeptidase?

A

Endopeptidases hydrolyse the interior portion of a protein essentially taking a chain and splitting it into two smaller fragments

40
Q

What are exopeptidase?

A

Exopeptidase’s act on the terminal amino acid chopping them off the end of the protein.

41
Q

What are the two types of exopeptidases?

A

Aminopeptidases = act at the amine terminal of the protein

Carboxypeptidases = act at the carboxyl end of the peptidase.

42
Q

What are the similarities between glucose/galactose transport and amino acid transport?

A

Virtually the same system (for our level)

Sodium gradient created by sodium potassium pump.
Deficit of sodium inside cell drives movement of sodium in from lumen along with amino acid.
Amino acid transported to blood by another transporter

43
Q

What is the name of the amino acid sodium coupled transporter?

A

SAAT1

44
Q

How are most proteins absorbed?

A

Most proteins are absorbed as small peptides rather than amino acids

45
Q

How does the uptake of small peptides occur?

A

Sodium potassium pump creates deficit of sodium inside epithelium.

Sodium transported into the cell from the lumen.
This time protons are pumped out in exchange for this sodium.
The sodium gradient pumps protons into the lumen creating a proton gradient.
NHE3 transporter

Protons want to move back into the cell. They are allowed to do this by another pump (PepT1) which also transports dipeptides into the cell.

It is not known how the dipeptides then get into the blood

46
Q

What does the proton gradient created by NHE3 create in the lumen?

A

The proton gradient creates an acid microclimate in the lumen

GI -S (29 decks)

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