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GI system > Small intestines > Flashcards

Small intestines Flashcards

1
Q

What is the main function of the intestines?

A

Digestion of chyme

Absorption of nutrients, electrolytes

Absorption of water

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2
Q

What do the intestines digest?

A

Carbohydrates

Protiens

Lipids

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3
Q

What are carbohydrates made up of?

A

Many monosaccharide or disaccharide units joined together to form polysaccharides

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4
Q

What form of carbohydrates is absorbed in the gut?

A

Monosaccharides

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5
Q

Where are carbohydrate polysaccharides digested into monosaccharides?

A

Brush border of small intestines

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6
Q

What digests carbohydrate polysaccharides into monosaccharides at the brush border in the small intestine?

A

Hydrolase enzymes attached to the brush border

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7
Q

What is the main polysaccharide in our diet?

A

Starch

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8
Q

What is starch made up of?

A

Amylose

Amylopectin

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9
Q

What is amylose made up of?

A

Straight chain of many glucose monosaccharides joined together

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10
Q

What type of bond joins glucose monosaccharides together in amylose?

A

A 1-4

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11
Q

What is amylopectin made up of?

A

Chains of glucose monosaccharides joined together

but with branches

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12
Q

What type of bond joins glucose monosaccharides together in amylopectin?

A

A 1-4 between the chains

A 1-6 at the branches

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13
Q

What are the enzymes responsible for digesting starch?

A

Amylase

Isomaltase

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14
Q

How does amylase digest starch?

A

Hydrolyses a 1-4 bonds

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15
Q

How does isomaltase digest starch?

A

Hydrolyses a 1-6 bonds

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16
Q

What does amylase digesting amylose produce?

A

Maltose

Glucose

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17
Q

What is maltose?

A

Disaccharide formed by two glucose monosaccharides joined together

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18
Q

What is the enzyme responsible for digesting maltose?

A

Maltase

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19
Q

What does maltase digesting maltose produce?

A

Glucose x2

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20
Q

What does amylase digesting amylopectin produce?

A

Alpha dextrins

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21
Q

What are alpha dextrins?

A

Several glucose monosaccharides joined together in chains

including branches

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22
Q

What is the enzyme resonsible for digesting alpha dextrins?

A

Isomaltase

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23
Q

What does isomaltase digesting alpha dextrins produce?

A

Maltose

Glucose

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24
Q

What does isomaltase digesting starch produce?

A

Amylose

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25
Q

Where along the GI tract is starch digested?

A

Mouth

Small intestines

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26
Q

What produces amylase that is found in the mouth?

A

Salivary glands

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27
Q

What produces amylase that is found in the small intestine?

A

Pancreas

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28
Q

What are the main dietary disaccharides?

A

Lactose

Sucrose

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29
Q

What is lactose made up of?

A

Disaccharide made up of glucose and galactose monosacharides joined together

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30
Q

What is sucrose made up of?

A

Disaccharide made up of glucose and fructose monosaccharides joined together

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31
Q

What does sucrase digesting sucrose produce?

A

Glucose

Fructose

32
Q

What is meant by absorption?

A

Movement of nutrients, electrolytes and water from the gut lumen into the blood

33
Q

What is the enzyme responsible for digesting lactose?

A

Lactase

34
Q

What does lactase digesting lactose produce?

A

Glucose

Glactose

35
Q

What are the routes of absorption?

A

Transcellular

Paracellular

36
Q

What is transcellular absorption?

A

Movement occurs across the apical domain of the enterocyte into the cytosol
then across the basolateral domain of the enterocyte into the interstitial fluid, blood

37
Q

What is paracellular absorption?

A

Movement occurs between enterocytes

38
Q

How are the intestines adapted for absorption?

A

Large surface area

  • plicae circulares
  • villi
  • microvilli

Contents move slowly through them

39
Q

How are monosaccharides absorbed?

A

Na+ K+ ATPase on basolateral domain of enterocyte
actively transports 3 sodium ions from enteroycte into blood, 2 potassium ions from blood into enterocyte

SGLT-1 transporter on apical domain of enterocyte
moves sodium ion down its concentration gradient whilst moving glucose/galactose against their concentration gradient from gut lumen into enterocyte, so by secondary active transport

GLUT-5 transporter on apical domain of enterocyte
moves fructose down its concentration gradient from gut lumen into enterocyte, so by facilitated diffusion

GLUT-2 transporter on basolateral domain of enterocyte moves glucose/galactose/fructose from enterocyte into blood, so by facilitated diffusion

40
Q

How does oral rehydration work?

A

Solution contains glucose, sodium ions and water
SGLT-1 transporter moves sodium ion and glucose molecule from gut lumen into enterocyte
Movement of sodium ions increases osmolality in direction of movement
Water follows this osmolality created by sodium ions

41
Q

What are the types of enzymes responsible for digesting proteins in the small intestine?

A

Exopeptidases

Endopeptidases

42
Q

What are exopeptidases?

A

Cleave off dipeptides and tripeptides from polypeptide chain

43
Q

What are endopeptidases?

A

Cleave polypeptide chains in the middle to produce shorter polypeptides

44
Q

What are some examples of endopeptidases?

A

Trypsin

Chymotrypsin

Elastase

45
Q

What are some examples of exopeptidases?

A

Carboxypeptidase

46
Q

What produces the enzymes responsible for digesting proteins in the small intestines?

A

Pancreas

47
Q

What form of the protease enzymes that digest proteins in the small intestine does the pancreas produce?

A

Zymogens, meaning inactive form

48
Q

What is the inactive form of trypsin?

A

Trypsinogen

49
Q

What activates trypsinogen into its active form?

A

Enteropeptidase in the duodenum

50
Q

What activates chymotrypsinogen, elastase, procarboxypeptidase into their active forms?

A

Trypsin

51
Q

What is the enzyme responsible for digesting sucrose?

A

Sucrase

52
Q

How are amino acids absorbed in the small intestine?

A

Sodium-amino acid co-transporter on apical domain of enterocyte
moves sodium ion down its concentration gradient whislt moving amino acid against its concentration gradient from gut lumen into enterocyte, so by secondary active transport

53
Q

What form of protein is most commonly absorbed in the small intestine?

A

Dipeptides

Tripeptides

54
Q

How are dipeptides and tripeptides absorbed in the small intestine?

A

Peptide transporter 1 on apical domain of enterocyte
moves hydrogen ion
whilst moving dipeptide/tripeptide from the gut lumen into the enterocyte

Inside the enterocyte
the dipeptide and tripeptide are digested into amino acids by cytosolic peptidases

55
Q

What routes of absorption does water follow?

A

Both transcellular and paracellular

56
Q

How is water absorbed in the intestines?

A

Sodium ions increase osmolality in their direction of movement
water follows this osmolality

57
Q

How are sodium ions absorbed in the small intestine?

A

Co-transported with other nutrients

58
Q

How are sodium ions absorbed in the large intestine?

A

Sodium ion channels

59
Q

What increases sodium ion channel activity in the large intestines?

A

Aldosterone

60
Q

What form of protein is absorbed in the small intestine?

A

Amino acids

Dipeptides

Tripeptides

61
Q

What is the osmolality of the solution reabsorbed in the small intestine? Why?

A

Isoosmotic

because it is absorbed with sodium

62
Q

What does calcium ion absorption depend on?

A

Levels of calcium in the blood

  • low
  • normal or high
63
Q

What is the route of calcium ion absorption when calcium levels in the blood are low?

A

Transcellular route

64
Q

How are calcium ions absorbed by the transcellular route?

A

Ca2+ ATPase on basolateral domain
actively transports calcium ions from the cell into the blood

In the cytosol, calbindin binds to calcium ion and moves it towards the basolateral domain

Calcium ion channel on apical domain
calcium ions move through it from gut lumen into enterocyte by facilitated diffusion

65
Q

What stimulates calbindin?

A

Vitamin D

66
Q

What increases vitamin D levels?

A

Parathyroid hormone

67
Q

What is the route of calcium ion absorption when calcium ion levels are normal/high?

A

Paracellular route

68
Q

How are calcium ions absorbed by the paracellular route?

A

Move from gut lumen, in between enterocytes, into blood

down their concentration gradient, so by simple diffusion

69
Q

What form of iron is absorbed?

A

Haem Fe2+ form

70
Q

How is non-haem Fe3+ form converted into haem Fe2+ form?

A

Gastric acid

71
Q

How is haem Fe2+ iron absorbed?

A

DMT1 transporter on apical domain

co-transports Fe2+ with H+ from gut lumen into enterocyte

72
Q

What happens to haem Fe2+ iron in the enterocytes?

A

When iron levels are low
ferroportin on basolateral domain of enterocyte
Fe2+ moves through it into the blood
binds to transferrin in the blood

When iron levels are normal/high
stored as ferritin in the cell
lost when enterocyte is replaced

73
Q

What is Fe2+-transferrin transported to by the blood? What happens to Fe2+ in those organs?

A

Bone marrow

Liver

Spleen

for haemaglobin synthesis, storage as ferritin

74
Q

Where in the small intestine is vitamin B12 absorbed?

A

Terminal ileum

75
Q

How is vitamin B12 absorbed?

A

Parietal cells produce intrinsic factor
IF binds to vitamin B12
IF-B12 complex binds to receptor on enterocyte
B12 is absorbed

76
Q

What are some of the causes of B12 deficiency?

A

Gastritis

Damage to terminal ileum, removal of terminal ileum

GI system (21 decks)

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