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Small intestines Flashcards

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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
Where along the GI tract is starch digested?
Mouth Small intestines
26
What produces amylase that is found in the mouth?
Salivary glands
27
What produces amylase that is found in the small intestine?
Pancreas
28
What are the main dietary disaccharides?
Lactose Sucrose
29
What is lactose made up of?
Disaccharide made up of glucose and galactose monosacharides joined together
30
What is sucrose made up of?
Disaccharide made up of glucose and fructose monosaccharides joined together
31
What does sucrase digesting sucrose produce?
Glucose Fructose
32
What is meant by absorption?
Movement of nutrients, electrolytes and water from the gut lumen into the blood
33
What is the enzyme responsible for digesting lactose?
Lactase
34
What does lactase digesting lactose produce?
Glucose Glactose
35
What are the routes of absorption?
Transcellular Paracellular
36
What is transcellular absorption?
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
What is paracellular absorption?
Movement occurs between enterocytes
38
How are the intestines adapted for absorption?
Large surface area - plicae circulares - villi - microvilli Contents move slowly through them
39
How are monosaccharides absorbed?
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
How does oral rehydration work?
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
What are the types of enzymes responsible for digesting proteins in the small intestine?
Exopeptidases Endopeptidases
42
What are exopeptidases?
Cleave off dipeptides and tripeptides from polypeptide chain
43
What are endopeptidases?
Cleave polypeptide chains in the middle to produce shorter polypeptides
44
What are some examples of endopeptidases?
Trypsin Chymotrypsin Elastase
45
What are some examples of exopeptidases?
Carboxypeptidase
46
What produces the enzymes responsible for digesting proteins in the small intestines?
Pancreas
47
What form of the protease enzymes that digest proteins in the small intestine does the pancreas produce?
Zymogens, meaning inactive form
48
What is the inactive form of trypsin?
Trypsinogen
49
What activates trypsinogen into its active form?
Enteropeptidase in the duodenum
50
What activates chymotrypsinogen, elastase, procarboxypeptidase into their active forms?
Trypsin
51
What is the enzyme responsible for digesting sucrose?
Sucrase
52
How are amino acids absorbed in the small intestine?
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
What form of protein is most commonly absorbed in the small intestine?
Dipeptides Tripeptides
54
How are dipeptides and tripeptides absorbed in the small intestine?
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
What routes of absorption does water follow?
Both transcellular and paracellular
56
How is water absorbed in the intestines?
Sodium ions increase osmolality in their direction of movement water follows this osmolality
57
How are sodium ions absorbed in the small intestine?
Co-transported with other nutrients
58
How are sodium ions absorbed in the large intestine?
Sodium ion channels
59
What increases sodium ion channel activity in the large intestines?
Aldosterone
60
What form of protein is absorbed in the small intestine?
Amino acids Dipeptides Tripeptides
61
What is the osmolality of the solution reabsorbed in the small intestine? Why?
Isoosmotic | because it is absorbed with sodium
62
What does calcium ion absorption depend on?
Levels of calcium in the blood - low - normal or high
63
What is the route of calcium ion absorption when calcium levels in the blood are low?
Transcellular route
64
How are calcium ions absorbed by the transcellular route?
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
What stimulates calbindin?
Vitamin D
66
What increases vitamin D levels?
Parathyroid hormone
67
What is the route of calcium ion absorption when calcium ion levels are normal/high?
Paracellular route
68
How are calcium ions absorbed by the paracellular route?
Move from gut lumen, in between enterocytes, into blood | down their concentration gradient, so by simple diffusion
69
What form of iron is absorbed?
Haem Fe2+ form
70
How is non-haem Fe3+ form converted into haem Fe2+ form?
Gastric acid
71
How is haem Fe2+ iron absorbed?
DMT1 transporter on apical domain | co-transports Fe2+ with H+ from gut lumen into enterocyte
72
What happens to haem Fe2+ iron in the enterocytes?
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
What is Fe2+-transferrin transported to by the blood? What happens to Fe2+ in those organs?
Bone marrow Liver Spleen for haemaglobin synthesis, storage as ferritin
74
Where in the small intestine is vitamin B12 absorbed?
Terminal ileum
75
How is vitamin B12 absorbed?
Parietal cells produce intrinsic factor IF binds to vitamin B12 IF-B12 complex binds to receptor on enterocyte B12 is absorbed
76
What are some of the causes of B12 deficiency?
Gastritis Damage to terminal ileum, removal of terminal ileum

GI system (21 decks)

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