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GI > Small Intestine > Flashcards

Small Intestine Flashcards

1
Q

What is the main site of action in the SI?

A

Jejenum

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2
Q

Which part of the duodenum do the bile duct and pancreatic duct drain into?

A

second part

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3
Q

What are the pile circulares?

A

mucosal layer is thrown into huge circular folds which increase SA and create turbulence for mixing of fluids

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4
Q

What is the role of crypts between microvilli?

A

small mucosal glands that secrete bicarb and mucus to neutralise acid and facilitate smooth fluid movement

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5
Q

What are microvilli?

A

further increase SA of villi

have brush borer enzymes that break down materials

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6
Q

What is the role of segmentation in motility?

A

Mixes food up and mixes it with intestinal secretions

Alternate contraction of neighbouring segments churns and fragment the bolus

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7
Q

What stimulates migrating motor complexes (slow, strong peristaltic waves)?

A

Motilin

Peptide secreted by M cells in the crypts

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8
Q

How often are migrating complexes?

A

Every 90 mins when gut is empty

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9
Q

What suppresses motilin?

A

feeding

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10
Q

what is the role of migrating motor complexes stimulated by motilin?

A

keep the gut clean
prevent reflux
prevent bacterial growth

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11
Q

What do amylases break down?

A

Carbohydrates
1,4 internal bonds
this leaves alpha limit dextrin (small chains with 1,6 links)

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12
Q

After amylase partially breaks down carbohydrates, what breaks down the short chains?

A

Specific enzymes on the burns border membrane break down disaccharides into monosaccharides so they can be actively transported into the cell

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13
Q

What protein absorbs glucose and galactose? Is this active or passive?

A

Specific glucose transporter 1 (SGLT1)

active

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14
Q

What protein absorbs fructose? actively or passively?

A

Glut5 transporter

passive

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15
Q

Where does proteolysis begin?

A

Stomach

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16
Q

What protease is secreted by crypt cells?

A

Enterokinase - cleaves trypsinogen into trypsin which then cleaves pancreatic enzymes into active forms
e.g. proelastase - elastase

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17
Q

Why is pepsin inactivated in the duodenum?

A

Higher pH

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18
Q

Where do endopeptidases cut?

A

Within a protein chain (usually within a certain pair of amino acids)
e.g. trypsin
chymotrypsin
elastase

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19
Q

Where do exopeptidase cut?

A

(ex = exit)

at the last peptide bond to cleave off the last amino acid

20
Q

Where are small peptides taken up in the SI?

A

Diffuse to brush border, where membrane bound peptidases chop them up into amino acids. These amino acids are taken up by sodium linked secondary active transporters.
Di peptides are taken up by proton linked secondary active transporters.

21
Q

What happens to the small amount of protein taken up into the cell by endocytosis?

A

Most is degraded
Except in M cells which overly Peyer’s patches (immune tissue under mucosa)
This allows the immune cells to detect how to handle the food - to respond or not?

22
Q

What is the role of bile salts?

A

Break up lipid droplets, creating a single layer of lipids and increasing surface area so enzymes can break down the lipids

23
Q

What is the role of pancreatic lipase in fat digestion?

A

Cleaves off fatty acids from the outside of lipids leaving a monoglyceride + 2 free fatty acids

24
Q

Where do mixed micelles (monoglycerides, fatty acids + bile salts) diffuse to and how?

A

Close to the brush border where they deliver their contents across the membrane

Bile salts make the molecule soluble

25
Q

What happens to fatty acids and monoglycerides in the cell?

A

Triglycerides are resynthesised and packaged into chylomicra which are exocytosed into the interstitium

26
Q

Where in the SI are conjugated bile salts absorbed?

A

Distal ileum

27
Q

Where do the rest of the bile salts that aren’t absorbed in the ileum go?

A

Colon - deconjugated by bacteria and reabsorbed

5% lost in faeces

28
Q

Which form of iron can we absorb, Fe3 or Fe2?

A

Fe2

29
Q

How do we absorb Fe3?

A

Enzymes in brush border reduce Fe3 to Fe2 and it is then transported into the cell

30
Q

What happens to Fe2 once it has lost the cell?

A

Converted back to Fe3, transported in blood bound to transporter protein to liver for storage

31
Q

Where in the SI is calcium actively reabsorbed?

A

duodenum

32
Q

What regulates calcium absorption in the duodenum?

A

Vitamin D and parathyroid hormone

in the rest of the small bowel it is absorbed paracellularly

33
Q

How is calcium stopped form having a signalling effect in the cell when it is taken up?

A

Binding calcium proteins bind

34
Q

How are fat soluble vitamins (A, D, E, K) absorbed?

A

Absorbed with lipids - dissolve in micelles and chylomicrons. Diffuse across cell membranes.

35
Q

How is vitamin B12 (cobalamin) absorbed?

A

Only absorbed when bound to intrinsic factor (released by gastric parietal cells) because it is a huge molecule. Enter cell by endocytosis after binding to receptor in ileum.

36
Q

Where does fat absorption mainly take place?

A

jejeunum

37
Q

Where do most minerals and carbohydrates get absorbed?

A

duodenum

quick digestion

38
Q

Where do water soluble vitamins, ions and water get absorbed?

A

jejenum and ileum

39
Q

Where do bile salts and vitamins B.12 get absorbed?

A

Ileum

40
Q

What kind of fluid does the small bowel secrete?

A

alkaline

41
Q

Where are hormones and mucus and bicarb secreted?

A

Hormones = blood

mucus and bicarb = lumen

42
Q

what 4 important hormones are secreted in the small intestine? By what cells?

A

CCK from I cells
Secretin from S cells
Motilin form M cells
Gastrin from G cells

43
Q

What is the role of CCK (cholecystokinin)?

A

Stimulates digestion of fat and protein (stimulates pancreas to secrete proteases and pancreatic lipase)

44
Q

What is the role of secretin?

A

stimulates the acinar cells of the pancreas to secrete water and bicarbonate into the pancreatic ducts that drain into the duodenum.

45
Q

What is the role of gastrin?

A

stimulates acid secretion by the parietal cells in the stomach
stimulates pancreatic acinar cells to secrete digestive enzymes

GI (10 decks)

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