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Block 1 > Small Intestine Physiology > Flashcards

Small Intestine Physiology Flashcards

1
Q

Where is mucus produced in the small intestine?

A

Brunner’s Gland in the duodenal mucosa

Viscous, alkaline rich fluid

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2
Q

Where is water secreted from in the small intestine?

A

Intestinal epithelium secretes Na+, Cl- and HCO3+ into the lumen, water follows by osmosis.

The hypotonicity of chyme encourages water to cross the small intestine by osmosis

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3
Q

What hormones are secreted by the small intestine?

A
  • Secretin
  • Cholecystokinin (CKK)
  • Motilin
  • Vasoactive intestinal peptide (VIP)
  • Gastric Inhibitory Peptide (GIP)
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4
Q

What does motilin do?

A

stimulates migrating motor complexes (MMCs) via both enteric and autonomic nervous system.

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5
Q

What do migrating motor complexes (MMCs) do?

A

MMCs act between periods of digestive motility. They sweept contents of the GI tract that cannot be digested out.

Responsible for the rumbling tummy in between meals

Involved in opening of sphincters and strong peristaltic movements

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6
Q

What does Vasoactive Intestinal Peptide (VIP) do?

A

Increase blood flow to the GI tract

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7
Q

What does Gastric Inhibitory peptide do? (GIP)

A

Glucose dependent insulinotropic peptide

  • Inhibits gastric secretion
  • Stimulates insulin secretion
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8
Q

What does Cholecystokinin (CKK) do?

A
  • Acts on exocrine pancreas to stimulate production of pancreatic enzymes.
  • Acts on gallbladder causing contraction and release of contents into small intestine
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9
Q

What does Secretin do?

A
  • Acts on the exocrine pancreas, stimulating bicarbonate production.
  • Stimulates liver to produce bile.
  • Inhibits gastric motility
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10
Q

Where are pancreatic enzymes secreted from?

A

Acinar Cells

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11
Q

What do the Acinar cells of the pancreas secrete?

A

secrete Enzymes into the duct, they leave the pancreas via the common bile duct

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12
Q

Where is alkali secreted from in the pancreas?

A

Duct cells in

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13
Q

What do the duct cells of the pancreas secrete?

A

Alkali

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14
Q

What is the function of the alkali secreted by pancreatic duct cells?

A
  • An isotonic solution rich in bicarbonate ions

- Neutralises duodenal contents - alkaline bile from the liver also helps

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15
Q

Name the digestive enzymes produced by the pancreas?

A

Proteases:

  • Trypsin
  • Chymotrypsin
  • Carboxypeptidase

Pancreatic amylase (breaks down starch)

Lipases (breaks down fats)

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16
Q

How are Pancreatic enzymes produced?

A

-Produced as ZYMOGENS (inactive enzymes)

E.g. Pancreas secretes inactive Trypsinogen

-Cleaved by membrane bound enterokinase to active peptidase TRYPSIN

Trypsin then acts on other inactive enzymes e.g. chymotrypsin & carboxypeptidase, releasing the active form of these enzymes.

17
Q

Outline Bicarbonate production in the Duct Cells

A
  • Similar to HCl prod in parietal cells but ion movements are reversed
  • Bicarb ions are secreted into the duct lumen
  • H+ ions are pumped out of duct cells and released into the blood
  • Reaction between CO2 + H2O is catalysed by Carbonic Anhydrase
18
Q

How is enzyme secretion in the pancreas controlled?

A
  • By CCK

- By Ach from parasympathetic postganglionic neurons of Vagus

19
Q

How is the alkali secretion of the pancreas stimulated?

A
  • Secretin

- Potentiated by CCK & Ach (vagal tone)

20
Q

Where does digestion of Fats, Starch and proteins occur?

A
  • Lumen of the duodenum and the proximal jejunum
21
Q

How are fats digested?

A
  • Fats (triglyceride) are digested by pancreatic lipase to monoglyceride and fatty acids

(lumen of duodenum and proximal jejunum)

22
Q

How is starch digested?

A
  • Starts in the mouth by salivary amylase, completed by pancreatic amylase
  • Disaccharides are broken down into monosaccharides by brush border enzymes on the luminal membrane of the small intestine
23
Q

How are proteins digested?

A
  • Protein digestion begind in the stomach by Pepsin
  • Broken down into peptide fragments by Trypsin and chymotrypsin
  • Peptide fragments are digested to free amino acids by carboxypeptidase (pancreas) and aminopeptidase (luminal membranes of small intestine epithelial cells)
24
Q

What is the role of pancreatic lipase in digestion?

A
  • Digest fats (triglyceride) into monoglyceride and fatty acids
25
Q

What is the role of pancreatic amylase in digestion?

A
  • Complete digestion of starch after it has been started by salivary amylase.
  • Into disaccharides
26
Q

How are disaccharides taken in from the diet digested?

A

-Broken down into monosaccharides by brush border enzymes in the luminal membrane of the small intestine

27
Q

What is the role of brush border enzymes in the luminal membrane of the luminal membrane of the small intestine?

A
  • Brush border enzumes are embedded in the membrane with the catalytic domain facing the lumen
  • Break down disaccharides into monosaccharides
28
Q

What is the role of trypsin and chymotrypsin?

A
  • Break proteins down into peptide fragments
29
Q

What is the role of carboxypeptidase and aminopeptidase?

A

Digest peptide fragments into free amino acids

after digestion by trypsin and chymotrypsin

30
Q

Where is carboxypeptidase secreted?

A

Protease secreted from pancreas

31
Q

Where is aminopeptidase secreted from?

A

Luminal membranes of small intestine epithelial cells

32
Q

What is the first step in Absorption of fats?

A
  • Emulsification of fats by bile salts and phospholipids:
  • Fats delivered at a controlled rate from duodenum
  • Bile salts surround fats, hold them in suspension…

presents surface to pancreatic lipase for digestion into monoglyceride + fatty acid

33
Q

After emulsification, what is the next step in fat absorption?

A
  • Fats are digested by pancreatic lipase, the products are held in micelles combined with bile salts and phospholipids
  • Fat soluble Vitamines D,A,K,E also carried in micelles.
34
Q

After fats are digested and the products are suspended in micelles, what happens next?

A
  • Micelles diffuse into unstirred layer next to surface of epithelial cells. Fatty acids and monoglycerides diffuse into epithelial cells.
  • Once inside, they are reassembled into fats.
  • Triglyceride droplets are packaged into chylomicrons
  • Chylomicrons are exported across the basolateral membrane and leave via lymph vessel.
35
Q

What are chylomicrons and how do they travel through the body?

A
  • After digestion and entry into the epithelial cell, Triglyceride droplets are packaged into chylomicrons
  • Chylomicrons are exported across the basolateral membrane and leave via lymph vessel.
36
Q

After digestion by brush border enzymes, how are monosaccharides transported across the epithelium into the hepatic portal vein?

REDO ANSWER

A

Fructose moves across the membrane via facilitated diffusion, down its concentration gradient

  • Glucose or galactose is transported via SGLT - secondary active transport, uses energy generated by movement of Na+ ions out of the cell, brings glucose or galactose with it across basolateral membrane
37
Q

What do aminopeptidases do?

A

Break down tri/dipeptides into amino acids

38
Q

What enzyme breaks tri/dipeptides down into amino acids?

A

Aminopeptidases

39
Q

How are amino acids transported into the portal vein from the epithelial cell?

A

Via co-transporters linked with sodium.

Different structures are needed depending on the character of the A As

Block 1 (11 decks)

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