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Block 1 Week 2 > Physiology of the Small Intestine > Flashcards

Physiology of the Small Intestine Flashcards

1
Q

Which glands the in duodenum produce mucus?

A

Brunner’s glands.

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2
Q

What 2 things cause secretion of water into the lumen of the intestine?

A
  1. The hypertonicity of the chyme.
  2. The intestinal epithelium secretes Na+, Cl-, and HCO3- into the lumen.

Water follows by osmosis.

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3
Q

Is there a large net loss or absorption of water from the small intestine?

A

Net absorption.

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4
Q

Where are Brunner’s glands located?

A

Duodenum

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5
Q

What is the main function of Motilin? How does it do this?

A

Stimulates migrating motor complexes (MMCs) via both the enteric and autonomic nervous systems.

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6
Q

List the 5 key intestinal hormones.

A
  1. Motilin
  2. VIP (vasoactive intestinal peptide)
  3. GIP (gastric inhibitory peptide)
  4. Cholecystokinin
  5. Secretin
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7
Q

What is the function of vasoactive intestinal peptide (VIP)?

A

Increases blood flow to the GI tract.

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8
Q

What are the 2 functions of gastric inhibitory peptide (GIP)?

A
  1. Inhibits gastric secretion.

2. Stimulates insulin secretion.

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9
Q

Which 2 hormones control pancreatic and biliary secretions?

A

Cholecystokinin and Secretin.

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10
Q

Secretin stimulates which organs to release which substances?

A

HCO3- from the pancreas, and bile from the liver.

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11
Q

What 2 things does Cholecystokinin stimulate?

A

Digestive enzyme secretion from the pancreas, and gallbladder contraction.

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12
Q

What are the main types of cells in the exocrine pancreas? What do they each secrete?

A

Acinar cells - secrete enzymes

Ductal cells - secrete bicarbonate

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13
Q

List the 5 main enzymes of the exocrine pancreas.

A
  1. Trypsin
  2. Chymotrypsin
  3. Carboxypeptidase
  4. Pancreatic amylase
  5. Lipases
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14
Q

Which enzymes of the exocrine pancreas are secreted in their inactive, precursor forms?

A
  1. Trypsin
  2. Chymotrypsin
  3. Carboxypeptidase
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15
Q

What is a zymogen?

A

A zymogen, also called a proenzyme, is an inactive precursor of an enzyme.

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16
Q

What activates inactive pancreatic digestive enzymes such as trypsinogen into active enzymes in the small intestine?

A

Enterokinase

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17
Q

Which enzyme turns CO2 and H2O into H+ and HCO3-?

A

Carbonic anhydrase

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18
Q

Other than Cholecystokinin, which other substance stimulates the secretion of pancreatic enzymes? What kind of substance is it?

A

Acetylcholine - a neurotransmitter.

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19
Q

Outline 7 steps of the digestion and absorption of fats in the small intestine.

A
  1. Fats (triglycerides) are emulsified by bile salts and phospholipids.
  2. Triglycerides are digested by pancreatic lipase to a monoglyceride and 2 fatty acids.
  3. The products are held in micelles, combined with bile salts and phospholipids.
  4. The micelles move next to the surface of the epithelial cells. When a micelle breaks down, the monoglycerides and fatty acids diffuse across the cell membrane.
  5. Once in the cell, the fatty acids and monoglycerides are reassembled into triglycerides.
  6. The triglycerides are packaged into chylomicrons.
  7. Chylomicrons leave the intestinal villus via its lymph vessel.
20
Q

In the digestion of fats (triglycerides), what are they emulsified by?

A

Bile salts and phospholipids.

21
Q

Pancreatic lipase turns triglycerides into what?

A

A monoglyceride and 2 free fatty acids.

22
Q

What is the primary product in the breakdown of starch and glycogen?

A

Maltose.

23
Q

How do glucose and galactose enter the luminal membrane of the intestinal epithelium?

A

Secondary active transport (SGLT1), coupled to Na+K+ATPase on the basolateral membrane.

24
Q

How does fructose enter the luminal membrane of the intestinal epithelium?

A

Facilitated diffusion (GLUT5).

25
Q

How do glucose, galactose and fructose leave the basolateral membrane of the intestinal epithelium?

A

Facilitated diffusion (GLUT2).

26
Q

Which enzymes in the small intestine break down proteins?

A
  1. Carboxypeptidase
  2. Trypsin
  3. Chymotrypsin
27
Q

How do amino acids enter the luminal membrane of the intestinal epithelium?

A

Secondary active transport (Na+ -amino acid co-transporters).

28
Q

How do dipeptides and tripeptides enter the luminal membrane of the intestinal epithelium?

A

H+ dependent co-transporters.

29
Q

How do amino acids leave the basolateral membrane of the intestinal epithelium?

A

Facilitated diffusion.

30
Q

How does Calcium enter the luminal membrane of the intestinal epithelium?

A

Ca2+ channels.

31
Q

Once inside the intestinal epithelium cells, what happens to Calcium?

A

It becomes reversibly bound to Calbindin.

32
Q

How does Calcium leave the basolateral membrane of the intestinal epithelium?

A
  1. Ca2+-ATPase

2. Na+/Ca2+ exchanger

33
Q

Absorption of Calcium is stimulated by what?

A

Vitamin D3.

34
Q

What are the dietary forms of iron?

A
  1. Haem iron

2. “Free” iron

35
Q

How does haem iron enter the luminal membrane of the intestinal epithelium?

A

Absorbed by receptor-mediated endocytosis.

36
Q

How does free iron enter the luminal membrane of the intestinal epithelium?

A

It is first reduced from Fe3+ to Fe2+ by membrane ferrireductase. Then Fe2+ crosses the membrane via divalent metal transporter 1 (DMT1).

37
Q

How does Fe2+ exit the basolateral membrane of the intestinal epithelium?

A

Via the transmembrane protein ferroportin 1.

38
Q

What happens to the iron left in the enterocytes which is not transported across the basolateral membrane into circulation?

A

It is bound to ferritin.

39
Q

What happens to the iron which is bound to ferritin in the enterocytes?

A

It is lost from the body in faeces when the intestinal mucosa is sloughed into the intestine.

40
Q

When iron is low in the body, how does the body compensate for this to enable more iron absorption?

A

The activity of ferroportin 1 on the basolateral membrane increases, allowing more iron to be absorbed into the blood and less lost by being bound to ferritin and lost from the body.

41
Q

What does B12 bind to in the stomach?

A

R protein.

42
Q

What does B12 bind to in the duodenum and jejunum?

A

Intrinsic factor.

43
Q

What happens to the B12-IF complex in the terminal ileum?

A

It is absorbed by receptor-mediated endocytosis.

44
Q

What is the site of pathology of Crohn’s disease? What are the specific defects in absorption associated with Crohn’s?

A

Ileum.

Vitamin B12 and bile salts/acid absorption.

45
Q

List some symptoms of malabsorption.

A
  1. Weight loss
  2. Abdominal distension
  3. Diarrhoea
  4. Steatorrhoea
  5. Pernicious anaemia
46
Q

How can excessive vomiting affect the acid-base balance?

A

Because it leads to large losses of secreted acids from the body, it may result in metabolic alkalosis.

47
Q

How can diarrhoea affect the acid-case balance?

A

The excessive loss of fluid and hence NaHCO3 in faeces may result in metabolic acidosis.

Block 1 Week 2 (10 decks)

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