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Gastrointestinal System > Session 6 - The Intestines > Flashcards

Session 6 - The Intestines Flashcards

1
Q

What is the role of the intestines?

A

Absorbs nutrients

Absorbs water/electrolytes

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2
Q

How is a large surface area created in the intestines?

A

Mucosa folded into villi

Surface covered in microvilli

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3
Q

What are plicae circulares?

A

Permanent folds of the intestines

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4
Q

What is the main epithelial cell of the intestines?

A

Enterocytes

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5
Q

Glucose can only enter enterocytes when it is co-transported along with what ion?

A

Na+

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6
Q

Where does the final digestion of carbohydrates occur?

A

The brush border of intestines

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7
Q

What are the common dietary carbohydrates?

A

Starch (polysaccharide)
Lactose (disaccharide)
Sucrose (dissacharide)

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8
Q

What bond holds glucose molecules together in starch?

A

Alpha 1-4 bonds

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9
Q

What enzyme converts alpha dextrins to glucose?

A

Isomaltase

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10
Q

What does lactase convert lactose into?

A

Glucose and galactose

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11
Q

What does sucrase convert sucrose into?

A

Glucose and fructose

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12
Q

Explain how monosaccharide absorption occurs in an enterocyte.

A

Glucose (or galactose) co-transported into cell with sodium through SGLT-1 transporter.
Fructose moves in through GLUT5 channel by facilitated diffusion.
GLUT2 channel allows glucose and fructose out of the cell, diffuses down concentration gradient into capillary blood.
Na+/K+ ATPase on basolateral membrane maintain low intracellular Na+

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13
Q

How is water taken up in the intestines?

A

Uptake of Na+ generates an osmotic gradient, water follows.
Glucose uptake stimulates further Na+ uptake, therefore a mixture of glucose and salt will stimulate maximum water uptake.

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14
Q

What cells release pepsinogen?

A

Chief cells

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15
Q

What converts pepsinogen to pepsin?

A

HCl

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16
Q

What is the action of pepsin?

A

Breaks down proteins to oligopeptides and amino acids (occurs in stomach)

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17
Q

What enzyme converts trypsinogen to trypsin?

A

Enteropeptidase

18
Q

What is the action of trypsin?

A

Breaksdown proteins

Activates other proteases (e.g. chymotrypsin)

19
Q

What is the difference between exopeptidases and endopeptidases?

A

Exopeptidases break bonds at the ends of polypeptide chains to produce dipeptides or individual amino acids.
Endopeptidases break bonds in the middle of polypeptide chains to produce shorter polypeptides.

20
Q

Give examples of endopeptidases and exopeptidases.

A 
Endopeptidases:
- trypsin
- chymotrysin 
- elastase
exopeptidases:
- carboxypeptidase
21
Q

How are amino acids transported into cells?

A 
Na+-amino acid co-transporters
Different ones (neutral, acidic, basic, imino)
22
Q

Are most protein products absorbed as amino acids or dipeptides/tripeptides?

A

Most protein products are ingested as dipeptides/tripeptides, not as amino acids.

23
Q

How are dipeptides/tripeptides absorbed?

A

Peptide transporter 1 (PepT 1)

24
Q

What happens to dipeptides/tripeptides once they have entered the enterocyte?

A

they are converted to amino acids inside the cell by cytosolic peptidases

25
Q

What is the difference in Na+ absorption between the small and large intestines?

A

In the small intestine Na+ is co-transported.

in the large intestine Na+ moves in through Na+ channels (which are induced by aldosterone).

26
Q

Calcium absorption is stimulated by what hormone?

A

Parathyroid hormone

27
Q

How does the absorption of calcium in the intestines differ between when calcium levels are low and when calcium is normal/high?

A

When there are low levels of calcium in the blood:

  • active transcellular absorption
  • enters cells via facilitated diffusion
  • Ca+ ATPase removes Ca+ from the basolateral membrane
  • this process requires vitamin D (calbindin)
  • stimulated by parathyroid hormone

When there are normal/high levels of calcium in the blood:
- passive paracellular absoprtion

28
Q

Why do PPIs decrease iron absorption?

A

Gastric acid is important in the uptake of iron in the intestines as iron is co-transported across the apical membrane with H+. Use of PPIs means less H+ so less iron absorption.

29
Q

how is iron distributed in body?

A

Approximately half of iron is in haemoglobin, the other half is stored in ferritin complexes in bone marrow, liver and spleen.

30
Q

Once iron has been taken up by enterocytes, what happens to it next depending on whether iron levels in the body are high or low?

A

When iron levels are low, iron binds to transferrin and is transported to iron stores (in bone marrow, spleen or liver).
When iron levels are high, iron remains contained in ferritin complexes within the enterocytes, meaning it is trapped there and then lost when the enterocyte is replaced.

31
Q

How are water soluble vitamins absorbed?

A

Na+ co-transport

32
Q

How is vitamin B12 absorbed?

A

Vitamin B 12 is absorbed in the terminal ileum bound to intrinsic factor.

33
Q

What cells secret intrinsic factor?

A

Gastric parietal cells

34
Q

Give two causes of vitamin B12 deficiency other than lack of dietary intake.

A

Gastritis (less intrinsic factor produced)

Terminal ileum removal (less vit B12 absorbed)

35
Q

What would the blood test of someone with coeliac disease show?

A 
Electrolyte imbalance (due to reduced ion absorption)
Anaemia (due to reduced iron absorption)
36
Q

Give some symptoms of coeliac disease.

A

Diarrhoea
Flatulence
Weight loss
Sensory loss

37
Q

What is coeliac disease?

A

Intolerance to the gliadin fraction of gluten resulting in an immune response.

38
Q

What damage does the immune response in coeliac disease cause to the intestines?

A

Damages mucosa of intestines:
- absence of intestinal villi
- lengthening of intestinal crypts
- infiltration of lymphocytes into epithelium
all result in impaired digestion and malabsorption

39
Q

What investigations can be used to help diagnose coeliac disease?

A

Upper GI endoscopy and biopsies - identifies mucosal pathology and whether villi are reduced or absent.
Bloods - serology, electrolyte imbalances, anaemia.

40
Q

How is coeliac disease treated?

A

Cut gluten out of diet.

Gastrointestinal System (13 decks)

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