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Gastrointestinal > Session 6 - The Intestines > Flashcards

Session 6 - The Intestines Flashcards

1
Q

How does the small intestine give great surface area for absorption?

A
  • Plicae Circulares - large folds
  • Mucosa folded into Villae.
  • Microvilli - cell surface covered in these (brush border)

Slow movement! for increased absorption.

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2
Q

What are the main types of cells in the small intestine?

A
  • Epithelial cells: enterocytes
  • Goblet cells: produce mucus

Intestinal Crypts

  • Stem cells at base
  • Enteroendocrine cells
  • Paneth cells (immune function)
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3
Q

What is digested and absorbed in the small intestine?

A

Carbohydrates, Proteins and Lipids

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4
Q

How are carbohydrates digested and absorbed?

A
  • Poly/di-saccharides broken down to monosaccharides (only molecules that can be absorbed)
  • Final breakdown is at brush border (brush border hydrolases)
  • Glucose can only enter with Na+ (cotransport)
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5
Q

What are the main monosaccharides?

A

Glucose, Fructose, Galactose

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6
Q

What are common dietary carbohydrates?

A

Starch, Lactose, Sucrose.

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7
Q

Which forms is starch found in?

A

Amylose (straight a 1-4 bonds)

Amylopectin (branches - a 1-6)

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8
Q

Which enzymes can break down starch?

A
  • Amylase - breaks down amylose (to glucose or maltose)
  • Alpha dextrins - break down amylopectin into smaller molecules, retain branching though.
  • Isomaltase - break down the bonds between branches.
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9
Q

What is maltose, what breaks it down?

A

Disaccharide composed of two glucose. Maltase.

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10
Q

What is Lactose made up of, what breaks it down?

A

Disaccharide of glucose and galactose. Lactase.

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11
Q

What is Sucrose made up of? What breaks it down?

A

Disaccharide containing glucose and fructose. Sucrase.

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12
Q

How are monosaccharides absorbed in the intestine?

A

Glucose/ Galactose via SGLT-1 on apical membrane with Na+
Fructose via Glut5 on apical membrane.

Move into blood via GLUT2 on basolateral membrane.

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13
Q

What drives the absorption of monosaccharides into the enterocytes?

A

Na/K ATPase on basolateral membrane establishes Na gradient, which drives Na and thus glucose/ galactose into the cell via SGLT-1.

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14
Q

How does oral rehydration therapy work?

A

Mixture of glucose and salt. Glucose uptake stimulates Na+ uptake.
Uptake of Na+ generates an osmotic gradient, thus water follows.
The mixture stimulates maximum water uptake.

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15
Q

How are proteins broken down at the stomach and small intestine?

A

In Stomach:
- Pepsinogen released from chief cells, converted to pepsin by HCL in stomach.

Small Intestine:

  • Pancreas releases proteases as zymogens.
  • Trypsinogen: is converted to trypsin by enteropeptidase.
  • Trypsin then activates other proteases.
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16
Q

What are exo/ endopeptidases?

A
  • Exopeptidases break bonds at the ends of the polypeptide to produce dipeptides/ amino acids.
  • Endopeptidases break bonds in the middle of the polypeptide producing shorter polypeptides.
17
Q

What are the major proteases in protein digestion?

A

Endopeptidases:

  • Trypsin
  • Chymotrypsin (activated by trypsin)
  • Elastase

Exopeptidases:
- Carboxypeptidase (A+B)

18
Q

Which protein products are absorbed in adults?

A

Only amino acids, dipeptides, and tripeptides are absorbed.

19
Q

How are amino acids transported into the cells in the intestines?

A
  • Via Na+/ amino acid co-transporters (similar to glucose).
20
Q

In what form are most protein products ingested? How are they transported?

A

Most moved as di/tri-peptides. (not AA)

  • Di/tri-peptides moved by H+ co-transporter: Peptide transporter 1 (PepT 1).
  • Inside cell these are converted to amino acids.
21
Q

What is the difference between electrolyte/water uptake in the small and large intestine?

A
  • Both have basolateral Na/K ATPase.

Small Intestine: Na+ is co-transported.
Large Intestine: Has Na+ Channels, induced by aldosterone.

22
Q

How is calcium uptake orchestrated in the small intestine?

A

(when Ca intake low)

  • Active transcellular absorption - Ca+ ATPase at basolateral membrane.
  • The process requires Vitamin-D. (calbindin)
  • This is stimulated by parathyroid hormone.
23
Q

How does calcium move into the body when calcium intake is normal/high?

A

It moves passively, by paracellular absorption.

24
Q

How is iron absorbed in the intestine?

A
  • Mostly in haem/Fe2+ form.

- Iron is absorbed across apical membrane, co-transported with H+.

25
Q

What happens to iron absorption and storage when iron levels are low or high?

A

Low
- Iron binds to transferrin (transported to stores: mainly ferriting complexes in bone marrow, liver and spleen. Half of iron is in haemoglobin!)

High
- Iron contained in ferritin complexes (trapped in cell).
This is lost when the enterocyte is replaced.

26
Q

How is vitamin B12 absorbed in the gut?

A
  • It is absorbed in the terminal ileum, bound to intrinsic factor. (IF)
  • IF is secreted by gastric parietal cells.
27
Q

What may cause a B12 deficiency?

A

Reduced secretion of Intrinsic Factor by gastric parietal cells, due to gastritis.
Or terminal ileal removal.

28
Q

What are the symptoms of coeliac disease?

A
  • Diarrhoea
  • Flatulance
  • Weight loss
    etc.
29
Q

What is coeliac disease?

A
  • Intolerance of the gliadin fraction of gluten.
    This is found in wheat, rye and barley.
    The intolerance results in an immune response which damages the mucosa of the intestines.
30
Q

What damage does coeliac disease do to the intestines?

A
  • Absence of intestinal villi.
  • Lengthening of intestinal crypts.
  • Lymphocytes infiltrate epithelium.

All causes impaired digestion/ malabsorption.

31
Q

What investigations would be done to rule out/ confirm coeliac disease?

A
  • Upper GI endoscopy/ biopsies (duodenum)
    (look for pathology/ villi structure)
  • Blood tests: serology, electrolyte imbalance, anaemia.
  • Treatment: diet

Gastrointestinal (9 decks)

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