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Gastrointestinal > The Small Intestine and Disorders > Flashcards

The Small Intestine and Disorders Flashcards

1
Q

What is the ileum, jejenum and duodenum a site of?

A

Digestion and absorption.

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2
Q

Compare the jejunum and ileum.

A

Jejunum is located in the upper left quadrant and ileum is located in the lower right quadrant.
The jejunum has a thick intestinal wall and the ileum has a thin intestinal wall.
The jejunum has a longer vasa recta and the ileum has shorter vasa recta.
The jejunum has less arcades (arterial loops) than the ileum.

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3
Q

What is the main blood supply of the jejunum and ileum?

A

Jejunum and ileal arteries off the Superior Mesenteric Artery.

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4
Q

What is the blood supply to the duodenum?

A

Proximal to bile entry: gastroduodenal artery and superior pancreaticoduodenal artery.
Distal to bile entry: Inferior pancreaticoduodenal artery.

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5
Q

What is the venous drainage of the small intestine?

A

The superior mesenteric vein, which joins the splenic vein and the inferior mesenteric vein (which usually combines with the splenic first) to form the portal vein.

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6
Q

What is the state of chyme in the start of the small intestine?

A
  1. Isotonic.
  2. Neutral.
  3. Digestion is nearly complete.
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7
Q

What is required of the small intestine in order to absorb effectively?

A
  1. Needs a large surface area which is supplied by the mucosa folding into vili and the surface covered in microvilli (a brush border) as well as the plicae circulares.
  2. Slow movements of contents which is from the precise control of the small intestine.
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8
Q

What cells make up the epithelial cells of the small intestine?

A

The epithelial cells make up an intestinal gland called the Crypts of Lieberkuhn.

  1. Enterocytes.
  2. Goblet cells.
  3. Enteroendocrine cells.
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9
Q

What type of epithelia is found in the small intestine?

A

Tall columnar cells.

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10
Q

What intestinal gland is present in the small intestine?

A

Crypts of Lieberkuhn.

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11
Q

What cells make up the Cryps of Lieberkuhn?

A
  1. Stem cells.

2. Paneth cells.

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12
Q

Is the small intestine mucosa constantly shed, and if so how frequently?

A

Yes. Every 3-6 days.

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13
Q

What do the stem cells do in the Crypts of Lieberkuhn?

A

Stem cells at the base which migrate to the surface, maturing as they migrate into a variety of cells.

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14
Q

What do the Paneth cells do in the Crypts of Lieberkuhn?

A

Paneth cells in the base of the crypt (innate mucosal defence cells), produce antimicrobial peptides.

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15
Q

What do enteroendocrine cells do?

A

Produce hormones.

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16
Q

What do goblet cells do?

A

Produce mucus.

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17
Q

What do enterocytes do?

A

Absorb. They make up the majority of cells in the small intestine.

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18
Q

What form of carbohydrate can be absorbed by the small intestine?

A

Monosaccharides (glucose, galactose and fructose).

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19
Q

Can all carbohydrates be digested in the small intestine?

A

No, there are carbohydrates of plant origin that cannot be utilised. They are partially digested in the colon by bacteria and provide nutrients for the colonic mucosa.

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20
Q

Name some common dietary carbohydrates.

A
  1. Starch (polysaccharide).
  2. Lactose (disaccharide).
  3. Sucrose (disaccharide).
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21
Q

Describe the structure of starch.

A

Straight chains of glucose are amylose (alpha 1-6 glycosidic bonds) and branched chains are amylopectin (alpha 1-6 bonds and alpha 1-4 glycosidic bonds).

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22
Q

Describe the digestion of starch.

A
  1. Salivary and pancreatic amylase breaks down alpha 1-4 bonds in amylose and amylopectin.
  2. Amylose breakdown forms maltose (glucose and glucose). Amylopectin breaks down into alpha dextrins.
  3. Isomaltase is required to break the branched alpha 1-6 bonds. Maltase breaks down maltose into 2 glucoses.
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23
Q

How is lactose digested?

A

Lactose is digested using the enzyme lactase (a brush border enzyme) which breaks lactose into glucose and galactose.

24
Q

How is sucrose digested?

A

Sucrose is digested using the enzyme sucrase (a brush border enzyme) which breaks sucrose into glucose and fructose.

25
Q

How is glucose and galactose absorbed from the lumen into the blood?

A

Sodium Glucose Transporter 1 (SLUT1) is a co-transporter that moves glucose/galactose into the enterocyte with sodium, using sodiums favourable concentration gradient.
Sodiums favourable concentration gradient is formed from the Na-K-ATPase which moves 3 sodiums out of the cell into the blood for every 2 potassiums into the cell.
Glucose, galactose and fructose then use GLUT2 (using their concentration gradient) to move into the blood at the basolateral membrane.

26
Q

How is fructose absorbed from the lumen into the blood?

A

Fructose moves into the enterocyte by the GLUT5 (facilitated diffusion) and then into the blood via the GLUT2.

27
Q

How is the sodium concentration gradient maintained to allow glucose and galactose to move into the enterocyte?

A

By Na-K-ATPase moving 3 sodium ions out into the blood and 2 potassium ions into the cell.

28
Q

How is protein digested in the stomach?

A
  1. Pepsinogen is released from chief cells which is converted to pepsin by HCl from parietal cells.
  2. Pepsin acts on proteins making oligopeptides and amino acids which move to the small intestine.
29
Q

How is protein digested when in the small intestine lumen?

A
  1. Pancreas releases trypsinogen (and other zymogens).
  2. Trypsinogen is converted to trypsin by enterokinase.
  3. Trypsin activates other proteases.
30
Q

Describe the 2 major types of proteases released from the pancreas?

A
  1. Endopeptidases, produces short polypeptides, breaking bonds in the middle of the polypeptide.
  2. Exopeptidases, produces dipeptides and amino acids breaking bonds at the end of the polypeptide.
31
Q

Give 3 examples of endopeptidases,

A
  1. Trypsin.
  2. Chymotrypsin.
  3. Elastase.
32
Q

Give an example of an exopeptidase.

A

Carboxypeptidase A and B.

33
Q

How is protein digested at the brush border of the lumen?

A

The brush border also contains some proteases as the enterocyte expresses peptidases in their brush border. Sometimes cannot digest proteins down to amino acids.

34
Q

What proteins can be absorbed in the enterocyte?

A

Intestine can absorb short peptides and amino acids.

35
Q

How are proteins absorbed into the enterocyte?

A

Dipeptides and tripeptides along with amino acids can be absorbed in the cell by Peptide Transporter 1.
Amino acids can travel with sodium on a sodium-amino acid co-transporter into the cell.

36
Q

How is protein. (di,tri and amino acids) digested in the cystol of the enterocyte?

A

The small peptides are acted on by the cytosolic peptidases and broken down into amino acids. Certain di and tri peptides can be absorbed into the blood by a transporter.

37
Q

Describe the complete absorption of proteins.

A

Amino acids can be transported into the enterocyte by a sodium amino acid co-transporter or by Peptide Transporter 1. The sodium concentration gradient is maintained by Na-K-ATPase and amino acids and tri- and di- peptides move into the blood via a transporter down their concentration gradient.

38
Q

How is water absorbed back into the blood?

A

Absorption is driven by movement of sodium into the enterocyte.
Sodium is moved by active transport out of the cell on the basolateral membrane and diffuses into epithelial cells.
Water can move into the intracellular space.
Osmotic gradient from all the absorption leads. to uptake of water. The fluid absorbed is iso-osmotic.

39
Q

What is the basis of electrolyte and water uptake in the whole of the intestine?

A

Both the small and large intestine have Na-K-ATPase on their basolateral membrane.
However, the small intestine has Na+ co-transported with glucose and amino acids on its apical membrane and the large intestine has ENaC induced by aldosterone.

40
Q

How do we medically rehydrate someone?

A

Give them a mixture of glucose and salt to stimulate maximum water uptake as contained in oral rehydration fluid. Uptake of Na+ generates osmotic gradient. Water follows and glucose uptake stimulates Na+ uptake.

41
Q

How is water secreted into the lumen?

A

Secretion is. driven by chloride movement mainly.

42
Q

What can Vitamin B12 deficiency lead to?

A

Megaloblastic anaemia and neurological symptoms.

43
Q

What are the causes of Vitamin. B12 deficiency?

A
  1. Lack of intrinsic factor from parietal cells which means B12 cannot bind to the stomach and this creates pernicious anaemia.
  2. Hypochlorhydria (inadequate stomach acid).
  3. Inadequate intake of food like in strict vegetarians.
  4. Inflammatory disorders of the ileum where B12 is absorbed, like in Crohn’s disease.
44
Q

What is the medical term for inadequate stomach acid?

A

Hypochlorhydria.

45
Q

Where is B12 absorbed?

A

Ileum.

46
Q

What causes lactose intolerance?

A

A deficiency in the enzyme lactase which is a brush border enzyme.

47
Q

Describe the clinical presentation of lactose intolerance and explain the symptoms.

A

After the age of 2 lactase is expressed less. When lactose is consumed in a quantity it cannot be absorbed it remains int he gut lumen and creates a high osmotic effect. Water is not absorbed back into the blood and this causes diarrhoea. Lactose is fermented in the gut by the bacteria and this produces flatulence and bloating.

48
Q

What are the symptoms of Irritable Bowel Syndrome?

A
  1. Abdominal pain.
  2. Bloating.
  3. Flatulence.
  4. Diarrhoea/constipation.
  5. Rectal urgency.
49
Q

What are the causes of IBS?

A

Multifactorial but it is more common in females and 20-40s and is associated with psychological disorders.

50
Q

How is IBS diagnosed?

A

In the absence of documented abnormalities IBS is a. common disorder.

51
Q

What is the pathology in Coeliac disease?

A

It arises from an immunological response to the gliadin fraction of gluten which is found in wheat, rye and barley.
It damages the mucosa of small intestines:
1. Destroys intestinal vili.
2. Lengthens intestinal crypts.
3. Lymphocytes infiltrate the epithelium.
4. Consequently impaired digestion/malabsorption.

52
Q

What is the cause of Coeliac disease?

A

Genetic factors are involved.

53
Q

What are the symptoms of Coeliac Disease?

A

Malabsorption associated.

  1. Diarrhoea.
  2. Weight loss.
  3. Flatulence.
  4. Abdominal Pain.
  5. Anaemia (impaired iron absorption).
  6. Neurological symptoms as a result of hypocalcaemia.
54
Q

What investigations should you do in someone with suspected coeliac disease?

A
  1. Bloods: IgA antibodies to smooth muscle endomysium and tissue transglutaminase.
  2. Upper GI endoscopy and biopsy to look for mucosal pathology and to see if the villi are reduced or absent.
55
Q

How do you treat Coeliac Disease?

A

With a strict gluten free diet. There will be clinical improvement in days/weeks and histological improvement in weeks/months.

56
Q

How is trypsinogen converted into trypsin?

A

Via enterokinase.

Gastrointestinal (10 decks)

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