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GI > The intestines > Flashcards

The intestines Flashcards

1
Q

What forms the intestines?

A
  • duodenum
  • jejunum
  • ileum

The site of digestion and absorption

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2
Q

Where is the jejunum located?

A

the upper left quadrant

-has a thick intestinal wall

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3
Q

Where is the ileum found?

A

lower right quadrant

-has a thin intestinal wall

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4
Q

What is the blood supply of the intestines?

A

the SMA comes off the AA at L1 and gives off jejunal and ileal arteries (arcades)
-more arcades in the ileum thats the jejunum

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5
Q

What are the other branches of the SMA?

A
  • ileocolic artery (supplies to the lower right hand side (right iliac fossa/caecum)
  • right colic artery (area of ascending colon)
  • middle colic artery (transverse colon)

-also lots of anastomoses forming the marginal arteries (branches of the SMA)

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6
Q

What is found in the SI to help absorption?

A

-large SA - place circulares
(the mucosa is folded into villi with the surface covered in microvilli(brush border)
-slow movement of contents (precise controlled)

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7
Q

What epithelial is found in the intestines?

A
  • enterocytes (absorptive cells)
  • goblet cells (secrete mucus)
  • enteroendocrine cells (produce hormones)
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8
Q

What cells are in the intestinal glands?

A
  • AKA crypts of lieberkuhm
  • stem cells at the base which migrate to the surface as mature as they migrate
  • paneth cells at the base which produce antimicrobial peptides and act as innante mucosal defence cells
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9
Q

How often is the intestinal mucosa shed?

A

every 3-6 days - constantly

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10
Q

What are carbohydrates?

A
  • chains of sugars

- poly,di or mono

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11
Q

Which carbohydrates can be absorbed?

A

only monosccharides

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12
Q

NOTE

A
  • there are carbohydrates that we can’t break down (dietary fibre)
  • important as it binds bile salts which are mainly cholesterol so that is why fibre in diet helps to reduce cholesterol
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13
Q

What types of monosaccharides are there?

A

glucose
galactose
fructose

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14
Q

What is starch?

A

straight chains of glucose (amylose) - alpha 1-4 bonds and branched chains of glucose (amylopectin) - alpha 1-6 bonds

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15
Q

What breaks the alpha 1-4 bonds?

A

salivary and pancreatic amylase breaks the alpha 1-4 bonds in amylose (no effect on alpha 1-6 bonds)
-this produces maltose (glucose + glucose)

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16
Q

what is the end product called when amylase breaks the alpha 1-4 bond in amylopectin?

A

get shorter but still branched chains of glucose called alpha dextrins

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17
Q

How can you break alpha 1-6 bonds?

A

using the enzyme isomaltase

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18
Q

What are brush border enzymes?

A

maltase and isomaltase lactase and sucrase (secreted from the brush border)

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19
Q

What monosaccharides make up lactose?

A

glucose and galactose

-lactase breaks it down

20
Q

What monosaccharides make up sucrose?

A

glucose and fructose

-sucrase

21
Q

How is glucose taken up by enterocytes?

A

glucose is taken up via the SGLT 1 co transporter (with sodium) which only works because on the basolateral membrane there is a Na+/K+ ATPase which creates a low Na+ concentration inside the cell so Na+ will want to move in

22
Q

How does glucose get into the blood?

A

The GLUT 2 transported transports glucose out of the enterocyte and it diffuses down a gradient into the capillary blood

23
Q

How is protein digested?

A

multi-step process

1) stomach
2) intestinal lumen
3) b rush boreder
4) cytosolic peptidases

24
Q

How does protein digestion occur in the stomach?

A

chief cells secrete pepsinogen which is activated by acid (H+ ions)
-pepsin acts on proteins breaking them down into smaller chains (oligopeptides or even AA

25
Q

How does the SI digest protein?

A

pancreas release proteases as zymogens e.g. trypsinogen

-enterokinase (brush border enzyme) converts trypsinogen to trypsin which activates other proteases

26
Q

What do endopeptidases do?

A

break bonds in the middle of the polypeptide to produce short polypeptides

  • trypsin
  • chymotrypsin
  • elastase
27
Q

What do exopeptidases do?

A

break bonds at the ends of polypeptide to produce dipeptides or individual AA e.g. carboxypeptidase

28
Q

How are AA transported into enterocytes?

A

co-tranported with sodium into the enterocyte

29
Q

If AA can be transported with co-transport, what is the reason PepT 1 occurs?

A

PepT1 transporters allow short peptides that haven’t been digested down to AA to move into the enterocytes

30
Q

What happens to the proteins inside the enterocytes?

A

converted into AA by cytosolic peptidases

31
Q

How does water move into the cell?

A

absorption of water is driven by the movement of sodium into enterocytes and as sodium is a osmotically active ion, water will follow

32
Q

What is the difference of water uptake between SI and LI?

A

-btoh SI and LI have Na+/K+ ATPase on their basolateral membrane which creates a Na+ gradient allowing Na+ to move in (through the apical membrane)
in the SI - Na+ is co-transported in with glucose with SGLT1
in the LI - there are Na+ channels that are induced by aldosterone

33
Q

What is the principle of oral rehydration?

A
  • not point just giving water as will not be absorbed in the cell
  • need to have a mixture of glucose and salt which allows maximum water uptake
34
Q

How is water secreted from a cell into the gut? (especially in the duodenum)

A
  • driven by Cl- movement
  • chloride enters crypt epithelia cell (co transported with Na+ and K+)
  • Cyclic AMP increases inside cell
  • increasse cAMP activates CFTR so Cl- ions are secreted
  • Na+ is drawn into lumen across tight junctions
  • NaCl secretion creates osmotic gradient so water moves into lumen
35
Q

How does vitamin B 12 deficiency come about?

A
  • lack of intrinsic factor secreted by parietal cells in the stomach
  • less B12 is bound in the SI so less is tranported to the ileum so less is reabsorbed

-disorders in the ileum where absorption should occur could be a reason too e.g. Chron’s disease

36
Q

What can vitamin B12 deficiency lead to?

A

megaloblastic anaemia and neurological symptoms

37
Q

What is lactose intolerance?

A

cause by deficiency in the enzyme lactase
-when lactose is consume in quantity it can’t be absorbed so remains in the gut lumen creating a high osmotic effect - the water is not absorbed resulting in diarrhoea

38
Q

Why would a patient who is lactose intolerant present with a lot of bloating and flatuence?

A

-lactose is fermented in the gut producing gas

39
Q

IBS

A

talked about in later lecture

40
Q

What is coeliac disease?

A

it arises from an immunological response to the gliadin fraction of gluten

41
Q

Where is gluten found?

A

wheat, rye, barely

42
Q

What occurs in coeliac disease?

A

damages mucosa of intestines

  • absence of intestinal villi
  • hypertrophy/lengthening of intestinal crypts
  • lymphocytes infiltrate epithelium and lamina propria
  • imparied digestion/malabsorption
43
Q

What are the symptoms of coeliac disease?

A
  • diarrhoea
  • weight loss
  • flatulence
  • abdominal pain
  • anaemia (imparied iron absorption)
  • neurological symptoms (hypocalcaemia)
44
Q

What investigations would you do to diagnose coeliac disease?

A
  • blood test looking at IgA and tissue transglutaminase

- upper GI endoscopy and biopsies to look for mucosal pathology and to see health of villi

45
Q

What is the treatment of coeliac disease?

A
  • strict gluten free diet

- will see clinical improvement quickly and histological improvement in a few weeks/months

GI (10 decks)

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