The intestines

Question 1

What forms the intestines?

Answer 1

• duodenum
• jejunum
• ileum

The site of digestion and absorption

Question 2

Where is the jejunum located?

Answer 2

the upper left quadrant

-has a thick intestinal wall

Question 3

Where is the ileum found?

Answer 3

lower right quadrant

-has a thin intestinal wall

Question 4

What is the blood supply of the intestines?

Answer 4

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

Question 5

What are the other branches of the SMA?

Answer 5

• 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)

Question 6

What is found in the SI to help absorption?

Answer 6

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

Question 7

What epithelial is found in the intestines?

Answer 7

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

Question 8

What cells are in the intestinal glands?

Answer 8

• 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

Question 9

How often is the intestinal mucosa shed?

Answer 9

every 3-6 days - constantly

Question 10

What are carbohydrates?

Answer 10

• chains of sugars

- poly,di or mono

Question 11

Which carbohydrates can be absorbed?

Answer 11

only monosccharides

Question 12

NOTE

Answer 12

• 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

Question 13

What types of monosaccharides are there?

Answer 13

glucose
galactose
fructose

Question 14

What is starch?

Answer 14

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

Question 15

What breaks the alpha 1-4 bonds?

Answer 15

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

Question 16

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

Answer 16

get shorter but still branched chains of glucose called alpha dextrins

Question 17

How can you break alpha 1-6 bonds?

Answer 17

using the enzyme isomaltase

Question 18

What are brush border enzymes?

Answer 18

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

Question 19

What monosaccharides make up lactose?

Answer 19

glucose and galactose

-lactase breaks it down

Question 20

What monosaccharides make up sucrose?

Answer 20

glucose and fructose

-sucrase

Question 21

How is glucose taken up by enterocytes?

Answer 21

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

Question 22

How does glucose get into the blood?

Answer 22

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

Question 23

How is protein digested?

Answer 23

multi-step process

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

Question 24

How does protein digestion occur in the stomach?

Answer 24

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

Question 25

How does the SI digest protein?

Answer 25

pancreas release proteases as zymogens e.g. trypsinogen | -enterokinase (brush border enzyme) converts trypsinogen to trypsin which activates other proteases

Question 26

What do endopeptidases do?

Answer 26

break bonds in the middle of the polypeptide to produce short polypeptides - trypsin - chymotrypsin - elastase

Question 27

What do exopeptidases do?

Answer 27

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

Question 28

How are AA transported into enterocytes?

Answer 28

co-tranported with sodium into the enterocyte

Question 29

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

Answer 29

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

Question 30

What happens to the proteins inside the enterocytes?

Answer 30

converted into AA by cytosolic peptidases

Question 31

How does water move into the cell?

Answer 31

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

Question 32

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

Answer 32

-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

Question 33

What is the principle of oral rehydration?

Answer 33

- 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

Question 34

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

Answer 34

- 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

Question 35

How does vitamin B 12 deficiency come about?

Answer 35

- 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

Question 36

What can vitamin B12 deficiency lead to?

Answer 36

megaloblastic anaemia and neurological symptoms

Question 37

What is lactose intolerance?

Answer 37

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

Question 38

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

Answer 38

-lactose is fermented in the gut producing gas

Question 39

IBS

Answer 39

talked about in later lecture

Question 40

What is coeliac disease?

Answer 40

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

Question 41

Where is gluten found?

Answer 41

wheat, rye, barely

Question 42

What occurs in coeliac disease?

Answer 42

damages mucosa of intestines - absence of intestinal villi - hypertrophy/lengthening of intestinal crypts - lymphocytes infiltrate epithelium and lamina propria - imparied digestion/malabsorption

Question 43

What are the symptoms of coeliac disease?

Answer 43

- diarrhoea - weight loss - flatulence - abdominal pain - anaemia (imparied iron absorption) - neurological symptoms (hypocalcaemia)

Question 44

What investigations would you do to diagnose coeliac disease?

Answer 44

- blood test looking at IgA and tissue transglutaminase | - upper GI endoscopy and biopsies to look for mucosal pathology and to see health of villi

Question 45

What is the treatment of coeliac disease?

Answer 45

- strict gluten free diet | - will see clinical improvement quickly and histological improvement in a few weeks/months