The Intestines

Question 1

What are the characteristics of chyme when in the intestines?

Answer 1

Isotonic

Neutral

Digestion nearly complete

Question 2

What is the role of the intestines?

Answer 2

Absorb nutrients

Absorb water/electrolytes

Question 3

How does the characteristics of the gut allow for maximal absorption?

Answer 3

Surface area = villi/microvilli

Slow movement = maximal time against surface area

Question 4

What are plicae circulares?

Answer 4

Permanent crescentic folds of mucous membrane in the SI especially in the lower part of the duodenum and the jejunum

Increase the surface area available for absorption

Question 5

What cell types are present in the intestines

Answer 5

Ep = enterocytes

Crypts (glands) = stem cells at base maturing as they migrate to surface, enteroendocrine glands, paneth cells

Question 6

Briefly outline carb digestion

Answer 6

Only monosaccharides can be absorbed

Glucose can only enter with Na

Final enzyme digestion takes place in brush border

Question 7

Name the common dietary carbs

Answer 7

Starch

Lactose

Sucrose

Question 8

Describe the digestion of starch

Answer 8

Amylase = break alpha 1-4 bonds

End up with = glucose, maltose, alpha dextrins

Question 9

How do monosaccharides get absorbed?

Answer 9

Na/K ATPase on basolateral mem = maintains low intracellular Na

Na binds SGLT-1 = allows gluose binding = Na/glucose moves into cell

GLUT2 = transports glucose out of enterocyte down gradient into capillary

Question 10

What is the principle of oral rehydration

Answer 10

Uptake of Na generates osmotic gradient = water follows

Glucose uptake stim Na uptake = stim max water uptake

Question 11

In what structure can proteins be absorbed?

Answer 11

AA

Dipeptides

Tripeptides

Question 12

How are proteins digested?

Answer 12

Chief cells = pepsinogen = pepsin via HCL = acts on proteins = oligopeptides/AA

Question 13

What is trypsinogen?

Answer 13

Zymogen

Converted to trypsin by enteropeptidase

Trypsin = activates other proteases

Question 14

Name the major proteases

Answer 14

Endopeptidases = trypsin, chymotrypsin, elastase

Exopeptidases = carboxypeptidase

Question 15

How are AA transported into cells?

Answer 15

Na/AA co-transporters

Question 16

How are di/tripeptides absorbed?

Answer 16

H co-transporter

Peptide transporter 1 (pepT1)

Inside cell these are converted to AA

Question 17

How does Na move on the apical membrane in the SI vs the large?

Answer 17

SI = Na co-transported

Large = Na channels

Question 18

Outline the uptake of Ca

Answer 18

When low = active transcellular, requires vit D

When normal/high = passive paracellular

Question 19

Outline the uptake of iron

Answer 19

When low = binds transferrin (transported to stores)

When high = contained in ferritin complexes (trapped in enterocytes)

Question 20

How are water soluble vits absorbed?

Answer 20

Cotransport with Na

Vit B12 absorbed in terminal ileum bound to intrinsic factor

Question 21

What cells secrete intrinsic factor?

Answer 21

Gastric parietal cells

Question 22

What is coeliac disease?

Answer 22

Intolerance of gliadin fraction of gluten

Results in immune response =absence of intestinal villi, lengthening crypts, lymphocytes infiltrate ep = impaired digestion/malabsorption

Question 23

What investigations can be used to identify coeliac disease?

Answer 23

Upper Gi endoscopy + biopsies

Bloods = serology, electrolyte imbalances, anaemia

Question 24

What significant artery can be injured if a duodenal ulcer perforates?

Answer 24

gastro-duodenal artery