Case 3 - The pancreas

Question 1

Where are proteins digested and what are they digested to?

Answer 1

stomach, pancreas, brush border,

amino acids, dipeptides and tripeptides

Question 2

Where are polysaccharides digested and what are they digested to?

Answer 2

saliva, pancreas, brush border

monosaccharides

Question 3

Where are triglycerides digested and what are they digested to?

Answer 3

free fatty acids and monoglycerides

stomach, pancreas, bile salts

Question 4

What are the different methods of absorption across the SI

Answer 4

simple diffusion - lipids

carrier mediated - amino acids and sugars e.g. facilitated diffusion and secondary active transport

receptor mediated - B12 and intrinsic factor, cholesterol e.g. endocytosis

Question 5

What is the main site of absorption

Answer 5

small intestine - duodenum and jejunum

Question 6

What is absorbed in the ileum?

Answer 6

vitamin B12, bile salts and potassium

Question 7

What causes the surface area of the SI to decrease and what are the consequences?

Answer 7

Crohns or coeliac disease

Leads to malabsorption

Question 8

What mechanism is used for carbohydrate absorption

Answer 8

carrier mediated - secondary active transport

Question 9

Describe the process of carbohydrate absorption from the lumen into isf

Answer 9

absorbed as monosaccharides, glucose/fructose via a sodium coupled transporter

SGLT1
glucose and sodium bind to the carrier, sodium binds first x2 and opens the binding site for glucose, transport channel undergoes a conformational change and empties the glucose into the cell.

accumulation of glucose moves glucose out of the cell via GLUT2 carrier facilitated diffusion

Question 10

What is the function of an SGLT1 transporter

Answer 10

sodium and glucose transporter

Question 11

How are peptides absorbed?

Answer 11

Absorbed via pep T1 co transporter with Hydrogen ions, the peptides are hydrolysed to amino acids in the enterocytes

Question 12

How is alanine absorbed

Answer 12

Via Bo contrasporter sodium

Question 13

How is glutamate absorbed?

Answer 13

Via Xag: a co-transporter of alanine, sodium x2 and others e.g. glutamate.

Question 14

What is Hartnup disease

Answer 14

rare genetic disease,c causes appearance of amino acids in urine

Question 15

Why is fat digestion dependent on bile salts?

Answer 15

Bile salt emulsify the fat droplets to increase surface area for digestion by lipase

formation of mixed micelles will stabilise the products of tg hydrolysis (mg +fa) while they are transported to apical membrane

absence of bile leads to steatorrhoea

Question 16

What is the function of pancreatic lipase?

Answer 16

Breaks down triacyglycerol into monoaglycerol and x2 free fatty acids

Question 17

How is fat absorbed

Answer 17

simple diffusion

FFA transporters

MA - carrier mediated mechanisms

Question 18

Describe the absorption and re-synthesis of triaglycerol

Answer 18

FFA and monoacyglycerol are absorbed in the same way via carrier mediated

triaglycerol is resynthesises in the SER and packaged in chylomicrons which then leave the cell by exocytosis into the lymphatics and travel to the liver

Question 19

How is cholesterol absorbed from the lumen to i.s.f. how can this be targeted pharmacologically

Answer 19

Occurs in the duodenum, receptor mediated endocytosis

ezetimibe inhibits endocytosis, decreasing plasma cholesterol

Question 20

How are short chain fatty acids absorbed?

give examples of SCFA

Answer 20

e.g. butyrate, propionate, acetate

absorbed via a SMCTI co transporter with sodium and is used by the colonocyte for intracellular metabolism

Question 21

What are the route for water absorption

Answer 21

via functional complexes between cells

via