Intestinal Physiology & digestion

Question 1

how much water is secreted endogenously?

Answer 1

7000ml

Question 2

why is most of the water absorbed in the small intestine?

Answer 2

because ions are absorbed and H2O follows down a concentration gradient

Question 3

what molecules are absorbed in the duodenum?

Answer 3

glucose
fat & fat soluble vitamins 
calcium 
magnesium 
iron

Question 4

what molecules are absorbed in the jejunum?

Answer 4

fat & fat soluble vitamins
sucrose
lactose
glucose
proteins 
amino acids

Question 5

what is absorbed in the ileum?

Answer 5

proteins
amino acids
water soluble vitamins
Vit B12 = terminal ileum with intrinsic factor

Question 6

what is absorbed in the colon?

Answer 6

water
potassium
NaCl
fatty acids from fiber digestion

Question 7

what are the 2 methods of water absorption?

Answer 7

1. paracellulary - water and ions pass between tight junctions of cells
2. transcellularly - through the cells due to osmotic pressure generated from pumping stuff into cells.

Question 8

where are the three places carbohydrates are digested and by what?

Answer 8

1. in the mouth by alpha amylase
2. in the duodenal lumen by alpha pancreatic amylase breaks 1-4 links and not 1-6 links
3. brush border enzymes that break off single monosaccharides

Question 9

how are glucose, glactose and fructose absorbed?

Answer 9

glucose is absorbed with Na+ using a symporter.
galactose uses the same method and symporter as glucose
fructose is absorbed by facilitated diffusion

Question 10

how are proteins digested?

Answer 10

• pepsin breaks proteins in to shorter chains
• pancreatic proteases (trypsin, chymotrypsin and elastase) break down protein chains further
• terminal bonds are broken by brush border proteases giving rise to some amino acids and some di & tri peptides

Question 11

how are amino acids absorbed?

Answer 11

with Na+ via a symporter

Question 12

how are di & tri peptides are absorbed?

Answer 12

facilitated diffusion

Question 13

what is the process of lipid digestion?

Answer 13

• bile salts emulsify lipid globules to emulsion droplets (increasing SA)
• co-lipases bind to the surface of droplets and lipase binds to colipase and breaks the triglycerides into monoglycerides + FFA
• monoglycerides + FFA + cholesterol + phospholipids + bile salts + any lipid soluble vitamins = micelles which aid transport to the brush border and then it’s contents diffuse freely into the cell
• FFAs and monoglycerides are quickly converted back into triglycerides in the cell to maintain a concentration gradient
• triglycerides + cholesterol + apolipoproteins are packaged into special vesicles called chylomicrons
• chylomicrons enter the lacteal and are transported through the lymphatics and enter the blood through the thoracic duct