GIT physiology 4

Question 1

What 5 factors increase the rare of GIT absobtion

Answer 1

1. Reducing nutriance size
2. Motility
3. Large surface area
4. Transport across epithelium
5. Removal from the intersital space

Question 2

Why is motility important for absorption

Answer 2

To ensure the correct rate of travel through the GIT
Segementation - bring chyme in contact with enzymes + absorpitive surfaces
Relaxation - enables storage during absorption
Peristalsis - enables movement when absoption complete

Question 3

What two factors are required when crossing the epithelium for absoption

Answer 3

1. Driving force -
   - chemical/electrical/ electrochemical gradient
   - osmotic gradient
   - active transport ( atp burnt )
2. method of transport -
   paracellular pathway through tight junctions (leaky in SI, tight in LI)
   Transcellular pathway through 2 membranes ( lipid solubles diffuse, water solubles require channesl or transporters )

Question 4

Why is it important to move products out from the interstital space

Answer 4

Maintains a high conc dradient within the cell to drive products towards intersitial space
Drained via:
Fats - lymphatic lacteal
Water solubles - Blood via capillarys

Question 5

What can undergo passive paracellular transport

Answer 5

Cannot occur in the large instestine
Monosaccharides
aminoacids
Na+
H2O - 90% within SI driven by osmotic gradient

Question 6

What is the function of Na+/K+ ATPase

Answer 6

Located basolaterally

Pumps Na+out from cell and K+ into the cell
Keeps the conc of Na+ inside cell very low to enable am electrochemical gradient from lumin to cellular side

Question 7

What is the method of absorption for Di/Tri peptides

Answer 7

Na/KATPase - used to create negative intracellular environment
H+/peptide co transport - moves down electric gradient into the cell -> peptidases break to AA

AA leave via AA channels

Question 8

What travels transcellular via Na+/x co transporter + basal x transporter

Answer 8

Monosacharides
amino acids
Water soluble vitamins

Question 9

How does B12 get absorped

Answer 9

It is bound to intrinsic factor which is detected by cell surface receptors within the ileum where it is endocytosed
Then attached to transcobalamin before blood transport

Question 10

How do lipids get absoped

Answer 10

micelles close to membrane -> passive diffusion FFA + MAGs -> move to ER, synthesised back to TAGs + packed into chylomicrons -> exocytosed into blood

Question 11

How are fat soluble vitamins and water trancellularly absobed

Answer 11

Water via aquaporins -> driven by osmotic gradient - SI (9%)
LI - amount dependant on body requirements

Fat vitamins (ADEK) -> dissolved in micelles with MAGs+FFA