L3 Absorption Across The Epithelium

Question 1

Substances must be transported all the way through whole cellular sheet rather than simple through cell membrane
What is this?

Answer 1

Victorian transport

Question 2

What are the sites of victorian transport

Answer 2

Exists through
Intestinal epithelium 
Epithelium of renal tubules
Epithelium of all exocrine glands
Epithelium of gall bladder
Membrane of choriod plexus of brain
The placenta and other membranes

Question 3

What is the basic mechanism for victorian transport

Answer 3

Active transport through cell membrane on one side of transporting cells
Then
Simple or facilitated diffusion through membrane on opposite side of cell

Question 4

How is the unidirectional transport of substances achieved

Answer 4

By presence of non uniform distribution of transporters present on opposing face of cell
SLC influx
ABC efflux

Question 5

What are the factors affecting absorption across epithelium (physiological)

Answer 5

Temperature
Surface area
Diffusion distance

Question 6

What are the factors affecting absorption across epithelium (pharmacological)

Answer 6

▪️Stomach acidity: acid labile drugs and can impair their intestinal absorption so must be given as enteric coated tablets for proper absorption
▪️GIT motility changes:
Delay in gastric emptying time(such as during food intake) will dec rate of intestinal absorption so some drugs are take on an empty stomach
An inc in intestinal motility (diarrhea)can decrease contact time needed for proper absorption of some drugs thus dec their absorption
▪️Presence of efflux transporters: as p glycoprotein extrude back some drugs such as losartan to intestinal lumen to decrease its absorption
▪️Use of inhibitors of P-Gp as verapamil will prevent its back efflux to enhance more its absorption
▪️Presence of variable food or other drugs such as caffeine and vit c can accelerate absorption of acetaminophen and iron

Question 7

How does the substance itself affect rate of absorption

Answer 7

Size and mol weight
If substance is a drug can either be ionized or non ionized=
Weak acids are more absorbed with low ph and accumulate in high ph such as acetyl salicylic acid
Weak bases are more absorbed with high ph and accumulate in low ph such as atropine

Question 8

How can cholesterol be lowered using drugs

Answer 8

Ezetimibe to inhibit selective cholesterol transporter: Neiman peck transporter in enterocyte

Question 9

How are drugs used in treatment of diabetes and control of heart failure manifestations

Answer 9

Use of dapaglifozin to inhibit sodium glucose transporter 2 to block glucose reabsorption in to proximal convoluted tubule to the plasma to lower blood glucose level

Question 10

What are drugs that can cause effects when they interact together

Answer 10

Digoxin used to control advanced heart failure manifestations can have adverse effects with other drugs due to interaction occurring in link to ABC efflux transporters
Antibiotics:
such as erythromycin that inhibit P-Gp efflux transporters will:
Inc digoxin absorption in intestine
Suppress its elimination in urine

Toxicity:
Anti epileptics as carbamazepine activate the P- Gp efflux transports which will:
Suppress digoxin absorption from intestine
Enhance its elimination in urine