Membrane Transport 2

Question 1

What is transepithelial (vectorial) transport?

Answer 1

Transepithelial transport refers to the movement of solutes across epithelial cells in a unidirectional manner, maintaining a polarized distribution of transport proteins.

Question 2

What are the two main types of epithelial function in membrane transport?

Answer 2

1. Absorptive epithelia – active Na⁺ transport drives solute and water reabsorption.
2. Secretory epithelia – active Cl⁻ transport drives fluid secretion.

Question 3

What are the apical and basolateral membranes?

Answer 3

• Apical membrane: Faces the lumen (also called mucosal or luminal membrane).
• Basolateral membrane: Faces the extracellular fluid (also called serosal or contraluminal membrane).

Question 4

How do tight junctions contribute to epithelial transport?

Answer 4

Tight junctions regulate paracellular transport by controlling the passage of ions and molecules between epithelial cells. They can be leaky (allow bulk movement) or tight (restrict movement and maintain gradients).

Question 5

What is the role of the Na⁺/K⁺-ATPase in absorptive epithelia?

Answer 5

It actively pumps Na⁺ out of the epithelial cell into the extracellular fluid, maintaining a low intracellular Na⁺ concentration. This drives secondary active transport of other solutes across the apical membrane.

Question 6

Transepithelial transport is unidirectional and relies on

Answer 6

membrane polarity.

Question 7

Absorptive epithelia use Na⁺ gradients to

Answer 7

drive solute uptake.

Question 8

Secretory epithelia actively transport Cl⁻ into the lumen, creating

Answer 8

osmotic gradients for water movement.

Question 9

Leaky tight junctions allow bulk

Answer 9

solute and water movement (e.g., small intestine, kidney proximal tubule).

Question 10

Tight tight junctions prevent

Answer 10

paracellular movement (e.g., kidney distal tubule, colon).

Question 11

Vesicular transport includes

Answer 11

endocytosis (into the cell) and exocytosis (out of the cell).

Question 12

Channelopathies are diseases caused by dysfunctional

Answer 12

ion channels (e.g., LQTS, cystic fibrosis).

Question 13

The apical membrane always faces the bloodstream.

Answer 13

False (It faces the lumen; the basolateral membrane faces the bloodstream.)

Question 14

Leaky tight junctions allow bulk transport of solutes and water.

Answer 14

True

Question 15

The Na⁺/K⁺-ATPase pumps Na⁺ into the cell.

Answer 15

False (It pumps Na⁺ out and K⁺ in.)

Question 16

Secretory epithelia transport Cl⁻ actively into the lumen.

Answer 16

True

Question 17

Receptor-mediated endocytosis is a selective process.

Answer 17

True

Question 18

______ transport moves solutes in one direction across an epithelium.

Answer 18

Transepithelial (Vectorial)

Question 19

The ______ membrane faces the extracellular fluid, while the ______ membrane faces the lumen.

Answer 19

Basolateral, Apical

Question 20

______ epithelia use active Na⁺ transport to drive solute reabsorption.

Answer 20

Absorptive

Question 21

Secretory epithelia transport ______ into the lumen, creating an osmotic gradient.

Answer 21

Cl⁻ (Chloride)

Question 22

______ tight junctions allow paracellular movement of ions and water, whereas ______ tight junctions restrict movement.

Answer 22

Leaky, Tight

Question 23

What is the main difference between absorptive and secretory epithelia?
A) Absorptive epithelia actively transport Na⁺ into the lumen.
B) Secretory epithelia use Na⁺ gradients for solute absorption.
C) Absorptive epithelia use Na⁺ transport to drive reabsorption, while secretory epithelia use Cl⁻ transport for secretion.
D) Both absorptive and secretory epithelia transport Cl⁻ actively.

Answer 23

C) Absorptive epithelia use Na⁺ transport to drive reabsorption, while secretory epithelia use Cl⁻ transport for secretion.

Question 24

Which of the following is NOT a function of tight junctions?
A) Regulating paracellular transport
B) Holding epithelial cells together
C) Allowing free movement of all molecules between cells
D) Controlling ion and water passage

Answer 24

C) Allowing free movement of all molecules between cells

Question 25

Which transport process requires ATP? A) Simple diffusion B) Facilitated diffusion C) Vesicular transport D) Osmosis

Answer 25

C) Vesicular transport

Question 26

In receptor-mediated endocytosis, which of the following plays a key role in vesicle formation? A) Actin filaments B) Clathrin-coated pits C) Aquaporins D) Na⁺/K⁺-ATPase

Answer 26

B) Clathrin-coated pits

Question 27

Scenario 1: A patient has a genetic mutation in their CFTR gene. How would this affect membrane transport in their epithelial cells?

Answer 27

Answer: CFTR is a Cl⁻ transporter involved in secretory epithelia. A mutation leads to defective Cl⁻ transport, reducing water secretion and causing thick mucus buildup, characteristic of cystic fibrosis.

Question 28

Scenario 2: A researcher adds ouabain, a Na⁺/K⁺-ATPase inhibitor, to kidney epithelial cells. What would happen to Na⁺ and glucose transport?

Answer 28

Answer: Inhibition of Na⁺/K⁺-ATPase would prevent Na⁺ from being pumped out of the cell, disrupting the Na⁺ gradient needed for Na⁺-dependent glucose symport, reducing glucose absorption.

Question 29

Scenario 3: A genetic disorder affects amino acid transporters in the kidney and intestine, leading to increased amino acid excretion in urine. What disease is this, and what symptoms may occur?

Answer 29

Answer: Hartnup disorder, caused by mutations in the SLC6A19 gene encoding a sodium-dependent amino acid transporter. Symptoms include aminoaciduria, light-sensitive skin rash, and ataxia.

Question 30

Transepithelial transport:

Answer 30

Movement of molecules in one direction across an epithelium.

Question 31

Apical membrane:

Answer 31

The membrane facing the lumen.

Question 32

Basolateral membrane:

Answer 32

The membrane facing the extracellular fluid.

Question 33

Tight junctions:

Answer 33

Cell junctions that regulate paracellular movement.

Question 34

Na⁺/K⁺-ATPase:

Answer 34

A pump that maintains low intracellular Na⁺ levels.

Question 35

CFTR:

Answer 35

A chloride transporter involved in fluid secretion.

Question 36

Receptor-mediated endocytosis:

Answer 36

Selective uptake of extracellular molecules via vesicles.

Question 37

Hartnup disorder:

Answer 37

A genetic disorder affecting neutral amino acid transport.