Unit 1 - 3.2 Epithelial Transport, Osmolarity, & Tonicity Flashcards

Flashcards covering key concepts from the lecture on epithelial transport, osmolarity, and tonicity, including definitions, mechanisms, and cellular fluid movement scenarios.

What are the two main surfaces of an epithelial lining crucial for transport?

The apical membrane (facing the lumen of an organ) and the basolateral membrane (facing the extracellular fluid).

What is the general process of epithelial transport?

Moving substances across a layer of epithelial cells, specifically involving movement across both the apical and basolateral membranes.

What is 'absorption' in the context of epithelial transport?

The transport of substances from the lumen of an organ to the extracellular fluid (ECF).

What is 'secretion' in the context of epithelial transport?

The transport of substances from the extracellular fluid (ECF) to the lumen of an organ.

What are the two main types of epithelial transport?

Paracellular transport and transcellular transport.

Describe paracellular transport.

It involves the movement of substances through the junctions between adjacent epithelial cells.

Describe transcellular transport.

It involves the movement of substances through both the apical and basolateral membranes, either with the help of carrier proteins or by transcytosis.

What is transcytosis?

A combination of endocytosis, vesicular transport across the cytoplasmic space, and exocytosis that allows the transport of macromolecules across a cell while remaining intact.

What unit is typically preferred to express the concentration of uncharged substances such as glucose or urea?

Molarity.

How is 'one mole' of a solute defined?

The atomic or molecular weight of the solute in grams.

How does an osmole relate to a mole of solute?

A mole of solute that dissociates into 'n' discrete particles in a solution is equal to 'n osmoles' of solute.

What is the difference between osmolarity and osmolality?

Osmolarity describes the number of particles in a given volume of solution (which is temperature dependent), while osmolality describes the number of particles per kilogram of H2O (preferred for body fluid regulation as it's temperature independent).

What is an isotonic solution in relation to cellular fluid movement?

A solution with the same osmolality as the extracellular fluid (e.g., 0.9% NaCl), causing no net movement of water into or out of cells, and thus no change in cell volume.

What happens to red blood cells when placed in a hypotonic solution?

They swell as there is a net movement of water from the extracellular fluid into the cells.

What happens to red blood cells when placed in a hypertonic solution?

They shrink as there is a net movement of water from the intracellular fluid into the extracellular fluid.

What is oncotic pressure?

The osmotic pressure generated by proteins in blood plasma, which helps to retain fluid in the vascular compartment and prevent tissue edema.

How is tonicity defined?

A solution's ability to change the volume of cells by altering their water content, considering both its osmolality and the solute's ability to cross the cell membrane.

Why is it incorrect to equate osmolality to tonicity in a given solution?

Because tonicity also considers the ability of the solute to cross the cell membrane, which directly affects cell volume changes, unlike osmolality which only accounts for the number of particles.

Explain why a 300 mOsm/kg H2O urea solution is hypotonic for red blood cells, even though it's iso-osmotic to the cell.

The RBC membrane is permeable to urea, allowing urea to rapidly enter the cell. This increases the intracellular solute concentration, which then draws water into the cell, causing it to swell and burst (acting as a hypotonic solution).