L1-2 Membrane Transport

Question 1

How does negative feedback control homeostasis?

Answer 1

1. Sensor: Monitors magnitude of a control variable
2. Itegrator: Compares sensor’s input with a set point
3. Effector: makes response to bring controlled variable back to set point

Question 2

How is positive feedback and what are some examples?

Answer 2

Positive feedback Drives physiological values away from set point; destabilizing

Examples: uterine contractions and opening of Na channels during membrane depolarization

Question 3

What does Extracellular fluid (ECF) consist of?

Answer 3

Plasma, interstitial fluid

Question 4

What is osmosis?

Answer 4

net diffusion or movement of water down its concentration gradient (moves to area of higher solute concentration)

Question 5

What is Fick’s Law?

Answer 5

Molecules diffuse across membranes to maintain equal concentrations on both sides.

Question 6

What is effective osmotic pressure?

What is hydrostatic pressure?

Answer 6

The amount of pressure needed to stop the flow of water down its concentration gradient. Osmotic pressure is directly proportional to the concentration of solutes in solution.

Hydrostatic pressure is the force exerted by a fluid in a column due to gravity. Plasma membranes deform easily so hydrostatic pressure difference in cells is usually 0.

Question 7

What is osmolarity?

Answer 7

Osmolarity/Osmolality is the total concentration of particles
(permeant and impermeant) per amount of solution.

Osmolarity = (# particles/moles in solution) X (solute
concentration)

ICF and ECF osmolarity = 290mOsm

Question 8

Define:

Isoosmolar

Hypoosmolar

Hyperosmolar

Answer 8

Isoosmolar = ECF osmolarity equals ICF osmolarity

Hypoosmolar = Having a lower osmolarity
than normal extracellular fluid

Hyperosmolar = having a greater
osmolarity than normal extracellular fluid

Question 9

What is Effective Osmolality?

What is tonicity?

Answer 9

Refers to those particles that will exert an actual osmotic
effect (water movement) on a cell:

Non-permeable particles only

Tonicity refers to the effect a solution has on cell volume due to non-permeable solutes.

Question 10

What’s a hypotonic solution? Hypertonic?

Answer 10

A hypotonic solution has lower concentration of non-penetrating solutes than normal body cells, causing cell to swell from osmosis.

A hypertonic solution has more non-penetrating solutes than normal body cells, causing cells to shrink by osmosis.