Physiology - Membranes

Origin

Single cell’s connect to pairs, then, rings - inside of the ring is an inside of the body.

Ocean rich in Na+ = Na+ rich extracellular fluid.

Osmotic pressure

Pressure of liquid at different concentration measured as tonicity.

Tonicity

Ability of the solution to move water in or out of the cell.

Hypotonic

Less electrolytes, water in

Hypertonic

More electrolytes, water out

Electrochemical gradient

Generated by extra & intra cellular fluids by +/- charges that store energy.

Ion movement

Ions follow chemical gradient creating @@charge imbalance@@ and @@negative membrane@@ from inside.

Electrical force oppose chemical one = no ion movement = equilibrium.

Membrane permeability determined by:

• Amout of channels / transporters
• Open / closed channels and transporters
• Amout allowed to enter

Facilitated diffusion

Substrate supported by membrane proteins when those can’t cross on their own.

Energy from concentration gradient.

Active transport Na/K pump

1. 3 Na+ ions from cytosol bind to the pump on the membrane
2. ATP binds
3. ATP split to ADP + phosphate. Energy force shape change of protein, moving Na+ out
4. 2 K+ ions bind to the pump from outside, cause phosphate release
5. No phosphate = pump return to original shape, squeezing K+ in

Antiporters

In opposite direction

Symporters

In the same direction

Opening & closing channels

• trigger: ligands, voltage, physical association
• constitutively active: random

Hydration shell

Surround ions, made of water. Scraped down in selectivity filter in the channel.