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.