Membrane Physiology I- Chapters 3 & 5

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1

Membrane

Two Meanings

1. Membranous (Protective) Tissue- Surrounds structure, pericardial membrane that covers heart, or epithelial tissue that separate areas
2. Boundary Layer- Cell membrane (plasmalemma) encloses cells. Phospholipid bilayer

2

History of the Phospholipid layer

1935- Davidson and Danielli: sandwich model
protein-lipid-lipid-protein

1971- Singer and Nicolson: Fluid mosaic model
Proteins are irregularly laid
Modifications: Non-motile proteins, Glycoproteins present

3

Cell Membrane Components

1. Cholesterol- anchor, stability, rigidity
2. Phospholipids- bilayer
3. Carbohydrates- surface, recognition, protection
4. Proteins- reception, chanels

4

Cell Membrane Functions

1. Barrier isolates cell (impermeable) chemically, physically
2. Regulates exchange
3. Cell communications
4. Cell structure and Support

5

Types of Proteins in a membrane

1. Peripheral- loose attachment, enzymes
2. Integral- Trans-membrane
3. Lipid anchored- covalently bound outside of main layer

6

Diffusion

Movement across a membrane

uses kinetic energy and does NOT require and outside energy source

Molecules diffuse from an area of higher concentration to an area of lower concentration

Continues until equilibrium

7

Permeant and Impermeant

Permeant- passes a membrane

Impermeant- Cannot pass through a membrane

8

Molecule Diffusion

random dispersion of molecules toward an equal concentration

It's passive
ATP is NOT required
Moves from high concentration to low concentration

It is a net movement until equilibrium
rapid over short distances
Directly related to temperature
Inverse related

9

When is diffusion faster?

1. Along higher concentration gradients
2. Over shorter distances
3. At higher temperatures
4. For smaller molecules

10

When is the rate of diffusion through a membrane faster?

When...

1. the membrane's surface area is larger
2. the membrane is thinner
3. the concentration gradient is larger
4. the membrane is more permeable to the molecule

11

Membrane permeability to a molecule depends on...

1. the molecule's lipid solubility
2. the molecule's size
3. the lipid composition of the membrane

12

Fick's Law of Diffusion

States characteristics of diffusion

13

Osmosis

Diffusional movement of water across a membrane

Is when water moves across a membrane down its concentration gradient
higher water to lower water
moves to equilibrium
osmotic pressure is created

Salts concentration are inverse of water concentration,and do not cross a membrane.

14

Osmotic pressure

force that counteracts pressure that water movement creates
a force needed to stop water movement

created by osmosis

15

Molarity

Mole dissolved per liter (to make 1 liter) with water

(M)

16

Osmolarity

Total number of particles
accounts dissociation

17

Equation for Osmolarity

Molarity X number of particles dissociating

EX: 1.0 M glucose= 1.0 X 1= 1 Osmolar solution (1Osm)

18

Equation for molarity

Osmolarity - total number of particles

19

Osmolarities of Solutions

1. isosmotic---A=B, both have the same number of paricles
2. Hyperosmotic---A>B, "A is hyperosmotic to B"
3. Hypoosmotic---B>A, "B is hypoosmotic to A"

20

Tonicity of Solutions

Volume impact at equilibrium when solution contacts cell

"Effective" strength of solution compared to cell

Depends on the nature of solutes, permeant to membrane or not

Types:
1. Isotonic
2. Hypotonic
3. Hypertonic

21

Isotonic

Example:

Red blood cells; if they are dipped into a solution of 0.9% NaCl, there is NO CHANGE in size
Because the solution is isotonic (no Hemoglobin in the solution)

22

Hypotonic

Example:

Red blood cells; if dipped into distilled water, it will SWELL up until it breaks apart
water is hypotonic to red blood cells

23

Hypertonic

Example:

Red blood cells; if dipped in salty ocean water (3% NaCl), the cell will SHRINK because the salt water is drying out the cell
Salt water is hypertonic

Causes CRENATION (shrinking of the cell)

24

Rules for Osmolarity and Tonicity

1. Assume that all intracellular solutes are non-penetrating
not a perfect rule
2. Compare osmolarities before the cell is exposed to the solution (cell and solution are isosmotic at equilibrium)
after equilibrium
3. Determine tonicity by comparing non-penetrating solute concentrations in the cell and the solution.
Who has more non-penetrating's (NP)
4. Hyposomtic solutions are always hypotonic

25

Physiological Saline

FOR HUMANS

0.9% Saline (normal saline)
Osmolarity= isosmotic
Tonicity= Isotonic
Used when someone is suffering from HYPOtension

26

What moves across membranes?

Dextrose (glucose) in some cells
Urea

27

What doesn't move across membranes?

Na+Cl-
LARGE molecules
EX: Dextrans and large carbohydrates

28

Transport Processes

Membrane Transport
Permeable vs. Impermeable
passive Transport vs. active transport
May use concentration gradients