MEMBRANE TRANSPORT

· Plasma membrane

· Passive transport - no energy (ATP) is needed

· Simple diffusion

Osmosis- movement of water, flowing from

region of high water concentration to an

area of lower water concentration.

Facilitated diffusion- requires carrier proteins

transport of glucose and amino acids

· Active transport- ATP needed

Sodium/potassium pump

· Tonicity

Isotonic

Hypotonic

Hypertonic

· Osmotic pressure

· Exerted to oppose the movement of H2O (osmosis).

· Molecules that are osmotically active

plasma proteins such as albumin.

cannot readily diffuse across cell membrane

help regulate the flow of water between the

tissues and the blood

· Pure water has an osmotic pressure of zero.

· The greater the solute concentration, the greater the osmotic pressure.

example:

120 g/L glucose solution has twice the osmotic pressure of a 60 g/L glucose solution.

· Osmoreceptors, neurons that monitor the osmolality of blood plasma, are located in the

Hypothalamus

· Cell signaling—cell-to-cell communication by signaling each other chemically.

· Three categories of chemical regulatory molecules released by neurons and endocrine glands, and by different cells within an organ

1. Paracrine signaling—release of regulatory molecules that act within the organ in which they are made, e.g. gastrin

2. Synaptic signaling – release of neurotransmitter by axon endings

3. Endocrine signaling—release of hormones, transported via blood to their target tissues