Intracellular- within the cell

Extracellular- consists of blood plasma and interstitial fluid which is derived from and returns to plasma.

Passive transport- Net movement of molecules and ions across a membrane from higher to lower concentration (down concentration gradient); does not require metabolic energy.

Active transport- Net movement across a membrane that occurs against a concentration gradient (to region of higher concentration); requires expenditure of energy (ATP).

Osmosis can be prevented by and opposing force. ex. If 2 sacs composed of a semipermeable membrane (to water, not sucrose) were filled with one 180 g/L sucrose solution and the other with 360 g/L sucrose and suspended in beakers of pure water, but enclosed in a rigid box, each sac would expand until it presses against its box  with enough pressure to stop osmosis. The force required to stop osmosis (osmotic pressure) would be twice as great in the 360 g/L sucrose solution than the 180 g/L solution.

1)there must be a difference in the concentration of a solute on the two sides of a semipermeable membrane

2)the membrane must be relatively impermeable to the solute

This is when molecules that are too large to pass through by simple diffusion are transported across plasma membranes by carrier proteins. The characteristics are:

Specificity- only interacts with specific molecules

Competition- Carriers for some amino acids transport some a.as but not others. Two a.as that are transported by the same carrier compete with each other, lowering the rate of transport than if each were present alone.

Saturation- As the concentration of a transported molecule is increased, its rate of transport is increased, but only up to its transport maximum (Tm). If the concentration is greater than the transport maximum, it is saturated.

Simple diffusion- membrane transport not requiring carrier proteins and involves the diffusion of ions, lipid soluble (nonpolar) molecules and water; powered by thermal energy  and involves the net transport of molecules from the side of higher concentration to side of lower concentration.

Facilitated diffusion- like simple diffusion, in that it involves net transport from side of higher concentration to lower. However, it requires the properties of carrier mediated transport and carrier proteins for large molecules to enter the cell.

Facilitated diffusion- requires properties of carrier mediated transport and carrier proteins for large molecules to enter and leave the cell, however, it does not require an expenditure of energy (ATP) and molecules always move from area of higher concentration to lower.

Active transport- requires properties of carrier mediated transport and carrier proteins, however, it requires an expenditure of ATP because molecules always move against its concentration gradient (from lower to higher).

1)Steep gradient provides energy for "coupled transport" of other molecules

2)Gradients for Na+ and K+ concentrations across the plasma membranes of nerve and muscle cells are used to produce electrochemical impulses ex. heart muscle

3)Active extrusion of Na+ is important for osmotic reasons. If pumps stop, increased Na+ concentrations promote osmotic inflow of water, damaging cells.

1) Ca2+ within the cell binds to sites in the carrier protein

2) ATP is hydrolyzed into ADP and Phosphate (p1) and the phosphate is added to the carrier protein, causing a hinge-like motion of the carrier protein

3) Hinge-like motion of the carrier protein allows Ca2+ to be released into the extracellular fluid.  

1) 3 Na+ ions in the cytoplasm move partway into the pump and bind to 3 amino acid sites

2) This activates ATPase, hydrolyzing ATP into ADP and P1, blocking each exit

3) ADP is released producing shape change in carrier, opens passageway for the 3 Na+ ions to exit into the extracellular fluid

4) 2 K+ ions in extracellular fluid bind to the carrier, causing P1 to be released

5) Release of P1 allows pump to return to its intial state, permitting 2 K+ ions to move into the cytoplasm.

1) If a cell were at equilibrium (for K+) the rate of K+ entry (due to electrical attraction) would equal the rate of K+ exit (diffusion)

2) At this equilibrium there would still be a higher concentration of negative charges within the cell (because of fixed anions) than outside

3) At this equilibrium, the inside of the cell would be -90mV compared to the outside.

1) If a cell were at equilibrium (for Na+) the rate of Na+ entry (due to electrical attraction) would equal the rate of Na+ exiting (diffusion)

2) At this equilibrium, there would still be a lower concentration of positive charges within the cell (due to fixed cations) than outside, repelling Na+

3) At this equilibrium, the inside of the cell would be 66mV compared to the outside.

It is dependent on:

1) Its concentration gradient

2) Its membrane permeability

1) synaptic- release of neurotransmitter between synapse and target organ

2) endocrine- release of hormones into the extracellular fluid, entering the blood and goes to all cells in the body (only target cells can respond)

3) paracrine- release of regulatory molecules that diffuse through the extracellular matrix to nearby target cells (also known as target control)

Because they are isotonic to blood plasma.

Glucose, which is 5g/100ml = .3m

Normal saline, which is .9g of NaCl per 100 ml = .15m

The mechanism is negative feedback.

1) Increased plasma osmolality stimulates osmoreceptors in the hypothalamus

2) Osmoreceptors in hypothalamus then stimulate the tract of axons that terminate in the posterior pituitary, causing it to release antidiuretic hormone into the blood (AKA ADH or vasopressin)

3) ADH acts on the kidneys to promote water retention, so a lower volume of more concentrated urine is secreted

4) Then the dehydrated person drinks more and urinates less (negative feedback).

Primary active transport - when hydrolysis of ATP is directly responsible for the function of its carriers (pumps). ex. Ca2+ and Na+K+ pumps.

Secondary active transport- when the energy needed for the "uphill" movement of a molecule or ion is obtained by the "downhill" movement of molecules into the cell. ATP is not required, but chemical energy from Na+ moving down its concentration gradient provides energy for Glucose to move from higher to lower concentration.  ex. Na+ enters the carrier protein (toward lower concentration) and glucose enters protein at the same time (toward higher concentration).  This is cotransport, or symport.  Counter transport would move one molecule in the opposite direction of the other molecule (antiport).