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Ch 6
Interactions Between Cells and the Extracellular Environment
34
Physiology
Undergraduate 2
02/04/2009

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Term
Describe the intracellular and extracellular compartments of the body:
Definition

Intracellular- within the cell

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

Term
Describethe extracellular matrix:
Definition
It is composed of collagen, elastin and an amorphorous ground substance.  Ground substance contains glycoproteins and proteoglycans, forming a hydrated gel and collagen and elastin fibers provide structural support.
Term
Identify the components of passive transport:
Definition
Diffusion, osmosis and facilitated diffusion.
Term
Distinguish passive from active transport:
Definition

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).

Term
Define diffusion:
Definition
The molecules of a solution are in a constant state of random motion- If there is a concentration gradient (difference) between the two regions, the random motion tends to eliminate the concentration difference as the molecules become more spread out.
Term
What are the factors that influence the rate of diffusion?
Definition
1)Magnitude of concentration gradient, 2)permeability of membrane to it, 3)temperature, 4)surface area of membrane 5)molecular weight (size of molecule)
Term
How does osmosis relate to osmotic pressure?
Definition

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.

Term
Define osmosis:
Definition
Net diffusion of water (the solvent) across the membrane
Term
What are the 2 conditions required for osmosis to occur?
Definition

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

Term
What is osmolality?
Definition
Osmolality depends on the chemical nature of the solute molecules.  A solution of glucose and fructose would have a total of 2 Osm (because there are 2 molecules, each has a MW of 180, equaling 360 g/L) and a solution of of 360 g/L glucose would have 2 Osm (because it is double the MW) and 2m. However, an ion like NaCl is 1m, but it ionizes to form 1m Na+ and 1m Cl-. So 1m NaCl solution is equal to a total concentration of 2 Osm.
Term
How does osmosis relate to osmolality?
Definition
ex. If a semipermeable membrane to water, but not glucose or Na+ or Cl-) seperates a 1m glucose solution, water will move by osmosis to the NaCl solution, because 1m NaCl will ionize to form 1m Na+ and 1m Cl- (2 Osm) which means that the NaCl solution is less concentrated with water. After osmosis, the total concentration, or osmolality, is equal.
Term
Explain the nature and significance of hypotonic solutions:
Definition
They have a lower concentration (osmolality) of solutes than of plasma, and therefore a lower osmotic pressure; this draws water into the cell, causing it to swell ad even burst- called hemolysis.
Term
Explain the nature and significance of isotonic solutions:
Definition
They have an equal concentration of solutes (osmolality) as plasma, and therefore the same osmotic pressure.  This doesn't draw water in or draw water out of a cell.
Term
Explain the nature and significance of hypertonic solutions:
Definition
They have a higher concentration of solutes (osmolality) than plasma, and therefore a higher osmotic pressure.  This draws water out of a cell, causing it to shrink- called crenation.
Term
Describe the characteristics of carrier-mediated transport:
Definition

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.

Term
Distinguish between simple diffusion and facilitated diffusion:
Definition

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.

Term
Distinguish between facilitated diffusion and active transport:
Definition

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).

Term
Explain the significance of the Ca2+ pump:
Definition
It removes Ca2+ from the cytoplasm (low in Ca2+) by pumping it out into the extracellular fluid (high in Ca2+). When the pump opens (because of the intracellular concentration gradient created) Ca2+ rapidly diffuses down its concentration gradient down into the cytoplasm, triggering diverse processes.
Term
Explain the significance of the Na+/K+ pumps:
Definition

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.

Term
Explain the action of Ca2+ pumps:
Definition

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.  

Term
Explain the action of Na+/K+ pumps:
Definition

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.

Term
Describe the equilibrium potentials for K+:
Definition

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.

Term
describe the equilibrium potentails for Na+:
Definition

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.

Term
Describe membrane potential:
Definition
It is the extent to which each ion contributes to the potential difference across the plasma membrane, because there are many inorganic ions in the intracellular and extracellular fluid that are maintained at specific concentrations.  Membrane potential can also be thought of as "membrane voltage"
Term
How is membrane potential produced?
Definition

It is dependent on:

1) Its concentration gradient

2) Its membrane permeability

Term
distinguish between synaptic, endocrine and paracrine regulation:
Definition

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)

Term
Identify where receptor proteins are located within target cells:
Definition
They may be located on the plasma membrane, cytoplasm or nucleus.
Term
Describe the distribution of fluid in the body:
Definition
67% of body water is contained within cells, the remaining 33% is in the extracellular compartment. 20% of extracellular fluid is blood plasma, and the other 80% makes up interstitial (tissue) fluid.
Term
What is the importance of matrix metalloproteinases?
Definition
They break down extracellular matrix proteins. They aid in tissue remodeling (such as in embryonic development) and wound healing, but can be harmful such as in the case of cancer. If cancer metastasizes, active MMPs break down collagen of the basal lamina, allowing cancer cells to migrate.
Term
Why do hospitals use 5% dextrose and normal saline as intravenous solutions?
Definition

Because they are isotonic to blood plasma.

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

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

Term
Explain how the body detects changes in the osmolality of plasma, and describe the regulatory mechanisms by which a normal range of plasma osmolality is maintained:
Definition

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).

Term
What is primary and secondary active transport?
Definition

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).

Term
What role do the Na+/K+ pumps play in establishing the resting membrane potential?
Definition
It maintains constant concentrations and constant resting membrane potential.  It also contributes to the negative intracellular charge. Because 3 Na+ are pumped out for every K+ taken in, the pump is electrogenic (it adds about -3mV to RMP)
Term
What is resting membrane potential?
Definition
RMP is the membrane voltage of cell when its not producing impulses.
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