Lecture 3

Question 1

1. Understand the general concepts of homeostasis and the principles of positive and negative feedback in physiological systems.

Answer 1

• Each compartment has different electrolyte constituents kept in a defined range. Osmolarities are equal but solute conc not in chemical equilibrium
• Homeostasis: not about reaching equilibrium but having parameters kept in a defined range- maintaining an ideal steady state (energy).
• Negative Feedback: disturbance sense by sensor and comparator/ integrator REVERSES initial disturbance to back to “normal” value

ie: estradiol
ie: blood glucose: more glucose = pancreas increases insulin = insulin reputes glucose into cells so less glucose in blood

• Positive Feedback: Disturbance sensed by sensor and comparator/ integrator AMPLIFIES signal. Usually unstable and have a definite end point***
ie: ovulation, birth, ejaculation, blood clot formation

Question 2

5. Contrast the following units used to describe concentration: mM, mEq/L, mg/dL, mg%. List the typical value and normal range for plasma Na+, K+, H+ (pH), HCO, -, Cl-, Ca+2, and glucose, and the typical intracellular pH and concentrations of Na+, K+, Cl-, Ca+2, and HCO3

Answer 2

mM

mEq/L

mg/dl

mg

Question 3

12. Define the term “steady state,” and differentiate it from “equilibrium.” Relate the pump leak model of steady-state ion content to cell solute gradients and cell volume maintenance.

Answer 3

Steady State:

• maintenance of a state that does not change over time
• internal stability
• may need ATP

Equilibrium: no net flux

Note:
ECF: Na is 144
ICF: Na is 6
–> Na wants to come in

ECF: K is 5
ICF: K is 156
–> K wants to come out
“Knock Out”