Lecture 1 - Homeostasis Flashcards
Name certain variables which the body has to control to keep its internal environment separate from the external environment.
pH, temperature, PO2, PCO2, water
Define homeostasis.
Ability of the body to keep its internal environment stable despite external variances
What percentage water are males? Females?
Males: 60%
Females: 50%
What are the internal body compartments and their constitution of total body water?
Plasma: 3L
Interstitial fluid: 12L
Intercellular fluid: 28L
What are the intracellular and extracellular values for sodium and potassium?
Intracellularly:
14 mEq/L Na
120 mEq/L K
Extracellularly:
140 mEq/L Na
4 mEq/L K
What is the normal range and average value for plasma osmolarity?
Normal range: 270-300 mOsm/L
Average value: 290 mOsm/L
What is the main difference between steady state and equilibrium?
A steady state requires that energy be expended to keep variables within a predetermined range, whereas equilibrium does not require energy.
Between the ECF and ICF, there is water and there are solutes. Which is in equilibrium and which is in a steady state?
Water is in equilibrium between the ECF and ICF, but solutes are in a steady state.
How do most homeostatic mechanisms operate?
Through negative feedback.
List some examples of positive feedback.
- ovulation
- parturition
- ejaculation
- thrombosis
What mechanism controls blood glucose?
Negative feedback.
What is the difference between feed-forward control and feedback mechanisms?
Feedback mechanisms institute a change based on external variances. Feed-forward anticipates a change before it happens.
What is an example of a 24 hr cycle set point deviation?
Potassium excretion (greater during day)
What are the four reasons for set point deviations?
- 24 hr cycle
- environmental change
- protective response
- aging or pathology
Increased redundancy in feedback mechanisms is present when?
When the variable is a vital parameter
