3. Homeostasis Flashcards
Temperature of human environments
Outside: -10 and +40 C
Inside: 37 C
PO2 of human environments
Outside: 160 mmHg
Inside: PaO2 95mmHg
PCO2 (breathing) of human environments
Outside: 0.23 mmHg
Inside: 40 mmHg
Water of human environments
Outside: 0-90 g/kg of air
Inside: 600 g/kg tissue
pH of Human environments
Outside: ?/variable
Inside: pH 7.4
Ability of the body to maintain a relatively stable internal environment despite external variances
Homeostasis
The study of the various mechanisms that maintain homeostasis
Physiology
Water distribution
40% body weight; 28L
2/3 of total body water
Intracellular water
Water distribution
20% body weight; 14L
1/3 of total body water
Extracellular water
Water distribution
Part of extracellular
15% body weight; 10.5L
Interstitial fluid and lymph water
Water distribution
Part of extracellular water
5% body weight; 3.5L
Plasma (blood) water
Water distribution
60% body weight; 42L
Total body water
Gender with 60% water
Men
More testosterone leads to less body fat
Gender with 50% water
Women
More body fat
Ionic composition of ICF and ECF
Intracellular: 14 Extracellular: 140
Na+
Ionic composition of ICF and ECF
Intracellular: 120 Extracellular: 4
K+
Ionic composition of ICF and ECF
Intracellular: 1x10^4 (very low) Extracellular: 2.5
Ca2+
Ionic composition of ICF and ECF
Intracellular: 20 Extracellular: 0.8
Mg2+
Ionic composition of ICF and ECF
Intracellular: 10 Extracellular: 105
Cl-
Ionic composition of ICF and ECF
Intracellular: 10 Extracellular: 24
HCO3-
Ionic composition of ICF and ECF
Intracellular: 7.1 Extracellular: 7.4
pH
Ionic composition of ICF and ECF
Intracellular: 290 Extracellular: 290
Osmolarity
Cerebrospinal, synovial, and pleural fluids
Different from Plasma
Interstitial fluids
Maintenance of a state that does not change with time, and energy expenditure may be necessary
Eg. ICF [Na+] < ECF [Na+] and concentrations are maintained at a set level balanced over time → requiring energy
Steady state
Na/K - ATPase pump
Solutes are in a steady state (body expends effort and energy to maintain uneven solute concentrations to allow optimal function)
Implies that two compartments have the same amount of free energy so there is no net energy transfer between two compartments.
Equilibrium
Water is in equilibrium between ICF and ECF due to solute concentration difference
Homeostatic Mechanisms
Physiological parameter being controlled
Controlled Variable
Homeostatic Mechanisms
Receptor type (sense organ) that detects changes in the controlled variable
Sensor
Homeostatic Mechanisms
Integration center that analyzes data from the sensor and compares to set point
Integrator/Comparator
Homeostatic Mechanisms
“Normal” values predetermined but influenced by environmental adaptations
Set Point
Homeostatic Mechanisms
Nerve pathways, hormones, cells, tissues that carry out the response needed to restore homeostasis
Effectors
Set Point deviation
Since daily routine is so variable set points often vary between active (day) and
passive (night) times i.e. K+ excretion is greater during the day than at night –
more ingested during the day
24 hour cycle
Circadian rhythm
Set Point deviation
Changes in external environment i.e. Acclimation → one goes to live at high altitudes, set point
for PO2 levels change
Environmental Changes
Set Point Deviations
During infections i.e. Fever - increase in body temperature is an adaptation of set-point to minimize viral replication i.e. Plasma iron concentration decreases significantly to deprive bacteria of iron needed for replication
Protective Response
Set Point Deviations
As disease progresses, set point elevates more and more
i.e. Atheramatous plaques in blood vessels increase BP and resetting of BP set point → blood pressure continues to increase chronically as cardiovascular disease progresses
Aging or Pathological changes
The more vital the parameter to be controlled the more
homeostatic mechanisms needed to control it
• Complex interplay may exist among various control systems
• If one mechanism fails then others can still maintain that
parameter around set point → multiple control systems
• Often there is more than 1 control mechanism as a back-up
Redundancy
Example: Blood hemorrhage: Brain is Cardiovascular control center. Compares BP to set point and adjusts vascular tone and cardiac output accordingly.
Where set-point of some variables may be altered in order to maintain others i.e. changes in skin blood vessel diameter during exercise.
Homeostatic Hierarchy
During exercise, outflow increases causing vasoconstriction, helps maintain BP.
With strenuous exercise, temp control in hypothalamus inhibits sympathetic outflow to skin blood vessels causing vasodilation and heat loss
During maximum exercise, the need to maintain blood pressure takes priority over maintaining body temp, blood vessels constrict again.
Deficient Homeostatic Mechanisms
In many disease processes the normal negative feedback mechanisms may initially work to the benefit of the individual but as the disease progresses then normal compensatory responses
fail and the normal negative feedback mechanisms are overtaken by positive feedback loops with disastrous consequences.
i.e. In chronic heart failure cardiac output falls and the body
responds by retaining fluid. The retention of fluid increases the
work load of the heart thus eventually making it even more likely
to fail.
