3. Homeostasis

Question 1

Temperature of human environments

Answer 1

Outside: -10 and +40 C
Inside: 37 C

Question 2

PO2 of human environments

Answer 2

Outside: 160 mmHg
Inside: PaO2 95mmHg

Question 3

PCO2 (breathing) of human environments

Answer 3

Outside: 0.23 mmHg
Inside: 40 mmHg

Question 4

Water of human environments

Answer 4

Outside: 0-90 g/kg of air
Inside: 600 g/kg tissue

Question 5

pH of Human environments

Answer 5

Outside: ?/variable
Inside: pH 7.4

Question 6

Ability of the body to maintain a relatively stable internal environment despite external variances

Answer 6

Homeostasis

Question 7

The study of the various mechanisms that maintain homeostasis

Answer 7

Physiology

Question 8

Water distribution
40% body weight; 28L
2/3 of total body water

Answer 8

Intracellular water

Question 9

Water distribution
20% body weight; 14L
1/3 of total body water

Answer 9

Extracellular water

Question 10

Water distribution
Part of extracellular
15% body weight; 10.5L

Answer 10

Interstitial fluid and lymph water

Question 11

Water distribution
Part of extracellular water
5% body weight; 3.5L

Answer 11

Plasma (blood) water

Question 12

Water distribution
60% body weight; 42L

Answer 12

Total body water

Question 13

Gender with 60% water

Answer 13

Men
More testosterone leads to less body fat

Question 14

Gender with 50% water

Answer 14

Women
More body fat

Question 15

Ionic composition of ICF and ECF

Intracellular: 14 Extracellular: 140

Answer 15

Na+

Question 16

Ionic composition of ICF and ECF

Intracellular: 120 Extracellular: 4

Answer 16

K+

Question 17

Ionic composition of ICF and ECF

Intracellular: 1x10^4 (very low) Extracellular: 2.5

Answer 17

Ca2+

Question 18

Ionic composition of ICF and ECF

Intracellular: 20 Extracellular: 0.8

Answer 18

Mg2+

Question 19

Ionic composition of ICF and ECF

Intracellular: 10 Extracellular: 105

Answer 19

Cl-

Question 20

Ionic composition of ICF and ECF

Intracellular: 10 Extracellular: 24

Answer 20

HCO3-

Question 21

Ionic composition of ICF and ECF

Intracellular: 7.1 Extracellular: 7.4

Answer 21

pH

Question 22

Ionic composition of ICF and ECF

Intracellular: 290 Extracellular: 290

Answer 22

Osmolarity

Question 23

Cerebrospinal, synovial, and pleural fluids
Different from Plasma

Answer 23

Interstitial fluids

Question 24

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

Answer 24

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)

Question 25

Implies that two compartments have the same amount of free energy so there is no net energy transfer between two compartments.

Answer 25

Equilibrium
Water is in equilibrium between ICF and ECF due to solute concentration difference

Question 26

Homeostatic Mechanisms
Physiological parameter being controlled

Answer 26

Controlled Variable

Question 27

Homeostatic Mechanisms
Receptor type (sense organ) that detects changes in the controlled variable

Answer 27

Sensor

Question 28

Homeostatic Mechanisms
Integration center that analyzes data from the sensor and compares to set point

Answer 28

Integrator/Comparator

Question 29

Homeostatic Mechanisms
“Normal” values predetermined but influenced by environmental adaptations

Answer 29

Set Point

Question 30

Homeostatic Mechanisms
Nerve pathways, hormones, cells, tissues that carry out the response needed to restore homeostasis

Answer 30

Effectors

Question 31

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

Answer 31

24 hour cycle
Circadian rhythm

Question 32

Set Point deviation
Changes in external environment i.e. Acclimation → one goes to live at high altitudes, set point
for PO2 levels change

Answer 32

Environmental Changes

Question 33

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

Answer 33

Protective Response

Question 34

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

Answer 34

Aging or Pathological changes

Question 35

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

Answer 35

Redundancy
Example: Blood hemorrhage: Brain is Cardiovascular control center. Compares BP to set point and adjusts vascular tone and cardiac output accordingly.

Question 36

Where set-point of some variables may be altered in order to maintain others i.e. changes in skin blood vessel diameter during exercise.

Answer 36

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.

Question 37

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.

Answer 37

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.