Lecture 3 Flashcards
the ability of the body to maintain a relatively stable internal environment
Homeostasis`
Vital parameters that homeostasis maintains (7)
BP Gas tensions (O2 and CO2) Glucose concentration Osmotic pressure Ion concentrations pH Temperature
Basic function of homeostasis
to ensure that all cells receive adequate O2 and nutrients by
- maintaining composition of fluid compartments
- regulating BP and blood volume
- regulating body temperature
- regulating pH
percentage of water in our body
60%
Ratio of intracellular water to extracellular water
60% :20%
1/3 of total body water is ?
Extracellular fluid (ECF)
What does ECF includes? (3)
Plasma
interstitial fluid
specialized transcellular fluid comparments (cerebrospinal, synovial, pleural fluids)
2/3 of total body water is?
intracellular fluid (ICF)
Major anion and cation of ICF
Anion
- protein
- organic phosphates
Cation
- potassium
- magnesium
Major anion and cation of ECF
Anion
- chlorine
- HCO3-
Cation
- sodium
- calcium
What is common composition between ECF and ICF
Osmolarity
Why is osmolality the same between ECF and ICF?
Because water moves freely between ICF and ECF, so they are in a state of osmotic equilibrium.
How do you call this state when there is no net flux of energy from one compartment to another ; rate of forward reaction = rate of reverse reaction
equilibrium
Why are the ionic composition of the ECF and ICF not in equilibrium?
The ionic differences are due to the Na+-K+ATPase pump which pumps Na+ out of cell and K+ into cells. This requires energy, so it is not equilibrium. Instead it is “steady state”
How do you call this state?
Amount or concentration of a substance is constant over time, and there is no net gain or loss of a substance and might require energy to maintain this state.
Steady state
Why water is in equilibrium between compartments in our body?
due to solute concentration difference achieved by Na+K+ATPase (steady state)
What does abnormalities in K+ conc. cause pathologically?
affect membrane potential and excitability of the heart, skeletal muscle and CNS
E.G. Heart arrhythmias and muscle weakness and paralysis
What does abnormalities in Na+ conc. cause pathologically?
affect movement of water across cell membrane
e.g. shift of fluid into and out of brain cells leading to seizures, coma and death
3 mechanisms of homeostasis
- negative feedback loops
- feedforward control
- positive feedback loops
3 Elements of negative feedback loop
- Sensor
- Comparator (Usually CNS)
- Effector
Explain what happens when hemorrhage occur using negative feedback
- Sensor (baroreceptor) at carotid sinus sense fall in BP and info is sent to CNS
- Comparator compare the signal to set point. Then error signal is sent out via efferent pathways to act on effector organs (autonomic NS)
- Effector organ (Sympathetic response): vasoconstriction, increased cardiac output which leads to increase BP.
3 Examples of effector
- ANS
- Motor system
- hormones
How does tonic discharge work when there is high BP?
Afferent signals increase, and effectors decrease sympathetic NS and increase Parasympathetic NS.
How does baroreceptors monitor increase or decrease in BP? What is the method called?
Tonic discharge : it sends impulses to the brain at all times.
What is local negative feedback mechanism? and give 1 example.
Negative feedback mechanism that does not involve brain.
ex) change in blood glucose level
Explain what happens when blood glucose increase?
change in glucose level is sensed by pancreatic beta cell.
Then it secretes insulin which shift glucose into cells, lowering the glucose level.
Why could set point vary individually? (4 factors)
- 24hr cycle (circadian rhythm)- vary between day and night
- environmental change - acclimation, so set point of PO2 levels change
- protective response during infection - fever is an adaptation of set-point to minimize viral replication
- plasma iron concentration decrease to deprive bacteria of iron needed for replication - ageing or pathological changes
- As disease progresses, set point elevates more and more
e. g. atheromatous plaques in blood vessel increase BP and reset setpoint. So BP continues to increase chronically.
perturbation of a variable is sensed and comparator tries to change effector activity to decrease perturbation
negative feedback loops
3 redundant homeostatic mechanism of blood pressure
baroreceptor reflex
renin-Angiotensin system
Volume receptors and atrial natruietic peptide
Explain Renin angiotensin system when blood volume decrease
When blood volume decrease, mean atrial pressure decrease, which increase sympathetic NS. One way is to stimulate secretion of renin which cleave angiotensinogen into angiotensin I, which is further cleaved to angiotensin II. It stimulates adrenal gland to secrete aldosterone which increases retention of salt and water, thus increasing blood volume.
Another way is to stimulate vasoconstriction of renal arterioles which decrease glomerular filteration rate (GFR), thus increasing salt and water retention.
Occurs when body anticipates a variable is about to change and it effects responses which prepare body for the change.
Feedforward control
Give example of feedforward control
heat rate and ventilation increase in anticipation of exercise
Positive feedback loops
- deviation of a controlled variable becomes even grater and response itself reinforces deviation.
- terminated by event outside loop
3 example of positive feedback loop
- Parturition
- Generation of action potential
- Ovulation
Which one is higher priority in terms of feedback loop; change in skin blood vessel diameter or cardiovascular control which constrict blood vessel.
Cardiovascular control by medulla
