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.