L2 - Homeostasis & Control Flashcards
What is homeostasis?
maintenance of a relatively constant internal environment
essential for the survival of each cell… and hence the individual
What are the five steps to maintaining homeostasis?
1) detect changes (sensor)
2) afferent message to controller/integrator
3) controller/integrator compares to set point
4) efferent message to effector
5) response resulting in return to within desired range (negative feedback loop)
Give an example of homeostasis.
fall in blood pressure below normal set point activates pressure-monitoring nerve cells which stimulate the heart
and results in an increase in blood pressure to normal which inhibits pressure-monitoring nerve cells (response leads to a negative feedback loop as pressure-monitoring nerve cells sense normal blood pressure and cease stimulation of the heart)
What are the two integration pathways in the body?
endocrine (hormonal) and neural pathways
How does a simple endocrine reflex proceed?
internal or external change -> endocrine system sensor-integrating sensor -> efferent signal: hormone -> effectors -> response
How does a simple neural reflex proceed?
internal or external change -> receptor -> afferent path: sensory neuron -> neural system integrating centre -> efferent neuron -> effectors -> response
How does a complex neuroendocrine reflex proceed?
internal or external change -> receptor -> afferent path: sensory neuron -> neural system integrating centre -> efferent neuron or neurohormone -> endocrine integrating centre -> efferent signal #2: hormone -> effectors -> response
What is an example of a complex neuroendocrine reflex?
maintaining blood glucose levels while eating a meal
Could a positive feedback loop maintain homeostasis?
no
What does a positive feedback loop do? Give some examples.
reinforces the stimulus and escalates the response e.g. birth, ovulation and Na channels in action potential
What is diffusion?
a passive spontaneous process by which net movement of molecules occurs to eliminate concentration gradients
What is the purpose of the cell membrane and what will easily pass through?
separates cell from the environment
small lipid soluble uncharged molecules will pass through e.g. lipids, water, O2, CO2
What will not easily pass through the cell membrane?
lipid insoluble charged molecules will not pass through e.g. ions, proteins
Is Na+ a penetrating or non-penetrating solute?
non-penetrating
What is osmolarity?
the total concentrations of solutes, penetrating and non-penetrating
normal cell osmolarity is approximately 300 mOsm
What is tonicity?
the concentration of only the non-penetrating solutes (in reference of the extracellular non-penetrating solute concentration compared to the cell’s non–penetrating solutes)
a solution can be isotonic, hypertonic or hypotonic with respect to the cell
Why is the body in osmotic equilibrium?
this is because water moves between intra- and extracellular space and always dilutes the more concentrated solution via osmosis (does not mean an even distribution of different types of particle)
What is the formula for Fick’s Law?
Q = ΔC x P x A / (√MW x ΔX) Q is net rate of diffusion P is permeability of membrane to substance A is surface area of membrane MW is molecular weight of substance ΔX is membrane thickness
Hypotonic solutions have ________ than isotonic solutions.
lower concentrations of non-penetrating solutes
A cell contains 300 mOsm of non-penetrating solutes. If the extracellular fluid also contains 300 mOsm of non-penetrating solutes, the extracellular solution is…
isotonic and the cell will not change volume
A cell contains 300 mOsm of non-penetrating solutes. If the extracellular fluid also contains 250 mOsm of non-penetrating solutes, the extracellular solution is…
hypotonic and the cell will swell
non-penetrating solutes cannot cross the cell membrane to equilibrate; therefore, water moves in because the osmotic gradient is in opposite direction, and water can move
