L2 - Homeostasis & Control

Question 1

What is homeostasis?

Answer 1

maintenance of a relatively constant internal environment

essential for the survival of each cell… and hence the individual

Question 2

What are the five steps to maintaining homeostasis?

Answer 2

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)

Question 3

Give an example of homeostasis.

Answer 3

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)

Question 4

What are the two integration pathways in the body?

Answer 4

endocrine (hormonal) and neural pathways

Question 5

How does a simple endocrine reflex proceed?

Answer 5

internal or external change -> endocrine system sensor-integrating sensor -> efferent signal: hormone -> effectors -> response

Question 6

How does a simple neural reflex proceed?

Answer 6

internal or external change -> receptor -> afferent path: sensory neuron -> neural system integrating centre -> efferent neuron -> effectors -> response

Question 7

How does a complex neuroendocrine reflex proceed?

Answer 7

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

Question 8

What is an example of a complex neuroendocrine reflex?

Answer 8

maintaining blood glucose levels while eating a meal

Question 9

Could a positive feedback loop maintain homeostasis?

Answer 9

no

Question 10

What does a positive feedback loop do? Give some examples.

Answer 10

reinforces the stimulus and escalates the response e.g. birth, ovulation and Na channels in action potential

Question 11

What is diffusion?

Answer 11

a passive spontaneous process by which net movement of molecules occurs to eliminate concentration gradients

Question 12

What is the purpose of the cell membrane and what will easily pass through?

Answer 12

separates cell from the environment

small lipid soluble uncharged molecules will pass through e.g. lipids, water, O2, CO2

Question 13

What will not easily pass through the cell membrane?

Answer 13

lipid insoluble charged molecules will not pass through e.g. ions, proteins

Question 14

Is Na+ a penetrating or non-penetrating solute?

Answer 14

non-penetrating

Question 15

What is osmolarity?

Answer 15

the total concentrations of solutes, penetrating and non-penetrating
normal cell osmolarity is approximately 300 mOsm

Question 16

What is tonicity?

Answer 16

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

Question 17

Why is the body in osmotic equilibrium?

Answer 17

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)

Question 18

What is the formula for Fick’s Law?

Answer 18

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

Question 19

Hypotonic solutions have ________ than isotonic solutions.

Answer 19

lower concentrations of non-penetrating solutes

Question 20

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…

Answer 20

isotonic and the cell will not change volume

Question 21

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…

Answer 21

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