Physiology Intro

Question 1

Define homeostasis

Answer 1

maintenance of a relatively stable internal environment through self-regulating processes
eg. - blood water volume and ionic composition
- blood pressure and flow
- core body temp
- membrane potential

Question 2

What are the four components of homeostatic control systems?

Answer 2

Controlled variable:
- what the system is trying to manage
Receptors(s)/Sensor(s):
- different types of receptors; chemoreceptors, mechanoreceptors nociceptors, and special sense receptors
Control centre:
- can be the same cells as those detecting a change or can be an entirely different organ
Effectors:
- may be a cell type, or may be an entire organ system, but works to change the controlled variable

Question 3

Describe the percentages of water in the body water compartments and what their roles are

Answer 3

TBW = 55% body weight female and 60% body weight male
ECF = 1/3 of TBW = 80% interstitial fluid and 20% plasma

• ECF is the ‘transitional compartment’ so water goes into and out of the body and water can move relatively freely between interstitial fluid and plasma
• water moving into ad out of cells is a tightly controlled process and depends on the osmotic gradient between ECF and ICF + permeability of membrane
• ECF and ICF have same osmolarity diff composition

Question 4

What is the cells ion composition in ECF and ICF at rest?

Answer 4

ECF = high Na+
ICF = high K+

solutes include proteins and ions

• normal cells at rest have low Na+ and K+ permeability (channels are mostly closed = not permeable)
• resting membrane potential = -70mV
• osmolarity drives water movement

Question 5

Describe the transmembrane protein Pore (AQP)

Answer 5

• opening in cell membrane (water permeability)
• AA’s and PTMs can cause selectivity

Question 6

Describe the transmembrane protein Ion channel

Answer 6

• opening in cell membrane that can be closed or open
• selectivity filter regulates ion permeation

Question 7

Describe the transmembrane protein transporter

Answer 7

1. substrate binds
2. causes conformational change
3. moves substrate across membrane
   - can act as facilitated diffusion protein
   - can be ‘secondary active transport’ and use the driving force for one molecule to move another (same direction or opposite direction)
   - can be ‘primary active transport’ and use ATP hydrolysis to drive molecules against their electrochemical gradient (eg. Na+/K+ ATPase)

Question 8

Describe how Na+/K+ ATPase works

Answer 8

3 Na+ atoms bind to the protein
- ATP hydrolysed: ADP leaves; Pi remains bound (protein is phosphorylated) and the protein shifts
- The Na+ is released outside of the cell
- 2K+ atoms bind to the protein
- Pi leaves the protein (dephosphorylated) and the protein shifts
- the K+ is released into the cell
- a new molecule of ATP binds to the protein

maintains gradients between ICF and ECF