Homeostasis

Question 1

Negative feedback

Answer 1

• returns the variable to the set-range after disturbance of the variable
• change is proportional to the size of initial variation

Question 2

Feed Forward

Answer 2

Anticipatory changes before change to the variation e.g. incretin effect

Question 3

Positive feedback

Answer 3

• amplifies any changes to the variable

- de-stabilises and accelerates transitions between different states e.g. uterine contractions and coagulation cascade

Question 4

Molarity

Answer 4

Moles per litre solution

Question 5

Molality

Answer 5

Moles per kg solvent

Question 6

Tonicity

Answer 6

Describing two solutions separated by a membrane:

1. Hypotonic - lower osmotic pressure outside cell (cell lyses) 600mM
2. Isotonic - equal osmotic pressure in and out of cell 300mM
3. Hypertonic - higher osmotic pressure inside cell (cell crenates) 100mM

Question 7

Homeostasis

Answer 7

Maintenance of a constant condition in the internal environment

[NA+] = 145mM
[K+] = 4mM
Osmolarity = 300mOsm kg-1
Temperature = 37.1
pH = 7.4

Question 8

Dual effectors/antagonistic effectors

Answer 8

Increase precision of control of homeostatic systems e.g. blood glucose regulation by insulin and glucagon

Question 9

What is the osmolarity of mammalian fluid?

Answer 9

300 mosmolar (ions, proteins, sugars, lipids etc all contribute to this)

Question 10

Osmotic pressure

Answer 10

Minimum pressure which needs to be applied to a solution to prevent inward flow of water across a semipermeable membrane.
(It depends on number of particles present per unit volume of solvent)
By definition: 1 g of a non-dissociating substance in 1kg of water exerts an osmotic pressure of 1 ormolu

Question 11

What is the equation for osmotic pressure (π)?

Answer 11

π = MRT

M - molarity, R - gas constant, T - thermodynamic temperature

Question 12

Why do proteins exert a very small osmotic pressure?

Answer 12

Their molecular mass is very high (per g of protein - osmotic pressure is much lower)