Topic 9.1-2 Homeostasis and chemical control in mammals

Question 1

What is homeostasis?

Answer 1

Internal enviroment is maintained in dynamic equilibrium within set limits around an optimum.

Question 2

Why is it important that core body temperature remains stable?

Answer 2

Maintain stable rate of enzyme-controlled reactions.

Temperature too low = enzyme and substrate molecules have insufficient kinetic energy.

Temperature too high = enzymes denature

Question 3

Why is it important that blood pH remains stable?

Answer 3

Maintain stable rate of enzyme controlled reactions (and optimium conditions for other proteins).

Acidic pH =H⁺ ions interact with hygdrogen bonds and ionic bonds in tertiary structure of enzymes -> shape of active site changes so no ES complex can form

Question 4

Why is it important that blood water potential remains stable?

Answer 4

Prevent osmotic lysis/ crenation of cells

Question 5

Define negative feedback

Answer 5

Self-regulatory mechanism return the internal envioment to optimum when there is a fluctuation.

Question 6

Define postive feedback

Answer 6

A fluctuation triggers changes that result in an even greater deviation from the normal level.

Question 7

What are hormones?

Answer 7

Proteins secreted by endocrine glands and transported in bloodstream. Specific tertiary structure is only complementary to receptors on certain cells.

Question 8

Outline the general stages involved in negative feedback

Answer 8

Receptors detect deviation -> coordinator -> corrective mechanism by effector -> receptors detect that conditions have returned to normal

Question 9

Suggest why separate negative feedback mechanisms control fluctuations in different directions

Answer 9

Provides more control, especially in case of ‘overcorrection’, which could lead to a deviation in the opposite direction from the original one .

Question 10

Why is there a time lag between hormone production and response by an effector?

Answer 10

It takes time to:
* Produce hormone
* Transport hormone in the blood
* Cause required change to the target protein

Question 11

Explain the mode of action of adrenaline

Answer 11

Secondary messenger model:

1. Hormone-receptor complex forms
2. Conformational change to receptor activates G-protein
3. Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP)
4. cAMP activates protein kinase A pathway
5. Results in glycogenolysis

Question 12

Explain the mode of action of oestrogen

Answer 12

1. Steriod hormone diffues through cell membrane
2. Forms hormone-receptor complex with ER α receptor in cytoplasm
3. Complex enters the nucleus and acts as a transcription factor