Introduction

Question 1

What are the key differences between the endocrine and nervous system modes of communication?

Answer 1

Endocrine communication - Hormones travel in the blood to their target organs/tissues

Neural communication - Neurotransmitters travel across the synaptic cleft to the postsynaptic cell to influence its activity, i.e they act locally within the cleft and DO NOT travel within the blood

Question 2

How are endocrine hormones classified and what are their mechanisms of action?

Answer 2

1) Peptide hormones

What are they? Chains of amino acids

What do they do? Open or close ion channels, activate or inactivate enzymes

2) Steroid hormones

What are they? All dervied from cholestorol

What do they do? Increase of decrease protein synthesis

3) Amine hormones

What are they? All derived from either tryptophan (melatonin only) or tyrosine

What do they do? Produce the fight or flight response

Question 3

What determines the availability of a hormone or neurohormone to its target cell?

Answer 3

1) Is the hormone being produced?
2) Can the hormone be carried to its target cell/tissue? Is the hormone carrier protein available?
3) Are the hormone receptors available?

Question 4

What are the major categories of physiological function that are governed by endocrine pathways and mechanisms?

Answer 4

Reproductive

Renal

GI

Thyroid

Adrenal

Pituitary

Hypothalamus

Question 5

What are the main routes and types of signal that determine the rates of hormone synthesis and secretion by a typical endocrine cell?

Answer 5

1 - Negative feedback signal

2 - Neural feedback loops e.g. adrenaline released by adrenal medulla following sympathetic activation.

3 - Prolonged periods of low hormone concentration in plasma, there is often up-regulation where there is an increase in the number of hormone receptors on target tissues (increasing sensitivity)

4 - Prolonged periods of over exposure to high plasma concentrations of a hormone and we see down-regulation where there is a decrease in receptor number on target tissues.

5 - One individual hormone may have effects on other hormones:

Permissive effects – Where the presence of one hormone enhances the effect of another hormone (increase in thyroid hormone leads to increase in epinephrine)

Antagonistic effects – Where the presence of one hormone leads to inhibition of the effect of another hormone.