Week 1. Introductory Endocrinology

Question 1

Define:
Autocrine
Paracrine
Endocrine
Intracrine

Answer 1

Autocrine: a hormone that acts on the same cell in which it is synthesised

Paracrine: a hormone that acts on a neighbouring cell to the one in which it is synthesised.

Endocrine: a hormone that is released into the bloodstream to act on a distant cell/tissue

Intracrine: a hormone that has a regulatory function in the cell in which it is synthesised, by binding to intracellular receptors

Question 2

What are the similarities between the nervous system and the endocrine system?

Answer 2

Both are communication systems, both integrate the stimuli and response and both are required for a coordinated response

Question 3

What are the differences between the nervous and endocrine systems?

Answer 3

The nervous response is quick, the endocrine response is slower.

The endocrine system is anatomically discontinuous; the nervous system exerts point to point control, whilst the endocrine system broadcasts hormonal messages.

Question 4

Outline the protein peptide class of hormones.

Answer 4

1. Most hormones are peptides.
2. Synthesises as pre-prohormones —> undergo post translational processing when required
3. May contain glycoproteins
4. Stored in secretory granules and excreted by endocytosis

Question 5

Outline the steroid class of hormones.

Answer 5

1. Steroids are synthesised and released as and when required.
2. They’re derived from cholesterol.
3. Synthesised in the mitochondria and smooth ER.
4. They’re lipid soluble; they travel bound to proteins in plasma
5. They can pass freely through the plasma membrane

Question 6

Outline the amino acid derivatives class of steroid hormone.

Answer 6

1. Synthesised by tyrosine and tryptophan.
2. Have an ‘ine’ suffix
3. Adrenaline/noradrenaline: synthesised in medulla of adrenal gland.
4. Thyroxine: synthesised in thyroid
5. Melatonine/serotonine/ dopamine: synthesised in brain
6. Synthesised as needed

Question 7

How are hormones transported?

Answer 7

Proteins/peptides/amines: travel freely in blood

Steroids and thyroid hormones: travel bound to transport proteins.

Question 8

What type of protein are hormone transport proteins and where are they synthesised?

Answer 8

They are globular proteins, and synthesised in the liver

Question 9

Describe hormone binding proteins.

Answer 9

They’re globular proteins which are synthesised in the liver. Some are hormone specific.

Question 10

How is a hormone cleared?

Answer 10

Through the liver or bound to a receptor. The liver inactivates the hormone; the kidney excretes them.

Question 11

Define agonist and antagonist.

Answer 11

Agonists trigger a cellular response.

Antagonists block a cellular response.

Question 12

What two features do hormone receptors have and why are they important?

Answer 12

High affinity - the ability to bind receptor to hormone. Allows for lower levels of hormone to be secreted.
High specificity - allows receptor to distinguish between similar hormones.

Question 13

Outline the function of cell membrane hormone receptors.

Answer 13

Used by peptides that can’t freely cross the membrane.

Three types:

• ligand gated ion channels
• G protein coupled receptors
• Phosphatidylinositol pathway

Question 14

Outline the two types of intracellular receptors and which hormone class they respond to.

Answer 14

Steroids.

Nuclear and cytoplasmic.

Question 15

Outline hormone receptor regulation.

Answer 15

Up regulation increases the chances of hormone receptor binding.
Down regulation occurs when too much hormone is circulating, so fewer receptors are required.

Question 16

Outline the three ways in which hormone release can be controlled.

Answer 16

Hormone release is controlled by homeostasis.

Neural - sympathetic and parasympathetic nervous systems

Hormonal - hormones can trigger or suppress the release of another hormone (tropic hormones). Hormone inhibition is an important mechanism of negative feedback.

Nutrient regulation - plasma concentrations of mineral ions can control hormone secretion. A major function of a hormone is to regulate the plasma ion/nutrient controlling its secretion.