Intro To endocrinology

Question 1

What are the endocrine glands in the body?

Answer 1

Hypothalamus, Pituitary gland, Thyroid Gland, Parathyroid gland, Adrenal glands, Pancreas, Ovary and Testis

Question 2

What is the Definition of a hormone?

Answer 2

A chemical substance which is synthesised and secreted by a specific ENDOCRINE cell type. It is transported though circulation at very low concentrations. It elects a specific response in a distant tissue.

Question 3

What is the passage of an endocrine hormone?

Answer 3

1. Discharged into extracellular fluid.
2. Diffuses into blood vessel down a concentration gradient
3. By simple diffusion flows out of blood vessel into surrounding tissues.
4. only cells with appropriate receptor will act.

Question 4

What are the four modes of cell:cell communication?

Answer 4

1. Endocrine- hormone -> blood vessel -> target cell
2. paracrine and Autocrine- Autocrine produced in the cell, paracrine secreted to a local cell
3. Neuroendocrine - axon terminal: blood vessel which diffuses to target cell
4. Neurotransmitter- neurone to neurone

Question 5

3 Classes of hormones

Answer 5

Proteins and Peptides e.g. growth hormone = hydrophilic
Cholesterol derivatives e.g. steroids and vitamin D = hydrophobic
Modified amino acids = e.g. adrenaline (hydrophilic) and thyroid hormones (hydrophobic)

Question 6

Describe a hydrophilic Hormone

Answer 6

• can’t cross membranes i.e. extracellular receptor
• Soluble in the blood = no carrier so vulnerable to degradation
• Can’t cross membranes, stored for rapid release

Question 7

Describe Hydrophobic hormones

Answer 7

• Can cross membranes i.e. intracellular receptor
• Insoluble in blood, needs a carrier = more resistant to degradation
• Harder to store - can cross membranes, synthesised on demand or has a binding partner
• tend to be excreted as they are protected by binding partners, longer half life

Question 8

Describe steroid hormone synthesis

Answer 8

1. cholesterol taken up by cell
2. stored in esterified form in lipid droplets
3. transported to mitochondria where CYTOCHROME P450 SIDE CHAIN CLEAVAGE ENZYME removes a side chain from cholesterol converting it to PROGENOLONE
4. pregenolone undergoes further enzyme activity to yield progesterone, androgens, oestrogen, glucocorticoids, mineralocorticoids

Question 9

Describe synthesis of Peptide/protein Hormones

Answer 9

1. Translated/synthesises from specific mRNA in rough ER
2. Initially synthesised as PRE-PROHORMONES
3. Processed to generate active hormone by ENDOPEPTIDASE removing single (PRE) hormone to give PROHORMONES.
4. Prohormones sent via golgi to secretory granules, stored waiting for secretion signal.