PHYS Endocrine Compartments - Week 11

Question 1

Exocrine glands vs endocrine glands

Answer 1

Exo - products secreted into ducts.
Endo - products secreted directly into bloodstream.

Question 2

3 x classes of hormones

Answer 2

Protein/peptide, steroids, amine.

Question 3

Examples of protein/peptide hormones.

Answer 3

Insulin.

Question 4

Examples of steroid hormones.

Answer 4

Testosterone, oestrogen, progesterone, cortisol.

Question 5

Examples of amine hormones.

Answer 5

Thyroxine, epinephrine, norepinephrine.

Question 6

From what are steroid hormones derived? Hydrophilic/hydrophobic?

Answer 6

Cholesterol. Hydrophobic.

Question 7

Process of protein/peptide hormone synthesis.

Answer 7

1. Preprohormone generated @ ribosome
2. Transported to lumen of ER via signal-sequence of aa
3. Signal peptide cleaved by enzymes @ ER -> inactive pro-hormone
4. Pro-hormone passes through ER to golgi -> modification
5. Secretory vesicle buds off golgi
6. Enzymes within vesicles cleave pro-hormone -> active hormone
7. Secretory vesicle fuses with cell membrane to release active hormone into extracellular fluid via exocytosis.
8. Hormone travels to target cell/s.

Question 8

Process of steroid hormone synthesis.

Answer 8

Protein hormones (generally from pituitary) regulate steroid hormone synthesis
1. For example, protein kinase A (e.g., ACTH for cortisol synthesis or LH for testosterone synthesis) binds to extracellular receptor on steroid hormone producing cell.
2. Protein kinase A increase synthesis of steroidogenic acute regulatory protein (STAR)
3. STAR moves cholesterol into mitochondria [rate-limiting step]
4. Hormone synthesis & released into circulation via diffusion (often transported bound to proteins w small amounts free in circulation).
5. Hormone diffuses through plasma membrane of target cell
6. Binds to intracellular receptor
7. Receptor-hormone complex enters nucleus & binds to DNA
8. Binding initiates transcription of the gene to mRNA
9. mRNA directs protein synthesis.

Question 9

What regulates steroid hormone synthesis?

Answer 9

Steroid hormones are synthesised on an as req basis via protein hormones synthesised from pituitary glands.

Question 10

Rate of action steroid hormones vs protein hormones.

Answer 10

Steroid hormones are often slower acting than protein hormones due to binding to protein carriers in plasma.

Question 11

What are amine hormones derived from?

Answer 11

Tyrosine.

Question 12

2 x types of amine hormones.

Answer 12

Catecholamines & thyroid hormones.

Question 13

Where are catecholamines made?

Answer 13

Adrenal medullar or hypothalamus.

Question 14

Where are thyroid hormones made?

Answer 14

Thyroid gland.

Question 15

Compare & contrast hydrophilic/lipophilic nature of catecholamines & thyroid hormones as well as typical transport mechanisms & location of receptors?

Answer 15

Catecholamines - hydrophilic, transported freely via plasma, receptors on target cell.
Thyroid hormones - lipophilic, transport w aid of carrier/transport proteins, receptors in target cell.

Question 16

What 3 x factors determine plasma hormone levels?

Answer 16

1. Rate of synthesis & secretion
2. Binding proteins in plasma
   a. Most peptide & all catecholamine hormones are water-soluble – transported in ‘free form’ dissolved in plasma
   b. Steroids & thyroid hormones are poorly soluble – transported primarily bound to plasma proteins.
   NB: Binding proteins slow the metabolism of hormones as hormones can only have an effect in a ‘free form.’
3. Rate of removal from blood via excretion , metabolic activation/inactivation.

Question 17

What 3 x factors stimulate hormone secretion?

Answer 17

Factors which stimulate hormone secretion:
* Changes in blood ions/nutrient concentration (e.g., reduction in circulating Ca2+ levels)
* Neurotransmitters released from neurons that terminate on the endocrine cell
* Hormones acting on the endocrine cell

Question 18

Example of a hormone which exerts negative feedback?

Answer 18

Insulin.