Endocrinology 1 - Principles

Question 1

How are Protein/polypeptide hormones made?

Answer 1

1. Blood supply provides amino acids to the cell.
2. Pro-hormone gene transcribed and mRNA formed.
3. mRNA moves to ER + translocated = pro-hormone formed.
4. Pro-hormone endocytosed by Golgi apparatus.
5. Pro-hormone is packed into vesicles with enzymes that pinch off Golgi.
6. Pro-hormone cleaved = Active hormone.
7. Vesicles with active hormone accumulate at cell membrane and wait for signal to release.

Question 2

How are Steroid hormones made?

Answer 2

1. LDL transports fatty acid esters to the cell.
2. Fatty acid esters seen as fatty droplets in vesicles in cell.
3. Esterase liberates cholesterol from fatty acids.
4. Cholesterol taken into the Mitochondria using StAR protein (rate limiting step).
5. Steroid hormone made using enzymes - final enzymes different for in different cells that produce different hormones.
6. Hormone released to cytoplasm - lipid soluble and hence diffuses out of the cell to the blood.

Question 3

How are Protein/polypeptide hormones transported in blood?

Answer 3

Secreted into blood and travel unbound. Hence they are sensitive to enzymatic breakdown - short half lives.

Question 4

How are Cholesterol hormones transported in blood?

Answer 4

Plasma proteins bind to cholesterol in blood (Albumin). Protein bound cholesterol cannot enter cells, however some free cholesterol left. Free cholesterol enters tissues.

Question 5

What is the mechanism of Protein/polypeptide hormones? Use ACTH as an example.

Answer 5

ACTH example

1. Hormone binds to ACTH receptor (G-protein receptor) on the cell membrane.
2. Activates Adrenal Cyclase - increase cAMP - activates Protein Kinase A.
3. Esterase phosphorylated - cholesterol liberated.
4. StAR also phosphorylated - cholesterol enters mitochondria - steroid hormone production.

Question 6

What is the mechanism of Steroid hormones?

Answer 6

1. Free steroid hormones enter the cell.
2. Bind to intracellular receptors.
3. Translocate into nucleus + bind to DNA and promotes transcription of certain genes = increase translocation + production of proteins.

Question 7

What is Negative Hormone feedback? What is positive feedback?

Answer 7

Negative hormone feedback is when the hormone switches off its own production. E.g. Anterior pituitary (AP) stimulated by stress = ACTH released. Acts on adrenal glands = Cortisol produced + enters blood. Cortisol returns to AP and switches off ACTH = Cortisol also switches off.
Positive feedback = LH and Oestrogen.

Question 8

What are differences in polypeptide and steroid hormone secretion?

Answer 8

1. Polypeptide hormones are stored in vesicles in the cell and await a stimulus triggering exocytosis.
2. Steroid hormones are secreted into the blood stream as soon as they are produced - they are lipid soluble.

Question 9

Is free or bound steroid hormones able to enter the cells?

Answer 9

Free steroid hormones only.

Question 10

What is the equilibrium of plasma protein bound and unbound steroid hormone in the blood?

Answer 10

Hormone + Plasma Protien <====> Protein Bound Hormone.