Intro To Endo

Question 1

How are hormones categorised?

Answer 1

• Polypeptide or protein hormones are synthesised initially as pro/prepro hormone then Golgi converts it to hormone by proteolytic enzymes then stored in vesicles.
• Steroid hormones are produced from cholesterol. LDL from plasma is endocytosed and the cholesteryl esters are stored in the cytoplasm. When needed, esterase liberates the cholesterol and using Steroidogenic Acute Regulatory transporter it is transported into the mitochondria where enzymes present for specific hormone synthesis. The hormone then diffuses freely back into the plasma.

Question 2

How are the different types of hormones transported?

Answer 2

PEPTIDE/AMINO ACID Hormones: usually water soluble, stored in vesicles and released when needed and circulate freely.

STEROID: Usually insoluble so needs to be bound to plasma/transport proteins like albumin or specific ones like CBG.

Question 3

Explain the equilibrium plasma protein bound hormones

Answer 3

Only the free hormone in the blood is biologically active

Hormone + Plasma Protein bound hormone

Therefore le chateliers principle applies

To ensure free hormone availability is constant secretion rates are also altered.

Question 4

How do peptide hormones and chatecolamines cause a response on target cell?

Answer 4

The hormone binds to a GPCR (high affinity and specificity due to low concentrations of hormone) as it cannot enter cells easily. It triggers an intracellular signalling pathway.

Eg. ACTH binds to receptor which stimulates activation of Adenylyl Cyclase. Producing cAMP. cAMP activates protein kinase A which activates cholesterol esterase liberating more cholesterol and up-regulating production of StAR so more uptake into mitochondria

Question 5

How do steroid hormones cause a response in target cell?

Answer 5

Diffuse in across membrane passively as they’re lipid soluble. They then bind to receptors in nucleus or cytoplasm then this complex acts as a transcription factor.

Eg. Cortisol binds to glucocorticoid receptor in cytoplasm. Causing cell growth etc.

Question 6

Compare effects of steroid and protein hormones

Answer 6

Steroid hormones have a more powerful effect as they interact with nucleus. But they are slower acting than peptide hormones.

Question 7

Hormone homeostasis is usually ________________ feedback?

Answer 7

NEGATIVE