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What is the endocrine system?

A system that integrates and controls organ function via the secretion of hormones from cells, tissues or glands which are then carried in the blood to target organs


Endocrine hormones should not be confused with what other types of hormones?

Paracrine - acting on local sites
Autocrine - acting within the same cell
Exocrine - secreted into ducts


How do hormones enact specific responses in different target tissues?

Specific receptor (either GPCR or tyrosine kinase coupled)


What is the definition of a neuroendocrine system?

A system where the nervous system and endocrine system combine e.g. hypothalamic-posterior pituitary axis


What three types of endocrine hormones are there?

1. Peptide hormone
2. Steroid hormone
3. Amine hormone


What can be said about the solubility of peptide hormones?



How does the solubility of peptide hormones affect their storage?

Can be bound in vesicles


How are peptide hormones synthesised?

Initial protein produced by ribosomes as large, inactive preprohormones.

Packed into vesicles by the Golgi apparatus along with proteolytic enzymes which convert the preproxhormones into prohormones ready for secretion.


When a prohormone is cleaved, it leaves fragments, how are these clinically relevant?

Measuring the concentration of the fragments may be helpful diagnostically (e.g. C-peptide as a fragment of endogenous insulin)


How are steroid hormones produced?

As needed, due to their lipophilic nature they cannot be contained in cell membranes.


How do steroid hormones travel in the body?

Bound in complex with proteins like albumin.


What effect does the albumin-hormones complex have on the lifespan of a hormone?

Protects it from enzymatic damage and extends their life (60-90 mins vs 2 mins for amine hormones)


What organs secrete steroid hormones?

Gonads, Placenta, kidneys, adrenal cortex


How do steroid hormones bring about a response in target tissues?

Intracellular receptors have a genomic effect


What are all steroid hormones derived from?



What are all amine hormones derived from?

Tryptophan or tyrosine


What can be said about the lifespan of catecholamine and peptide hormones?

Short-lived and excreted easily


What can be said about the lifespan of steroid and thyroid hormones?

Take a long time to excrete as they are protein bound


What mechanisms control the secretion of hormones?

1. Negative feedback
2. Neural feedback
3. Up-regulation/down-regulation
4. Permissive effects
5. Antagonistic effects


What is up-regulation?

After long exposure to low hormone concentrations, up-regulation occurs and increases the number of hormone receptors on the target tissue (increasing its sensitivity)


What is a permissive effect?

The presence of one hormones enhances the effect of another (e.g. cortisol has a permissive effect on epinephrine)