Overview and Hormonal Mechanisms

Question 1

What is TSH? Where is it released from and where does it act?

Answer 1

Thyroid-Stimulating Hormone
Released from anterior pituitary gland
Acts on thyroid gland

Question 2

What are T3 and T4 and where do they act?

Answer 2

Thyroid hormones, act on practically all cells of the body

Question 3

What is autocrine signalling? Give an example of an autocrine signal

Answer 3

Substance released by cell comes back and acts on cell that released it e.g. prostaglandins

Question 4

What is paracrine signalling? Give an example of a paracrine signal

Answer 4

Substance travels a short distance and targets neighbouring cell e.g. somatostatin inhibits release of insulin and glucagon from islets of Langerhans

Question 5

What is another name for somatostatin?

Answer 5

GHIH (growth hormone-inhibiting hormone)

Question 6

How are neurohormones produced, stored, and released? Give an example of neurohormones in action.

Answer 6

Hormones produced by nerve cells, stored in axon terminus, then released into circulation to act on target cell e.g. oxytocin and ADH (arginine vasopressin)

Question 7

Which gland secretes oxytocin and ADH?

Answer 7

Posterior pituitary gland

Question 8

What is another name for ADH?

Answer 8

Arginine vasopressin

Question 9

What are steroid hormones derived from? Give a few examples of steroid hormones

Answer 9

Derived from cholesterol

E.g. cortisol, aldosterone, sex hormones

Question 10

What are catecholamines and what are they derived from?

Answer 10

. Adrenaline with a bit of noradrenaline and dopamine

. Derived from aromatic ring of tyrosine

Question 11

Give a couple of examples of tyrosine-derived hormones

Answer 11

Catecholamines and thyroid hormones (e.g. T3 and T4)

Question 12

Compare the solubility of peptide and steroid hormones

Answer 12

Peptide hormones are hydrophilic (water-soluble), steroid hormones are lipophilic (fat soluble)

Question 13

What is a pre-prohormone and what does it do?

Answer 13

. Hydrophobic signal peptide present in synthesis of peptide hormones
. Lets cell know that protein needs further processing (post-translation modification e.g. more folding, add disulphide bridges, glycosylation etc.) before it’s ready to leave cell

Question 14

How is a pre-prohormone converted to a pro-hormone?

Answer 14

The ‘pre’ signal is cleaved

Question 15

By what process do peptide hormones leave the cell?

Answer 15

Exocytosis (because hydrophilic, need vesicle to pass through lipid bilayer)

Question 16

How is steroid hormone synthesis different from peptide hormone synthesis?

Answer 16

. Steroid hormones derived from cholesterol so no DNA involved, just cholesterol and biosynthetic enzymes
. Steroid hormone lipophilic so not stored (unlike peptide hormone which is stored as prohormone until needed, then released as hormone via exocytosis)
- Steroid hormone just passes through lipid membrane by simple diffusion into blood

Question 17

Compare the transport mechanisms of peptide and steroid hormones to their target cells.

Answer 17

. Steroid (and thyroid) hormones lipophilic so don’t dissolve in blood, therefore bound by carrier plasma protein to transport them
. Peptide hormones hydrophilic so just dissolve in plasma and carried to target cells via bloodstream

Question 18

Compare the half-life of peptide hormones vs. steroid and thyroid hormones

Answer 18

. Peptide hormones (hydrophilic) circulate freely in blood, so free to act on target tissues. Prone to degradation by enzymes in blood e.g. proteases, so short half life (couple of minutes)
. Steroid and thyroid hormones (lipophilic, protein-bound) are protected from degradation so have reservoir to act on target tissues over longer period of time= longer half life (hours-days)

Question 19

Because peptide hormones are hydrophilic, they can’t just cross the lipid bilayer into target cells. So how do they act on target cells? Can you give examples?

Answer 19

. Use second messenger pathways
. Glucagon acts via GPCRs, adenylyl cyclase, cAMP pathway –> signal transduction to have bigger effect
. Insulin acts via tyrosine kinase –> signal transduction to have bigger effect

Question 20

How do steroid hormones act on target cells?

Answer 20

. Lipophilic so can diffuse into cells and bind to intracellular receptor, or can bind to membrane receptors
. Receptors activate and act as hormone-regulated transcription factors
. Bind to promoter of genes to affect transcription of gene and change protein production and levels
. Takes a long time to have effect (hours-days))

Question 21

Which hormones does the anterior pituitary release?

Answer 21

FSH, LH, GRH, ACTH, prolactin

stress, growth, reproduction, lactation

Question 22

Which hormones does the posterior pituitary release?

Answer 22

Oxytocin and ADH