Overview and Hormonal Mechanisms Flashcards
What is TSH? Where is it released from and where does it act?
Thyroid-Stimulating Hormone
Released from anterior pituitary gland
Acts on thyroid gland
What are T3 and T4 and where do they act?
Thyroid hormones, act on practically all cells of the body
What is autocrine signalling? Give an example of an autocrine signal
Substance released by cell comes back and acts on cell that released it e.g. prostaglandins
What is paracrine signalling? Give an example of a paracrine signal
Substance travels a short distance and targets neighbouring cell e.g. somatostatin inhibits release of insulin and glucagon from islets of Langerhans
What is another name for somatostatin?
GHIH (growth hormone-inhibiting hormone)
How are neurohormones produced, stored, and released? Give an example of neurohormones in action.
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)
Which gland secretes oxytocin and ADH?
Posterior pituitary gland
What is another name for ADH?
Arginine vasopressin
What are steroid hormones derived from? Give a few examples of steroid hormones
Derived from cholesterol
E.g. cortisol, aldosterone, sex hormones
What are catecholamines and what are they derived from?
. Adrenaline with a bit of noradrenaline and dopamine
. Derived from aromatic ring of tyrosine
Give a couple of examples of tyrosine-derived hormones
Catecholamines and thyroid hormones (e.g. T3 and T4)
Compare the solubility of peptide and steroid hormones
Peptide hormones are hydrophilic (water-soluble), steroid hormones are lipophilic (fat soluble)
What is a pre-prohormone and what does it do?
. 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
How is a pre-prohormone converted to a pro-hormone?
The ‘pre’ signal is cleaved
By what process do peptide hormones leave the cell?
Exocytosis (because hydrophilic, need vesicle to pass through lipid bilayer)
How is steroid hormone synthesis different from peptide hormone synthesis?
. 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
Compare the transport mechanisms of peptide and steroid hormones to their target cells.
. 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
Compare the half-life of peptide hormones vs. steroid and thyroid hormones
. 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)
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?
. 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
How do steroid hormones act on target cells?
. 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))
Which hormones does the anterior pituitary release?
FSH, LH, GRH, ACTH, prolactin
stress, growth, reproduction, lactation
Which hormones does the posterior pituitary release?
Oxytocin and ADH
