Principles of Endocrinology Flashcards
Identify the hormone classifications
> Protein/polypeptides = ACTH
Steroids(cholesterol)
Miscellaneous = other substances e.g. iodine
Describe protein/polypeptide hormones
- Synthesised in rough ER
- Determined by specific gene and mRNA sequence
- Translation = POMC, prohormone larger than the bioactive version
- Transport to Golgi and processed by proteolytic enzymes
- Stored in secretory granules
Describe steroid hormones
- cholesterol from blood through passive diffusion
- Several enzymes produce mature enzymes
- Freely cross membrane without being in secretory granules
Outline protein hormone synthesis
PRODUCED IN ANTERIOR PITUITARY
- Amino acids enter the cytoplasm
- Send signal to initiate transcription
- Translation of specific mRNA to POMC in rough ER
- Transported to Golgi and is processed by proteolytic enzymes
- Release ACTH into pituitary capillary via exocytosis
Outline steroid hormone synthesis
PRODUCED IN ADRENAL CORTICAL CELL
- LDL(low density lipoproteins) enter via endocytosis
- cholesterol is removed and stored as fatty acid esters
- esterase and StAR protein drive cholesterol into the mitochondria (rate limiting step)
- Mature hormone is produced and freely diffuses into blood
Describe hormone transportation
Proteins = more water soluble, circulate freely
Steroid/thyroid = more insoluble, bind to plasma/transport proteins
-only free hormone is bioactive
Albumin (non selective transport = weak)
CBG/TBG/SHBG (high affinity binding sites for specifics)
Outline how available free hormone remains constant
Bound and free hormones are in dynamic equilibrium
=changes in plasma protein or free hormone result in changes in hormone secretion
Recall the different types of membrane receptor and intracellular mechanisms induced by PROTEIN hormones
ACT ON ADRENAL CORTICAL CELL
- ACTH bind to Gs coupled receptor
- Adenylate cyclase activation (convert ATP to cAMP)
- cAMP binds to protein Kinase A
- Activate cholesterol esterase (esters to free cholesterol)
- StAR protein mediates cholesterol transfer from outer to inner mitochondria
Recall the intracellular mechanisms induced by steroid hormones
- Enters by passive diffusion
- Bind to specific glucocorticoid (GC) receptors in cytoplasm
- hormone-receptor complex binds to specific DNA binding sites = changes in transcription rate
- Translation of mRNA to protein in ER
Where are steroid hormones produced?
Adrenal and gonads
What are key features of protein hormones?
- stored in the cells that produce them = wait for signals
- have a short half life
State how the steroid equilibrium can be shifted
> > Steroid uptake into tissues = release of protein bound hormones (restore free hormone levels) (cortisol)
> > Plasma protein increases = formation of protein bound hormones (pregnancy)
Outline the ACTH and cortisol feedback loop
Stress = stimulate anterior pituitary = ACTH release = act on adrenal glands = increase cortisol production = cortisol affects the anterior pituitary and switches off production
Outline the difference between the endocrine and nervous system
ENDOCRINE -chemicals into the blood -hormones -longer affect (seconds to days) NERVOUS -chemicals across synapse -neurotransmitters -effect within milliseconds
