Intro to endocrinology Flashcards
Endocrine meaning
Hormone’s action on target cells at a distance from source
Paracrine meaning
Hormone’s action on nearby target cells
Autocrine meaning
Hormone has effect on its own immediate source
Endocrine system vs Nervous system
Release of chemical in bloodstream vs across synapse
Effect on many target cells spread throughout body vs restricted to target cells actually innervated
Effect takes place over longer time span than nervous
Steroid hormones
Transport across cell membrane?
Stored?
Precursor= always cholesterol
Passive diffusion
Once produced, can cross membrane without needing secretory granules
Protein hormone synthesis
Location?
What’s required?
What happens in cells?
Amino acids need to be transferred from blood from diet by transporter proteins
Signal to DNA which initiates transcription of relevant mRNA to produce pro-hormone
Pro-hormone cycled into Golgi apparatus that packages hormone with proteolytic enzymes that can cleave pro-hormone into active hormone
Active hormone packaged into vesicles in cytoplasm near cell surface
Released by exocytosis
Pro-hormone of ACTH
POMC produced in anterior pituitary gland
Which vessels are pituitary hormones secreted into?
Pituitary capillary
Steroid hormone synthesis
What do you need?
What happens in cell?
Need cholesterol from LDL
LDL receptors transports them into cell+ cholesterol removed from LDL and stored as fatty acid esters (distinguishable as clear droplets in cell)
Esterase liberates cholesterol from fatty acid esters+ cholesterol transported to mitochondria using StAR protein (Steroidogenic Acute Regulatory Protein) because mitochondria has enzymes required
Pathway followed to modify cholesterol+ make enzyme
Hormone= lipid soluble, hormone not stored in cell, directly diffuse out into bloodstream
What is often the regulating step in steroid hormone synthesis?
Mitochondrial enzymes
Protein hormone transport
Half-life?
Removed?
When is it secreted?
Short half-life
Removed quickly
Secreted as required
Steroid hormone transport
Regulation of amount available?
Bind to specific plasma proteins, storage= in blood
Plasma proteins too big= hormone can’t get out of blood
Pool of free hormone= Active Pool, can move in and out of cells
Hormone+ Plasma Protein ⇌ Protein Bound Hormone, dynamic equilibrium, ensures free hormone available to tissues= constant
Greater binding capacity of plasma proteins= slower clearance rate of hormone
Protein hormone signalling- ACTH example
Leads to what?
Biological response depends on what?
Binds to extracellular target= high affinity+ highly specific G-protein coupled receptor mechanism= activates Adenylate cyclase protein on cell surface which converts ATP to cAMP= increase cAMP
Leads to steroid hormone synthesis (activates PKA which activates esterase+ StAR protein)= modification of cell function
No. of receptors on target cell, conc. of hormone in circulation, affinity of hormone-receptor
Steroid hormone signalling- Cortisol example
Property with steroid hormone signalling?
Receptors?
Hormone enters cell by passive diffusion
Receptors= Intra-nuclear (adrenal+ gonadal)
Binds to Glucocorticoid Receptors (GR)= go into nucleus+ bind to DNA binding sites and upregulate/ downregulate transcription+ protein synthesis
Elimination of hormone+ re-establishment of receptor
More powerful but slower
Steroid hormone homeostasis
E.g. cortisol
Feedback system:
Hormone diffuses back into gland where it is produced
Cortisol → anterior pituitary gland →ACTH → Adrenal gland →cortisol again
