Endocrine system overview Flashcards
(27 cards)
How is an endocrine gland different to an exocrine gland?
Endocrine glands are ductless and release hormones into the blood. Exocrine glands excrete substances into a duct where they are either released from the body (eg as sweat) or enter the lumen of another organ.
What are the 3 major classes of hormones?
steroid
amine
peptide/protein
What are amine hormones derived from?
tyrosine
Hormones secreted by adrenal cortex vs adrenal medulla?
Cortex>aldosterone and cortisol (steroids)
Medulla>epinephrine and norepinephrine (catecholamines)
Examples of amine hormones
Thyroid hormones
epinephrine and norepinephrine
Examples of peptide/protein hormones
insulin, glucagon
Processing of peptide hormones
Synthesised as protein preprohormones on ribosomes then cleaved into prohormones in RER
packaged into secretory vesicles
cleaved into active hormones
secreted into bloodstream
Processing and maturation of insulin
signal sequence cleaved from preproinsulin then proinsulin cleaved to form mature insulin and a c peptide
What are steroid hormones derived from?
cholesterol
Where are steroid hormones produced from?
adrenal cortex and gonads
properties of steroid hormones
ring structures
very hydrophobic
Which mechanism mainly stimulated production of steroid hormones?
adenylyl cyclase and cAMP pathway via protein kinase A
hormone from anterior pituitary gland
Which hormone type needs carrier proteins to transport round the bloodstream?
eg of carrier protein
steroid hormones
eg albumin
Factors influencing hormone concentration in the plasma
secretion from endocrine gland>dependent on stimulus
metabolism and excretion of hormones
Whether they circulate free or bound to plasma proteins
plasma volume changes and redistribution
binding of target cells
Major sites of metabolic inactivation
liver and kidneys
What are tropic hormones?
hormones that induce the secretion of other hormones
3 inputs that control hormone secretion
ions or nutrients
neurotransmitters
hormones
What is the adrenal medulla stimulated by
sympathetic preganglionic fibres
Are thyroid hormones free or bound to proteins?
bound to proteins
Most common signalling mechanism by steroid and thyroid hormones/
binding to intracellular receptors that alter gene expression
3 main second messengers
cAMP
IP3 (inosine triphosphate)
DAG (diacylglycerol)
Downregulation
when concentration of hormones in blood is low, number of receptors is low
prolonged exposure to low concs can cause upregulation to increase target cell responsiveness
Upregulation
When the blood concertation increases the number of receptors increases too
prolonged exposure to high concs can cause down regulation to prevent overstimulation
Hyposecretion
too little hormones secreted
