introduction to endorinology Flashcards
exocrine
epithelial lining forms ducts
endocrine
sheets of cells secrete hormones into the bloodstream
how is communication between glands & other tissues achieved?
but the secretion of a hormone into the blood stream & transport to a target site
how is specificity of signalling achieved?
- chemically distinct hormones
- specific receptors for each hormone
- distinct distribution of receptors across target cells
hypothalamus
highest level of the endocrine system, major centre of pituitary control
parathyroid
calcium
adrenal gland
aldosterone
testes
steroid precursors & testosterone
thyroid
thyroxine
what are the 3 main classes of chemical natural hormones?
- glycoproteins & peptides
- steroids
- tyrosine & tryptophan derivatives
which is the most diverse class of the chemical natural hormones?
glycoproteins & peptide
what does the glycoprotein & peptides class encompass?
amino acid chains of variable length, can be simple or contain disulphide bonds or be multiple chains
give an example of the glycoproteins & peptides
oxytocin
insulin
what are steroids derived from?
cholesterol
give an example of tyrosine & tryptophan derivatives
adrenaline
thyroid hormones
melatonin
describe the synthesis, storage and attitude to water of amines?
pre-synthesised stored in vesicles
hydrophilic
when are amines released from their vesicles?
in response to stimuli by calcium dependent exocytosis
how are amines mainly transported?
“free” in plasma
what’s special about the vesicles that store hormones?
usually protected from effects of that hormone
describe the synthesis, storage and attitude to water of peptides & proteins?
pre-synthesised usually from a longer precursor & stored in vesicles, hydrophilic
when are peptides & proteins usually released from their vesicle?
in response to stimuli by calcium dependant exocytosis
how are peptides & proteins transported?
“free” in plasma
what is the major trigger for the release of insulin?
the sensing of glucose in the intracellular space between beta cells of the pancreas
describe the synthesis, storage and attitude to water of steroids?
synthesised & secreted upon demand, hydrophobic
what do the stimuli of steroid synthesis increase?
increase cellular uptake & availability of cholesterol & increase the rate of conversion of cholesterol to pregnenolone
what is the rate limiting step of steroid synthesis?
the conversion of cholesterol to pregnenolone
how are steroids transported?
mainly found to plasma proteins
are steroids active when bound to plasma proteins?
no, only “free” is biologically active
how soluble are steroids & thyroxine in plasma?
relatively insoluble
what do carrier proteins do for steroids & thyroxine?
increase the amount transported in blood
prevent rapid excretion
how do plasma proteins prevent rapid excretion of steroids & thyroxine?
prevent filtration at the kidney
what does cortisol-binding globulin do?
binds cortisol in a selective manner & some aldosterone
what does thyroxin-binding globulin do?
binds thyroxine selectively & some triiodothyronine
what does sex steroid-binding globulin do?
binds manly testosterone & estradiol
what does albumin do in terms of being a carrier protein?
binds many steroids & thyroxine
what does transthyretin do?
binds thyroxine & some steroids
why do proteins & peptides not require carrier proteins for transport?
they are soluble in plasma
what do carrier proteins do altho helps maintain relatively constant concentrations of free lipophilic hormone in the blood?
act as buffer & reservoir, free & bound hormone are in equilibrium
can free or bound hormone cross the capillary wall to activate receptors in target tissue?
only free
how are surges in hormone secretion buffered?
by binding to carriers, free concentration then doesn’t rise abruptly
how is free hormone removed from plasma & what is it replaced by?
removed by elimination & replaced by bound hormone dissociating from carrier protein
what is the primary determinant of plasma concentration?
rate of secretion
what does negative feedback do?
maintains plasma concentration at a set level
what does tropic mean?
a hormone that acts upon another endocrine gland to regulate its secretion of hormone
what does a neuroendocrine mechanism do?
elicits sudden burst in secretion to meet a specific stimulus
what does diurnal (circadian) rhythm mean?
secretion rate fluctuates up & down as a function of time, entrained to external cues
how does elimination occur?
several routes
where does metabolism tend to take place?
liver
where does excretion tend to take place?
kidneys
how can the plasma concentration of a hormone be described in terms of secretion & elimination
secretion - elimination
when should cortisol levels be checked if a deficiency is suspected?
9am, should be at optimum level
when should cortisol levels be checked if an excess (cushing’s syndrome) is suspected?
midnight, should be very low
name some hormones other than cortisol that exhibit diurnal variation
growth hormone
testosterone
when are testosterone levels highest in men?
in the morning
what are the 3 types of hormone receptor?
- G-protein coupled receptors (GPCR)
- receptor kinases
- nuclear receptors
which of the 3 types of hormone receptor is found intracellularly?
nuclear receptors
how are nuclear receptors reached by hormones?
the ligand of the hormone is lipophilic so can diffuse across the plasma membrane of cells
what are GPCRs activated by?
amines & some proteins/peptides
which GPCRs are involved in major signalling pathways?
Gs
Gi
Gq
what are receptor kinases activated by?
some proteins/peptides
what are nuclear receptors divided into?
class 1 class 2 hybrid class
what are class 1 nuclear receptors activated by?
many steroid hormones
in the absence of activating ligand, where are class 1 nuclear receptors mainly located?
in the cytoplasm bound to inhibitory heat shock proteins
where do class 1 nuclear receptors move to in the presence of an activating ligand?
the nucleus
where are class 2 nuclear receptors found?
constitutively present in the nucleus
what are class 2 nuclear receptors activated by?
mostly by lipids
what are hybrid class nuclear receptors activated by?
thyroid hormone & other symptoms
hybrid class nuclear receptors function is similar to which other class?
class 1
