Hormone structure and action Flashcards
forms of chem communication
autocrine
neurocrine
paracrine
endocrine
pheromone
allomone
autocrine comm
Chemical released by cell affects its own activity
neurocrine (synaptic) comm
Chemical released by neuron diffuses across synaptic cleft and affects postsynaptic membrane
paracrine comm
Chemical released into extracellular env and affects nearby target cells
endocrine (hormone) comm
Chemical released into bloodstream and selectively affects (distant) organs
pheromone comm
Chemical released into external env and affects conspecifics (members of same species)
allomone comm
Chemical released into external env and affects heterospecifics (members of other species)
what are hormones
Bioregulators of endocrine system
Secreted by specialised cells directly into the blood
Selectively act on target cells
chem messengers
3 main types of hormones
protein (peptide)
amine
steroid
transmission of endocrine signals
target cell has to have right type of receptor
protein hormones
Chain of AAs
Peptide hormones have short chain
types of protein hormones
Oxytocin
Vasopressin
Prolactin
Insulin
Glucagon
Growth hormone (GH)
Thyroid-stimulating hormone (TSH)
Luteinising hormone (LH)
Follicle-stimulating hormone (FSH)
Releasing hormones, inc. corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH)
Most released from hypothalamus
amine hormones
Modified single AA (a.k.a. monoamine hormones)
Smaller and simpler than protein hormones
types of amine hormones
Adrenaline (epinephrine)
Noradrenaline (norepinephrine)
Thyroid hormones
Melatonin
action of protein and amine hormones
don’t travel into cell
Bind to specific receptors on outside of cells
Act ‘rapidly’ (secs-mins)
Can have prolonged effects
Sensitivity can be altered by increasing (upregulating)/decreasing (downregulating) numbers of receptors on cell
Stored in vesicles and secreted on demand
steroid hormones
Derived from cholesterol
Made from 4 interconnected carbon rings
Soluble in lipids - dissolve in fats - imp consequences - cross cell membrane
types of steroid hormones
Oestrogen
Progestins
Androgens (e.g. testosterone)
Glucocorticoids
action of steroid hormones
Act on specific receptors inside cells
Act ‘slowly’ (hrs)
Gave long-lasting effects via transcription of DNA
Sensitivity can be altered by presence/absence of co-factors necessary for cells to respond
Cannot be stored - must be synthesised on demand
endocrine glands/organs
Exocrine - release substances onto surface - sweat, salivary, tear ducts
heavily vascularised with blood vessels
follicles of endocrine cells secrete hormones into lumen
hormone transported into thin-walled capillary and flows into bloodstream - 1 cell thick
ductless - no ducts leading to bloodstream
endocrine system subdivisions
Endocrine - typically respond to levels of chems in blood - not directly controlled by nervous system
what controls hormone production?
Needs to be constantly managed
Feedback loops play key role
Usually involved neg feedback: high levels hormone inhibit further production —> maintains homeostasis
Sometimes involves pos feedback
E.g. oxytocin secretion in milk letdown reflex
key hormone production pathways
Autocrine feedback
Target cell feedback
Brain reg
Brain and pituitary reg
autocrine feedback example
prostaglandins - inhibit acid secretion - e.g. HCl
target cell feedback example
insulin pathway - reg of blood sugar
brain regulation example
alarm response
brain and pituitary regulation example
temp regulation
the pituitary gland
Consists of 2 parts, do diff things:
- Anterior pituitary/adenohypophysis
- Posterior pituitary/neurophypophysis
how do hormones act within the body?
ST effects - e.g. oxytocin milk letdown reflex
LT effects - e.g. growth hormone: bone growth
ST effects example
Oxytocin: milk letdown reflex
LT effects example
Growth hormone (GH/somatotropin): reg of bone growth
Some LT effects can be reversed
e.g. psychosocial dwarfism
organisms use several types of chem communication
Hormones just one variety of modes chem communication between cells
Ntms cross tiny gap during synaptic transmission
Autocrine signal and paracrine signals
Pheromones and allomones
hormonal actions can be organised according to general principles
Unlike neuronal signalling, hormones spread more slowly and act throughout the body
Some hormones act on receptors in wide variety of cells and can coord influences on activities of most cells in the body
Other hormones have receptors in only certain special cells/organs
peptide and amine hormones
Bind to receptor molecules at surface of target cell membrane and activate second-messenger molecules inside cell
Steroid hormones pass through membrane and bind to receptor molecules inside cell, ultimately regulating gene expression
feedback control mechanisms regulate the secretion of hormones
Neg feedback system monitors and controls rate of secretion of each hormone
Hormone acts on target cells, leading them to change amount of substance they release
In simplest case, hormone also acts on endocrine cells, and this regulates further output of endocrine gland
Other hormones controlled by releasing hormone from hypothalamus that regulates release of anterior pituitary tropic hormone, which in turn controls secretion by endocrine gland
Endocrine gland hormone then provides neg feedback to hypothalamus and pituitary
the posterior pituitary
Posterior pituitary hormones manufactured by neuroendocrine cells in supraoptic and paraventricular nuclei of hypothalamus, which send axons down pituitary stalk to terminate on caps there
When neuroendocrine cells stimulated to produce AP, release oxytocin/vasopressin into circulation
hypothalamic releasing hormones and anterior pituitary
Anterior pituitary hormones controlled by overlying hypothalamus
Hypothalamic neuroendocrine cells send axons to median eminence to secrete releasing hormones into hypophyseal portal system, which transports releasing hormones to pituitary
Diff hypothalamic releasing hormones either stimulate/inhibit anterior pituitary cells that secrete tropic hormones
the gonads produce steroid hormones, reg production
Hypothalamic cells secrete gonadotropin-releasing hormone (GnRH) into hypophyseal portal system to stimulate anterior pituitary cells to release follicle-stimulating hormone (FSH) and luteinising hormone (LH), which stimulates the gonads to release steroid hormones
The principle gonadal steroids in males = androgens such as testosterone, while ovaries release oestrogen such as estradiol and progestins such as progesterone
hormonal and neural systems interact to produce integrated responses
Many behaviours require coord of neural and hormonal components
Messages may be transmitted in body via neural-neural, neural-endocrine, endocrine-endocrine/endocrine-neural links
Experience affects hormone secretion, and hormones affect behaviour and therefore future experiences
hormones are chemical messengers that are
Produced in endocrine cells
Secreted into the bloodstream
Transported by the bloodstream
Act on specific target cells - typically some distance away from where produced
Anterior pituitary/adenohypophysis
Synthesises and secretes hormones
Posterior pituitary/neurophypophysis
Stores and secretes only (no synthesis)
autocrine signal
acts upon cell that released it
paracrine signal
act on nearby cells
pheromones
chem signals to indvs of same species
allomones
communicate with indvs of other species
