Hormones Flashcards
what is a hormone?
any substance secreted by one cell to regulate another cell
what do hormones do?
they can be delivered by autocrine, paracrine or endocrine (involves circulatory system)
amplification of a signal transduction cascade usually causes biologic response
many hormones can evoke cellular and tissue effects at very low conc.
most hormones effect multiple targets in the body
duration of hormonal action can vary from seconds to days
hormone secreting glands
pineal hypothalamus pituitary thyroid parathyroids thymus adrenals pancreas ovary / testes
hypothalamic control
hypothalamus - endocrine director, it has the highest level of endocrine control
how does the hypothalamus integrate the activities of the nervous and endocrine system
- secretion of regulatory hormones (these control activity of anterior pituitary cells)
- synthesis of hormones (and then transports them to the posterior pituitary via the infundibulum)
- direct neural control (hypothalamic autonomic centres control secretion of adrenaline and noradrenaline by the adrenal medulla)
what is the diurnal control of hormone levels (circadian rhythm)
external cues (light/dark) cause fluctuations in hormone secretions (e.g. cortisol)
hormonal levels are also influenced by the rate at which they are eliminated by the body
example of complementary actions of hormones
sympathetic response and actions of adrenaline, cortisol and glucagon on BG levels
examples of antagonistic actions of hormones
hormonal control of glucose homeostasis
what are the 3 classes that hormones are grouped into based on their structure?
Steroids (e.g. oestrogen, bind to intracellular receptors generally have a prolonged time of action)
Amine-derived (e.g. adrenaline/epinephrine, generally bind to membrane-bound receptors e.g. GCPR)
Peptides and proteins (e.g. oxytocin and ADH, growth hormone and insulin)
what are steroid hormones?
lipids derived from cholesterol
amount is controlled by the synthesis rate
once secreted, synthesised steroids are NOT stored
they are hydrophobic/lipophilic and are mostly (90%) transported in the blood plasma by binding to carrier proteins
what is the 2 step process initiated when steroid hormones pass through the plasma membrane?
- formation of activated hormone-receptor complex within the cell
- complex binds to DNA and activates specific genes (gene activation leads to production of key proteins)
cortisol
secreted from the adrenal cortex involved in mediating stress responses
testosterone and oestradiol
secreted form the gonads and placenta, responsible for male and female characteristics
what are amine hormones?
derived from amino acids (e.g. tyrosine)
secreted from the thyroid and adrenal medulla
they bind to membrane bound receptors to evoke cellular responses
catecholamine amine hormones
hydrophilic, transported unbound or ‘free’ in blood plasma
