endocrine cell signalling Flashcards
describe autocrine regulation of the endocrine system
chemicals released from the cell binds to target receptors on the same cell. this is a negative feedback loop
describe paracrine regulation of the endocrine system
chemicals released from the cells bind to receptors on adjacent cells.
describe endocrine regulation - where the chemicals are transported
chemicals released form secretory cells are usually transported via the circulatory system to reach target cells to create a cellular response
what is the classical definition of a hormone?
Any substance elaborated by one cell to regulate another cell. May be delivered by autocrine, paracrine, or endocrine routes
how do hormones create a biological response?
generally the result of an amplification of a signal transduction cascade
which endocrine gland provides the highest level of endocrine control?
hypothalamus
how does the hypothalamus integrate activities of nervous & endocrine systems?
1) Secretion of regulatory hormones which control activity of anterior pituitary cells
2) Synthesises hormones & transports them to the posterior pituitary via the infundibulum
3) Direct neural control function: hypothalamic autonomic centres control secretion of Adrenaline & Noradrenaline by the adrenal medulla.
what time is there a cortisol spike at?
around 9am
how does diurnal control of hormone levels work?
responds to external cues e.g. light and dark causing fluctuations, and are influenced by rate of elimination in the body
what are the 3 classes of hormones based on structure?
-steroid hormones (cholesterol backbone)
-amine-derived
-peptides
what are examples of steroid hormones?
cortisol, oestrogen & testosterone
what is an example of an amine-derived hormone?
adrenaline
what are examples of peptide hormones?
oxytocin, growth hormone, insulin
describe steroid hormones
Lipids derived from cholesterol
Synthesis rate controls amounts
Once synthesised steroids are secreted, they are not stored
Steroids are hydrophobic & lipophilic and are transported in blood plasma by binding to carrier proteins (~90%). ‘Free’ (or unbound) steroids are biologically active.
where is cortisol secreted form and what does it do?
secreted from adrenal cortex plays a role in mediating stress responses
how do steroid hormones work?
pass through plasma membrane initiating 2 step process:
1) Activated hormone-receptor complex forms within the cell
2) The complex binds to DNA & activates specific genes –> Gene activation leads to production of key proteins
describe amine hormones
-Catecholamine Amine hormones are hydrophilic and are transported unbound or ‘free’ in blood plasma
-Thyroid amine hormones are bound to carrier proteins
-Secreted from thyroid & adrenal medulla
-Amines like adrenaline (epinephrine) stored as vesicles in the cytoplasm until needed
-Amine hormones bind to membrane bound receptors to evoke cellular responses
describe peptide hormones
-Peptide hormones are hydrophilic and are transported unbound or ‘free’ in blood plasma
-Large majority of hormones produced
-Synthesised as precursor molecules and stored in secretory vesicles
-Different end hormones can be made by cleaving a common precursor with a different enzyme
where are peptide hormones secreted from?
pituitary , parathyroid, heart, stomach, liver, kidneys
what is the structure of peptide hormones?
May be composed of a ring structure due to disulfide bonds as in the case of somatostatin
may be composed of 2 chains e.g. insulin held together by disulfide bonds
what do cortisol and thyroxine bind to in the blood?
Cortisol-binding globulin (CBG) – binds cortisol in a selective manner (also some aldosterone)
Thyroxine-binding globulin (TBG) – binds thyroxine (T4) selectively [also some triiodothyronine (T3)]
