the endocrine system Flashcards
List the three chemical classifications of vertebrate hormones and the properties which describe them
1) Peptide and protein hormones = specific aminoacids arranged in a chain of varying length e.g. insulin
2) The amines = derived from amino acid tyrosine and include all hormones secreted by thyroid gland and adrenal medulla
3) Steroids= neutral lipids derived from cholesterol, insects cant synthesize the core steroid molecule so must ingest suitable precursors in order to synthesize their primary steroid
How do hormones produce their effects on a target cell
1) membrane receptors= hydrophilic hormones cant pass through the membrane so bind to specific receptors located on the outer plasma membrane which change conformation allowing passage or cause the release of secondary messengers
2) internal receptors= lipophilic steroids and thyroid hormones easily pass the membrane and bind with receptors inside the cell
what factors determine the plasma concentration of a hormone
if it is hydrophilic or lipophilic
1) Hydrophilic, lipophobic peptide hormones are transported in dissolved plasma or bound to specific carrier proteins
2) lipophilic steroids and thyroid hormones are hydrophobic so cant dissolve in plasma so circulate bound to plasma proteins
what is the difference between tropic and non-tropic hormones
tropic = act indirectly by stimulating glands to release other specific hormones
non= act directly upon tissues and cellular target sites
what are the different types of signalling
1) Endocrine= signalling which occurs between distant cells and is mediated by hormones released from specific endocrine cells
2) Paracrine = type of cell signalling in which cells secrete a chemical which affects the behaviour of a nearby cell
3) autocrine = a form of cell signalling in which a cell secretes a hormone that binds to autocrine receptors on the same cell leading to changes in the cell
what is the difference between neurohormones vs neurotransmitters
NT= only have one action at a small volume where release occurs
NH= can have a wide variety of actions across many targets, possibly away from the site of synthesis
how are peptide hormones synthesised
by the same method of any other protein which is to be exported
large precursor proteins synthesised in ribosomes> processed in ER> packaged into secretory granules by Golgi complex>stored>exocytosis
outline the synthesis of steroid hormones
1) cholesterol cant alwasy be synthesised so must be obtained through diet but some can
2) requires a series of enzymic reactions that modify the type and position of side groups attached to the cholesterol framework
3) cant be stored after formation so once formed they immediately diffuse through the plasma membrane to enter circulatory system where they sometimes undergo further conversion
what are the general mechanisms which regulate hormone secretion rates
1) Negative feedback= output counteracts a change in input
2) Neuroendocrine reflexes = purpose is to produce a sudden increase in hormone secretion like a reset mechanism in response to specific stimuli
3) circadian and other biological rhythms= although negative control regulates hormone secretion rates they still fluctuate as a function of time characterized by repetitive oscillations in gene expression which correspond with changes in physiology, metabolism and behaviour
what hormone effects proportional to
- number of receptors
- post binding regulation
- hormone concentration
what are the three ways in which hormones interact
1) permissiveness- presence of one hormone increases the activity of another e.g. thyroid hormone increases epinephrine receptors allowing increased activity of epinephrine
2) Synergism= complementary action so that their combined activities are greater than separate activities e.g. glucagon and epinephrine increase glucose levels
3) Antagonism= one hormone opposes the action of another e.g. insulin and glucagon have opposing effects on glucose
what is the role of melatonin in determining the onset of the breeding season
helps to keep body in inherent circadian rhythms in synchrony with the light dark cycle, secretion increases ten fold in darkness
short day breeders rely on steadily increasing concentrations where as long day breeders rely on decreasing levels to trigger reproduction
how does the hypothalamus and posterior pituitary gland form a neurosecretory system
release of hormones from posterior controlled by hypothalamus as it connects by a neutral pathway and when appropriate releases into the blood vasopressin (increases permeability of DT and collecting duct and causes vasoconstriction) and oxytocin (stimulates uterine contractions and milk ejection during breast feeding) synthesised in the hypothalamus
how does the hypothalamus and anterior pituitary gland form a neurosecretory system
also controlled by the hypothalamus connected by a vascular link but hormones synthesised in the anterior gland not hypothalamus producing 6 peptide hormones
what are the central endocrine glands of vertebrate
hypothalamus= part of the brain aka the command centre
pituitary glands = unity to release hormones essential for maintaining water balance and reproduction
pineal gland
