the endocrine system Flashcards
what is the endocrine system
glands or organs that secrete hormones (chemical messengers), glands are typically ductless (e.g. pituitary), other organs can release hormones (pancreas), secrete hormones into the blood system, excite or inhibits activity of other organ or tissue
what are target organ cell
what hormones are directed to
other systems that produce hormones
stomach- gastrin, small intestine- peptides secretin, kidney- erythropoietin
main functions of endocrine system
sodium and water balance- blood volume, calcium and phosphate balance, energy balance and control of macronutrient (lipid, glucose) utilisation and storage, responses to stress, reproduction, sexual development and growth
categories of hormones- non-steroidal hormones
attach to specefic membrane receptors and work by secondary messenger mechanism. they are whole proteins, with shorter chains of amino acids
how do non-steroidal hormones work
work as lock and key concept. once hormones attach, chemical reactions occur, activate molecules within the cell to do things (secondary messengers). these cause further reactions and may secrete more hormones
categories of hormones- steroidal hormones
small lipid soluble hormone can pass through the cell membrane of the target organ. the chemical structures affects where it can travel within the body.
how do steroidal hormones work
once inside they pass through cytoplasm and enter nucleus, then bind to receptor in nucleus, forming hormone receptor complex- cause DNA of cell to do specific things (alters activity). usually much slower
non-steirod hormones- protein or peptide hormones
majority of hormones, vary in size, they are synthesised as prrehormones, in which they undergo transformation at required time, stored I secretary glands and are exocystose from the cell
e.g. insulin, glucagon
non-steirod hormones- amino acid derived hormones
synthesised from other amino acids. e.g. adrenaline and noradrenaline
steroidal hormones- cholesterol
derived from cholesterol and synthesised in adrenal cortex, glands and placenta
lipid soluble (able to cross cell membrane) require binding proteins in blood
e.g. testosterone, oestrogen
pathways to hormone effect- paracrine pathway
hormones produced in a cell, secreted, act directly on nearby receptive cells, e.g. histamine
pathways to hormone effect- autocrine pathway
cell is able to produce hormone and every effect on itself, receptor cells are also secretory cells
pathways to hormone effect- endocrine (AKA telecrine) pathway
hormones produce in a cell , secreted and travel through blood vessels to distant cells, attach to receptor, act on cell
pathways to hormone effect- synaptic pathway
hormones produced within neurone, secreted and travel along axon to synapse where they are released and take up by nearby neurone with appropriate receptors to exert an effect
pathways to hormone effect- neuroendocrine pathway
hormones produced in neurone, secreted along axon to synapse, released, taken up into vascular system, travel to distant cells with appropriate receptors to exert an effect
the hypothalamus
contains neurones that synthesise inhibiting and releasing hormones to act on pituitary gland. common releasing hormones from the hypothalamus- Growth hormone RH, thyrotropin RH, (thyroid stimulating hormone), corticotrophin (triggers release of cortical), gonadotropin RH- produce reproductive hormones, all stimulate pituitary gland
common releasing hormones from hypothalamus
Growth hormone RH, thyrotropin RH, (thyroid stimulating hormone), corticotrophin (triggers release of cortical), gonadotropin RH- produce reproductive hormones, all stimulate pituitary gland
pituitary gland
responds to hypothalamic triggers and acts accordingly
what are feedback mechanisms
what triggers hypothalamus or pituitary to initiate a hormone release? all provide input to the hypothalamus to regulate bodily functions. this occurs through negative and positive feedback loops
examples of feedback mechanisms
neurotransmitters, injury, release of chemical mediators after injury, neuroendocrine signals
regulation of hormone secretion- negative feedback loop
most common mechanism. affected by environmental and body temperature, stress, nutrition and precedes of specific body substances
e.g. thyroid hormone or insulin and blood sugar level
regulation of hormone secretion- positive feedback loop
uncommon. amplify changes rather than reverse them, precedes of hormone stimulates increased production of the hormone until there is an interruption in the cycle
e. g. oxytocin at birth
causes of altered hormone function
impairment of the hypothalamus or pituitary gland, endocrine gland
too little/ much hormone produced or secreted,
inactive hormone receptor binding
lack of responses by target cell to hormone
impaired negative feedback loop
hormone produced ecotopically
impaired hormone metabolism
