The Endocrine System Flashcards
what does the endocrine system regulate?
- growth - in both embryos and adults
- development - childhood and puberty
- reproduction - menstrual cycle, pregnancy, lactation
- blood pressure
- concs of ions in blood
- behaviour - survival instincts or our mood
what are the basic principles of the endocrine system?
- hormones are secreted from endocrine tissues/glands into ECF
- transported by blood stream to target tissues
- move into interstitial fluid and bind to cell surface receptors (ionotropic, metabotropic, kinase linked) or intracellular receptors (nuclear)
- can work paracrine or autocrine
what are the 3 main classes of hormones?
- peptide
- amino acid derived
- steroidal
what are peptide hormones?
- synthesised from amino acids
- mainly released by endocrine tissues rather than glands
- secreted by exocytosis via secretory granule fusion with plasma membrane
- act on cell membrane surface receptors
- seconds-minutes response
what are amino acid derived hormones?
- derivatives of tyrosine
- tyrosine requires specific enzymes in the cell to be converted to a hormone
- stored in vesicles
- released by exocytosis
- act on cell surface receptors
- take seconds-minutes to act
which hormone is the exception of the amino acid derived hormones?
thyroid hormone:
- thyroid hormone use facilitated transport to leave cells
- they bind to intracellular receptors and use facilitated diffusion to enter cells
- they take hours-days to produce a response
what are steroidal hormes?
- metabolites of cholesterol
- cells that make steroidal hormones have specific enzymes to convert cholesterol
- lipid-soluble so can diffuse across the bilayer
- they are only made when release is required otherwise overproduction will occur
- diffuse into cells and bind to intracellular receptors
- hours-days response
what are the 7 main endocrine glands?
- pituitary gland (anterior and posterior)
- located underneath hypothalamus - thyroid: located above trachea
- parathyroids: located posterior to thyroid
- there are 4 of these - adrenals (cortex and medulla)
- ovaries
- testes
- endocrine pancreas
what are the main endocrine tissues?
- hypothalamus
- kidneys
- GI tract (enteric nervous system)
- heart
- liver
- adipose tissue
- paracrine factors and neuropeptides
what is the thyroid gland?
- made up of follicles, which are made of follicular cells with colloid in centre
- contain hormones T3 and T4
- T3 and T4 are produced by follicular cells by iodine which forms prohormones
- prohormone is stored extracellularly in colloid
- when needed, follicular cells take prohormone back up and is converted into hormones T3 and T4
- T3 and T4 leave via facilitated diffusion
what are the hormonal actions of the thyroid hormones?
- bind to nuclear receptors
- regulate transcription of genes and translation of proteins
- essential for development, growth and metabolism
what is the difference between hypothyroidism and hyperthyroidism?
hypothyroidism: metabolic rate is too low, leading to obesity
hyperthyroidism: metabolic rate is too high, leading to underweight
what is the parathyroid gland?
2 different cell types:
- chief cell releases parathyroid hormone via exocytosis
- oxyphil cell
- synthesises and secretes parathyroid hormone (peptide hormone) by secretory granules on demand
what are the hormone actions of parathyroid hormones?
- increase bone calcium reabsorption to be distribute via plasma
- increase Ca2+ absorption in kidney tubule and GI tract
- negative feedback loop of chief cells: receptor activated by high Ca2+, leading to prevention of parathyroid hormone release and less calcium reabsorption
- regulates phosphate levels
what are the 3 zones of the adrenal gland?
- zona glomerulosa - releases aldosterone (mineralocorticoid) which regulates Na+ levels
- zona fasciculata - releases cortisol (glucocorticoid) which regulates plasma glucose levels
- zona reticularis - releases androgens (DHEA and androstenedione)
what is the adrenal medulla?
- the centre of the adrenal gland
- chromaffin postganglionic cells release adrenaline/noradrenaline (catecholamines)
how do the adrenal cortex and adrenal medulla integrate?
- blood enters adrenal gland via small blood vessels
- as cortisol is released, it travels through blood vessels to medulla and stimulates chromaffin cells to release adrenaline/noradrenaline
what are the two gonads?
- ovaries
2. testes
what are the ovaries?
- cells within developing follicles of the ovary produce oestrogen and progesterone
- oestrogen stimulates proliferation of the endometrium (peak in proliferative phase)
- progesterone stimulates secretions and maturation of tissues (peak in secretory phase)
what are the testes?
- testicular lobules contain seminiferous tubules
- tubules contain mature sperm in centre and Leydig cells around the edges
- leydig cells produce testosterone which stimulates protein sythesis
- testosterone causes development and growth
what is the endocrine pancreas?
isles of langerhans:
- beta cells: release insulin to lower blood glucose levels
- alpha cells: release glucagon to increase blood glucose levels
both are released into portal blood straight to liver for rapid response
what is the anterior pituitary (adenohypophysis)?
- anterior lobe of pituitary gland
- develops from an upward projection of the pharynx (doesn’t contain neural tissue)
- troph cells stimulated by releasing hormones from small diameter neurons of the hypothalamus in a portal vein
what is the posterior pituitary (neurohypophysis)?
- posterior lobe of pituitary gland
- develops from downward projection of brain so contains neural tissue
- releases hormones from large diameter neurons directly into systemic circulation
what are the major hormones of the anterior pituitary?
tropic hormones: stimulate release of more hormones
- adrenocorticotropic hormone stimulates release of cortisol by adrenal cortex
- thyroid stimulating hormone stimulates release of thyroid hormone by thyroid gland
growth hormones
prolactin: stimulates lactation
what are the major hormones of the posterior pituitary?
- vasopressin: regulates water balance
- oxytocin: positive feedback loop in parturition and lactation
how is hormone secretion regulated?
neural mechanisms:
- indirect feedback via physiological responses (blood pressure)
- if neural system has affect on blood vessel diameter, this is fed back to endocrine system to influence hormone release
cortical control: limbic system/stress
- hierarchical control of descending input from cerebral cortex
- cause release of hormones by hypothalamus, causing release of tropic hormones and others
