University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

36

Pages:

3
Author:

Mariam A. A.

BASCIS OF HORMONES Hormones • • • Liberated from one site → transported in blood → effects distant site Hormone secreting cells o Clusters of specialised cells in discrete ‘endocrine glands’ e.g. thyroid, adrenal o Clusters of specialised cells embedded within other organ and tissues e.g. gastrin secreting cells in stomach, erythropoietin secreting cells in kidney (trigger RBC production) Glands: pituitary, pineal, thyroid, parathyroid (behind thyroid), thymus, adrenal, endocrine pancreas, ovaries/tests Transport • • Water soluble hormones – in solution in plasma e.g. adrenaline, calcitonin → free=biologically active o 0.1-10% Non-water soluble hormones – bound to plasma proteins e.g. cortisol o 90-99.9% o Inactive Hormones Communicate regulating signals to distant cells Chemically diverse • Derived from single amino acid e.g. adrenaline, melatonin, thyroxin • Polypeptides e.g. angiotensin II, HGH • Steroid compounds derived from cholesterol e.g. cortisol, testosterone, aldosterone Released by diverse stimuli • Chemical environment (e.g. glucagon and insulin in response to blood glucose levels) • Neural (e.g. adrenaline, oxytocin) • Other hormones – releasing/trophic hormones (e.g. growth hormone releasing hormone GHRG) Hormones exert their action by binding to receptors on or in target cells → activation of receptor • Some change the ion permeability of the membrane → activate or inhibit cell activity e.g. ACh • Stimulate production of intracellular compounds (secondary messengers) → trigger or regulate cellular activity e.g. glucagon Some hormones exert action by entering the target cells and altering gene expression to change the amount of key enzymes/proteins produced e.g. cortisol, aldosterone Hormones exert action over variable time spans • Some have ½ lives of seconds or minutes e.g. adrenaline • Some have ½ lives of minutes or hours e.g. insulin, cortisol • Some have ½ lives of hours or days e.g. growth hormone Hormones release is regulated by: • Levels of the substance it is regulating (feedback) e.g. glucose • Levels of itself in the plasma e.g. thyroxin • Levels of neural activity e.g. adrenaline Hierarchical feedback control Neurotransmitters Chemical compound that communicate regulating signals to adjacent cells Chemically diverse • Noradrenaline, GABA, ACh, VIP etc. Released by a change in polarity Likewise with neurotransmitters • On: noradrenaline • In: nitric oxide Not usually the case for neurotransmitters, but take note of Long Term Potentiation and memory Milliseconds to seconds