Endocrine System PDF

Endocrine System Fidelma Butler Decisions to be made Life history... but, how do they know? Animals respond to cues … environmental, behavioural, physiological Birds build nests, territory singing … day length Bayliss and Starling 1902 Secretin Hormone Chemical messengers Signaling m...

Endocrine System Fidelma Butler Decisions to be made Life history... but, how do they know? Animals respond to cues … environmental, behavioural, physiological Birds build nests, territory singing … day length Bayliss and Starling 1902 Secretin Hormone Chemical messengers Signaling molecules Hormones –GREEK horman – to excite/activate The function of the endocrine system is the production and regulation of chemical substances called hormones. Pheromones Not all signaling molecules act within the body Classes of hormones Three major chemical classes Polypeptides e.g. insulin - water soluble Amines e.g. thyroxine, epinephrine – water soluble Steroids e.g. cortisol – a lipid – lipid soluble Some differences... Water soluble hormones cannot diffuse through the plasma membranes of target cells – bind to cell-surface receptors - --- induce changes in cytoplasmic molecules and sometimes alter gene transcription Lipid soluble hormones diffuse out across the membranes of endocrine cells, they bind to transport proteins in the blood then diffuse into the target cells and bind to receptors in the cytoplasm or nucleus --- trigger changes in gene transcription Some hormones can induce more than one effect e.g. epinephrine (adrenalin) can induce multiple effects … Adrenal glands Where are endocrine cells in the body? Grouped in ductless organs called endocrine glands – secrete hormones directly into the surrounding fluid Exocrine glands have ducts e.g. salivary glands Hormones are also made in other organs in the body e.g. stomach, brain, kidneys etc.  Neuroendocrine Hypothalamus The endocrine system and nervous Pituitary system work together to help maintain homeostasis. The hypothalamus is a collection of Hypothalamus specialized cells located in the brain, and is the primary link between the two systems. It produces chemicals that either stimulate or suppress Posterior hormone secretions of the pituitary Pituitary gland. Anterior Pituitary How is hormone secretion controlled? Feedback – positive or negative Negative --- the endocrine cells respond to an internal or environmental stimulus by secreting a hormone. The hormone travels to the target cell, where it interacts with the specific receptor to bring about a physiological response. Positive feedback is where continued stimulation causes an increase in the Suckling secretion of the hormone e.g. Oxytocin Positive feedback amplifies both stimulus and response Negative feedback helps to restore a pre- existing state ====== hormone pathways involved in homeostasis involve negative Smooth muscle feedback in mammary glands Co-ordination of Endocrine and Nervous Systems Invertebrates Ecdysis Giant silk moth Hyalophora cercopia PTTH Ecdysteroid Moult or Metamorphosis Juvenile hormone Insect growth regulators Vertebrates Hypothalamus Pituitary gland Posterior pituitary – extension of hypothalamus Anterior pituitary Antidiuretic hormone (ADH) Oxytocin Anterior pituitary releasing or inhibiting hormones e.g. Prolactin releasing hormone prolactin Hormone cascade pathway Hypothalamus Anterior Pituitary Target endocrine gland Target tissue What stimulates endocrine glands to secret hormones? blood concentrations of non-hormone chemicals e.g. ADH another hormone neural stimuli e.g. noradrenaline and adrenaline. Evolution of hormone function Same hormones – different functions e.g. Prolactin Mammals – growth of mammary glands and milk production Birds – regulates fat metabolism, reproduction (parental care) Amphibians – delays metamorphosis FW fish – regulates salt and water balance