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Endocrinology
Organisation of the Body
| Question | Answer |
|---|---|
| What is a hormone | A chemical signal released from an endocrine cell to influence the activity of another cell via a receptor May act via the bloodstream or locally |
| Examples of endocrine systems | Pituitary Thyroid Parathyroid Pancreas Adrenal Gonads Gut hormones Local endocrine signalling |
| Endocrine glands | A well defined collection of endocrine cells Produce and secrete hormones |
| Neuroendocrine systems | Neurons that release hormones into the blood and into the CNS |
| Diffuse endocrine systems | Endocrine cells not arranged in glands but dispersed e.g. gut, respiratory tract, heart, kidney, fat |
| Types of endocrine communication | Endocrine - in bloodstream Paracrine - Local action not via blood Autocrine - acts on the hormone that secretes it e.g. in tumour cells to enhance growth |
| Functions of endocrine systems | Development, growth and differentiation Maintaining a long term stable internal environment homeostasis Responding to an altered external environment Control of reproduction |
| How quick are endocrine actions | Rapid - seconds or minutes Intermediate - mins Prolonged - hours or days Depends on rapidity of release, half life of the hormone and rapidity of action |
| Example of fast action - Adrenaline | Fight or flight response Rapid release - secs Short half life - 10 secs Rapid action - secs Released in response to stress e.g. during asphyxia Stored in granules for release |
| Example of intermediate action - Insulin | Regulation of plasma glucose after a meal - alters number of transmembrane glucose transporters in cells Rapid release - secs Short half life - 3-5 mins Intermediate action |
| Example of slow action - cortisol | From the fetal adrenal gland - causes production of surfactant Lack of this causes IRDS Half life of 90 mins Actions - hours |
| Hormone release in pulses | Hormone secretion is dynamic Precise patterns of frequency and magnitude for each hormone e.g. prolactin oscillated in the day and peaks in morning Growth hormone pulses in the day but peaks at night Need to be careful when samples are taken |
| Diurnal rhythms | Pulses vary during the day E.g. release of ACTH and cortisol is influenced by light due to inflammation of the retina Secretion peaks in the hours before waking to prepare the body for waking Pattern comes less pronounced with age |
| Feed forward control | Usually stimulatory How glands are triggered to release hormones E.g. hypothalamus secretes CRH, which stimulates the anterior pituitary to release ACTH which stimulates the endocrine gland to release cortisol |
| Feed back control | Usually inhibitory - the hormone inhibits its production E.g. cortisol inhibits ACTH release from anterior pituitary and CRH release from hypothalamus |
| Chemical types of hormone | Amino Acid derived - T3, adrenaline Polypeptide - insulin Protein - prolactin Glycoprotein - LH Steroids - testosterone Prostaglandins Gaseous mediators - NO |
| Regulated secretion | Proteins concentrated and stored in secretory vesicles (dense cored) vesicles Many secretory vesicles are stored in the cell Vesicles quickly release their content by exocytosis in response to a stimulus |
| Constitutive secretion | Proteins are not concentrated Vesicles are not stored in the cell Contents are released as produced Regulation is by control of transcription e.g. growth factors, secretion from tumours |
| Structures of anterior pituitary cell | Euchromatic nucleus - highly transcriptionally active Prominent ER and golgi Lots of dense cored vesicles |
| Protein hormones produced as pro hormones | Rough ER - pre prohormone has a signal peptide Golgi - prohormone Vesicle - cleaved at dibasic sites to form active hormone and other peptide (may also be active) |
| Prohormones containing several copies of a hormone | Pro thyrotrophin-releasing hormone made in the hypothalamus Prohormone is a chain of 3 AA hormones cleaved to form lots of active hormones |
| Prohormones containing multiple hormones | POMC protein initially produced is cleaved into MSH, ACTH, lipotropin and endorphin |
| Structure of Chromaffin cells | Euchromatin - high transcription rate Lots of RER and golgi Lots of secretory granules - similar to peptide synthesis Contents released on stimulation by stimulation by preganglionic sympathetic fibres |
| Adrenaline synthesis | Tyrosine - L-DOPA by tyrosine hydroxylase in cytoplasm L-DOPA - dopamine by Dopa decarboxylase Transported into vesicle Dopamine - noradrenaline by dopamine hydroxylase Back to cytoplasm Noradrenaline - adrenaline by phenyl N-methyltransferase |
| Steroids | Testes - testosterone Ovary - oestrogen and progesterone Adrenal - cortisol and aldosterone |
| Biosynthesis of steroid hormones | Made rapidly from cholesterol via enzymes in mitochondria and SER Not stored Highly hydrophobic so can diffuse across membranes |
| Structure of a steroid producing cell | Droplets of lipid - cholesterol ester Mitochondria with tubular cristae SER - almost fills cytoplasm |
| Biosynthesis of prostaglandins | Precursor lipids in membranes cleaved by lipases to release aracnadonic acid This is converted to different prostaglandins by cyclooxygenase Produced on demand Prostaglandin E2 - mucus secretion in stomach Prostaglandin F2 alpha - uterine contractions |
| Aspirin | An inhibitor of cyclooxygenase Reduces pain and inflammation by blocking prostaglandin production Should eat with aspirin to protect the stomach from damaging effects of reduced mucus production |
| Transport of hormones in blood | Hydrophilic hormones can circulate freely in plasma Most steroid and thyroid hormones are bound to specific binding proteins in the plasma This reduces their clearance and thus extends their half life |
| Metabolism and secretion of hormones | Hormones internalised with their receptor are degraded in lysosomes Steroid hormones are degraded in the liver - liver failure in men leads to build up of estrogen and breast growth Hydrophilic hormones are lost by excretion in the kidneys |
| Endocrine pathology | Can involve production of hormone, release of the hormone and its mechanism of action Caused by genetic factors, tumours and autoimmune disease |
| Diabetes mellitus | Type 1 - autoimmune, lack of insulin Type 2 - mechanism of action defect = hormone resistance syndrome |
| Graves disease | Autoimmune disease leading to an overactive thyroid Antibodies mimic the thyroid stimulating hormone - binds to receptors and activates the thyroid Thyroid produces excess thyroid hormone Leads to fast metabolism - weight loss and anxiety |
| Cushing's Disease | Too much cortisol from an adrenal cortex tumour Large quantities of cortisol lead to obesity This is reversible - once tumour removed symptoms disappear |
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