| 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 |
