Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
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University of Leeds (UoL)
University of Leeds
Year 1 MBChB: IMS
All documents for this subject (12)
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ENDOCRINOLOGY
OVERVIEW
Main endocrine glands
Hypothalamus/pituitary, thyroid, parathyroid (behind the thyroid), pancreas, adrenal, ovaries/testicles
Anterior pituitary - produces various hormones
Growth hormone (GH) –skeletal growth- and excess leads to acromegaly in adults and gigantism in children
Adrenocorticotrophic hormone (ACTH) - stimulates the adrenals to produce steroids
Gonadotrophins (FSH and LH) - stimulate the testicles or ovaries to produce sex hormones
Thyroid stimulating hormone or thyrotrophin (TSH) - Stimulates the thyroid to produce TH’s
Prolactin (PRL) - stimulates breast milk production
Posterior pituitary - stores the hormones produced in the hypothalamus
Antidiuretic hormone (ADH) - stimulates water reabsorption by the kidneys
Oxytocin - helps uterine contractions during labour
How the pituitary is controlled
Corticotrophin releasing hormone (CRH): stimulates ACTH secretion
Growth hormone releasing hormone (GHRH): stimulates GH secretion
Thyrotropin releasing hormone (TRH): stimulates TSH secretion
Gonadotrophin releasing hormone (GnRH): stimulates FSH and LH secretion
Secretion is on and off
Prolactin releasing hormone does not exist and prolactin is under the inhibitory effect of the hypothalamus
Switching off pituitary hormones – NEAGTIVE FEEDBACK
Cortisol switches off ACTH and CRH
Growth hormone, switches off GH and GHRH
Thyroid hormones switch off TSH and TRH
Sex hormones switch off FSH/LH and GnRH
Pituitary controls: thyroid, part of adrenal cortex (for corticosteroids and androgens), tests/ovaries, and skeletal
growth
Glands not controlled by the pituitary
Adrenal medulla- produces adrenaline and noradrenaline
Parathyroid- controls calcium levels
Pancreas- controls sugar levels
Gut hormones
Thyroid gland
Composed of midline isthmus (below cricoid cartilage), right lobe, left lobe
Thyroid cells are arranged in follicles and produce TH’s
Contains C cells, which produce calcitonin (calcium metabolism)
Thyroid hormones interact with their receptors in various organs - regulates gene
expression and aspects of organ function
T3 is active, T4 is inactive – gets converted to T3 from different organs, catalysed by
deiodinase
Calcium metabolism
Mainly controlled by 4 parathyroid glands sitting behind the thyroid
Kidneys: calcium excretion and production of active vitamin D
Gut: absorption of calcium
Bone: storage of calcium
Adrenal gland
Adrenal cortex (90% of gland) – corticosteroids (cortisol), androgens, mineralocorticoid (aldosterone)
Adrenal medulla (10% of gland) – catecholamines (adrenaline, noradrenaline and dopamine)
Catecholamine secretion is not controlled by the pituitary (related to blood pressure)
, Mineralocorticoid secretion is not controlled by the pituitary (related to renin-angiotensin system, which controls
the BP)
Low BP – increase in renin – increase in aldosterone
ACTH causes cortisol production and androgens
Ovaries
Situated either side of the uterus, in the pelvis
Contain follicles, which contain oocytes, at different stages of maturation during
reproductive life
Oestrogen, more in first half of menstrual cycle, controlled by FSH
Progesterone, more in second half of menstrual cycle, controlled by LH
Testes
The testes are found in the scrotum, except in a minority with testicular maldescent
Composed of:
o Interstitial or leydig cells - produce testosterone
o Seminiferous tubules – made up of germ cells producing sperms
o Sertoli cells – help in sperm production and produce inhibin
FSH controls sperm production
LH controls testosterone production
Clinical abnormalities of the various glands
Hormonal over secretion – primary/secondary
Hormonal under secretion – primary/secondary
Testing for hormonal abnormalities
Static tests: can diagnose abnormalities of thyroid, sex glands, prolactinoma
Primary hyperthyroidism (TH overproduction), test for T3, T4 and TSH
Stimulation tests: suspected hormonal under-secretion where a static test isn’t enough (equivocal results)
E.g. giving ACTH to test for adrenal insufficiency
If an individual fails to respond to a stimulation test, gland failure is diagnosed
GST and IST for pituitary failure (tests for ACTH and GH response)
Suppression tests: some hormonal over-secretion
Giving steroids and testing for endogenous steroid production (external steroids should switch off internal
steroid production)
Giving glucose and testing GH secretion (glucose switches off GH secretion in normal individuals)
Secondary hyperthyroidism – pituitary gland causes the problem
Diseases of the endocrine glands
Over secretion (usually benign tumours)
Under-secretion: gland destruction due to inflammation, infarction, other
Tumours/nodules with normal hormone production
Prolactin oversecretion
Usually due to a pituitary tumour secreting prolactin – prolactinoma
Symptoms:
o Galactorrhoea (breast milk production), amenorrhoea in women and decreased sex drive in men
o Headaches and visual field problems in large tumours as the optic nerve is close to pituitary
Static test is enough for diagnosing prolactinoma
Mildly raised prolactin
May be due to: sex, nipple stimulation, stress, large number of drugs (including antipsychotics and
antidepressants), non-functioning pituitary tumour (compressing the hypothalamus and interfering with the
inhibitory effect on prolactin secretion)
Only over-secreting pituitary tumours can be treated medically as they very rarely require surgical intervention
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