ENDOCRINOLOGY WEEK 1 Flashcards
what are the 4 categories of hormone and give a brief description
- Circulating factors which act on remote target organs
- Endocrine
o Source organ goes into blood and effects target tissues - Paracrine
o Acts on cells in its own neighbourhood - Autocrine
o Acts back on its own cells – turning off or on - neurotransmitters
o peptides – adrenaline, dopamine working on synaptic cleft in brain
what are the main endocrine glands and what hormones do they release
- thyroid o thyroxine, calcitonin - adrenal cortex o cortisol, aldosterone, DHE - adrenal medulla o adrenaline, noradrenaline - ovary o oestrogen, inhibin - testis o testosterone - pancreas o insulin, glucagon - parathyroid o PTH - pituitary o ACTH, LH, FSH, GH, PRL, TSH, AVP - most other organs make or metabolise hormones too
adipose tissue - what hormones does it make and what are their effects
- makes leptin, adiponectin, resistin, TNFa, IL6, cortisol, angiotensinogen, PAI-1
- supposed to signal from fat to brain but in obesity become resistant to leptin telling brain to stop eating
- fat generating cortisol
give examples of the 3 types of hormone
Peptides from gene products
- growth hormones, insulin, thyroxine
Amines from modified Amino acids
- adrenaline, noradrenaline
Steroids from cholesterol
- oestrogen, androgen, glucocorticoids, vitamin D
what are the types of receptors and give a brief description
Peptide and amine receptors
- surface receptors
- second messengers
- multiple cellular effects
Steroids and thyroid hormones receptors
- nuclear receptors
- vis transcription/ translation
- many target genes
what are the 3 main control centres of hormones
Brain (hypothalamus) -> pituitary hormones released -> glands (thyroid, adrenals, ovaries/testis) this feeds back on pituitary
what are the symptoms of loss of testosterone before puberty
- someone who’s never gone through puberty
- no testosterone produced
- small penis and balls
- feminine body shape
- long arms and legs because these limbs require testosterone to stop growing
- genetic disturbance
what are the symptoms of loss of testosterone after puberty
- pituitary problem
- testicular control disappeared as an adult
what are the symptoms of XXY chromosome complement
- small testes
- breast enlargement
- extra x chromosome
- testosterone production failed halfway through puberty
- phenotypic female
- genetically 46 XY
- because she has no receptors for testosterone
- so with no sex hormones morphology is female
- you need testosterone to masculise form and function
pituitary tumours effects
- small pituitary tumour very common
- 10-20% never cause illness
- If the tumour bulges into optic chiasm it causes bitemporal hemianopia
o Loss of outer field (temporal field) vision
o Patients bump into things as they can’t see out laterally
acromegaly - how does it manifest and what is it and
Acromegaly is a disorder that results from excess growth hormone (GH) after the growth plates have closed. The initial symptom is typically enlargement of the hands and feet. There may also be an enlargement of the forehead, jaw, and nose.
- A disorder that develops over many years
- Takes time to manifest
- Testosterone/ puberty is relevant
- Average time of diabetes/ obesity/ high blood pressure to be reported in Cushing’s disease is 2 years
what’s growth hormone and how is it regulated
- Pituitary peptide
- Acromegaly in adults
- Gigantism in children
Regulated - Growth hormone releasing hormone (GHRH) released from hypothalamus
- Stimulates pituitary to directly produce GH
- Which then has complex cascade of control through receptor coupled with g protein
- Drives the synthesis of GH in pituitary cell
- GH acts on the liver, muscles and other tissues
- Liver produces insulin and IGF1
- 1GF1 feedbacks on the hypothalamus to inhibit GH production
what are reasons for growth hormones excess
Genetic - Mutations in Gsa (gs alpha) inside the growth hormone producing cell Immune - Antibodies stimulating GH Tumours - Pituitary - Or tumours producing IGF1 or IGF2 from any cancer Overstimulation - GHRH hypersecretion from typically benign tumours Downstream path - IGF1 tumours Factitious/ iatrogenic - Body builders/ athletes
what are causes of hormone deficiency
- Genetic/ developmental failure
o Thyroid synthetic enzyme defects
- Autoimmune o Common o Antibodies destroy thyroid when immune system is activated by a virus o Failure of immune tolerance o Eg Hashimotos
- Tumours/ infiltrations
o Rarely infiltrate thyrois - Iatrogenic
o Overuse of treatment
o Carbimazole, radioiodine - Surgery
o Thyroidectomy
what are 2 reasons for target organ resistance
- Pre-receptor defects
o Monodeiodinase defects - Receptor mutations
o Thyroid resistance syndrome
replacement monitoring of thyroid hormone
- Thyroid hormone feeds back on hypothalamus and pituitary
- You can measure TSH
- Thyroid hormone and TSH are stable
- So if you want to know if you’re giving the right amount of therapy you can measure TSH
o If it’s high not giving enough thyroid hormone
o If it’s low give less
endocrine vs exocrine glands
ENDOCRINE GLANDS
- Do not have ducts
- Products secreted directly into blood
- Eg pituitary, thyroid, adrenal, parathyroid glands, gonads (testis and ovaries)
EXOCRINE GLANDS
- Products secreted via ducts to epithelial surfaces inside or outside the brain
- Eg sweat, salivary, mucus, mammary, gastric, prostate gland, lover bile ducts
explain paracrine, autocrine and intracrine signalling
PARACRINE (LOCAL) SIGNALLING - Hormone diffuses through tissue - To receptors on ‘target’ cells AUTOCRINE (LOCAL) SIGNALLING - Hormone diffuses through tissue fluids - To receptors on the same cell INTRACRINE - Inactive prohormone enters a cell - Activated intracellularly - Eg (sex steroids) o Eg oestrogen so that post-menopausal endometrium isn’t exposed to lots of oestrogen o Except this happens in steroid hormone replacement which is why there’s increased risk of cancer with it
what’s the composition and general mechanisms of the 3 types of hormones
Peptide
- Water soluble – circulate in blood
- Bind to cell surface receptors
- GPCRs or receptor kinases
Amine
- Transported on plasma ‘carrier’ proteins
- Bind to cell surface receptors
- GPCRs or receptor kinases
Steroid
- Cholesterol backbone
- Transported on plasma ‘carrier’ proteins
- Lipid soluble – bind to intracellular receptors
what’s the actions of peptides and amides
- Hypothalamic-releasing hormones
- Pituitary ‘trophic’ hormones
- Target organ peptide hormones
- Quick acting
what’s the actions of steroid hormones
- Hormone binds to receptor
- Hormone-receptor complex enters nucleus
- Complex binds to receptor sites on chromatin, activating mRNA transcription
- mRNA leaves nucleus
- ribosomes translate mRNA into new protein
- takes 24-48 hrs
circadian biological clock in relation to hormones
- suprachiasmatic nucleus (SCN0 rhythm generator controls daily endocrine system cycles (entrained by daily light and dark cycle)
- cortisol stimulated by light which wakes you up
- hormones peak in the morning and lower in the evening
hypothalamus where’s it located and whats it’s associations
HYPOTHALAMUS
- neuoendocrine component of the NS within the brain
- located at the base of the brain
- linked via the pituitary stalk to the pituitary gland outside the brain
pituitary gland - what are the 2 parts and how are these differentiated
- 2 glands in one
- Anterior and posterior pituitary have different embryological origins
- Anterior pituitary
o Blood supply from median eminence - Posterior pituitary
o Innervated by hypothalamic access
hypothalamus cns inputs
- Stimuli from somatic and visceral sense organs
- Transmitted via sensor and motor neurons from the forebrain and mid brain
- Produce ‘stimulatory’ or ‘inhibitory’ neurotransmitters
o Dopamine, adrenaline, noradrenaline, serotonin, acetylcholine, various neuopepetides - Act on distinct hypothalamic nuclei stimulate production of hypothalmic-releasing hormones
nuclei in the hypothalamus and what hormones are produced here
Nuclei in the hypothalamus
- Supraoptic nucleus – AVP/oxytocin
- Preoptic nucleus – GnRH
- Arcuate nucleus – GHRH/ dopamine
- Paraventricular nucleus – AVP/ oxytocin/ TRH
- Periventricular nucleus – somatostatin
There’s lots of peptide synthesis in these nuclei
Transported down the long axon fro stroage in nerve terminals
MEDIAN EMINENCE - blood supply, capillary bed name, functional anatomy, structure of the nerve terminals
- Supplied by arterial blood from superior hypophysial artery (a branch of the internal carotid artery)
- Cappilary bed – special peithelial cells called FENESTRATED EPITHELIAL CELLS
- Leads to direct contact with blood vessels
- Very dense area of nerve terminals
- Nerve terminals are on the surface of the blood vessels in this area
o Intimate contact
o Leading to peptides passing from nerve terminals into the blood
o PORTAL CIRCULATION
2 cappilary beds joined by circulation wihtout circling back through heart and lung
pituitary gland - size, dysfunction, DI
Pituitary gland about the size of a pea on the end of a wee stalk
- It can waggle about ie in car crash
- If pituitary stalk gets damaged eg whiplash
- This stops the transport of oxytocin and AVP
- Experience cranial diabetes insipidus
o Pee out 6-7 litres of urine in couple of hours
o Because lost AVP control in the kidney (recruites aquapoin in distal tubule)
what’s the principle blood supply of the pituitary gland
THE MEDIAN EMINENCE IE THE SUPERIOR HYPOPHYSIAL ARTERY
anterior pituitary gland - cell types and what hormones act on these
- GHRH (somatoliberin) acts on somatotropha
- GnRH acts on gonadotropha
- CRG acts on corticotropha
- TRH acts on thyrotrophs
- DA, inhibits Lactotrophs
- Somatostasin (SS) inhibits somatotrophs & thyrotrophs
anterior pituitary - what cell types make what hormones
- ACTH from corticotrophs
- TSH from thyrotrophs
- FSH and LH frome gonadotrophs
- GH (somatrophin) from somatotropha
- PRL from lactotropha
posterior pituitary cell types
- Oxytocin and vasopressin stored and released in response to neural stimulation
what does a tumour in a target gland lead to in terms of hormone levels
- Produceses lots of target gland hormone
- Ask where the problem is
o it’s in target gland and feedback loop is still intact leading to huge feedback in the anterior pituitary gland and hypothalamus
o leading to production of all of their hormones going down to zero – low levels of pituitary gland hormones - good diagnostically as have lots of target gland hormone but almost no hypothalamic or pituitary hormones
what does a tumour in the pituitary gland lead to in terms of hormone levels
- produces lots of pituitary gland hormone
- overstimulates target gland leading to high levels of target gland hormone
- pituitary tumour is unresponsive to feedback
what does failure of a target gland (ie hormone deficiency) lead to in terms of hormone levels
- target gland stops working eg injury
- failure of target gland results in low levels of target hormone
- reduces feedback on hypothalamus and pituitary
- leading to high levels of hypothalamic releasing and anterior pituitary hormones which can be measured
suppression testing examples
OVERNIGHT DEXAMETHASONE SUPPRESSION TEST
- mimics effects of cortisol
- synthetic glucocorticoid suppresses pituitary ACTH secretion and cortisol production from adrenal cortex (negative feedback)
Comes in 2 flavours
- low dose - suppresses pituitary ACTH secretion and cortisol production in normal individuals, but not from a pituitary adenoma
- high dose – part-inhibits ACTH secretion from a pituitary adenoma, but not from a cortisol-producing adrenal adenoma or an ectopic ACTH-producing tumour
stimulation testing examples
SynACTHen (synthetic ACTH) stimulation test
- Quantifies adrenal function or lack of function (insufficiency)
Comes in 2 flavours
- Low dose – to measure cortisol production
- High dose – to assess total adrenal cortex function
Oral Glucose Tolerance test
- Diagnosis of diabetes (exaggerated glucose response)
- Diagnosis of acromegaly (GH fails to be supressed as normal)
hormones rarely measured in plasma (measured via petrosal sinus sampling)
- Hypothalamic hormone
- CRF
- GnRH
- GHRH
- TRH
hormones often measured in plasma for diagnosis
- Pituitary hormone
- ACTH
- LH/FSH (male)
- LH/FSH (female)
- GH
- TSH
- ADH/ vasopressin
- Prolactin
hormones measured in plasma for diagnosis and to monitor hormone reduction or replacement
- End organ hormone
- Cortisol
- Testosterone
- Oestrogen, progesterone
- IGF1 (GH in children)
- Thyroxine
- Desmopressin/ DDAVP
what must be considered when collecting a blood sample
Dietary restrictions?
- Do patients need to fast
- Effects glucose, cholesterol, triglycerides
Timing
- Diurnal variation – cortisol, testosterone (male)
TDM
- Time from last dose (peak or trough)
Stability?
- Eg ACTH stable 30 mins
- Get to lab as quickly as possible
Affected by venous stasis?
- Protein bound components increase eg Ca++
Posture
- Renin and aldosterone
- Do you want them lying down for a while first
what are the different tubes used for collecting blood samples and in what settings are they used
- Plain serum (no gel)
- Plain serum (gel)
o These are for clotted blood
o Blood goes in and is allowed to clot for 30-60 mins
o Gel provides a barrier so that in the lab it can be spun and easily separate plasma from red cells - Lithium heparin (anticoagulant)
o Good for A&E
o Advantage = don’t need to wait for blood to clot
o Good for paediatrics bc can obtain more plasma in this sample than if bloods allowed to clot - Potassium EDTA (anticoagulant)
o Used for taking full blood count
o EDTA binds calcium
o Stops platelets clumping to get accurate FBC - Tri-sodium citrate (anticoagulant)
o Also binds calcium but more reversible than EDTA
o Allows for clotting studies eg INR
o For liver function tests - Sodium fluoride/ potassium oxalate (anticoagulant)
o Oxalate binds calcium
o Fluoride is an inhibitor of respiration so stops metabolism of glucose in the sample
o Stops from giving falsely low glucose measure