Endo Flashcards
Six hormones produced from the anterior pituitary
Growth hormone
Prolactin
TSH
LH
FSH
ACTH
How does blood get from the hypothalamus to the anterior pituitary
Portal circulation (capillaries on both ends)
Difference between primary and secondary failure in the thyroid, adrenal cortex and the gonads?
Primary: the gland itself is failing
Secondary: problem / no signals from the hypothalamus or the anterior pituitary
How can you tell the difference between primary and secondary hypothyroidism
T3 and T4 would fall in both
TSH increases in primary (due to less negative feedback - no problem with the pituitary) but is low in secondary as it can’t be made
Primary vs secondary hypoadrenalism
Cortisol falls in both but ACTH increases in primary hypoadrenalism but ACTH falls in secondary as it can’t be made
Primary vs secondary hypogonadism
Primary : testosterone and oestrogen fall, LH & FSH INCREASE
Secondary : LH/FSH fall, testosterone and oestrogen fall
Which hormone is affected by hypoadrenalism
Cortisol (regulated by ACTH)
Not aldosterone (regulated by renin-angiotensin)
Congenital causes of Hypopituitarism
Rarely congenital - mostly because of mutations in anterior pituitary transcription factor genes
Hypoplastic anterior pituitary (MRI)
Acquired causes of Hypopituitarism (7)
Tumours (press on pituitary, pushing it against sella turcica which stops function)
Radiation (check brain function in children with brain tumour)
Infection (meningitis)
Trauma
Pituitary surgery
Hypophysitis (pituitary inflammation) - difficult to diagnose
Pituitary apoplexy (haemorrhage) - small tumour which bleeds causes severe headache
Peri partum infarction
Outline the Pathophysiology of Sheehans Syndrome
During pregnancy lactotrophs are enlarged however the blood supply to the pituitary remains the same, therefore trauma or haemorrhage during delivery would cause a drop in blood pressure meaning there is decreased blood flow to the pituitary. This causes infarction. (cell death due to hypoxia)
What is the total loss of function from both anterior and posterior pituitary called?
Panhypopituitarism
Hypopituitarism due to radiotherapy
Radiotherapy (direct to pituitary or indirect to CNS tumour)
Higher does - higher risk of HPA axis damage
Which hormone axes are most sensitive to radiotherapy?
GH
Gonadotrophin (therefore radiotherapy can cause infertility)
Risks persist up to 10 yrs later - annual assessments
Presentation of reduced FSH/LH
Reduced libido
Secondary amenorrhoea
Erectile dysfunction
Reduced pubic hair
Presentation of low ACTH in Hypopituitarism
Fatigue
Presentation of low TSH in Hypopituitarism
Fatigue
Low pulse rate
Presentation of low GH in Hypopituitarism
Reduced quality of life
Short stature (only in children)
Presentation of low prolactin in Hypopituitarism
Inability to breastfeed
What is lactotroph hyperplasia
Anterior pituitary enlargement due to pregnancy, therefore post partum haemorrhage can lead to pituitary infarction
Symptoms of Sheehan’s Syndrome
Lethargy, anorexia/weight loss (all expected after pregnancy so usually ignored). Due to TSH/ACTH/GH deficiency
Failure of lactation due to prolactin deficiency (some people don’t want to so can’t therefore not a definitive sign)
Menses don’t resume post delivery
No damage to AVP as posterior pituitary is not affected
What is pituitary apoplexy?
Bleeding (haemorrhage) into the pituitary
Normally due to existing adenoma
Can be precipitated by anticoagulants
Symptoms of pituitary apoplexy
Severe headache with sudden onset
Bitemporal hemianopia
Haemorrhage May press CN III, IV, V : therefore cavernous sinus involvement can cause Diplopoda (double vision) or ptosis (droopy eyelid)
Why is biochemical diagnosis of Hypopituitarism difficult?
Hormone levels are pulsatile/ are higher at different times, impacting diagnosis
How is dynamic pituitary function used in Hypopituitarism diagnosis?
Body is put under stress by insulin-induced hypoglycaemia which stimulates GH and ACTH release
Injected with insulin, TRH and GnRH
TRH stimulates release of TSH
GnRH stimulates FSHand LH release
What is used for radiological diagnosis of Hypopituitarism?
MRI
What is empty sella syndrome?
Small tumour which pushes pituitary along rim of sella and which later infarcts
The pituitary still works after this but sella looks empty
Which hormone do you not need to replace for Hypopituitarism and why?
Prolactin- controlled negatively therefore a tumour normally means there’s an increase in PRL
Function not major therefore doesn’t need replacement
Which hormone can’t be taken orally in Hypopituitarism treatment and why?
Growth hormone
It is a peptide hormone meaning it would be broken down by gastric acid in the stomach
Taken as an injection
What is the treatment for GH deficiency?
Daily injection
Measure the response by :
- improvement in QoL
-plasma IGF-1 which is constant not pulsatile therefore easier to measure
What is the treatment of TSH deficiency?
levothyroxine once daily
Can’t use TSH to adjust the dose of levothyroxine like in primary hypothyroidism
Therefore change dose with aim for a T4 above the middle of the reference range
What’s the treatment for ACTH deficiency in Hypopituitarism?
Replace cortisol not ACTH
Synthetic glucocorticoids:
Prednisolone once daily am
Hydrocortisone three times a day (short half life so 3)
Difficult to mimic cortisols diurnal pattern
Symptoms of adrenal crisis
Dizziness
Hypotension
Vomiting
Weakness
May result in collapse and death
Triggered by undercurrent illness in people with primary/secondary adrenal failure
What are sick day rules?
Wear steroid alert/pendant
Take double the glucocorticoid does if fever/ intercurrent illness (to avoid crisis)
If unable to take tablets eg vomiting, inject IM or go A&E
What is the treatment of FSH/LH deficiency in men?
No fertility required :
Replace testosterone-topical / intramuscular
(Measure plasma testosterone)
Does not restore sperm production , normal QoL and libido
Fertility :
Spermatogenesis induction using Gonadotrophin injections (LH and FSH twice a week)
Best response if after puberty
Measure testosterone and semen analysis to check dosage for spermatogenesis (may take 6-12 months)
What’s the treatment for LH/FSH deficiency in women?
No fertility required :
Replace oestrogen and (if uterus intact) progestogen (prevents endometrial hyperplasia/ cancer)
Oral or topical
Fertility:
IVF - carefully timed Gonadotrophin injections
How can you tell the difference between the anterior pituitary and the posterior pituitary on an MRI?
Posterior appears as a bright spot vs anterior is grey
What stimulates AVP release?
Increase in plasma osmolality
Detected by osmoreceptors in hypothalamus
How do osmoreceptors regulate AVP?
If deprived of water extracellular sodium concentration increases and so osmoreceptors release water causing them to shrink. This change in shape causes increased osmoreceptor firing. This stimulates release of AVP from hypothalamic neurones. Avoids dehydration as water is reabsorbed from the urine.
What are two physiological responses to water deprivation?
Thirst
Increased AVP release (reduces urine volume and increases its osmolality. Decreases plasma osmolality)
What are the two problems/diseases relating to vasopressin?
Arginine Vasopressin Deficiency
Arginine vasopressin resistance
What’s AVP-D?
Cranial diabetes insipidus
Unable to make AVP because of a problem with the hypothalamus/ posterior pituitary
What’s AVP-R?
Nephrogenic diabetes insipidus
Kidney (collecting duct) unable to respond to it even though the post pituitary can make the AVP
(Resistance)
Outline the presentation of AVP-D/AVP-R.
AVP problem results in impaired concentration of urine in renal collecting duct. Therefore large volumes of dilute urine (hypotonic). Means increased plasma osmolality and sodium. Causes stimulation of osmoreceptors-> thirst /polydipsia .
As long as patient has access to water circulation continues normally
How can AVP-R / AVP-D result in death?
No access to water will result in dehydration and death
What is the presentation of AVP deficiency / resistance
Polydipsia
Nocturia
Polyuria
What are the symptoms of diabetes insipidus usually a sign of?
Diabetes Mellitus due to osmotic diuresis. Therefore if a patient normally presents they most likely have DM not DI
What are causes of AVP deficiency?
Mostly acquired, rarely congenital
1- traumatic brain injury
2- pituitary surgery/tumour
3- inflammation of the pituitary stalk eg TB.. therefore the AVP can’t travel down the stalk
4-autoimmune
What are causes of AVP resistance?
Less common than deficiency
Congenital: eg mutation in gene for V2 receptor
Acquired: drugs eg lithium (normally used for bipolar affective disorder)
What is the presentation of diabetes insipidus?
Large volumes of Hypo-osmolar urine
Hyper-osmolar plasma.
Patient is dehydrated
Hypernatraemia
Normal blood glucose
What is psychogenic polydipsia?
No problem with AVP, problem is that the patient drinks too much water so passes large volumes of dilute urine.
Sometimes in psych patients as meds cause dry mouths which leads to the polydipsia
What happens in psychogenic polydipsia?
Increased drinking -> drop in plasma osmolality and sodium -> less AVP secretion -> large volumes of hypotonic urine -> plasma osmolality returns to normal
What test is used to distinguish between DI & psychogenic polydipsia?
The water deprivation test
What is the water deprivation test?
No access to anything to drink for about 8 hrs
Monitor urine volumes, urine concentration, plasma concentration
Normally urine conc increases as water is reabsorbed due to the high plasma osmolality
What is the water deprivation test?
No access to anything to drink for about 8 hrs
Monitor urine volumes, urine concentration, plasma concentration
Normally urine conc increases as water is reabsorbed due to the high plasma osmolality