Endocrinology Flashcards
Where does the posterior pituitary hypothalamic magnocellular neurons originate in
Supraoptic and paraventricular hypothalamic nuclei
What are the hormones of posterior pititary
AVP and oxytocin
What does diuresis mean
Production of urine
What is the action of AVP/ADH
Stimulation of water absorption in the RENAL COLLECTING DUCT, which concentrates the urine via V2 receptor in the kidney
Vasoconstriction via V1 receptor
Stimulates ACTH release rom anterior pituitary
CRH - corticotrophin releasing hormone stimulates ADH
How does vasopressin concentrate urine? -scientific pathway
??
How does posterior pituitary look on MRI
Bright spot
Is posterior pituitary bright spot absence on MRI an abnormal finding?
No it is not visualized in all healthy individuals
What stimulates vasopressin release
Osmotic:
Rise in plasma osmolality sensed by osmoreceptors in hypothalamus ( and also in carotid artery)
Non-osmotic:
Decrease in arterial pressure sensed by atrial stretch mechanoreceptors receptors / baroreceptors
What is the role of Organum vasculosum &
subfornical organ
??
The circumventricular organs (CVO) are structures that permit polypeptide hypothalamic hormones to leave the brain without disrupting the blood-brain barrier (BBB) and permit substances that do not cross the BBB to trigger changes in brain function.
Where does Organumvasculosum&
subfornical organ sit and what are they called and what is their featurical importance
Both nuclei sit around 3rd ventricle and are called circumventricular, they have no blood brain barrier so neurons can respond to changes in the systemic circulation
They are highly vascularised for this feature
Neurons project to supraoptic nucleus - site of vasopresinergic neurons
What are the 2 nuclei in posterior hyothalamus
Supraoptic and paraventricular
What change in osmoreceptor causes AVP release from hypothalamus
Increase in extracellular sodium causes the water in osmoreceptor cells to leave the cell and the cell shrinks
*this causes increased osmoreceptor firing and thus AVP release form hypothalamic neurons
What is the location of atrial stretch receptor pressure detection
Right atrium
What is the response of high pressure detection in stretch receptors
Inhibit vasopressin release via vagal affarent to hypothalamus
What is the response of reduction in circulating volume
Less strech of atrial receptors so less inhibition o vasopressin
Which receptors are responsible for vasopressin action on kidney for increased water reabsorption
V2
Which receptors are responsible for vasopressin action on vasoconstriction
V1
What happens to plasma osmolality during WATER DEPRIVATION and what is the cascade of events following this
Plasma osmolality increases
Osmoreceptor firing rate increases
This causes thirst and increased AVP release
Increased AVP release increases water absorption from renal collecting duct
Reduced urine volume
Increased urine osmolality
Reduction in plasma osmolality
What are other names for vasopressin
AVP
ADH
Arginine vasopressin
Antiduiretic hormone
What are the symptoms associated with osmotic diuresis
Polyuria
Nocturia
Thirst - often extreme
Polydispia
What are the symptoms of diabetes indispidus
Polyuria
Nocturia
Thirst
Polydipsia
What is the most common cause of polyuria, nocturia, polydipsia
Diabetes mellitus
What are two types of diabetes insipidus
Cranial (central) diabetes insipidus
Nephrogenic diabetes insipidus
What is the problem in cranial (central) diabetes insipidus
Hypothalamus / posterior pituitary is unable to make arginine vasopressin
VASOPRESSIN INSUFFICIENCY
What is the problem with nephrogenic diabetes insipidus
Kidney is unable to respond to vasopressin
But the vasopressin production is fine
VASOPRESSIN RESISTANCE
What are the causes of cranial diabetes insipidus
Acquired:
Traumatic brain injury
Pituitary surgery
Pituitary tumors
Metastasis to the pituitary gland - eg. from the breast
Granulomatous infiltration of pituitary stalk - eg. TB, sarcoidosis ??
Autoimmune
What is a congenital cause of nephrogenic diabetes insipidus
Mutation in the gene encoding V2 receptor, aquaporin 2 type water channel
What is an acquired cause of nephrogenic diabetes insipidus
Drugs - lithium (used in bipolar disorder)
What is a terminologic description of the state of urine and plasma in diabetes insipidus
Urine:
Hypo-osmolar (very dilute)
Large volume
Plasma:
Hyper-osmolar, hypotonic (increased concentration)
Hypernatraemia (increased sodium)
Glucose should be normal - check this in a patient with these symptoms
How is the circulating volume maintained in a diabetes insipidus patient
Increased plasma osmolality
> stimulation of osmoreceptors
>thirst and polydipsia
> maintain the circulating volume AS LONG AS there is access to water
What is psychognic polydipsia
Polydipsia, polyuria, nocturia
But no problem with arginine vasopressin
Patient drinks all the time so passes large volumes of dilute urine
What is the cascade of events in polydipsia
Polydipsia > plasma osmolality falls >less AVP by pp > large volumes of hypotonic dilute urine >plasma osmolality returns to normal
How do you distinguish between diabetes insipidus and psychogenic polydipsia
WATER DEPRIVATION TEST Measure over time: Urine volumes Urine concentration - osmolality Plasma concentration - osmolality
What is the risk of water deprivation test and what should you do about it
Losing >3% body weight shows severe dehydration which can occur in diabetes insipidus so weight regularly
What is the trend of urine osmolality in normal vs psychogenic polydipsia vs diabetes insipidus
Normal: goes up and levels off at about 6th hour
Psychogenic polydipsia: urine osmolality increases but at a slower rate than normal
Diabetes insipidus: stays the same > instead have progressive increase in plasma osmolality
What is the name of replacement for vasopressin
Desmopressin - ddAVP
How do you distinguish between cranial and nephrogenic diabetes insipidus
GIVE ddAVP
In cranial, there is a response to desmopressin, urine concentrates
In nephrogenic there is no response and urine osmolality stays the same
What is the normal range for plasma osmolality for diabetes insipidus
275-285 mOsm/kg H2O
What is the plasma osmolality ranges for diabetes insipidus and polygenic polydipsia
Diabetes insipidus >285
Psychogenic polydipsia<275
How would you treat cranial diabetes insipidus
Desmopressin either tablet or intranasal, selective for V2 receptor (V1 receptor activation would be unhelpful)
What is the problem with the nasal spray
Can be easily disregarded as not important and can lead to death if the person can not drink and do not have fluids
What is the treatment of nephrogenic diabetes insipidus
Rare condition
Give thiazide diuretics eg. bendofluazide
Paradoxical unclear mechanism
What is the name for the syndrome of too much arginine vasopressin
Syndrome of Inappropriate Anti-Diuretic Hormone SIADH
What is the osmolality levels in SIADH
High urine osmolality
Low plasma osmolality - water retention
Dilutional hyponatraemia
What can cause SIADH
CNS • Head injury, stroke, tumour, Pulmonary disease • Pneumonia, bronchiectasis Malignancy • Lung cancer (small cell) Drug-related • Carbamazepine, Serotonin Reuptake Inhibitors (SSSRIs) Idiopathic
What is the management of SIADH
Common cause of prolonged hospital stay
Restrict fluids
Can use vasopressin antagonist - vaptan, binds to V2 receptors in kidney but is very expensive
