Endocrinology Flashcards by xx xx

Where does the posterior pituitary hypothalamic magnocellular neurons originate in

Supraoptic and paraventricular hypothalamic nuclei

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What are the hormones of posterior pititary

AVP and oxytocin

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What does diuresis mean

Production of urine

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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

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How does vasopressin concentrate urine? -scientific pathway

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How does posterior pituitary look on MRI

Bright spot

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Is posterior pituitary bright spot absence on MRI an abnormal finding?

No it is not visualized in all healthy individuals

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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

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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.

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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

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What are the 2 nuclei in posterior hyothalamus

Supraoptic and paraventricular

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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

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What is the location of atrial stretch receptor pressure detection

Right atrium

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What is the response of high pressure detection in stretch receptors

Inhibit vasopressin release via vagal affarent to hypothalamus

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What is the response of reduction in circulating volume

Less strech of atrial receptors so less inhibition o vasopressin

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Which receptors are responsible for vasopressin action on kidney for increased water reabsorption

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Which receptors are responsible for vasopressin action on vasoconstriction

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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

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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