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Endocrinology > Pituitary > Flashcards

Pituitary Flashcards

1
Q

How does hormone secretion by the posterior pituitary become stimulated? and what hormones does it secrete?

A

Stimulated via a neuronal link with the hypothalamus. The posterior pituitary secretes vaspopressin and oxytocin

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2
Q

Name some examples of oxytocins actions? When is the rate of secretio highest?

A

Contraction of the womb during lactation and childbirth. Aiding in contraction of seminal vesicles of the testis and increase lipolysis in the adipocytes. Increased response during suckling and end of pregnancy.

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3
Q

How is the AVP precursor modified?

A

The post translational modification cleaves the signal peptide (N-terminus) and a glycoprotein (C-terminus).

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4
Q

AVP is released in response to…..

A

A decrease in plasma volume or increase in plasma osmolality

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5
Q

Describe the actions of AVP

A

AVP act on either V1R, to increase vascular resistance, or V2R, to increase blood volume, which both results in increased arterial pressure.

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6
Q

Name some conditions associated with inappropriate secretion of AVP

A

Syndrome of inappropriate antidiuresis (SIADH) and diabetic insipidus (cranial and nephrogenic)

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7
Q

Describe the biochemical characterisation of SIADH

A

Nomovolaemic (normal BP) hyponatraemia (low serum Na)

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8
Q

Name some causes of SIADH with the

A

It can be caused by drugs (NSAIDs, opiates), CNS disorders (stroke, trauma), or a hereditary defect in the AVP receptors.

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9
Q

How is SIADH diagnosed?

A

SIADH is diagnosed by exclusion

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10
Q

What is the criteria for diagnosing SIADH?

A 
Euvolemic hyponatraemia
Low serum osmolality (<275mOsm/kg)
Urine sodium > 25mmol/L
Urine osmolality >100mOsm/kg
No renal, adrenal or thyroid disease
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11
Q

What is the treatment of SIADH?

A

Firstly attempt to remove the cause if possible (e.g. drugs). Restrict water intake (500-750mL/day), increase solute intake, using low dose loop diuretic with oral sodium chloride.

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12
Q

How does the AVP production biochemically present in diabetes insipidus?

A

The lack of AVP production causes polydipsia, or lack of response of AVP causing polyuria.

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13
Q

What happens when a patient with diabetes insipidus does not have free access to water?

A

Develop dehydration and hypernatraemia

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14
Q

What is the difference between cranial and nephrogenic DI?

A

Cranial: lack of AVP production
Nephrogenic: normal AVP production, but kidney does not respond

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15
Q

How can DI be assessed?

A

Typically use water deprivation test, where at 0800 the weight and urine + serum osmolality samples are taken. Commence fluid restriction. Hourly the patient is weighed and take urine and serums samples for osmolality. The test needs to be aborted if the fall in weight is greater than 5% or serum osmolality rise above 300mosm/kg (dangerously dehydrated)

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16
Q

When should a desmopressin test be administered?

A

The desmopressin test will be done following the water deprivation test if urine osmolality is still <750mosm/kg after 8h fluid restriction

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17
Q

What is the desmopressin test?

A

Desmopressin is a synthetic AVP, which is used to determine whether the DI is cranial or nephrogenic. Patients with cranial DI will respond to the desmopressin to restore a normal urine osmolality (concentrated)

18
Q

How can you diagnose DI based of the two tests?

A

Both types of DI show a serum osmolality of >293 and a urine osmolality of <300. Cranial DI has a desmopressin urine osmolality of >750 whilst nephorgenic has <300

19
Q

How do you treat cranial DI?

A

Give synthetic desmopressin via nasal spray

20
Q

How do you treat nephrogenic DI?

A

Use hydrochlorothiazide diuretic to inhibit NaCl transporter in DCT to decrease urine output

21
Q

How does the anterior pituitary get stimulated?

A

Via a capilliary link with the hypothalamus

22
Q

What hormones are released by the anterior pituitary?

A

TSH, ACTH, FSH, LH, growth hormone, prolactin, endorphins

23
Q

Draw the different hormone axis.

A

Look them up to double check

24
Q

What is hyperprolactinoma and what causes it?

A

This is defined by a raised level of prolactin in the blood. It can be caused by hypothalamic dopamine deficiency (tumours, arteriovenous malformations, inflammations), physiological (stress, pregnancy or lactation), defective dopamine transport (pituitary or stalk tumours, dissection of the pituitary stalk) or it can be factitious due to cross-reactivity in the testing, simulation of lactotrophs (increased TRH production in hyperthyroidism), prolactin secreting tumour (prolactinoma), lactotroph insensitivity to dopamine (phenothiazines e.g. chlorpromazine).

25
Q

How is hyperprolactinoma diagnosed?

A

Through differential diagnosis. Measuring thuroid functionto exclude hyperthyroidism, then looking at drug history. Important to use imaging to look for tumours

26
Q

What is the difference between functional and non-functional tumours?

A

Functional (hormone producing) thus excess hormone production

27
Q

What are some symptomes of non-functional tumours?

A

Tend to be due to mass effects of the tumour and may include headache, hypopituitarism, visual field defects

28
Q

Difference between micro and macroadenomas?

A

Micro are <10mm at widest diameter and macro are >10mm and impinge on adjacent sellar structures

29
Q

What is a prolactinoma?

A

This describes a non-cancerous tumour which results in excess lactinoma secretion.
Microadenoma prolactin < 4000mU/L
Macroadenoma > 4000mU/L - if less than then may be non-functioning tumour blocking dopamine.

30
Q

Name some pituitary tumours

A 
Rathkes cysts
Granular cell tumours 
Chordomas
Craniopharyngiomas
Meningiomas
Gliomas
Mucocele
31
Q

What are some clinical features of mass effects?

A

Headaches, visual field defects, cranial nerve palsies and temporal lobe epilepsy

32
Q

How can pituitary tumours be diagnosed?

A

Typically we use imaging (CT, MRI), but baseline hormone measures can describe it well

33
Q

How is F18-fluorodeoxyglucose utilised in diagnosis?

A

It is used to diagnosed pituitary tumours. The chemical is a tracer, a labelled glucose which is taken up by tumour tissue and PET can be used to differentiate between residual or recurrent tumours and post-operative changes

34
Q

Describe the treatment of pituitary tumours

A

Observation necessary for small non-functioning tumours.
Hyperprolactinomas can be treated using carbergoline or bromocriptine.
Typically surgery will be the first option, or radiotherapy (external beam radiation)

35
Q

WHat is hypopituitarism and what causes it?

A

Deficiency in one or more hormone of the pituitary gland. This can be caused by tumours, infarctions, inflammation, autoimmune, trauma, radiation treatment to brai, genetic

36
Q

How can hypopituitarism be diagnosed?

A

Baseline assessment of pituitary and target gland hormones

37
Q

What is dynamic function test? What is the difference between indirect and direct?

A

Dynamic function testing is complementary to baseline hormone testing to assess functional reserve in pituitary disease. Direct test uses hypothalamic releasing hormones. Indirect uses pharmacological stimuli that results in release of secretagogues from the hypothalamus.

38
Q

Describe the insulin tolerance test

A

Administer insulin to induce hypoglycaemia causing a stress response to stimulate pituitary end organ axis to increase hormone production (cortisol and GH)

39
Q

Describe the glucagon tolerance test

A

Alternative when ITT is contraindicated. Glucagon stimulates release of GH and ACTH by a hypothalamic mechanism. This test is not appropriate for people with hypothyroidism or severe adrenal insufficiency and has been shown to be unreliable for patients with DM. A normal response is if baseline values are within ref range and there is at least doubling of LH and FSH after 20min

40
Q

Describe the gonadotrophin tolerance test

A

Used to diagnose hypothalamic-pituitary disease in precocious and delayed puberty in children with low baseline gonadotrophins.
The results need to be interpreted with attention to the patient’s age. Normal baseline for a pre-pubertal child is <2 IU/L for LH and FSH.

Endocrinology (12 decks)

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