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Year 2 - Endocrinology > Pituitary Gland And Regulation Of The Endocrine System > Flashcards

Pituitary Gland And Regulation Of The Endocrine System Flashcards

1
Q

How are the pituitary gland and the hypothalamus connected?

A

The pituitary lies inferior to the hypothalamus, and is connected to it by a slender pituitary stalk called the infundibulum

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2
Q

Name the three main places in the hypothalamus that neurons travelling to the pituitary arise.

A

Ventral hypothalamus
Paraventricular nuclei
Supraoptic nuclei

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3
Q

When all the neurons from the hypothalamus join together, what do they form?

A

The hypothalamic hypophyseal tract - becomes the posterior pituitary lobe

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4
Q

What is the name of the circulation system in the hypothalamus/pituitary that carriers hormones from one to the other?

A

Hypophyseal portal system

  • primary capillary plexus
  • hypophyseal portal vein
  • secondary capillary plexus
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5
Q

What are the secretly cells of the anterior pituitary called?

A

Secretory cells of the adenohypophsysis

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6
Q

What is the neurophypophysis?

A

A storage for hypothalamic hormones in the posterior pituitary

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7
Q

What happens in the primary capillary plexus?

A

Hormones from the hypothalamus are released into the hypophyseal portal system, and flow down, mainly towards the anterior pituitary

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8
Q

What is the blood supply to the infundibulum and pituitary?

A

Superior hypophyseal artery

Inferior hypophyseal artery

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9
Q

Which cells in the anterior pituitary react to growth hormone releasing hormone (GHRH), and what do they release?

A

Somatotrophs (50%)

- release growth hormone

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10
Q

Which cells in the anterior pituitary react to gonadotropin releasing hormone (GnRH) and what do they release?

A

Gonadotrophs (10%)

  • follicle stimulating hormone (FSH)
  • luteinising hormone (LH)
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11
Q

Which cells in the anterior pituitary react to corticotrophic releasing hormone (CRH), and what do they release?

A

Corticotrophs (10-15%)

- adrenocorticotrophic hormone (ACTH)

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12
Q

Which cells in the anterior pituitary react to thyroid releasing hormone (TSH), and what do they release?

A

Thyrotrophs (5%)

- Thyroid stimulating hormone (TSH)

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13
Q

Which cells in the anterior pituitary react to dopamine, and what do they release?

A

Lactotrophs (20%)

- dopamine inhibits prolactin release

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14
Q

Briefly describe the growth hormone axis.

A

The hypothalamus releases growth hormone releasing hormone and somatostatin
GHRH induces GH release from the anterior pituitary and somatostatin inhibits GH release
GH acts on the liver, bone, adipose tissues and metabolism
The liver produces IGF-1 - which excerpts an indirect effect on bone, adipose tissue and metabolism
GH and IGF-1 both have a negative feedback effect on the pituitary and hypothalamus

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15
Q

What is notable about GH secretion?

A

It is pulsatile - and mainly only has effects in childhood

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16
Q

Which physiological occurrences increases GHRH release?

A

Stress
Exercise
Sleep
Hypoglycaemia

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17
Q

Which physiological occurrences increase the amount of CRH?

A

The time of the day
Illness
Stress

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18
Q

What large molecule is ACTH a derivative of?

A

POMC - Pro-opiomelanocorticotrophin

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19
Q

What effects does testosterone have on the HPG axis?

A

It stimulates Sertoli cells (which produce inhibin)

It has a negative effect on the hypothalamus and the anterior pituitary

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20
Q

What are the actions of prolactin, and when is it upregulated?

A

It develops the mammary gland and stimulates lactation

- only physiologically active in pregnancy

21
Q

What hormones have a positive and a negative effect on prolactin release?

A

Positive - oestrogen

Negative - dopamine (from hypothalamus)

22
Q

Which two hormones does the posterior pituitary release?

A

ADH

Oxytocin

23
Q

What is the function of oxytocin?

A

Important in labour and breastfeeding
Stimulates cervical dilation and uterine contractions by increasing prostaglandin production
Important in sexual arousal, recognition, trust, anxiety and mother-infant bonding - the love hormone
‘Let-down’ reflex in response to suckling

24
Q

Name two disorders of the posterior pituitary.

A

Diabetes insipidus - lack of ADH release

Syndrome of inappropriate ADH (SIADH - too much ADH)

25
Q

Name two general pituitary disorders.

A

Pituitary tumours

Hypopituitarism

26
Q

Which hormones form the antiretroviral pituitary can easily be produced in excess

A

ACTH
TSH
GH
Prolactin

27
Q

Describe the normal action of ADH.

A

ADH binds to vasopressin receptor 2 on the basolateral membrane of the kidney collecting duct cells
This promotes insertion of aquaporin 2 channels on the apical membrane, increasing water reabsorption from the tubule
- decreases urine volume
- maintains blood pressure

28
Q

What is diabetes insipidus?

A

Either a lack of ADH, or a resistance to ADH

Leads to massive water loss in the urine

29
Q

What are the clinical features of diabetes insipidus?

A

Polyuria
Polydipsia
Nocturia
- DM and hypercalcaemia must be excused first

30
Q

What are the cranial and nephrogenic causes of DI?

A

Cranial
- lack of ADH production by the posterior pituitary
- can be genetic or caused by trauma, infections or inflammatory conditions of the posterior pituitary
Nephrogenic
-resistance to ADH
- can be genetic or secondary to drugs (e.g. Lithium), metabolic upset or renal disease

31
Q

To test for DI, you must perform a water deprivation test. What is this?

A

The patient is deprived of fluid for 8 hours

The plasma and urine osmolality must be checked every 2-4hrs

32
Q

What results would you expect from a water deprivation test, if the patient has DI?

A

Their starting plasma osmolality will be high

Their final urine osmolality will be less than 300mOsmol/l (compared to a normal person - over 600mOsmol/l)

33
Q

To assess whether the problem is cranial or nephrogenic, what should you do after the 8 hours?

A

Give a synthetic ADH (ddAVP) and asses urine osmolality

  • if the cause is cranial, the osmolality should rise back to normal levels
  • if the cause is cranial, the osmolality will remain low
34
Q

What is the treatment of cranial DI?

A

Desmopressin (ADH analogue)

  • can be given orally, nasal spray, injection
  • keep monitoring plasma sodium and osmolality to ensure they aren’t taking too much and retaining too much water
35
Q

How is nephrogenic DI treated?

A

This is more difficult because the kidney isn’t responding to ADH, whether it is present or not.
Try and treat the underlying cause
Try very high doses of ddAVP

36
Q

How common are pituitary adenomas, and how serious are they?

A

10% of the population has one

  • relatively not dangerous
  • asymptomatic
37
Q

If a pituitary adenoma is found, what tests need to be done to make sure it isn’t causing a problem?

A

Check for any hormone excess
Check for hypopituitarism
Assess visual fields
- pituitary is located just below the optic chiasm
- tumour can extend up and push on chiasm, reducing peripheral vision (bitemporal hemianopia)

38
Q

Give some examples of secretory pituitary adenomas.

A

Prolactin - Prolatinoma - 30%
ACTH - Cushing’s disease - 20%
GH - Acromegaly - 15%
TSH - TSHomas - very rare, less than 1%

39
Q

What are the clinical features of a prolactinoma?

A

Galactorrhoea
Menstrual disturbance and sub-fertility in women
Reduced libido and erectile dysfunction in men

40
Q

How are prolactinoma’s managed?

A

Dopamine agonists, increase dopamine to keep prolactin down
- cabergoline
Surgery if the tumour is large and has visual field effects

41
Q

What are the signs and symptoms of acromegaly?

A

Sweats, headache, tiredness, increasing ring/shoe size, joint pains
Coarse facial appearance, enlarged tongue, hand + feet and visual field loss

42
Q

What are some of the complications associated with acromegaly?

A

Hypertension
Diabetes or impaired glucose tolerance
Increased risk of bowel cancer
Heart failure

43
Q

How do you diagnose acromegaly?

A

Glucose tolerance test
- normally glucose administration reduces GH levels dramatically, adenomas of the somatotrophs don’t allow this feedback
-may show underlying DM or IGT
IGF-1 test
- long half life, so better than measuring GH levels
Pituitary MRI
- tumour usually a macroadenoma (>1cm), extending into surrounding structures

44
Q

How is acromegaly managed?

A 
Surgery
- by transsphenoid route
- often not curative 
Medical therapy
- before and after surgery 
- somatostatin analogues to inhibit GH secretion 
Pituitary radiotherapy 
- to treat residual tumour 
- risk of hypopituitarism and long term problems
45
Q

What is hypopituitarism

A 
Failure of (anterior) pituitary function 
Most commonly affects a single  hormone axis (normally FSH/LH), but can affect all of them (parahypopituitarism)
46
Q

What does hypopituitarism lead to?

A

Secondary gonadal/adrenal/thyroid failure

47
Q

In hypopituitarism, hormone replacement is needed. If all the axis are affected, which hormone should be replaced first?

A

Cortisol

48
Q

List some of the causes of hypopituitarism.

A

Tumours - sometimes maintained or slightly increased prolactin
Radiotherapy
Infarction
- called Sheehan’s syndrome if postpartum
Infiltration (e.g. Sarcoid) - can also affect posterior pituitary
Trauma

Year 2 - Endocrinology (14 decks)

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