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203 - Theme 1 - The Endocrine System > L9 - The hypothalamic pituitary axis - clinical aspects > Flashcards

L9 - The hypothalamic pituitary axis - clinical aspects Flashcards

1
Q

Releasing factors

A

CRH

AVP

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2
Q

Tropic hormones

A

ACTH

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3
Q

Target organ hormones

A

Cortisol

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4
Q

What two types of factors does the hypothalamus produce?

A

releasing factors

inhibiting factors

to the pituitary

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5
Q

Pituitary releases?

A

tropic hormones

to target organ

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6
Q

Adrenal cortex hormone production

A

Glucocorticoid
- cortisol

Mineralocorticoid
- aldosterone (RAAS)

Sex steroids
- androgens

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7
Q

Binding proteins

A

90% cortisol bound to cortisol binding globulin (CBG)

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8
Q

Receptors

A

Intracellular glucocorticoid and mineralocorticoid receptors (GR and MR)

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9
Q

Enzymes in HPA

A

11-B-hydroxysteroid dehydrogenase (11-B-HSD)

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10
Q

Effects of glucocorticoids (6)

A

Maintenance of homeostasis during stress
-e.g. haemorrhage, infection, anxiety

Anti-inflammatory

Energy balance/metabolism
-increases/maintains normal (glucose)

formation of bone and cartilage

regulation of BP

cognitive function, memory, conditioning

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11
Q

Circadian rhythm and cortisol levels

A

rise during the early morning

peak just prior to awakening

fall during the day

are low in the evening

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12
Q

Ultradian rhythm - ‘pulsatility of hormone release’

A

spontaneous pulses of varying amplitude

amplitude decrease in the circadian trough

it is hard to distinguish the stress response

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13
Q

Circulating androgens: what do the adrenal glands release?

A

DHEAS

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14
Q

Circulating androgens: what do the testes release?

A

testosterone

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15
Q

How is testosterone converted into oestrogen?

A

the enzyme aromatase

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16
Q

How is testosterone converted into dihydrotestosterone

A

the enzyme 5-a-reductase

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17
Q

DHEAS and testosterone both converted into?

A

androstenedione

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18
Q

Enzymes - MR receptor

A

In vitro, the MR receptor has the same affinity for aldosterone and cortisol

19
Q

Enzymes - what is specificity conferred by?

A

a ‘pre-receptor’ mechanism

20
Q

What inactivates cortisol in the kidneys?

A

11-B-HSD-2 in the kidney inactivates cortisol, enabling aldosterone to bind the MR

21
Q

11-B-HSD enzymes: tissue specificity

A

gating of GC access to nuclear receptors

amplification of GC signal in target cells

22
Q

Features of Cushing’s syndrome

A 
weight gain
central obesity
hypertension
insulin resistance
neuropsychiatric problems
osteoporosis
23
Q

Cushing’s syndrome: pathogenesis

A

excess cortisol:
-pituitary adenoma: ACTH-secreting cells (‘Cushing’s disease’)

  • adrenal tumour: adenoma (or carcinome)
  • ‘ectopic ACTH’: carcinoid, paraneoplastic
  • iatrogenic: steroid treatment (‘cushingoid’)
24
Q

Cushing’s syndrome: clinical features

A

central obesity with thin arms and legs

fat deposition over upper back (‘buffalo hump’)

rounded ‘moon’ face

thin skin with easy bruising, pigmented striae

hirsutism

hypertension

diabetes

psychiatric manifestations

osteoporosis

25
Q

What disease is too little cortisol?

A

Addison’s

26
Q

Addison’s disease: the patient

A
  • gradually falls of in general health
  • becomes languid & weak
  • indisposed to either bodily or mental exertion
  • the body wastes
  • slight pain is referred to the stomach
  • there is occasionally actual vomiting
  • discolouration of the skin
  • at length pt gradually skins and expires
27
Q

Addison’s disease: pathogenesis

A

Primary adrenal insufficiency

  • addisons disease
  • usually autoimmune in UK
  • rare causes include metastases or TB
  • decreased production of all adrenocortical hormones

Other causes of hypoadrenalism

  • secondary to pituitary disease (rare)
  • iatrogenic
  • patients on high does, long term steroid Rx, which is suddenly stopped at a time of stress
28
Q

Addison’s disease: Clinical features

A

malaise, weakness, anorexia, weight loss

increased skin pigmentation: knuckles, palmar creases, around/inside the mouth, pressure areas, scars

hypotension/postural hypotension

hypoglycaemia

29
Q

Autoimmune polyendocrine syndromes: Type 1

A

rare

onset in infancy

Ar(AIRE gene)

common phenotype

  • addisons disease
  • hypothyroidism
  • candidiasis
30
Q

Autoimmune poluendocrine syndromes: Type 2

A

commoner (still rare)

infancy to adulthood

polygenic

common phenotype

  • addisons disease
  • T1 diabetes
  • autoimmune thyroid disease
31
Q

Autoimmune conditions that may occur together?

A 
Type 1 diabetes
Autoimmune thyroid disease (hypo- or hyper-)
    -Also gestational / post-partum thyroiditis
Coeliac disease 
Addison’s disease
Pernicious anaemia-low B12
Alopecia
Vitiligo
Hepatitis
Premature ovarian failure
Myasthenia gravis
32
Q

Autoimmune polyendocrine syndromes: clinical implications

A

high index of suspicion for additional autoimmune endocrine disorders

  • T1 DM with fatigue, weight loss and hypos: addisons?
  • T1 DM with non-specific GI symptom/diarrhoea: coeliac disease?
33
Q

Assessment of the HPAA: BASAL

A

blood

  • cortisol
  • SCTH

urine
-cortisol

saliva
-cortisol

34
Q

Assessment of the HPAA: dynamic tests

A

stimulated

  • ACTH
  • CRH
  • ‘Stress’
    • hypoglycaemia

suppressed

  • dexamethasone
    • synthetic glucocorticoid
35
Q

Assessment of the HPAA: basal collecting data

A

blood

  • timing
  • circadian rhythm
  • ultradian rhythm
  • stress

urine

  • 24hr collection
  • ‘area under curve’

saliva

  • timing
  • no stress!
36
Q

Too much cortisol?

A

24hr urinary free cortisol
-area under the curve

Midnight cortisol (blood/saliva)
-trough

9am ACTH (with paired cortisol)

  • pituitary/adrenal/ectopic
  • negative feedback at pituitary

Dexamethasone suppression
-sensitivity to GC negative feedback at pituitary

37
Q

Too little cortisol?

A

9am cortisol
-peak

SynACTHen test

  • adrenal response to ACTH
  • trophic effect ACTH on adrenals

Insulin tolerance test

  • response to hypoglycaemic stress
  • can be dangerous

U&E (decreased Na, increased K) in Addisons

  • due to mineralocorticoid deficiency
  • can measure renin & aldosterone concentrations

Decreased glucose

38
Q

2 golden rules

A

Never start investigating a patient for an endocrine condition unless their symptoms & signs suggest they may have it!
-Risk of false positive results

Never image any endocrine gland until you have established the diagnosis biochemically!
-Risk of discovering ‘incidentalomas’

39
Q

Imaging

A

CXR
MRI pituitary
CT adrenals

Patients with Addison’s disease seldom need imaging unless you are concerned they may have TB/metastatic cancer

40
Q

Cushing’s syndrome: management

A

Surgical (depending on cause)

  • transphenoidal adenectomy
  • adrenalectomy

Pituitary radiotherapy

41
Q

Addison’s disease: management 1

A

Steroid hormone replacement therapy (glucocorticoid)
-usually hydrocortisone (sometimes prednisolone)

Patients with primary adrenal insufficiency also need mineralocorticoid replacement therapy (fludrocortisone)

Patients with secondary adrenal insufficiency will often be taking other hormone replacement therapy (do not need fludrocortisone)

42
Q

Addison’s disease: management 2

A

Dose of glucocorticoids needs to be increased to cover ‘stresses’:
-intercurrent illnesses (e.g. flu)

Operations/post-op period
-recommendations depend on the procedure

Patients need IV/IM steroid if unable to take their tablets:

  • vomiting
  • ‘nil by mouth’
43
Q

Why may patients be treated with long-term steroids?

A

such as glucocorticoids usually prednisolone

usually the steroids are being used for their anti-inflammatory/immunosuppressive effects

conditions include severe asthma/COPD, temporal arteritis/polymyalgia rheumatics
-these patients may look ‘cushingoid’ especially those with COPD

44
Q

Why might the endogenous adrenal function of patients on long-term high dose steroid therapy be suppressed?

A

they may not mount an adequate stress response

their steroid treatment should not be stopped suddenly

if they need a major procedure/an operation, they require increased steroid cover as described

they should be given a ‘steroid treatment card’ to remind them and doctors about this

203 - Theme 1 - The Endocrine System (11 decks)

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