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MEH > The Hypothalamic Pituitary axis > Flashcards

The Hypothalamic Pituitary axis Flashcards

1
Q

Where does the hypothalamus sit?

A

In a socket of bone called sella turcica

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2
Q

Infundibulum

A

Pituitary stalk

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3
Q

Where do the anterior and posterior pituitary arise from?

A

Anterior - Arises from evagination of oral ectoderm (primitive gut tissue)

Posterior - Originates from neuroectoderm

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4
Q

Anterior and posterior pituitary glands are also called:

A

Adenohypophysis and neurohypophysis

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5
Q

Which two hormones are secreted by the pituitary gland? And where are they produced?

A

Oxytocin and ADH.

Produced by neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus.

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6
Q

Anterior pituitary function

A
  • Hormones synthesised in hypothalamus are transported down axons and stored in the median eminence
  • These hormones stimulate (or inhibit) target endocrine cells in the anterior pituitary gland
  • Has endocrine, paracrine and autocrine function
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7
Q

Tropic hormones of the hypothalamus (6)

A
  • Thyrotropin releasing hormone (TRH)
  • Prolactin release inhibiting hormone (Dopamine, PIH)
  • Corticotropin releasing hormone (CRH)
  • Gonadotropin releasing hormone (GnRH)
  • Growth hormone releasing hormone (GHRH)
  • Growth hormone inhibiting horome (Somatostatin, GHIH)
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8
Q

Tropic hormone definition

A

Affect the release of other hormones in the target tissue

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9
Q

Hormones produces by the anterior pituitary

A
  • Thyroid stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
  • Luteinising hormone (LH)
  • Follicle stimulating hormone (FSH)
  • Prolactin (PRL)
  • Growth hormone (GH)
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10
Q

Growth hormone

A
  • Produced in the anterior pituitary
  • Stimulated by hypothalamic GHRH
  • Inhibited by somatostatin
  • Contains signal peptide
  • In response to GH cells of the liver and skeletal muscle produce and secrete IGFs
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11
Q

When is there a increase or decrease in GH secretion?

A

Increase:

  • Onset of deep sleep
  • Stress
  • Exercise
  • Decrease in glucose or fatty acids
  • Fasting

Decrease:

  • REM sleep
  • Obesity
  • Increase in glucose
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12
Q

Long and short loop negative feedback

A

Long:

  • Mediated by IGFs
  • Inhibits release of GHRH from hypothalamus
  • Stimulates release of somatostatin
  • Inhibit release of GH from anterior pituitary

Short:
- Mediated by GH via stimulation of somatostatin release

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13
Q

Growth hormone deficiency

A
  • Proportionate dwarfism
  • Respond to GH therapy
  • Delayed or no sexual development
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14
Q

Growth hormone deficiency

A
  • In childhood esults in gigantism
  • Often caused by pituitary adenoma
  • In adulthood results in acromegaly
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15
Q

How does GH exert its effects on cells?

A
  • GH receptors activate Janus kinases (JAKs)
  • Tyrosine kinase receptors activate intracellular kinases which leads to transcription factor activation and IGF production
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16
Q

Insulin-like growth factors: two different types, actions, what do they modulate?

A
  • IGF1 major growth factor in adults
  • IGF2 mainly involved in fetal growth
  • Binding proteins modulate their availability
  • Actions can be paracrine, autocrine and endocrine
  • Modulate hypertrophy, hyperplasia, increase in the rate of protein synthesis, increase in the rate of lipolysis in adipose tissue
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17
Q

IGF and insulin receptors

A

There is cross activation of signalling pathways due to similarities in the receptors

18
Q

Other hormones that also influence growth and their actions

A
  • Insulin (enhances somatic growth)
  • Thyroid hormones (promotes CNS development and enhance GH secretion)
  • Androgens (accelerate pubertal growth spurt, increase muscle mass, promote closure of epiphyseal plated)
  • Estrogens (decrease somatic growth, promote closure of epiphyseal plates)
  • Glucocorticoids (inhibit somatic growth)
19
Q

Upwards growth of pituitary tumour causes:

A

Visual field loss due to pressure on optic chiasm (bitemporal hemianopia)

20
Q

Lateral growth of pituitary tumour causes:

A

Pain and double vision. Left sided eye compression (tumour invading left side)

21
Q

Hypopituitarism

A

Signal from hypothalamus does not reach pituitary gland. No control over hormone release and production

22
Q

Hormone deficiencies with pituitary tumours

A
  • Growth hormone, short stature in children, reduced quality of life in adults
  • Gonadotropin (LH and FSH), loss of secondary sexual characteristics, loss of periods
  • TSH and ACTH deficiency, late features of pituitary tumours, cold, weight gain, tiredness, low T4. Low cortisol, tired, dizzy, low BP, can be life threatening
23
Q

Hormone excess with pituitary tumours

A

Common:

  • Prolactin
  • GH
  • ACTH

Rare:

  • TSH
  • LH/FSH
24
Q

Biochemical assessment of pituitary disease

A
  • Thyroid axis, fT4 and TSH
  • Gonadal axis, LH, FSH, testosterone and oestradiol
  • Prolactin axis, serum prolactin
    Dynamic assessment
  • Cortisol
  • GH
25
Q

Adrenal axis dynamic tests

A

Deficiency:
- Direct stimulation by synACTHen
- Response to hypoglycaemia stress (insulin stress test)
Excess:
- Suppress ACTH axis with steroids (dexamethasone)

26
Q

GH axis dynamic tests

A

Deficiency:
- Response to hypoglycaemic stress (insulin stress test)
Excess:
- Suppress GH axis with gluc,ose load (glucose tolerance test)

27
Q

Prolactinoma

A
  • Prolactin secreting pituitary tumour

- Treated with dopamine agonist tablets (dopamine inhibits prolactin and shrink tumour)

28
Q

Hyperprolactinaemia symptoms in women and men

A
  • Prolactin directly inhibits LH secretion
    Women:
  • Menstrual disturbance
  • Fertility problems
  • Galactorrhoea (milky discharge)
    Men:
  • Present later than women (why? Lecture 8.2 slide 29)
  • Usually large tumours
  • Symptoms of low testosterone are non specific
  • May present with mass symptoms such as visual loss
29
Q

Likely diagnosis if prolactin levels are higher or lower than 5,000?

A

< 5,000 - disinhibition (stalk effect)

> 5,000 - active prolactin secretion (prolactinoma)

30
Q

Non functioning pituitary adenoma: clinical features, blood hormone levels

A
  • Clinical features are due to mass effect (bitemporal hemianopia) or symptoms of low pituitary hormones
  • Low testosterone, LH, FSH, cortisol, GH, IGF
  • High prolactin
31
Q

Long term complications of acromegaly

A
  • Premature cardiovascular death
  • Increased risk of colonic tumours
  • Hypertension
  • Diabetes
32
Q

Biochemical tests to confirm acromegaly

A
  • Oral glucose tolerance test with GH response
  • Elevated IGF-1 level (age related reference range
  • Growth hormone day curve
33
Q

Treatment of acromegaly

A
  • Surgical removal of tumour
  • Reduce GH secretion (dopamine agonist, somatostatin analogues)
  • Block GH receptor
  • Radiotherapy
34
Q

Cushing’s disease classical change in appearance

A
  • Round pink face with round abdomen
  • Skinny and weak arms and legs
  • Thin skin, easy bruising
  • Stiae on abdomen
  • High blood pressure and diabetes
  • Osteoperosis
35
Q

Difference between Cushing’s disease and Cushing’s syndrome

A

Cushing’s disease is due to a pituitary tumour, whereas Cushing’s syndrome may be caused by other pathologies e.g. adrenal tumour, ectopic ACTH or steroid medication

36
Q

What does antidiuretic hormone do?

A

Retains water in the body and constricts blood vessels (at high concentrations). Diuresis means increased urine.

37
Q

Diabetes insipidus types

A
  • Neurogenic and nephrogenic

- Unusual in standard pituitary tumours as those just affect anterior pituitary

38
Q

Consequences of untreated diabetes insipidus

A
  • Severe dehydration
  • Very high sodium levels
  • Reduced consciousness, coma and death
39
Q

Treatment of diabetes insipidus

A

Synthetic vasopressin

40
Q

Clinical presentation of pituitary apoplexy (stroke)

A
  • Sudden onset headache
  • Double vision
  • Visual field loss
  • Cranial nerve palsy
  • Hypopituitarism (cortisol deficiency most dangerous)

MEH (12 decks)

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