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BSMS203 endocrinology (Theme 1) > 2. Introduction to the hypothalamic-pituitary axis > Flashcards

2. Introduction to the hypothalamic-pituitary axis Flashcards

1
Q

Where is the pituitary gland located?

A

Below the brain, encased in skull

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2
Q

What is the are of brain directly above the pituitary gland

A

hypothalamus

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3
Q

where is the hypothalamus

A

directly above the pituitary gland

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4
Q

What does the infundibulum do?

A

Connects the pituitary gland to the brain

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5
Q

How many separate parts is the pituitary gland divided into and what are they?

A

Two separate parts:
anterior pituitary
posterior pituitary (neurohypophysis)

These function independently

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6
Q

Describe the posterior pituitary gland

A

The posterior pituitary gland is a down growth from the brain
sometimes called the neurohypophysis

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7
Q

What does the posterior pituitary gland secrete

A 
Antidiuretic hormone (ADH also called vasopressin)
Oxytocin
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8
Q

Describe ADH and oxytocin

A
  • peptide hormones, nine amino acids (7 identical ones)
  • hormones not synthesised within the gland but are synthesised by hypothalamic neurons (supraoptic nuclei and paraventricular nucleus)
  • the hormones are synthesised as inactive precursors
  • converted to active hormone within the posterior pituitary
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9
Q

How are inactive hormones transported from the hypothalamus to the posterior pituitary gland?

A
  • From supraoptic and paraventricular nuclei along hypothalamico-neurohypophyseal tract
  • stored within the posterior pituitary
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10
Q

What influences anti-diuretic hormone

A
  • plasma osmolarity
  • stimulation of V2 receptors causes translocation of aquaporins to the membrane of the kidney tubule, thus allowing water reabsorption
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11
Q

What does stimulation of V1 receptors cause?

A

Vasoconstriction but not at physiological concentrations

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12
Q

What do disorders of ADH secretion lead to?

A

Disorders of fluid balance

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13
Q

How does oxytocin act?

A
  • Oxytocin acts via Ip3 to cause contraction of smooth muscle
  • secretion of oxytocin is stimulated by stimulation of the genitals and nipples
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14
Q

When is oxytocin most important?

A

oxytocin is most important at parturition and during lactation

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15
Q

When does oxytocin synthesis increase?

A
  • during pregnancy

- but parallel increase in oxytocinase activity

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16
Q

what does oxytocin cause during parturition?

A

During parturition, oxytocin causes contraction of the uterine smooth muscle to help expel the infant

Continued stimulation of the cervix causes continues secretion

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17
Q

How does oxytocin affect lactation?

A
  • After parturition, oxytocin is responsible to milk ‘let down’ (expulsion)
  • suckling is stimulus
  • delay between start of suckling and milk let down
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18
Q

What is the role of oxytocin in labour?

A
  • Oxytocin isn’t necessary for initiation of normal labour

- oxytocin can be administered to induce labour

19
Q

Describe the anterior pituitary gland

A

-The anterior pituitary gland is an up growth from the palate

20
Q

What hormones are secreted by the anterior pituitary gland?

A 
Growth hormone
prolactin
thyroid stimulating hormone
adrenocorticotrophic hormone
follicle stimulating hormone
luteinising hormone
21
Q

How are the hormones synthesised within the anterior pituitary gland?

A

Separate cells within the anterior pituitary gland by separate cells.
E.g. thyrotrophe cells - thyroid stimulating hormones
E.g. corticotrophe cells - adrenocorticotrophic hormone
E.g. gonadotrophe cells - follicle stimulating hormone

22
Q

TRH

A
  • thyrotrophin releasing hormone
  • from hypothalamus
  • stimulates secretion of TSH (thyroid stimulating hormone)
23
Q

CRH

A

-corticotrophin releasing hormone
-from hypothalamus
stimulates secretion of adrenocorticotrophic hormone (ACTH)

24
Q

GnRH

A
  • Gonadotrophin releasing hormone
  • from hypothalamus
  • stimulates secretion of follicle stimulating hormone (FSH)
25
Q

GHRH

A
  • growth hormone releasing hormone
  • from hypothalamus
  • stimulates secretion of growth hormone
26
Q

Describe the route of releasing hormones to the anterior pituitary

A

The releasing hormones are secreted by hypothalamus

  • into the hypothalamico-adenohypophyseal portal vessel
  • this carries them into the anterior pituitary
27
Q

Where do the releasing hormones act?

A
  • On the pituitary gland

- do not enter the systemic circulation

28
Q

How do you test pituitary function?

A

-measurement of releasing hormones and the effects of hormone administration (negative feedback)

29
Q

What do you need to consider when testing pituitary function?

A

Timing of the tests (measuring hormones and their effects)

because of diurnal rhythms

30
Q

Clinical investigations

A
  • start with signs and symptoms

- follow up with biochemical tests (basal levels)

31
Q

What are some biochemical tests?

A 
TSH & FT4
Cortisol
LH & FSH
Prl (prolactone)
Testosterone/"periods"
32
Q

What must you do after biochemical tests?

A

Imaging e.g. MRI
Then
Visual Field Tests

33
Q

What is a common visual field finding related to the hypothalamic-pituitary axis?

A
  • Bilateral hemianopsia
  • due to compression of optic chiasm
  • overgrowth of pituitary gland
34
Q

Describe prolactin

A
  • 199 amino acid peptide

- synthesised in lactotrophe cells in the anterior pituitary

35
Q

How is prolactin secretion regulated?

A
  • secretion of prolactin is under hypothalamic control
  • prolactin release inhibiting factor aka DOPAMINE inhibits prolactin release
  • TRH stimulates prolactin synthesis
36
Q

Prolactin secretion is stimulated by:

A
  • mild stress
  • nipple stimulation
  • coitus
37
Q

What’s the primary role of prolactin?

A
  • promote lactation
  • develop breast tissue
  • most important in females after puberty and during/after pregnancy
38
Q

Who secretes prolactin

A

prolactin is secreted in both males and females

39
Q

Where is growth hormone synthesised?

A

In the somatotrophe cells of the anterior pituitary gland

40
Q

How is growth hormone secretion controlled?

A

-by hypothalamus
-via growth hormone releasing hormone (GHRH)
AND
-growth hormone releasing inhibiting hormone (GHRIH, somatostatin)

41
Q

How is growth hormone secretion regulated?

A

stimulated by:

  • decreased carbohydrates
  • decreased fatty acids
  • increased amino acids
  • in some tissues, GH acts via second messengers which are produced in the liver
42
Q

How does growth hormone act in some tissues?

A

Via second messengers which are produced in the liver:

  • insulin-like growth factor 1
  • insulin-like growth factor 2
43
Q

What are the effects of growth hormone?

A
  • promotes linear growth of adolescence
  • by increasing protein synthesis and collagen deposition
  • mediated via the nucleus
  • foetal growth is relatively independent of growth hormone
  • growth hormone is also involved in tissue turnover and repair

BSMS203 endocrinology (Theme 1) (26 decks)

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