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RE > The HPA Axis > Flashcards

The HPA Axis Flashcards

1
Q

The HPA axis is a complex ——– axis

A

neuroendocrine

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2
Q

HPA Axis:

A

insert diagram

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3
Q

HPA Axis

A

insert slide

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4
Q

Hypothalamus:
- location
- relation to ventricular
system
- relation to pituitary gland

A
  • positioned at the base of
    the forebrain = diencephalic
  • forms the lateral walls of
    the third ventricle with the
    thalamus
  • inferior aspect/median
    eminence gives rise to the
    pituitary stalk, which in turn
    gives rise to the posterior
    pituitary gland
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5
Q

Which nuclei located at the base of the hypothalamus regulate anterior pituitary gland function?

A

tuberal nuclei

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6
Q

Hypothalamus components:

A

insert diagram

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6
Q

Components of the Hypothalamus:

A

MASTPPS

  • mamillary bodies
  • autonomic centers
  • supraoptic nucleus
  • tuberal nuclei
  • preoptic areas
  • paraventricular nucleus
  • suprachiasmatic nucleus
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6
Q

What is the master endocrine gland?

A

the pituitary gland

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6
Q

Hypothalamus Components and Function:

A

insert slide

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7
Q

Lobes of the Pituitary Gland and Embryological Origins:

A
  • anterior pituitary = adenohypophysis ->
    embryonic pharynx
  • posterior pituitary = neurohypophysis
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8
Q

What connects the posterior pituitary to the hypothalamus?

A

The infundibulum

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9
Q

Pituitary Gland

A

insert diagram

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10
Q

What hormones are secreted by the anterior lobe of the pituitary gland?

A
  • ACTH: stimulates adrenal glands
  • FSH: works with LH for ovarian/testis
    function
  • LH: works with FH for ovarian/testis
    function
  • Growth Hormone: essential in
    development for growth and affects fat
    distribution/muscle mass in adults
  • Prolactin: stimulates breast milk
    production
  • TSH: stimulates thyroid gland
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11
Q

Hormones and Target Organs:

A

insert diagram

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12
Q

Generally, anterior lobe of the pituitary gland secretes

A

larger peptides

*also synthesizes

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13
Q

Posterior Lobe of Pituitary gland Hormones:

A
  • ADH: increases permeability of collecting
    duct to absorb H2O
  • Oxytocin: smooth muscle contraction,
    facilitating birth/milk ejection

*both are synthasised in the hypothalamus
and stored in the median eminence before
release

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14
Q

Posterior Lobe Hormones:

A

insert diagram

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15
Q

Pituitary Gland: Vasculature:

A
  • capillary beds and veins form DUCTAL
    system for hormone transport
  • arterial supply originates from the internal
    carotids
  • the superior hypophyseal artery supplies
    the primary capillary bed in the pituitary
    stalk, which drains into PORTAL VEINS
  • the posterior lobe receives direct supply
    from the inferior hypophyseal arteries,
    draining into the cavernous sinus
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16
Q

Vasculature of the Pituitary Gland:

A

insert diagram

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17
Q

Where are the adrenal glands located?

A
  • superior to the kidneys
  • T12
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18
Q

What is the adrenal gland divided into and functions?

A
  • Medulla (inner 10%) = acute stress response
  • Cortex (outer 90%) = chronic stress
    response, sodium/glucose homeostasis
  • synthesises steroid hormones
  • derived from cholesterol from the diet +
    cholesterol synthesised in gland
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19
Q

Adrenal Glands

A

insert diagrams

20
Q

The adrenal cortex is divided into three distinct layers and function:

A
  • outer to inner
  • zona glomerulosa -> mineralcorticoids
    (aldosterone)
  • zona fasciculata -> glucocorticoids
    (cortisol, corticosterone)
  • zone reticularis -> androgens
    (dehydroepiandosterone)
21
Q

What is synthesised in the adrenal medulla?

A
  • catecholamines
  • adrenaline, noradrenaline
22
Q

Adrenal Glands:

A

insert diagram

23
Q

Synthesis of adrenocortical steroid hormones:

A

insert diagram

24
Q

Synthesis, secretions and actions of mineralcorticoids and glucocorticoids are controlled

A

independently

25
Q

HPA Axis:

A

insert diagram

26
Q

Secretion of ACTH:
- manner and timings?
- affecting factors?
- pattern related to?

A
  • pulsatile secretion (related to pulsation)
  • peak in early morning, at time of waking
  • nadir (lowest) in the middle of the night
  • increased secretion at times of prolonged
    stress
  • pattern is related to sleep-wake patterns:
    disrupted by shift work and long-haul travel
27
Q

Cortisol Secretion:

A
  • similar to ACTH secretion, but peak and
    nadir is 2 hours later
  • also pulsatile
28
Q

Cortisol Awakening Response:

A
  • increase of cortisol levels within the first hour
    after awakening is separate from the
    increase in cortisol during the second half of
    the night
  • whilst the purpose is unclear, it is considered
    to be in response to anticipated stress and
    CAR provides a measure of reactivity
    capacity of the HPA Axis
  • CAR can impaired in chronic stress
  • possible: individuals with increased
    vulnerability for psychosis are more sensitive
    to the effects of psychosocial stress due to
    abnormalities within the HPA Axis
29
Q

Transport of Glucocorticoids:

A
  • 10% - free, active form
  • 90% - bound to plasma proteins:
    - 75% corticosteroid-binding globulin
    (CBG = single chain glycoprotein)
    - 15% albumin, most abundant circulating
    protein in plasma
  • same proteins transport other glucocorticoids
    and progesterone
30
Q

Cortisol levels in pregnancy:

A
  • increase in CBG (corticosteroid-binding
    globulin)
  • results in a compensatory increase in
    circulating plasma cortisol concentrations
  • amount of free cortisol remains stable
31
Q

What is the most physiologically important mineralcorticoid?

A

Aldosterone

32
Q

What is the most major factor controlling the secretion of aldosterone?

A

RAAS (renin-angiotensin-adlsoterone)

33
Q

Apart from RAAS, what is the secretion of aldosterone directly stimulated by?

A
  • trauma
  • anxiety
  • hyperkalaemia
  • hyponatraemia
34
Q

What is the secretion of aldosterone directly inhibited by?

A
  • Atrial Natriuretic Peptide
  • ANP
35
Q

What % of aldosterone during circulation is protein bound?

A

50%

36
Q

Effect of aldosterone on sodium and potassium ion transport?

A
  • causes expression of ion channels
  • that transport sodium and potassium across
    cell membrane
37
Q

RAAS:

A

insert diagram

38
Q

What is the action of aldosterone in the kidney?

A
  • stimulates reabsorption of Na+ in distal
    tubule, lesser effects in collecting duct,
    ascending loop and proximal tubule
  • Na+ reabsorption occurs in exchange for
    either K+ or H+
  • control of reabsorption of Na+ influences
    plasma sodium conc, which influences H2O
    reabsorption in collecting duct via an effect
    on ADH secretion
  • interaction of RAAS and ADH therefore
    controls blood volume and influences blood
    pressure
39
Q

RAAS:

A

insert diagram

  • interaction of RAAS and ADH therefore
    controls blood volume and influences blood
    pressure
40
Q

Where is the growth hormone secreted from and function?

A
  • anterior lobe of pituitary gland
  • growth and affects fat distirbution/muscle
    mass in adults
41
Q

What are the effects of synthesising high levels of GH in adult hood?

A
  • acromegaly
  • enlargement of hands, feet, forehead, jaw
    and nose
42
Q

What is the most common cause of acromegaly?

A

Pituitary adenoma (benign neoplasia)
treat via surgery/radiotherapy

43
Q

Cushing’s Syndrome: Cause:

A
  • occurs when an individual is exposed to
    excessive levels of cortisol
  • Endogenous Cushing’s = due to excessive
    secretion of cortisol as a result of elevated
    levels of circulating ACTH
  • elevated secretion of ACTH is most
    commonly due to a pituitary tumour
44
Q

Cushing’s Syndrome: Common Features:

A
  • weight gain and adipose deposits around
    midsection, upper back and face
  • fragile skin that bruises easily
  • slow healing of wounds
  • acne
45
Q

Cushing’s Syndrome: Diagnosis:

A
  • biomarkers for excessive cortisol
  • check for elevated ACTH in blood for
    endogenous cause
46
Q

Cushing’s Syndrome: Endogenous Cause: Treatement:

A
  • surgery
  • radiotherapy
47
Q

What is prolactinoma?

A

Excessive secretion of prolactin due to a pituitary tumour, cause of tumour is unknown

48
Q

What does prolactinoma lead to?

A
  • changes in menstrual cycle
  • mood disturbances
  • galactorrhoea (production of breast milk in
    those who are not pregnant or recently
    delivered)
49
Q

What is hypopituitarism?

A

Reduced secretion of one, or more of the pituitary hormones and can be causes by tumours, infections, vascular failure etc

50
Q

Hypopituitarism treatment:

A

= reversing causal mechanism eg HRT

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