Hypothalamic-Pituitary Adrenal Axis: Hormones and Assessment of Function Flashcards by David Houghton

What 3 parts make up the hypothalamic-pituitary Adrenal Axis (HPA axis)?

1 - hypothalamus
2 - pituitary gland
3 - adrenal gland

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The 3 parts make up the hypothalamic-pituitary Adrenal Axis (HPA axis) are the hypothalamus, pituitary and adrenal gland. What connects the hypothalamus and the pituitary gland?

pituitary stalk

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The 3 parts make up the hypothalamic-pituitary Adrenal Axis (HPA axis) are the hypothalamus, pituitary and adrenal gland. What hormone does the hypothalamus secrete to stimulate the anterior pituitary gland?

Corticotrophin Releasing Hormone [CRH]

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The 3 parts make up the hypothalamic-pituitary Adrenal Axis (HPA axis) are the hypothalamus, pituitary and adrenal gland. What hormone does the anterior pituitary gland secrete to stimulate the adrenal gland?

Adrenocorticotropic Hormone [ATCH]

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glucocorticoids

- specifically cortisol

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The 3 parts make up the hypothalamic-pituitary Adrenal Axis (HPA axis) are the hypothalamus, pituitary and adrenal gland. The anterior pituitary gland secretes Adrenocorticotropic Hormone (ATCH) to stimulate the adrenal gland. The adrenal gland, specifically the cortex releases glucocorticoids, specifically cortisol. Although this stimulates tissue as part of the stress response, what else are glucocorticoids involved with?

negative feedback loop
inhibits hypothalamus and pituitary gland
reduction in corticotrophin releasing hormone (CRH) and adrenocorticotropic hormone (ACTH)
overall regulates cortisol levels

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What is the inferior aspect of the hypothalamus called and what does it go on to create?

median eminence

- creates the pituitary stalk, also known as the infundibulum

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The inferior aspect of the hypothalamus is called the median eminence and creates the pituitary stalk, also referred to as the infundibulum. What does this then go onto form?

posterior pituitary gland

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There are a group of nuclei within the base of the hypothalamus that regulate the anterior pituitary gland. What is the name given for this group of nuclei?

tuberal nuclei

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The hypothalamus has a myriad of functions. What is the primary function of the mamillary bodies that we can see in the image below?

regulate feeding reflexes (swallowing)

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The hypothalamus has a myriad of functions. What is a key function the hypothalamus is involved that is able to modulate blood pressure and heart rate for example?

autonomic control

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The hypothalamus has a myriad of functions. What is the primary function of the supraoptic nucleus that we can see in the image below?

secretes anti-diuretic hormone (ADH)
anti - against
diuretic = diuresis (urinating a lot)

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The hypothalamus has a myriad of functions. The primary function of the supraoptic nucleus that we can see in the image below is to secrete anti-diuretic hormone (ADH). What is the purpose of secreting ADH?

ADH regulates osmolarity (ion concentration in blood, Na+, K+ etc…) and fluid levels
signal the retention of fluid by the kidneys and vasoconstrict blood vessels to maintain blood pressure
helps dilute osmolarity

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The hypothalamus has a myriad of functions. The primary function of the supraoptic nucleus is to secrete anti-diuretic hormone (ADH), which acts to reduce fluid loss from the body. Is ADH then secreted from the anterior or posterior pituitary gland?

posterior

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The hypothalamus has a myriad of functions. The primary function of the supraoptic nucleus is to secrete anti-diuretic hormone (ADH), which acts to reduce fluid loss from the body. ADH travels to the posterior pituitary gland via axons from the supraoptic nucleus. What is present in these axons and what is the purpose of them?

these axons contain out pouchings called herring bodies

- herring bodies store ADH

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What is the primary function of the tuberal nuclei?

control of the pituitary gland

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The hypothalamus has a myriad of functions. What is the primary function of the paraventricular nucleus?

synthesis of oxytocin

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The hypothalamus has a myriad of functions. What is the primary function of the suprachiasmatic nucleus?

control of circadian rhythm

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The hypothalamus has a myriad of functions. What is the primary function of the preoptic areas?

thermoregulation

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The posterior lobe of the pituitary gland is also referred to as the neurohypophysis, which means what?

neuro = neurologically developed
hypo = under
physis = growth

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The anterior lobe of the pituitary gland, which developed embryonically from the pharynx is also referred to as the adenohypophysis, which means what?

adeno = gland
hypo - under/below
physis = growth

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The main purpose of the pituitary gland is to synthesis and secrete hormones. Are both the anterior and posterior lobes of the pituitary gland able to synthesise and secrete hormones?

anterior = yes

- posterior = secrete only

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What does the anterior pituitary gland secrete that stimulates the adrenal glands?

adrenocorticotropic hormone (ACTH)

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What does the anterior pituitary gland secrete that stimulates the ovaries and testes?

follicle-stimulating hormone (FSH)

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What does the anterior pituitary gland secrete that stimulates the ovaries and testes alongside Follicle-stimulating hormone (FSH)?

- Luteinizing hormone (LH)

What does the anterior pituitary gland secrete that stimulates muscle, fat, liver and bones and is critical for growth and development?

- growth hormone

What does the anterior pituitary gland secrete that stimulates breast milk production?

- prolactin

What does the anterior pituitary gland secrete that stimulates the thyroid gland?

- thyroid stimulating hormone

The posterior pituitary gland is unable to synthesise hormones and therefore these must be synthesised and stored somewhere before being transported to the posterior pituitary gland. Where is this?

- oxytocin synthesised in paraventricular nucleus - anti-diuretic hormone synthesised in supraoptic nucleus - stored in herring bodies of axons from hypothalamus to posterior pituitary gland within the median eminence

What 2 key hormones does the posterior pituitary gland secrete?

- anti-diuretic hormone (ADH) | - oxytocin

What main artery does the pituitary gland receives its blood supply from, and what are the main smaller branches supplying the pituitary gland?

- internal carotid artery | - hypophyseal branches

The main artery that supplies the pituitary gland is the internal carotid artery. This then has 2 main branches that directly supply the upper and lower aspects of the pituitary gland. What are these called?

1 - superior hypophyseal | 2 - inferior hypophyseal

The main artery supplying the pituitary gland is the internal carotid artery. This then has 2 main branches that directly supply the pituitary gland, the superior and inferior hypophyseal. What do the superior hypophyseal and inferior hypophyseal supply directly?

- superior hypophyseal artery = pituitary stalk, which drains into portal vessels - inferior hypophyseal artery = posterior lobe draining into the cavernous sinus

Roughly what % of the adrenal glands is composed of the medulla and cortex?

- adrenal medulla = 10% | - adrenal cortex (outer layer) = 90%

The adrenal glands are composed of the medulla and cortex. Which is associated with acute and chronic stress?

- adrenal medulla = acute | - adrenal cortex (outer layer) = chronic and Na+ and glucose homeostasis

The adrenal cortex can be subdivided into 3 areas, and each of these contains specific enzymes, meaning each zone is able to synthesise different hormones. Using the labels below label the 3 zones of the adrenal cortex? zona glomerulosa zona fasciculata zona reticularis

1 - zona glomerulosa 2 - zona fasciculata 3 - zona reticularis

The adrenal cortex can be subdivided into 3 areas, and each of these contains specific enzymes, meaning each zone is able to synthesise different hormones, as seen in the image below. Using the labels below, which zone synthesises which hormones in the 3 zones? ``` Adrenal androgens ( androgen precursors) Glucocorticoids [e.g. cortisol] Mineralocorticoids [e.g. aldosterone] ``` (remember the deeper it gets the sweeter it gets)

1 - Mineralocorticoids [e.g. aldosterone] 2 - Glucocorticoids [e.g. cortisol] 3 - Adrenal androgens ( androgen precursors)

Does the release of adrenocorticotropic hormone from the pituitary gland secrete continuously or are there times when it peaks?

- it is pulsatile - peaks early morning - lowest at night (melatonin is highest during darkness) CAN BE ALTERED BY CHRONIC STRESS AND/OR LONG HAUL FLIGHTS

The release of adrenocorticotropic hormone (ACTH) from the pituitary gland secrete are slowly continuous, but peaks early morning and dips in the middle of the night. What would cause a spike in ACTH?

- perception of stress

What is the Cortisol Awakening Response?

- cortisol peaks when we wake, normally 30-45 minutes after waking - preparation for any potential dangers

What % of cortisol within the blood is free and not bound to plasma proteins?

- 10%

10% of cortisol within the blood is free and not bound to plasma proteins. What plasma proteins does the other 90% bind with?

- albumin = 15% | - corticosteroid binding globulin (CBG) also known as transcortin = 75%

10% of cortisol within the blood is free and not bound to plasma proteins. Albumin = 15% and corticosteroid binding globulin (CBG) also known as transcortin = 75%. What happens during pregnancy to the the CBG levels?

- CBG levels increase - modulates the circulating plasma cortisol concentrations - free cortisol remains stable though

What is the main mineralocorticoids secreted by the most outer layer of the cortex called the zona glomerulosa?

- aldosterone

What is the main function of aldosterone?

- stimulates mineralocorticoid receptors in the distal tubules and collecting ducts of the nephron - influences reabsorption of Na+ and retention of H2O - increases the excretion of K+ - contributes to maintaining blood volume and blood pressure

Aldosterone is the main mineralocorticoids secreted by the most outer layer of the cortex called the zona glomerulosa. What system is the main stimulus for initiating the secretion of this hormone?

- renin-angiotensin-aldosterone (RAAS) system

In addition to the renin-angiotensin-aldosterone [RAAS] system, what else can contribute to the secretion of aldosterone?

- trauma - anxiety - hyperkalaemia - hyponatraemia - INHIBITED by atrial natriuretic peptide released by heart, which tries to remove fluid and Na+)

How much of aldosterone is bound to plasma proteins?

- aprox 50%

What does acromegaly mean?

- acro is greek for extremities of the body - megaly is greek for enlarged - caused by excessive levels of growth hormone

What is growth hormone acromegaly?

- excessive levels of growth hormone causing abnormal growth | - mainly affects hands, feet, forehead, jaw and nose

Growth hormone acromegaly is excessive levels of growth hormone causing abnormal growth, mainly affecting the hands, feet, forehead, jaw and nose. What is the main cause of this?

- pituitary adenoma (benign growth) | - treated with surgery and/or radiotherapy

What is Cushing syndrome?

- endocrine disorder causing elevated cortisol in the blood

What is the difference between endogenous and exogenous cushings?

- exogenous = factors outside the body are the cause | - endogenous caused by factors within the body

What is the main cause of endogenous Cushings?

- pituitary tumour - causes increased levels of adrenocorticotropic hormone (ACTH) - continuous stimulation of the adrenal cortex zona fasciculata (middle layer of the adrenal cortex) - means continuous release of cortisol

What are some of the most common features of cushings?

- weight gain (mid region specifically) - fragile and bruised skin - muscle and bone soreness

To diagnose cushings what can we measure?

- cortisol in blood, urine and saliva | - identify tumour using imaging

What is prolactinoma?

- prolactin = hormone involved in breast milk production - oma = tumour - excessive secretion of prolactin

Prolactinoma is the excessive secretion of prolactin. What can this cause in women?

- changes in menstrual cycle - mood disturbances - galactorrhoea (production of breast milk in those who are not pregnant/recently delivered)

What is the main cause of prolactinoma, the excessive secretion of prolactin?

- tumour on pituitary gland | - cause is really unknown

What does hypopituitarism mean?

- hypo = lower | - pituitarism = inflammation of the pituitary gland

What is hypopituitarism?

- lower or lack of secretion/synthesis of one or multiple hormones from the pituitary glands

Hypopituitarism is a lower or lack of secretion/synthesis of one or multiple hormones from the pituitary glands. What are the 3 main causes?

1 - tumour 2 - infection 3 - vascular failure

Cushings syndrome can cause severe muscle, bone and skin breakdown and soreness. Why is this?

- muscle, bone and skin are main sites of protein storage - elevated cortisol causes proteolysis as a source of energy - small amounts are good in acute stress response, but chronic can be bad

Cushings syndrome can cause central adiposity. Why is this?

- cortisol increases gluconeogenesis, increasing blood glucose levels - insulin secretion is increased, preferentially storing glucose in adipocytes - specifically adipocytes in central region are targetted