2 - The hypothalamus-adenohypophysial axis Flashcards by Bridget Butler

Where is the pituitary gland located?

Tiny structure attached to the base of the brain, under the hypothalamus.
Lies in a bony dip.
Saddle shape.
It is not part of the brain (it’s a different type of tissue)

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What is the pituitary gland sometimes called?

Hypophosis

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What are the 2 lobes of the pituitary gland?

Anterior lobe

Posterior lobe

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What is the anterior lobe called?

Where does it grow from?

Adenohypophysis
(needs a blood supply)
Upward growth from buccal cavity

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What is the posterior lobe called?

Where does it grow from?

Neurohypophysis
- Neural part (made of nerve axons)
Down growth from base of brain

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What are hypothalamic nuclei?

A collection of neuronal cell bodies in the hypothalamus.

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What is the region of median eminence do?

Border between the hypothalamus and pituitary gland.
Some neutron axons terminate here.
(Blood brain barrier)

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How does circulation work between the hypothalamus and the pituitary gland?

Blood enters from superior hypophyseal artery.
Blood enters the primary capillary plexus (fenestrated) in the median eminence.
Blood drains through the long portal veins into second capillary plexus (fenestrated) in anterior pituitary. This is called a PORTAL NETWORK - blood from systemic circulation drains from one capillary network to another before returning to the heart.
Blood flows out into venous system via cavernous sinus and leaves through jugular veins.

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How many adenohypophysial cells are there?

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What are the 5 adenohypophysial cells?

SOMATOTROPHS

LACTOTROPHS

THYROTROPHS

GONADOTROPHS

CORTICOTROPHS

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What do SOMATOTROPHS produce?

Growth Hormone (Somatotrophin)

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What do LACTOTROPHS produce?

Prolactin

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What do THYROTROPHS produce?

Thyroid Stimulating Hormone (TSH, Thyrotrophin)

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What do GONADOTROPHS produce?

Luteinising Hormone, Follicle Stimulating Hormone (LH and FSH)

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What do CORTICOTROPHS produce?

AdrenoCorticoTrophic Hormone (ACTH, Corticotrophin)

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What does trophin mean?

‘Stimulates the growth and development of’

What does POMC stand for? What is it?

ProOpioMelanoCorticotrophin

It is a prohormone for ACTH

What are the different types of adenohypophysial hormones?

PROTEINS (largest)

Growth hormone
Prolactin

GYLCOPROTEINS (alpha and beta subunits)

TSH
LH, FSH

POLYPEPTIDE (smallest)
- ACTH

What hypothalamic hormone STIMULATES the release of Growth Hormone (somatotrophin)?

Growth hormone releasing hormone (GHRH, somator=trophin releasing hormone)

What hypothalamic hormone INHIBITS the release of Growth Hormone (somatotrophin)?

Somatostatin (SS)

What hypothalamic hormone INHIBITS the release of Prolactin?

What is special about this?

DOPAMINE (DA)
This controls prolactin, it is under negative control.
A reduction in dopamine = release of prolactin

What hypothalamic hormone STIMULATES the release of Prolactin?

Thyrotropin releasing hormone (TRH).

This only has a small effect.

What hypothalamic hormone STIMULATES the release of Thyroid Stimulating Hormone (TSH, Thyrotrophin)?

Thyrotrophin Releasing Hormone (TRH)

What hypothalamic hormone STIMULATES the release of LH and FSH?

Gonadotrophin releasing hormone (GnRH)

What hypothalamic hormone STIMULATES the release of ACTH (corticotrophin)?

Corticotrophin releasing hormone (CRH) | Vasopressin (VP)

What is the main target cell of Growth hormone?

General body tissue | Liver

What is the main target cell of prolactin?

Breasts in lactating women

What is the main target cell of thyrotrophin?

Thyroid

What is the main target cell of gonadotrophins LH and FSH?

Testes (Men) | Ovaries (Women)

What is the main target cell of corticotrophin?

Adrenal cortex.

How does Growth hormone stimulate growth?

1. Adenohypophysis releases growth hormone. 2. Growth hormone goes to liver (a tiny bit goes straight to body tissues). Lots of GH receptors are on hepatocytes (liver cells). 3. Liver produces somatomedins IGF I (and IGF II). 4. IGF I (and IGF II) go to body tissue and stimulate growth and development.

What metabolic actions happen to increase growth following growth hormone release?

- Stimulation of amino acid transport into cells (muscle) and protein synthesis - More gluconeogenesis - Stimulation of lipolysis = more fatty acid production - More cartilaginous growth & somatic cell growth

What factors stimulate production of GH (somatotrophin)?

``` Sleep Stress Oestrogen Fasting (hypoglycaemia) Amino acids (arginine) Grelin (from stomach) ```

How does the negative feedback cycle work for GH?

IGF-I has direct feedback to Anterior pituitary and indirect effects on hypothalamus to reduce GHRH. Short feedback Negative feedback of GH to hypothalamus.

Explain negative feedback of neuro-endocrine reflex arc with PROLACTIN

- Prolactin released - Milk production - Suckling by baby - Stimulation of tactile receptors - Afferent neural pathway, suppression of hypothalamic dopaminergic neurones - Less dopamine produced - More prolactin released

What is the body of the anterior pituitary called?

Pars distalis

What is the pars tuberalis?

Part of the anterior pituitary that wraps around the pituitary stalk.

Explain how the hypothalamus-adenohypophysial axis works.

1. Hypothalamic nuclei - Have neurones that go to the median eminence - They release neurosecretions (hormones) which get into blood 2. Hormones travel in blood, neurosecretion acts on Anterior pituitary target cells in the adenohypophysis. 3. Adenohypophysial hormones released.