The hypothalamo-adenohypophyseal axis: anterior pituitary Flashcards
What is the alternative name for the pituitary gland?
HYPOPHYSIS
Why is the pituitary gland know as the master gland?
Regulates a series of other and it controls many body systems
What is the alternate name for the anterior pituitary gland?
adenohypophysis
What is the alternate name for the posterior pituitary gland?
neurohypophysis
Describe the embryology of the pituitary gland?
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The 2 components of the pituitary gland develop from different structures. There is a upward growth from the buccal cavity called Rathke’s pouch towards a downward growth from the base of the brain - these two growths combine to make one gland.
So the pituitary gland has 2 components, 1 secretory part derived from the buccal cavity the adenohypophysis and 1 neural part, the neurohypophysis, made up of nerve axons derived from the base of the brain.
Glandular Tissue - Buccal Cavity (pharyngeal region of the mouth) has an extension that starts growing upwards Nervous Tissue - there is a downwards movement of tissue from the developing hypothalamus .
These two tissues then fuse and normally lose contact with the rest of the buccal cavity. So one part of the pituitary is derived from glandular tissue (adenohypophysis) and the other part is derived from neural tissue (neurohypophysis)
Besides hormonal effects, what can a tumour of the pituitary gland cause and why can it do this?
The optic chiasm is near the anterior pituitary and this will become relevant n Y2 Endocrinology lectures when you learn that tumours of the pituitary gland can cause visual disturbance. add pic
What are groups of nueronal cell bodies known as?
Groups of neuronal cell bodies are called nuclei.
The hypothalamus surrounds one of the ventricles of the brain What is the name of this ventricle?
3rd Ventricle
What is the region of median eminence?
Median Eminence = an area that lies between the top of the pituitary stalk and the hypothalamus add pic
A different population of neurons have shorter axons and these terminate in the part of the hypothalamus which abuts the pituitary gland Name this region?
Region of median eminence
What is the body of the anterior putituary gland known as?
Pars distalis is the body of the anterior pituitary add pic
What is the part of the pituitary gland that wraps around the pituitary stalk?
the pars tuberalis is the part of the anterior pituitary which wraps around the pituitary stalk add pic
What is the Neurohypophysis mainly made up of ?
What does the Adenohypophysis consist of?
Neurohypophysis- (mainly nerve axons and nerve terminals) Adenohyphysis- Secretory cells add pic
Where do some of the axons coming from the hypothalmic nuclei terminate at?
Neurohypophysis and the Region of median eminence add pic
Describe the THE HYPOTHALAMIC – HYPOPHYSIAL PORTAL CIRCULATION? Start at the superior hypophyseal artery
It starts with blood arriving in the SUPERIOR hypophyseal artery and this enters a capillary network in the median eminence.
From this capillary network, blood drains to a second capillary network in the anterior pituitary – a portal network.
From the secondary capillary system, blood would flow out into the venous system via the cavernous sinus.
This system is critical for control of anterior pituitary function. The importance of the HYPOTHALAMIC – HYPOPHYSIAL PORTAL CIRCULATION is that it can carry messages from the hypothalamus to the anterior pituitary gland
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What is a portal network?
A portal network is where blood from the systemic circulation drains from one capillary network to another before returning to the heart.
What does fenestrated mean?
Fenestrated capillary is a leaky capillary
What in the hypothalmic-hypophysial portal circulation is fenestrated?
Primary Capillary Plexus Secondary Capillary Plexus
Where do many nuerones (not all) coming from the hypothalmic nuclei terminate at?
Lots of neurones coming from the hypothalamic nuclei terminate on the walls of the PRIMARY CAPILLARY PLEXUS
How does the hypothalamus play a major part in controlling anterior pituitary function?
Those short hypothalamic neurones which terminate in the median eminence lie on the surface of that primary capillary plexus.
These specific hypothalamic neurones, which abut the primary capillary network, when stimulated, release neurosecretion – hormones – which are going to get into the blood flowing through this primary capillary plexus and then they will be transported to the anterior pituitary where there will exert their effects and stimulate release of anterior pituitary hormones.
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What two types of Nuerosecretions from the nureons in the hypothalamus are there?
HYPOTHALAMIC RELEASING/INHIBITING HORMONES
What do Samatotrophs produce?
Growth Hormone (Somatotrophin)
What do Lactotrophs produce?
Prolactin
What do thyrotrophs produce?
Thyroid Stimulating Hormone (TSH, Thyrotrophin)
What do Gonadotrophs Produce?
Luteinising Hormone, Follicle Stimulating Hormone (LH and FSH)
What do Corticotrophs produce?
AdrenoCorticoTrophic Hormone (ACTH, Corticotrophin)
Name the cells that make up the anterior pituitary gland and name their coressponding hormone?
REMEBER THERE ARE 6 HORMONES AND 5 CELL TYPES add pic
Name the 2 Protein hormones (Very large in size) produced by the anterior pituitary gland?
GROWTH HORMONE (SOMATOTROPHIN ) 191 aa PROLACTIN 199 aa
Name the Glycoprotein hormones made by the Anterior pituitary gland?
THYROID STIMULATING HORMONE (TSH, THYROTROPHIN) b-sub-unit 110 aa 2 GONADOTROPHINS both have 115 aa b-sub-unit - LUTEINISING HORMONE (LH) - FOLLICLE STIMULATING HORMONE (FSH)
What is similar to all of the Glycoprotein Hormones (in terms of their structure) and what distinguishes them?
Alpha subunit is common to all, Beta subunit is different and hence determines the characteristics of the molecule
Name the Stimulatory and Inhibitory hypothalmic hormones for somatotrophin (Growth hormone).
Growth Hormone Releasing Hormone (GHRH, somatotrophin releasing hormone )- STIMULATORY
Somatostatin (SS)-INHIBITORY
Neurosecretions from different hypothalamic nuclei – GHRH in bold as this is the dominant signal and stimulates GH release. SS is a short polypeptide which is inhibitory on GH release – minor compared to dominant GHRH. It is the pulse of these hormones in relation to each other which will dictate GH release.
Name the Stimulatory and Inhibitory hypothalmic hormones for Prolactin?
Dopamine (DA)-INHIBATORY
Thyrotrophin releasing hormone (TRH)-STIMULATORY
Name the stimulatory hypothalmic hormone for TSH
TRH- Thyrotropin-releasing hormone
Name the stimulatory hypothalmic hormone for LH and FSH?
Gonadotrophin releasing hormone (GnRH
Name the stimulatory hypothalmic hormone for ACTH (corticotrophin).
Corticotrophin releasing hormone (CRH) Vasopressin (VP)
Some hypothalamic hormones are dominant over their counterpart Name 2 examples of this
Somatrotophin Releasing Hormone (SRH or GHRH) - dominant over somatostatin
Dopamine - dominant over thyrotrophin releasing hormone
How are hypothalmic hormones released and how does this effect the way that the anterior pituitary hormones are released?
Hypothalamic hormones are released in pulsatile fashion and hence, anterior pituitary hormones are released in a pulsatilefashion
Name the only hypothalmic hormone where it is the dominant single is the inhibatory signal?
Dopamine
List all of the ADENOHYPOPHYSIAL HORMONES AND THEIR MAIN TARGET CELLS?
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Name ALL of the effects of the Growth hormone in the body?
Lots of GH Rs on hepatocytes – binding of GH to these receptors causes production of IGF-1 (and 2) which mediates some of the effects of GH in the tissues.
Somatomedins are a group of proteins that promote cell growth and division in response to stimulation by growth hormone (GH) also known as somatotropin (STH). Somatomedins have similar biological effects to somatotropin. add pic
Name some examples of somatomedins
IGF 1 and IGF 2
Name the two ways somatotrophins work?
Direct Effect - binding to somatotrophin receptors in general cells of the body Hepatocytes - stimulating hepatocytes to produce IGF I Both these pathways mean that somatotrophin controls large aspects of metabolism
List the 4 Metabolic Actions of Somatotrophin ?
Increased cartilaginous growth and somatic cell growth.
Stimulation of lipolysis leading to increased fatty acid production.
Increased gluconeogenesis
Stimulation of amino acid transport into cells (e.g. muscle) and protein synthesis
SIIM
Why can Growth hormone predispose you to Diabetes Mellitus?
GH increases gluconeogenesis
Why does growth hormone cause the increase of amino acids into cells?
Certain glucogenic amino acids can stimulate growth hormone release.
Makes sense because after a meal you will have lots of amino acids coming in so by stimulating growth hormone release, you increase amino acid movement into the cells and increase protein synthesis at the nuclear level
Name things that stimulate growth hormone release?
Sleep (stages III and IV)
Stress
Oestrogens
Exercise
Fasting (hypoglycaemia)
Amino acids eg arginine (Maramite is rich in arginine)
Ghrelin (from stomach)
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Name the direct and indirect inhibotors of somatotrophin?
Inhibitors of somatotrophin: Direct - IGF I back to the pituitary. Indirect - IGF I back to the hypothalamus . Somatotrophin also has its own negative feedback effects - back to the hypothalamus - auto-negative feedback loop. add same pic as before
Describe the feedback loop for prolactin?
Stimulationn of Tactile receptors (SUCKLING)
This cause the suppression of hypothalmic dopaminergic neurones hence less dopamine release. add pic
