L3- Organistaion of the hypothalamus and pituitary Flashcards
Where is pituitary gland?
What happens to pituitary gland if it has tumours?
What is the protective mechanism to this delicate structure?
- directly beneath the hypothalamus
- it is very common for pituitary gland to get tumours-> as it is situated in sphenoid bone so limited space for expansion. Therefore, the gland can only extend upwards and compress cranial nerves, optic chiasm and cavernous sinus.
- it is protected by (superiorly) diaphragma sella, a dura layer, and (inferiorly) sella turcica of sphenoid bone
What is the hypothalamo-pituitary axis?
- it’s interface between central nervous and endocrine systems where neuronal signals have been converted into chemical signals eg hormones
- it maintains homeostatic function for several systems, eg. reproduction, appetite control, growth and development…
What are the borders of pituitary gland?
- anterior: lamina terminalis
- posterior: mammillary bodies (below is median eminence part of tuber cinereum)
- superior: thalamus
- inferior: sella turcica of sphenoid bone
What is tuber cinereum?
- it’s the swelling of hypothalamus (at the base) and where pituitary gland would locate directly beneath it
What is infundibulum?
- it’s also known as pituitary stalk
What is median eminence?
- bottom half of hypothalamus that is contained in tuber eminence
How are nuclei of hypothalamus arranged?
- in 3 zones surrounding the 3rd ventricle. most medial to 3rd ventricle= periventricular nuclei -> medial -> lateral
Where are the endocrine nuclei?
- locate in medial and periventricular zones
What are the hypothalamic neurosecretory cells?
- these are the cells transduce neural information into hormonal info, ie making hormones
- they contain larger cell bodies as it contains all components needed for hormone synthesis
- they mostly terminate in median eminence but some can terminate elsewhere in brain
How do neurosecretory cells produce and release hormones?
- hormones are synthesised in cell bodies of these neurosecretory cells then they are being packaged into vesicles and store in the axon terminals. When AP arrives, vesicles release hormones.
- They usually produce peptides
How are output of hormones determined in the neurosecretory cells?
- rate of AP firing at the axons and hence release of hormones
- rate of hormone synthesis in cell bodies
What does pulsatile secretion in neruosecretory cells mean?
- where activity of ‘like’ neurones, ie ones synthesis the same hormones, are fired and released hormones at the same time
What are the neural connections of hypothalamus? ( descending, ascending, and extensive intrahypothalamic connections)
- descending: from hippocampus, amygdala and septal nuclei
- ascending: from locus ceruleus and dorsal vagal complex (NA), from midbrain raphe (serotoninergic) and from midbrain ventral tegmentum (dopaminergic)
- extensive intrahypothalamic conenctions: some peptidergic
What are cicumventricular organs?
- these lie on midline along 3rd and 4th ventricles, e.g. subfornical organ, organum vasculosum of lamina terminalis and area postrema
- these are the leaky area of brain where large molecules can cross the blood-brain barrier and so can influence the brain
- eg. angiotensin(thirst), leptin(appetite), cytokines(fever)
- median eminence is also considered to be a circumventricular organ
How is pituitary gland developed?
- there is a down-growth of diencephalon to form infundibulum (the neural tissues) and a up-growth of oral ectoderm to form Rathke’s pouche (glandular tissues)
- the Rathke’s pouche eventually becomes detached from the oral ectoderm and meets the infundibulum’s process. Eventually fuse together and form the intermediate lobe of pituitary gland
- sphenoid bone is developing too
What do car crashes can easily cause lesion of pituitary gland?
- because pituitary gland situates in clinoid process where the pituitary stalk (infundibulum) can be easily banged against.
What is empty sella syndrome?
- where CSF is allowed to enter the pituitary fossa and leads to compression of pituitary gland. This means some hormones are unable to form= hypopituitarism
What is the component of anterior pituitary (aka adenohypophysis)?
- pars tuberalis (surrounding the pituitary stalk), pars distalis (the main anterior lobe) and pars intermedia (the intermediate lobe)
- glandular tissues so RELEASE HORMONES!
What are the components of posterior pituitary gland? ( neurohypophysis)
- Median eminence, infundibulum and pars nervosa (posterior lobe)
Blood supply of pituitary gland (anterior pituitary)
- For anterior pituitary: begins in anterior pituitary lobe by superior hypophyseal artery -> median eminence -> primary portal plexuses -> forms long portal vessel -> and then forms secondary plexus -> to systemic blood via cavernous sinus, superior/inferior petrosal sinuses, jugular bulb and vein
Blood supply of pituitary gland (posterior pituitary)
- For posterior lobe: supplies by both middle and inferior hypophyseal arteries then form the posterior pituitary capillary bed -> efferent veins -> systemic blood via cavernous sinus, inferior/superior petrosal sinuses, jugular bulb & vein
How is posterior pituitary gland innervated?
- magnocellular hypothalamic neurosecretory neurones DIRECTLY innervating the posterior pituitary lobe via paraventricular nucleus (more lateral part) and supraoptic nucleus
- Direct innervation bceause it is via pituitary stalk, release neurohyoiohysial hormones into systemic blood
How is anterior pituitary lobe innervated?
- by parvocellular hypothalamic neurosecretory neurones INDIRECTLY controlling the anterior pituitary lobe via arcuate nucleus, medial part of paraventricular nucleus and periventricular zone.
- it is indirect because parvocellular neurones terminate in median eminence and release hypophysiotrophic hormones via the primary portal plexus and secondary plexus
What are the 5 cell types found in pituitary gland?
- somatotroph, lactotroph, gonadotroph, thyrotroph, corticotroph
What hormone does somatotroph produce?
- growth hormone (up to 50%)
What hormone does lactotroph produce?
- prolactin (10-25%)
What hormone does gonadotroph produce?
- Luteinising hormone and follicle stimulating hormone (10-15%)
What hormone does thyrotroph produce?
- thyroid stimulating hormone (<10%)
What hormone does corticotroph produce?
- adrenocorticotrophic hormone (ACTH) ( 15-20%)
What do folliculostellate cells do?
- supporting cells like glial cells
- has a potential paracrine role
- release peptides to regulate neighbouring cells
What is Sheehan’s syndrome?
- increase in size of pituitary gland so put pressure on pituitary stalk and blood vessels
- leads to necrosis of pituitary gland tissues
What does pars intermedia produce?
- melanotrophs -> Melanocyte-stimulating hormone
* no hormones produced in posterior pituitary gland
