L3- Organistaion of the hypothalamus and pituitary

Question 0

Where is pituitary gland?
What happens to pituitary gland if it has tumours?
What is the protective mechanism to this delicate structure?

Answer 0

• 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

Question 1

What is the hypothalamo-pituitary axis?

Answer 1

• 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…

Question 2

What are the borders of pituitary gland?

Answer 2

• anterior: lamina terminalis
• posterior: mammillary bodies (below is median eminence part of tuber cinereum)
• superior: thalamus
• inferior: sella turcica of sphenoid bone

Question 3

What is tuber cinereum?

Answer 3

• it’s the swelling of hypothalamus (at the base) and where pituitary gland would locate directly beneath it

Question 4

What is infundibulum?

Answer 4

• it’s also known as pituitary stalk

Question 5

What is median eminence?

Answer 5

• bottom half of hypothalamus that is contained in tuber eminence

Question 6

How are nuclei of hypothalamus arranged?

Answer 6

• in 3 zones surrounding the 3rd ventricle. most medial to 3rd ventricle= periventricular nuclei -> medial -> lateral

Question 7

Where are the endocrine nuclei?

Answer 7

• locate in medial and periventricular zones

Question 8

What are the hypothalamic neurosecretory cells?

Answer 8

• 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

Question 9

How do neurosecretory cells produce and release hormones?

Answer 9

• 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

Question 10

How are output of hormones determined in the neurosecretory cells?

Answer 10

• rate of AP firing at the axons and hence release of hormones
• rate of hormone synthesis in cell bodies

Question 11

What does pulsatile secretion in neruosecretory cells mean?

Answer 11

• where activity of ‘like’ neurones, ie ones synthesis the same hormones, are fired and released hormones at the same time

Question 12

What are the neural connections of hypothalamus? ( descending, ascending, and extensive intrahypothalamic connections)

Answer 12

• 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

Question 13

What are cicumventricular organs?

Answer 13

• 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

Question 14

How is pituitary gland developed?

Answer 14

• 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

Question 15

What do car crashes can easily cause lesion of pituitary gland?

Answer 15

• because pituitary gland situates in clinoid process where the pituitary stalk (infundibulum) can be easily banged against.

Question 16

What is empty sella syndrome?

Answer 16

• 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

Question 17

What is the component of anterior pituitary (aka adenohypophysis)?

Answer 17

• pars tuberalis (surrounding the pituitary stalk), pars distalis (the main anterior lobe) and pars intermedia (the intermediate lobe)
• glandular tissues so RELEASE HORMONES!

Question 18

What are the components of posterior pituitary gland? ( neurohypophysis)

Answer 18

• Median eminence, infundibulum and pars nervosa (posterior lobe)

Question 19

Blood supply of pituitary gland (anterior pituitary)

Answer 19

• 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

Question 20

Blood supply of pituitary gland (posterior pituitary)

Answer 20

• 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

Question 21

How is posterior pituitary gland innervated?

Answer 21

• 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

Question 22

How is anterior pituitary lobe innervated?

Answer 22

• 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

Question 23

What are the 5 cell types found in pituitary gland?

Answer 23

• somatotroph, lactotroph, gonadotroph, thyrotroph, corticotroph

Question 24

What hormone does somatotroph produce?

Answer 24

• growth hormone (up to 50%)

Question 25

What hormone does lactotroph produce?

Answer 25

• prolactin (10-25%)

Question 26

What hormone does gonadotroph produce?

Answer 26

• Luteinising hormone and follicle stimulating hormone (10-15%)

Question 27

What hormone does thyrotroph produce?

Answer 27

• thyroid stimulating hormone (<10%)

Question 28

What hormone does corticotroph produce?

Answer 28

• adrenocorticotrophic hormone (ACTH) ( 15-20%)

Question 29

What do folliculostellate cells do?

Answer 29

• supporting cells like glial cells
• has a potential paracrine role
• release peptides to regulate neighbouring cells

Question 30

What is Sheehan’s syndrome?

Answer 30

• increase in size of pituitary gland so put pressure on pituitary stalk and blood vessels
• leads to necrosis of pituitary gland tissues

Question 31

What does pars intermedia produce?

Answer 31

• melanotrophs -> Melanocyte-stimulating hormone

* no hormones produced in posterior pituitary gland