Pituitary and Pineal Glands
H and E staining fo the pituitary gland -how can you distinguish PD from PN? How does the PT stain? How about the infundibular process, which is underneath the PT? -what's a key feature of the PI?
-PD stains really intensely because it has a lot of secretory granules [think PD is intense] vs. PN is full of unmyelinated axons so it stains poorly -PT is an upward extension of PD so it also stains intensely -Underneath the PT is infundibular process which stains just like the PN -PI - has big holes called follicles for hormones [think it's a connector]
What is meant by endocrine secretion? Synaptic secretion? and less importantly, autocrine? paracrine? What's the t1/2 of the hormone for each type? Where does synaptic secretion occur?
-autocrine - secretes chemical that will act on its own (auto) receptors. short t1/2 -paracrine - expands more in the neighborhood. short t1/2 -endocrine secretion - secrete chemical messengers -> systemic circulation -> very distant target organ -> comes out of capillaries and binds to receptors in target organ cells. V slow process, hormones must have a long t1/2 -synaptic secretion - CNS only! Synthesize and secrete hormones that will be stored along the axon and released upon a cue to the target cell. t1/2 of hormone has to be long
How can you decide if an empty space is a sinusoid or a chromophobe? How do acidophils stain on Mallory stain? Why?
-empty space: if there's a nucleus -> chromophobe. If not -> sinusoid -Acidophils stain orange on Mallory stain [think they're more red anyway - close to orange]- intense orange means lots of granules
How do the hypothalamus and neurohypophysis communicate?
directly via the infundibulum (aka parks tuberalis and infundibular process. Not median eminence) (read notes on slide)
higher mag of pineal gland - how do the pinealocytes stain?
euchromatin - stains poorly. Nuclei are oval. -Long glial like cells with dark nuclei.
How are the secretory granules discharged into fenestrated capillaries?
exocytosis -hormones from the anterior hypophysis are stored in secretory granules -hormones are released in a pulsatile or cyclic manner
mechanisms of secretion of neuroendocrine cells - what are Herring bodies? What is the role of pituicytes?
hormones are secreted in the soma of the hypothalamic neurons -> They travel down and are stored in the Herring body -Pituicytes have cytoplasmic processes making contact with axons and capillary, preventing hormones from diffusing into BVs. To release hormones into the bloodstream, cell processes need to retract (which can happen in response to a specific neural cue) look at attached pic!
Secretory functions of neuroendocrine cells - what do ADH/oxytocin do? What does absence/reduction in vasopressin lead to?
hypothalamic DI = neurogenic = cranial
Subdivisions of the neurohypophysis. What does it consist of?
neurohypophysis = pars nervosa + infundibulum
histo lab slide of the pituitary
notice PD stains intensely. PI has follicles
Histo of the pineal gland what makes up most of the parenchyma? what's the giveaway that you're in the pineal gland?
pinealocytes = 95% of the parenchyma brain sand is the giveaway! [think piney boys are a big dark topic - brain sand]
Where does the pineal gland develop from embryologically?
roof of posterior diencephalon [posterior - remember back up that pine! If I don't do it I will die!] -final structure = incomplete lobules separated by CT septa [p isn't complete without v!]
high mag of pars nervosa
tracks and tracks of unmyelinated axons with nuclei belonging to pituicytes. Some can have lipid accumulation, lipofuscin, that you find in an aging brain.
Where (gross anatomy) is the pituitary gland located? What are anterior and posterior landmarks? What are the two types of hormones secreted by the pituitary?
-in the *sella turcica* = a depression of the *sphenoid bone*. Below the base of the brain. Anterior = optic chiasm, posterior = mamillary body. -Pituitary gland gets protection from the sella turcica, and also from the dura mater which dips down -the pituitary stalk connects the pituitary to the brain - this area is NOT protected and is thus vulnerable. 2 types of hormones secreted by the pituitary: 1) hormones acting on non-endocrine tissue, such as growth hormone 2) hormones acting on other endocrine glands = *tropic* hormones (eg TSH)
Histo of the pars tuberalis -what is it anatomically (what is it an extension of, what does it wrap around)? -What cell type does it mainly contain?
-pars tuberalis = upward extension of pars distalis -pars tuberalis wraps around the infndibular process -most cells are gonadotrophs secreting low levels of FSH and LH, which are not physiologically significant [think FSH and LH have to do w ur reproductive TUBEs aka tuberalis]
How are acidophils and basophils distributed in the pars distalis?
-somatotrophs are located on the sides of the PD [think I am growing at my sides] -thyrotrophs and corticotrophs are found in the median portion of the pars distalis -mammotrophs and gonadotrophs are scattered throughout the pars distalis [think hos scattered around]
HDI vs Nephrogenic DI
-Hypothalamic: ADH levels are down. So you can treat with ADH. -Nephrogenic: ADH is fine, it's the AQP-2/ADH V2 receptors that are messed up, so ADH doesn't do anything. So you can't treat with ADH (ADH binds to its receptor called ADH V2 receptor -> inc cyclic AMP -> activates PKA -> phosphorylates aquaporin 2 - brings in water from the lumen side, aka urine side -> water molecules are transported into the cell -> transported out view another water channel called aquaporin 3 -> blood. )
What are the three vessels that constitute the primary blood supply to the hypophysis? What major vessels do these originate from? What vessels supply adenohypophysis vs neurohypophysis? Describe the trajectory of these vessels and the functions of the various capillary loops?
-superior hypophysial, trabecular, and inferior hypophysial arteries are all derived from the internal carotid artery -read notes on slide -think the neurohypophysis is in the back so it needs some help - takes middle and bottom vessels -make sure you read the purpose of the secondary capillary loop of the pituitary portal system!
How does the hypothalamus contact the adenohypophysis?
-via the pituitary portal vessels [remember ADENohypophysis - AGAIN with the vessels aka portal system] read notes on slide
What are the two major types of endocrine cells in the pars distalis?
1) *chromophils* = stained cytoplasm a) *acidophils* : *s*omatotrophs (make growth hormone - think work - grow your body) *m*ammotrophs (make prolactin) [Drink acidic oj in the AMs] Acidophils stain a red pink color b) *basophils* : Thyrotrophs (TSH) Gonadotrophs (FSH and LH - this is the only type that makes two hormones) Corticotrophs (ACTH) 2) *Chromophobes* -unstained cytoplasm - looks like empty space -most likely undifferentiated cells
What are the ways that endocrine cells can be distributed anatomically (3)?
1) *endocrine gland* = endocrine cells gathered together 2) can form *discrete clusters* within a specialized organ such as the Islands of Langerhans in the pancreas 3) can disperse among other cells in epithelial tissues to form the *diffuse neuroendocrine system* (gut and respiratory tract. These are v powerful cells that secrete catecholamines. V powerful, unexplained HTN think about a tumor here.)
What are the two distinct embryonic origins of the pituitary gland? From which layer is the pars intermedia derived? What's its function?
1) Adenohypophysis - ectodermal origin (rathke's pouch. Comes from roof of primitive mouth - grows upward. Think Rakhee has a big mouth and is ectroverted aka ectoderm! And your mouth is anterior!) 2) Neurohypophysis - neural origin (diencephalon. Falls from floor of diencephalon) Infundibulum connects the neurohypophysis to the diencephalon. -Pars intermedia is remnant of inner layer of Rathke pouch [Think Rakhee is like a Mom. She birthed this little remnant.] Has no functionality in humans -Stem connecting Rathke pouch degenerates, although there can be some residual tissue (labeled 5 in attached pic) - can form craniopharyngioma - benign but needs to be resected because it will squeeze the pituitary gland which will then impinge upon the optic chiasm nearby. This tumor is rare.
What are the 3 components of the pars distalis?
1) Cords of epithelial cells (endocrine cells) 2) Minimal supporting connective tissue [think it's distant, doesn't have much connection] 3) numerous fenestrated capillaries
What are the three histologic components of the neurohypophysis?
1) fenestrated capillaries derived from the inferior hypophysial artery 2) Pituicytes = glial cells providing support to axons [think glial cells accompany neurons and are thus in the neurohypophysis] 3) Unmyelinated axons of neuroendocrine cells located in nuclei of the hypothalamus
Corticotrophs - what percentage of the cell population? What is the function of the hormone it secretes?
Corticotrophs = 20% of the cell population -Corticotrophs secrete ACTH (Adrenocorticotropic hormone). ACTH stimulates growth and secretory activities of the adrenal gland, more specifically the zona fasciculata (ZF - cortisol) and zona reticularis (ZR). -Cortisol is the dominant regulatory factor -Low levels of cortisol stimulate ACTH release. High levels of cortisol inhibit ACTH release (when you're stressed you don't feel like starting your day. ACTH is released before you wake up so you wake up ready for the day. But, need to balance, because too much ACTH gives you high bp.) -High levels of stress stimulate ACTH release (go to sleep wired up). More class notes: When you put a pt on high levels glucocorticoids -> take them all away -> pt won't be happy bc the corticoptrophs would have been so depressed by the glucocorticoids so will sleep poorly at night. So you need to slowly decrease the glucocorticoid level.
Gonadotrophs - make up what percentage of the cell population? Role?
Gonadotrophs = 10% of the cell population -a single gonadotroph can synthesize and release both FSH and LH (remember these are the exception - they make 2 types of hormone) -a lack of FSH and LH in females and males leads to infertility (notes from class: Gonadotrophs are activated by gonadotropic releasing hormone (GRH) and activin (less imp) -> make FSH and LH Female: FSH acts on developing oocyte -> proliferation of cell from granulosa (gray) -> will proliferate and produce estradiol LH will act on the corpus luteum, which is formed at the second half of the menstrual cycle. Corpus luteum makes progesterone under the cue of the LH hormone. If pregnancy doesn't occur -> corpus luteum will regress. If pregnant, it remains, so LH remains high, and corpus luteum makes lots of progesterone. Males: FSH acts on Sertoli cells in seminiferous tubules of testes -> Sertoli cells make androgen binding proteins (ABPs). LH acts on Leydig cells in the testes, responsible for making testosterone.
Hallmarks of an endocrine gland -are there ducts? -are there vessels? -how are hormones delivered to target organs?
Hallmarks of an endocrine gland: -*NO duct system* to transport hormonal secretions. Endocrine glands are ductless glands -Endocrine glands are *heavily vascularized* -Numerous *fenestrated capillaries* in order to deliver secreted hormones to target tissues
Histology of the pars intermedia -humans - what's it left over from? -what structures does it contain?
Histology of the pars intermedia -in humans, it's *rudimentary* (left over of the inner layer of the rathke's pouch) -presence of basophils with small secretory granules and follicles filled with colloid (*Rathke's cysts*). These follicles have cuboidal epithelium
Major subdivisions of the hypophysis -What are the 3 components of the adenohypophysis? -What are the 2 components of the neurohypophysis? -What constitues the pituitary stalk?
Major Subdivisions of the hypophysis 1) Adenohypophysis = anterior -pars distalis -pars tuberalis (upward extension of the distalis. Think tube tops bring you up) -pars intermedia 2) Neurohypophysis -pars nervosa -infundibulum = median eminence (funnel like extension of the hypothalamus) and infundibular process (underneath pars tuberalis. Pars tuberalis essentially wraps around this.) -*pituitary stalk* = infundibular process + pars tuberalis. Does not include median eminence (think this is really an extension of the hypothalamus) Hypothalamohyphophysial system - they work in junction
Mammotrophs - what hormone does it secrete? How is it regulated?
Mammotrophs = 15-20% of the cell population -secretion of prolactin is mainly regulated by INHIBITION rather than stimulation [think you're mainly NOT lactating] -Dopamine is the main inhibitor [you'd be a dope to have kids now! Don't lactate!]. Suckling during lactation is the major stimulus of prolactin secretion read notes on slide!
Somatotrophs -make up what percentage of the cell population? -What hormone does it secrete? When is the peak level of secretion? How does this hormone work? How is it shut off? -What inhibits secretion of this hormone? -what pathology does decreased release of this hormone lead to? Excess?
Somatotrophs: 40-50% of the cell population -GH is secreted at peak levels *before awakening* [think sleep is really imp for kids so they can grow!] -high glucose levels inhibit GH release and therefore the GH-IGF-I axis in children with type I diabetes. (-> Need to equilibrate glucose levels late night/early AM). (Notes on GH-IGF-I axis: GH itself doesn't induce growth! GH binds to receptors on hepatocytes which will make IGF-1 -> IGF-1 binds receptors in chondrocytes and epiphyseal plates on long bones -> induces growth. When IGF-1 reaches a certain threshold it will give a two-part negative feedback -> a) somatotrophs start decreasing activity, b) hypothalamus starts making somatostatin which blocks somatotrophs so that GH is no longer released). -Decrease of GH in children -> dwarfusm -Excess of GH in children -> gigantism -Excess of GH in adults -> acromegaly (Bc the epiphyseal plates can't undergo growth. Enlarged jaw, feet, hands, soft tissue. Address with surg).
What is the role of the pineal gland - what does it respond to and how?
The Endocrine Activity of the Pineal Gland is Modulated by Light through Nervous Pathways -light -> eye -> suprachiasmatic nucleus (in hypothalamus) -> hypothalamospinal tract -> superior cervical ganglion - postganglionic fibers go along arteries -> pineal gland. The pineal gland activity is DEPRESSED by light [think your pine is most active in the dark]
Thyrotrophs - what percent of the cell population? What is its role? Try to draw out arrows for T3, T4, and TSH for hyper and hypo thyroidism caused by pituitary vs thyroid glands.
Thyrotrophs = 5% cell population, but powerful TSH -> thyroid -> T4 -> T3 -> T3 provides negative feedback and shuts down thyrotrophs. *Only T3 has an inhibitory feedback action on TSH synthesis and release by thyrotrophs.* Thyroid problems can be due to the thyroid gland or due to the pituitary gland.
High mag of the pars distalis
basophils stain darker! [think that base is heavy]
