Neuroendocrinology Flashcards
what are the 3 mechanisms that the hypothalamus uses to regulate endocrine systesm
- ANS centers exert nervous control on adrenal medulla
- vasopressin/antidiuretic hormone (ADH) and oxytocin production (released from pituitary gland)
- regulatory hormone production (RH and IH) controls pituitary gland directly and all other endocrine glands indirectly
what are the neurohormones produced in the hypothalamus (9)
- oxytocin: milk let down, luteolysis, sexual function
- antidiuretic hormone/vasopressin: water balance, magnocellular neurons of supraoptic nucleus
- gonadotropin releasing hormone (GnRH/LHRH): reproductive functions, rostral hypothalamus within preoptic area
- corticotropin releasing hormone (CRH): stress, parvocellular neurones of the paraventricular nucleus
- thyrotropin releasing hormone (TRH): metabolism, parvocellular neurones of the paraventricular nucleus
- prolactin inhibiting factor (PIF)/dopamine: lactation, parental behaviour, arcuate nucleus
- prolactin releasing factor (PRF)?
- growth hormone releasing hormone (GHRH): growth, metabolism, lactation, arcuate nucleus
- somatostatin (SS)
where does the hypophysis sit
sits within hypophysial fossa of cranial floor
in sella tunica of the sphenoid bone
what is the gross strucutre of the hypophysis
dura invests the gland and roofs the depression apart from the diaphragma sella
venous channels (cavernous sinus) either side link the ophthalmic plexus rostrally and externally jugular and ventral venous plexus caudally
transverse (intercavernous) sinuses rostral and caudal completes venous ring
lateral to cavernous sinus are cranial nerves that supply eye
what are the two main parts of the hypophysis
- posterior pituitary gland/pars nervosa/neurohypophysis
- anterior pituitary/pars distalis/adenohypophesis
how does the posterior pituitary form
down growth of nervous tissue from hypothalamus (neuroecoderm)
how does the anterior pituitary form
upgrowth of epithelium of the roof of the oral cavity Rathkes pouch (oral ectoderm)
what are these two structures
hypophysial cleft (lumen of rathke’s pouch)
pars intermedia intermediate lobe, tissue caudal to cleft applied to neurohypophysis, secrete melanocyte stimulating hormone
what is the hypophyseal portal system
two capillary networks in serial arrangment
portal veins: blood vessels that link two capillary networks
what are the cells that make up the anterior piituitary
specialized glandular epithelium
what is the function of the anterior pituitary
procues trophic and direct action hormones
what ist he anterior pituitary regulated by
hypothalamus
releasing or inhibiting hormones
via a unique system of portal veins
what are the secretory cells of the anterior pituitary
- chromophils
- acidophils
- basophils
- chromophobes: resting or degranulated chromophils
- basement membrane
- fenestrated sinusoid (extensive capillary network)
what cells are these
gonadotrophs LH/FSH
5% population
basophils
large cells, secretory granules of varying size
what cells are these
somatotrophs GH - most numerous
~50% acidophils
packed with secretory granules of moderate size
what cells are these
corticotrophs ACTH
20% basophil
EM sparse secretory granules, located at extreme periphery
what cells are these
mammotrophs (lactotrophs) –> prolactin
acidophils
20% but changes with physiological state
what cells are these
thyrotrophs - TSH
5% basophil
small granules, located peripherly
what is the function of posterior pituitary
release oxytocin and antidiuretic hormone (ADH or vasopressin) into circulation
where are the hormones produced in the posterior pituitary
ADH - supraoptic nucleus
Oxy - paraventricular nucleus
where are the posterior pituitary transported to and stored in and why are the released
neuronal terminals
released in response to nervous impulses from other brain areas
what are the features of the axons in the posterior pituitary
non myelinated
what are the cells in the posterior pituitary supported by
pituicytes (similar to neuroglia)
what are herring bodies
scattered, large and bluish-violet (in PAAB/PAS/orange G stain) masses –> dilations of nerve fibres filled by small vesicles containing the neurosecretory products of the hypothalamic cells
what strucutres is this
herring bodies
what is are the features of pars intermedia histology
basophilic cells
irregular clumps
cells contain secretory granules –> synthesized and split into ACTH, MSH, endorphins, lipotrophins
what is the pineal gland/epiphysis
small, dark pigmented outgrowth from posterior roof of the third ventricle, before rostral colliculi
connected via short stalk
named due to resemblance to pine cone
what are the cells in the pineal gland
- pinealocytes (most abundent) –> modified neurones
- neuroglia/astrocytes –> small dark nuclei
- endothelial cell nuclei
- astrocytes
what are the cells shown
atrocytes
pinealocytes
what is pineal sand
in aging pineal –> basophilic, extracellular bodies, concentric layers of calcium and magnesium phosphate
what are the features of pinealocytes and astrocytes
long processes tissues appear stringy nuclei
where are endothelial cell nuclei found
found in association with vessels and capillaries traversing the tissue
what does the pineal secrete
melatonin
what are the key features of neuroendocrine systems
- negative feedback
- maturation of hypothalamo-pituitary axis leads to puberty
- hypothalamus integrates disparate information –> afferents from other nuclei (kisspeptin), the output is altered secretion of releasing/inhibiting hormone (GnRH)
what are neuroendocrine reflexes
- milk let down –> oxytocin
- milk production
receive information from other neural systems
what is the hypothalamo-pituitary-thyroid axis
classic negative feedback
disrupted by low iodine
what is primary and secondary hypothyroidism
- primary: lymphocytic thyroiditis and idiopathic atrophy
- secondary: space-occupying tumour (pituitary adenoma)
what is hyperthyroidism
functional thyroid adenoma (cats), thyroid carcinoma (dogs)
what is the role of the HPA
metabolic rate (nuclear action)
brain development and bone maintanance
cardiac and digestive funciton, muscle control
what are the cells of the thyroid
- thyroid follicles –> spherical, single layer cuboidal epithelium bounded by basement membrane
what are thyroid follicles filled with
colloid, a proteinaceous depot of thyroid hormone precursor (thyroglobulin) produced by principle cells
what do the size of the follicle cells in the thyroid reflect
activity
squamous cells - inactive
cuboidal to columnar - active
what is the fibroud outer capsule in follicles
loose areolar connective tissue from which fine septa extend dividing into lobules
septa convey blood supply, lymphatics and nerves
