Endocrine Histology - Wright Flashcards
General considerations of endocrine system, 4 things
Regulates metabolic activities, maintains homeostasis
Slow-acting system
acts via hormones
endocrine glands = ductless
3 classes of Hormones
Peptides / proteins
AA derivatives
Steroids / FA derivatives
Signal transduction of hormones
Hormones bind to receptors :
on surface of plasmalemma
for peptide / protein hormones
Within the cytoplasm (other types)
Signal Transduction: different types
Endocrine: passes through bloodstream to get to target cell
Paracrine: Signaling cell passes through local mediator to get to other cells
Neuronal: Signal goes through neurotransmitter
Contact-Dependent: Signaling cell goes to target cell via membrane-bound signal molecule
General signaling pathway
Starts from extracellular signal -> receptor -> intracellular signaling proteins ->
a.) metabolic enzyme -> altered metabolism.
b.) gene regulatory protein -> altered gene expression.
c.) cytoskeleton protein -> altered cell shape/movement.
Secondary Messanger examples
cAMP
cGMP
phsophatidylinositol
calcium ions
sodium ions
Integrated signaling
2 separate signaling molecules bind to 2 separate receptors in order to relay message.
Feedback of Low body temp
Low Body temp:
Hypothalamas secretes TRH -> targets anterior pituitary.
Anterior pituitary release TSH -> stimulates follicular cells
Follicular cells of thyroid release TH (T3)-> increase metabolic activities, increasing body temp
Increased body temp detected by hypothalamas -> secretion of TRH inhibited. TH also blocks TRH
2 glands in pituitary gland & what it does
adenohypophysis (anterior pituitary): develops from hypophyseal (Rathke’s) pouch (oral ectoderm). Adeno means glandular, so these are glandular type cells that actually secrete things. Originates from oral cavity
neurohypophysis (posterior pituitary): develops from neuroectoderm. Made of nervous tissue (axons glial cells). Originates from neuroectoderm (head area)
Pituitary gland produces hormones that regulate growth, reproduction, metabolism
Location of Pituitary Gland
What does it sit in
Inferior to hypothalamus - connected to it by hypophyseal stalk
Sits in hypophyseal fossa in sella turcica
Roles of hypothalamus
Secretes “releasing hormones” or “inhibiting hormones” that control function of anterior pituitary
controls ANS, receives input from CNS
Controls posterior pituitary function via neurosecretory innervation
Overall role: REGULATE HOMEOSTASIS
Stimulating / inhibiting factors of hypothalamas
neurons from hypothalamus terminate on capillary, release releasing and inhibitory hormones:
TRH (stimulates release of TSH)
CRH (stimulates release of ACTH)
GHRH (stimulates release of GH)
Somatostatin (inhibits release of GH/ACTH/TSH)
GnRH (stimulates release of LH and FSH)
PRH (stimulates release of prolactin)
Dopamine (PIF, or prolactin inhibiting factor)
Thyroid hormones
Thyrotropin-releasing hormone (TRH) causes Thyroid-stimulating hormone (TSH) which makes thyroid gland release T3 and T4.
T3 and T4: increased metabolism; growth and development, increased catecholamine effect
Pituitary circulation
Very rich in circulation
Anatomical regions of pituitary
Anterior pituitary:
-pars distalis (on pars anterior)
-pars intermedia (next to posterior, the middle)
-pars tuberalis (on the tube)
Posterior pituitary:
-median eminence (top part)
-infundibulum (stem and process)
-pars nervosa (lobe)
Adenohypophysis (Anterior pituitary): Pars distalis
Types of cells within:
extra: chromophils: acidophils / basophils
VERY IMPORTANT SLIDE
Somatotrophs: release somatotropin (growth hormone); stimulated by SRH
Lactotrophs (Mammotrophs): release prolactin; stimulated by PRH and inhibited by PIF
Corticotrophs - secrete ACTH and LPH; stimulated by CRH
Thyrotrophs - secrete TSH; stimulated by TRH
Gonadotrophs - secrete FSH and LH (ICSH); stimulated by LHRH
Pars intermedia
contains___ which secrete ____, a precursor to:
contains basophils, secrete proopiomelanocortin (POMC), a precursor to:
a-MSH (melanocyte-stimulating hormone)
Corticotropin
b-lipotropin
b-endorphin
Precursors to POMC, what they stimulate
a-MSH: regulates movement of melanin, also controls appetite/sexual behavior
Corticotropin: stimulates adrenal cortex / secrete hormones
b-lipotropin: stimulates melanin production, lipolysis, steroidogenesis
b-endorphin: binds to opioid receptors: decreases bodily stress, pain management, reward effects, behavioral stability
Location of pars tuberalis
short slide… skip it prob
surrounds infundibular stalk anteriorly
contain vessels of hypophyseal portal system
contains basophilic cuboidal cells with granules which show immunoreactivity to ACTH, FSH, LH
neurohypophysis (posterior pituitary)
Neurosecretory cells in ____ and ___ nuclei of hypothalamus travel down stalk and terminate in posterior pituitary near capillaries
Neurons release:
Hormones bind to:
Hypothalamohypophyseal tract
Supraoptic and paraventricular nuclei
Neurons release vasopressin (ADH) and Oxytocin
Hormones bind to neurophysin (carrier protein) release them into bloodstream in the posterior pituitary
What makes up the hypothalamohypophyseal tract
Paraventricular hypothalamic nucleus and supraoptic hypothalamic nucleus lead down to stalk, where hypothalamohypophyseal tract is. Still above ant/post glands.
Neurohypophysis: pars nervosa
What does it contain?
Main part of posterior lobe.
Contains axons / axon terminals of neurons of paraventricular / supraoptic.
Neurohypophysis: pars nervosa
Axon and axon terminals contain accumulations of neurosecretory granules: these dilated axon terminals are called ___.
Herring bodies.
These release contents into perivascular spaces to be taken up by bloodstream.
Supraoptic nucleus release ____.
Paraventricular nucleus release ___.
vasopressin (AVP or ADH)
oxytocin
VS OP
Neurohypophysis hormones
Role of ADH
Role of oxytocin
Role of ADH: targets distal convoluted tubules and collecting ducts of kidneys, modulates permeability of cells, lowering urine volume but increasing urine concentration
Role of oxytocin: stimulates contraction of myometrium during labor; stimulates milk EJECTION from mammary glands.
Note: Milk production is from prolactin, but milk ejection is from oxytocin
Pituicytes
thought to be glial type cells
Main role is to assist storage and release hormones of posterior pituitary
