Hormone & Receptor Physiology Flashcards
functions of the endocrine system
- maintain homeostasis
- coordinate growth and development
- regulate sexual reproduction
homeostasis
the maintenance of steady states in an animal by coordinate physiological processes or feedback mechanisms
what effect do endocrine diseases have on hormone production
increase, decrease, or no change
what are the endocrine glands
- pituitary
- thyroid
- parathyroid
- adrenals
- pineal
- testes/ovaries
what are exocrine glands that have an endocrine component
kidneys, pancreas
where tissues have endocrine cells scattered throughout
GI tract, heart, kidney, liver, adipose tissue
function of endocrine glands
responsible for the regulated secretion of chemical messengers (hormones) into systemic circulation
how to hormones enter circulation
via fenestrated capillaries
hormones
chemical which affects target cells or organs via transport in the bloodstream
what does the response of a cell depend on
- hormone concentration
- number of receptors
- binding strength
do hormones create new reactions within a cell
NO - modulate reactions already occurring in the cell
what concentration are hormones present in circulation
low concentrations
negative physiological response driven feedback loop
the physiological response of the body to the release of a hormone will inhibit further release of that hormone
positive physiological response driven feedback loop
the physiological response of the body to the release of a hormone will stimulate further release of that hormone
negative endocrine axis driven feedback loops
the release of a hormone stimulates the release of more hormones from different endocrine glands, and the response of the body to those hormones will result in inhibition of the axis
ex. hypothalamic-pituitary-adrenal axis
what controls the level of hormones in the body
- biosynthesis
- precursor processing
- hormonal release
- protein binding
- metabolic clearance
- feedback loops
what are the types of hormones
- peptides/proteins
- amino acid derivatives (catecholamines, thyroid hormones)
- steroid hormones
polarity, protein binding, half life, and receptor type of peptide/protein hormones
- polar (water soluble)
- non protein bound
- short half life
- cell surface receptors
metabolism/clearance, biosynthesis, and release of peptide/protein hormones
- endocytosis and enzymatic degradation
- protein synthesis (DNA to RNA to mRNA to preprohormone to prohormone to hormone)
- storage in membrane bound vesicles OR immediate release
examples of peptide/protein hormones
POMC
what amino acid are catecholamines and thyroid hormones derived from
tyrosine
polarity, protein binding, half life, and receptor type of catecholamines
- polar
- non protein bound OR loosely albumin bound
- short half life
- cell surface receptor
metabolism/clearance, biosynthesis, and release of catecholamines
- enzymatic degradation and endocytosis
- enzyme modifications of tyrosine
- stored in secretory vesicles
examples of catecholamines
epinephrine, norepinephrines
polarity, protein binding, half life, and receptor type of thyroid hormones
- non polar
- highly protein bound
- long half life
- intracellular receptors
metabolism/clearance, biosynthesis, and release of thyroid hormones
- inactivated by deiodination and phase II metabolism
- iodide + AA uptake into follicular lumen, iodination of tyrosine residues on thyroglobulin, coupling of iodinated residues, release of T3/T4 from thyroglobulin
- storage in colloid of follicular lumen
examples of thyroid hormones
T3 (active)
T4 (inactive)
categories of steroid hormones
progestins: progesterone
mineralocorticoids: aldosterone
glucocorticoids: cortisol
androgens: testosterone
estrogens: estrogen
polarity, protein binding, half life, and receptor type of steroid hormones
- non polar
- highly protein bound
- variable half life
- intracellular receptors
metabolism/clearance, biosynthesis, and release of steroid hormones
- metabolized in liver to inactivate, excreted in urine after phase I and II metabolism
- enzymatic modification of cholesterol (steroid hydroxylase, dehydrogenase)
- NO storage - produced and released as needed
hormone receptors
bind specific hormones with high affinity and specificity
what are the types of intracellular receptors
cytosolic
nuclear
what are the types of cell surface receptors
GPCRS (seven transmembrane)
single transmembrane (growth factor, cytokine)
signal transduction
a pathway of events by which each component participates in the process of transmitting a signal to the target molecular within the cell
hormone –> receptor –> signal mediator –> target molecule –> response
what are the ligands for cell surface receptors
water soluble hormones (peptides/proteins, catecholamines)
what are the methods of signal transduction of cell surface receptors
growth factor: protein activity (kinase/phosphatase), ion movement
cytokine: transcriptional modification
G-protein coupled receptors (GPCRs)
seven transmembrane receptors (cross the membrane 7x)
subtypes: Gi, Gq, Gs, G12
single transmembrane receptors
only cross the membrane one time
growth factor receptors and cytokine receptors
growth factor receptors
extracellular binding site + intracellular tyrosine kinase domain
- hormone binding induces conformational change
- autophosphorylation of tyrosine residues on kinase
- recruits secondary effector protein
- signal cascade
cytokine receptors
- hormone binds
- recruits effector protein
- autophosphorylation of kinase
- recruits secondary effector protein
- receptor dimerizes
- signal cascade
what are the ligands for intracellular receptors
lipid soluble hormones (thyroid and steroid hormones)
what are the methods of signal transduction of intracellular receptors
transcriptional regulation by binding directly to DNA
subregions of intracellular receptors
- activation region - ligand-independent activation
- DNA binding - binds to specific DNA sequence, dimerization
- ligand binding - site of ligand binding, hetero/homodimerization
- coactivator/repressor - site of regulatory factor binding
location and ligands used by cytosolic receptors
receptor located in the cytosol
used by steroid hormones (glucocorticoid, mineralocorticoid, androgen, and progesterone receptors)
mechanism of cytosolic receptors
- ligand binding releases repressor (heat shock protein)
- induces homodimerization of receptor
- receptor-ligand complex binds to DNA sequence (HRE) to alter transcription
location and ligands of nuclear receptors
receptor located already bound to DNA sequence
used by thyroid hormones and estrogen
mechanism of nuclear receptors
- ligand enters directly into nucleus and binds receptor already bound to DNA segment
- releases repressor (NOT heat shock protein except estrogen)
- induces heterodimerization
- regulates gene transcription
features of endocrine glands
- ductless
- highly vascularized
- contain secretory cells (cords, single cells, clusters, or follicles)
- prominent nuclei, mitochondria, ER, golgi, secretory vesicles
- store or secrete hormones directly
pituitary gland
down growth of neural tissue from the hypothalamus
site of diverse hormone production BUT each cell type only produces one hormone
pituitary hormone function
- act directly on non-endocrine tissues
- modulate the activity of other endocrine glands
anterior pituitary
adenohypophysis; glandular portion of pituitary
highly vascularized
contains epithelial cells
pars of the anterior pituitary
pars distalis
pars intermedia
pars tuberalis
pars distalis
anterior lobe; main glandular part and site of majority of hormone production
cords of epithelial cells surrounding fenestrated capillaries that extend from the hypothalamus
contains secretory granules w/ hormones
pars intermedia
intermediate lobe between the anterior and posterior pituitary
some hormone production
pars tuberalis
non-secretory tissue that surrounds the infundibular stalk
provides support
posterior pituitary
neurohypophysis; neural portion of the pituitary
contains axon terminals of hypothalamic neurons (neuroendocrine cells)
pars nervosa
neural lobe
non-myelinated axons with neurosecretory activity (hormones produced in hypothalamus and transported to pituitary via secretory granules and stored in pituitary in herring bodies)
hormones: ADH, oxytocin
infundibular stalk
pituitary stalk
median eminence
extension of the base of the hypothalamus; down growth of neural tissue into a capillary bed
what are the two main capillary beds in the pituitary
- primary plexus
- secondary plexus
primary plexus
capillary bed where neural cells can release releasing hormones (small peptides)
drains into the large capillary bed of the adenohypophysis via portal veins
secondary plexus
large capillary bed within the adenohypophysis where the releasing factors bind to receptors to stimulate release of hormones into systemic circulation
thyroid gland
endocrine gland essential for normal growth and development
has large extracellular storage compartment within follicle lumen (stores hormone precursors)
highly vascularized
produces T3/T4 to increase metabolic rate
thyroid follicles
single layer of cuboidal epithelial cells (follicular epithelium) surrounding a colloid-filled lumen
what is the colloid made of
contains thyroglobulin and proteolytic/mucoproteins
what does shape of follicular cells depend on
activity level
active = columnar
inactive - cuboidal
principal/follicular cells
secrete thyroglobulin and create T3/T4
smaller, darker staining
parafollicular cells
secrete calcitonin to regulate calcium
paler staining
adrenal gland
endocrine gland located above the kidneys
secretes steroids and catecholamines
adrenal cortex
secretes steroids (cortisol, aldosterone, androgen)
blood supply of the adrenal gland
capsular plexus surrounds the adrenal, branches into the fenestrated cortical capillaries and medullary artery
fenestrated cortical capillaries
drains from capsular plexus to supply blood throughout the layers of the cortex and into the medulla; drains into the central vein in the medulla
what are the zones of the cortex
- zona glomerulosa
- zona fasciculata
- zona reticularis
zona glomerulosa
outermost layer; produces mineralocorticoids (aldosterone)
contains sup capsular arterial plexus
columnar or pyramidal cells in rounded clusters
zona fasciculata
middle layer; produces glucocorticoids (cortisol)
long cords of large/spongy cells separated by collagen and capillaries
contains lipid droplets (pale staining)
zona reticularis
innermost layer; produces sex steroids (DHEA)
smaller, irregular cords/clusters that are closely arranges
less lipid droplets (darker)
adrenal medulla
secretes catecholamines (epinephrine, norepinephrine)
medullary artery
direct blood supply to the medulla; bypasses the cortical capillaries to allow for rapid release of catecholamines into circulation
central vein
located within the medulla; drains the cortical capillaries and medullary artery
dual blood supply of the medulla
medulla receives blood from the medullary artery (direct) and fenestrated cortical capillaries (shared with the cortex)
chromaffin cells
modified postganglionic sympathetic neurons
have secretory granules containing epinephrine and norepinephrine
how does signaling in the adrenal medulla work
- preganglionic fibers terminate on chromaffin cells and release Ach
- stimulates catecholamine synthesis and secretion
endocrine pancreas
regions of endocrine cells within the otherwise exocrine tissue
function: regulate blood glucose levels
islets of langerhans
regions of endocrine cells (a, b, d) within the pancreas
highly vascularized - arterioles enter islets directly and branch into capillaries
what do the cells of the islets of langerhans produce
a cells: glucagon
B cells: insulin
d cells: somatostatin
