Endocrinology Flashcards
Compare Nervous system and Endocrine system
Nervous: rapid response, short-duration response, acts via AP and Neurotransmitters, acts at specific locations, act over short distances
Endocrine: slow response, long duration response, acts via hormones into blood, acts at diffuse locations, and hormones act over long distance
Autocrine
chemical that exerts effects on same cells that secrete them
Paracrine
locally acting chemicals that affect cells other than those that secrete them
Water-soluble hormones
amino-acid except thyroid
act on plasma membrane receptors
act vis G proteins second messengers
cannot enter cell
Lipid-Soluble hormone
steroid and thyroid hormone
act on intracellular receptors that directly activate genes
can enter cell
Compare cAMP and PIP2-Ca signaling mechanism
cAMP: hormone binds to receptor-> activates G protein -> activates or inhibits adenylate cyclase -> adenylate cyclase then convert ATP to cAMP -> cAMP activates protein kinase to phosphorylate other proteins
PIP2-Ca: hormone on membrane activates G protein -> activates phospholipase C -> splits PIP2 into diacylglycerol activate protein kinase and inositol triphosphate release Ca
Intracellular Receptor mechanism
lipid-soluble hormones and thyroid hormone can diffuse into target cell bind to intracellular receptors -> enters the nucleus and binds to specific region of DNA -> helps initiate DNA transcription to produce mRNA -> mRNA then translated into specific protein
Stimulation of Endocrine Gland
Humoral stimuli: changing blood levels of ions and nutrients directly stimulate secretion of hormones
Neural stimuli: nerve fibers stimulate hormone release
Hormonal Stimuli: hormone stimulate other endocrine organs to release their hormones
Posterior pituitary
composed of neural tissue that secrete neurohormones
Anterior pituitary
consists of glandular tissue
ADH Regulation
Stim: by impulses from hypothalmic neurons in response to ncreased blood solute concentration or decreased blood vol; also timulated by pain, some drugs, low BP
inhib: adequate hydration of body and alcohol
ADH Target organ and effect
kidneys: stimulates tubule cells to reabsorb water from the forming urine back into blood
ADH patho
↑ syndrome of inappropriate ADH secretion
↓ diabetes insipidus
T4 composition
DIT plus DIT
T3 composition
DIT plus MIT
Where is Iodide located in the thyroid gland?
cytoplasm of follicular cells
T3 Function
7 Bs
brain maturation, bone growth, B adrenergic effects, basal metabolic rate, blood sugar, break down lipids, babies stimulates surfactant synthesis
What is T3 impact on heart?
increase cardiac output, HR, SV, and contractility
Oxytocin regulation
stim: impulses from hypothalamic neuros in response to stretching of the uterine cervix or sucking of infant at breast
inhib: adequate hydration of the body and by alcohol
Oxytocin pathway
neurons in paraventricular nucleus of hypothalamus
Oxytocin target organ and effect
uterus: stimulates uterine contractions, initiates labor
breast: initiates milk ejection
Wolff-Chaikoff effect
sudden exposure to excess iodine temporarily turns off thyroid peroxidase; dec T3/T4 production
reg: chemoreceptors locally of thyroid tissue
protective autoregulation
GH reg
stim: by GHRH which is triggered by low blood levels of GH, deep sleep, hypoglycemia, increases in blood levels of amino acids, low levels of fatty acids, exercise, and other types of stressors
inhib: feedback inhibition exerted by GH and IGFs, hyperglycemia, hyperlipidemia, obesity, and emotional deprivation via either increased somatostatin or decreased GHRH release
GH Target organ and effect
liver, muscle, bone, cartilage, and other issues: anabolic hormone, stimulates somatic growth, mobilizes fats, spares glucose
growth-promoting effects mediated indirectly by IGFs
GH patho
↑ gigantism in kids, acromegaly in adults
↓ dwarfism in kids, GH insufficiency in adults
TSH reg
stim: by TRH and in infants indirectly by cold temperature
inhib; by feedbakci nhibitiion exerted by thyroid hormones on ant pituitary and hypothalamus and by GHIH
17 aplha-hydroxylase patho
increase in progesterone and aldosterone
decrease in cortisol and sex hormone
17 aplha-hydroxylase clinical
a typical genitalia, undescended testes, lack of secondary sexual development, hypertension, hypokalemia,
21-hydroxylase patho
allow the sex hormones to go forward, low cortisol and aldosterone
21-hydroxylase clinical char
salt wasting, hypotension, and hyperkalemia
11beta-hydroxylase patho
stops conversion of 11-deoxycortisoterone to corticosterone and stops conversion of 11-deoxycortisoal (increases BP) to cortisol
cortisol and aldosterone decrease
increased androgens
11beta-hydroxylase clinical
hypokalemia, hypertension,
posterior pituitary hormones (made by hypothalmic neurons, stored in post pituitary)
oxytocin, antidiuretic hormone (ADH)
oxytocin chemical structure and cell type
peptide, mostly from neurons in paraventricular nucleus of hypothalamus
antidiuretic hormone (ADH) other names, chemical structure and cell type
vasopressin
peptide, mostly from neurons in supraoptic nucleaus of hypothalamus
growth hormone (GH) chemical structure and cell type
protein, somatotropic cells
thyroid stimulating hormone (TSH) chemical structure and cell type
glycoprotein, thyrotropic cells
TSH target organs and effects
thyroid gland: sitmulates thyroid gland to release thyroid hormones
TSH patho
↑ primary hyperthyroidism, secondary/tertiary hypothyroidism, graves, pituitary adenoma
↓ primary hypothyroidism; may cause myxedema, secondary/tertiary hyperthyroidism
adrenocorticotropic hormone (ACTH) chemical structure and cell type
peptide, corticotropic cells
ACTH regulation
stimulated: by CRH; stimuli that increase CRH release include fever, hypoglycemia, and other stressors
inhib; feedback inhibition exerted by glucocorticoids
ACTH target organs and effects
adrenal cortex: promotes release of glucocorticoids and androgens (mineralcorticoids to a lesser extent)
ACTH patho
↑ cushings disease
↓ rare
follicle-stimulating hormone (FSH) composition
glycoprotein, gonadotropic cells
FSH regulation
stimulated; GnRH
inhibi; by feedback inhibition exertion by inhibin, and estrogens in females and testosterone in males
FSH target organ and effect
ovaries and testes
in females, stimulates ovarian follice maturation and production of estrogens
in males, stimulates sperm production
FSH patho
↑ no important effects
↓ failure of sexual maturation
luteinizing hormone (LH) composition
glycoprotein, gonadotropic cells
LH regulation
stim; GnRH
inhib; feedback inhibition exerted by estrogens and progesterone in females and testosterone in males
LH target organ and effects
ovaries and testes;
females: triggers ovulation, stimulates ovarian production of estrogens and progesterone
males; promotes testosterone production
LH patho
same as FSH
↑ no important effects
↓ failure of sexual maturation
prolactin (PRL) composition
protein, prolactin cells
PRL regulation
stim; decreased PIH; release enhanced by estrogens, birth control pills, breastfeeding, dopamine blocking drugs
inhib; PIH (dopamine)
PIH target organ and effects
breast secretory tissue; promotes lactation
PRL patho
↑ inappropriate milk proiduction (galactorrhea); cessation of menses in females, impotence in males, low libido, gonadal dysgenesis
↓ poor milk production in nursing women, hypopituitarism, excessive dopamine, D2 agonists
anterior pituitary hormones
GH, TSH, ACTH, FSH, LH, PRL
where is insulin synthesized and by what cells
beta cells in pancreas
insulin chemical composition
2 amino acid chains connected by disulfide linkages
explain the processes of insulin synthesis
preproinsulin > proinsulin > exocytosis of insulin and C peptide equally
synthesized by beta cells in pancreas
describe insulin release and circulation
insulin is secreted into blood via secretory granules; unbound circulation in blood
half life 6 min, clearance 10-15 min
degraded by insulinase in the liver
why is c peptide measurement useful in type I diabetics?
determines how much natural insulin is being produced
explain the activation of target cells by insulin
within secs of insulin binding to membrane receptors, 80% of body cells increase glucose uptake (esp muscle and adipose, not neurons in brain)
increased glucose transport into cells > converted into energy
cell membrane more permeable to AA, K+, P+
adjustment of activity levels of enzymes intraceullatrly occur over 10-15 mins
changes rate of transcription and translation at the DNA and RNA level
hypothalamus hormones
TRH, CRH, GhRH, GhIH, GnRH, Dopamine/prolactin inhibiting factor, somatostatin, Vasopressin and oxytocin
what are the hormones released by thyroid?
thyroxine (T4)
triiodothyronine (T3)
calcitonin
adrenal cortex hormones
cortisol
aldosterone
adrenal medulla hormones
norepinephrine/epinephrine
pancreas hormoens
insulin
glucagon
parathyroid hormones
parathyroid hormone
testes hormones
testosterone
ovaries hormones
estrogen and progesterone
what are steroid hormones synthesized from and stored? lipid or water soluble?
synthesized from cholesterol, not stored
lipid soluble
which hormones are amine hormones
thyroid and adrenal medullary hormones
what are amine hormones derived from
tyrosine
most hormones have what composition?
polypeptides and proteins
polypeptides > 100AA = proteins
polypeptides <100AA = peptides
what cellular component are most hormones synthesized on? where are they then transferred to?
synthesized on rough end of ER; prohormones transferred to golgi to be packaged into secretory vesicle where they are stored until needed
what is the metabolic clearance rate?
rate of removal of hormones from blood
rate of disappearance of hormone from plasma/concentration of hormone
how are hormones cleared from plasma
metabolic destruction by tissues, binding with tissues, excretion by liver into bile, excretion by kidneys into urine
what hormones have receptors in or on surface of the cell membrane
protein, peptide, catecholamine hormones
what hormones have receptors in the cell cytoplasm
steroid hormones
what hormones have receptors in the cell nucleus
thyroid hormones
what types of things cause down regulation of hormone receptors
inactivation of receptor molecules, inactivation of intracellular protein signaling molecules, destruction of receptors by lysosomes, decreased production of receptors, temp sequestration of receptor to inside of cell
what is a hormone receptor complex
formation of complex alters funciton of receptor > activated receptor imitates hormonal effects
describe an ion channel linked receptor
all neurotransmitter substances combine with receptors in postsynaptic membrane
change in structure of a receptor (opening/closing a channel for ions)
Na, K, Ca, etc
describe a G protein linked hormone receptor
activate receptors that indirectly regulate activity of target proteins by coupling with groups of cell membrane proteins > GTP (G) binding proteins
heterotrimeric guanosine triphosphate, 7-transmembrane segments
inhibitory and stimulating G proteins
describe an enzyme linked hormone receptor
proteins that pass through membrane only once; hormone binding site EC and catelytic/enzyme bindnig site IC
ex: tyrosine kinase > leptin receptor
describe IC hormone receptors; activation of genes
adrenal and gonadal steroid hormones, thyroid hormones, vit D, and retinoid hormons bind with protein receptors within the cell (lipid soluble, pass through plasma membrane)
activated complex binds with regulatory (promotor) sequence of DNA (hormone response element) > activation/repression of transcription of genes and mRNA
describe the adenylyl cylcase-cAMP second messenger system
hormone binds receptor > coupling of receptor to G protein
adenylyl cylase (membrane bound enzyme) > converts small amount of cAMP inside cell > acitvates cAMP dependent protein kinase > phosphorylates > enzyme cascade activated
small amount of hormone = large effect
describe the phospholipase C second messenger system
enzyme catalyzes breakdown of phospholipids in cell membrane
PIP2 (second messengers)
- inositol triphosphate (IP3) > mobilizes Ca ions from mitochondria and ER
- diacylglycerol (DAG) > activates enzyme protein kinase C
describe thyroid hormones INC gene transcription
T3 and T4 bind to receptors in nucleus (receptors = activated transcription factors within chromosomal complex); once bound to intranuclear receptors > thyroid hormones continue to express control function for days/weeks
control function of gene promotors
activate genetic mechanisms for synthesizing many types of IC proteins
what is the main role of the thyroid hormones
control bodys metabolic rate
what cellular component forms thyroglobulin
ER and golgi apparatus
how/where are T4/T3 formed
formed from tyrosine in thyroglobulin molecule
iodine binds with thyroglobin molecule = organification > can store 2-3 months of hormones
what is the iodide pump? what does it do/mechanism?
transports iodides from blood into thyroid cells/follicles
sodium iodide symporter (iodide trapping)
basal membrane of thyroid can pump iodide into the cell
symporter co-transports 1 iodide along with 2 sodium ions
where does the energy for the sodium iodide symporter come from
NA/K ATPase pump > pumps Na out of cell giving low IC Na conc and gradient for facilitated diffusion of Na into cell
melatonin comes from what gland?
pituitary
function of melatonin
regulates circadian rhythm and reproductive hormones
hypersecretion of melatonin can result in what
in children inhibits sexual development
regulation of melatonin
external light (-) seratonin
synthesis of melatonin
tryptophan > 5htp > seratonin > melatonin
what is necessary for the synthesis of thyroid hormone
iodine
in the synthesis of thyroid hormone, iodine transport is ___
active
structural difference between T3 and T4
T4 = 2 DIT residues T3 = 1 DIT residue + 1 MIT residue
structural difference between T3 and T4
T4 = DIT + DIT T3 = DIT + MIT
explain conversion of T4 > T3
follicles of thyroid 5’-deiodinase converts T4 to T3 in peripheral tissue
what factors inhibit peripheral conversion of T4 > T3
glucocorticoids, beta-blockers, propylthiouracil (PTU)
what is reverse T3 (rT3)
metabolically inactive byproduct of peripheral conversion of T4 and its production
what increases rT3
GH and glucocorticoids
functions of thyroid peroxidase
oxidation, organification of iodine, coupling of monoiodotyrosine (MIT) and diiodotyrosine (DIT)
explain the release of T4/T3 from thyroid gland
cleaved by thyroglobulin molecule > free hormone release
pinocytic vesicles enter thyroid cell > lysosomes fuse with vesicles > proteases digest thyroglobulin adn release T4/T3 > diffuse through base of thyroid cell to capillaries
how is T4/T3 transported to tissues
bound to plasma proteins (synthesized in liver) > thyroxine binding globulin
released slwoly to tissue cells > bind with IC proteins and stored
slow onset and long duration of action (long latent period) - max rate after 10-12 days
triiodothyronine (T3) functions
7 B’s
-Brain maturation
-Bone growth (synergistic with GH)
-B-adrenergic effects (increases B1 reeptors in heart > increased CO, HR, SV, contractility)
-Basal metabolic rate (via increased Na+/K+- ATPase leading to increased O2 consumption, RR, and body temp)
-Blood sugar (via glycogenolysis and gluconeogensesis)
-Break down lipids (through lipolysis)
Babies > stimulates surfactant synthesis
effects of thyroid functions
increase transcription of genes
increase cellular metabolic activity
effects on growth
effects on certain body functions
most thyroxine –>
triiodothyronine
prior to acting on genes to INC genetic transcription
1 iodide removed
where are thyroid hormone receptors in relation to DNA?
attached to DNA genetic strands OR located in proximity to them
thyroid hormone receptor forms a hetereodimer with retinoid X receptor (RXR) at specific parts of DNA
why is most thyroxine > triiodothyronine
IC thyroid receptors have high affinity for T3
what are the cellular metabolic activities of T4/T3
increased number, size, and activity of mitochondria
- total membrane surface area inc in proportion of inc metabolic rate of whole animal
- inc ATP production
increased active transport of ions through cell membranes
- Na+/K+ ATPase increased > inc rate of transport of Na and K ions through cell membranes > increases heat in body
- cell membrane = leaky to Na ions
thyroid function on body tissues
normal arterial presure
muscle tremor
effects on: plasma and liver fats muscle function sleep other endocrine glands sexual function
increased: vitamin requirement BMR blood flow and CO HR and heart strength respiration GI motility carb metabolism fat metabolism
decreased:
body weight
how does thyroid stimulate carb metabolism
rapid glucose uptake by cells, increased glycolysis, increased insulin secretion
how does thyroid stimulate fat metabolism
lipids mobilized rapidly from fat tissue, decreasing fat stores in body
what is the thryoid effect on plasma and liver fats
increased thyroid hormone > decreased concentration of cholesterol, phospholipids, and TGs BUT increased free fatty acids
explain why thyroid > increased vitamin requirement
inc body enzymes, including vitamins. vitamin def with too much thyroid
how does thyroid increase blood flow and CO
inc tissue metabolism > inc oxygen use > vasodilation
what regulates thyroid secretion?
thyrotropin (TSH) inc thyroid secretion
TRH > stimulates TSH release > stimulates follicular cells
negative feedback control through free T3/T4
- ant pit > dec sensitivity to TRH
- hypothalamus > dec TRH secretion
thyroxine binding globulin (TBG) binds most T3/T4 in blood (making it inactive)
functions of TSH
increased:
proteolysis of thyroglobulin (w/in 30 mins)
activity of iodide pump
iodination of tyrosine
size and secretory activity of thyroid cells
# of thyroid cells
explain thyroid regulation via cyclic adenosine monophosphate
(activation of second messenger cAMP system of cell)
TSH binds with TSH receptors on basal membrane of thyroid cell > adenlyl cylase activated in membrane > inc cAMP formation inside cell, which acts as a 2nd messenger to activate protein kinase > phosphorylations t/o cell > immediate release in secretion of thyroid hormones and prolonged growth of thyroid gland tissue
chemical composition of TSH/thyrotropin
glycoprotein
chemical composition of TRH
tripeptide amide
explain TRH regulation of TSH secretion
TRH secreted by hypothalamus, acts on ant pit to regualte TSH secretion
binds with TRH receptors in pituitary cell membrane > activation of phospholipase 2nd messenger system inside cells > large amts of phospholipase C produced > 2nd messengers inc Ca ions > release of TSH
how does cold exposure affect TRH/TSH
cold exposure > excitation of hypothalmic centers for body temp control > inc TSH > > BMR inc 15-20%