Intro to Endocrine (Creamer) Flashcards
hormone signaling where the cell releases a hormone that acts on the cell itself or on a similar cell in the same tissue
autocrine signaling
hormone signaling where one cell releases a hormone that acts on different cell, typically within the same tissue/organ
paracrine
hormone signaling where one cell releases a hormone within the blood stream to a target cell of a different cell/tissue type
endocrine signaling
hormone signaling where a neuron releases a hormone into the blood stream to act on a target cell of a different tissue/organ
neuroendocrine
(there is also neurocrine where neuron releases a hormone that acts directly on target tissue)
Name the hypothalamus hormones, their classification, and major actions:
Hypothalamus
- thyrotropin-releasing hormone (TRH): peptide, stim secretion of TSH and prolactin
- corticotropin-releasing hormone (CRH): peptide, stim secretion of ACTH
- gonadotropin-releasing hormone (GnRH): peptide, stim secretion of LH and FSH
- somatostatin or somatotropin release-inhibiting hormone (SRIF): peptide, inhibits secretion of growth hormone
- dopamine or prolactin-inhibiting hormone (PIF): amine, inhibits secretion of prolactin
- growth hormone-releasing hormone (GHRH): peptide, stim secretion of growth hormone (GH)
Name the anterior pituitary hormones, their classification, and major actions:
Anterior pituitary
- thyroid-stimulating hormone (TSH): peptide, stim synthesis/secretion of thyroid hormones
- follicule-stimulating hormone (FSH): peptide, stim sperm maturation in Sertoli cells of testes, stim follicular development and estrogen syn in ovaries
- luteinizing hormone (LH): peptide; stim testosterone syn in Leydig cells of testes, stim ovulation, formation of corpus luteum, estrogen/progesterone syn in ovaries
- growth hormone (GH): peptide, stim protein syn and overall growth
- prolactin: peptide, stim milk prod/secretion in breasts
- adrenocorticotropic hormone (ACTH): peptide, stim syn/secretion of adrenal cortical hormones (cortisol, androgens, aldosterone)
- melanocyte-stim hormone (MSH): peptide, stim melanin synthesis
Name the posterior pituitary hormones, their classification, and major actions:
Posterior pituitary
- oxytocin: peptide, stim milk ejection from breasts and uterine contractions
- vasopressin or antidiuretic hormone (ADH): peptide, stim water reabsorption in principal cells of collecting ducts and constriction of arterioles
Name the thyroid hormones, their classification, and major actions:
Thyroid
- triiodothyronine (T3) and L-thyroxine (T4): amines, stims skeletal growth, oxygen consumption, heat prod, protein, fat, and carb utilization, perinatal maturation of CNS
- calcitonin: peptide, decreases Ca2+ levels
Name the parathyroid hormones, their classification, and major actions:
Parathyroid
- parathyroid hormone (PTH): peptide, increases Ca2+ levels
Name the adrenal cortex hormones, their classification, and major actions:
Adrenal cortex
- cortisol (glucocorticoid): steroid, stim gluconeogenesis, inhibits inflammatory response, suppresses immune response, enhances vascular responsiveness to catecholamines
- aldosterone (mineralocorticoid): steroid, increases renal Na+ reabsorption, K+ secretion, and H+ secretion
- dehydroepiadrosterone (DHEA) and androstenedione (adrenal androgens): steroids, actions of testosterone
Name the testes hormones, their classification, and major actions:
Testes
- testosterone: steroid, stim spermatogenesis, stim male secondary sex characteristics
Name the ovaries hormones, their classification, and major actions:
Ovaries
(also prod by corpus luteum)
- estradiol: steroid; stim growth/development of female repro system, follicular phase of menstrual cycle, development of breasts, prolactin secretion, maintains pregnancy
- progesterone: steroid; stim luteal phase of menstrual cycle, maintains pregnancy
Name the placenta hormones, their classification, and major actions:
Placenta
- human chorionic gonadotropin (HCG): peptide, stim estrogen/progesterone syn in corpus luteum of early pregnancy
- human placental lactogen (hPL), or human chorionic somatomammotropin: peptid, growth hormone-like and prolactin-like actions during pregnancy
- estriol
- progesterone
Name the pancreas hormones, their classification, and major actions:
Pancreas
- insulin (beta-cells): peptide, decrease blood glucose
- glucagon (alpha-cells): peptide, increase blood glucose
Name the kidney hormones, their classification, and major actions:
Kidney
- renin: peptide, catalyzes conversion of angiotensinogen to angiotensin I
- 1,25-dihydroxycholecalciferol: steroid, increases intestinal absorption of Ca2+, bone mineralization
Name the adrenal medulla hormones, their classification, and major actions:
Adrenal medulla
- norepi, epi: amines, actions of sympathetic ANS
How are protein and peptide hormones synthesized?
DNA > mRNA (nucleus)
mRNA > preprohormone (ribosomes)
preprohormone > prohormone (ER)
prohormone > hormone (golgi)
hormone stored and secreted via secretory vesicles
How are steroid hormones synthesized?
- all produced as derivatives of cholesterol
- either side chains, hydroxylations, aromatizations are added
- synthesized within the adrenal cortex, gonads, corpus luteum, and placenta
- lipid soluble, thus are not stored within endocrine tissue due to ability to pass through membrane
- act on intracellular receptors at target tissues
How are amine hormones synthesized?
- all synthesized from tyrosine
- catecholamines: syn via enzymatic conversion of tyrosine in cytosol and secretory granules; act through cell membrane associated receptors at target tissues
(L-tyrosine > L-DOPA > dopamine > norepi > epi)
- thyroid hormones: syn via thyroid gland and stored as thyroglobulins in follicles within gland; cross cell membranes at target tissues and act through nuclear receptors
(L-tyrosine > MIT > DIT > thyroxine > triiodothyronine > rT3)
What is the general half life of each hormonal sub-group?
(the more the hormone binds w/ a protein, the slower the metabolic clearance will be, aka longer half-life)
(MC = metabolic clearance ml/minute)
- thyroid:
~99% protein binding
- T4 has 6 day 1/2 life and 0.7 MC
- T3 has 1 day 1/2 life and 18 MC
*relatively long 1/2 lives*
- steroids:
cortisol: 94% protein binding, 100 min 1/2 life, 140 MC
testosterone: 89% protein binding, 85 min 1/2 life, 860 MC
aldosterone: 15% protein binding, 25 min 1/2 life, 1100 MC
*moderate 1/2 lives that range depending on hormone*
- proteins:
thyrotropin: little protein binding, 50 min 1/2 life, 50 MC
insulin: little protein binding, 8 min 1/2 life, 800 MC
antidiuretic hormone: little protein binding, 8 min 1/2 life, 600 MC
*relatively short 1/2 lives*
What are the 2 mechanisms of hormonal secretion control?
- neural: neural input to endocrine cell, signal causes increase/decrease in secretion (example: sympathetic preganglionic innervation of adrenal medulla, when stim causes release of catecholamines into circulation)
- feedback: positive and negative, some element of endocrine will feedback either directly/indirectly on an endocrine gland
Describe positive feedback within hormones:
- a hormone stimulates further production of itself
- rather rare in humans
- examples: oxytocin production in post pit during labor; estradiol production during ovulation
Describe negative feedback within hormones:
- stimulus causes release of hormones whose effects inhibit further release of itself
- more common in humans, this is how most hormones are controlled
- example: testosterone production in testes
(side note: long loops go from peripheral gland to central organ controlling production, short loops go from 2nd > 1st tier or something similar, ultra-short loops act within the same organ/gland)
Major endocrine axes:
Describe how the first tier of the endocrine axes is regulated:
How are hormone receptors regulated?
- receptors confer specificity to hormone actions: hormone-receptor complex, generally high affinity due to low conc of hormones
- responsiveness of target tissue is expressed in dose-response relationship: sensitivty (hormone conc that produces 50% of maximal response, EC50)
- responsiveness can be changed in two ways: changing the # of receptors or changing the affinity of the receptors for the hormone
Describe the adenylyl cyclase mechanism for hormonal signal transduction:
- 1st messenger: hormones (ACTH, LH, FSH, TSH, glucagon) bind to the receptor that is coupled w/ a G protein
- G protein becomes activated, GTP substituted for GDP on alpha subunit of Gs protein
- primary effector (adenylyl cyclase) is activated and converts ATP > cAMP
- cAMP (2nd messenger) accumulates and is converted to 5’ AMP (inactive)
- cAMP also activates secondary effector, protein kinase A (PKA), which triggers the phosphorylation of proteins and physiological actions
(hormones: ACTH, LH, FSH, TSH, ADH (v2 receptor), HCG, MSH, CRH, calcitonin, PTH, glucagon, beta1/beta2 receptors)
Describe the phospholipase C mechanism for hormonal signal transduction:
- 1st messenger hormone (GnRH, TRH, oxytocin) bind to receptor that is coupled w/ Gq protein
- Gq protein becomes activated, GTP substituted for GDP on alpha subunit of Gq protein
- primary effector (phospholipase C) is activated and converts PIP3 > diacyglycerol (DAG) and IP3
- IP3/DAG/Ca2+ (2nd messengers) activate secondary effectors, PKC or calmodulin, to produce physiologic actions
(hormones: GnRH, TRH, GHRH, angiotensin II, ADH (v1 receptor), oxytocin, alpha1 receptors)
Describe the steroid mechanism for hormonal signal transduction:
- most hydrophobic steroids are bound to plasma protein carriers, only unbound hormones can diffuse into target cell
- receptors are in the cytoplasm or nucleus
- receptor-hormone complex binds to DNA and activates/represses one or more genes
- activated genes create new mRNA that moves back to cytoplasm
- translation produces new proteins for cell processes
- some steroid hormones also bind to membrane receptors that use second messenger systems to create rapid cellular responses
(hormones: glucocorticoids, estrogen, progesterone, testosterone, aldosterone, 1,25-dihydroxycholecalciferol, thyroid hormones)
Describe the guanylyl cyclase mechanism for hormonal signal transduction:
- peptide hormone binds to ligand on receptor
- guanylyl cyclase is activated, and converts GTP > cGMP
- cGMP either activates cGMP kinases in response to ANP, or results in relaxation of vascular smooth muscle in response to NO
(hormones: atrial natriuretic peptide (ANP), nitric oxide)
Describe the tyrosine kinase mechanism for hormonal signal transduction:
two types:
- receptor tyrosine kinases: intrinsic tyrosine kinase activity, when activated tyrosine kinase phosphorylates downstream proteins
- tyrosine kinase-associated receptors: associate non-covalently to proteins that have kinase activity, when activated kinase phosphorylates downstream proteins
(hormones: insulin, IGF-1, growth hormone, prolactin)
