Module #1: Intro to the Endocrine System Flashcards
What are the primary organs of the endocrine system?
Hypothalamus
Pituitary gland (hypophysis)
Thyroid gland
Parathyroid gland
Adrenal glands
Pancreras (islets cells) aka endocrine pancreas
Gonads
Placenta
Hormones/hormone-like substances produced in other organs (heart/kidney/GI tract)
What is the main purpose of the endocrine system?
coordinate and integrate cellular activity throughout the body to maintain homeostasis
How does the endocrine system coordinate/integrate cellular activites?
Chemical messengers (hormones); uses circulatory pathways
What are the 4 functions of the endocrine system?
Homeostasis (maintenance of the internal environment)
Control of storage and utilization of energy substrates
Regulation of growth, development, and reproduction
Regulate the body’s response to environmental stimuli
Compared to the nervous system, what are the actions of the endocrine system?
slower in response
but more prolonged response
“more diffuse”
What are the 3 main components of the endocrine system?
Endocrine glands
Target Organs
Hormones
What are endocrine glands?
ductless glands that secrete hormones into the blood stream
What are target organs?
organ that contains cells w/ receptors that have hormone specific receptors
What are hormones?
Chemical messengers released by one cell and exert a biological action on a target cell/tissue/organ
classical definition refers to those that are transported via bloodstream
Where do hormones bind and what do they do?
specific receptors of target tissues
mediate some function
Can a single hormone facilitate multiple effects?
Yes, can bind to different target tissues
different receptors mediate different responses
What are the different responses that can be mediated by epinephrine?
Alpha Receptors: BV of intestines = constriction
Beta receptors: BV of skeletal muscle = dilation; Liver = glycolysis
Can a single physiological function be regulated by the sum of multiple hormones?
Yes
BP influenced by ADH/aldosterone/epinephrine
What are the 4 types of hormone signaling?
Endocrine
Paracrine
Autocrine
Intracrine
In endocrine signaling where are the target tissues, and how do the hormones reach the target tissues?
Target tissues = distant from where hormone release
hormones travel through blood stream to reach target tissue
In paracrine signaling where are the target tissues and how do the hormones reach the target tissue?
target tissues = local or immediate near cells that release hormone
hormone released by one cell acts locally on nearby cell
What are some examples of paracrine signaling?
Nitric Oxide
Bradykinin
Neurotransmitters
Cytokines
Prostoglandins
What does Nitric Oxide do?
promotes BV vasodilation
What does bradykinin do?
promote BV vasodilation
part of inflammatory/immune cascade
What are 2 examples of paracrine neurotransmitters?
Epinephrine
Norepinephrine
What are cytokines and what do they do?
small proteins (act as signaling molecules)
involved in immunoregulation and growth function
What are some examples of cytokines?
interleukins = IL2, IL4, etc
TNF = tumor necrosis factor
IF = interferon
Growth Factors = bone morphic factor, TGF - transforming growth factors
What are prostoglandins and how are they produced?
fatty acids produced in most organs
What do prostoglandins do?
Numerous Functions:
Smooth muscle: contract/relax (depending on receptor)
inflammatory response throughout tissues of body
pain: hyperalgesia - sensitize neurons in spinal cord
kidney: mesangial cells (contract) after GFR
hypothalamus: thermoregulatory nuclei - produce fever
mediate platelet aggegation/disaggregation
What do prostoglandins do in the uterus?
uterine contraction:
menstrual cycle
labor
What do prostoglandins do in the lung?
bronchoconstriction
bronchodilation
What do prostoglandins do in the GI tract?
contriction
relaxation
Clinically what kind of drugs work via prostoglandins?
NSAIDs
In autocrine signaling where are the target tissues and how do the hormones reach the target tissue?
Target tissue = same cell
hormone released by cell that then acts on receptors located on same cell
In intracrine signaling where are the target tissues?
hormone produced in a cell acts WITHIN cell itself
theory of some steroid action and also some malignant pathways
How is hormone secretion regulated?
Negative Feedback
Positive Feedback
Describe Negative Feedback
most common feedback mechanism
hormone actions directly or indirectly inhibit further release of that hormone
Describe Positive Feedback
Rare feedback mechanism
hormone actions directly or indirectly stimulates further release of that hormone
How are hormones classified?
Derivative content classification
Solubility classification
What are some derivative content classifications?
Amino acid derivatives
Peptide/protein derivatives
Steroid derivatives
Fatty acid derivatives
What are 2 examples of amino acid derivatives?
catecholamines
thyroid hormones
What are some examples of peptide/protein derivatives?
Glycoproteins
releasing hormones formed from peptides
What are some examples of steroid derivatives?
Estrogens
Testosterone
What are some fatty acid derivatives?
eicosanoids –> prostaglandins
What are the 2 solubility classifications of hormones?
Lipid soluble = lipophilic
Water soluble = hydrophilic
Which types of hormone derivatives are lipophilic?
Steroid hormones
Thyroid hormones
What is the precursor for all steroid hormones?
cholesterol
Describe how lipophilic hormones are circulated
circulate bound to plasma proteins
don’t break down easily –> have longer half life (hours to days)
hormone/plasma protein carrier disassociate @ target tissues
Which types of hormone derivatives are hydrophilic?
most hormones = water soluble
GH
TSH
PTH
etc
Describe how hydrophilic hormones are circulated?
circulate “freely” in plasma
easily broken down –> short half life (1-30 minutes)
Where are hormone receptors located?
on cell membrane
w/ in cell itself
Are there a fixed number of receptors?
No; continuous turnover
What are the 2 types of receptor turnover?
Up regulation
Down regulation
Under what circumstances are receptors up regulated?
low concentrations of a hormone will INCREASE the number of receptors on target tissue
What will receptor up regulation result in?
lead to increased sensitivity to the hormone
Under what circumstances are receptors down regulated?
high concentrations of hormone will DECREASE number of receptors on target tissue
What will receptor down regulation result in?
lead to decreased sensitivity to the hormone
What is signal transduction?
process by which extracellular signals (hormones) are communicated into a cell
What are the 2 types of signal transduction messengers?
Primary messengers
Secondary messengers
Describe what happens in primary messenger signal transduction
hormone ITSELF enters cell and mediates cell function
most target tissue receptors are located w/ in the cell itself
Which type of messengers are lipophilic hormones?
primary messenger
lipophilic hormones easily diffuse across cell membrane to communicate to receptors w/ in cells
Describe what happens in secondary messenger signal transduction
secondary messenger “links” primary messanger (hormone) and inside of cell
- hormone attaches to target tissue receptors located on cell membrane
- secondary messenger/mechanism communicates to interior structures of cell to produce desired physiological action
What types of hormones require secondary messengers?
hydrophilic (water soluble) hormones
Why do hydrophilic hormones need a secondary messenger?
can’t diffuse across membrane –> “needs” mechanism to communicate w/ interior structures of cell –> physiological action
What are some examples of secondary messengers?
cAMP (adenosine monophosphate)
Ca2+
cGMP (guanosine monophosphate)
What is the hypothalamic- Pituitary Axis (HPA)?
critical signaling pathway for the endocrine system
How is the Hypothalamic-Pituitary Axis (HPA) divided?
Anterior pituitary
Posterior pituitary
How does the hypothalamus communicate with the anterior pituitary?
hypothalamus releases “pituitary releasing hormones”
hormones descend through the hypophyseal portal system
What does the hypophyseal portal system do?
allow capillaries in hypothalamus to communicate w/ pituitary capillaries BEFORE entering venous system
What do the hypothalamic hormones do to the anterior pituitary?
Most stimulate release of pituitary hormones
some inhibit release of pituitary hormones
How does the hypothalamus communicate with the posterior pituitary?
hypothalamic nuclei synthesize pituitary hormones
hormones descend to pituitary via DIRECT neural connection (so through nerves) to posterior pituitary –> axons of hypothalamic neuron transport hormone
What are the 2 major posterior pituitary hormones?
ADH
Oxytocin
What is the major function of the hypothalamus?
links CNS to endocrine system
Where is the hypothalamus located?
diencephalon of CNS
What is the hypothalamus
collection of nuclei that “control” release of hormones from pituitary gland
What are the hormones released from hypothalamus that control anterior pituitary gland?
TRH = thyrotropin releasing hormone
GnRH = gonadotropin releasing hormone
Somatostatin = aka SRIF (somatoropin release-inhibiting factor)
GHRH = growth hormone releasing hormone
CRH = corticotropin releasing hormone
Substance - P
Dopamine = old terminology = PIF (prolactin inhibiting factor)
PRF = prolactin releasing factor
What does TRH (thyrotropin releasing hormone) do?
stimulates release of TSH (thyroid stimulating hormone) from anterior pituitary
What does GnRH (gonadotropin releasing hormone) do?
stimulates release of LH (leutenizing hormone) and FSH (follicle stimulating hormone) from anterior pituitary
What does somatostatin do?
INHIBITS release of GH (somatotropin) and TSH (thyroid stimulating hormone) from anterior pituitary
What does GHRH (growth hormone releasing hormone) do?
stimulates release of GH (growth hormone) from the anterior pituitary
What does CRH (corticotropin releasing hormone) do?
stimulates release of ACTH (adrenocorticotropic hormone) and Beta-endorphin from anterior pituitary
What does substance - P do?
inhibits synthesis/release of ACTH (adrenocorticotropic hormone) from anterior pituitary
stimulates release of GH (growth hormone), FSH (follicle stimulating hormone), LH (leutinizing hormone) and prolactin from anterior pituitary
What does dopamine do?
inhibits synthesis/release of prolactin from anterior pituitary
What does PRF (prolactin releasing factor) do?
stimulates release of prolactin from anterior pituitary
What are the 2 hormones synthesized in nuclei of hypothalamus and descend to posterior pituitary?
ADH (antidiuretic hormone)
Oxytocin
What is another name for the pituitary gland?
Hypophysis
How is the pituitary gland divided?
Anterior pituitary = adenohypophysis
Posterior pituitary = neurohypophysis
What is the “master gland” of the endocrine system?
Pituitary gland
What are the 3 regions of the anterior pituitary?
Pars distalis
Pars tuberalis
Pars intermedia
What is the function of the pituitary gland?
regulates activity of most endocrine glands in the body
What is the posterior pituitary made of?
neural tissue
What are the 3 regions of the posterior pituitary?
Median eminence
Infundibular stem aka pituitary stem
Infundibular process aka pars nervosa, neural lobe, posterior lobe
Where is the median eminence located?
base of the hypothalamus
What is the infundibular stem (pituitary stem) and what does it contain?
neural connection (conduit) between hypothalamus
contains neural axons that originate in hypothalamus
What is the infundibular process?
site where hypothalamic axons terminate
site of hormone release
Describe how hormones are synthesized and released from the hypothalamic nuclei
Neural cell bodies synthesize hormones
Hormones transported down neural axon to posterior pituitary
Terminal neural axon releases hormones from the posterior pituitary gland
What does oxytocin do in females?
stimulates milk ejection
stimulates uterine contraction (synthetic versions of oxytocin given to induce labor)
What does oxytocin do in males?
suggested to have role in sperm motility
suggested to be elevated in plasma during sexual activities (females too)
What are the target tissues of oxytocin?
mammary glands (lactation)
uterus during pregnancy
What are some stimuli of oxytocin release?
distention of cervix @ end of pregnancy
Breast stimulation (during labor/sucking reflex on lactating breast)
Positive emotional responses (seeing/hearing newborn)
What kind of feedback mechanism does oxytocin have?
Positive feedback mechanism
oxytocin release stimulates more release
What are some inhibition signals of oxytocin release?
External stimulus stops (breastfeeding)
Negative emotional factors –> stress, fear, noise, pain
What are some clinical uses of oxytocin?
Synthetically used to induce labor –> Pitocin, Misoprostol
Not common to have excess oxytocin disease
Oxytocin deficiency will impair nursing
What is the function of ADH (antidiuretic hormone)
Control osmolality/osmolarity of plasma –> blood volume
ADH will INCREASE blood volume –> decreasing osmolarity and increasing blood pressure
What are the target tissues of ADH?
Collecting ducts in kidney (DCT and collecting duct)
Vascular smooth muscle
What is the effect of ADH on the collecting ducts in kidney?
increases water reabsorption by increasing permeability of collecting duct
What is the effect of ADH on vascular smooth muscle?
promotes blood vessel contraction to assist in elevating BP
What are the stimuli for ADH release?
Increased plasma osmolarity
decreased blood volume
angiotensin II (indirectly)
Stress/trauma/exercise/heat
drugs: nicotine, morphine
How does increased plasma osmolarity stimulate ADH release?
osmoreceptors in hypothalamus detect increases of plasma osmolarity
= primary control of ADH release
How much change in osmolality is required to stimulate release of ADH?
1%
How does decreased blood volume stimulate ADH release from the posterior pituitary?
mechanoreceptors (baroreceptors) in the atria, aortic arch and carotid sinus detect blood volume changes
**not as effective as osmoreceptors in hypothalamus
How much of a drop in blood pressure is needed to stimulate the release of ADH?
10%
How does angiotension II promote ADH release from the posterior pituitary?
renin-angiotensin system synergistically trying to increase blood volume and pressure
Angiotension II:
increase sensitivity of osmoreceptors in hypothalamus
stimulate thirst centers in hypothalamus
What other stimuli effect ADH release?
Stress
Trauma
Exercise
Heat
Various drugs –> nicotine, morphine
What inhibits ADH release?
Decreased plasma osmolality
Increased blood volume/pressure
Alcohol/Caffeine
Which receptors detect plasma osmolality?
osmoreceptors
What receptors detect blood volume/pressure?
mechanoreceptors in atria, aortic arch and carotid sinus
What happens with ADH in pts w/ diabetes insipidus?
too little or ineffective ADH
Describe central diabetes insipitus
most common form of diabetes insipitus
decreased release of ADH from posterior pituitary
Describe nephrogenic diabetes insipitus
less common
kidneys aren’t able to respond to ADH
What are the signs and symptoms of diabetes insipitus?
polyuria (excessive urine volume)
polydipsia (excessive thirst)
What is a medication that is given to treat diabetes insidious (central diabetes)
desmopressin
What happens in pts w/ syndrome of inappropriate ADH secretion (SIADH)
too much ADH
elevated ADH secretion –> excessive water reabsorption in kidney
What is hypervolemia caused by?
excessive ADH release –> water reabsorption in DCT/collecting duct
What does hypervolemia lead to?
hypoatremia (decreased Na+ in blood)
natriuresis (excessive Na+ secretion)
Why does hypervolemia lead to hypoatremia?
increased extracellular fluid –> inhibits RAAS (renin/angio/aldosterone system)
Describe what causes natriuresis (excessive Na+ excretion) (3 things)
expansion of exracellular fluid volume reduces Na+ resorption in kidney
baroreceptors in atria/aorta to release ANp –> reduces Na+ resrption (decreased Na+ resorption in proixmal convoluted tubule)
decreased aldosterone release –> reduces Na+ resorption in kidney
Name some of the etiologies of SIADH (syndrome of inappropriate ADH secretion)
tumors
head injuries
meningitis
bronchiogenic tumors (produce vasopressin)
diabetes mellatus
side effect of some drugs
Name the drugs that can cause SIADH (syndrome of inappropriate ADH secretion)
chlorpropamide
cyclophosphamide
carbamazepine
selective serotonin reuptake inhibitors (SSRIs; type of antidepressant)
What is another name for the anterior pituitary?
adenohypophysis
What are the 3 parts of the anterior pituitary?
Pars distalis
Pars tubularis
Pars intermedia
What does the pars distalis do?
produce and secrete anterior pituitary hormones
What is the pars tubularis?
thin layer of cells that wrap around anterior/lateral infundibular stem (pituitary stalk)
What is the pars intermedia?
small layer of cells located between pars distal is and pars nervousa
How is the release of anterior pituitary hormones regulated?
hypothalamic-hypophyseal portal system
Describe how the hypothalamic-hypophyseal portal system works
releasing/inhibiting hormones are released from hypothalamus
circulation from hypothalamic capillaries travels to hypophysis via hypophyseal portal system
circulating hormones stimulate the anterior pituitary to inhibit or release specific hormones
What are the 6 hormones synthesized and released by the anterior pituitary?
prolactin
GH (growth hormone)
TSH (thyroid stimulating hormone)
GnRH (gonadotropin releasing hormones)
ACTH (adrenocorticotrophic hormone)
MSH (melanocyte stimulating hormone)
There are 2 GnRH (gonadotropin releasing hormones), what are they?
LH (luteinizing hormone)
FSH (follical stimulating hormone)
What does prolactin do?
breast development during puberty and pregnancy
stimulate milk production after birth (lactogenesis)
inhibit ovulation
What is the target tissue of prolactin hormone?
mammary glands during puberty, pregnancy, and while lactating newborns
What stimulates prolactin release from the anterior pituitary gland?
Puberty (breast development)
Pregnancy (breast/duct growth)
Lactation (milk production)
Miscellaneous factors that stimulate release
What specifically during puberty stimulates the release of prolactin?
combined presence of growth hormone, estrogen, progesterone, thyroid releasing hormone
**these guys also inhibit dopamine (which is a prolactin inhibiting factor)
What specifically during pregnancy stimulates prolactin release from the anterior pituitary?
combined presence of elevated estrogen and progesterone
What specifically during lactation (milk production) stimulates prolactin release from the anterior pituitary?
breast feeding
What are the other miscellaneous factors that stimulate release of prolactin from the anterior pituitary?
sleep
dopamine antagonists
What inhibits prolactin release from the anterior pituitary?
dopamine (a constant tonic release) from hypothalamus
elevated levels of prolactin stimulates hypothalamus to increase release of dopamine
dopamine agonists (bromocriptine)
What is another name for growth hormone?
somatotropin
How is growth hormone (GH) release and when is the peak of release?
released in pulsing/cyclic pattern
peaks during adolescence
What is the function of GH (and IGF-1)?
stimulates all tissue growth and maturation (anabolic function)
How does GH (and IGF-1) function to stimulate tissue growth/maturation?
work synergistically
promote growth of tissues
regulates metabolism to facilitate growth
Where does growth hormone and IGF-1 not function?
central nervous system
Besides growth and maturation what are some other functions of growth hormone?
aging
sleeping
reproductive hormone function
Which tissues does growth hormone have a direct effect, and how does it have a direct effect?
Binds directly to growth hormone receptors
Liver
Muscle
Adipose Tissue
Describe how growth hormones produce an indirect effect
GH stimulates the liver –> produces/secretes IGF-1
When do IGF-1 levels peak?
peak @ puberty –> decline gradually w/ age
What are the target tissues of IGF-1?
Bone
Cartilage
Visceral Organs
What does IGF-1 stand for?
Insulin Like Growth Factor 1
What are the actions of growth hormone in the liver?
IGF synthesis
Protein synthesis
What are the actions of growth factor in adipose tissue?
increase lypolysis
decrease glucose uptake
What are the actions of growth factor in muscles?
increase amino acid uptake/protein synthesis
Decrease glucose uptake
Generally, what is the action of IGF-1 throughout the body
mediate cell growth in most tissues
What are the actions of IGF-1 in cartilage?
Stimulate cartilage matrix growth/balance
increase synthesis of matrix (chondroitin sulfate/collagen)
Amino acid uptake/protein synthesis –> DNA/RNA synthesis
** critical for linear bone growth during development
What are the actions of IGF-1 in muscles, bones, and organs?
Amino acid uptake/protein synthesis –> DNA/RNA synthesis
Increase cell size/number
Bone = facilitate osteoblast/osteoclastic activity
What does IGF-2 do?
inhibitory (antagonistic) effect on tissue growth
What are the metabolic actions of growth hormone/ IGF-1?
GH (directly) and IGF-1 (indirectly) regulate fat, carbohydrate and protein metabolism to facilitate growth
Specificially what does GH/IGF-1 do to protein metabolism?
stimulate amino acid uptake/synthesis and protein anabolism in tissues
Specifically what does GH/IGF-1 do to carbohydrate metabolism?
assist in maintaining blood glucose levels
impair glucose uptake
stimulate liver glycogenolysis
Specifically what does GH/IGF-1 do to fat metabolism?
increase lipolysis
decrease glucose uptake into fat cells
How is IGF-1 involved in feedback?
inhibits growth hormone release from pituitary
stimulates somatostatin (growth hormone inhibiting factor) release from hypothalamus
What are the factors that stimulate growth hormone release from the anterior pituitary gland?
GHRH = growth hormone releasing hormone from hypothalamus
Elevated sex hormones –> puberty
Dietary Protein –> increase ingestion of amino acids (provide building blocks for growth)
Hypoglycemia –> inhibits somatostatin (GH inhibitor from hypothalamus)
Stage 4 (deep) sleep (esp. in kids)
Exercise –> stress response to exercise
What are the factors that inhibit GH release from the anterior pituitary?
Somatostatin –> hypothalamic hormone
Glucocorticoids
Hyperglycemia
What is the name of the syndrome that causes excessive corticosteroid production, and what does it cause?
Cushing’s syndrome
inhibits the release of growth hormone from the anterior pituitary
Name some glucocorticoid drugs that can inhibit the release of GH from the anterior pituitary, what is a potential consequence of using these drugs?
Prednisone
Prednisilone
Dexamethasone
Can inhibit growth in kids
What will elevated levels of growth hormone do (in regards to feedback)?
inhibits the release of GH from the anterior pituitary
What will elevated levels of IGF-1 do (in regards to feedback)?
inhibit GH release from the anterior pituitary
stimulate somatostatin (GH inhibiting factor) release from the hypothalamus
What will excessive androgen levels do?
inhibit release of GH from the anterior pituitary
What are the 3 phases of growth?
Phase I = prenatal to first year of growth
Phase II = juvenile growth (1 - puberty)
Phase III = Puberty
What influences phase I growth?
not well understod
What influences phase II growth?
growth hormone
thyroid hormones
insulin
What influences phase III growth?
added influence of sex steroid hormones (testosterone/estrogen) –> thought to increase GH levels
What are the hormones that influence growth?
Growth Hormone
Thyroid Hormones
Gonadal Steroid Hormones
Insulin
Cortisol
How does growth hormone influence growth?
metabolic changes to favor growth/maturation
direct/indirectly stimulate cell growth (synergistic w/ IGF-1)
How do the thyroid hormones influence growth?
maintenance function/stimulate GH
necessary for CNS development
necessary for normal function of IGF-1
How do gonadal steroid hormones influence growth?
stimulate growth spurt @ puberty
necessary for normal GH secretion
How does insulin influence growth?
Stimulate fetal and postnatal growth
How does cortisol influence growth?
inhibits GH release –> INHIBITS growth
decreases efforts of growth factors on epiphysis (growth plates) of bone
What is a consequence of insufficient GH?
dwarfism
In dwarfism, WHEN do you see GH dysfunction?
BEFORE growth plates close
impaired GH secretion or GH receptors
What is the consequence of excessive GH?
Gigantism
Acromegaly
In gigantism, when do you see GH dysfunction?
see increase of GH BEFORE epiphyseal plates close
In acromegaly, when do you see GH dysfunction?
see increase of GH AFTER epiphyseal plates close
Which parts of the body are usually effected in acromegaly?
chin
hands
feet
What type of bone growth do you have in acromegaly?
enlargement of structures due to periosteal bone growth
What might you see in Excessive GH disorders (gigantism/acromegaly)?
Adenomas = benign glandular tumors
What are the clinical findings of long-term excessive growth hormone?
arthropathy
neuropathy
cardiomyopathy/hypertension
respiratory disease
carbohydrate intolerance/diabetes
increased risk of malignancy
DECREASED lifespan
What does TSH (thyroid stimulating hormone) do?
stimulate syntehsis/release of thyroid hormones (t3 and T4)
What are the 2 gonadotropin hormones?
LH = luteinizing hormone
FSH = follicle stimulating hormone
What does luteinizing hormone do in females?
simulate ovulation
formation of corpus luteum
synthesis of progesterone in the ovaries
What does luteinizing hormone do in males?
stimulates synthesis and secretion of testosterone
What does follicle stimulating hormone do in females?
stimulates the growth of ovarian follicles
stimulates estrogen secretion
What does follicle stimulating hormone do in males?
stimulates sperm maturation in testicles
What does ACTH (adrenocorticotropic hormone) do?
stimulates synthesis and secretion of adrenal cortical hormones
What does MSH (melanocyte stimulating hormone) do?
stimulates melanin synthesis/release from melaonocytes in the skin –> increases pigmentation
