Lesson 3 - Endocrine Pt 1 Flashcards
gap junctions
pores in cells membranes that allow signaling molecules, nutrients, and electrolytes to move from cell to cell
neurotransmitters
released from neurons to travel across the synaptic cleft to a second cell
paracines
secreted into tissue fluids to affect nearby cells
hormones
chemical messengers that travel in the bloodstream to stimulate physiological responses in other tissues and organs
endocrine system
glands, tissues, and cells that secrete hormones
endocrinology
the study of the endocrine system and the diagnosis and treatment of its disorders
endocrine glands
organs that are sources of hormones
exocrine glands
have ducts that carry secretion to an epithelial surface or the mucosa of the digestive tract: “external secretions”
examples of exocrine glands
sweat glands
endocrine glands
no ducts; contain dense, fenestrated capillary networks which allow easy uptake of hormones into the bloodstream: “internal secretions”
what kind of effects do endocrine glands produce?
intracellular effects such as altering target cell metabolism
speed and persistence of response: nervous
reacts quickly (msec timescale) and stops quickly
speed and persistence of response: endocrine
reactly slowly (seconds or days), effects may continue for days or longer
adaptation to long-term stimuli: nervous
response declines, adapts quickly
adaptation to long-term stimuli: endorcine
responses persist, adapts slowly
area of effect: nervous
targets and specific (one organ)
area of effect: endocrine
general, widespread effects (many organs)
True or False: Chemicals can only act as hormones or neurotransmitters, not both
false, several function as BOTH hormones and neurotransmitters
examples of chemicals that are both hormones and neurotransmitters (3)
norepinephrine, dopamine, and antidiuretic hormone
both the nervous and endocrine system can have similar effects on target cells (example)
both norepinephrine and glucagon cause glycogen hydrolysis in the liver
an example of how the nervous system and endocrine system can regulate each other
neurotransmitters can affect glands and hormones can affect neurons
cells that share characteristics with both the nervous and endocrine system are called
neuroendrocine cells; neuron-like cells that secrete oxytocin into the blood
target organs/cells
those organs or cells that hve receptors for a hormone and can respond to it
what do some target cells posses?
enzymes that convert a circulating hormone to its more active forms
three chemical classes of hormones
steroid, monoamines, and peptides
lipid-derived hormones
derived from fats like sex steroids from gonads and corticosteroids from adrenal glands
monoamines (biogenic amines)
made from amino acids, like tyrosine used to produce the catecholamines and thyroid hormone
catecholamines (3)
dopamine, epinephrine, and norepinephrine
peptide hormones
created from chains of amino acids
examples of peptide hormones (4)
thyroid-stimulating hormone, luteinizing hormone, follicle-stimulating hormone, insulin
prohormones
inactive molecules that are converted to the active hormones before or after they are secreted; many peptide hormones are synthesized as these
steroids
derived from cholesterols
leukotrienes
have secondary roles as hormones causing inflammation during allergic reactions
prostaglandins
involved in coordinating local cellular activities and can be converted to thromboxanes (vasoconstrictor) or prostacyclins (vasodilator)
eicosanoids
derived from arachidonic acid (a 20-carbon fatty acid)
steroids released by reproductive organs: testes
androgens
steroids released by reproductive organs: ovaries (2)
estrogens and progestins
steroids released by reproductive organs: cortex of adrenal glands
corticosteroids
steroids released by reproductive organs: kidneys
calcitriol
proinsulin
a prohormone, has a middle portion called a connecting peptide that is removed to form the active form of insulin (two peptide chains connected by disulfide bridges)
melatonin is synthesized from
amino acid tryptophanh
what are some monoamines synthesized from?
tyrosine
don’t forget slide 19, you don’t understand it
hormone secretion fluctuates on…(5)
- the circadian rhythm
- a woman’s monthly cycle
- under the influence of neural, hormonal, or humoral stimuli
stimuli for hormone secretion: neural stimulation
nerve fibers supply some endocrine glands and elicit the release of their hormone
examples of neural stimuli for hormone secretion (2)
- the sympathetic nervous system stimulates the adrenal medulla to secrete epinephrine and norepinephrine in situations of stress
- in childbirth, the positive feedback loop of oxytocin
stimuli for hormone secretion: hormonal stimuli
hormones from the hypothalamus regulate secretion by the anterior pituitary gland
examples of hormonal stimuli for hormone secretion
pituitary hormones stimulate other endocrine glands to release thyroid hormone, sex hormones, and cortisol
stimuli for hormone secretion: humoral stimuli
refers to blood-borne stimuli; rising blood glucose concentration stimulates the release of insulin
rising blood glucose concentration stimulates the release of _____
insulin
low blood osmolarity stimulates the secretion of _____
aldosterone
low blood calcium level stimulates the secretion of _____
parathyroid hormone
hormones may or may not be stored prior to secretion: peptide hormones and catecholamines
stored in secretory vesicles of the endocrine cell until needed and released by exocytosis when the cell receives a stimulus to do so
hormones may or may not be stored prior to secretion: steroid hormones
these are not stored, but are released as fast as they are synthesized by diffusion through the cell surface
hormones may or may not be stored prior to secretion: thyroid hormone
diffuses freely through plasma membranes, but does accumulate in the gland awaiting stimulus for secretion (TSH); stored in the extracellular spaces enclosed by the thyroid follicles
stimuli such as _____ and _____ can increase the synthesis and release of a steroid hormone by several-fold within hours
FSH, ACTH
most monoamines and peptides are _____, and mix easily with blood plasma
hydrophilic
steroids and thyroid hormones are _____, and have protein carriers
hydrophobic
transport proteins
albumins and globulins synthesized by the liver that help hormones last longer in blood
bound hormones
hormones that have bound to a transport protein
only _____ hormone leaves capillaries to reach the target cells
unbound (free)t
thyroid hormone binds to _____, _____, and _____
albumin, thyretain, and thyroxine-binding globulin (TBG)
steroid hormones bind to _____
globulin
hormone receptors
protein or glycoprotein molecules on plasma membranes, in the cytoplasm, or in the nucleus
hormone receptors act like
switches, turning on metabolic pathways when the hormone binds to them
hormone specificity
receptor for one hormone will not bind another hormone
hormone saturation
when all receptor molecules are occupied by hormone molecules
peptides and catecholamines are
hydrophilic, cannot penetrate target cell membrane; they bind to surface receptors and activate intracellular processes, metabolic pathways through second messenger systems
three major second-messengers
- cyclic adenosine monophosphate (cAMP)
- diacylglycerol (DAG)
- inositol triphosphate (IP3)
reasons unbound hormones only last about one hour in blood (3)
- diffuse out of the bloodstream and bind onto receptors on target cells
- are broken down and absorbed by cells of the liver or kidneys
- broken down by enzymes in the blood plasma of interstitial fluid
cAMP as a second messenger (example) (6)
- hormone-receptor binding activated a G protein
- G protein activates adenylate cyclase
- adenylate cyclase produces cAMP
- cAMP activates protein kinase
- protein kinases phosphorylate enzymes, activating some and deactivating others
- activated enzymes catalyze metabolic reactions with a wide range of possible effects on the cell
where do steroid/thyroid hormone bind in the cell? (2)
receptors in the cytosol or nucleus
- if receptors in the cytosol, the hormone:receptor is transported into the nucleus
hormone-receptor complex
a hormone bound to its specific receptor
signal amplification (cascade effect)
seen in hormones that trigger second messengers; one hormone molecule triggers the synthesis of a large number of enzyme molecules
how potent are hormones?
very small stimulus can produce very large effects; it allows the circulating hormone concentrations to remain relatively low
up-regulation
number of receptors is increased; sensitivity is increased
down-regulation
number of receptors is reduced; call less sensitive to hormone and also happens with long-term exposure to high hormone concentrations
hypothalamus
shaped like a flattened funnel, forms the floor and walls of the third ventricle of the brain
functions of the hypothalamus (4)
regulating primitive functions from water balance and thermoregulation to sex drive and childbirth
pituitary gland (hypophysis)
suspended from the hypothalamus by a stalk (infundibulum)
two parts of the pituitary gland
anterior and posterior pituitary
anterior pituitary
adenohypophysis
constitutes anterior three-quarters of the pituitary
how is the anterior pituitary linked to the hypothalamus?
via blood vessels of the hypophyseal portal system
_____ _____ in the hypothalamus connected to _____ _____ in the anterior pituitary by _____ _____
primary capillaries, secondary capillaries, portal venules
hypothalamic hormones _____ anterior pituitary cell secretions
regulate
posterior pituitary
neurohypophysis
constitutes the posterior quarter of the pituitary; composed of nerve tissue but isnt a real gland
nerve cell bodies in the hypothalamus pass down the stalk as the _____-_____ _____ and end in the posterior lobe
hypothalamo-hypophyseal tract
hypothalamic neurons secrete hormones that were stored where?
in the neurohypophysis (posterior pituitary) until released into the blood
six hypothalamic hormones regulate the anterior pituitary
- gonadotropin-releasing hormone (GnRH)
- thyrotropin-releasing hormone (TRH)
- corticotropin-releasing hormone (CRH)
- prolactin-inhibiting hormone (PIH)
- growth hormone-releasing hormone (GHRH)
- somatostatin
gonadotropin-releasing hormone (GnRH)
stimulates release of gonadotropins (FSH, LH) from the anterior pituitary
thyrotropin-releasing hormone (TRH)
stimulates the release of thyroid-stimulating hormone (TSH, thyrotropin) from the anterior pituitary
corticotropin-releasing hormone (CRH)
stimulates release of adrenocorticotropic hormone (ACTH, corticotropin) from the anterior pituitary
prolactin-inhibiting hormone (PIH)
inhibits the release of prolactin from the anterior pituitary
growth hormone-releasing hormone (GHRH)
stimulates release of growth hormone (GH) from the anterior pituitary
somatostatin
inhibits the release of GH and TSH from anterior pituitary
two hypothalamic hormones are store in the posterior pituitary and released on demand, what are they?
oxytocin (OT) and antidiuretic hormone (ADH)
oxytocin (OT)
stimulates labor concentrations (uterus) and milk release (mammary glands), also released during sexual arousal and orgasm for satisfaction emotional bonding
where is oxytocin produced?
in the paraventricular nuclei of the hypothalamus
antidiuretic hormone (ADH)
aka vasopressin, it stimulates water retention by the kidneys thus reducing urine volume and preventing dehydration
where is antidiuretic hormone produced?
by the supraoptic nuclei of the hypothalamus
the anterior lobe of the pituitary synthesizes and secretes these six major hormones
- follicle-stimulating hormone (FSH)
- luteinizing hormone (LH)
- thyroid-stimulating hormone (TSH)
- adrenocorticotropic hormone (ACTH)
- prolactin (PRL)
- growth hormone
follicle-stimulating hormone (FSH)
aka follitropin
stimulates the secretion of ovarian sex hormones, development of ovarian follicles, and sperm production
luteinizing hormone (LH)
aka lutropin
stimulates ovulation, corpus luteum secretion of progesterone, and testosterone secretion by testes
gonadotropins
FSH and LH, they target the ovaries and testes
thyroid-stimulating hormone (TSH)
aka thyrotropin
stimulates secretion of thyroid hormone (TH) from the thyroid gland
adrenocorticotropic hormone (ACTH)
aka corticotropin
stimulates adrenal cortex to secrete glucocorticoids
prolactin (PRL)
after birth, stimulates mammary glands to synthesize milk
growth hormone (GH)
aka somatotropin
stimulates mitosis and cellular differentiation
arginine vasopressin (AVP)
another name for antidiuretic hormone because it can cause vasoconstriction (but only at unnaturally high concentrations)
how are hormonal rates of secretion regulated? (3)
they are regulated by the hypothalamus, other brain areas, and feedback from target organs
hypothalamic and cerebral control of hormone secretion
brain monitors conditions and influences anterior pituitary accordingly
in time of stress, the hypothalamus triggers the release of _____
ACTH - adrenocorticotropic hormone
during pregnancy, the hypothalamus triggers _____ secretion
prolactin
the posterior pituitary is controlled by _____ reflexes
neuroendocrine
what triggers the release of ADH when they detect a rise in blood osmolarity?
hypothalamic osmoreceptors
infant suclking triggers hypothalamuc response to release _____
oxytocin
negative feedback inhibition
increased target organ hormone levels inhibits release of hypothalamic and/or pituitary hormones
example of negative feedback inhibition
thyroid hormone inhibits release of TRH by the hypothalamus and of TSH by the anterior pituitary
growth hormone (GH) has widespread effects including:
- inducing the liver to produce growth stimulants
- stimulate target cells in diverse tissues
somatomedins
insulin-like growth factors IGF-1 and IGF-II
growth hormone half-life
6-20 minutes
IGF-1 half-life
about 20 hours
mechanisms of GH-IGF action: protein synthesis
boosts transcription and translation; also increases amino acid uptake into the cells
mechanisms of GH-IGF action: lipid metabolism
stimulates adipocytes to catabolize fats, release fatty acids for body cells to use as fuel instead of proteins; aka the protein-sparing effect
mechanisms of GH-IGF action: carbohydrate metabolism
mobilizing fatty acids reduces dependence of most cells on glucose, freeing more for the brain aka the glucose-sparing effect; stimulates glucose secretion by the liver
mechanisms of GH-IGF action: electrolyte balance
promotes Na+, K+, and Cl- retention by the kidneys, enhances Ca2+ absorption in the intestine; makes electrolytes available to growing tissues
mechanisms of GH-IGF action: growth
stimulates bone, cartilage, and muscle growth especially during childhood and adolescence
GH secretion fluctuates with….
- time of day
- activity level
- age
where can GH secretions be high? (3)
- high secretion during the first two hours of sleep
- can peak in response to vigorous exercise
- activated by ghrelin
ghrelin
a hormone released by the stomach that activates GH
