chapter 18: endocrine system Flashcards
what communication involves the use of chemical messengers to transfer signals between cells in a single tissue?
paracrine
the secretion produced by endocrine cells is called a what? chemically it could be the same as a neurotransmitter but rather than being released at the synapse it travels to the target cell via what?
hormone, blood
which is the smallest molecule: amino acid derivative, a peptide hormone, or a glycoprotein?
amino acid deritative
what are eicosanoids constructed from that is made up of essential fatty acids from the diet?
arachidonic acid
what determines if a cell is a target cell for a particular hormone?
induce transcription & translation to get new proteins (enzymes) made that hadn’t been present in the cell before
in the second messenger mechanism of a hormone activity, existing protein enzymes get turned on or off to change activity of the target cell. explain how intracellular hormone receptors are different with regard to the proteins/enzymes that result in activity?
the presence of receptors on/in the cell for that hormone
free hormones don’t require a carrier but what does this mean in regard to longevity?
broken down quickly, short-term message
what’s the interaction is the type of hormone interaction where one hormone is needed for the other to cause its effects?
permissive
there are three major stimuli for hormone release. which stimuli are where ion & nutrient levels in the blood trigger the release of the hormone?
humoral
name the two hormones that are made by the hypothalamus but released from the posterior pituitary?
ADH & oxytocin
where specifically is your pituitary gland located?
inferior to hypothalamus, resting in sella turcica of sphenoid bone
what will be released from the anterior pituitary in response to TRH from the hypothalamus?
thyroid stimulating hormone (TSH)
GnRH from the hypothalamus promotes the release of what hormone from the anterior pituitary, which promotes the production of gonadal hormones?
luteinizing hormone
what cells does MSH from the anterior pituitary target?
melanocytes
what does oxytocin promote in the reproductive system?
smooth muscle contraction
growth hormone functions to accelerate what synthesis in most cells?
protein syntheis
thyroid follicle cells constantly synthesize what, the precursor to T3 & T4?
thyroglobulin
the production of T3 and T4 what element in an ion form?
iodine
what’s the autoimmune disorder where antibodies overstimulate the thyroid gland, resulting in high blood levels of T3 &
T4?
graves’ disease
what effect does calcitonin have on osteoclasts?
inhibits
how many parathyroid glands does the average person have?
four
what structure/type of hormones are produced by the adrenal cortex?
steroids
what effect would an overstimulation of the zona glomerulosa have on blood pressure?
increase
which tissues/organs are affected by the norepinephrine released by the adrenal medulla?
smooth muscle of blood vessels, causes constriction
what does the zona reticularis produce?
gonadocorticoids
pancreatic polypeptide is produced by what cells of the pancreatic islets?
f cells
beta cells of the pancreas produce what, which has many
actions that result in a reduction of blood glucose level?
insulin
what does glucagon trigger adipocytes to do?
breakdown triglycerides & release of fatty acids
what gland produces melatonin?
pineal gland
the hormones of the gastrointestinal tract are produced by what
cells located in multiple organs?
enteroendocrine
what does the kidney produce that provides negative feedback on PTH release and more?
calcitrol
the effects of the hormone that results from renin are the opposite of the effects of the hormone produced by what organ?
heart (renin makes angiotensin II, heart releases ANP)
hormones from the thymus are important for the maturation of what?
t lymphocyte
what’s the hormone from adipocytes that reduces hunger?
leptin
direct communication (intracellular communication)
occurs between 2 cells of the same type through gap junctions via ions or small solutes
paracrine communication (intracellular communication)
uses chemical messengers to transfer signals between cells in a single tissue (messenger = cytokines or local hormones)
endocrine communication (intracellular communication)
uses hormones to coordinate cellular activities in distant portions of the body, gradual, coordinated but not immediate
hormone
chemical messengers released from one tissue & transported into blood to reach target cells in other tissues
synaptic communication
involves neurons
releasing neurotransmitters at a synapse close to target, immediate but short-lived
endocrine system
-consists of glands & glandular tissue involved in paracrine & endocrine communication
-endocrine cells produce secretions ->
released into ECF -> enters blood -> body-wide distribution to find target
amino acid derivatives (hormone structure)
-structurally similar to or based on amino
acids
-e.g. catecholamines (epinephrine,
norepinephrine, dopamine), thyroid
hormones, melatonin
peptides (peptide hormones -> hormone structure)
- <200 amino acids
-e.g. ADH,
oxytocin, GH
what is a peptide hormones?
chains of amino acids
glycoproteins (peptide hormones -> hormone structure)
- > 200 amino acids
with carbohydrate
side chain
-e.g. TSH
steroid hormones (lipid derivatives -> hormone structure)
-structurally similar
to/based on cholesterol
-e.g. Androgens,
Estrogens, Calcitriol
eicosanoids (lipid derivatives -> hormone structure)
-derived from arachidonic acid
-not circulating:
autocrine or paracrine only
-eg. leukotrienes, prostgaldins
leukotrienes (eicosanoids -> lipid derivatives -> hormone structure)
from leukocytes, coordinate
inflammation
prostaglandins (eicosanoids -> lipid derivatives -> hormone structure)
from Mast cells, coordinate local activities (smooth muscle contraction, clotting, etc.)
mechanism of action for hormones
-hormones circulate in blood: contact all cells
-receptors present on a cell determine the
cell’s hormonal sensitivity
target cell
has a receptor for a specific hormone
hormone stimulus effects in target cells:
- alter plasma membrane permeability or
transmembrane potential by opening /
closing ion channels - stimulate synthesis of structural proteins,
receptors, regulatory enzymes within cell - activate or deactivate enzymes
- induce secretory activity
- stimulate mitosis
cell membrane hormone receptors
-catecholamines, peptide hormones,
glycoprotein hormones, eicosanoids
-bind receptors on cell surface
-indirectly trigger events inside cell via
second messengers (cAMP, Ca ++ )
-2nd messenger acts as activator, inhibitor,
or cofactor for ICF enzymes
-receptor linked to 2nd messenger by
G protein
what do hormones that bind to cell surfaces receptors work through?
second messengers to open ion channels or activate/deactivate enzymes
what does the second messenger mechanism (cAMP or Ca++) result in?
amplification of the hormone signal
cAMP mechanism
-hormone binds receptor
-G protein-activated
-adenylate cyclase-activated
- ATP -> cAMP
-kinases activated
-proteins (enzymes) phosphorylated -> enzymes activated/ deactivated
-eg. epinephrine, TSH
PIP-calcium mechanism
-hormone binds receptor
-G-protein activated
-phospholipase C (PLC) activated
-phospholipids (PIP2) cleaved into diacylglycerol (DAG) & inositol triphosphate (IP3)
- DAG opens Ca++ channels on membrane
-IP3 release Ca++ from ER
-calcium binds to calmodulin -> enzymes activated
-eg. oxytocin, regulatory hormones
2nd messenger mechanism results in
amplification of hormone signal:
one hormone molecule binds one receptor but
can result in millions of final products
intracellular hormone receptors
-steroid hormones, thyroid hormones
-result in direct gene activation by hormone
-hormone diffuses across membrane, binds receptors in cytoplasm or nucleus
-protein production
protein production (intracellular hormone receptors)
hormone + receptor bind DNA ->
transcription -> translation = metabolic enzymes, structural proteins, secretions
target cell activation depends on:
- blood level of hormone
- relative number of receptors
- Affinity of bond between hormone &
receptor
-if hormone levels are excessively high for too
long cells can reduce receptor number or
affinity & become non-responsive to a
hormone
distribution & duration of hormones
-circulating hormones either free or bound to
carrier/transport proteins
-free hormones last seconds to minutes:
rapidly broken down by liver, kidney,
or plasma enzymes in blood
-bound hormones last hours to days in blood
-effect on target cell can take seconds to days
depending on mechanism & final
effect, but hormones, once bound to receptor, are broke down quickly
interactions of hormones at target cells
-target cells have receptors for multiple
hormones
-effects of one hormone can be different depending on presence or absence of
other hormones
antagonistic (hormone interaction)
hormones oppose each other
synergistic (hormone interaction)
hormones have additive effects
permissive (hormone interaction)
one hormone is needed for the
other to cause its effects
control of endocrine activity
synthesis & release of most hormones
regulated by negative feedback: stimulus -> hormone release -> effects at target
how is hormone release turned on & off?
turned on by stimuli & off by negative feedback but can be
modified by the nervous system
humoral stimuli (major stimuli for hormone release)
–ion & nutrient levels in blood trigger
release (e.g. PTH released when blood Ca++ is low)
neural stimuli (major stimuli for hormone release)
autonomic nervous system
–nerve fibers directly stimulate release
(e.g. sympathetic -> adrenal medulla = epinephrine release)
hormonal stimuli (major stimuli for hormone release)
–hormones stimulate the release of other
hormones
(e.g. releasing hormones of hypothalamus
cause release of hormones from anterior pituitary)
hypothalamus
-located at the base of
3rd ventricle
-master regulatory organ
-integrates nervous &
endocrine systems
what are the three mechanisms of control of the hypothalamus?
- secrete regulatory hormones to control
secretion from anterior pituitary (hormones from anterior pituitary
control other endocrine organs) - act as an endocrine organ (produce ADH
& oxytocin) - has autonomic centers for neural control of adrenal medulla (neuroendocrine
reflex)
pituitary gland (hypophysis)
-hangs inferior to
hypothalamus via
infundibulum
-in sella turcica of sphenoid bone
-anterior lobe secretes 7 hormones: function
via cAMP 2nd messenger
-posterior lobe secretes 2 hormones: function via cAMP 2nd messenger
anterior lobe of pituitary gland (adenohypophysis)
-glandular tissue
-anterior pituitary
hormones are all
tropic hormones
-secretion of the
hormones controlled by releasing & inhibiting hormones from hypothalamus
tropic hormones
turn on secretion or support function of other organs
thyroid stimulating hormone (TSH), thyrotropin (anterior pituitary hormone)
-hypothalamus control = thyrotropin-releasing hormone (TRH)
-promotes release of thyroid hormones by thyroid gland
adrenocorticotropic hormone (ACTH), corticotropin (anterior pituitary hormone)
-hypothalamus control= corticotropin releasing
hormone (CRH)
-promotes release of corticosteroid hormones (glucocorticoids) from adrenal cortex
follicle stimulating hormone (FSH), follitropin (anterior pituitary hormone)
-hypothalamus control = gonadotropin releasing hormone (GnRH)
-promotes gamete production in ovaries & testes
luteinizing hormone (LH), lutropin (anterior pituitary hormone)
-hypothalamus control = gonadotropin releasing hormone (GnRH)
-promotes production of gonadal hormones (estrogens & androgens)
prolactin (PRL), mammotropin (anterior pituitary hormone)
-hypothalamus control = prolactin inhibiting
hormone (PIH)
-stimulates mammary gland development & milk production in females (can assist androgen production in males)
growth hormone (GH), somatotropin (anterior pituitary hormone)
-hypothalamus control = growth hormone
releasing hormone
(GH-RH) & growth hormone inhibiting hormone (GH-IH), somatostatin
-accelerates rate of protein synthesis in most cells, especially skeletal muscle &
chondrocytes
indirect mechanism of growth hormone (GH) (hormone of anterior pituitary)
stimulates liver to release somatomedins (insulin-like growth
factors (IGFs) ) which trigger cells to absorb amino acids & synthesize proteins
with them
direct mechanism of growth hormone (GH) (hormone of anterior pituitary)
stimulates stem cell division in epithelia & CT, stimulates adipose to hydrolyze triglycerides & release fatty acids, stimulates liver to hydrolyze glycogen & release glucose
melanocyte stimulating hormone
(MSH), melanotropin (anterior pituitary hormone)
-hypothalamus control = release inhibited by
dopamine
-stimulates melanocytes to produce melanin
excess growth hormone diseases
usually due to pituitary tumor
-before epiphyseal closure = gigantism
-after = acromegaly: excessive growth of
hands, feet, face, internal organs
deficiency of growth hormone disease
pituitary dwarfism: failure to thrive (extremely short)
posterior lobe of pituitary gland (neurohypophysis)
-neural tissue
-contains axons of hypothalamus: release
hormones to posterior lobe for storage
antidiuretic hormone
(ADH), vasopressin (posterior pituitary hormone)
-hypothalamus site of production = supraoptic nuclei
-released in response to rise in blood electrolytes or ↓ BP
-triggers water retention at kidney & vasoconstriction
oxytocin (OT) (posterior pituitary hormone)
-hypothalamus site of production = paraventricular nuclei
-females: stimulates smooth muscle to promote labor & delivery and milk ejection
-role in sexual arousal & orgasm in both sexes (smooth muscle contraction)
thyroid gland
-inferior to larynx
-left and right lobes
connected by isthmus
-largest pure endocrine organ
-tissues: follicles & parafollicular/C cells
follicles (thyroid gland tissue)
-spheres of simple
cuboidal epithelium
-filled with colloid: thyroglobulin
-thyroglobulin protein constantly synthesized
by follicle cells & exocytosed into
follicle for storage
-upon stimulation by TSH, thyroglobulin is
processed into thyroid hormones (T3/T4)
Receptors for thyroid hormones located in all cells except where?
adult brain, spleen, testes, uterus, thyroid
3 receptors in target cells for thyroid hormones:
-cytoplasm: holds hormone in reserve
-mitochondria: increase cellular respiration
-nucleus: activate genes for enzymes involved in energy transformation & utilization
overall effect of thyroid hormones
increase metabolic rate & body heat production, and regulate tissue growth & development
formation & release of thyroid hormones 1-2:
- iodine ions (I-) from diet accumulate in cytoplasm of follicle cells
- at apical surface thyroid peroxidase converts I- to I+ (activated form) & links it to 4 tyrosine molecules in the previously formed protein thyroglobulin in the follicle
formation & release of thyroid hormones 3-5:
- iodated tyrosines in thyroglobulin are chemically bonded to create the thyroid hormones T4 & T3
- stimulated by TSH, follicle cells endocytose iodinated thyroglobulin
- iodinated thyroglobulin is broken down in the lysosome, releasing T3, T4, & free amino acids into
cytoplasm
thyroid hormones
thyroxine/tetraiodothyronine (T4) & triiodothyronine (T3)
formation & release of thyroid hormones 6-7:
- T3 & T4 is exocytosed at the basement membrane into the blood (90% is T4)
- T3 & T4 are bound to transport proteins for circulation to tissues (at target tissues, T4 can be converted to T3, the more active form of thyroid hormone)
hypothyroidism
lack of T3/T4
myxedema (adults)
lack of iodine causes
low body temp, muscle weakness, slow
reflexes, cognitive dysfunction & goiter
goiter
swollen thyroid (produce thyroglobulin but fail to endocytose)
cretinism (infants)
a genetic defect causes
lack of skeletal & nervous system
development
hyperthyroidism
excessive T3/T4, causes high metabolic rate, high heart rate,
restlessness, fatigue
Graves disease
autoimmune disorder,
produce antibodies that mimic TSH, causing overproduction of thyroid hormones
parafollicular cells / C cells (thyroid gland)
-in basement membrane of follicles
-produce Calcitonin
-parafollicular cells respond directly to blood calcium levels, not controlled by
hypothalamus
calcitonin release (parafollicular cells/ C cells -> thyroid gland)
Ca2+ 20% above normal
calcitonin stimulates
decrease in blood
calcium levels (parafollicular cells/ C cells -> thyroid gland):
- inhibits osteoclasts
- promotes Ca++ loss
at the kidneys
parathyroid glands
-four glands embedded in posterior side of lobes of thyroid
-two cell types: oxyphils & chief cells
oxyphils (parathyroid gland cell)
few, function unknown
chief cells (parathyroid gland cell)
majority, produce parathyroid hormone (PTH)
parathyroid hormone (PTH) /parathormone
-most important regulator of blood calcium
-secreted when blood calcium low
-acts to raise blood calcium levels by acting
on various tissues
parathyroid hormone (PTH) effect on bone tissue
stimulates osteoclasts & inhibits osteoblasts
parathyroid hormone (PTH) effect on kidney tissue
enhances reabsorption of Ca 2+
parathyroid hormone (PTH) effect on intestinal tissue
promotes conversion of VitD to calcitriol in kidney to enhance Ca2+ & PO43- absorption in small intestine
adrenal glands
-2 glands, in renal
fascia, superior to
kidney
-glandular adrenal
cortex
-medulla mostly
nervous tissue
-in general: adrenal hormones used to cope with stressors
adrenal cortex (adrenal glands)
-produces 24+ corticosteroids: in target alter gene transcription to affect metabolism
-3 layers: zona glomerulosa, fasciculta, reticularis
zona glomerulosa (adrenal cortex -> adrenal glands)
-mineralocorticoids
-control water & electrolyte balance
aldosterone (zona glomerulosa -> adrenal cortex -> adrenal glands)
-makes up 95%
-stimulates Na+ retention & K+ loss (humoral)
-released in response to ↓ Na+ or ↑ K+, renin-angiotensin mechanism, low blood pressure or volume (hormonal), excessive ACTH (hormonal)
zona fasciculata (adrenal cortex -> adrenal glands)
-glucocorticoids
-cortisol (hydrocortisone)
-secretion controlled by ACTH
cortisol (hydrocortisone) (zona fasciculata -> adrenal cortex -> adrenal glands)
-cortisol = natural
-hydrocortisone = administred
-metabolic hormone control glucose metabolism, most common
effect of zona fasciculata (adrenal cortex -> adrenal glands)
glucogenesis in liver, release of fatty acids from adipose, triggers protein hydrolysis to release free amino acids from skeletal muscle, triggers body cells to utilize fatty acids & amino acids instead of glucose
excess of cortisol (hydrocortisone) (zona fasciculata -> adrenal cortex -> adrenal glands)
anti-inflammatory, inhibit immune response & healing
zona reticularis (adrenal cortex -> adrenal glands)
-gonadocorticoids
-mostly androgens, may ai on onset of puberty
-excess = androgential syndrome (over masculine in males + females)
adrenal medulla (adrenal glands)
-neural, produces catecholamines (epi, norepi.) to enhance effect of other adrenal hormones
-chromaffin cells
chromaffin cells (adrenal medulla -> adrenal glands)
modified ganglionic sympathetic neurons that release epinephrine (80%) & norepinephrine (20%) in response to sympathetic stimuli
epinephrine effects (adrenal medulla -> adrenal glands)
-stimulate heart & metabolic activities:
-skeletal muscle mobilize
glucogen reserves, accelerate ATP production
-adipose promotes release of fatty acids
-liver promotes release of glucose
norepinephrine effects (adrenal medulla -> adrenal glands)
stimulate peripheral vasoconstriction to increase blood pressure (e.g., fight or flight response)
Cushing’s syndrome
excessive
corticosteroids (ACTH from pituitary
tumor), results in hyperglycemia, ↓ muscle & bone mass, hypertension, edema, poor healing, chronic infections
Addison’s disease
deficient in
corticosteroids, results in weight loss,
hypoglycemia, ↓Na+ ↑K+ in plasma, dehydration, hypotension
pancreas
-inferior & posterior to stomach
-mostly exocrine cells: pancreatic acini, secrete digestive enzymes
-1% endocrine: pancreatic islets
alpha cells (pancreatic islets cell type)
glucagon:↑ blood glucose
beta cells (pancreatic islets cell type)
insulin: ↓ blood glucose
delta cells (pancreatic islets cell type)
somatostatin: suppresses glucagon & insulin release slows
enzyme release into intestine
f cells (pancreatic islets cell type)
pancreatic polypeptide: regulates
production of pancreatic enzymes
insulin (pancreas)
-secreted in response to high blood glucose or ANS: parasympathetic =↑ insulin
sympathetic = ↓ insulin
-effects only on insulin dependent cells (have
receptors)
-brain, kidney, GI mucosa & RBCs all
insulin independen
effects of insulin
beta cells secrete insulin(↑ in blood glucose level) -> ↑ rate of glucose transport into target cell, ↑ rate of glucose utilization & ATP generation, ↑ conversion of glucose to glycogen (liver, skeletal muscle), ↑ amino acid absorption & protein synthesis, ↑ triglycerides synthesis (adipose tissue) -> blood glucose conc. ↓ -> homeostasis restored
effects of glucagon
alpha cells secrete insulin (↓ in blood glucose level) ->↑ breakdown of glycogen to glucose (liver, skeletal muscle), ↑ breakdown of fats to fatty acids (adipose tissue), ↑ synthesis & release of glucose (liver) -> blood glucose conc. ↑ -> homeostasis restored
diabetes mellitus
too much glucose in blood (hyperglycemia)
-type I = failure to produce insulin
-type II = insulin resistance, sometimes
insulin deficiency
ketoacidosis
cells do not utilize glucose, ketone bodies
produced, too many
glucagon (pancreas)
secreted in response to low blood glucose or
sympathetic stimulation
pineal gland
-posterior of third ventricle
-pinealocytes: synthesize melatonin from serotonin
-secretion on diurnal cycle: high at night, low
during daylight
melatonin (pineal gland) functions:
-play role in timing of sexual maturation
-antioxidant (free radical protection)
-sets circadian rhythms
gastrointestinal tract
-enteroendocrine cells in GI mucosa secrete
many hormones: coordinate digestive activity
-mostly paracrine communication
-cholecystokinin
-enterocrinin
-gastric inhibitory peptide
-gastrin
-secretin
-vasoactive intestinal
peptide
kidney
various endocrine cells, three products: calcitriol, erythropoietin & renin
calcitriol (steroid hormone -> kidney)
released in response to PTH
-hormonal response
calcitriol effects (steroid hormone -> kidney)
-stimulate Ca2+ , PO43- absorption in GI
-stimulate osteoclast activity
-stimulate Ca2+ retention in kidney
-suppress PTH production
erythropoietin (peptide hormone -> kidney)
-released in response to low O2 in kidney
-stimulates erythrocyte production
-humoral response
renin (enzyme -> kidney)
-released in response to sympathetic
stimulation or decline in renal blood flow
-converts angiotensin in blood into Angiotensin II (hormone)
-neural response
angiotensin II effects (renin -> enzyme -> kidney):
-stimulate secretion of aldosterone (adrenal)
-stimulate secretion of ADH (pituitary)
-stimulate thirst
-elevate BP (both aldosterone & ADH restrict Na+ & H2O loss at kidney)
heart
-some cells of atrial walls secrete Atrial Natriuretic Peptides in response to stretch
-ANP promotes Na+ & water loss in kidney, inhibits release of renin, ADH & aldosterone to reduce BP & volume
thymus
-located deep into sternum
-cells produce thymosins
-promote development & maturation of T
lymphocytes & immune response
testes (gonads)
interstitial cells produce androgens in
response to LH
testosterone (testes -> gonads)
-most common
-produces male secondary sex characteristics, promotes sperm production & maintains secretory glands
ovaries (gonads)
follicle cells produce estrogens in response
to LH and FSH
estradiol (ovaries -> gonads)
-most important
-produce female secondary sex characteristics
-support maturation of oocytes
-stimulate growth of uterine lining
-surge in LH causes ovulation, follicle
reorganizes to form corpus luteum:
produces estrogens & progestins
progesterone (ovaries -> gonads)
-most important
-prepares uterus for embryo growth
-accelerates movement of oocyte/embryo to
uterus
-enlargement of mammary glands
adipose (endocrine)
-secretes leptin in response to absorption of glucose & lipids
-triggers satiation in appetite center
of hypothalamus
-permissive effect on gonadotropins
-also secretes resistin
-reduces insulin sensitivity
age-related changes for endocrine system
-very little change in most hormone levels
-adverse effects due to changes in target
tissues: prevent reception or response to hormone
-gonads decrease in size & hormone
production
