Endocrine System Flashcards
(174 cards)
1
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endocrine system
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glands, tissues and cells that secrete hormones
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endocrinology
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the study of this system and the diagnosis and treatment of its disorders
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endocrine glands
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organs that are sources of hormones
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endocrine system function
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regulates long-term processes: growth, development, reproduction
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exocrine glands
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have ducts; carry secretion to an epithelial surface or the mucosa of the digestive tract: “external secretions”
extracellular effects (food digestion)
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endocrine glands
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no ducts; contain dense, fenestrated capillary networks which allow easy uptake of hormones into bloodstream; “internal secretions”; intracellular effects such as altering target cell metabolism
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direct communication
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occurs between two cells of the same type through gap junctions via ions or small solutes
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paracrine communication
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uses chemical messengers to transfer signals between cells in a single tissue
messenger = cytokines or local hormones
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endocrine communication
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uses hormones to coordinate cellular activities in distant portions of the body
gradual, coordinated but not immediate
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hormones
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chemical messengers released from one tissue and transported in blood to reach target cells in other tissues
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synaptic communication
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involves neurons releasing neurotransmitter at a synapse close to target
immediate but short lived
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speed and persistence of response nervous vs endocrine
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quickly, stops quickly vs slowly, effect may continue for days or longer
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adaptation to long-term stimuli nervous vs endocrine
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declines (adapts quickly) vs persists (adapts slowly)
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area of effect nervous vs endocrine
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targeted and specific (one organ) vs general, widespread effects (many organs)
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the endocrine system
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consists of glands and glandular tissue involved in paracrine and endocrine communication
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endocrine cells produce secretions
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released into extracellular fluid-> enters blood-> body-wide distribution to find target
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target cell
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specific cells that possess receptors needed to bind and “read” hormonal messages
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endocrine cells located in
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hypothalamus, pituitary gland, thyroid gland, thymus, adrenal glands, pineal gland, parathyroid glands, heart, kidney, adipose tissue, digestive tracts, pancreatic islets, gonads
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hypothalamus
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master regulatory organ
integrates nervous and endocrine systems
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hypothalamus secretes
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regulatory hormones to control secretion from anterior pituitary gland
hormones from anterior pituitary control other endocrine organs
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hypothalamus acts as
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endocrine organ
produce ADH and oxytocin
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autonomic centers of hypothalamus
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neural control of adrenal medulla-> neuroendocrine reflex
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pituitary gland
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hangs inferior to hypothalamus via infundibulum in sella turcica of sphenoid
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anterior lobe
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secretes 7 hormones
function via cAMP 2nd messenger
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posterior lobe
secretes 2 hormones
function via cAMP 2nd messenger
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portal vessels
blood vessels link two capillary networks
entire complex is portal system
ensures that regulatory factors reach intended target cells before entering general circulation
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hypothalamic control of the anterior lobe
two classes of hypothalamic regulatory hormones: releasing and secreting
rate of secretion is controlled by negative feedback
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releasing hormones (RH)
stimulate synthesis and secretion of one or more hormones at anterior lobe
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inhibiting hormones (IH)
prevent synthesis and secretion of hormones from the anterior lobe
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anterior lobe (adenohypophysis)
glandular tissue
anterior pituitary hormones are all tropic hormones
secretion of the hormones controlled by releasing and inhibiting hormones from the hypothalamus
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tropic hormones
turn on secretion or support function of other endocrine organs
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diseases cause by the growth hormone in excess
usually due to pituitary tumor
before epiphyseal closure = gigantism
after = acromegaly, excessive growth of hands, feet, face, internal organs
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diseases cause by the growth hormone deficiency
pituitary dwarfism: failure to thrive
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posterior lobe (neurohypophysis)
contains unmyelinated axons or hypothalamic neurons
supraoptic and paraventricular nuclei
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anterior lobe produces
ACTH, TSH, GH, PRL, FSH, LH, MSH
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posterior lobe produces
ADH, OXT
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supraoptic and paraventricular nuclei manufacture:
ADH and oxytocin
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hypothalamus produces
regulatory factors that adjust activities of anterior lobe of pituitary gland, which produces 7 hormones
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most hormones control
other endocrine organs, including thyroid gland, adrenal gland and gonads
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thyroid gland
inferior to larynx
largest pure endocrine organ
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left and right lobes of thyroid gland connected by
isthmus
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tissue of thyroid gland
follicles
parafollicular cells/C cells
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follicles
spheres or simple cuboidal epithelium
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parafollicular cells/C cells
between follicles
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follicles filled with
colloid-> thyroglobulin
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thyroglobulin protein
constantly synthesized by follicle cells and exocytosed into follicle for storage
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upon stimulation by TSH thyroglobulin is processed into
thyroid hormones (T3/T4)
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actively transported into thyroid follicle cells
iodide ions
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iodide ions
stimulated by TSH form reserves in thyroid follicles
excess removed from blood at kidneys
deficiency limits rates of thyroid hormone production
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iodated tyrosines
in tyroglobulins are chemically bonded to form T3 and T4
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iodated tyroglobulins
are broken down to release T3 and T4
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thyroid hormones
released into blood circulation
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receptors for thyroid hormones
located in all cells except adult brain, spleen, testes, uterus, thyroid
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receptors in thyroid target cells found in
cytoplasm
mitochondria
nucleus
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function of cytoplasm target cell for thyroid
hold hormone in reserve
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function of mitochondria target cell for thyroid
increase cellular respiration
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function of nucleus target cell for thyroid
activate genes for enzymes involved in energy transformation and utilization
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overall effect of thyroid hormones
increase metabolic rate and body heat production
regulate tissue growth and development
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hypothyroidism
lack of T3/T4
myxedema
cretinism
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myxedema
adults
low body temp, muscle weakness, slow reflexes, cognitive dysfunction and goiters-> swollen thyroid
produce thyroglobulin but fail to endocytose
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cretinism
infants = genetic defect
causes lack of skeletal and nervous system development
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hyperthyroidism
excessive T3/T4
high metabolic rate, high heart rate, restlessness, fatigue
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graves disease
autoimmune disorder
produce antibodies that mimic TSH causing overproduction of thyroid hormones
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parafollicular cells/C cells
in basement membrane of follicles
produce calcitonin
respond directly to blood calcium levels, not controlled by hypothalamus
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calcitonin
stimulates decrease in blood Ca++ levels
inhibits osteoclasts
promotes Ca++ loss at kidneys
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parathyroid glands
four glands embedded in posterior surface of thyroid gland
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two cell types in parathyroid gland
oxyphiles: few, functions unknown
chief cells: majority
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function of chief cells in parathyroid gland
produce parathyroid hormone (PTH)/Parathormone
most important regulator of blood calcium
secreted when blood calcium is low
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effects of PTH
acts to raise blood calcium levels by acting on various tissues
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PTH acts on
bone, kidney, intestines
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PTH effects on bone
stimulates osteoclasts and inhibits osteoblasts
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effects of PTH on kidney
enhances reabsorption of Ca++
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effects of PTH on intestines
promotes conversion of vitamin D to calcitrol in kidney to enhance Ca++ and PO43- absorption in small intestine
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thyroid gland produces
hormones that adjust tissue metabolic rate
a hormone that usually plays minor role in calcium ion homeostasis by opposing action of parathyroid hormone
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adrenal gland
2 glands, in renal fascia, superior to kidney
glandular adrenal cortex
adrenal medulla mostly nervous tissue
in general-> adrenal hormones are used to cope with stressors
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adrenal cortex
produces 24+ corticosteroids
in target alter gene transcription to affect metabolism
glandular
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3 layers of adrenal cortex
1. zona glomerulosa
2. zona fasciculata
3. zona reticularis
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zona glomerulosa
mineralcorticoids
95% aldosterone
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function of hormones produces in zona glomerulosa
control water and electrolyte balance
stimulates Na+ retention and K+ loss
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hormones produces in zona glomerulosa released in response to
low Na+ or high K+
angiotensin mechanism
low blood pressure or volume
excessive ACTH
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zona fasciculata
glucocorticoids
metabolic hormones
control glucose metabolism-> cortisol (hydrocortisone), corticosterone
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function/effects of hormones produces in zona fasciculata
gluconeogenesis in liver
release of fatty acid from adipose tissue
triggers protein hydrolysis to release free amino acids from skeletal muscle
triggers body cells to utilize fatty acids and amino acids instead of glucose
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hormones produces in zona fasciculata released in response to
ACTH
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zona reticularis
gonadocorticoids
mostly androgens, may aid onset of puberty
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function/effects of hormones produces in zona reticularis
taken up by the testes and ovaries to produce testosterone and the estrogens respectively
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hormones produces in zona reticularis released in response to
ACTH
excess = androgenital syndrome
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adrenal medulla
contains two types of secretory cells
epinephrine (75-80% of secretions)
norepinephrine (20-25% of secretions)
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epinephrine and norepinephrine activation of the adrenal medulla effects in skeletal muscles
mobilization of glycogen reserves
accelerate the breakdown of glucose to provide ATP
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activation of the adrenal medulla effects in adipose tissue
stored fats are broken down into fatty acids
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activation of the adrenal medulla effects in the liver
glycogen molecules are broken down
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activation of the adrenal medulla effects in the heart
triggers an increase in the rate and force of cardiac muscle contraction
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adrenal glands produce hormones that
adjust metabolic activities at specific sites
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adrenal gland hormones affect
pattern of nutrient utilization, mineral ion balance, or rate of energy consumption by active tissues
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pineal gland
posterior of third ventricle
pinealocytes
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pinealocytes
produce melatonin from serotonin
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pinealocytes secretion
diurnal cycle
high at night, low during daylight
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melatonin functions
play role in timing of sexual maturation
antioxidant-> free radical protection
sets circadian rhythms
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pancreas
inferior and posterior to stomach
mostly exocrine cells-> pancreatic acini- secrete digestive enzymes
1% endocrine-> pancreatic islets
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exocrine pancreas
pancreatic acini and their attached ducts
takes up roughly 99% of pancreatic volume
gland and duct cells secrete alkaline, enzyme rich fluid-> reaches the lumen of the digestive tract through a network of secretory ducts
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endocrine pancreas
consists of cells that form clusters known as pancreatic islets, or islets of Langerhans
alpha, beta, delta, F cells
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alpha cells
produce glucagon
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beta cells
produce insulin
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delta cells
produce peptide hormone identical to GH-IH
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F cells
secrete pancreatic polypeptide (PP)
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when blood glucose levels rise
beta cells secrete insulin, stimulating transport of glucose across plasma membranes
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when blood glucose levels decline
alpha cells release glucagon, stimulating glucose release by liver
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five effects of insulin
1. accelerates glucose uptake
2. accelerates glucose utilization and enhances ATP production
3. stimulates glycogen formation
4. stimulates amino acid absorption and protein synthesis
5. stimulates triglyceride formation in adipose tissue
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three effects of glucagons
1. stimulates breakdown of glycogen in skeletal muscle and liver cells
2. stimulates breakdown of triglycerides in adipose tissue
3. stimulates production of glucose in liver
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diabetes mellitus
too much glucose in blood (hyperglycemia)
type 1 or 2
cells cannot use glucose-> ketone bodies produced-> too many ketone bodies leads to ketoacidosis
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type 1
failure to produce insulin
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type 2
insulin resistance, sometimes insulin deficiency
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pancreatic islets release
insulin and glucagons
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insulin is released
when blood glucose levels rise
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insulin stimulates
glucose transport into, and utilization by, peripheral tissues
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glucagon released
when blood glucose levels decline
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glucagon stimulates
glycogen breakdown, glucose synthesis, and fatty acid release
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many organs of other body systems have secondary endocrine functions
intestines (digestive system)
kidneys (urinary system)
heart (cardiovascular system)
thymus (lymphatic system and immunity)
gonads (reproductive system)
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gastrointestinal tract
enteroendocrine cells in GI mucosa secrete many hormones-> coordinate digestive activity
mostly paracrine communication
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hormones in GI tract
gastrin
gastrin inhibitory peptide
secretin
cholecystokinin
enterocrinin
vasoactive intestinal peptide
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kidneys
various endocrine cells
three products
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three products of kidneys
calcitrol
erythropoeitin
renin
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calcitrol
steroid hormone
stimulate Ca++, PO43- absorption in GI
stimulate osteoclast activity
stimulate Ca++ retention in kidney
suppress PTH production
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erythropoeitin
peptide hormone
released in response to low O2 in kidney
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renin
enzyme
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renin effect
released in response to sympathetic stimulation or decline in renal blood flow
converts angiotensin in blood into Angiotensin 2 (hormone)
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Angiotensin 2 effects
stimulate secretion of aldosterone-> adrenal
stimulate secretion of ADH-> pituitary
stimulate thirst
elevate blood pressure (BP)
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heart
some walls of atrial walls secrete atrial natriuretic peptide (ANP) in response to stretch
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ANP effects
promotes Na+ and water loss at kidney
inhibits release of renin, ADH, and aldosterone-> reduce BP and volume
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thymus
located deep to sternum
cell produces thymosin hormones
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thymosin hormones
promote development and maturation of T lymphocytes and the immune system
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thymuses of the newborn and adult
newborn thymus is large for antibodies and to build an immune system and shrinks to adulthood
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testes
interstitial cells produce androgens in response to LH
testosterone, most common
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testosterone effects
produces male secondary sex characteristics
promotes sperm production
maintains secretory glands
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ovaries
follicle cells produce estrogens in response to FSH and LH
estradiol
progesterone
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function of estradiol
regulates menstrual female reproductive cycles
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effects of estradiol
produce female secondary sex characteristics
support maturation of oocytes
stimulate growth of uterine lining
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surge in LH in ovaries causes
ovulation
follicle reorganizes to form corpus luteum
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function of progesterone
involved in the menstrual cycle, pregnancy and embryogenesis
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effects of progesterone
prepares uterus for embryo growth
accelerates movement of oocyte/embryo to uterus
enlargement of mammary glands
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adipose tissue
leptin secretion
resistin secretion
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leptin secretion
in response to absorption of glucose and lipids
triggers satiation in appetite center of hypothalamus
controls normal levels of GnRH, gonadotropin synthesis
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resistin secretion
reduces insulin sensitivity
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hormones can be divided into 3 groups
amino acid derivatives
peptide hormones
lipid derivatives
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amino acid derivatives
structurally similar to or based on amino acids
e.g. catecholamines (epinephrine, norepinephrine, dopamin), thyroid hormones, melatonin
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peptide hormones
chains of amino acids
peptides
glycoproteins
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peptides
<200 amino acids
e.g. ADH, oxytocin, GH
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glycoproteins
>200 amino acids with carbohydrate side chain
e.g, TSH
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lipid derivatives
steroid hormones
eicosanoids (local hormones)
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steroid hormones
structurally similar to/based on cholesterol
e.g. Androgens, Estrogens, Calcitrol
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eicosanoids (local hormones)
derived from arachidonic acid
not circulating autocrine or paracrine only
E.g. leukotrienes, prostaglandins
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leukotrienes
from leukocytes-> coordinate inflammation
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prostaglandins
from mast cells-> coordinate local activities (smooth muscle contractions, clotting, etc.)
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hormone mechanism of action
hormones circulate in blood-> contact all cells
only cause effects in cells with receptors for hormone-> called target cells
receptors present on a cell determines the cell's hormonal sensitivity
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hormone stimulus effects in target cells
1. alter plasma membrane permeability or transmembrane potential by opening/closing ion channels
2. stimulate synthesis of-> structural proteins, receptors, regulatory enzymes within cell
3. activate or deactivate enzymes
4. induce secretory activity
5. stimulate mitosis
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hormone receptors
located on plasma membrane or inside target
1. cell membrane hormone receptors
2. intracellular hormone receptors
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peptides and catecholamines
hydrophilic, so cannot penetrate target cell membrane
work through second messenger systems
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three major second-messengers
cyclic adenosine monophosphate (cAMP)
diacylglycerol (DAG)
inositol triphosphate (IP3)
hormonal effects are relatively quick- don't depend on cell synthesizing new proteins
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cAMP mechanism
1. hormone binds receptor
2. G-protein activated
3. adenylate cyclase activated
4. ATP-> cAMP
5. kinases activated
6. proteins (enzymes) phosphorylated
7. enzymes activated/deactivated
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phospholipids-calcium mechanism
1. hormone binds receptor
2. G-protein activated
3. phospholipase C (PLC) activated
4. phospholipids cleaved into diacylglycerol (DAG) and inositol triphosphate (IP3)
5. DAG can open Ca++ channels on membrane
6. IP3 releases Ca++ from ER
7. kinases activated
8. enzymes phosphorylated and activated
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cell membrane hormone receptors
2nd messenger mechanism results in amplification of hormone signals
one hormone molecule binds one receptor but can result in thousands of final products
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intracellular hormone receptors
steroid hormones, thyroid hormones
result in direct gene activation by hormone
hormone diffuses across membrane, binds receptors in cytoplasm or nucleus
hormone + receptor bind DNA-> transcription-> translation= protein production-> metabolic enzymes, structural proteins, secretions
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target cell activation depends on
1. blood level of hormone
2. relative number of receptors
3. affinity of bond between hormone and receptor
if hormone levels are excessively high for too long-> cells can reduce receptor number or affinity and become-> non-responsive to a hormone
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distribution and duration of hormones
circulating hormones either free or bound to carrier/transport proteins
effects at target cell can take seconds to days depending on mechanism and final effect, but hormone once bound to receptor is broken down quickly
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free hormones
last for less than 1 hour
rapidly broken down by liver, kidney, or plasma enzymes in blood
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bound hormones
last hours to days in blood
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interaction 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
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hormone interactions
antagonistic
synergistic
permissive
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antagonistic
hormones oppose each other
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synergistic
hormones have additive effects
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permissive
one hormone is needed for the other to cause its effect
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aging and hormone production
causes few functional changes
decline in concentration of growth hormone and reproductive hormones
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hormones coordinate
cell, tissue and organ activities
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hormones circulate
in extracellular fluid and bind to specific receptors
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hormones modify cellular activities by
altering membrane permeability
activating or inactivating key enzymes
changing genetic activity
