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