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Endocrine System
The Endocrine System
Major controlling system in
the body
Endocrine system has a
slower and more prolonged
response (US Mail service)
than the nervous system
(email) but usually effects last
Maintains homeostasis by
releasing chemicals called
hormones into the
bloodstream from glands
The Endocrine System
Act as messengers by
binding to cellular
receptors on the plasma
membrane of a target cell
or organ
Alter the activity of body
cells that control growth,
reproduction and
maintenance of
electrolyte, water and
nutrient balance of the
blood, regulation of
cellular metabolism and
energy balance
The Endocrine System
Organ that produces and releases a substance
Exocrine glands
Produce substances such as sweat and saliva and have
ducts that carry these substances to a membrane surface
Endocrine glands (ductless glands)
Produce hormones and lack ducts; release their hormones
into the bloodstream
The Endocrine System
Two general groups of hormones
Steroid hormones (does enter cell)
Produced from cholesterol
Binds to a receptor in the cell’s nucleus
Activates a gene to transcribe mRNA
Non-steroid hormones (doesn’t enter cell)
Most hormones are amino acid based
Proteins, peptides and amino acids
Binds to a plasma membrane receptor
Act through a second messenger such as cyclic AMP
The Endocrine System
All hormones circulate to virtually every tissue but a given
hormone influences the activity of only certain tissue cells
called target cells
Protein receptors are found on the plasma membrane that
respond to only a specific hormone
When the binding occurs the hormone influences the cell
by either turning on specific genes or using a secondary
messenger to initiate a response
The Endocrine System
How are blood levels of all hormones regulated?
Negative feedback system
Goal is to shut off the stimulus or reduce its intensity back to
normal range of functioning
Hormone secretion is triggered by a stimulus
Hormonal stimulus – stimulated by another endocrine gland
Humoral stimulus - stimulated by changes in certain ions and
nutrients in the bloodstream
Neural stimulus - stimulated by a neuron
Endocrine Glands
Endocrine organs are
usually smaller and
unimpressive compared to
other organs and scattered
throughout the body
Pituitary gland
Thyroid gland
Parathyroid glands
Pineal glands
Thymus gland
Adrenal glands
Ovaries and testes
Endocrine Glands
Produces and releases hormones that control other endocrine glands
Considered a neuroendocrine organ
Endocrine Glands
Pituitary gland
Seated in the sella turcica of the sphenoid bone
Size and shape of a grape
Hangs below the hypothalamus by the infundibulum or stalk
Secretes eight hormones
Two functional lobes controlled by the hypothalamus
Anterior pituitary (glandular tissue) releases hormones
Posterior pituitary (nervous) releases hormones that are stored
here from the hypothalamus
Endocrine Glands
Anterior Pituitary Gland - “Master endocrine gland”
Many of the hormones it produces regulates the activity of other
endocrine organs called tropic hormones
Thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH),
follicle stimulating hormone (FSH) and luteinizing hormone (LH)
Endocrine Glands
Anterior Pituitary Gland
Growth hormone (GH)
Promotes most body cells to increase in size and divide
Major target is to stimulate the growth of skeletal muscles and bones
Endocrine Glands
Anterior Pituitary Gland
Growth hormone (GH)
Hypersecretion in children results in gigantism
Abnormally tall often 8 feet with normal body proportions
Usually results from an anterior pituitary tumor
Hyposecretion in children leads to slowed long bone growth called
pituitary dwarfism
Abnormally short around 4 feet with fairly normal body proportions
Can be corrected with growth hormone replacement therapy
On the downside, athletes use the synthetic GH as bodybuilding
Endocrine Glands
Anterior Pituitary Gland
Thyroid stimulating hormone (TSH)
Regulates the growth and activity of the
thyroid gland
Endocrine Glands
Anterior Pituitary Gland
Adrenocorticotropic hormone (ACTH)
Stimulates the adrenal cortex gland to release hormones that help
resist stressors
Stimulated by stress, major surgery, trauma or fever
Endocrine Glands
Anterior Pituitary Gland
Follicle-stimulating hormone (FSH)
and Luteinizing hormone (LH)
Regulate the function of the gonads
and not present until puberty
Follicle-stimulating hormone (FSH)
Stimulates gamete (sperm or egg)
Luteinizing hormone (LH)
Promotes the production of gonadal
Females – LH works with FSH to
cause ovarian follicle to mature
LH then triggers ovulation
Males - stimulates the testes to
produce testosterone
Endocrine Glands
Anterior Pituitary Gland
Prolactin (PRL)
Stimulates and maintains milk production in mammary glands of females
Function unknown in males
Stimulated by the infant’s suckling on the breasts
Hypersecretion causes inappropriate lactation, lack of menses and
impotence in males
Endocrine Glands
Posterior Pituitary Gland
Stores antidiuretic hormone (ADH) and oxytocin that are made and
sent from the hypothalamus
Stimulated when cervix or uterus stretches or suckling of infant at breast
Causes smooth muscle contractions specifically in the uterus and breasts
Initiates labor and milk ejection
Released in high amounts during childbirth and nursing women
Natural and synthetic oxytocic drugs are used to induce labor
Endocrine Glands
Posterior Pituitary Gland
Antidiuretic Hormone (ADH)
Diuresis is urine production
An antidiuretic is a substance that inhibits or prevents urine formation
Prevents wide swings in water balance helping the body avoid
dehydration and water overload
Osmoreceptors continually monitor the blood to control ADH release
Targets the kidney tubules and causes more water to be reabsorbed
Drinking alcohol inhibits ADH secretion and causes lots of urine output
Dry mouth and intense thirst of the ‘hangover’ reflect this dehydrating
effect of alcohol
Endocrine Glands
Posterior Pituitary Gland
Antidiuretic Hormone (ADH)
Hyposecretion of ADH can result in diabetes insipidus (tasteless)
(not diabetes mellitus (honey))
Syndrome marked by huge amounts of urine outputs and intense
Usually caused by head trauma that damages the posterior
Not serious when the thirst center is operating properly and
enough water is drunk
Can be life threatening in unconscious or comatose patients
Hypersecretion of ADH occurs in children with meningitis, after
neurosurgery or secretion from cancer cells
Symptoms include retention of fluid, headache, disorientation due
to brain edema, and weight gain
Endocrine Glands
Thyroid Gland
Butterfly-shaped; located in the anterior neck on the trachea just
inferior to the larynx
Largest pure endocrine organ in the body
Secretes two hormones
Thyroid hormone (TH) and calcitonin
Endocrine Glands
Thyroid Gland
Thyroxine (T4) and Triiodothyronine (T3)
make up the thyroid hormone (TH)
Regulated by thyroid stimulating
hormone (TSH)
Stimulates metabolism in every cell in
the body
Increases the rate at which glucose is
burned and body heat production
Iodine is essential for formation of the
Regulated by blood calcium levels
Decreases blood calcium levels
Initiates bone resorption
Stimulates calcium uptake and
deposits into bones
Endocrine Glands
Thyroid Gland
Hypothyroid syndrome, myxedema, can
be caused by lack of TSH or lack of iodine
in diet
Symptoms include low metabolism,
chilled, thick, dry skin, puffy eyes, edema,
lethargy, obesity and mental sluggishness
Goiter - lack of Iodine causes the thyroid
gland to enlarge
Endocrine Glands
Thyroid Gland
Hyperthyroidism usually results in an
autoimmune disease called Grave’s
Person makes abnormal antibodies
directed against the thyroid cells and
cause the TH to be constantly stimulated
Symptoms include high metabolic rate,
excessive perspiration, irregular
heartbeat, nervousness, weight loss, and
exophthalmos (protruding eyeballs)
Endocrine Glands
Parathyroid Gland
Four tiny glands nearly hidden from view on the
posterior aspect of the thyroid gland
Parathyroid hormone (PTH)
Stimulated by blood calcium levels
Increases blood calcium levels
Stimulates bone destruction by osteoclasts
Resorption of calcium by the kidneys
Uptake from intestines
Endocrine Glands
Parathyroid Gland
Hypoparathyroidism usually follows parathyroid gland trauma or
Low amounts of calcium in the blood leads to classical symptoms
of tetany such as loss of sensation, muscle twitches, and
Endocrine Glands
Adrenal Glands
Located over the top of the kidneys
Structurally two endocrine organs in one
Adrenal cortex (hormone)
Two major steroid hormones (aldosterone and cortisone)
Adrenal medulla (sympathetic nervous system)
Two hormones (epinephrine and norepinephrine)
Endocrine Glands
Adrenal glands
Responds to short and long
term stress
Short term stress response
= adrenal medulla
Stimulated by the
Releases epinephrine and
Long term stress response
is adrenal cortex
Stimulated by ACTH
Releases mineralcorticoids
and glucocorticoids
Endocrine Glands
Adrenal Cortex
Synthesizes over two dozen steroid
hormones called corticosteroids
Mineralcorticoids (primarily aldosterone)
Regulate the electrolyte concentrations in
extracellular fluids
Glucocorticoids (primarily cortisol)
Influence the energy metabolism of most
body cells and help us to resist stressors
Adrenal sex hormones
Endocrine Glands
Adrenal Cortex
Aldosterone (mineralocorticoids)
Regulated by a decrease in sodium
levels or elevated potassium levels
Promotes reabsorption of sodium and
excretion of potassium in the kidneys
Hypersecretion usually results from
Symptoms include hypertension and
edema due to excessive sodium and
water retention
Endocrine Glands
Adrenal Cortex
Cortisone (glucocorticoids)
Stimulated by adrenocorticotropic hormone (ACTH)
Increases blood glucose
Endocrine Glands
Adrenal Cortex
Addison’s disease
Hyposecretory disease of the adrenal cortex
Deficits in glucocorticoids and mineralocorticoids
Symptoms include weight loss, decrease levels of glucose and sodium,
increase in potassium levels, severe dehydration and hypotension are
Endocrine Glands
Adrenal Medulla
Neural stimulus by the sympathetic nervous system
Two hormones secreted epinephrine (adrenaline) and
Blood glucose levels rise, blood vessels constrict, heart
beats faster, blood is diverted from nonessential organs
to the heart and skeletal muscles
Epinephrine is used as a heart stimulant in heart attack
patients and a bronchodilator in asthma attacks
Endocrine Glands
Adrenal Medulla
Hypersecretion of epinephrine and norepinephrine are usually
caused by a tumor
Produces symptoms of uncontrolled sympathetic nervous system
Hyperglycemia (elevated blood glucose), increased metabolic rate,
rapid heartbeat and palpitations
Endocrine Glands
Pineal gland
Tiny, pine cone shaped; located in the third ventricle in the brain
Function is still somewhat a mystery
Major secretory product is melatonin
Involved in rhythmic activities (daily and seasonal)
Levels in the blood rise and fall in a daily cycle
Highest at night making us drowsy and lowest occurring around
Regulated by visual cues of daylight
Endocrine Glands
Located partially behind the stomach in the abdominal cavity
Mixed gland composed of both endocrine and exocrine gland cells
Exocrine cells produce enzyme rich juice for digestion
Endocrine cells called islets of Langerhans secrete glucagon and
insulin that help regulate blood glucose levels
Endocrine Glands
Glucagon (hyperglycemic hormone)
Major target is the liver
Humoral stimulation due to blood glucose
levels falling
Raises blood glucose levels from the
breakdown of glycogen to glucose, makes
glucose from lactic acid and releases
glucose to the blood by liver cells
Endocrine Glands
Insulin (hypoglycemic hormone)
Humoral stimulation due to blood glucose
levels rising
Lowers blood glucose levels by enhancing
membrane transport of glucose into body
cells, inhibiting the breakdown of glycogen
to glucose, inhibiting the conversion of
amino acids or fats to glucose and
promoting protein synthesis or fat storage
Endocrine Glands
Hyposecretion or hypoactivity of insulin
results in diabetes mellitus
When insulin is absent blood sugar levels
remain high after a meal because glucose is
unable to enter the cells
Eventually excess of glucose begins to be lost
from the body in the urine (glycosuria)
Three cardinal signs of diabetes are polyuria
(huge urine outputs), polydipsia (excessive
thirst), and polyphagia (excessive hunger and
food consumption)
Can be treated with synthetic insulin
Endocrine Glands
Hyperinsulinism results in low
blood glucose levels or
Triggers the release of
hyperglycemic hormones like
Causes anxiety, nervousness,
tremors, and weakness
Insufficient glucose in the brain
causes disorientation,
convulsions, unconsciousness
and even death
Treated with ingesting sugar
Endocrine Glands
Produce steroid sex hormones testosterone
and estrogen/progesterone
Regulated by gonadotropins (FSH and LH)
Endocrine Glands
Ovaries (women)
Found in the pelvic cavity of the female
Produce estrogen and progesterone
Maturation of the reproductive organs
Development of the secondary sex
characteristics at puberty
Stimulates uterine lining
Prepare uterus to receive fertilized egg
Acts with estrogen to bring about the
menstrual cycle
Promotes the growth of uterine lining
Endocrine Glands
Temporary endocrine organ
Secretes estrogen, progesterone and human
chorionic gonadotropin (hCG) that influence
the course of the pregnancy
Endocrine Glands
Testes (men)
Paired glands suspended in the scrotum
Produce testosterone
Maturation of the male reproductive organs during puberty
Development of secondary sex characteristics
Stimulates the male sex drive
Needed for normal production of sperm