All organisms maintain an internal environment to live (homeostasis)
Endocrine system works closely with nervous system to regulate body processes & maintain
homeostasis
Nervous system & endocrine system work together to do this but nervous system is quicker &
response is shorter while endocrine system response is slower but lasts longer
ANATOMY
Types of Glands
Exocrine
Produce secretions transported through ducts to their destination
Function within particular system of body
Ex. Sweat, salivary, mucus
Endocrine
Make up their own system
Secrete hormones directly into blood or surrounding fluids
Heterocrine
Combination of exocrine/endocrine
Ex. Pancreas
Hormones
Regulatory organic chemicals secreted by endocrine glands into blood to be transported to
target cells to regulate functions there
Target cells
Cells with the receptor proteins on cell membranes that receive that specific hormone
Types of Hormones
Protein (peptide) Hormones
Made of amino acids in peptide chains
Majority of hormones are of this type
In hormone therapy they must be injected intravenously, intramuscularly or
subcutaneously since those taken orally would be digested (broken down)
Steroid Hormones
Lipids made from cholesterol
Human body has 20 including the sex hormones (ex. Aldosterone, cortisone, estrogen,
progesterone, testosterone)
In hormone therapy, can be taken orally or intravenously
Amine (biogenic) Hormones
Made of amino acids without peptide chains
Have a ring structure
In hormone therapy, can be administered orally, subcutaneously, intravenously or as
an inhalant
Prostaglandins
Like steroids but not produced by specific glands
Act locally (where they are made) & aren’t secreted into bloodstream
Cause relaxation of smooth muscles, contraction of uterus/intestine and help
regulate blood pressure
Pituitary gland (hypophysis)
Located on bottom of brain in diencephalon, attached to brain by pituitary stalk
Pea shaped, covered by dura mater, supported by sphenoid bone
Divided into
Neurohypophysis (posterior pituitary)
Releases 2 hormones made by hypothalamus
Made of bulb shaped lobus nervosa & funnel shaped infundibulum
Adenohypophysis (anterior pituitary)
Secretes its own hormones
Primary target of the hormones from the hypothalamus
“master gland” since its products often regulate release of other hormones in
body
2 parts in adults: pars distalis is bulb part & pars tuberalis is extension in
contact with infundibulum
Fetus also contains strip of tissue between anterior/posterior lobes called
pars intermedia
Hormones- most secreted by pars distalis, 1 by pars intermedia, 2 from hypothalamus
Growth hormone (GH)- somatotropin
Regulates rate of growth of body cells & promotes mitosis by permitting
amino acids to move through cell membrane
Major targets are bones/skeletal muscles
Thyroid stimulating hormone (TSH)- thyrotropin
Regulates thyroid gland & its secretion of thyroxine
May be influenced by exposure to cold, certain illnesses, emotional stress &
pregnancy
Adrenocorticotropic hormone (ACTH)- corticotrophin
Promotes normal functioning of adrenal cortex & helps cells to breakdown fats
May be influenced by stress
Follicle stimulating hormone (FSH)- one gonadotropin
Males- stimulates testes to make sperm
Females- regulates monthly development of follicle/egg and stimulates
secretion of estrogen
Luteinizing hormones (LH)- another gonadotropin
Males- called interstitial cell stimulating hormone since it stimulates secretion
of testerosterone
Females- helps to bring about ovulation, stimulates formation of corpus luteum
& production of progesterone
Prolactin
Males- may influence sensitivity of cells in testes
Females- assists other hormones in starting milk production, regulates
mammary gland growth
Melanocyte stimulating hormone (MSH)
Exact job unknown & its secretion has little effect on humans
Can cause skin to darken by stimulating dispersion of melanin granules
Usually ceases secretions prior to adulthood
Oxytocin
“cuddle hormone” since it may influence maternal behavior & bonding
Decreases heart rate, modulates stress, social behavior & anxiety
Males- induces smooth muscle contraction causing prostate to release its
part of semen
Females- released near end of gestation; helps to begin labor & stimulate
milk ejection by mammary glands
Antidiuretic hormone (vasopressin)
Inhibits formation of urine by kidneys
Pineal gland
Small cone shaped gland posterior to epithalamus in brain; near 3rd ventricle
Composed of pinealocytes
Larger in children & begins to shrink at age 7
Secretes melatonin
Tied to daily/seasonal changes in light
Secretion increases at night & decreases in day
May affect synthesis of some hypothalamic regulatory hormones
Function isn’t well understood in humans
Stomach
Secretes gastrin & ghrelin
Both produced by stomach lining
Ghrelin sends information to hypothalamus to register hunger & hippocampus to sharpen
learning/memory
Thyroid gland
In neck below larynx, on either side of trachea
Largest endocrine gland, abundant blood supply
Consists of spherical hollow sacs called follicles which are filled with protein rich fluid colloid
Follicles surrounded by parafollicular cells
2 major hormones (thyroxine, triiodothyronine) & 1 minor hormone (calcitonin)
Stimulate protein synthesis, promote nervous system maturation & increase rate of
energy use in body
Calcitonin works to regulate calcium ion levels in blood by inhibiting bone tissue
breakdown & stimulating excretion of calcium ions by kidneys; both actions
lowers calcium ion levels in blood
Major hormones stored in follicles & released as needed; minor hormone is secreted by
parafollicular cells
Secretion of hormones controlled by hypothalamus/pituitary gland
Parathyroid glands
2-6 small flattened glands embedded on surface of thyroid
Small yellowish brown bodies made of 2 types of epithelial cells
Principle cells make parathyroid hormone (parathromone)
Oxyphil cells support the principle cells & their other functions are not known
Parathyroid hormone
Promotes rise in blood calcium ion levels by acting on bones, kidneys & small
intestine
Activates osteoclasts in bone to release calcium
Prevents loss of calcium ions during urine formation
Pancreas
Both endocrine & exocrine functions (heterocrine gland)
Exocrine part is related to digestive system
Endocrine part is made of scattered clusters called islets of Langerhans found in
body & tail of pancreas
Located behind stomach
Cells of islets
Alpha cells secrete glucagon (stimulates liver to convert glycogen to glucose which
makes blood sugar level rise)
Beta cells secrete insulin (decreases level of blood sugar by promoting the movement
of glucose through cell membranes)
Delta cells secrete growth hormone inhibiting hormone
F cells secrete pancreatic polypeptide to regulate delta cell secretions
Thymus gland
2 lobed organ below thyroid on trachea & behind manubrium of sternum
Size is large in newborns & shrinks after puberty
Main job is to help with immunity but does secrete thymosin
Thymosin stimulates T cells after they leave thymus; stimulates/promotes
differentiation, growth & maturation of T cells
Adrenal glands
Pyramid shaped organs that sit on top of kidneys
Two areas function as separate glands
Adrenal cortex- divided into 3 zones (zona glomerulosa, zona fasciculate, zona
reticularis)
Produces over 30 hormones called corticoids
Zona glomerulosa- secretes mineralcorticoids which regulate levels of
extracellular electrolytes
Aldosterone- controls sodium/potassium levels in kidneys
Zona fasciculate- secretes glucocorticoids which influence metabolism of
carbohydrates, proteins & fats; also helps body resist stress
Cortisol- hydrocortisone; anti-inflammatory compound
Zona reticularis- secretes small amounts of androgen sex hormones
Adrenal medulla- composed of tightly packed clusters of chromaffin cells
Produce epinephrine & norepinephrine (both amines)
Increase heart rate, dilate blood vessels, increase mental alertness,
increase respiratory rate & eleveates metabolic rate
Gonads
Primary sex organs that produce sex hormones to control development/function of
reproductive systems
Testes- interstitial cells make/secrete testosterone
Controls development/function of penis, accessory glands, ducts
Promotes secondary sex characteristics & sex drive
Ovaries- produce estrogen & progesterone
Estrogen- made in ovarian follicles, placenta, corpus luteum, adrenal cortex & testes
Needed to develop secondary sex characteristics, controls menstrual changes
in uterus & regulates sex drive
Progesterone- made by corpus luteum
Associated with pregnancy & preventing abortion
Placenta
Secretes large amounts of estrogen, progesterone as well as other hormones such as human
chorionic gonadotropin (hCG) & somatomammotropin
hCG is what pregnancy tests check for & stimulates ovary to make estrogen/progesterone
during pregnancy
PHYSIOLOGY
Hormones work to speed up or slow down metabolism in the target cells that have specific receptor
sites on the cell membrane
How some hormones work
Protein hormones
Act by first attaching itself to a receptor protein on membrane of target cell
Once it is attached, it activates enzymes in membrane which release energy by
making cAMP (cyclic adenosine monosphosphate) which activates other
enzymes inside cell
Steroid hormones
Diffuse through cell membrane & enter cytoplasm
Binds to receptor molecule in cytoplasm which then enters nucleus
Stimulates genes to make more enzymes to promote reactions by making RNA
Endocrine system is controlled by negative feedback mechanism
Negative feedback
Mechanism that maintains a balance between supply/demand between hormone
normal levels & needs of target cells
Gland secretes hormones until message comes back saying there is enough
This way hormones are only secreted when they are needed
Prevents overproduction
End product inhibits the first step
Example: Hormone A stimulates the production of hormone B while B inhibits the
secretion of A as B’s level rises in the blood
Example: Blood sugar (substance A) stimulates the production of insulin (hormone B)
Insulin causes the blood sugar level to drop. Once level of blood sugar drops
far enough, insulin is no longer secreted
Example: similar to furnace & thermostat relationship in house
Some endocrine glands are stimulated by neural impulses from the autonomic NS; ex. Adrenal medulla
Many hormones may be present in the blood at the same time
Steroid hormones travel attached to plasma proteins in blood
Protein hormones travel dissolved in blood plasma
Thyroid gland
Hormones
Thyroxine- concerned with cellular metabolism by regulating metabolic rate & heat
production; stimulates protein synthesis, promotes maturation of nervous
system, increases cellular respiration
Calcitonin- aids in maintaining calcium ion balance in blood; lowers blood calcium ion
levels; inhibits breakdown of bone & stimulates excretion of calcium by kidneys
Disorders
Hypothyroidism
Underactive thyroid in children due to gland defect, lack of TSH or iodine
Twice as common as overactive one
May be caused by radiation therapy, pituitary tumors or certain drugs
Symptoms: fatigue, feeling cold, diminished concentration/memory, weight
gain, dry skin, brittle nails, constipation, photophobia, slow heart rate,
depression
Treatment- hormone replacement therapy
Myxedema
Hypothyroidism in adults
More common in females
Symptoms: lowered metabolic rate, body temperature drops, impaired
physical/mental development, increased weight, swelling of hands,
feet, face, etc, accumulation of fluids/mucoproteins in subcutaneous
tissue
Treatment: thyroxine hormone replacement
Hyerthyroidism
Results from inflammation of thyroid
Symptoms: rapid heartrate, nervousness, irritability, muscle weakness,
softening of nails, hair loss, weight loss, high basal metabolic rate, some
have bulging eyeballs as fluid builds up behind eyes
Treatment- removal of part of thyroid, use of hormone blockers or by use of
injections of radioactive iodine to destroy thyroid cells
Grave’s disease (toxic goiter)
Women are more affected than males
~1 million people in US affected
Auto-antibodies exert TSH-like effect on thyroid so there is a loss of
feedback control
May be hereditary but are not sure
Simple goiter
Develops due to lack of iodine in diet
Can’t produce normal amounts of thyroxine so thyroid enlarges
TSH still stimulates thyroid so it grows
No negative feedback
Can be reversed if treated with iodine
Cretinism
Reduction in metabolic rate due to deficiency of thyroid hormone at end of
1st trimester up until 6 months of age
Thyroxine is needed for proper development of CNS
Can be treated with thyroxine after birth & it will almost completely restore
intelligence
Parathyroid glands
Hormone
Parathormone- regulates calcium/phosphate ion levels in blood; promotes rise in
blood calcium by stimulating breakdown of bone & inhibiting release of calcium
in urine
Disorders
Adenoma (hyperparathyroidism)
Calcium ions are removed from bones
Symptoms: loss in muscle tone/bone strength, increase in kidney stones,
constipation, CNS function slows, memory is impaired, emotional mood
swings, depression
Treatment: surgical removal of gland
Hypoparathyroidism
Rare condition that may develop after neck surgery if blood supply to glands is
reduced or restricted
Symptoms: muscular weakness, formation of dense bones, mild tingling of
muscles or cramping
Treatment: hormone replacement is costly since it can’t be synthesized yet
Adrenal glands
Cortex
Hormone
Aldosterone- regulates water/salt balance in body by stimulating reabsorption
of sodium ions by kidneys; retain sodium & excrete potassium;
increases blood volume/pressure
Disorders
Hypoaldosteronism
Kidneys remove too much water & sodium ions
Blood volume drops & blood pressure falls
Hyperaldosteronism
Kidneys hold sodium ions but lose potassium ions
Blood pressure increases
Cushing’s Syndrome (hypersecretion of glucocorticoids)
Oversecretion of ACTH from pituitary or tumor in adrenal cortex
Symptoms: obesity, high blood pressure, muscle weakness, fat
deposited around cheeks/neck, hump back, extremities become
very thin, osteoporosis, salt retention, excessive hair growth
Treatment: surgical removal of part of cortex
Medulla
Hormones
Epinephrine & norepinephrine (adrenalin & noradrenalin)
Disorder
Addison’s Disease (hyposecretion)
President Kennedy was treated for this
Rare 1 in 100,000 people
Symptoms: low blood sugar, kidney failure, fall in blood pressure,
weakness, loss in weight, can’t tolerate stress, dehydration,
increase in melanin in skin (darkening, bronzing of skin) fatigue,
sodium/potassium ion imbalance
Treatment: oral hormone therapy
Pancreas
Hormones
Insulin- promotes storage/use of fatty acids, glucose & amino acids; made by beta cells
& secreted as blood sugar increases
Glucagon- accelerates conversion of glycogen into glucose; made by alpha cells &
secreted as blood sugar drops
Disorders
Hypoglycemia
Rise in blood glucose follows ingestion of carbohydrates which stimulates
excessive secretion of insulin which causes blood glucose level to fall
below normal range
Symptoms: weakness, changes in personality, mental disorientation
Diabetes mellitus (hypoproduction of insulin)
Due to drop in number of beta cells making insulin or resistance of body to
use insulin that is produced
Glucose is not absorbed by body & accumulates in blood
Incurable & chronic
Affects 16 million American (5.4 million don’t know
they have it)
Risk factors: female, African-American, Latinos, Asian-Americans, Native
Americans; sugary-fatty diet, not exercising, being stressed out, obesity,
stress, sedentary lifestyle
Symptoms: feeling tired/headachy, irritability, extreme hunger/thirst, trembling,
dizziness, fatigue, blurred vision, unusual weight loss, increased level of
sugar in blood/urine, frequent urination, nausea, vomiting, hard to heal
infections, tingling/numbness in hands/feet, dry itchy skin
Complications: retinal blindness, kidney failure, leg amputations, heart
problems, nerve function compromised, coma, death
Type 1 (juvenile diabetes or insulin dependent)
Develops before age 30; 10% of diabetics are this type, genetic but must
be triggered, insulin producing beta cells have been destroyed,
Must take insulin injections for life
Type 2 (adult-onset diabetes or insulin independent)
90% of diabetics are this type Obesity plays a role
Insulin resistance problems in body that interferes with insulin doing its
job; decrease in insulin production or in its effectiveness
Treated with diet, exercise, oral medications, insulin
Pituitary gland
Disorders
Gigantism (hyperproduction of growth hormone)
Occurs before puberty
Accelerates skeletal/organ growth, increases levels of blood sugar, results in
enormous internal organs & large tongue
Acromegaly (hyperproduction of growth hormone)
Occurs after puberty
Lower jaw enlarges, knuckles/hands enlarge, ridges develop over eyes,
internal organs increase in size, develop diabetes, thickening of bones
& growth of soft tissues
President Lincoln had this
Dwarfism (hypoproduction of growth hormone)
Occurs before puberty
Results in miniature person with abnormal fat distribution
Exists at birth due to lack of HGH but not evident until age 1
Treat with injections of HGH
Panhypopituitarism
Reduction of activity of pituitary
Causes other glands to shut down
Simmond’s disease (hyposecretion of growth hormone)
Occurs in adults
Results in premature aging
Hypothalamus
Hormone
Vasopressin- regulates retention of water by kidneys, acts on uterus to bring about birth
Oxytocin- stimulates release of milk by nursing breasts, regulates blood pressure &
stimulates smooth muscle contraction
Disorders
Diabetes insipidus (hypoproduction of vasopressin)
Symptoms: daily outputs of huge amounts of dilute sugarfree urine, dehydration
& thirst
Treatment: hormone replacement therapy
SIADH (hyperproduction of vasopressin)
Symptoms: increased body weight & water content