The Endocrine System
Hormones
• Hormones are secretions of the
endocrine system that help
maintain homeostasis on a daily
basis. They regulate smooth
muscle, cardiac muscle, and
some glands. They spur growth
and development influence
reproductive processes and
circadian rhythms.
Endocrine System
• Hormones are secreted into interstitial fluid (the fluid
between cells). It is then diffused into blood capillaries, and
blood carries them throughout the body.
• Glands: pituitary, thyroid, parathyroid, adrenal and pineal
• Organs/tissues that secrete hormones: hypothalamus,
thymus, pancreas, ovaries, testes, kidneys, stomach, liver,
small intestine, skin, heart, adipose tissue, and placenta.
Hormones
• Hormones travel throughout the body in the blood, it affects specific
target cells. The hormones influence their target cells by chemically
binding to specific protein receptors. (think about puzzle pieces fitting
together….target cells can only fit with the correct shaped piece
(receptor).
• Lipid-soluble hormones – are made from cholesterol, diffuse into the
cell (T3 and T4 , steroid hormones)
• Water-soluble hormones – most made from amino acids, bind to
receptors in the cell membrane (epinephrine and norepinephrine,
antidiuretic hormone, oxytocin, insulin, human growth hormone)
Hormones
• Hormone secretion is regulated by
1. Signals from the nervous system
2. Chemical changes in the blood
3. Other hormones
Types of Glands
• Endocrine – secrete hormones directly into bloodstream and are
ductless
• Exocrine – secrete substance through a duct. Examples: sweat,
salivary, pancreas
• Negative feedback system – (reverses a change in a controlled
condition). Drop in hormone level triggers a chain reaction
•
•
•
•
Blood level of hormone falls
Brain gets message and sends out hormone to stimulate gland
Gland secretes more hormone
When blood level of hormone increases, brain hormones stop
Pituitary Gland
• Nicknamed the “Master Gland”…..but it has a master…the
hypothalamus. This is the link between the nervous and
endocrine systems. They are connected by the
infundibulum. Hormones from them play important roles in
the regulation of virtually all aspects of growth,
development, metabolism and homeostasis.
• Size of a small grape
• 2 lobes….anterior and posterior
Anterior Pituitary Gland
• Human Growth Hormone (hGH)- secreted by the anterior
pituitary.
• hGH promotes the secretion of IGF’s (insulinlike growth
factors). They enter the blood stream and stimulate protein
synthesis that: maintain muscle and bone mass, promote
healing of injuries and tissue repair.
• Low blood glucose level (hypoglycemia)stimulates the
hypothalamus to secrete GHRH. This is an example of
negative feedback system.
Anterior Pituitary Gland
• Follicle Stimulating hormone (FSH) and luteinizing hormone
(LH).
• In females FSH initiates the development of several ovarian
follicles LH trigger ovulation
• In males FSH stimulates sperm production in the testes, and
LH stimulates the testes to secrete testosterone.
• MSH causes darkening of the skin…function is
unknown…very little in humans.
Posterior Pituitary
• Posterior pituitary does not synthesize hormones…it stores
2.
• Oxytocin – 2 target tissues. 1) uterus – during delivery it
enhances contraction of smooth muscle cells in the wall of
the uterus 2) mammary glands – it stimulates the milk
ejection from the glands.
Posterior Pituitary
• Antidiuretic hormone (ADH) – decreases urine production.
ADH causes the kidneys to retain water, thus decreasing
urine volume. It also decreases the water lost through
sweating and causes constriction of arterioles…effecting
blood pressure.
• Absence of ADH – urine output increases
Thyroid
• Butterfly shaped
• Located just below the larynx
• Produces T3 ( contains 3 atoms of iodine) and T4 (contains 4 atoms of
iodine).
• Thyroid hormones increase basal metabolic rate (BMR), oxygen
consumption, maintenance of normal body temperature, and blood
cholesterol levels.
• Along with hGH and insulin, thyroid hormones stimulate body
growth, particularly the growth of the nervous and skeletal systems.
Thyroid
• Calcitonin – produced by the thyroid. It can decrease the level of
calcium in the blood by inhibiting the action of osteoclasts.
• Hyperthyroidism – excess secretion of thyroid hormones. Symptoms
include increased heart rate, forceful heart beats, increased blood
pressure and increased nervousness.
• Hypothyroidism – under secretion of thyroid hormones.
Parathyroid
• Embedded in the thyroid gland
• Release the hormone PTH (parathyroid hormone) – major regulator of
levels of calcium, magnesium and phosphate ions in the blood.
• PTH – produces 3 changes in the kidney. 1)slows rate Ca and Mg are
lost from blood into the urine 2) increases loss of phosphate from
blood in urine 3) promotes formation of calcitriol, the active form of
vitamin D.
Pancreas
• It has both endocrine and exocrine functions.
• Endocrine – consists of clusters of cells called Islets of
Langerhans. 2 types of islet cells are created. 1) alpha cells –
create glucagon 2) beta cells – create insulin.
• Glucagon – increases blood glucose level when it falls below
normal
• Insulin – lowers blood glucose level by moving glucose into
cells, especially muscle cells
Adrenal glands
• Are on top of the kidneys
• Adrenal cortex (makes up 85% of the gland) and the adrenal
medulla
• Secretes corticoids (anti-inflammatory hormones),
Androgens, and adrenalin (fight or flight hormone)
Adrenal glands
• Androgens – After puberty in males androgens released by
the adrenal glands are insignificant. In females, they
contribute to their libido, and are converted into estrogen.
After menopause, when ovarian secretions cease, all female
estrogen come from adrenal androgens. Androgens also
stimulate growth of axillary and pubic hair, and contribute to
the growth spurt before puberty.
Adrenal medulla
• Innermost region of the gland.
• 2 main hormones are epinephrine and norepinephrine.
Responsible for the fight or flight response. Increases heart
rate, slows digestive process, increases blood pressure. They
also help the body resist stress.
Ovaries and testes
• Ovaries – produce estrogen and progesterone. They
regulate the menstrual cycle, maintain pregnancy,
prepare mammary glands for lactation, establish
female body shape (hips, breasts).
• Testes – produce testosterone, regulates production
of sperm, maintenance of masculine characteristics
like beard growth and deepening of voice.
Pineal gland
• Pinecone shaped
• Located in the brain
• It secretes melatonin which contributes to setting the
body’s biological clock. More melatonin is released
when it is dark than when it is daylight.
• Levels are higher in children and decline with age.
Stress response
• Any stimulus that produces a stress response is called a stressor. If
stress is extreme, unusual, or long lasting it triggers a stress response.
• Stress response can have 3 stages. 1) fight or flight 2) slower
resistance reaction- helps the body continue fighting after the flight
or flight dissipates. 3)exhaustion – from prolonged resistance
reaction.
• Stress – effects immune system, digestive system, cardiovascular
system, can cause migraine headaches, anxiety and depression.
People under stress at a greater risk of developing a chronic disease
or dying prematurely.
Aging and the endocrine system
• hGH – decreases ….which is one cause of muscle atrophy
• Thyroid – decreases production of hormones causing a decrease in
metabolic rate, increase in body fat, hypothyroidism
• Ovaries decrease in size, estrogen level decreases which leads to
conditions such as osteoporosis, high blood cholesterol and
arterosclerosis.
Common disorders
• Pituitary Gland
• Giantism – over secretion of hGH causing abnormal increase in the
length of long bones.
• Diabetes insipidus – due to defects in antidiuretic hormone ADH. Too
much water is lost in the urine, person can dehydrate very easily.
• Thyroid
• Goiter – thyroid gland enlarges 2 – 3 times normal size
Common disorders
• Adrenal
• Cushings syndrome – hypersecretion of glucocorticoids, breaks down
muscles and redistribution of body fat (skinny arms and legs, round
face and “tummy”)
• Pancreas
• Type 1 diabetes – insulin level is low, usually begins before 20 yrs
• Type 2 diabetes – glucose level is high, after 35 yrs, usually
overweight. Can be controlled with diet, exercise, weight loss. Need
insulin injections.