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The Endocrine System
A. Overview
• Second messenger system of the body (first is
nervous)
• Uses chemical messages (hormones) that are
released into blood
• Hormones control several major processes
– Reproduction
– Growth and development
– Mobilization of body defenses against stress
– Maintenance of much of homeostasis
– Regulation of metabolism
B. Hormones
• Produced by specialized
cells in glands
• Cells secrete hormones
into extracellular fluids
• Blood transfers hormones to target sites or
effectors
• Hormones regulate activity of other cells in
effector
• Three chemical classifications of
hormones
–Amino acid-based hormones
• Proteins
• Peptides
• Amines
–Steroids – made from cholesterol
–Prostaglandins – made from highly
active lipids
C. Hormones in Action
• Affect only target tissues/organs via receptors
– (that’s why heart muscle won’t produce
sperm – no receptors for that action)
• Once hormone binds to receptor, alters
cellular activity
– Increases or decreases normal metabolic
process
• Binding of receptor causes up to four
changes
– Changes in plasma membrane permeability
or electrical state (chemicals in/out)
– Synthesis of proteins, such as enzymes
(digestion)
– Activation or inactivation of enzymes
– Stimulation of mitosis (growth)
• If steroid hormone:
– Hormones diffuse through the plasma
membrane of target cells (steroids are lipidbased)
– Enters the nucleus
– Bind to a specific protein within the nucleus
– Hormone-protein complex binds to specific
sites on the cell’s DNA
– Activate genes that result in transcription &
translation to synthesize new proteins
Steroid Hormone Action
Figure 9.1a
• If non-steroid hormone (amino-acid or
prostaglandins) …
– Hormone binds to a membrane receptor (can’t
pass through membrane itself)
– Hormone does not enter the cell
– Sets off a series of reactions that activates an
enzyme
– Catalyzes a reaction that produces a second
messenger molecule (either cAMP, Ca2+, or protein)
– Messenger molecule oversees additional
intracellular changes to promote a specific
response
Non-steroid Hormone Action
Figure 9.1b
D. Control of Hormone Release
• Most hormone levels in blood are maintained
by negative feedback
• External (5 senses) or internal stimulus or low
hormone levels in blood triggers release of
more hormone
• Hormone release stops once appropriate
level in blood is reached
– Three stimuli types:
1. Hormonal Stimuli
• Endocrine glands are
activated by other
hormones
Figure 9.2a
2. Humoral Stimuli
• Changing blood levels
of certain ions or
nutrients stimulate
hormone release
– Blood chemistry
Figure 9.2b
3. Neural Stimuli
• Nerve impulses
stimulate hormone
release
• Most are under control
of the sympathetic
nervous system –
“flight or fight”
Figure 9.2c
E. Major Endocrine Organs
Figure 9.3
1. Pituitary Gland
• Size of a grape
• Hangs by a stalk from the
hypothalamus
• Protected by the sphenoid bone area called
“Turk’s saddle”
• Has two functional lobes
– Anterior pituitary – glandular tissue
– Posterior pituitary – nervous tissue
• Six anterior pituitary hormones
– Two affect non-endocrine targets
• Growth hormone (GH) – overall growth (synthesizing
protein), breaks down fats
• Prolactin – stimulates breast milk production (lactation)
– Four stimulate other endocrine glands (tropic hormones)
• Thyroid stimulating hormone (TSH)- thyroid gland
• Adrenocorticotropic hormone (ACTH) - cortex of adrenal
gland
• Follicle stimulating hormone (FSH) – follicles in ovaries
and sperm in testes
• (women) Luteinizing hormone (LH) – ovulation of egg
• (men) Interstitial cell-stimulating hormone (ICSH) –
testosterone production in testes
• Characteristics of all anterior pituitary hormones
– Proteins (or peptides)
– Act through second-messenger systems
– Regulated by hormonal stimuli, mostly negative
feedback
• Posterior pituitary is not strictly an endocrine
gland so it doesn’t MAKE hormones
• Posterior pituitary releases two hormones
made by hypothalamus:
– Oxytocin
• Stimulates contractions of uterus during labor
• Causes milk ejection triggered by suckling
– Antidiuretic hormone (ADH)
• inhibits urine production
• In large amounts, causes vasoconstriction
leading to increased blood pressure (as a result
sometimes called vasopressin)
Hormones of the Posterior Pituitary
Figure 9.5
2. Hypothalamus
• produces the two
hormones that are
transported to
neurosecretory cells of
the posterior pituitary
(ADH & oxytocin)
3. Thyroid Gland
• Found at base of throat
• Consists of two lobes and a
connecting isthmus
• Produces two hormones:
– Thyroid hormone (TH) Combines with iodine at thyroid
gland to produce thyroxine.
• Thyroxine (T4) – TH + 4I
controls rate of body’s
metabolism
+I
• Triiodothyronine (T3) – TH +
3I conversion of T4 at target
tissues
– Calcitonin - Decreases blood calcium levels by causing it to be
deposited on bone
Thyroxine Control
4. Parathyroid Glands
• Tiny masses on posterior
of thyroid
• Secrete parathyroid
hormone or
parathormone (PTH)
– Stimulate osteoclasts to
remove calcium from bone
when levels in blood are
too low
– Stimulate kidneys & intestine to absorb more calcium
– Raise calcium levels in the blood (opposite calcitonin)
Calcitonin vs PTH
Figure 9.9
5. Adrenal Glands
• Two glands that sit on top of
kidneys
• Divided into two areas:
– Cortex – outer glandular
region in three layers
– Medulla – inner neural tissue
region
• Cortex produces three major groups of steroid
hormones collectively called corticosteroids
• Produce over 50 different hormones themselves
• CORTICOSTEROIDS:
– Mineralocorticoids (mainly aldosterone)
• Produced in outer adrenal cortex
• Regulate mineral content in blood, water, and electrolyte
balance (target organ is kidney)
• Production stimulated by renin (produced in kidneys) and
aldosterone
• Production inhibited by atrial natriuretic peptide (produced by
heart)
– Glucocorticoids (including cortisone and cortisol)
•
•
•
•
Produced in middle layer of adrenal cortex
Promote normal cell metabolism
Help resist long-term stressors (work, family, health stress)
Released in response to increased blood levels of ACTH
– Sex hormones
• Produced in inner layer of adrenal cortex
• Androgens (male) and some estrogen (female)
Hormones of the Adrenal Cortex
Figure 9.10
• Two hormones produced by medulla called
catecholamines which are triggered by
sympathetic nervous system
– Epinephrine (adrenaline)
– Norepinephrine (noradrenaline)
• prepare the body to deal with short-term
stress as in fight-or-flight scenarios
Adrenal Glands in Stress Response
Figure 9.12
6. Pancreas (Pancreatic Islets)
• pancreas is a mixed gland
• Islets of Langerhans in pancreas produce
hormones
– Insulin (from beta cells) – allows glucose to cross
plasma membranes into cells
• Blood glucose now delivered to cells for energy
– Glucagon (from alpha cells) – allows glucose to
enter blood
• Converts stored glucose (glycogen) back into glucose
– these hormones are antagonists that maintain
blood sugar homeostasis
Pancreatic Islets
Figure 9.13
Blood Sugar Hormones
Figure 9.14
Glucose ($)
blood
Glycogen ($100)
liver
Fats/protein (£)
7. Pineal Gland
• Found on third
ventricle of brain
• Secretes melatonin
– Helps establish body’s
wake/sleep cycles
– May have other asyet-unsubstantiated
functions
8. Thymus
• Located posterior to
sternum
• Largest in infants and
children
• Produces thymosin that
– Matures & activates
lymphocytes (WBC) in infants
& children (other organs
produce WBC during
adulthood) in immune
system
9. Ovaries
• Produce estrogens
– Produced by Graafian follicles
in ovaries or placenta
– Stimulates development of
secondary female
characteristics
– Matures female reproductive
organs
– Helps prepare uterus to receive
a fertilized egg
– Helps maintain pregnancy
– Prepares breasts to produce
milk
• Also produce progesterone
– Produced by corpus luteum
– Acts with estrogen to bring about menstrual cycle
– Helps in implantation of an embryo in uterus
10.Testes
• Interstitial cells of testes are
hormone-producing
• Produce several androgens
• Testosterone is the most
important androgen
– Responsible for adult male
secondary sex characteristics
– Promotes growth and
maturation of male
reproductive system
– Required for sperm cell
production
11.Placenta
• Produces hormones that
maintain pregnancy
• Some hormones play a
part in baby delivery
• Produces human chorionic
gonadotropin (hCG) in
addition to estrogen,
progesterone, and other
hormones
• Home pregnancy tests
check for presence of hCG
12.Others
• Duodenum (first part) of small intestine
– Gastrin – delivered to stomach to inhibit HCl
– Secretin – stimulates pancreas to release high pH
juice; stimulates release of bile from liver
– Cholecystokinin (CCK) – stimulates pancreas to
release enzymes; gallbladder to release stored bile
• Stomach
– Gastrin – stimulates stomach glands to release HCl
• Adipose tissue
– Leptin – stimulates brain to suppress appetite &
increase energy usage
• Complete hormone table as shown below.
There are 35 hormones in your notes – yes,
really.
Hormone
Producing Agent
Growth hormone (GH) Anterior pituitary
Function
Overall growth; synthesize proteins;
breakdown fats
Gastrin
Duodenum &
stomach
Control HCl production in stomach
Thyroxine (T4)
Thyroid
Type of iodine-containing thyroid
hormone secreted by thyroid follicles
F. Diseases/Disorders
• Long-term imbalance of particular
hormones leads to diseases or disorders
of endocrine system
–Acromegaly (gigantism)
–Goiter
–Addison’s disease
–Diabetes mellitus (Type I & Type II)
–Sterility (male & female)
–PCOS
Acromegaly
Sandy Allen
7’7 ¼”
• Hypersecretion (excess) of
pituitary growth hormone (GH)
even after long bones have
grown results in acromegaly or
gigantism.
– Facial bones, hands and feet
enlarge tremendously
– Height can reach between 8 – 9
feet!
– Results from tumor on pituitary
gland that secretes GH too.
Goiter
• Enlargement of thyroid gland as a result of
deficiency of iodine
– Iodine is needed to make thyroxine
– When TSH stimulates thyroxine production, it’s
produced, but it’s disfunctional
– TSH continues to stimulate thryoid, so in turn, it
grows to meet demands (although demands are
never met)
• Iodine only found naturally in seafood, so USA
added iodine to salt
– Other land-locked areas continue to produce
goiters
Addison’s Disease
• Hyposecretion (deficiency) of all
adrenal hormones results in
Addison’s disease, and a bronzing of
skin is the effect (melanocytestimulating hormone overactive).
– Low aldosterone leads to water &
electrolyte loss
– Low glucocorticoids leads to
hypoglycemia (too little glucose in
blood), and suppression of immune
system
• No glucocorticoids would mean
death
Diabetes Mellitus
• Hyperglycemia or excess glucose (sugar) in
blood
– Literally from Latin “something sweet is being
siphoned from body”
• Normal fasting blood glucose 80 – 120 mg/100
mL blood
– Diabetes is higher than 126 mg (121-125 is
borderline)
– Autoimmune disorder where beta cells are
attacked, so pancreas does not produce insulin
(Type I) or cells’ receptors don’t recognize it (Type
II)
• No glucose means no fast energy
– Body must then break down proteins or fats for
energy, blood becomes acidic
• Acidosis or ketosis results which can lead to coma or
death
• Three main signs of diabetes:
– Polyuria = excessive urination to rid body of
glucose/ketones
– Polydipsia = excess thirst from lack of water
– Polyphagia = hunger since cells don’t receive
glucose energy
“Juvenile Diabetes”
No insulin produced
“Adult-Onset Diabetes”
Insulin produced, receptors weaker
• Long-term effects of uncontrolled diabetes (I
or II):
– Cardiovascular disease
• Excess glucose in blood makes it more viscous, causes
heart to beat faster (hypertension/high blood
pressure), circulate slower leading to tissue damage
(possible gangrene), eventually heart attack
– Chronic renal (kidney) failure
• Kidneys have to filter so much glucose, eventually shut
down from overwork
– Blindness (retinal damage)
• Blood vessels in retina get damaged & retina can’t
process image
Sterility
• Hormonal imbalances (too much or too little)
leads to sterility in both males and females
– Males
• Less FSH – little/no sperm production
• Less LH – less testosterone
• Less testosterone – little/no sperm production
– Females
•
•
•
•
Excess prolactin – no ovulation
Less FSH and/or LH – no ovulation
Less estrogen – less FSH/LH – no ovulation
Less progesterone - miscarriage
Polycystic Ovary Syndrome (PCOS)
• PCOS occurs when ovaries grow
many small cysts causing a chain
reaction of hormone imbalance
• Cysts make excess male
androgens which then leads to
hormone imbalance.
• Inhibits further growth and
release of mature eggs.
• First noticed in teen years affecting 1
out of 15 women
• There is a high genetic component.
PCOS
• Symptoms of PCOS
• No ovulation
• Irregular periods (too little, too much)
• Weight gain
• Excess acne
• Facial & body hair
• Thinning hair
• Results in
• Infertility
• Insulin resistance (leading to diabetes II)
• Depression
• High cholesterol
• Heart disease
G. Development
• In utero
– Up to 11 weeks pregnant, both males &
female fetuses have same genital makeup
– At 12 weeks, Y chromosome triggers
testosterone to form male genitals;
absence of Y chromosome triggers
estrogen to form female genitals
– If hormone levels are off, can result in
intersex (formerly hermaphrodite)
Embryo at 11 weeks
individual
• Chromosomes show male or female
but genitalia something in between
• 46 XY Intersex
– Male chromosomes, external
genitals incomplete or female-like
• 46 XX Intersex
– Female chromosomes, ovaries,
male-like external genitalia
• Gonadal Intersex
– Both ovarian and testicular tissue
– May be either XY or XX
• Complex/Undetermined Intersex
– XO, XXX, XXY, XYY
• Puberty
– Increase in hormone production by ovaries or
testes to initiate secondary sex characteristics
and be able to reproduce
– Girls: begins at 10-11 and complete by 15-17
– Boys: begins at 12-13 and complete by 16-18
• Adulthood
– Most endocrine organs operate smoothly until old
age
• Late Adulthood
– Menopause in women is brought about by lack of
efficiency of the ovaries
• Problems associated with reduced estrogen are
common (hot flashes, insomnia, moodiness)
– Growth hormone production declines with age
– Many endocrine glands decrease output with age
including testes