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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
• Hormone levels in blood are maintained by negative
feedback
• External or internal stimulus or low hormone levels
in blood triggers release of more hormone
– Stimuli types:
• Hormonal – hormones trigger endocrine glands
• Humoral (blood chemistry) – levels of ions &
nutrients
• Neural – nerve fibers trigger release (“flight or
fight”)
• Hormone release stops once appropriate level in
blood is reached
Hormonal Stimuli
• Endocrine glands are
activated by other
hormones
Figure 9.2a
Humoral Stimuli
• Changing blood levels
of certain ions
stimulate hormone
release
Figure 9.2b
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) - two
active iodine-containing
hormones
• Thyroxine (T4) – secreted by
thyroid follicles
• Triiodothyronine (T3) –
conversion of T4 at target
tissues
– Calcitonin - Decreases blood calcium levels by causing it to be
deposited on bone
4. Parathyroid Glands
• Tiny masses on posterior
of thyroid
• Secrete parathyroid
hormone (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
• 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 and aldosterone
• Production inhibited by atrial natriuretic peptide
– 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 pancreas produce hormones
– Insulin – allows glucose to cross plasma
membranes into cells from beta cells
• Blood glucose delivered to cells for energy
– Glucagon – allows glucose to enter blood from
alpha cells
• 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 (€)
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
– Matures some types of
white blood cells
– Important in developing the
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
Hormone
Producing
Agent
Function
Growth h. (GH)
Ant. Pituitary
Overall growth; synthesize proteins;
breakdown fats
Prolactin
Ant. Pituitary
Stimulates lactation
Thyroid stimulating h. (TSH)
Ant. Pituitary
Adrenocorticotropic h. (ACTH)
Ant. Pituitary
Follicle stimulating h. (FSH)
Ant. Pituitary
Luteinizing h. (LH)
Ant. Pituitary
Interstitial cell-stimulating h.
(ICSH)
Ant. Pituitary
Oxytocin (released by post.
pituitary)
Hypothalamus
Antidiuretic h. (ADH) (released
by post. pituitary)
Hypothalamus
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)
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 blood glucose 80 – 120 mg/100 mL
blood
– Diabetes is higher than 126 mg (121-125 is
borderline)
– 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 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
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