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Lecture Outline
The Endocrine System
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Endocrine Glands
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Endocrine glands are ductless
Secrete hormones
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Chemical signals that influence:
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Metabolism
Growth and development
Homeostasis
Categories of hormones
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Peptides (proteins, glycoproteins, and
modified amino acids) – most hormones
Steroid hormones
Endocrine Glands
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How Hormones Function
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Second messenger system
Peptide hormone binds to a receptor
protein on the plasma membrane
Peptide hormone (“first messenger”)
activates a “second messenger” (cyclic
AMP and calcium)
Second messenger sets in motion an
enzyme cascade that leads to a cellular
response
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Change in cellular behavior
Formation of an end product that leaves the cell
Endocrine Glands
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Intracellular mechanism of hormone
function
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Steroid hormones (lipids) diffuse across
the plasma membrane
Once inside the cell, steroid hormones
bind to receptor proteins
Hormone-receptor complex binds to DNA,
activating particular genes
Gene activation leads to production of
cellular enzymes that cause cellular
changes
Endocrine Glands
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Hormone Control
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Many hormones affect concentrations
of certain substances in the blood
Other hormones are involved in
normal function of various organs
Release of hormones controlled by
one or more of the following:
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The nervous system
The action of other hormones
Negative feedback mechanisms
Hypothalamus and Pituitary Gland
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Hypothalamus
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Controls secretions of the pituitary
gland
Neurosecretory cells produce
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Antidiuretic hormone (ADH)
Oxytocin
Hypothalamus and Pituitary Gland
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Posterior pituitary
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Stores hypothalamic hormones ADH
and oxytocin
ADH
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Released when neurons in the
hypothalamus detect that the blood is too
concentrated with salt
Causes more water to be reabsorbed into
kidney capillaries
Raises blood pressure by vasoconstriction
of blood vessels
Diabetes insipidus results from the
inability to produce ADH
Hypothalamus and Pituitary Gland
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Oxytocin
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Causes uterine contraction during
childbirth
Causes milk letdown when a baby is
nursing
Release of oxytocin is controlled by
positive feedback
Hypothalamus and Pituitary Gland
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Anterior pituitary
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Controlled by hypothalamic hormones
Hormones that affect other glands
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Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Gonadotropic hormones
Effects of other hormones
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Prolactin (PRL)
Growth hormone (GH)
Hypothalamus and Pituitary Gland
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Effects of growth hormone
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Affects the height of an individual
Pituitary dwarfism results if too little GH
is produced during childhood
If too much GH is produced during
childhood, a person can become a giant
Acromegaly results when too much GH is
secreted in adulthood
Thyroid and Parathyroid
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Thyroid Gland
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Two forms of thyroid hormone
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Triiodothyronine (T3) contains 3 iodine
atoms
Thyroxine (T4) contains 4 iodine atoms
Effects of thyroid hormone
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Increase the metabolic rate
Stimulate all cells of the body
Thyroid and Parathyroid
• Simple goiter
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Caused by a lack of
iodine
Thyroid enlarges in
response to constant
stimulation by the
anterior pituitary
Thyroid and Parathyroid
• Congenital hypothyroidism
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Thyroid fails to develop
properly
Undersecretion of thyroid
hormone
Individuals are short and
stocky
• Myxedema
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Hypothyroidism in adults
Characterized by
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Lethargy
Weight gain
Loss of hair
Slower pulse rate
Lowered body
temperature
Thick and puffy skin
Thyroid and Parathyroid
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Hyperthyroidism (Grave’s Disease)
Oversecretion of thyroid hormone
Exophthalmic goiter forms
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Edema in eye socket tissues
Swelling of the muscles that move the eyes
Symptoms include
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Hyperactivity
Nervousness and irritability
Insomnia
Thyroid and Parathyroid
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Calcitonin
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Helps control blood calcium levels
Secreted when the blood calcium levels
rise
Brings about the deposit of calcium in the
bones
Thyroid and Parathyroid
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Parathyroid Glands
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Posterior surface of the thyroid gland
Produces parathyroid hormone (PTH)
Causes blood phosphate (HPO42-) level to decrease
Causes blood calcium (Ca2+) level to increase
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Promotes the release of calcium from the bones
Promotes the reabsorption of calcium by the kidneys
Activates vitamin D in the kidneys, which
stimulates the reabsorption of calcium from the
intestines
Hypocalcemic tetany results when there is
insufficient secretion of PTH
Adrenal Glands
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Adrenal Medulla
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Inner portion
Under nervous control
Secretes epinephrine (adrenaline) and
norepinephrine (noradrenaline)
Causes “fight or flight” responses
Provide a short-term response to
stress
Adrenal Glands
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Adrenal Cortex
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Outer portion – 3 layers, each
produces a different set of hormones
Under the control of ACTH
Hormones
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Provide a long-term response to stress
Mineralcorticoids
Glucocorticoids
Male and female sex hormones
Adrenal Glands
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Glucocorticoids (cortisol)
Raises the blood glucose level in at least
2 ways:
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Counteracts the inflammatory response and can
relieve swelling and pain
Can also make a person susceptible to injury
and infection
Adrenal Glands
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Mineralcorticoids (aldosterone)
Targets the kidney
Promotes renal absorption of sodium and water
Promotes renal excretion of potassium
ACTH is not the primary controller for aldosterone
secretion
Renin-Angiotensin mechanism stimulates
aldosterone secretion when the blood sodium level
and blood pressure are low
Renin-Angiotensin-Aldosterone system raises
blood pressure in two ways:
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Angiotensin II constricts arterioles
Aldosterone causes the kidneys to reabsorb sodium
Atrial natriuretic hormone (ANH) is antagonistic to
aldosterone
Adrenal Glands
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Malfunction of the Adrenal Cortex
Addison Disease
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Hyposecretion of adrenal cortex hormones
Excessive (but ineffective) ACTH causes
bronzing of the skin
Because glucose cannot be replenished without
cortisol, individuals are susceptible to infection
Lack of aldosterone results in the development
of low blood pressure and possibly severe
dehydration
Cushing Syndrome
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Hypersecretion of adrenal cortex hormones
Tendency towards diabetes mellitus
Excess aldosterone leads to hypertension
Pancreas
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Composed of two types of tissue
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Exocrine – secretes digestive juices
Endocrine tissue (pancreatic islets or
islets of Langerhans) produces:
Insulin
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Secreted when blood glucose level is high
Stimulates the uptake of glucose by most body
cells
Glucagon
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Secreted when blood glucose levels are low
Targets liver and adipose tissue
Stimulates liver to break down glycogen to
glucose
Pancreas
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Diabetes Mellitus
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Insulin-sensitive body cells are unable
to take up and/or metabolize glucose
Blood glucose level is elevated
(hyperglycemia)
Symptoms:
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Polyphagia – extreme hunger
Glycosuria – glucose in the urine
Polyuria – excessive water loss through
urine
Polydipsia – extreme thirst
Pancreas
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Two forms of diabetes mellitus
Type I – insulin-dependent diabetes
mellitus
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Pancreas does not produce insulin
Immune cells destroy the pancreatic islets
Type II – non-insulin-dependent diabetes
mellitus
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Normal or elevated amounts of insulin are
present in the blood
Receptors on the cells do not respond to insulin
Other Endocrine Glands
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Testes and ovaries
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Testes produce androgens
(testosterone)
Ovaries produce estrogens and
progesterone
Secretion is controlled by the
hypothalamus and the pituitary
Other Endocrine Glands
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Androgens
Increased testosterone secretion during
puberty stimulates the growth of the
penis and the testes
Brings about and maintains the male
secondary sex characteristics
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Facial, axillary, and pubic hair
Enlargement of larynx and the vocal cords
Muscular strength
Stimulates oil and sweat glands of the
skin
Other Endocrine Glands
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Estrogen and Progesterone
Required for breast development
Regulation of the uterine cycle
Estrogens
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Stimulate the growth of the uterus and the
vagina during puberty
Necessary for egg maturation
Responsible for secondary sex characteristics
Female body hair
Fat distribution
Other Endocrine Glands
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Thymus Gland
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Most active during childhood
Transforms lymphocytes into thymusderived lymphocytes (T-lymphocytes)
Epithelial cells secrete hormones
called thymosins
Pineal Gland
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Located in the brain
Produces the hormone melatonin
Melatonin is involved in daily sleepwake cycle
Other Endocrine Glands
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Hormones from Other Tissues
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Leptin
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Produced by adipose tissue
Signals satiety in hypothalamus
Growth Factors – stimulate cell
division and mitosis
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Granulocyte and macrophage colonystimulating factor
Platelet-derived growth factor
Epidermal growth factor and nerve
growth factor
Tumor angiogenesis factor
Other Endocrine Glands
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Prostaglandins
Potent chemical signals
Act locally
Some effects of prostaglandins include:
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Uterine contractions
Mediate the effects of pyrogens
Reduce gastric secretion
Lower blood pressure
Inhibit platelet aggregation
The Importance of Chemical Signals
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Cells and organs communicate
with one another using chemical
signals
Chemical signals between
individuals
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Called pheromones
Humans produce airborne chemicals
from a variety of areas
Effects of Aging
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Thyroid disorders
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Hypothyroidism
Hyperthyroidism
Diabetes
Homeostasis
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The endocrine system and the
nervous system work together to
maintain homeostasis
The endocrine system helps
regulate the following:
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Digestion
Fuel metabolism
Blood pressure and volume
Calcium balance
Response to the external environment