Endocrine System
LEARNING OBJECTIVES:
1. List the functions of hormones.
2. Classify hormones into their major chemical categories.
3. Describe how the hypothalamus of the brain controls the
endocrine system.
4. Name the endocrine glands and state where they are located.
5. Describe the functional relationship between the hypothalamus
and the pituitary gland
6. List the major hormones and their effects on the body.
7. Indicate the endocrine role of the kidneys, the stomach and
intestine, the heart, and the placenta
8. Discuss some of the major diseases of the endocrine system
and their causes.
Endocrine glands, also
called ductless glands,
produce hormones
The Endocrine System
• Second controlling system of the body
• Uses chemical messages (hormones)
that are released into the blood
• Hormones control several major
processes
• Reproduction
• Growth and development
• Mobilization of body defenses
• Maintenance of much of homeostasis
• Regulation of metabolism
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Hormone Overview
• Hormones are produced by specialized
cells
• Cells secrete hormones into extracellular
fluids
• Blood transfers hormones to target sites
• These hormones regulate the activity of
other cells
• Endocrinology is the scientific study of
hormones and endocrine organs
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Mechanisms of Hormone Action
• Hormones affect only certain tissues or
organs (target cells or organs)
• Target cells must have specific protein
receptors
• Hormone binding influences the working
of the cells
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The Chemistry of Hormones
• Amino acid-based hormones
• Proteins
• Peptides
• Amines
• Steroids – made from cholesterol
• Prostaglandins – made from highly
active lipids
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Control of Hormone Release
• Hormone levels in the blood are
maintained by negative feedback
• A stimulus or low hormone levels in the
blood triggers the release of more
hormone
• Hormone release stops once an
appropriate level in the blood is reached
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Hormonal Stimuli of Endocrine Glands
• Endocrine glands
are activated by
other hormones
HORMONAL
Figure 9.2a
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Humoral Stimuli of Endocrine Glands
• Changing blood
levels of certain
ions stimulate
hormone release
HUMORAL
Figure 9.2b
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Humoral Stimuli of Endocrine Glands
• Sympathetic nervous
system stimulation of
the adrenal medulla to
release
catecholamines
(norepinephrine and
epinephrine) during
periods of stress
NEURAL
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Location of Major Endrocrine Organs
Figure 9.3
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Hypothalamus
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Pituitary Gland
• Size of a grape
• Hangs by a stalk from the
hypothalamus
• Protected by the sphenoid
bone
• Has two functional lobes
• Anterior pituitary – glandular
tissue
• Posterior pituitary – nervous
tissue
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Hormones of the Anterior Pituitary
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Growth Hormone (GH)
• General metabolic hormone
• Major effects are directed to growth of
skeletal muscles and long bones
• Causes amino acids to be built into
proteins
• Causes fats to be broken down for a
source of energy
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Functions of Other Anterior Pituitary
Hormones
• Prolactin (PRL)
• Stimulates and maintains milk production
following childbirth
• Function in males is unknown
• Adrenocorticotropic hormone (ACTH)
• Regulates endocrine activity of the adrenal
cortex
• Thyroid-stimulating hormone (TSH)
• Influences growth and activity of the thyroid
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Functions of Other Anterior Pituitary
Hormones
• Gonadotropic hormones
• Regulate hormonal activity of the gonads
• Follicle-stimulating hormone (FSH)
• Stimulates follicle development in
ovaries
• Stimulates sperm development in
testes
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Functions of Other Anterior Pituitary
Hormones
• Gonadotropic hormones (continued)
• Luteinizing hormone (LH)
• Triggers ovulation
• Causes ruptured follicle to become the
corpus luteum
• Stimulates testosterone production in
males
• Referred to as interstitial cell-stimulating
hormone (ICSH)
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POSTERIOR PITUITARY GLAND
Hormones of the Posterior Pituitary
• Oxytocin
• Stimulates contractions of the uterus during
labor
• Causes milk ejection
• Antidiuretic hormone (ADH)
• Can inhibit urine production
• In large amounts, causes vasoconstriction
leading to increased blood pressure
(vasopressin)
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Hormones of the Posterior Pituitary
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Thyroid Gland
• Found at the base of the throat
• Consists of two lobes and a connecting
isthmus
• Produces two hormones
• Thyroid hormone
• Calcitonin
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Thyroid Gland
Figure 9.6
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Thyroid Hormone
• Major metabolic hormone
• Composed of two active iodine-
containing hormones
• Thyroxine (T4) – secreted by thyroid
follicles
• Triiodothyronine (T3) – conversion of T4 at
target tissues
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 9.24
Calcitonin
• Decreases blood
calcium levels by
causing its
deposition on bone
• Antagonistic to
parathyroid
hormone
• Produced by C
(parafollicular)
cells
Figure 9.9
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Parathyroid Glands
• Tiny masses on the posterior of the
thyroid
• Secrete parathyroid hormone
• Stimulate osterclasts to remove calcium
from bone
• Stimulate the kidneys and intestine to
absorb more calcium
• Raise calcium levels in the blood
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Congenital Hyperthyroidism
Congenital hypothyroidism
can be caused by a variety
of factors, only some of
which are genetic. The most
common cause worldwide
is a shortage of iodine in
the diet of the mother and
the affected infant. Iodine
is essential for the
production of thyroid
hormones.
Congenital Hyperthyroidism
Hypothyroidism is a
common condition
where the thyroid
doesn't create and
release enough thyroid
hormone into your
bloodstream.
Hyperthyroidism
(overactive
thyroid) occurs when
your thyroid gland
produces too much
of the hormone
thyroxine.
Hyperthyroidism can
accelerate your body's
metabolism, causing
unintentional weight
loss and a rapid or
irregular heartbeat.
Adrenal Glands
• Two glands
• Cortex – outer glandular region in three
layers
• Medulla – inner neural tissue region
• Sits on top of the kidneys
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Hormones of the Adrenal Cortex
• Mineralocorticoids (mainly aldosterone)
• Produced in outer adrenal cortex
• Regulate mineral content in blood, water,
and electrolyte balance
• Target organ is the kidney
• Production stimulated by renin and
aldosterone
• Production inhibited by atrial natriuretic
peptide
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Hormones of the Adrenal Cortex
Figure 9.10
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Hormones of the Adrenal Cortex
• Glucocorticoids (including cortisone and
cortisol)
• Produced in the middle layer of the adrenal
cortex
• Promote normal cell metabolism
• Help resist long-term stressors
• Released in response to increased blood
levels of ACTH
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Hormones of the Adrenal Cortex
• Sex hormones
• Produced in the inner layer of the adrenal
cortex
• Androgens (male) and some estrogen
(female)
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Hormones of the Adrenal Medulla
• Produces two similar hormones
(catecholamines)
• Epinephrine
• Norepinephrine
• These hormones prepare the body to
deal with short-term stress
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Pancreatic Islets
• The pancreas is a mixed gland
• The islets of the pancreas produce
hormones
• Insulin – allows glucose to cross plasma
membranes into cells from beta cells
• Glucagon – allows glucose to enter the
blood from alpha cells
• These hormones are antagonists that
maintain blood sugar homeostasis
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Pancreatic Islets
Figure 9.13
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Pineal Gland
• Found on the third ventricle of the brain
• Secretes melatonin
• Helps establish the body’s wake and sleep
cycles
• May have other as-yet-unsubstantiated
functions
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Thymus
• Located posterior to the sternum
• Largest in infants and children
• Produces thymosin
• Matures some types of white blood cells
• Important in developing the immune system
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Hormones of the Ovaries
• Estrogens
• Produced by Graafian follicles or the placenta
• Stimulates the development of secondary
female characteristics
• Matures female reproductive organs
• Helps prepare the uterus to receive a fertilized
egg
• Helps maintain pregnancy
• Prepares the breasts to produce milk
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Hormones of the Ovaries
• Progesterone
• Produced by the corpus luteum
• Acts with estrogen to bring about the
menstrual cycle
• Helps in the implantation of an embryo in
the uterus
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Hormones of the 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
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Other Hormone-Producing Tissues and
Organs
• Parts of the small intestine
• Parts of the stomach
• Kidneys
• Heart
• Many other areas have scattered
endocrine cells
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Endocrine Function of the Placenta
• Produces hormones that maintain the
pregnancy
• Some hormones play a part in the
delivery of the baby
• Produces HCG in addition to estrogen,
progesterone, and other hormones
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Developmental Aspects of the Endocrine
System
• Most endocrine organs operate smoothly
until old age
• Menopause is brought about by lack of
efficiency of the ovaries
• Problems associated with reduced estrogen
are common
• Growth hormone production declines with age
• Many endocrine glands decrease output with
age
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