Endocrine System
Chapter 10
Endocrine Glands
• Endocrine glands are
ductless glands and
tissues that secrete
hormones directly into
the bloodstream.
• Hormone
– Hormon- gr. to excite.
– Chemical messengers.
– Released in small
amounts.
– Affect target cells.
General Functions of Hormones
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Growth and development
Reproduction
Metabolism
Biological clock
Contraction of cardiac and smooth muscle
Glandular secretion
Feedback mechanisms regulate
the secretion of hormones
• Negative feedback- the outcome of a
process feeds back on the system,
shutting down the process.
• Antagonistic feedback- one hormone has
an opposite effect of another hormone on
the system.
• Positive feedback- the outcome of a
process feeds back on the system, further
stimulating the process.
Negative Feedback
Antagonistic Feedback
Positive Feedback
“I’m good enough, I’m smart enough, and
doggone it, people like me!”
Positive Feedback- Oxytocin (OCT)
• Sucking by the infant stimulates
nerve receptors in the nipple.
• The resulting impulses travel
along nerves to the
hypothalamus.
• The hypothalamus signals the
posterior pituitary to release
OCT.
• OCT travels via the
bloodstream to the mammary
glands.
• Milk is ejected from the
mammary glands.
Hypothalamus
• Anatomy
– Part of the diencephalon,
inferior to the thalamus.
• Functions
– Regulates the internal
environment through the
autonomic nervous system.
– Controls glandular
secretions of the pituitary
gland.
Pituitary Gland- anatomy
• Anatomy
– Pea-shaped
structure.
– ½ inch in diameter.
– Lies in the sella
turcica of the
sphenoid bone.
– 2 anatomically and
functionally
different portions.
Posterior
Anterior
Posterior
Pituitary
Anterior
Pituitary
Pineal Gland
• Anatomy
– Pine cone shape.
– In the epithalamus.
– Covered by a capsule
made of pia mater.
• Function
– Secretes melatonin
that targets the brain;
involved in regulating
daily sleep-wake cycle.
Thyroid Gland
• Anatomy
– Inferior to the larynx.
– 2 lobes, shield-shaped and
deep red in color.
– Isthmus connects the lobes.
– 30g in weight (=1 oz.).
• Functions
– Increases metabolic rate.
– Regulate growth and
development.
Isthmus
The Thyroid Gland Secretes
Thyroid Hormone (TH)
• Hypothyroidism- undersecretion
of the thyroid hormone.
– Fetus or infant- cretinism.
• Dwarfism and mental retardation.
– Adult- myxedema.
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Weight gain.
Lethargy.
Loss of hair.
Lowered body temperature.
• Hyperthyroidism- oversecretion
of thyroid hormone.
– Adult- Graves’ disease
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Increased metabolic rate.
Enlargement of the thyroid gland.
Rapid heart rate.
High blood pressure.
Exophthalmos.
– Treatment for Graves’
disease
• Surgery.
• Ingestion of radioactive
iodine.
Parathyroid Glands
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Anatomy- 4 small masses at the back of the thyroid gland.
Hormones- parathyroid hormones.
Target- bones, kidneys, intestines.
Hormone Functions
– Increase blood calcium level.
– Antagonistic action between calcitonin and parathyroid hormone
maintains blood calcium levels.
Thymus Gland
• Anatomy
– Upper mediastinum.
– Large in infants (70 g),
atrophied in adult (3 g).
– 2 lobed organ.
• Hormones- thymosins.
• Target- T lymphocytes
(white blood cells).
• Hormone Functions
– Promote production and
maturation of T
lymphocytes.
Adrenal Glands
• Anatomy
– Almond-shaped, located at the tops
of the kidneys.
– Consists of adrenal medulla and
adrenal cortex.
• Hormones and Functions
– Adrenal Medulla
• Epinephrine- adrenaline. Fight or flight.
• Norepinephrine- noradrenaline. “ “
– Adrenal Cortex
• Sex Hormones. Development.
• Mineralocorticoids. Salt & water balance.
• Glucocorticoids. Regulate glucose levels.
• Targets- all tissues.
Pancreas
• Anatomy
– 5-6 inches long, 1 inch thick.
– Attached to the duodenum,
posterior to the stomach.
– Two tissue types.
• Exocrine tissue- produce and
secrete digestive juices.
• Endocrine tissue- produce and
secrete insulin and glucagon
directly into the blood.
• Target- liver, muscles,
adipose tissue.
• Hormones and Functions
– Insulin- lowers blood sugar.
– Glucagon- increases blood
sugar.
Testes
• Anatomy
– Scrotum of male.
– 2 oval glands.
– 2 inches long, 1 inch in
width.
• Hormone- testosterone.
• Target- gonads, skin,
muscles, bones.
• Hormone Function
– Stimulate male sex
characteristics.
Ovaries
• Anatomy
– Abdomen of female
– 5 cm X 2.5 cm (2 X 1 inch).
• Hormones
– Estrogens.
– Progesterone.
• Targets
– Gonads, skin, muscles,
bones.
• Hormone Function
– Stimulate female sex
characteristics.