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
• 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.
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
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. • Weight gain.• Lethargy. • Loss of hair.• Lowered body temperature.
• Hyperthyroidism- oversecretion of thyroid hormone. – Adult- Graves’ disease
• 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• 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.