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

• 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

AnteriorPituitary

PosteriorPituitary

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.

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.