Endocrine System

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 Functions 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 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 Figure: 10-06 Title: The two lobes of the pituitary gland. Caption: The two lobes of the pituitary gland, their connections with the hypothalamus, and the hormones they secrete.

Pineal Gland Anatomy Function 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 Functions 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 Hormones- thymosins. 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 Hormones and Functions Targets- all tissues. 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 Target- liver, muscles, adipose tissue. 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 Hormone- testosterone. 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 Hormones Estrogens. Progesterone. Targets 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.