Chapter 14 Endocrine System

Outline Endocrine Glands Hypothalamus and Pituitary Posterior vs. Anterior Thyroid Gland Parathyroid Glands Adrenal Glands Pancreas Other Endocrine Glands Homeostasis

Endocrine Glands Endocrine glands are ductless glands and tissues that secrete hormones directly into the bloodstream. Hormone secretion by an endocrine gland is often controlled by negative feedback. Actions of a hormone can also be controlled by the presence of an antagonistic hormone.

Endocrine System

Hypothalamus and Pituitary Gland Hypothalamus regulates the internal environment through the autonomic system. Also controls glandular secretions of the pituitary gland.

Posterior Pituitary Posterior pituitary releases two hormones produced by the hypothalamus. Antidiuretic hormone (ADH). Causes water to be reabsorbed into kidney capillaries. Negative feedback control. Oxytocin. Causes uterine contraction during childbirth and milk letdown. Positive feedback control.

Anterior Pituitary Hypothalamus controls the anterior pituitary by producing hypothalamic-releasing and -inhibiting hormones. Anterior pituitary also produces: Thyroid Stimulating Hormone (TSH). Adrenocorticotropic Hormone (ACTH). Gonadotropic Hormones (FSH and LH). Prolactin (PRL). Growth Hormone (GH).

Effects of Growth Hormone Growth hormone is produced in greater quantities during childhood and adolescence. Too little GH produced during childhood may lead to pituitary dwarfism. Too much GH produced during childhood may lead to giantism. Too much GH produced as an adult may lead to acromegaly.

Thyroid Gland The thyroid gland actively acquires iodine to produce triiodothyronine and thyroxine. A diet lacking iodine cannot produce thyroid hormones, and the thyroid may enlarge resulting in a simple goiter. Cretinism may result if the thyroid fails to develop properly.

Thyroid Gland Hypothyroidism in adults produces the condition of myxedema. Hyperthyroidism (Graves Disease) may cause an exophthalmic goiter to form due to an overactive thyroid. Blood calcium level is regulated in part by calcitonin. Hormone secreted by the thyroid gland when the blood calcium level rises.

Parathyroid Glands Parathyroid hormone is produced by the parathyroid glands and causes the blood phosphate level to decrease and the blood calcium to increase. Antagonistic action of calcitonin and parathyroid hormone maintain blood calcium levels within normal limits.

Adrenal Glands Each adrenal gland consists of an adrenal medulla and an adrenal cortex. Epinephrine and norepinephrine are produced by the adrenal medulla and rapidly bring about bodily changes when an individual reacts to an emergency. Mineralocorticoids regulate salt and water balance and glucocorticoids regulate metabolism.

Malfunction of the Adrenal Cortex When the level of the adrenal cortex hormones is low due to hyposecretion, a person develops Addison disease. When the level is high due to hypersecretion, a person develops Cushing syndrome.

Addison Disease and Cushing Syndrome

Pancreas The pancreas is composed of two tissue types. Exocrine tissue produces and secretes digestive juices. Endocrine tissue, pancreatic islets, produces and secretes insulin and glucagon directly into the blood. Antagonistic.

Diabetes Mellitus Diabetes mellitus is a hormonal disease in which liver cells and other body cells are unable to take up and/or metabolize glucose. Type I - Pancreas is not producing insulin. Type II - Pancreas produces insulin, but the liver and muscle cells do not respond in the normal fashion.

Other Endocrine Glands Testes and Ovaries. The testes produce androgens (testosterone) and the ovaries produce estrogens and progesterone. Puberty. Secondary sexual characteristics.

Other Endocrine Glands Thymus Gland. Secretes thymosins that aid in the differentiation of lymphocytes inside the lobules of the thymus. Pineal Gland. Secretes melatonin that is involved in regulating daily sleep-wake cycle.

Hormones from Other Tissues Growth Factors. Stimulate cell division and mitosis. Prostaglandins. Chemical signals produced within cells from fatty acid. Act locally.

Homeostasis Hypothalamus produces ADH and thus regulates blood water balance. Endocrine system controls secretion of epinephrine and norepinephrine and thus controls fight or flight responses. Controls blood calcium levels. Muscle contraction. Insulin encourages uptake of glucose by cells and storage of glucose as glycogen in the liver and muscles.

Review Endocrine Glands Hypothalamus and Pituitary Posterior vs. Anterior Thyroid Gland Parathyroid Glands Adrenal Glands Pancreas Other Endocrine Glands Homeostasis