Chapter 10: The Endocrine System

Second messengers

A chemical substance inside a cell that carries information farther along the signal pathway from the internal part of a membrane-spanning receptor embedded in the cell membrane.

Hormones

A complex chemical substance produced in one part or organ of the body that initiates or regulates the activity of an organ or a group of cells in another part. Hormones secreted by the endocrine glands are carried through the blood stream to the target organ. Other hormones are released by organs for local effect, most commonly in the digestive tract.

Cyclic Adenosine Monophosphate (cAMP)

A cyclic nucleotide formed from adenosine triphosphate by the action of adenyl cyclase. This cyclic compound, known as the "Second messenger", participates int he action of catecholamines, vasopressin, adrenocorticotropic hormone, and many other hormones.

Endocrine glands

A ductless gland that produces and secretes hormones into the blood or lymph nodes, affecting metabolism and other body processes. The endocrine glands include the pituitary, pineal, hypothalamus, thymus, thyroid, parathyroid, adrenal cortex, medulla, pancreatic islands of Langerhans, and gonads. Cells in other structures, such as in the gastrointestinal mucosa, kidneys, heart, and placenta, also have endocrine functions.

Exocrine glands

A gland that discharges its secretions through ducts opening on internal or external surfaces of the body.

luteinizing hormone (LH)

A glycoprotein hormone produced by the anterior pituitary gland. It stimulates the secretion of sex hormones by the ovary and the testes and is involved in the maturation of spermatozoa and ova. In males, it induces the secretion of testosterone by the interstitial cells of the testes. In females, LH, working together with follicle-stimulating hormone, stimulates the growing follicle in the ovary to secrete estrogen.

follicle-stimulating hormone (FSH)

A gonadotropin that stimulates the growth and maturation of graafian follicles in the ovary and promotes spermatogenesis in the male. It is secreted by the anterior pituitary gland.

adrenocorticotropic hormone (ACTH)

A hormone of the anterior pituitary gland that stimulates the growth of the adrenal gland cortex and the synthesis and secretion of corticosteroids. ACTH secretion, regulated by corticotropin releasing hormone (CRH) from the hypothalamus, increases in response to a low level of circulating cortisol and to stress, fever, acute hypoglycemia, and major surgery. Under normal conditions, a diurnal rhythm occurs in ACTH secretion, with an increase beginning after the first few hours of sleep and reaching a peak at the time a person awakens and a low in the evening. ACTH may be used in the treatment of rheumatoid arthritis, MS, and myasthenia.

Prolactin (PRL) lactogenic hormone

A hormone produced and secreted into the bloodstream by the anterior pituitary gland. It stimulates the development and growth of the mammary glands after the glands have been prepared by estrogen, progesterone, thyroxine, insulin, growth hormone, glucocorticoids, and human placental lactogen. After parturition, prolactin, together with glucocorticoids, is essential for the initiation and maintenance of milk production.

growth hormone (GH)

A single-chain peptide secreted by the anterior pituitary gland in response to growth hormone-releasing hormone. Its secretion is controlled in part by the hypothalamus. Growth hormone promotes protein synthesis in all cells, increases fat mobilization and use of fatty acids for energy, and decreases use of carbohydrates. Growth effects depend on the presence of thyroid hormone, insulin, and carbohydrate. Somatomedins, proteins produced chiefly in the liver, play a vital role in growth hormone-induced skeletal growth.

Thyroid-stimulating hormone (TSH)

A substance secreted by the anterior lobe of the pituitary gland that controls the release of thyroid hormone and is necessary for the growth and function of the thyroid gland. The secretion of TSH is regulated by thyrotropin-releasing hormone, elaborated in the median eminence of the hypothalamus and circulating-thyroid hormone levels.

What hormones are secreted by the posterior pituitary gland?

1. Antidiuretic hormone (ADH) 2. Oxytocin (OT)

What are the hormones secreted by the anterior pituitary gland?

1. Thyroid-stimulating hormone 2. Adrenocorticotropic hormone 3. Follicle-stimulating hormone 4. Luteinizing hormone 5. Growth hormone 6. Prolactin (PRL) lactogenic hormone

Target cell

Any cell having a specific receptor that reacts with a specific hormone, antigen, antibody, antibiotic, sensitized T cell, or other substance.

Steroid hormones

Any of the ductless gland secretions that contain the basic steroid nucleus in their chemical formulae. The natural steroid hormones include androgen,s estrogens, and adrenal cortex secretions.

What is the function of Prolactin (PRL) lactogenic hormone?

Stimulates breast development during pregnancy and milk secretion (milk letdown) after pregnancy.

What is the function of growth hormone (GH)?

Stimulates growth in all organs; mobilizes food molecules, causing an increase in blood glucose concentration.

Endocrine system

The network of ductless glands and other structures that elaborate and secrete hormones directly into the bloodstream, affecting various processes throughout the body such as metabolism, growth, and secretion from other organs. Glands of the endocrine system include the thyroid, the parathyroid, the anterior pituitary, the posterior pituitary, the pancreas, the suprarenal gland, and the gonads. The pineal gland is also considered an endocrine gland because it is ductless.

What is the function of follicle-stimulating hormone (FSH)?

Tropic hormone. In females it stimulates development of ovarian follicles and secretion of estrogens. In males, it stimulates seminiferous tubules of testes to grow and produce sperm.

What is the function of luteinizing hormone (LH)?

Tropic hormone. In females, it stimulates maturation of ovarian follicle and ovum; stimulates secretion of estrogen, triggers ovulation; stimulates development of corpus luteum (luteinization). In males, it stimulates interstitial cells of the testes to secrete testosterone.

What is the function of adrenocorticotropic hormone (ACTH)?

Tropic hormone; stimulates secretion of adrenal cortex hormones

What is the function of thyroid-stimulating hormone (TSH)?

Tropic hormone; stimulates secretion of thyroid hormones

Hypersecretion

excessive production of a bodily secretion (as gastric acid, mucus, or growth hormone)

Hyposecretion

production of a bodily secretion at an abnormally slow rate or in abnormally small quantities

Nonsteroid hormones

General type of hormone that does have the lipid steroid structure (derived from cholesterol) but is instead a protein or protein derivative; also sometimes called protein hormone.