Hormones Definition: Natural secretion of the endocrine system that exert important functional effects upon other tissues in minute concentrations. Exceptions: Epinephrine secreted in large amounts. Endocrine system: Composed of group of glands called “Endocrine glands”. Endocrine glands: Glands that pour their secretion directly to the blood.

Components of the Endocrine System

Hypothalamus: Located at the base of the brain Hypothalamus: Located at the base of the brain. It secretes Releasing and Inhibiting hormones that target the Anterior Pituitary gland and control its secretions.

Anterior Pituitary gland: Secretes hormones that control the secretion of the other endocrine organs such as adrenal and thyroid glands. Secretion of the Anterior Pituitary is called “tropic hormones or adenohypophyseal hormones.

Adrenal Cortex: The adrenal glands are located on the superior surface of the kidney. They are two glands in a single capsule. The Adrenal cortex secrets corticosteroids.

Gonads: The female and male genital system Gonads: The female and male genital system. In females ovary secrets Estrogens and Progestins.While in males tests secretes Androgens. Pancrease: The endocrine part of the pancreases includes: a-cells that secretes Glucagons b-cells that secretes Insulin Thyroid and Parathyroid glands: The thyroid gland is located at the base of the neck. It is a highly vascular bilobed structure connected by small strip called isthmus. The thyroid gland secretes Thyroxin. Parathyroid glands are embedded in the thyroid gland. They secrete Parathyroid hormone and calcitonin.

Hormonal analogs: Synthetic or Semisynthetic compounds that fits same hormonal receptors to give similar action. However they differ from natural hormones in being orally active, prolonged action and or more specific in their effects.e.g Diethylsttilbestrol. Uses: Hormones and their analogs are used as replacement therapy in case of deficiency.

Hormonal Antagonists: They are of two types due to their mechanism of inhibition: Inhibition of Hormone synthesis: They inhibit the final step or intermediate steps in the biosynthetic pathway of the hormone e.g. Antithyroid drugs. Receptor Antagonists: They block the receptor sites e.g. Clomiphene that block the estrogenic receptors. Uses: They are used in case of excessive secretions of hormones.

Regulation of the Endocrine secretion: Neural or Neuroendocrine control. Negative feed back Mechanisms Hormones control other hormones e.g. Thyroid stimulating hormone control the level of Thyroxin.

Mechanisms of Hormonal Actions: Hormones with plasma membrane receptors e.g. peptide hormones as Insulin. Hormones with cytoplasmic or nuclear membrane receptors e.g. Steroidal Hormones.

Hormones and Recombinant DNA Technology: Enable the production of some peptide hormones by bacterial or Eukaryotic cells. This is achieved by incorporation of the genes responsible for the production of certain hormone into the bacteria genome. The bacterial cells consequently will start to produce the corresponding hormone.

Advantages: Scares hormones are now available e.g. Growth hormone. Enable the study of the hormonal structures. Over come the immunological problems due to the use of animal hormones e.g. bovine or procine Insulin.

Classification of Hormones A- Steroidal Hormones: 1- Adrenocorticoids: Glucocorticoids e.g. Hydrocortisone. Mineralocorticoids e.g. Aldosterone. 2- Sex Hormones: Female sex hormones e.g. Estrogens and Progestins Male sex hormones e.g. Androgens.

B- Amino acids derived hormones: 1- Hormones derived from single amino acid e.g. Thyroxin. 2- Peptide hormones: a- Only amino acids: Anterior Pituitary hormones: Prolactin, Growth Hormone and Placental lactogen. Corticotropins: Adrenocorticotropic hormone ACTH. Insulin Parathyroid hormone and Calcitonin. b- Glycoproteins (Amino acids and sugars): Anterior Pituitary Hormones: Leuteinizing hormone (LH). Follicle Stimulating hormone (FSH), Chorionic Gonadotropin (CG), Thyroid Stimulating hormone (TSH).