Hormones Lecture 1 PDF

Hormones Definition Hormones are organic compounds produced by endocrine system and secreted directly into blood to act near to their site of release or at a distant organ. Endocrine System The endocrine system consists of a group of glands and organs that regulate and control various body function...

Hormones Definition Hormones are organic compounds produced by endocrine system and secreted directly into blood to act near to their site of release or at a distant organ. Endocrine System The endocrine system consists of a group of glands and organs that regulate and control various body functions by producing and secreting hormones. The glands of the endocrine system do not have ducts but rather release their hormones directly into the bloodstream.  General functions of hormones 1-Regulation of metabolism: Hormones affect the metabolism of carbohydrates, protein, lipids and minerals, directing their synthesis, storage, mobilization and utilization according to body needs. 2-Hormones support cell growth. 3-Hormones maintain internal homeostasis. 4-Hormones have an important role in behavior such as fear, depression and sex behavior. 5-Hormones coordinate reproduction. 6-Hormones facilitate responses to external stimuli.  Characters of Hormones 1. Hormones are molecules synthesized by specific tissues (glands). 2. They are secreted directly into the blood. 3. They are carried by the blood to their site of action (target organs or tissues).  Local Hormones These are physiologically active substances that are released from general or specific sites in tissues but that act at or near their point of origin and normally destroyed (rapidly) before they have a chance to disperse further. They include: (1) Acetyl choline. (2) Histamine. (3) Serotonin. (4) Prostaglandins. (5) Prostacyclin. (6) Thromboxanes. (7) Plasma polypeptides: as angiotensin and plasma kinins.  Classification of hormones 1- Classification of hormones based on their chemical composition: 1. Proteins: such as insulin, growth hormone, TSH, LH, FSH, parathyroid hormones and prolactin. 2. Polypeptides: such as pituitary hormones (oxytocin, ADH and ACTH). 3. Lipids (steroids): such as sex hormones (estrogen, progesterone and androgens) 4. Amino acid derivatives: such as thyroid hormone(T3 & T4), epinephrine, norepinephrine and serotonin.  Classification of hormones (cont.) 2-Classification of hormones based on their mechanism of action: According to mechanism of action, hormones may be classified into two main groups: Group I: Hormones that bind to intracellular receptors, which includes steroids, T3, T4 and calcitriol. The mechanism of action of this group based on the diffusion of hormones through cell membrane of the target cells and binding to specific receptor protein in cytosol or nucleus, forming hormone- receptor complex.  Classification of hormones (cont.) Group I: This hormone-receptor complex undergoes activation reaction leads to changes in size, conformation and surface charges of this complex, making it able to bind to DNA at specific region called hormone response element (HRE), which will activate or inactivate metabolic process.  Classification of hormones (cont.) Group II: Hormones that bind to cell surface receptors. A hormone, which is the first messenger, binds to specific receptor located in the cell membrane to activate a second messenger located in cytosol.  ENDOCRINE GLANDS The major glands of the endocrine system, each of which produces one or more specific hormones, are the hypothalamus, the pituitary gland, the thyroid gland, the parathyroid glands, the islets of the pancreas, the adrenal glands, the testes in men, and the ovaries in women. During pregnancy, the placenta also acts as an endocrine gland in addition to its other functions. Not all organs that secrete hormones or hormone like substances are considered part of the endocrine system. For example, the kidneys produce the hormones renin and angiotensin to help control blood pressure and erythropoietin to stimulate the bone marrow to produce red blood cells. In addition, the digestive system produces a variety of hormones that control digestion (such as gastrin, secretin and cholecystokinin).  The Hypothalamus The hypothalamus is a portion of CNS located at the base of the brain, just above the pituitary gland. It releases hormones that actually control the release of other hormones from the pituitary gland Hypothalamus secretes different releasing hormones which regulate the secretion of anterior pituitary hormones  Hypothalamic Pituitary Hormones Target Gland Hormones Affected Corticotropin R.H Adrenocorticotropic H. Adrenal cortex (ACTH) Thyrotropin R.H. Thyroid stimulating H. Thyroid gland (TSH) Gonadotropin R.H. Luteinizing H. (LH) Testis and Follicle stimulating H. ovary (FSH) Growth hormone Growth H. (GH) Liver R.H. Growth H. release- Growth H. (GH) Liver inhibiting H. (somatostatin) Prolactin release- Prolactin (PRL) Mammary inhibiting H. gland Regulation of hypothalamic hormones The hypothalamic hormones are secreted under control of higher brain centers, anterior pituitary hormones and final target hormones (feed back regulation) TRH secretion is inhibited by excess concentration of TSH, T3 and T4. Regulation of hypothalamic hormones  The Pituitary Gland The pituitary gland is located at the base of the brain. It is sometimes called the 'master gland' because its hormones affect many of the body's organs. Pituitary gland is composed of two lobes, anterior and posterior. The anterior pituitary regulates and controls the function of most other endocrine glands by specific hormones.  Anterior pituitary hormones Classification of anterior pituitary hormones:- Anterior pituitary glands secretes three groups of hormones: I- Protein hormones: This includes: Prolactin (PRL) and Growth hormone (GH). II- Glycoprotein hormones: This includes: Thyroid-stimulating hormone (TSH), Luteinizing hormone (LH) and Follicle-stimulating hormone (FSH). III- Pro-opio-melano-cortin (POMC) peptide hormones: This includes: Adrenocorticotropin (ACTH), Melanocyte stimulating hormone (MSH), β-Lipotropin (β-LPH), Endorphin and Enkephalin.  I- Protein hormones ( PRL, GH) A- Prolactin (PRL): The length of the mature hormone is between 194 and 199 amino acids, depending on species. Physiologic Effects of Prolactin: Prolactin, in combination with estrogens and progesterone initiates and maintain lactation. Prolactin has two major roles in milk production: 1- Prolactin induces growth of the mammary gland. 2- Prolactin stimulates lactogenesis or milk production afte giving birth.  Control of Prolactin Secretion In contrast to all other pituitary hormones, the hypothalamus suppresses prolactin secretion from the pituitary gland. Dopamine serves as the major prolactin-inhibiting factor or brake on prolactin secretion.  Disease States of Prolactin Excessive secretion of prolactin - hyperprolactinemia - is a relatively common disorder in humans. This condition has numerous causes, including prolactin-secreting tumors and therapy with certain drugs (Anti-dopamenerdic drugs such as metaclopramide). Common manifestations of hyperprolactinemia in women include amenorrhea (lack of menstrual cycles) and galactorrhea (excessive or spontaneous secretion of milk).  Disease state in Men - Men with hyperprolactinemia typically show hypogonadism, with decreased sex drive, decreased sperm production and impotence. Such men also often show breast enlargement, but very rarely produce milk. Such condition is called Gynecomastia. Growth hormone (GH, Somatotropin) Growth hormone is a protein consisting of 191 amino acids. Physiological action of GH: GH is an anabolic hormone increases the transport of amino acids into muscle cells and increase protein, DNA and RNA synthesis. GH promotes the release of free fatty acids and glycerol from adipose tissues (stimulate lipolysis, fatty acid oxidation and ketogenesis in liver). GH increase mineral absorption (calcium, magnesium and phosphate) and help their incorporation in the skeleton. Prolactin like effect of GH: It binds lactogenic receptors and thus stimulates mammary gland and milk production.  Disorders of GH Gigantism and Acromegaly (Overproduction of GH): Gigantism: is a disease resulting from excessive production of GH before the closure of epiphyseal plates, where there is accelerated growth of the long bones. Acromegaly: is a disease resulting from excessive production of GH after the closure of epiphyseal plates and the cessation of long bones growth. It is marked by enlargement of the bones of the extremities, face, and jaw.  Disorders of GH(cont.) Dwarfism (Underproduction of GH): There is a deficiency of GH in infants leads to failure of growth. Symptom of dwarfism is abnormally and significantly shorter stature with respect to other persons in the same age, and especially in adults who have reached their final heights.  Disorders of GH (cont.) Acromegaly Gigantism Dwarfism