Hormones PDF

Almaaqal University HormoneS Dr/ Wael Sobhy Darwish Biochemistry PhD  Introduction Definition Hormones are “chemical substances released from ductless or endocrine glands directly to the blood a...

Almaaqal University HormoneS Dr/ Wael Sobhy Darwish Biochemistry PhD  Introduction Definition Hormones are “chemical substances released from ductless or endocrine glands directly to the blood and are responsible for controlling and regulating the activities of certain cells and organs”. A more modern definition of a hormone is that it is synthesized by one type of cells and transported through blood to act on another type of cells. The nervous system and endocrine system are the major control mechanisms that integrate the functions of the tissues in the body.  Function of hormones Hormones control many different bodily processes, including: Metabolism. Homeostasis (constant internal balance), such as blood pressure and blood sugar regulation, fluid (water) and electrolyte balance and body temperature. Growth and development. Sexual function. Reproduction. Sleep-wake cycle. Mood.  The endocrine system releases chemical mediators or hormones into the circulation. Signal transduction is the process of transferring the signal into the cell. There are two types of cells in signal transduction 1- The sender cell where the signal originates 2- The target cell that receives the signal. The signal alters or modulates the activity/function of the cell.  Types of signal 1- Autocrine signaling: which a cell secretes a hormone or a chemical substance that binds to the receptors on the same cell. The same cell acts as sender and recipient, e.g., growth and differentiation  2- Paracrine signaling Paracrine signaling is affected by local mediators which have their effect near the site of secretion without entering the circulation, the effect is rapid and transient. Signaling occurs between cells that are close to each other. 3 - Juxtacrine signaling occurs when the two types of cells are adjacent to each other so that contact is established through gap junctions or through protein molecules on the surface of the two cells. 4- Endocrine signaling is between cells which are located at a distance from each other and the target cell, they bind to specific target cell receptors with high affinity. Hypothalamus  The Hypothalamus The hypothalamus produces two types of endocrine factors; (a) Hypothalamic neuropeptides (b) Hypothalamic releasing factors a) Hypothalamic neuropeptides (Posterior Lobe) These neurohormones are antidiuretic hormone (ADH) and oxytocin. They are released to bloodstream by exocytosis. (b) Hypothalamic releasing, (Anterior Lobe) Pituitary gland is the master gland: The pituitary is a small, pea-sized gland situated at the base of the brain. Pituitary controls 3 endocrine glands: thyroid, adrenal glands and gonads. Three endocrine glands not controlled by pituitary; parathyroid, adrenal medulla and pancreas. Anterior pituitary The anterior pituitary secretes six hormones, each with distinct functions and target organs: 1) Growth hormone (somatotropin) 2) Thyroid stimulating hormone (TSH) 3) Adrenocorticotropic hormone (ACTH) 4) Follicular stimulating hormone (FSH) 5) Luteinizing hormone (LH) 6) Prolactin(PRL)  Several other glandular tissues are considered to secrete hormones: Heart: atrial natriuretic peptide (ANP). kidney: produce the hormone erythropoietin, renin &1,25(OH)2cholecalciferol. Thymus: This produces a hormone that circulates from this organ to stem cells in lymphoid organ inducing them to become immunologically competent lymphocytes ex: Thymopoietin and thymosin. GI tract: Few hormones are also produced by certain specialized cells of GI tract and they are called GI Hormones ex: gastrin, CCK, secretin, somatostatin  Character of endocrine hormone: 1- They are secreted directly in blood in small amount (very active). 2- Some hormones have generalizer action e.g., growth hormone & thyroxine. Others affect specific target organs e.g., sex hormones & ACTH. 3- Hormones are removed either by target cell uptake, metabolism inactivation by liver or excretion by kidney. 4- Hormones play a key role in regulation almost all body functions including metabolism, growth, development, H2O and electrolyte balance, reproduction and behavior.  Biochemical structure & synthesis hormones Hormones may classified according to biochemical nature to: 1. Steroid hormones: These are steroid in nature such as adrenocorticosteroid hormones, androgens, estrogens and progesterone. 2. Amino acid derivatives: These are derived from amino acid tyrosine, e.g., epinephrine, norepinephrine and thyroid hormones. 3. Peptide/Protein hormones: These are either large proteins or small or medium size peptides, e.g., Insulin, glucagon, parathormone, calcitonin, pituitary hormones, etc Hormones may classified according to solubility