Overview

• The endocrine system is a collection of ductless glands scattered around the body with diverse functions involving the control of various activities in different organs.
• The functions of the endocrine system include addressing the growth and reproductive requirements of the individual and responding to changes within the body like those caused by stress.
• Endocrinology deals with the structure, function, and the diagnosis and treatment of disorders of the endocrine system.
• Hormones are chemical messengers released from a region of the body that exert their effect in other regions of the body.
• Exocrine glands secrete or discharge their chemical products through ducts or tubes, while endocrine glands secrete their chemical products into interstitial fluid.
• Extracellular fluid is body fluid that surrounds and bathes the cells of the body, and hormones diffuse into the blood capillaries and blood carries them into their target cells.
• Exclusively endocrine glands include the pituitary, thyroid, parathyroid, adrenal, and pineal glands.
• Mixed-function glands not exclusively endocrine in function include the hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissues, placenta.
• Chemical nature of hormones can be lipid-soluble or lipophilic, which includes steroid hormone and thyroid hormones, or water-soluble, which includes catecholamines and peptide hormones.
• Steroid hormones are neutral lipids that are derivatives of cholesterol, produced by the adrenal cortex & reproductive endocrine glands, and are unique due to the presence of different chemical groups attached to different sites in its ring.
• Thyroid hormones are amino-acid derivative hormones synthesized by attaching to the amino acid tyrosine, and their functions include development of organs and the regulation of metabolism.
• Water-soluble hormones or hydrophilic hormones include catecholamines, serotonin, melatonin, and peptide hormones, and are synthesized by modifying the amino acid tyrosine.
• Catecholamines are amino-acid derivative hormones responsible for the responses during stress, and include epinephrine, norepinephrine, and dopamine.
• Serotonin and melatonin are derivatives of the amino acid tryptophan.
• Peptide hormones are polymers of amino acids, water-soluble in nature, and are synthesized in the endoplasmic reticulum and modified in the Golgi complexes of the secretory cells.
• Hydrophilic hormones are dissolved in the plasma and circulate in the bloodstream.
• Erythropoietin (from the kidneys) targets the bone marrow to stimulate the production of red blood cells.
• Lipophilic hormones are transported by plasma proteins.
• Endocrine System: chemical messengers or hormones are released into and transported via blood cells throughout the body.
• Water-soluble hormones (peptide and amine) target the cell membrane or the surface of the cell.
• Growth hormone from the anterior pituitary gland indirectly stimulates the growth of bones and soft tissues.
• The production of a secondary messenger occurs inside the cell.
• Secretin and cholecystokinin (from the intestinal cells) control the motility and secretion to facilitate the digestive and absorptive processes.
• Cyclic adenosine monophosphate (cAMP) is the most common secondary messenger that stimulates some proteins in the cytosol and results in gene expression.
• Epinephrine and norepinephrine are secreted by the adrenal medulla to contribute to stress adaptation and blood pressure regulation.
• Lipid-soluble hormones (steroid and thyroid) target cells.
• Estrogen stimulates the development of follicles in the ovaries.
• Non-tropic hormones exert their effect on non-endocrine structures and do not affect the release of hormones in another gland.
• Progesterone prepares the uterus for a possible pregnancy.
• Insulin stimulates the synthesis of glycogen in the liver for storage, while it stimulates triglyceride synthesis in fat tissues.
• Functional aspects of the ES include metabolic rate, water and mineral balance, growth, stress response, reproduction.
• Nervous System: nerve impulses or action potentials are conducted in axons and trigger the release of neurotransmitters in synapses.
• The receptor is a molecule in the target that directly responds to the presence of the hormone.
• The first messenger is a molecule that binds to the receptors on the cell surface.
• General functions of the ES include regulation of nutrient metabolism, water, electrolyte balance that are important in maintaining the normal functions of the other organ systems.
• Tropic hormones regulate the production and secretion of another hormone or the regulation of hormone secretion of another endocrine gland.
• Thyroid-stimulating hormone stimulates the release of T3 and T4.
• Insulin and glucagon regulate blood glucose levels.
• Human growth hormone stimulates the growth of organs.
• Vasopressin regulates water balance.