* The endocrine system is much slower than the nervous system.* Instead of shooting impulses straight to the brain through nerves, the hormones are released and move through the bloodstream to their target cells (2).* The endocrine system controls more of the internal body than the nervous system.
* Hormones are chemical messengers and are produced by the ENDOCRINE SYSTEM. They are distributed throughout the body by diffusion into the bloodstream. They travel through the blood to whichever organ or muscle they are meant to effect which are called target organs or target cells. Only the specific target will be affected by the particular hormone that goes with it. Endocrine glands are ductless glands. The glands make the hormones but the hormones are not excreted through ducts but by diffusion.
* These are the major endocrine glands: The Hypothalamus, the Pituitary and the Pineal gland are located in the brain. The Thyroid and Parathyroid glands are each paired and are located in the neck. The Thymus gland is located right in the center of the chest (also called the mediastinum.) The Adrenal glands are a pair and they are located in the abdominal cavity. Also in the abdominal cavity are the Pancreatic Islets, near the pancreas. In a female, there are two ovaries located in the pelvic cavity. In a male, there are two Testes, located in the scrotum. Another Endocrine gland is the placenta in a pregnant female.* There are many useful ways to classify the various hormones that these glands produce. One way is by function. Tropic hormones target other endocrine glands and stimulate their growth and secretions. Sex hormones, the kind we are most familiar with, relate to reproductive organs and their functions. Anabolic hormones stimulate anabolism in their target cells.
* Steroid hormone molecules are manufactured by endocrine cells from cholesterol, an important type of lipid in the human body.* Nonsteriod hormones are synthesized primarily from amino acids rather than from cholesterol. Some nonsteroid hormones are protein hormones.
* Hormones signal a cell by binding to specific receptors on or in the cell.* In a “lock-and-key” mechanism , hormones will bind only to receptor molecules that “fit” them exactly. Any cell with one or more receptors for a particular hormone is said to be a target of that hormone.* A common type of combined action of hormones is seen in the phenomenon of antagonism. In antagonism, one hormone produces the opposite effect of another hormone.
Hormone Source Targets Principal ActionGrowth hormone-releasing hormone Hypothalamus Adenohypophysis Stimulates secretion of growth hormoneGRH (somatotrophs)Growth hormone- inhibiting hormone Hypothalamus Adenohypophysis Inhibits secretion of growth hormoneGIH, or somatostatin (somatotrophs)Corticoptropin- releasing hormone CRH Hypothalamus Adenohypophysis Stimulates release of adrenocorticotrophic hormone ACTH (corticotrophs)Thyrotropin-releasing hormone TRH Hypothalamus Adenohypophysis Stimulates release of thyroid-stimulating TSH (thyrotrophs)Gonadotropin- releasing hormone Hypothalamus Adenohypophysis Stimulates release of gonadotropins (FSH and LH)GNRH (gonadotrophs)Prolactin-releasing hormone PRH Hypothalamus Adenohypophysis Stimulates secretion of prolactin (corticotrophs)Prolactin- inhibiting hormone PIH Hypothalamus Adenohypophysis Inhibits secretion of prolactin (corticotrophs)Growth hormone GH (somatotrophs Adenohypophysis General Promotes growth by stimulating protein anabolism[STH]) (somatotrophs)Prolactin PRL (lactogenic hormone) Adenohypophysis Mammary glands Promotes milk secretion (lactotrophs) (alveolar secretory cells)Thyroid-stimulating hormone TSH Adenohypophysis Thyroid gland Stimulates development and secretion in the thyroid gland (thyrotrophs)Adenocorticotrophic hormone ACTH Adenohypophysis Adrenal cortex Promotes development and secretion in the adrenal cortex (corticotrophs)Follicle-stimulating hormone FSH Adenohypophysis Gonads (primary Female: promotes development of ovarian follicle; stimulates (gonadotrophs) sex organs) estrogen secretion Male: promotes development of testis; stimulates sperm productionLuteinizing hormone LH Adenohypophysis Gonads Female: triggers ovulation; promotes development of corpus luteum (gonadotrophs) Male: simulates production of testosteroneAntidiuretic hormone ADH Neurohypophysis Kidney Promotes water retention by kidney tubulesOxytocin OT Neurohypophysis Uterus and Stimulates uterine contractions; stimulates ejection of milk into mammary gland mammary glands
Hormone Source Targets Principal ActionTriiodothyronine (T3) Thyroid gland (follicular cells) General Increase rate of metabolismTetaiodothyronine (T4) Thyroid gland (follicular cells) General Increases rate of metabolism (usually converted to T3 first)or thyroxineCalcitonin CT Thyroid gland (parafollicular cells) Bone tissue Increases calcium storage in bone; lowering blood Ca++ levelsParathyroid hormone Parathyroid glands Bone tissue and kidney Increases removal from storage in bone and produces thePTH or parathromone active form of vitamin D in the kidneys, increasing absorption of calcium by intestines and increasing blood Ca++ levelsAldosterone Adrenal cortex (zona glomerlulosa) Kidney Stimulates kidney tubules to conserve sodium, which, in turn, triggers, the release of ADH and the resulting conservation of water by the kidneyCortisol (hydrocortisone) Adrenal cortex (zona fasciculata) General Influences metabolism of food molecules; in large amounts, it has an anti-inflammatory effectAdrenal androgens Adrenal cortex (zona reticularis) Sex organs, other Exact role uncertain, but may support sexual function effectorsAdrenal estrogens Adrenal cortex (zona reticularis) Sex organs Thought to be physiologically insignificantEpinephrine (adrenaline) Adrenal medulla Sympathetic effectors Enhances and prolongs the effects of the sympathetic division of the autonomic nervous systemNorepinephrine Adrenal medulla Sympathetic effectors Enhances and prolongs the effects of the sympathetic division of the autonomic nervous systemGlucagon Pancreatic islets (alpha [a] cells or A General Promotes movement of glucose from storage and into the cells) bloodInsulin Pancreatic islets (beta [b] cells or B General Promotes movement of glucose out of the blood and into cells cells)Somatostatin Pancreatic islets (delta [d] cells or D Pancreatic cells and Can have general effects in the body, but primary role seems cells) other effectors to be regulation of secretion of other pancreatic hormonesPancreatic polypeptide Pancreatic islets (pancreatic Intestinal cells and Exact function uncertain, but seems to influence absorption polypeptide [PP] of F cells) other effectors in the digestive tract
Prolactin- inhibiting Hypothalamus Adenohypophysis Inhibits secretion ofhormone prolactinGrowth Hormone Adenohypophysis General Promotes growth by stimulating protein anabolism and fatProlactin Adenohypophysis Mammary glands Promotes milk secretionThyroid-stimulating Adenohypophysis Thyroid Glad Stimulateshormone development and secretion in the thyroid glandAdrenocorticotropic Adenohypophysis Adrenal Cortex Promotes development and secretion in the adrenal cortex
Follicle-stimulating Adenohypophysis Gonads Female: Promoteshormone development of ovarian follicle; simulates estrogen secretion Male: development of testies; sperm productionsLuteinizing hormone Adenohypophysis Gonads Female: triggers ovulation; promotes corpus luteum Male: stimulates production of testosteroneAntidiurectic hormone Adenohypophysis Kidney Promotes water retention by kidney tubulesOxytocin Uterus and Stimulates uterine mammary contractions; stimulates ejection in mammaryTriiodothyronine Thyroid gland General Increases rate of metabolismTetraiodothyronine Thyroid Gland General Increases, rate of metabolism
lowering blood Ca levelParathyroid Parathyroid Gland Bone Tissue and Increases calcium removal fromhormone Kidney storage in bone and produces the active form of vitamin D in the kidneys, increasing absorption of calcium by intestines and increasing bloodAldosterone Adrenal Cortex Kidney Stimulates kidney tubules to conserve sodium, which in turn, triggers the release of ADH and the resulting conservation of water by the kidneyCortisol Adrenal Cortex General Influences metabolism of food moleculesAdrenal Adrenal Cortex Sex organs other Exact role uncertain, but may supportAndrogens effectors sexual functionAdrenal Adrenal Cortex Sex organs Though to be physiologicallyEstrogens insignificantEpinephrine Adrenal Medulla Sympathetic Enhances and prolongs effects of effectors sympathetic division of nervous systemNorenpine- Adrenal Medulla Sympathetic Enhances and prolongs effects ofphrine effectors sympathetic division of nervous system
Glucagon Pancreatic Islets General Movement of glucose to bloodInsulin Pancreatic Islets General Movement of glucose out of blood into cellsSomatostatin Pancreatic Islets Pancreatic cells and Secretion of pancreatic other effectors hormonesPancreatic Polypeptide Pancreatic Islets Intestinal Cells and Influence absorption in other effectors digestive tract