Chapter 7 endocrine Exam 3 review sheet The specificity of a hormone depends on its receptors and associated signal transduction pathways Hormone is a chemical secreted into the blood by a cell or group of cells for transport to a distant target Hormones are effective at very low concentrations Pheromones are chemical signals secreted into the external environment Hormones bind to receptors to initiate cellular mechanism of action Insulin is an example of a hormone with varied effects in muscle and adipose tissues it alters glucose transport proteins and enzymes for glucose metabolism In the liver it modulates enzyme activity The variable responsiveness of a cell to a hormone depends on the cells receptor and signal transduction pathways Hormone activity is limited by terminating secretion removing hormone from the blood or terminating activity at the target cell Hormones have a half life hormones in the blood are degraded into inactive metabolites by enzymes found in the liver and kidneys Hormones bound to membrane receptors have their activity terminated by enzymes in the plasma peptide hormones or the entire complex is brought into the cell by exocytosis 3 types of hormones peptide protein hormones steroid hormones and amino acid derived hormones Amine hormones act by modifying existing proteins and activate second messenger systems Secretory vesicles containing peptides are stored in the cytoplasm of the endocrine cell until needed Peptide hormones are synthesized as inactive preprohormones then processed to prohormones Preprohormones contain one or more copies of a peptide hormone and the signal sequence is removed in the Golgi apparatus Prohormones are chopped into active hormones and peptide fragments Peptide hormones dissolve in the plasma have a short half life They bind to surface receptors on their target cells and initiate a rapid cellular responses thru signal transduction G protein coupled adenylyl cyclase cAMP system is the signal transduction system for many protein hormones ATP cAMP activates protein kinase Simplest reflex control pathways in the endocrine system where an endocrine cell directly senses a stimulus and responds by secreting a hormone In this type of pathway the endocrine cell acts as both sensor and integrating center Ex PTH is secreted by 4 small parathyroid glands that lie behind the thyroid The parathyroid endocrine cells monitor plasma Ca2 with the aid of G protein coupled Ca2 receptors on their cell membranes When a certain number of receptors are bound to Ca2 PTH is inhibited Steroid hormones are synthesized as needed because they are lipophilic they could just slide out are hydrophobic and generally bound to protein carriers Synthesized in the adrenal cortex 1 Steroid receptors are generally inside the target cells where they turn genes on or off and direct the synthesis of new proteins some steroid hormones also bind to membrane receptors that use 2nd messenger systems for a more rapid response Cell response is slower than with peptide hormones most hormone receptor complexes go to the nucleus where they turn genes on causing new mRNA to be made not rapid Steroid hormones may bind to membrane receptors and have nongenomic effects Amine hormones can behave like typical peptide hormones or like a combination of a steroid hormone and a peptide hormone Many endocrine reflexes involve the nervous system by either neurohormone or through neurons that influence hormone release Neurohormones are chemical signals released into the blood stream Pituitary gland is composed of the anterior pituitary an endocrine gland and the posterior pituitary which is an extension of the brain Posterior pituitary releases oxytocin and vasopressin both made in the hypothalamus Trophic hormones control the secretion of other hormones Hypothalamic releasing hormones and inhibiting hormones control the secretion of anterior pituitary hormones The hypothalamic trophic hormones reach the pituitary thru the hypothalamic hypophyseal portal system 6 anterior pituitary hormones prolactin growth hormone FSH LH TSH and ACTH The signals that regulate secretion of the anterior pituitary hormones come from neurohormones These neurohormones are secreted into the circulation in the hypothalamus to the pituitary through the hypothalamic hypophyseal portal system Hormones secreted into a portal system have an advantage over hormones secreted into general circulation a much smaller amount is needed in the portal system Hormones of the anterior pituitary control many vital functions In complex endocrine reflexes hormones of the pathway act as negative feedback signals If the combination of two or more hormones yields a result that is greater than additive it is called synergism If one hormone cannot exert its effects fully unless a second hormone is present the second hormone is permissive to the first If one hormone opposes the action of another the two are antagonistic Diseases of hormone excess are usually due to hypersecretion Symptoms of hormone deficiency occur when too little hormone is secreted Abnormal tissue responsiveness may result from problems with hormone receptors or signal transduction pathways Primary pathologies arise in the last endocrine gland in a reflex A secondary pathology is a problem with one of the tissues producing trophic hormones Short loop negative feedback pituitary hormones feed back to decrease hormone secretion by the hypothalamus Ex ACTH Long loop negative feedback last hormone in a pathway loops back to suppress secretion of its trophic hormones Ex Cortisol secreted from adrenal cortex feeds back to suppress secretion of hypothalamic corticotropin releasing hormone CRH and adrenocorticotropin ACTH 2 Chapter 12 muscles Muscles generate motion force and heat 3 types of muscle are skeletal cardiac and smooth Skeletal and cardiac muscle are striated They appear striated because of the alternating light and dark bands Skeletal muscles are attached to bones by tendons The origin is the end of the muscle attached closest to the trunk or most stationary part of the bone The insertion is the more distal or mobile attachment Smooth muscle is in blood vessels tubes urinary tract bladder stomach Its function is to influence the movement of material into out of and within the body Skeletal muscles are described as voluntary but a certain degree of conscious control can be learned over smooth and cardiac muscle Skeletal muscles are unique in that they contract