国外动物学34.PPT

国外动物学34 Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望HormoneslA hormone is a chemical signal that is secreted into the circulatory system and communicates regulatory messages within the body.lHormones may reach all parts of the body,but only certain types of cells,target cells,are equipped to respond.Systems of Internal CommunicationlAnimals have two systems of internal communication and regulation:lThe nervous systemlThe endocrine systemSystems of Internal CommunicationlThe nervous system conveys high-speed electrical signals along specialized cells called neurons.lThe endocrine system,made up of endocrine glands,secretes hormones that coordinate slower but longer-acting responses to stimuli.HormoneslAdvantages of using chemical messengers:lChemical molecules can spread to all tissues through the blood.lChemical signals can persist longer than electrical ones.lMany different kinds of chemicals can act as hormones;different hormones can target different tissues.GlandslMany hormones are secreted by ductless endocrine glands.lObtain raw materials from and secrete hormones directly into the bloodstream.lExocrine glands have ducts for discharging secretions onto a free surface.lSweat glands,salivary glands,enzyme-secreting glands in the digestive tract.HormoneslHormones convey information via the bloodstream to target cells throughout the body.lPheromones carry messages outside the body to other individuals.HormoneslThree major classes of molecules function as hormones in vertebrates:lProteins and peptideslAmines derived from amino acidslSteroidsHormoneslSignaling by any of these molecules involves three key events:lReceptionlSignal transductionlResponseHormoneslThe hypothalamus regulates the neuroendocrine system,maintaining homeostasis in the body.lThe hypothalamus can use motor nerves to send short-lived electrical messages or hormones to send chemical messages with a longer duration.The Chain of CommandlThe hypothalamus produces seven different“releasing”hormones that travel to the pituitary gland.lEach releasing hormone stimulates the pituitary to release a corresponding hormone which travels to an endocrine gland and causes it to start producing a particular endocrine hormone.Membrane-Bound ReceptorslMany hormones are too large,or too polar,to pass through plasma membranes.lBind to transmembrane proteins that act as receptor sites on target cell membranes.lHormone is first messenger.lCauses activation of a second messenger in the cytoplasm.lcAMPNuclear ReceptorslSteroid hormones are lipid soluble molecules that bind to hormone receptors in the cytoplasm of the target cell.lSite of activity is the nucleus.lSteroids are manufactured from cholesterol.lEstrogen,progesterone,testosterone,cortisol.Nuclear ReceptorslThyroid hormones and insect-molting hormone(ecdysone)also act through nuclear receptors.lBinds to transmembrane protein that uses ATP to move it into the cell.Control Pathways and Feedback LoopslA common feature of control pathways is a feedback loop connecting the response to the initial stimulus.lNegative feedback regulates many hormonal pathways involved in homeostasis.Invertebrate HormoneslEcdysone regulates molting in insects.lJuvenile hormone favors the retention of juvenile characteristics.The PituitarylThe pituitary gland is located below the hypothalamus.lNine major hormones are produced here.lThese hormones act primarily to influence other endocrine glands.The PituitarylThe posterior lobe of the pituitary regulates water conservation,milk letdown,and uterine contraction in women.lThe anterior lobe regulates the other endocrine glands.The Anterior PituitarylThyroid stimulating hormone(TSH)stimulates the thyroid gland to produce thyroxine which stimulates oxidative respiration.lLuteinizing hormone(LH)plays an important role in the menstrual cycle.It also stimulates the production of testosterone in males.The Anterior PituitarylFollicle-stimulating hormone(FSH)plays an important role in the menstrual cycle.In males,it causes the testes to produce a hormone that regulates sperm production.lAdrenocorticotropic hormone(ACTH)stimulates the adrenal gland to produce steroid hormones.Some regulate glucose production,others balance sodium&potassium in the blood.The Anterior PituitarylGrowth hormone(GH)stimulates the growth of muscle and bone.lProlactin stimulates milk production.lMelanocyte-stimulating hormone(MSH)in reptiles&amphibians,this hormone stimulates color change.The Posterior PituitarylAntidiuretic hormone(ADH)regulates the kidneys retention of water.lOxytocin initiates uterine contraction during childbirth and milk release in mothers.lThese hormones are actually synthesized in the hypothalamus and stored in the posterior pituitary.Biological ClockslThe pineal gland is located in the brain of most vertebrates.lEvolved from a light sensitive“third eye”.lPrimitive fish&some reptiles still have a third eye.Biological ClockslIn other vertebrates it functions as an endocrine gland secreting melatonin.lMelatonin controls color change in amphibians&reptiles.lRelease of melatonin is controlled by light/dark cycles.lThe primary functions of melatonin appear to be related to biological rhythms associated with reproduction.lCircadian rhythms 24 hours long.The ThyroidlThe thyroid gland,located in the neck,produces:lThyroxine increases metabolic rate and promotes growth.lTwo iodine-containing hormones,triiodothyronine(T3)and thyroxine(T4).lCalcitonin stimulates calcium uptake by bones.The ThyroidlThe hypothalamus and anterior pituitary control the secretion of thyroid hormones through two negative feedback loops.The ThyroidlThe thyroid hormones play crucial roles in stimulating metabolism and influencing development and maturation.The ParathyroidslThe parathyroid glands are four small glands attached to the thyroid.lThe hormone they produce is parathyroid hormone(PTH)which regulates the level of calcium in the blood.lEssential that calcium is kept within narrow limits for muscle contraction,including the heart.Calcium HomeostasislTwo antagonistic hormones,parathyroid hormone(PTH)and calcitonin,play the major role in calcium(Ca2+)homeostasis in mammals.Calcium HomeostasislCalcitonin,secreted by the thyroid gland,stimulates Ca2+deposition in the bones and secretion by the kidneys,thus lowering blood Ca2+levels.lPTH,secreted by the parathyroid glands,has the opposite effects on the bones and kidneys,and raises Ca2+levels.lAlso has an indirect effect,stimulating the kidneys to activate vitamin D,which promotes intestinal uptake of Ca2+from food.The AdrenalslMammals have an adrenal gland above each kidney.lAdrenal medulla is the inner core which produces adrenaline(epinephrine)and norepinephrine.lAdrenal cortex is the outer shell that produces the steroid hormones cortisol and aldosterone.Adrenal MedullalThe adrenal medulla releases adrenalin(epinephrine)and norepinephrine in times of stress.lIdentical to the effects of the sympathetic nervous system,but longer lasting.lAccelerated heartbeat,increased blood pressure,higher levels of blood sugar and increased blood flow to heart and lungs.Adrenal CortexlThe adrenal cortex produces the steroid hormone cortisol(hydrocortisone).lReduces inflammation.lSynthetic derivatives such as prednisone are used as anti-inflammatory agents.lStimulates carbohydrate metabolism.Adrenal CortexlThe adrenal cortex also produces aldosterone.lAldosterone acts in the kidney to promote the uptake of sodium&other salts from the urine.lThese salts are important in nerve conduction.lAldosterone and PTH are the only two hormones essential for survival.The PancreaslThe pancreas is located behind the stomach and is connected to the small intestine by a small tube.lIt secretes digestive enzymes into the digestive tract(exocrine function).lEndocrine function production of insulin and glucagon.Glucose HomeostasislThe islets of Langerhans in the pancreas secrete insulin and glucagon.lInsulin removes glucose from the blood.lGlucagon returns glucose to the blood.DiabeteslDiabetes mellitus,perhaps the best-known endocrine disorder,is caused by a deficiency of insulin or a decreased response to insulin in target tissues.lMarked by elevated blood glucose levels.DiabeteslType I diabetes mellitus(insulin-dependent diabetes)is an autoimmune disorder in which the immune system destroys the beta cells of the pancreas.lType II diabetes mellitus(non-insulin-dependent diabetes)is characterized either by a deficiency of insulin or,more commonly,by reduced responsiveness of target cells due to some change in insulin receptors.