BIL 360: Chapter Outlines for Exam 3
BIL 360: Chapter Outlines for Exam 3 BIL 360
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Ch 16 part 2 pg 436453 10292014 Endrocrine control of nutrient metabolism in mammals 0 Animals get nutrients carbohydrates lipids proteins from eating 0 But many animals don t eat continuously 0 Cells still need consistent nutrients 0 Cells require dif proportions of nutrients than found in digested foods 0 Nutrient metabolism requires feeding and management of storage mobilization molecular interconversions of nutrients o 2 main hormones insulin and glucagon Insulin regulates shortterm changes in nutrient availability 0 Many mammals eat and then don t eat for periods of time o to prevent feastfamine at cell level have mechanisms that store nutrients after meal and mobilization of nutrients from storage hours after meal 0 insulin manages shortterm uctuations of nutrient availability 0 during digestion many factors stimulate beta cells in pancreatic islets of Langerhans to incr secretion of insulin 0 rising conc glucose and AAs in blood gastrointestinal hormones parasympathetic activity 0 insulin dominant hormone in fed state 0 favors storage 0 promotes uptake of glucose fatty acids AAs from blood to tissues muscle fat brainliver don t depend on insulin have constitutive glucose transporter molecules that permit glucose uptake continuously o skeletal muscles in exercise don t depend on insulin insulin has hypoglycemic effect causes decr in blood glucose levels 0 stimulates enzymes that synthesize storage molecules glycogen from glucose lipids from fatty acidsglucose proteins from AAs o and inhibits enzymes that break down these large molecules lnsulin secretion decr at end of digestion o Shifts to net mobilization of nutrients o Breaks down glycogenlipids o Glucosefatty acids released to blood 0 lnsulin levels low at unfed state negative feedback stabilizes blood conc of nutrients Blood conc not stable but much more stable with negative feedback from insulin 0 Diabetes mellitus secretion of abnormally low amts of insulin or diminished tissue responsiveness to insulin 0 Higher glucose levels so high that kidneys unable to recover all glucose ltered from blood in urine formation glucose excreted in urine and waste Glucagon works with insulin to ensure stable levels of glucose in the blood Glucagon peptide hormone secreted by alpha cells of pancreatic islets o Stimuli for release low glucose in blood sympathetic stimulation of alpha cells high levels AAs in blood 0 Main effect incr production glucose and its release into blood 0 Hyperglycemic effect causes blood glucose levels to rise Stimulates liver to break down glycogen glycogenolysis and to release that glucose into blood 0 Inhibits lipid synthesis 0 Stimulates fat cell breakdown into fatty acidsglycerol release into blood Stimulates gluconeogenesis in liver new glucose molecules formed from noncarbohydrate molecules AAsglycerol Blood glucose level rises l glucagon secretion decr from negative feedback 0 Insulin and glucagon contribute to stable blood glucose levels Under stressexercise sympathetic stimulation causes secretion of epinephrine from adrenal medulla and incr synaptic input to alpha cells 0 Epinephrine stimulates alpha cells to secrete glucagon and inhibit beta cells from secreting insulin Glucagon secreted in unfed state low glucose and fatty acid levels 0 Secretion incr when AA level high 0 So glucagon often secreted in fed state depending on nutrient composition of the meal Highcarb meal l glucose rises l insulin secretion rises l glucagon secretion decr Low level of glucagon reinforces actions of insulin 0 After highprotein meal both insulin and glucagon rise 0 lnsulin promotes incorporation of AAs into proteins 0 Glucagon has adaptive advantage high protein meal supplies little glucose but brain needs glucose incr glucagon ensures output of glucose from liver glycogen stores with high insulin Interactions bw insulin and glucagon key in maintaining nutrient homeostasis o Absorbed nutrients l gastrointestinal hormones sympathetic and parasympathetic inputs l act at alpha and beta cells of islets of Langerhans l in uence secretion glucagoninsulin Brain continuously integrates afferent info from secreted hormones and nutrients o Transduces inputs into efferent signals to coordinates glucose production by liver insulinglucagon secretion in pancreas glucose uptake by muscle cells Other hormones contribute to regulation of nutrient metabolism Growth hormone and glucocorticoids act synergistically with epinephrine to enhance it s effect on lipid breakdown Permissive role 0 Glucocorticoid levels prevent glucose levels from plummeting during fastingstress Stimulate glucose formation Required for glucagon and epinephrine to exert their effects Hormones key role in growth of young animals 0 Growth hormone thyroid hormones androgens promote formation of proteins 0 Work synergistically to enhance each other Hormones alter nutrient metabolism during exercisefasting 0 Both require mobilization of fuel from stores 0 lnsulin secretion decr l glycogenlipidprotein breakdown gluconeogenesis incr o Glucagon secretion incr l glycogenolysis and gluconeogenesis in liver 0 Prolonged fasting l thyroid hormone decr l lowers metabolic demands conserves fuel Endocrine Control of Salt and Water Balance in Vertebrates Antidiuretic hormones conserve water Vasopressin AVP antidiuretic hormone ADH produced by neuroendocrine cells in hypothalamus released from axon terminals in posterior pituitary gland o Acts to conserve water by preventing production of large volume of urine Mammals use arginine vasopressin AVP some relatives use lysine vasopression LVP o Nonmammals use arginine vasotocin AVT target tissue nephron of kidneys stimulates reabsorption of water from lumen of nephron water returns to extracellular uid and not excreted o AVP stimulates incorporation of aquaporin AQP water channel molecules in membrane of epithelial cells 0 Water in lumen of tubule destined for excretion unless passes thru ep cells back into interstitial uid and plasma 0 Receptors for AVP on basal side of cells 0 AVP secreted travels in blood to kidneys binds to receptors 0 Thru 2nOI messenger system AVP stimulates movement of AQP2 from intracellular storage vesicles to apical membrane facing lumen 0 Water moves out of lumen osmotically passes into ep cell and out basal side thru AQP3 always present and open Extracellular uid has high osmotic conc or volume low l neurons in CNS stimulate AVP neuroendocrine cells in hypothalamus to secrete AVP o AVP l AQP2 incorporated into apical mem of ep cells l reabsorption of water Extracellular uid low osmotic conclarge volume absence AVP l AQP2 not in membrane no water reabsorption water excreted Endorcrine Principles in Review 5 common patterns of hormonal control 1 Control of any single system likely involved 1 hormones 2 Hormones that affects functions of 1 system probably affects other systems as well 3 Hormones may interact synergistically permissively or antagonistically 4 Most endocrine controls associated with neural controls 5 Many molecules that function as hormones function as diff types of chemical signals in diff contexts Table 164 pg 446 Chemical Signals along a Distance Continuum Categories of mechanism of communication bw cells based on distances involved 1 Gap junctions formed by connexon protein channels bw adjacent cells 0 channels open allow ions and other small molecules to diffuse directly from 1 cell to next 2 Cell adhesion molecules CAMs on external surface of cell membranes important in signaling bw adjacent cells involved in embryonic development wound repair cell growth and differentiation 3 Neurotransmitters released by presynaptic neurons in response to electrical signals 0 diffuse across synaptic cleft to interact with receptors on postsynaptic cell neuron muscle cell endocrine cell 4 Paracrines and autocrines diffuse short distances to in uences cells in local environment including themselves case of autocrines 5 Hormones and neurohormones longdistance communication within animal 0 cytokines communication long dist and locally o 6 Chemical signals outside body 0 pheromones animals of same species 0 kairomones members of dif species 0 ectocrines chem signals that act outside body on members of same or different species Paracrines and autocrines are local chemical signals distributed by diffusion Locally acting chem messengers neuromoduators cytokines eicosanoids Neuromodulators released from synaptic nerve terminals bind to speci c receptors on post synaptic cells 0 Longer duration than neurotransmitters 0 Modify post response to a neurotransmitter by changing conductances of speci c membrane channels 0 Also affect nearby cells with receptor sites Potential to modify functions of entire neuronal circuits Cytokines peptides or proteins secreted by many types of cells 0 Made on demand when needed 0 Act locally as paracrines control cell development and differentiation and immune response long dist 0 Control angiogenesis development of new blood vessels Important in growing animal would healing rebuilding uterine lining after menstruation incr vascular supply to cardiac and skeletal muscle during endurance training Eicosanoids lipidderived paracrines involved in in ammation and allergic responses 0 Produced from arachidonic acid fatty acid 0 2 main classes leukotrienes secreted by white blood cells cause constriction airways in lungs anaphylaxis prostanoids thromboxanes prostagandins cause constriction of blood vessels and aggregation of platelets clot formation n involved in pain in ammation fever Pheromones and kairomones are used as chemical signals bw animals Pheromones chem signals act bw members of same species 0 Produced in animal released to environment 0 Convey info social status sexual readiness food trails alarm o Onset of puberty estrous cycling in uenced o Verts detect with vomeronasal organ VNO olfactory organ 0 Inverts detect with variety of chemosensory structures Kairomones chem released to environment to give info unintentionally to members of diff species 0 Not for communicating released for another function 0 Other species exploit to bene t them may be detrimental to releasing species 0 Elicit behavioral and physiological responses Insect Metamorphosis Metamorphosis life cycles of most insects involve changes in form of animal at different stages Insect metamorphosis may be gradual or dramatic Hemimetabolous gradual metamorphosis 0 Bugs grasshoppers cockroaches 0 Egg hatches Juvenile form of adult nymphs l moltsecdyses l adult 0 Ecdysis with each molt epidermal cells underlying cuticle exoskeleton synthesize a new cuticle od cuticle shed new cuticle expanded while still soft Expands by taking air into foregut incr pressure o Instars periods bw molts Last instar turns into adult Holometabolous dramatic metamorphosis o Beetles butter ies moths Egg l Larva l pupa adult Larvae and pupa don t look like adults Larvae undergo multiple molts turns into pupa Pupa has adult tissues thicker cuticle adult specialized for reproduction O O O O Hormones and neurohormones control insect metamorphosis 3 main hormones prothoracicotropic hormone P39ITH ecdysone juvenile hormone JH molting process begins with neuroendocrine cells producing P39ITH o neurohormone input from brain 0 P39ITH axons extend to pair structures associated with brain corpora allata where axon terminals secrete P39ITH into hemolymph Ecdysis triggered by day length temp crowding o Neurons detect this send excitatory signal to P39ITH cells in brain to stimulate secretion P39ITH carried in hemolymph to thorax stimulates prothoracic glands to secrete ecdysone prohormone that s converted to molting hormone l stimulates epidermis to secrete enzymes that digest old cuticle and synthesize new one JH maintains juvenile characteristics in developing animal 0 Released from nonneural endocrine cells in corpora allata Molting hormone 20hydroxyecdysone and high level ole I insect molts into larger larva or nymph Low level JH l produces adult or pupa Molting hormone and JH soluble in lipids pass thru cell membrane and bind with intracellular receptors in target cells complexes activateinhibit transcription of speci c genes Treat with additional JH become large larvanymph 0 Do with silk worms to get more silk What Aspects of Reproduction Do Physiologists Study Mechanisms of mate association how mates nd each other 0 Pheromones estrus Control of the annual cycle of reproduction mechanisms for reproduction coordinated with annual envir cycles and for seasonal changes Mechanisms of function of the reproductive cellsorgans Coordination of the reproduction organs by neural endocrine and neuroendocrine mechanism 0 Reproductive endocrinology endocrine coordination Delivery of resources to offspring by parents 0 Prenatal transfer large quantities of resources to offspring synthesizing egg yolk o Postnatal bringing food to young nursing o Offspring provisioning processes of feeding young Physiology of the young young at each stage of development maturation process reproduction only successful if young reach sexual maturity Will focus on sexual reproduction o Asexual mechanisms also important polyps on corals produced asexually by budding Parthenogenesis development of an egg Wo fertilization sh bugs Reproduction Once or More Than Once Semelparity vs lteroparity Important reproductive attribute times individual capable of reproducing o Semelparity reproduces single time in life Species is semelparous Ex Marine polychaete worm metamorphoses into reproductive form epitoke release eggsperm undergo programmed death phenoptosis Parents sacri ce their life for vigor of their offspring n Ex Octopus stops eating and protects young until she dies Ex may ies reproductive form has no mouth reproduce and then starve Ex salmon reach sexual maturity migrate up river to spawn stop feeding when enter river catabolize own body for energy to swim spawn then die Rare in mammals o lteroparous individuals capable of 2 separate periods of reproductive activity during life More common Many undergo reproductive cycles a Endocrine and neuroendocrine controlled ovulation induced or spontaneous Very different and more complex parental investment in offspring n bc to reproduce again must refrain from risking own life to protect a life span important determinant of parental investment 0 parents with high probability of early death predicted to make greater sacri ce of their own resources for sake of their young than parent with long future life expectancy Eggs Provisioning and Parental Care 0 Primitive condition small lightly provisioned eggs that hatch into small immature and lightly provisioned offspring 0 Common with aquatic species 0 Huge number of eggs 0 Female has certain amt of yolk available split up to have many eggs egg provisioned with little amt of yolk run out quickly offspring must feed themselves soon after hatching Reproductive diversi cation evolved strategies of delivering increased quantities of provisions to each offspring o More yolk in each egg sharks have huge amt yolk Can only produce a few eggs Yield bigger more mature offspring more likely to survive Ex birds turtles lizards squid o Tradeoff many eggs with little yolk with little survival chance or small number of yolk rich eggs with higher survival chance 0 Other mechanism of providing more provisions to ea offspring o Prenatal provisioning transfer of nutrients form bloodstream of mom to bloodstream of developing offspring Placental animals and species with placentallike structures Mom produces eggs that don t develop to maturity to feed developing offspring many sharks 0 Postnatal provisioning parents gather food for young Lactation Wasps lay eggs on prey serve as food when offspring hatch o Provisioning aids offspring but imposes cost on parents Parents must eat more than normal to provide food they donate to young Parents face reproductive costs per offspring The Environment as a Player in Reproduction Aspects of immediate envir its nutritional social physical aspects crucial Nutritional environment reproductive success threatened if amt food inadequate 0 Eggs hatch in area without suf cient food 0 Reproduction impaired young mice reach puberty later than normal with unfed Malnutrition in reproducing female mammals halt secretion of gonadotropins stops maturation of eggs Social environment males and females must nd each other and achieve states of mutual sexual readiness 0 Male elk don t mate until years after physiologically ready bc must be big and experienced to dominate competing males 0 Males need to control territories to have access to females Physical environment day length temp etc often alter reproduction o Photoperiod hours daylight per day signi cant for species at temp latitudes Varies with time of year provides info on timing of seasons Animals commonly synchronize reproduction with seasons 0 2 main mechanisms for using photoperiod 1 Orchestrate events in annual reproductive cycles by using internal circannual timing mechanisms that endogenously time events for entire year in each cycle a prevailing photoperiod used to adjust internal clock to synchronize with annual events 2 Most don t use endogenous circannual timing instead continually adjust to immediate prevailing photoperiod n Ex mice become reproductively ready during long photoperiods Downregulate readiness when photoperiod shortened n Refractoriness noncyclic endogenous timing process 0 Become unresponsive to photoperiod after exposed for extended length of time o Mammals melatonin an endocrine signal in photoperiod control of reproduction Secreted at night inversely related to photoperiod Pattern of melatonin encodes the photoperiod o Envir temp used as cue for reproduction in temp climates Mate with warm temps Fine tunes timing determined by photoperiod Others tidal cues lunar cues Deserts animals don t depend on cycle instead respond to immediate presence of essential resources rainfall Temperaturedependent sex determination nest temp determines whether egg develops into male or female turtles Temp in uences how fast offspring growreach reproductive maturity Reproduction Endocrinology of Placental Mammals Most mammals are spontaneous ovulators Females ovulate periodically and exhibit menstrual or estrous cycles 0 Female mammals produce all egg cells oocytes during fetal life 0 Total oocytes crucial to fertility de ned at birth 0 may not be true additional oocytes produced after birth from germline stem cells 0 ln fetal ovaries o oogonia diploid germ cells divide repeatedly by mitosis produce many oogonia each undergoes rst stage of meiosis chromosome replicated during fetal life primary oocytes remain as primary oocytes don t complete rst meiotic division until ovulated 0 After female sexual maturity 0 Each ovulation cycle few primary oocytes in ovaries mature undergo ovulation release from ovaries 0 Primary oocyte completes rst meiotic division when ovulated 0 Complete 2nOI meiotic division only if fertilized Spontaneous ovulation females ovulate in cycles until they become pregnant interrupts ovulation cycles 0 Menstrual cycles menstruate each cycle that doesn t result in pregnancy Shed uterine lining and bloodtinged discharge from vagina o Estrous cycles go into estrous heat in synchrony with ovulation During estrus use behaviors and pheromones to indicate they re sexually receptive last few hours to days during each cycle 0 Difference estrus occurs at same time as ovulation menstruation occurs long after ovulation Ovulation occurs in response to surge of luteinizing hormone LH 0 Released from anterior pituitary gland o LH surge produced endogenously in female by series of interacting endocrine and neuroendocrine events Events in the ovaries After female born primary oocyte in ovaries enclosed by single layer of somatic cells 0 Primordial follicle oocyte and its layer of somatic cells Folliculogenesis after reproductive maturity some primordial follicles recruited to mature further during each cycle 0 Follicular phase part of cycle when follicles mature Early follicular phase somatic cells around primordial follicle become cuboidal granulosa cells 0 Follicle now a primary follicle Further maturation primary oocyte incr size secretes around itself a noncellular layer of glycoproteins zona pellucida o Granulosa cells incr form multiple layers Maturation into secondary follicle uid lled cavity antrum opens win layer of granulosa cells 0 Connective tissue on outer part of granulosa cells differentiate into layer of theca cells Only some follicles attain full maturity 0 Species with single offspring 1 dominant follicle matures fully grows by mitotic proliferation of granulosa and theca cells expansion of antrum o Follicular phase ends LH surge oocyte of dominant follicle complete 1st meiotic division 1 daughter cells produced becomes the secondary oocyte fertilized if mating successful Mature Graafian preovulatory follicle fully developed follicle o Positioned under outer epithelium of ovary bulges outward All other unmatured follicles degenerate by programmed cell death atresia 0 Also occurs in species with litters just have multiple follicles mature fully and undergo ovulation During maturation of follicle oocyte and granulosa communicate to coordinate development 0 Make gap junctions across zona pellucida o Granulosa provides signals and nutrient that support oocyte development in uence with oocyte genes expressed o Oocyte paces follicular development sends signals to stimulate granulosa proliferation LH surge activates ovulation enzymes secreted by mature follicle break down layer of ovarian epithelium and follicular wall antral uid pours out carries oocyte Fertilization of ovulated oocyte occurs in oviducts fallopian tubes 0 Oocytes released from ovary swept to opening by ciliary acUon Ovulation end of follicular phase and start of luteal phase 0 Cells of ruptured follicle in ovary reorganize to form corpus luteum o If oocyte not fertilized corpus luteum degenerates o If fertilization occurs corpus luteum grows secretes hormones for establishingmaintaining pregnancy Follicles and corpora lutea endocrine structures Events in the uterus o Endometrium glandular epithelia lining of uterus o Cyclically prepares for pregnancy 0 Pregnancy fails reverts to unprepared state 0 Menstrual cycle sloughs of during menstruation regrows to prepare again 0 Estrous cycle reabsorbed Menstrual phase when sloughing occurs 0 Proliferative phase endometrium regrows rapid thickening redevelops glands and circulatory vascularization o Completes as ovulation occurs Secretory phase endometrium matures to point that its fully ready to accept implantation of embryo and provide embryo with nutritive support during early postimplantation development 0 overlaps with ovarian luteal phase 0 implantation midway thru phase if ovulated egg fertilized Endocrine Control of the follicular phase 0 2 gonadotropic hormones gonadotropins secreted by anterior pituitary major roles in both cycles luteinizing hormone LH and folliclestimulating hormone FSH o secretion controlled by gonadotropinreleasing hormone GnRH neurohormone released from hypothalamus and by hormones created by ovaries o GnRHsecreting ces receive integrated neuralneuroendocrine inputs l generates pulses of APS release GnRH by exocytosis l GnRH carried by blood to anterior pituitary l stimulates secretion of LHFSH in pulses GnRHsecreting ces in uenced by many factors to make integrated message 0 Malnutritionstress l impair GnRH secretion no reproduction o Envir signals photoperiod l affect female reproductive statue seasonal breeders o Kisspeptin neurons role in controlling GnRHsecreting cells respond to steroid estrogen signals 0 During follicular phase blood conc of LHFSH constant 0 Few days before ovulation incr dramatically peak at time of ovulation o LH binds to receptors on theca cells enclosing the follicle Produce androgens Androgens diffuse thru theca cells to granulosa cells 0 FSH binds to receptors on granulosa cells Stimulates enzyme aromatase converts androgens into estrogen by aromatization 0 Result in secretion of estrogen by the follicles Positive feedback estrogen produced by granulosa stimulates mitotic multiplication of granulosa incr cells produce incr amts of estrogen process supports continued proliferation Granulosa cells of dominant follicles don t have LH receptors until later when they incorporate them permits cells to respond to surge of LH that triggers ovulation Estrogen conc in blood affects anterior pituitary and hypothalamus 0 Early follicular development low estrogen levels l negative feedback keeps LHFSH levels low 0 Late follicular development high estrogen levels l increased LHFSH and GnRh secretion l LH surge l triggers ovulation Estrogen stimulates endometrium growth of uterus proliferative phase 0 Stimulates endometrium produce receptors for progesterone steroid in preparation for events after ovulation End of follicular phase granulosa of dom follicles incr inhibin hormone secretion l inhibits FSH secretion Endocrine control of ovulation LH surge causes multiple effects on granulosa cells of dom follicle o Granulosa secrete chemical mediators induce oocyte to complete rst meiotic division 0 Granulosa secrete progesterone decr secretion of E release enzymeprostaglandins breakdown outer follicular membranes an ovarian epithelium Membraneepithelium rupture l antral uidoocyte released from ovary LH causes remaining granulosa and theca cells to transform into corpus luteum Endocrine control of the luteal phase New corpus luteum begins to function Anterior pituitary secrete low level of LH maintains corpus luteum Middle of luteal phase corpus luteum secretes progesterone estrogen inhibin o Conc peak at max endometrial thickness 0 Progesterone and E exert neg feedback on anterior pituitary keep GnRHLHFH secretions low 0 Inhibin suppresses FSH secretion Development of new follicles suppressed bc low LHFSH in luteal phase Corpus luteum establishes conditions for implantationpregnancy o Progesterone secreted by luteum l bind to new receptors on endometrial lining of uterus l exocrine glands secrete glycogenenzymes and more blood vessels develop endometrium Thickened endometrium can support implantation o Progesterone inhibits contractions of smooth muscle in uterusoviducts Pregnancy occurs l embryo provides hormonalparacrine signal prevents degeneration of luteum No pregnancy l luteal cells stop secreting hormone degenerates Degeneration of corpus luteum sets stage for new cycle of folliculogenesis o Hypothalamuspituitary feed of neg feedback LHFSH can rise again Estrus endometrium reabsorbed Menstruation endometrium sloughed off 0 Lack of luteal hormones l endometrium secrete prostaglandins l deterioration of super cial layers l constriction of uterine blood vessels contraction of myometrium smooth muscle on uterine wall l prevents 02nutrients reaching endometrium l cell dies super cial layers lost in menstrual ow leave base of endometrium for next cycle Males produce sperm continually during the reproductive season The testes and production of sperm Paired testes testicles spermhormone production 0 ln scrotum sac suspended outside body cavity 0 Can be brought into body not during reproductive season 0 Must be kept at cooler temp than body some exceptions Sperm produced in coiled seminiferous tubules of testis join coiled tube next to testis in scrotum epididymis Epididymis continuous with vas deferens empties urethra Seminiferous tubules composed of spermproducing cells in various stages and signal layer of somatic cells that supportregulate production of sperm Sertoli cells Connective tissue lls space bw seminiferous tubules Leydig cells interstitial cells located in connective tissue secrete testosterone androgen Endocrine control in males 0 First trimester of embryonic life leydig cells secrete T role in sex differentiation of male structures 0 1214th week after conception genitalia determined Leydig cells less active for remained of uterine life 0 1 month after birth leydig secretes T for short time o puberty leydig secretes T again T remains high throughout life declines gradually after middle age 0 Adult testes T controlled by pituitary gonadotropins production of sperm controlled by gonadotropins and T o Hormones involved same as females 0 GnRH released from hypothalamus in pulses FSHLH secreted from anterior pituitary LH binds to Leydigs l simulates production of T FSH binds to Sertoli cells l in uenced by T from Leydigs o Stimulates spermatogenesis production of sperm haploid thru meiosis in testis o Sertoli cells secrete Paracrine substances promote proliferationdifferentiation of sperm Products that nourish developing sperm lnhibin inhibits FSH secretion Fluid that lls lumens of seminiferous tubules n Fluid contains androgenbinding proteins bind T keep hormone at high conc in lumens of tubules T secreted into general circulation masculinizes tissues 0 Puberty grow of penistestes deepens voice facial hair growth in muscle mass 0 Negative feedback of T and inhibin on anterior pituitaryhypothalamus l keep LHFSH secretions lowsteady o Constant hormone levels sustains continuous sperm 0 production Seasonal breeders hormonal changed shut downreactive sperm production Erection and ejaculation Penis shaft lled with 3 compartments of spongy tissue expanded with blood erection 0 Some animals have bone in penis Nitric oxide N0 messenger molecule immediate mediator of erection o Stimuli l release NO from nerve endings in penis l dilation of O 0 blood vessels blood lls spongy tissue Positive feedback for NO NO mediates synthesis of cyclic GMP 2ncl messenger Semen uid expelled from penis during ejaculation o Consists of sperm and secretion of accessory sex glands prostate seminal vesicles provide uid in semen uid provides energy source for sperm creates suitable envir contains messenger compounds prostaglandins Pregnancy and birth orchestrated by specialized endocrine controls Sperm travel to upper third of oviduct near ovary to meet secondary oocytes 0 Few arrive there only 1 fuses with oocyte to form zygote Capacitation enhances abilities of sperm to swim rapidly and to fuse with membrane of oocyte Sperm competition if female mates with 1 males in brief time sperm of the diff sources vie in reproductive tract to fertilize oocyte 0 Larger testes l more sperm l more sperm to compete After ovulation oocyte in upper third of oviduct bc lumen of oviduct constricted to block travel toward uterus but sperm can pass through Oocyte in oviduct enclosed in zona pellucida and surrounded by granulosa cells 0 For fertilization sperm traverse structures to reach oocyte membrane 0 Head of sperm has enzyme the breaks down extracellular matrix bw granulosa allows sperm to penetrate 0 At zona pellucida sperm releases enzyme by exocytosis from acrosome in head triggered when head binds to proteins on zona pellucida acrosomal reaction 0 Cuts through zona pellucida head adheres to oocyte membrane 0 Only 1 sperm fuses cytoplasms of the gametes become con nuous o Fertilization event which results in formation of a zygote 2 processes after fertilization o Cortical reaction blocks more than 1 sperm from fertilizing the oocyte Cortical granules organelles in fertilized oocyte s peripheral cytoplasm release substances into extracellular space alter membranezona pellucida Prevents adhesionfusion of more than 1 sperm Ensures only 1 haploid set of parental chromosomes 0 Oocyte completes 2nCI meiotic division After single haploid set of maternal chromosomes remains in oocyte 2 haploid sets join make zygote s diploid set Implantation luteal rescue and early pregnancy 0 Implantation entry of early embryo into cellular matrix of endometrium uterine epithelium o Zygote travels to uterus as it does so it undergoes mitotic cell divisions zygote single cell formed by fertilization matures into hollow early embryo blastocyst 0 Trip down oviduct slow possible bc rising levels of progesterone secreted by corpus luteum induce smooth muscles of oviduct to relax oviduct lumen opens o In uterus blastocysts hatches from zona pellucida remains free 3day in humans before implanting o Blastocyst cells that ultimately develop into newborn plus trophoblast cells that don t contribute to newborn help form placenta o Enzymes from trophoblasts enable blastocyst to bury in nutrientrich endometrium begins implantation Progesterone keeps endometrium in developed state 0 placenta main source after placenta develops 0 early pregnancy corpus luteum the main source luteum rescued so it doesn t degenerate must survive 5070 days until placenta takes over unlike 14 days when no pregnancy 0 Rescue of corpus luteum in primates o Chorion embryonic membrane that forms the placenta Secretes hormone chorionic gonadotropic CG l conc rises after fertilization l acts on luteum to extend its life CG excreted in urine basis for pregnancy tests 0 Horses independently evolved gonadotropin secreted by chorion functions similarly to CG to rescue luteum The Placenta First endometrium provides embryo with nutrientsmetabolic support Implanted embryo interacts with uterine structures to form placenta structure with bloods vessels of maternal and embryonic circulatory systems cosey juxtaposed so 02other materials can move readily bw bloodstreams of mom and embryo o Bloodstreams separated by intervening ceuar structures endothelia of blood capillaries substances can diffuse bw but bloods don t mix 0 Maternal blood ow thru placenta supplies embryo with 02nutrients and removes C02metabolic byproducts Placenta nutritive wasteremoval and endocrine structure 0 Secretes E progesterone other hormones to support pregnancy and prepares mom body for birthlactation o Progesterone maintains endometrium inhibits contractions of myometrium muscular portion of uterus o Estrogen stimulates growth of myometrium produced thru aromatase action from androgens Birth Factors that initiate birth parturition largely unknown 0 During period before birth changes occur to prepare mom and fetus late embryo for birth process E prepares myometrium for contractile activity in 2 ways 0 Stimulates myomerial smooth muscle cells to synthesize connexins protein that joins to make gap junctions Gap junctions aow electrical activity to spread thru entire myometrium to produce coordinated contractions o Stimulates myomerial smooth muscle to produce receptors for hormone oxytocin In some mammals reaxin hormone secreted by corpora lutea also helps prepare for birth induces softening of cervix uterine tissue that opens into vagina facilitates establishment of exible connections bw pubic bones n Eases exit of fetus from uterus rapid delivery Oxytocin principle hormone controlling forces that produce delivery 0 Secreted by hypothalamic neurosecretory ces released from posterior pituitary at birth stimulates uterine smooth muscle to producesecrete prostagandins o Oxytocin and prostagandins stimulate contractile activity O Contractions spread over body of uterus toward cervixvagina Forces fetus against cervix stimulates mechanoreceptors 0 Set up positive feedback mechanoreceptors in cervix send APs to hypothalamus l stimulate neurosecretory cells to secrete oxytocin l myomerial smooth muscles respond with contractions l incr contractions force fetus against cervix l mechanoreceptors stimulated more 0 As contractions incr cervical opening dilates permits passage of fetus then placenta delivered 0 Without placenta mom s progesteroneE levels decrease O Neural Control of Skeletal Muscle Is the Basis of Animal Behavior 0 Major function of animal s nervous system to generate its behavior 0 Coordinate motor output of nervous system produces behavior 0 Concentrating on neural circuits that produce simple patterns of motor output Neural circuits assemblies of neuron o What are the patterns of synaptic interconnections bw them that particular patterns of behavioral movements Invertebrate neural circuits involve fewer neurons than vertebrate circuits Invertebrates mostly arthropods and molluscs o 2 generalizations about invert and vert neural circuits 0 1 invert neuron can be a uniquely identi ed neuron neuron whose structure location electrical activity etc are sufficiently distinctive neuron can be recognizedstudied in every individual of a species nearly all vert neurons cannot be uniquely identi ed but can be recognized as member of a population 0 2 invert circuits single individual neurons play functional roles vert circuits many neurons participate in particular func on ex single arthropod neuron may act as command neuron neuron whose activity is sufficient to command a particular element of behavior 0 2 simple invert neural circuits each mediate a re ex a simple graded response to a speci c stimulus one circuit mediates startle escape response of cockroaches other controls gill withdrawal re ex in marine molluscs each circuit depends on tens of neurons in circuit few mechanosensory neurons excite central interneurons to excite some motor neurons inhibit others lead to selective activation of muscles to produce re exive response circuits of inverts can be re exive of centrally programmed Vertebrate spinal re exes compensate for circumstances and initiate movements Spinal re exes mediated by circuits of vert spinal cord 0 Best known of vert circuits 0 Sensory input from receptors of skin muscles tendons joints enter spinal cord thru dorsal roots input via intervening synapses in spinal cord excites motor neuronsinhibit other lead to movements by selectively activating muscular contraction 0 Inputs from diff populations of receptors have diff connections in cord initiate diff re exes The Stretch Re ex myotatic re ex a spinal re ex Essential for maintenance of posture and coordination of movements 0 Ex patellar re ex kneejerk rxn response to tap on patellar tendon at knee joint 0 All skeletal muscles continuously involved in generating stretch re exes Large axons and few synapses in circuit Hammer tap stretches knee extensor muscles in thigh stimulates muscle spindles contain stretchsensitive endings of receptors wrapped around noncontractile portions of specialized intrafusal muscle bers 0 1a afferent bers sensory axons associated with muscle spindles o afferent conducting toward CNS 0 1a largestmost rapidly conducting sensory bers in body 0 1a axons from spindles enter spinal cord make direct excitatory synaptic contact with motor neurons to same muscle 0 unusual most vert neurons directly synapse onto interneurons intrinsic neurons that don t leave the CNS OOOO 0 simple stretch re ex only involved 2 kinds of neurons 1a sensory and motor neurons muscle spindle stretched 1a generates train of nerve impulses elicit excitatory postsynaptic potentials EPSPs in motor neurons 0 if EPSPs depolarizations meet threshold motor neuron impulses contraction of stretched muscle leg kicks 0 muscle spindle are in parallel act besides with extrafusal bers generate substantive contractile forces of muscle sensitive to muscle length incr length l incr activity 1a axons also synapse on other neurons in addition to motor neurons 0 some connections stimulate excitatory interneurons that excite motor neurons to muscle that works in parallel with rst muscle 0 other synapses stimulate excitatory interneurons that inhibit motor neurons to that antagonist opposing muscle 0 tap excites motor neurons to extensor muscle to produce knee jerk also inhibits motor neurons to antagonist exor muscle Reciprocity principle muscles or groups of muscles tend to be arranged in antagonist pairs that oppose each other 0 Signals that activate movements coordinated to contract a set of muscles that work together agonists while relaxing the opposite set antagonist o Ensures 2 muscles don t counteract and suppress movement 0 Stretch re ex stretch extensor muscle activates extensor motor neurons contract extensor relieve stretch AND inhibit exor motor neurons prevent cocontraction Many neurons involved in even simple behaviors o la extensor motor neuron represent larger populations of these neuron types 0 Leg muscle has many muscle spindles stretch activates many sensory neurons 0 Each 1a neuron synapses with all motor neurons to same muscle and many interneurons of diff types convey info to higher brain centers The Flexion Re ex Ex Step on tack re exively withdraw foot drawn up by contraction of exor muscle of thigh Flexionre ex afferents array of sensory neurons in circuit mediating exion re ex o Endings in skin muscles joints sensitive to painnoxious stimuli 0 make excitatory synaptic contacts on interneurons in CNS excite motor neurons to exor muscles and inhibitory interneurons 0 make only indirect connections to motor neurons via at least 1 layer of intervening interneurons function protective o re ex circuit short local rapid o exionre ex afferent also connect to interneurons ascending spinal cord to brain so you re aware of painful stimulus slower so foot lifted before you know why 0 many receptors other than pain can trigger exion re exes 0 function provide proprioceptive and cutaneous info to brainspinal cord not just elicit re ex Ex step on tack also extend other foot to catch you 0 Flexionre ex afferents synapse onto interneurons that cross midline of spinal cord indirectly excite extensor motor neurons of contralateral opposite side leg 0 Right leg extended by exciting extensor motor neuronsinhibiting exor motor neurons while left leg exed by exciting exor motor neuronsinhibiting extensor motor neurons 0 Crossed extension re ex re ex extension of contralateral leg lntegral part of exion re ex Functional roles of re exes Protection posture Ex load compensation person jumps on your back re exively excites motor neurons to extensor muscles generated more muscle force to counteract increased load maintain posture Gamma motor neurons responsible for motor innervation to stretch receptor organ innervated population of motor neurons in intrafusal muscle bers 0 ln muscle spindles 1a neurons associated with intrafusal muscle bers innervated by population of small motor neurons gamma motor neurons 0 Extrafusal bers all other bers not part of muscle spindles innervated by alpha motor neurons 0 Activation of gamma excites 1a by contracting contractile ends of intrafusal bers stretches noncontractile central sensory portion of spindle distorts distal end of 1a 0 o 2 ways to incr musclespindle activity 0 stretching muscle 0 gamma motor neuron activity gamma and alpha motor neurons have opposite effects on spindle sensory activity 0 AP of gamma activity intrafusal ber contraction stimulates 1a 0 AP of alpha activity extrafusal contraction relieves stretch stimulus on spindle Motor neurons activated primarily by central input rather than by spinal re exes 0 Primary input to motor circuitry of spinal cord input from brainspinal cord circuits 0 Secondary input sensory bers mediating spinal re exes Major role of sensory input to spinal cord l supply sensory feedback modulatescorrects responses of motor neurons to central signals 0 Ex pick up pamphlet 0 Voluntary movement l CNS programs the activation of motor neurons 0 CNS estimates amt of forces needed to pick up sends command to motor neurons to generate that force 0 At same time stretch re ex mediates load compensation augmenting contraction if there s extra weightresistance added to intended movement 0 Alphagamma coactivation voluntary movement excited both types of motor neurons 0 2 functions 0 1 ensures that ongoing sensitivity of spindles maintained during muscle shortening wo shortening contraction would slacken intrafusal ber unload spindle decr sensitivity 0 2 allows spindle to determine whether muscle shortens during intended movement if CNS correct coactivation activates contraction of intra and extrafusal bers of working muscle if CNS estimates incorrectly and muscle spindle doesn t shorten stretch receptor activity serves as error signal loadcompensating servo loop neuron pair of stretch receptors and alpha motor neurons make re ex circuit that detects an error failure to shorten and counteracts more force with centrally commanded movement Neural Generation of Rhythmic Behavior 0 Most behavior consists of action patterns sequences of effector actions that results from sequences of motor outputs of nervous system Rhythmic behavior stereotyped repetitive sequences of movement waling swimming ying in which motor output is stable repeatable and predictable from cycle to cycle of the activity Locust ight results from an interplay of central and peripheral control 0 Movement of single wing updown oscillation generated by set of elevatorlevator and depressor muscles 0 Depressors activated when wings up 0 Levators activated when wings down 0 Flight results from generation in CNS of alternating AP bursts in lavatorydepressor motor neurons 0 2 hypotheses to explain neural basis of rhythmic movement 0 1 peripheral control each movement activates receptors that trigger the next movement in the sequence position of wing monitored by several proprioreceptors winghinge stretch receptor generates train of impulses when wing elevated others activated when wing down 0 2 central control ight sustained by central pattern generator CPG neural circuit in CNS generates sequential patterned activation of motor neurons to antagonistic muscles no sensory feedback required to trigger next movement 0 cut nerves could maintain ight in absence of sensory feedback 0 indicated central control responsible 0 but ight was slower indicates that sensory stimulation provides general excitation to CNS but not needed to supply timing info for pattern generation sensory input essential for correcting basic pattern uneven terrain Control and Coordination of Vertebrate Movements o How does a cat walk 0 Cat nervous system has 3 parts that can in uence movement brain spinal cord sensory input 0 Generators of walking spinal motor neurons 0 Motor neurons receive indirect input from 3 sources 1 input from brain 2 sensory input from proprioreceptorsother peripheral receptors 3 local input from intrinsic spinal circuits Locomotion in cats involves a spinal central pattern generator 0 Cat able to make fairly normal stepping movements after transection of spinal cord to remove brain in uence 0 Brain doesn t provide timing info for walking 0 Thought to command expression of walking pattern by spinal circuits lncr stimulation incr rate of locomotion gait changes 0 Brain may initiate locomotionmodulate to conditions Sensory feedback from hindlimbs unnecessary for stepping movements 0 Sensory feedback still has functional roles o Spinal re exes stabilizemodulate effects fo centrally patterned locomotor output Spinal re exes may be modulated by CPG o Reversal of spinal re ex shows that central events of stepping cycle can modulate re ex function Central pattern generators are distributed and interacting Interactions of CPGs sufficient to coordinate diff gaits as well as their transitions The generation of movement involves several area in the vert brain Locomotor movements don t require brain but brain important in initiation coordination regulation of normal movement Productioncontrol of complex motor functions attributed to brain structures and spinal motor circuits 0 O Cerebral cortex Primary motor cortex governs voluntary movement Pyramidal cells neurons of primary motor cortex mediate motor responses to stimulation Axons end on interneurons in spinal cord Activate spinal motor circuits directly via corticospinal tract and indirectly via brainstem motor nuclei Individual neuron activities encode forcedirection of movements For some amt of activity predicts amt of force For others predicts change of force Other predicts direction To initiate voluntary movement electrical activity in brain becomes localized to relevant portion of primary motor cortex preceding movement To organize movements mosaic area activate motor cortical regions connect directly to spinal cord Premotor areas properties of neurons in these area not simply motor Mirror neurons code for abstract concept of movement rather than its execution a Function in understanding of actions and imitative learning Cerebellum large highly convoluted structure at dorsal side of hindbrain O O Regulates movement indirectly adjusts descending motor output from other brain areas involved in coordination of movement wo voluntary movements still possible but are clumsy supports smoother and coordinated execution of complex movements by evaluating motor commands and sensory feedback provides error correction signals o coordinates ongoing movements and motor planning 0 learns motor tasks so they can be performed unconsciouslyautomatically in appropriate sensory context motor learning involves changes in synaptic strength Basal Ganglia set of nuclei clusters of brain neurons located in forebrain and midbrain 0 Basic circuits a loop circuit output of circuit loops back to site of input Important for motor control emotions etc 0 Important in selecting movements suppressing competingunwanted movements and initiating selected movement most neurons in circuit are inhibitory The interaction of brain areas in movement control 0 Decision to move starts in cortex 0 2 loop circuits from cortex involved in preprogramming a movement 0 1 loop goes thru basal ganglia selectioninitiation 0 other thru lateral cerebrocerebellum initial programming 0 both feed back to motor cortex which generates appropriate pattern of activity to initiate movement 0 command monitoring informs cerebellum of intended movement 0 integrates feedback All organized movements depend on generations of forces that require conversion of chemical energy to mechanical energy Contractile proteins myosin and actin 0 Muscle cells use molecular motor myosin to captureconvert chemical energy ATP into mechanical energy Interacts with actin to generate force 0 Muscle tissue consisting of specialized contractile cells 0 2 categories of muscle cells 0 Striated muscle have alternating transverse light and dark bands give striped appearance Sarcomeres repeating bands of contractile proteins Makes up skeletal attached to bones and cardiac heart muscles 0 Smooth muscle possesses contractile proteins not organized into sarcomeres Found in hollowtubular organs intestines uterus blood vessels Vertebrate Skeletal Muscle Cells Skeletal muscles composed of bundles of long cylindrical muscle berscells o Connective tissue holds bers together provides matrix for nerve bers and blood vessels to gain access to bers gives elasticity to whole muscle Weaves into tendons attach muscle to bond transmit force generated by bers to skeleton o Skeletal muscle bers are multinucleate contain many nuclei bc form by fusion of individual cells myoblasts Fiber surrounded by cell membrane sarcolemma Each ber contains hundreds of parallel cylindrical myo brils small in diameter but as long as ber 0 Each has repeating transverse bands 0 A bands major dark bands 0 l bands lighter bands only thin laments ln middle is a narrow dense Z disc Z line Sarcomere portion of myo bril bw 1 Z disc and next Z disc 0 1 myo bril consists of longitudinal series of repeating sarcomeres Myo brils sarcomeres contain 2 kinds of myo laments 0 thick laments composed of myosin con ned to A band of sarcomere 0 thin laments composed of actin consists of 2 chains of globular actin molecules wrapped around each other in helix anchored to proteins in Z discs extend partially into A band H zone central region of A band contains only thick laments and appears lighter than rest of A band M line narrow dense region that bisects the H zone Z disc and M line ensure that thin nor thick laments oat free Intermediate laments diameter bw thick and thin contribute to architectural integrity of muscle ber Crossbridges radial projects heads on myosin molecules 0 When ber stimulated to contract crossbridges interact transiently with overlapping actin thin laments o Interactions of crossbridges with actin generate force for muscle contraction Sarcomeres contain specialized proteins in addition to actinmyosin o Titin and nebulin structural proteins help align contractile proteins 0 Troponin and tropomyosin proteins associated with actin chains of thin laments regulates process of contraction by controlling whether or not myosin crossbridges can interact with thin laments When muscle ber contracts thick and thin laments don t shorten instead they slide by one another 0 sliding lament theory force of contraction generated by crossbridges of thick laments attaching to thin laments and actively pulls then toward center of the sarcomere Thick and thin laments are polarized polymers of individual protein molecules Myosin molecules large proteins each consisting of 2 globular heads joined to long rod tail 0 Heads are crossbridges 0 Tail contributes to backbone of thick lament 0 During polymerization myosins orient themselves with tails pointing to center of thick lament and heads toward ends Actin molecule globular protein Gactin O O O Gactin monomer forms chains of Factin lamentous actin 2 chains of Factin wind around each other in helix arranged in thin laments so that those on one side of Z disc have 1 orientation those on other side have opposite direction bc of polarized organization of thickthin laments l crossbridges in contact with thin laments can act like oars to pull thin laments toward center of sarcomere Muscles require ATP to contract Myosin heads cyclically attach to actin then swivel to pull on actin lament O 0 Each head as 2 biding sites 1 for actin other for ATP Binding site for ATP ATPase that splits inorganic phosphates from ATP captures released energy energy used to power crossbridge action Crossbridge cycle Cycle of molecular interactions underlying contraction O 1 rigor conformation transient state myosin head bound to actin but is not binding ATP brief bc myosin heads readily binds ATP 2 ATP required for myosin to unbind from actin not release of ATP myosin head binds to ATP causes head to detach from actin 3 myosin head hydrolyzes ATP to ADP and inorganic phosphate P ADP and P remain attached to head Energy released stored in myosinADPP complex 4 complex binds actin forming actinmyosinADPP complex initially actin binding weak triggers P release tighter binding 5 power stroke head swivels pulling attached actin toward middle of myosin lament o 6 end of power stroke ADP released myosin remains tightly bound to actin step 1 rigor with each cycle 1 ATP consumed myosin molecule moves actin lament short distance during single contractile event stimulated by muscle ber AP each crossbridge repeats several unbinding cycles works independently at any instant during contraction some bridges are bound to actin while rest are in other phases of cycle summed effect of repeated crossbridge cycles pulls thin lament toward middle of sarcomere Calcium and the regulatory proteins tropomyosin and troponin control contractions Resting muscle myosin head detached from actin hydrolyzed the ATP stores the energy primed for another cycle Regulatory proteins tropomyosin TM and troponin TN prevent contraction by inhibiting most of myosin heads from binding to actin 0 TM lies along groove bw 2 actin chains of thin lament 0 Single TM exends length of 7 actin molecules 0 Each TM associated with 1 TN TN is a complex of 3 subunits o handle binds to TM 0 quotclubquot binds to actin o TNC binds Ca2 ions Resting state TM lies over myosinbinding sites fo adjacent actins prevents crossbridges from binding to actin Contraction TM s inhibition counteracted by binding of Ca2 to TN 0 Key physiological regulator of muscle contraction is calcium 0 Ca2 binds to TNC triggers conformational changes in TN TM and actin 0 Now primed myosin crossbridges permitted to go thru cycles until Ca2 removed 0 Muscle only contracts when Ca2 available ExcitationContraction Coupling Excitation triggers skeletal muscle contraction 0 Each ber innervated by motor neuron 0 AP conducted to axon terminal of motor neuron releases acetylcholine binds to postsynaptic acetylcholine ACh receptors 0 Causes permeability changes results in depolarization of ber membrane sarcolemma and generation of an AP 0 Excitation depolarization of muscle ber leads to rapid activation of contractile machinery of ber 0 Excitationcontraction coupling relationship bc depolarization and contraction Excitationcontraction couple by 2 separate associated membrane systems 0 Transverse tubules ttubules system of tubules that s continuous with sarcolemma Each dips into ber at angle perpendicular to sarcolemma transverse to long axis of ber lnvaginates at regular intervals along length of sarcolemma ttubule membrane continuation of outer sarcolemma so tubule lumen continuous with extracellular space when sarcolemma depolarized ttubules conduct excitation into interior of ber ttubules come into close contact with 2nCI membrane system 0 sarcoplasmic reticulum SR branching network of tubules within the ber each myo bril enveloped in SR SR membrane has Ca2ATPase activetransport pumps that maintain low conc of Ca2 ion in cytoplasm and high conc within SR 0 SR compartment SR bw 2 ttubules 0 Each compartment forms sleeve around each myo bril 0 Terminal cisternae enlarges sacs next to ttubules Ca2 con ned here in resting muscle 0 AP conducted along sarcolemma depolarizes ttubule Ca2 ions released from SR into cytoplasm o In skeletal muscle membrane systems linked by 2 kinds of membrane proteins 0 DHPRs of ttubules voltagesensitive calcium channels ln skeletal muscle they don t permit Ca2 ux 0 RyRs of the SR membrane face the DHPRs 0 Both are calcium channels interact directly with each other oneonone 0 When RyRs open let Ca2 diffuse out of SR into cytoplasm Depolarization of ttubules changes conformation of DHPR alters conformation of RyRs in SR opens it to release Ca2 0 Motor neuron AP triggers excitation and contraction of muscle ber 0 RyR channels of SR open Ca2 diffuse to adjacent myo laments bind to troponin initiate processes that allow crossbridge action 0 When ber AP ends ttubules repolarize RyRs close 0 Ca2 no longer leaves SR Ca2 left is returned by action of Ca2ATPase pumps Cytoplasmic Ca2 conc decreases Ca2 unbinds from TN TM blocks myosinbinding sites on actin prevents crossbridge action relaxation occurs Vertebrate Smooth Muscle Main function of skeletal muscle locomotion Found in gastrointestinal respiratory reproductive urinary tract blood vessels 0 ln eye control size of pupil and shape of lens 0 At base of hairsfeathers In hollowtubular organs permits many functions 0 Changing in sizevolume bladderstomach o Propelling materials along tube intestine urine 0 Maintain tension for long periods of time walls of arterioles Variety in arrangement within organs types of stimuli types of electrical activity generated Use contractile proteins actinmyosin 0 not organized into sarcomeres o organized into bundles around periphery of cell 0 crossbridge action causes them to slide by one another l contraction has more actin more thin laments o actin laments attach to dense bodies in cytoplasm 0 intermediate laments also attach to dense bodies to help for cytoskeleton spindleshape widest diameter around nucleus tapered at ends 0 stimulated crossbridges actions causes cell to shorten plump up in center linked by mechanical connections and to surrounding connective ssue o ensures transmission of force thru entire tissueorgan small diameter single nucleus 0 absences of transverse tubules troponin nebulin reduced SR 0 invaginations of cell membrane contributes to rise of Ca2 bc of coupling groups of muscle cells depolarizedcontract together I function as single unit o spontaneously active electrical activity propagates via gap juncUons o activated by stretch multiunit smooth muscle fewno gap junctions muscle cells funcUonindependenUy o tonic smooth muscles maintain contractile force for long periods don t generate spontaneous contractions or APs phasic smooth muscles produce rhythmic or intermittent activity 0 contract rapidly produce spontaneous contractions generate APs that propagate from cell to cell via gap junctions Vertebrate Cardiac Muscle forms walls of heart function to propel blood thru vascular system 0 is striated has sarcomeres cells branched uninucleated functional properties contribute to pumping blood 0 intercalated discs gap junctions and localized mechanical adhesions desmosomes and fasciae adherentes bw adjacent cells adhesions provide ensure coordinated pumping electrical coupling at gap junctions ensures all cells contract synchronously o capable of generating endogenous APs at periodic intervals pacemaker cells impose rhythm 0 APS have very long durations ensure prolonged contraction 0 Ch 22 Introduction to Oxygen and Carbon Dioxide Physiology 0 Transport refers to all movements regardless of mechanism 0 Active transport mechanisms for 02 don t exist 0 For 02 to move conditions must be favorable for passive transport toward cells during each step along the way 0 Respiratory gases 02 and C02 0 Cannot survive Mo 02 o Urgency arises from role 02 plays as the nal electron acceptor in cellular respiration 0 Energy cannot be transferred from bonds to food molecules to bonds of ATP by aerobic catabolic apparatus of cell unless 02 available in mitochondria to combine with electrons exiting the e transport chain 0 Export of C02 a pressing concern bc accumulation of C02 in body can rapidly acidify body uids and exert other harmful effects 0 Respiratory gases move by 2 mechanisms simple diffusion and convection bulk ow 0 C02 sometimes actively transported in form of bicarbonate ions HC03 formed by rxn with water 0 Chemical potential and how its expressed in studies of gases 0 Diffusion of glucoseother uncharged solutes in aqueous solu 1 solute always diffuses from regions of solu with high concentration to regions of low conc 2 rate of diffusion directly proportional to its difference in conc bw regions 0 chemical potential strength of tendency of a chemical substance to undergo a physical or chemical change 0 provides basis for truly general law of diffusion in all cases of diffusion materials tend to move in net fashion from regions when their chemical potential is high to regions where its low and at a rate proportional to the diff in chemical potential 0 within a single aqueous solu concentration of a solute amt of solute per unit of volume useful surrogate for chemical potential 0 concentration not useful surrogate for chemical potential when analyzing diffusion of materials bw gas mixtures and aqueous solu o 02 and C02 exist in both phases and diffuse bw them 0 Use partial pressure to express chemical potential in study of gases The Properties of Gases in Gas Mixtures and Aqueous Solutions Gases dissolve in aq Solutions 0 When gas dissolved molecules of gas become distributed among H20 molecules they disappear 0 Gas phase gases in gas mixtures 0 Liquid phase gases in aq solu Gases in the gas phase Law of partial pressures total pressure exerted by mixture of gases is the sum of individual pressures exerted by each of the component gases 0 Partial pressure of a gas individual pressure exerted by any particular gas in gas mixture Independent of other gases present Partial pressure of each gas in mixture can be calculated from universal gas law PVnRT 0 To use set n equal to molar quantity of the particular gas of interest and V equal to volume occupied by the gas mixture as a whole Fractional concentrations proportions of gases in mixture 0 Mole fraction concentration of particular gas fraction of total moles of particular gas present 0 Volume fractional concentration of particular gas fraction of total volume of particular gas Equal molar quantities of diff gases occupy essentially equal volumes so the 2 should be about the same Partial pressure exerted by each gas in mixture is quotits fractionquot of the total pressure where quotits fractionquot means the mole or volume fractional conc of the gas 0 Px Fthot Ptot total pressure of gas mixture Px partial pressure of particular gas x in mixture Fx mole or volume fractional conc of that gas x In gas phase partial pressure and conc of any particular gas are proportional to each other at any given T Gases in aqueous solution 0 Partial pressure of a gas dissolved in an aq solution the particle pressure of the gas in a gas phase with which the solu is at equil Henry s law relates partial pressure and conc in aq solu 0 Absorption coefficient A the dissolved conc of a gas when partial pressure of the gas in solu is 1 atm A measure of gas solubility a High A high solubility a lot of gas will dissolve at any partial pressure Cx dissolved conc of the gas Cx APX ln gas phases this equation same as previous ln aq solu proportionality constant A varies among types of dissolved gas and depends on T and salinity of the water 0 3 important characteristics of gases dissolved in aq solutions 0 solubilities of diff gases are diff C02 has higher solubility than 02 or N2 0 Solubilities of gases in aq solu decrease with increasing water temp Gases tend to come out of solu and form bubble as water warms o Solubilities of gases in aq solu decrease with increasing salinity lncr salinity l drives gases out of solu saltingout OOOO Diffusion of Gases Gas molecules move ceaselessly at random on molecular scale when chemical potential of gas differs from place to place random movements carry more gas away from regions of high chemical potential net gas transport occurs Fundamental law of gas diffusion gases diffuse in net fashion from area of relatively high partial pressure to areas of relatively low partial pressure 0 Does not necessarily mean that diffusion occurs in direction of conc gradient 0 Min gas mixture of uniform temp or win aq solu of uniform temp and salinity if partial pressure of particular gas greater in 1 regions than another conc is also greater gases diffuse high to low partial pressure and diffuse from high to low conc o in complex situations gas can diffuse from low to high conc as long as moving from high to low partial pressure 0 equilibrium attained with respect to any given gas when partial pressure of gas is uniform everywhere in system 0 rate of gas diffusionJ K P1P2X 0 P1 high partial pressure 0 P2 low partial pressure 0 Gas permeability K depends on particular diffusing gas temp ease with which gas able to pass thru material separating the 2 regions of P Gases diffuse far more readily thru gas phases air than thru aqueous solutions 0 Burrowing and eqqburying animals receive 02 by diffusion of air thru interstitial spaces 0 Small amt uid in air spaces of lungs causes emergency bc of small diffusion distance that s tolerable with water present Gas molecules that combine chemically with other molecules cease to contribute to the gas partial pressure 0 Only gas molecules that exist as free gas molecules contribute to partial pressure of a gas 0 Only gas molecules that are free in solution unchanged affect the directionrate of gas diffusion Convective gas transport bulk ow occurs when gas mixture or aqueous solution ows and gas molecule are carried by uid ow 0 Ex Transport of 02 by blood ow Faster than gas diffusion forced fashion rather than depending on random movements 0 Do so by 2 processes breathing and pumping of blood Oxygen cascade sequential drop in partial pressure of 02 from one step to the next in the series of steps by which 02 is transported from the environment to mitochondria Ch 23 External Respiration The Physiology of Breathing
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