CardiovascularSystem心脏的发育-经典课件

Cardiovascular SystemNote: The cardiovascular system develops early, enabling the embryo to grow beyond the short dis-tances over which diffusion is efficient for transferring O2, CO2, and cellular nutrients &:From a simple tube, the heart undergoes differential growth into a four chambered structurewhile it is pumping blood throughout the embryo and into extra-embryonic membranes.

The heartinitiates a peristaltic pumping action by about 18 days in the ion of a Tubular Heart:The first evidence of heartamnionic cavitydevelopment is bilateral vesselformation within the cardiogenicembryoectodermplate, which is splanchnic mesodermsituated anterior and lateral to thecardiogenicendodermembryo. As the head process growsplateyolk sacmesodermupward and outward, bilateralendocardial tubes meet at the mid-line and fuse into a single endocar-embryodial tube. Splanchnic mesodermsurrounding the tube forms cardiacheartmuscle sacPrimitive Heart Regions:Differential growth of the endocardial tube establishes five primitive heart regions:1] Truncus arteriosus — the output region ofthe heart. It will develop into the ascendingaorta and pulmonary s2] Bulbus cordis — a bulb-shaped regionarteriosusdestined to become part of the right ventriclebulbus(conus arteriosus).cordus3] Ventricle — an enlargement destined tobecome the left cle4] Atrium — a region that will expand tobecome both right and left 5] Sinus venosus — a paired region intoLRLvenosusatriumwhich veins drain. The left sinus venosusbecomes the coronary sinus; the right isMidline FusionRTubular Heartincorporated into the wall of the right g a Four-Chambered Heart:A] The endocardial tube lengthens and loops on itself—this puts the bulbus cordis (right ventricle)beside the ventricle (left ventricle).23

B] Venous return is shiftedto the right side. The right sinusvenosus becomes enlarged andincorporated into the future rightatrium. The smaller, left sinusvenosus merges into the future rightatrium as coronary atrium expands and overliesthe interventricular opening, creating acommon atrioventricular opening (canal).A constriction, the future coronary groove,separates atria and future ventricles at thelevel of the atrioventricular lbulbuscordistruncus

arteriosusatriumsinus

venosuscommonatrioventricularopeningbulbuscordisventriclesinus

venosusatriumventriclecaudalSagittal SectionEndocardial TubeC] The common atrio-ventricular opening is partitioned into right and left A-V openings bygrowth of endocardial cushions. Subsequently, ventral growth of the cushions produces a septumthat closes the interven-endocardialtricular foramen (thetruncuscushionoriginal opening betweenarteriosusatriumthe bulbus cordis andatriumventricle).Incomplete closure ofthe interventricular septum(ventricular septal defect)results in blood flow from theleft to the right ventricle and anassociated murmur. Largedefects produce clinical signsof cardiac cordisventriclerightventricleinterventricular: foramen septumleftventricleVentricleDevelopmentD] The right andleft ventricles are formed by ventral growth and excavation of the bulbus cordis and ventricle,respectively. An interventricular septum, atrioventricular valves, chordae tendineae, papillarymuscles, and irregularities of the internal ventricular wall are all sculptured by selective excavationof ventricular wall tissue.E] Right and left atria are established by formation of an interatrial septum. Septum forma-tion is complicated by the need, until birth, for a patent septum that allows blood to flow from theright atrium to the left. The septal opening issecondary septumcalled the foramen rialTwo septae and three foramina are involved inopeningsecondarydividing the atria:foramenInteratrial Septum 1 grows from the dorsal wallpath ofof the atrium toward the endocardial cushions at theblood flowatrioventricular canal. The pre-existing Foramen 1 isobliterated as Septum 1 meets the endocardial rimary septumForamen 2 develops by fenestration of theatrium(valve of )foramendorsocranial region of Septum nteratrial Septum 2 grows from the cranialwall of the right atrium toward the caudal wall. Theseptum remains incomplete and its free edge forms theBlood Flow Through Foramen Ovaleboundary of an opening called the Foramen Ovale.24

NOTE: As long as blood pressure in the right atrium exceeds that of the leftatrium, blood enters the Foramen Ovale, flows between the two septae andexits through Foramen-2. When, at birth, pressure is equal in the two atria,Septum-1 is forced against the Foramen Ovale, acting as a valve to close theforamen and preclude direct blood flow between the atria.

An atrial septal defect is not a serious developmental anomaly as long as pressure isapproximately equal in the two atria, which is normally the case.F] Aorta and pulmonary trunk are formedaortaby partition of the truncus arteriosus

(and adjacentbulbus cordis). In a spiral pattern, ridges appear alongcaudal

the lumen wall, grow inward and merge creating avena cavapulmonaryspiral septum. As a result, the aorta and pulmonarytrunklefttrunk spiral around one another.

Failure of the septumrightatriumto spiral leaves the aorta connected to the right ventricle andatriumthe pulmonary trunk to the left ventricle—a fatal and pulmonary semilunar valves arerightleftformed like atrioventricular valves, by selectiveventricleventricleerosion of cardiac/vessel wall.

Improper valve sculptur-ing will produce valvular insufficiency in the case of exces-sive erosion or vessel stenosis (narrow lumen) in cases of notenough Arrangement of theAorta & Pulmonary Trunkaorta or pulmonary trunkvessel wall excavationsemilunarcuspNote: Neural crest cellsmigrate to theregion of thetruncus arteriosusflowand direct itsfrompartitioning by theheartspiral pment of semilunar valves by excavationAblation of theneural crest resultsin anomalies of thegreat ogy of Fallot:This is a cardiac anomaly that occurs in number of species, including humans. It involves a combination of fourdefects related to a defective spiral septum formation in the truncus arteriosus & bulbus cordis:• ventricular septal defect;• stenosis of the pulmonary trunk;• enlarged aorta that overrides the right ventricle (dextroposition of the aorta); and• hypertrophy of the right ventricle, secondary to communication with the high pressure left :Early in development, blood islands form in splanchnic mesoderm of the yolk sac andallantois. Angiogenesis (vessel formation) occurs when island vesicles coalesce to formchannels. Subsequently, hematopoiesis (blood cell formation) occurs in the liver and spleenand later in the bone marrow. The transition from fetal to adult circulation involves newvessel formation, vessel merger, and vessel degeneration.25

rightintersegmental aortacranialcardinal cardinal cal orticarchventralaortavitelline oicvesselscaudalcardinal ine cal ranchEarly

Arteries

& VeinsArteries:yolk sacvesselsDorsal and Ventral Aortae:The embryo develops paired ventral and dorsal aortae. The two ventral aortae receive bloodfrom the truncus arteriosus. Bilaterally, ventral and dorsal aortae are connected by a series of sixaortic arches. Each aortic arch is situated within a pharyngeal (branchial) ventral aortae fuse to form the brachiocephalic trunk. Caudal to the aortic arches, thepaired dorsal aortae merge to form a single descending aorta, as found in the adult.

The aorta gives offdorsal, lateral, and ventral branches, some of which persist asadult vessels. Aortic arches become carotid, subclavian, arch ofthe aorta, and pulmonary carotid alcarotid alcarotid ratingdorsalaortaductusarteriosuspulmonary 7thintersegmental ding aortaaorticarch 3dorsalaortaDisposition of Aortic Arches:Only the third, fourth, and sixth aortic archesbecome adult vessels.

The first two arches degenerate andthe fifth arch is rudimentary or third aortic arch becomes an internalcarotid artery.

The dorsal aorta degenerates between the thirdand fourth aortic arches. Consequently, the third arch suppliesthe head and the fourth arch supplies the more caudal external carotid artery buds from the third arch. Proximal tothis the third arch forms common carotid arch 4aorticarch 6right 7thintersegmental ratingright dorsal aortaThe left fourth aortic arch becomes the adultarch of the aorta.

The right fourth aortic arch becomes theproximal part of the right subclavian artery as the distal connec-tion between the arch and the dorsal aorta normally tence of a connection between the fourth aortic arch andthe descending aorta results in compression of the esophagus,accompanied difficult swallowing and an enlarged esophaguscranial to the Arches 3, 4, 6(Dorsal View)The proximal part of each sixth aortic arch becomes a pulmonary artery. The distal part of thearch degenerates on the right side but persists as ductus arteriosus on the left side.26

Note:The ductus arteriosus shunts blood from the pulmonary trunk to the shunt allows the right ventricle to be exercised in the face of limitedcapacity of the lungs to accept blood. At birth, constriction of the ductusarteriosus abruptly shifts pulmonary trunk output to the lungs. Eventually, aligamentum arteriosum replaces the constricted ductus arteriosus.A persistent ductus arteriosus results in a continuous murmur during both systole vian & Vertebral arteries:Each dorsal aorta gives off intersegmental arteries that pass dorsally between somites. The seventh cervicalintersegmental artery becomes the distal subclavian artery egmental arteries cranial to the seventh to form the vertebral artery (by degenerating proximally andanastomosing distally). Intersegmental arteries caudal to the seventh cervical become intercostal and lumbar the heart shifts caudally from the neck to the thoracic cavity, positions of aortic arch arteries are changedrelative to the heart. In particular the subclavian arteries becomes transposed from a position caudal to the heart to acranial es of Dorsal Aortae:Right and left vitelline arteries arise from right and left dorsal aortae, respectively, to supply the yolk sac. Theright vitelline artery becomes the cranial mesenteric artery. The left vitelline artery normally degenerates. Incompletedegeneration of the left vitelline artery can result in a fibrous band that may cause colic by entrapping a segment dorsal aorta terminates in an umbilical artery that supplies blood to the allantois. In the adult, umbilicalarteries persist proximal to the urinary bladder and degenerate distal to the bladder. External and internal iliac arteriesdevelop as outgrowths of the umbilical :The sinus venosus receives vitelline veins which drain the yolk sac, umbilical veins whichdrain the allantois, and cardinal veins which drain the embryo. The transition from embryonic toadult venous patterns involves the formation of new veins, anastomoses between veins, and theselective degeneration of embryonic l Vena CavaNote:Recall that venous return is shiftedDevelopment

(Dorsal View)to the right side so that the rightexternal

sinus venosus is incorporated intojugular v.R. sub-L. sub-the right atrium while the left sinuscalaviancalavianvenosus is reduced and becomes ry o-

cephalic l Vena Cava Formation:Each cranial cardinal vein becomes the adult internaldegeneratedleft cranial

jugular vein. The much larger external jugular and subcla-cardial veins arise by budding from the cranial cardinal anastomotic vein develops and runs from left toright cranial cardinal veins, shifting venous return to the rightside and becoming left brachiocephalic vein. The caudalsegment of right cranial cardinal vein along with the rightcommon cardinal vein becomes the cranial vena cava.(Failure of the anastomotic vein to develop results in a doublecranial vena cava, the typical condition in rats and mice.)anastomoticbranchcranialvena cavacaudalcoronary

right atriumvena cavasinus27

Caudal Vena Cava and Azygos Vein:Each caudal cardinal vein gives rise to supra-cardinal and sub-cardinal veins with extensive anastomoses amongall of the veins. These venous networks, located in intermediate mesoderm, supply embryonic kidneys and ive segments of particularly the right subcardinal venous network, including an anastomosis with theproximal end of the right vitelline vein form the caudal vena azygos vein develops from the supracardinal vein as well as the caudal and common cardinal veins of theright side (dog, cat, horse) or the left side (pig) or both sides (ruminants). The azygos vein will drain into the cranial venacava (or right atrium) on the right side and into the coronary sinus on the left Vein and Ductus Venosus:Proximally, vitelline veins form liversinusoids as the developing liver surrounds theveins. Anastomoses develop between right and leftvitelline veins, and enlargement or atrophy ofselective anastomoses and right/left segments ofvitelline veins gives rise to the portal cal veins, also engulfed by thedeveloping liver, contribute to the formation ofliver sinusoids. Within the embryo, the rightumbilical vein atrophies and the left conveysplacental blood to the liver. Within the liver, ashunt, the ductus venosus, develops between theleft umbilical vein and the right hepatic vein whichdrains into the caudal vena tally, the left umbilical vein becomes theround ligament of the liver located in the free edge of thefalciform cardianl atriumsinusvenosuscranial

cardinal inusoidsrightumbilical

ine TLIVERcaudalcardinal rating

segmentleftumbilical ine & Umbilical Veins(Ventral View)Note:Because a fetus is not eating and because the placenta is able todetoxify blood, it is desirable for venous return to bypass fetal liver sinusoidsvia the ductus venosus, a shunt that diverts blood to systemic tally, however, a continuing portosystemic shunt allows toxicdigestive products to bypass the liver. These toxic agents typically affect thebrain resulting in neurologic disorders at some time during life.A portosystemic shunt can be the result of a persistent ductus venosusor a developmental error that results in anastomosis between the portal veinand the caudal vena cava or the azygos vein. Since adult veins are establishedby patching together parts of embryonic veins, it is not surprising that mis-connections arise from time to time.28

Lymphatics:Lymph vessel formation is similar to blood angiogenesis. Lymphatics begin as lymph sacs inthree regions:

jugular (near brachiocephalic veins); cranial abdominal (future cysterna chyla); and iliac tic vessels (ducts) form as outgrowths of the hymeLymph nodes are produced by localized mesoder-mal invaginations that partition the vessel lumen intosinusoids.

The mesoderm develops a reticular framework withinwhich lymphocytes accumulate. The spleen and hemal nodes (inruminants) develop similar to the way lymph nodes idlymph duct lumenmesodermalinvaginationLymph Node Stretching umbilical arteries resultsin arterial constriction and reduced fetalblood flow to the placenta. Reduced venousreturn through the (left) umbilical vein andductus venosus allows the latter to gradu-ally close (over a period of days).Increased oxygen concentration inblood triggers constriction of the ductus ar-teriosus which, over time, is gradually con-verted to a fibrous structure, the ligamen-tum arteriosum. The increased blood flowto the lungs and then to the left atrium equal-izes pressure in the two atria which resultsin closure of the foramen In-Utero Adjustmentsductus

arteriosusLatriumaortic archpulmonary trunkforamen ovalecaudal vena cavaRatriumductusvenosusaortaliverumbilical cal aa.29