Human Embryology - Development of the Cardiovascular System PDF

Development of the Cardiovascular System Asst.Prof.Dr.Pornsawan Duangsuwan  First week of development: Ovulation to implantation 4-cells stage 8-cells stage Morula Blastocyst 2-cells stage Fertilized egg  Blastocyst Blastocyst composed of 1. Inne...

Development of the Cardiovascular System Asst.Prof.Dr.Pornsawan Duangsuwan  First week of development: Ovulation to implantation 4-cells stage 8-cells stage Morula Blastocyst 2-cells stage Fertilized egg  Blastocyst Blastocyst composed of 1. Inner cell mass (embryoblast) : future embryo 2. Trophoblast : thin outer layer of cells : future placenta 3. Blastocytic cavity : fluid-filled space 2nd week of development: Bilaminar embryonic disc Inner cell mass differentiate into 2 layers (Bilaminar embryonic disc) 1. Epiblast 2. Hypoblast 2 fluid filled sacs 1. Amniotic sac (amnion) : extend from epiblast : filled with amniotic fluid 2. Yolk sac : exocoelomic membrane extend from hypoblast : exocoelomic cavity  Migration directions of epiblast Primitive node Amnion (cut edge) Primitive groove rd CVS begins to develop in the 3 week of gestation heart primordium arises from splanchnic mesoderm toward cephalic end in cardiogenic region of the trilaminar embryo Development of the heart  Early development of the heart angiogenic cell cluster (angioblastic cord): horseshoe-shaped pattern cardiogenic region : cranial end of embryonic disc pericardial cavity : cranial end of intraembryonic coelom  Formation of endocardial heart tube: day 19 angioblastic cords develop in cardiogenic mesoderm and canalise to form bilateral endocardial heart tubes (very thin walled tubes) Embryonic folding Head folding brain grows in fast rate head bend around under the body heart tube pulled down to VENTRAL SIDE  Lateral folding and fusion of heart tubes trilaminar disk folds around flat shape 3D sphere primordial heart tubes fuse in midline to form single ventral heart tube apoptosis of cells along two edges cause forming one continuous tube Fusion begins cranially and extends caudally The primordial heart tubes fuse in the midline to form a single ventral heart tube. Fusion begins cranially and extends caudally. Development of the human heart: Day 15-21 Heart 2002 87: 487 Components of the primitive heart tube 1. endocardium endothelium of heart tube 2. cardiac jelly acellular matrix separate heart tube and myocardium further subendocardial layer 3. myocardium differentiate from splanchnic mesoderm surround coelom 4. epicardium (visceral pericardium) develops from mesothelial cells arising from the sinus venosus, spread cranially over myocardium  Formation of transverse pericardial sinus heart tube is suspended by the dorsal mesocardium thin strip of tissue ruptures and leaves the heart suspended in the pericardial space by the vasculature  Primitive heart tube As the tubular heart grows, it develops dilations and constrictions which form 5 basic regions Aorta & pulmonary trunk right ventricle left ventricle By day 22-24, coordinated contractions atrium of the heart tube are present and push blood cranially from the sinus venosus  Cardiac looping: Day 23-28 bulbus cordis RA LA ventricle RV LV atrium sinus venosus stright heart tube C-shaped loop S-shaped loop heart tube grows but limited by the pericardial space folded over linear heart tube bend ventrally rotation brings bulge of the ventral bend (bulbus cordis & ventricle) to the right, forming a C-shaped loop (bulboventricular sulcus) atrium move cranially, the poles of the heart converge, forming S-shaped loop (bulbus cordis – ventricle, atrium – sinus venosus) bulbus cordis and arterial trunk move ventral to the atrium to form the later outflow tract. The atrium now lies superior to the ventricle  Prior to this looping, there are 2 sides to this primitive heart tube and they are pumping blood the right blood that comes in the right sinus venosus horn and goes out the right truncus arteriosus and the same for the left. You have sort of a parallel circulation. Which will not work to bring blood to all the tissues of the very rapidly developing embryo. So this very primitive R-side-to-R-side and L-side-to-L-side circulation is replaced by the formation of these 4 septa, http://www.bionalogy.com/cardiovascular_system.htm  Embryonic circulation 1. vitelline veins (returning poorly oxygenated blood from the yolk sac) 2. umbilical veins (carrying well-oxygenated blood from the primordial placenta) 3. common cardinal veins (return poorly oxygenated blood from the body of the embryo). The vitelline venous system gives rise to the liver sinusoids and portal system, and forms the ductus venosus which shunts blood from the umbilical vein to the IVC.  Sinus venosus Lt sinus horn is reduced and pulled to the left Lt sinus horn loses connection with Lt anterior cardinal v. coronary sinus Lt ant. cardinal v. connects to Rt ant. cardinal v. Lt brachiocephalic vein remnant of Rt vitelline v. terminal segment of IVC Differentiation of atrium I th 5 week form trabeculated portion at ventral and lateral part of both Lt and Rt primitive atrium and auricles Rt atrium: right sinus horn incorporate into dorsal wall of right atrium as smooth-walled sinus venarum Lt atrium: single pulmonary vein develop in Lt primitive atrium pulmonary vein branches twice to produce 2 right and left pulmonary veins  Differentiation of atrium II th late 5 week pulmonary vein system undergo intussception (folding in of an outer layer) into dorsal wall of primitive atrium to form the definitive left atrium right horn sinus venosus :SVC, IVC orifices left horn sinus venosus: coronary sinus orifices left and right venous valves join cranially to form septum spurium (part of s. secundum) right venous valve: valve of IVC, valve of coronary sinus Differentiation of atrium III crista terminalis: - ridge tissue separate traeculated right atrium from smooth walled sinus venarum - conducting system carry impluse from SA to AV node 4 pulmonary veins are incoporated into the dorsal wall of left side primitive atrium complete formation of smooth walled part of future left atrium  Partitioning of the heart Partitioning of atrioventricular canal Septation of the atrium Septation of the ventricle Sepation of the outflow tract  Partitioning of the atrioventricular canal mesenchyme on dorsal and ventral sides form endocardial cushions at the central portion AV canal :- right tricuspid orifice tricuspid valve :- Left bicuspid orifice bicuspid (mitral) valve Septation of atria I th 5 week septum primum grows from the dorsal wall of the primitive atrium as a crescent shaped and leaves a gap called foramen primum foramen primum closes as the septum primum continues to grow to endocardial cushion Septation of atria II th 5 week before septum primum close, foramen primum is obliterated that coalesce to form foramen secundum septum secundum form at the right side of the septum primum Septation of atria III septum secundum covers up the foramen primum, but it leaves the foramen ovale oxygenated blood can pass From right to left atria in the developing fetus before birth after birth, it closes because the septum primum fuses with the septum secundum, fossa ovalis At this point the right and left atria have formed, having the foramen ovale through which oxygenated blood is passing, now have divided with valves in place to prevent the blood only from going from atria to ventricle and not back up, by the formation of the AV septum.  Septation of ventricles I thickening of myocardium and trabeculae form on inner wall of both ventricles anterior papillary muscle: ventral portion of muscular interventricular septum moderator band: right wall of muscular interventricular septum to anterior papillary muscle Septation of ventricles II muscular ventricular septum : groove between bulbus cordis - primitive ventricle, grows up forward the endocardial cushion but stop before it complete separate the ventricles. It will remain incomplete until the membranous septum is form later on in development, connecting the muscular septum to endocardial cushions Septation of cardiac outflow I th 5 week, right and left conotruncal swellings grow out from the walls of common outflow tract develop in spiral configulation fuse in cranial-caudal direction to form conotruncal septum aorta: send blood out of left ventricle pulmonary trunk: outflow of right ventricle to lungs  Septation of cardiac outflow II th 9 week, caudal end of conotruncal septum reach muscular inventricular septum and atrioventricular septum complete the interventricular septum  Formation of semilunar valve during formation of conotruncal septum (aorta - pulmonary trunk) two small cushion tissues form in the opposite quadrants of outflow tract new cushion tissue is excavated and remodeling to form 2 cavities Formation of atrioventricular valve th th begin in 5 - 8 wk. cusp: proliferate & diferentiate from endocardial cushion chordae tendinae: remodeling and erosion of ventricular myocardial wall papillary muscles: small hillocks of myocardium bicuspid valve: anterior & posterior cusp tricuspid valve: septal cusp develop during rd 3 month  Development of the aortic arches Asst.Prof.Dr.Pornsawan Duangsuwan  Early development of heart dorsal aorta U-shaped heart tube and the forming blood vessels are initially unconnected pericardial cavity heart tube dorsal aorta gut tube head fold, heart tube pulled down to beneath the pharynx heart tube vitelline vein  First aortic arch fused dorsal aorta 1st aortic arch VENTRICLE ATRIUM ORAL PLATE venous return from - cardinal v. - vitelline v. - umbilical v. dorsal aorta form independently and then grow to meet the ventral output from the heart in the aortic arches Paired dorsal aorta fuse to form single aorta, just caudal to pharyngeal arches  Aortic arches THE FOUR PHARYNGEAL POUCHES CORRESPOND TO THE FOUR BRANCHIAL CLEFTS LATERALLY EACH BRANCHIAL ARCH CONTAINS A CRANIAL NERVE AND AN AORTIC ARCH series of paired arterial channels encircling and supply developing pharyngeal arches th develop in the 4 week arise from aortic sac terminate in right and left dorsal aortae  Aortic arches pharyngeal pouches dorsal aorta aortic arches lung bud six pairs, but the 5th pair is poorly developed and disappears soon after formation all are not present at the same time dorsal aorta fuse to form single median vv. from 4th thoracic – 4th lumbar segment  Dorsal aorta ventral aortic branch : supply gut tube and derivatives lateral aortic branch : supply kidney,suprareal gland and gonad posterolateral aortic branch : intersegmental a. Ventral branches of descending aorta 1. vitelline a. : supply gut tube and derivatives celiac trunk: fore gut superior mesenteric a.: mid gut inferior mesenteric a.: hind gut 2. umbilical a. : carry poorly O2 blood to placenta proximal: superior vesical a. distal: medial umbilical ligament Lateral branches of descending aorta Postero-lateral branches of descending aorta somatic branches thirty or more pairs arise at serial segmental levels, run between somites supply body wall, limbs, brain, spinal cord Derivatives: cervical : join to form vertebral a. th : 7 pair --->subclavian a. thoracic : posterior intercostal a. abdominal : lumbar a. : 5th pair ---->common iliac a. sacral : lateral sacral a. Arterial system of the upper limb th 7 cervical intersegmental a. grow into limb buds to join the axis a. of the developing upper limb Arterial system of the lower limb th 5 lumbar intersegmental a. join the axis a. forming in the lower limb remnants: ishiadic a. (popliteal a., peroneal a.)  Embryonic venous system vitelline system: give rise liver sinusoid, portal system, portion of IVC umbilical veins cardinal system Vitelline and umbilical veins Rt. & Lt. vitelline v. form a portal system to drain blood from foregut, midgut and part of anorectal canal Rt. umbilical v.: disappear Lt. umbilical v.: anastomose with ductus venosus ---> shut O2 placental blood into IVC and right Atrium Lt.umbilical v. --> lig. teres hepatis ductus venosus --> lig. venosum  Systemic venous system anterior cardinal v. drain blood from both side of head and neck posterior cardinal v.: drain blood from trunk posterior cardinal v. are replaced by set of subcardinal and supracardinal v. Systemic venous system following remodeling of the subcardinal system, the supracardinal v. sprout remodeling of abdominal venous system occurs through obliteration of left supracardinal v. Left superior vena cava (LSVC) LSVC occurs in 0.3% to 0.5% of the normal population in 65% of cases, left brachiocephalic vein is also missing 4% of patients with CHD have an LSVC usually drains to the coronary sinus  Aortic arch development During week 6 to 8, the primitive aortic arch pattern is transformed into adult arterial arrangement of carotid, subclavian, and pulmonary arteries Derivatives of 1st pair complete by Day 24 nd regress as 2 arches form by Day 26 remaining parts form maxillary a. supply ear, teeth, muscles of eyes and face  Derivatives of 2nd pair complete by Day 26 th regress as 6 arches form by Day 29 remaining parts form stapedial a. supply stepes bone in developing ear  Derivatives of 3rd pair complete by Day 28 proximal part form common carotid a. : supply structures in head distal parts join with dorsal aorta to form int. carotid a. : supply ears, orbits, brain and meninges External carotid a. sprout from common carotid a.  Derivatives of 5rd pair disappears completely with NO vascular derivatives In other 50% of embryos, these arteries do not develop The fate of 1st - 3rd pairs of aortic arches are bilateral. The fate of 4th & 6th pairs of aortic arches differs on the right and left side.  Derivatives of 4rd pair form by day 28 th LEFT 4 aortic arch : form part of arch of aorta th RIGHT 4 aortic arch : becomes the proximal part of right subclavian a.  Arch of aorta proximal segment: derived form aortic sac th middle segment: derived from left 4 aortic arch distaL segment: derived from left dorsal aorta Subclavian arteries RIGHT subclavian a. th right 4 aortic arch right dorsal aorta th right 7 intersegmental a. LEFT subclavian a. th left 7 intersegmental a.  Derivatives of 6rd pair form by day 29 th LEFT 6 aortic arch proximal part: proximal part of left pulmonary a. distal part: ductus arteriosus (shunt between Lt. pul. a. & dorsal aorta) th RIGHT 6 aortic arch proximal part: proximal part of right pulmonary a. distal part: degenerate  Change in the original aortic arch system Obliteration of: st nd 1. Most of the 1 & 2 arches th 2. 5 arches completely th 3. Distal part of the right 6 arch 4. The segment of both aortae lying between the 3rd & 4th arch The segment of right aorta lying between the 7th intersegmental artery & the fused dorsal aortae Relation of recurrent laryngeal nerves to aortic arches recurrent laryngeal n. originally arise th below the level of 6 arch and cross th under right and left 6 arches LEFT recurrent laryngeal n. : remain loop under ductus arteriosus RIGHT recurrent laryngeal n. th : right 6 arch diappear th : 5 arch do not develop th : remain loop under 4 arch (right suclavian a.)