embryology and anatomy of cardiovascular.pdf

284 SEC TION III CARDIOVASCULAR ` CARDIOVASCULAR—EMBRYOLOGY ` CARDIOVASCULAR—EMBRYOLOGY Heart morphogenesis First functional organ in vertebrate embryos; beats spontaneously by week 4 of development. Cardiac looping...

284 SEC TION III CARDIOVASCULAR ` CARDIOVASCULAR—EMBRYOLOGY ` CARDIOVASCULAR—EMBRYOLOGY Heart morphogenesis First functional organ in vertebrate embryos; beats spontaneously by week 4 of development. Cardiac looping Primary heart tube loops to establish left-right Defect in left-right dynein (involved in left-right polarity; begins in week 4 of development. asymmetry) can lead to dextrocardia, as seen in Kartagener syndrome. Septation of the chambers Atria Septum primum grows toward endocardial 6. Septum primum closes against septum cushions, narrowing ostium primum. secundum, sealing the foramen ovale soon Ostium secundum forms in septum primum after birth because of  LA pressure and  RA due to cell death (ostium primum regresses). pressure. Septum secundum develops on the right 7. Septum secundum and septum primum fuse side of septum primum, as ostium secundum during infancy/early childhood, forming the maintains right-to-left shunt. atrial septum. Septum secundum expands and covers most of ostium secundum. The residual foramen is Patent foramen ovale—caused by failure of the foramen ovale. septum primum and septum secundum Remaining portion of septum primum forms to fuse after birth; most are left untreated. the one-way valve of the foramen ovale. Can lead to paradoxical emboli (venous thromboemboli entering the systemic arterial circulation through right-to-left shunt) as can occur in atrial septal defect (ASD). Septum Ostium Developing primum secundum septum secundum Ostium primum RA LA Dorsal Ostium Septum Septum endocardial secundum primum primum cushion Ostium primum Septum Ostium Degenerating secundum secundum septum primum Foramen Septum Foramen ovale primum ovale (closed) Septum secundum FAS1_2023_07-Cardio.indd 284 11/22/22 3:48 PM  CARDIOVASCULAR ` CARDIOVASCULAR—EMBRYOLOGY SEC TION III 285 Heart morphogenesis (continued) Ventricles Muscular interventricular septum forms. Ventricular septal defect—most common Opening is called interventricular foramen. congenital cardiac anomaly, usually occurs in Aorticopulmonary septum rotates and fuses membranous septum. with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen. Growth of endocardial cushions separates atria from ventricles and contributes to both atrial septation and membranous portion of the interventricular septum. Aorticopulmonary septum RA LA RA LA RA LA Interventricular foramen Membranous Atrioventricular interventricular canals septum Muscular interventricular septum Outflow tract Neural crest cell migrations Ž truncal and Conotruncal abnormalities associated with formation bulbar ridges that spiral and fuse to form failure of neural crest cells to migrate: aorticopulmonary septum Ž ascending aorta ƒ Transposition of great arteries. and pulmonary trunk. ƒ Tetralogy of Fallot. ƒ Persistent truncus arteriosus. Valve development Aortic/pulmonary: derived from endocardial Valvular anomalies may be stenotic, regurgitant, cushions of outflow tract. atretic (eg, tricuspid atresia), or displaced (eg, Mitral/tricuspid: derived from fused endocardial Ebstein anomaly). cushions of the AV canal. Aortic arch derivatives Develop into arterial system. 1st Part of maxillary artery (branch of external carotid). 1st arch is maximal. External Right recurrent carotid artery laryngeal nerve 2nd Stapedial artery and hyoid artery. Second = loops around Internal stapedial. carotid artery product of 4th arch (subclavian artery) 3rd Common carotid artery and proximal part Common of internal carotid artery. C is 3rd letter of carotid Left recurrent artery laryngeal nerve alphabet. loops around 4th On left, aortic arch; on right, proximal part of product of 6th arch (ductus arteriosus) right subclavian artery. 4th arch (4 limbs) = systemic. 3rd 4th 6th Proximal part of pulmonary arteries and (on left 6th only) ductus arteriosus. 6th arch = pulmonary and the pulmonary-to-systemic shunt (ductus arteriosus). FAS1_2023_07-Cardio.indd 285 11/22/22 3:48 PM  286 SEC TION III CARDIOVASCULAR ` CARDIOVASCULAR—EMBRYOLOGY Heart embryology EMBRYONIC STRUCTURE GIVES RISE TO Truncus arteriosus Ascending aorta and pulmonary trunk Bulbus cordis Smooth parts (outflow tract) of left and right ventricles Primitive ventricle Trabeculated part of left and right ventricles Primitive atrium Trabeculated part of left and right atria Left horn of sinus venosus Coronary sinus Right horn of sinus venosus Smooth part of right atrium (sinus venarum) Endocardial cushion Atrial septum, membranous interventricular septum; AV and semilunar valves Right common cardinal vein and right anterior Superior vena cava (SVC) cardinal vein Posterior cardinal, subcardinal, and Inferior vena cava (IVC) supracardinal veins Primitive pulmonary vein Smooth part of left atrium First aortic arch Aortic roots Pericardium SVC Aortic arch Bulbus Truncus Ascending aorta cordis Primitive arteriosus left atrium Pulmonary trunk Sinus Left horn atrium Ventricle Right Cardinal atrium veins Atrium Sinus venosus Left ventricle Ventricles 22 days 24 days 35 days 50 days FAS1_2023_07-Cardio.indd 286 11/22/22 3:48 PM  CARDIOVASCULAR ` CARDIOVASCULAR—EMBRYOLOGY SEC TION III 287 Fetal circulation Blood in umbilical vein has a Po2 of ≈ 30 mm Hg and is ≈ 80% saturated with O2. Umbilical 3 Ductus arteries have low O2 saturation. arteriosus 3 important shunts: LA Blood entering fetus through the Superior vena cava umbilical vein is conducted via the ductus Pulmonary venosus into the IVC, bypassing hepatic 2 Foramen ovale RA artery circulation. RV LV Most of the highly oxygenated blood 1 Ductus venosus reaching the heart via the IVC is directed through the foramen ovale into the left Aorta atrium. Deoxygenated blood from the SVC passes Inferior vena cava through the RA Ž RV Ž main pulmonary artery Ž ductus arteriosus Ž descending aorta; shunt is due to high fetal pulmonary Portal vein artery resistance. At birth, infant takes a breath Ž  resistance in pulmonary vasculature Ž  left atrial Umbilical vein pressure vs right atrial pressureŽ foramen ovale closes (now called fossa ovalis);  in O2 (from respiration) and  in prostaglandins Internal iliac artery (from placental separation) Ž closure of ductus arteriosus. High O2 Umbilical NSAIDs (eg, indomethacin, ibuprofen) or To placenta Moderate O2 arteries acetaminophen help close the patent ductus From placenta Low O2 arteriosus Ž ligamentum arteriosum (remnant Very low O2 of ductus arteriosus). “Endomethacin” ends the PDA. Prostaglandins E1 and E2 kEEp PDA open. Fetal-postnatal derivatives FETAL STRUCTURE POSTNATAL DERIVATIVE NOTES Ductus arteriosus Ligamentum arteriosum Near the left recurrent laryngeal nerve Ductus venosus Ligamentum venosum Foramen ovale Fossa ovalis Allantois Ž urachus Median umbilical ligament Urachus is part of allantois between bladder and umbilicus Umbilical arteries Medial umbilical ligaments Umbilical vein Ligamentum teres hepatis (round ligament) Contained in falciform ligament FAS1_2023_07-Cardio.indd 287 11/22/22 3:48 PM  288 SEC TION III CARDIOVASCULAR ` CARDIOVASCULAR—ANATOMY ` CARDIOVASCULAR—ANATOMY Heart anatomy A LA is the most posterior part of the heart A ; B enlargement of the LA (eg, in mitral stenosis) RV can lead to compression of the esophagus LV SVC RA (dysphagia) and/or the left recurrent laryngeal Azygos vein Aortic knob Pulmonary artery LA nerve, a branch of the vagus nerve, causing pv Ao hoarseness (Ortner syndrome). RA LA Descending aorta RV is the most anterior part of the heart and IVC RV LV most commonly injured in trauma. LV is about 2/3 and RV is about 1/3 of the inferior (diaphragmatic) cardiac surface B. Pericardium Consists of 3 layers (from outer to inner): Fibrous pericardium ƒ Fibrous pericardium Parietal pericardium ƒ Parietal pericardium Pericardial space ƒ Epicardium (visceral pericardium) Epicardium (visceral pericardium) Pericardial space lies between parietal Coronary vessels pericardium and epicardium. Pericardium innervated by phrenic nerve. Myocardium Pericarditis can cause referred pain to the neck, Endocardium arms, or one or both shoulders (often left). Coronary blood LAD and its branches supply anterior 2/3 of Dominance: supply interventricular septum, anterolateral papillary ƒ Right-dominant circulation (most common) muscle, and anterior surface of LV. Most = PDA arises from RCA commonly occluded. ƒ Left-dominant circulation = PDA arises PDA supplies posterior 1/3 of interventricular from LCX septum, posterior 2/3 walls of ventricles, and ƒ Codominant circulation = PDA arises from posteromedial papillary muscle. both LCX and RCA RCA supplies AV node and SA node. Infarct Coronary blood flow to LV and interventricular may cause nodal dysfunction (bradycardia septum peaks in early diastole. or heart block). Right (acute) marginal artery Coronary sinus runs in the left AV groove and supplies RV. drains into the RA. PV PV LA LCA (or LM) LA LCX SVC Aorta SVC OMA RCA RA LAD IVC Key: PT AMA = Acute marginal artery RA LAD = Left anterior descending artery LCA (or LM) = Left (main) coronary artery LCX = Left circumflex artery OMA = Obtuse marginal artery LV LV PDA = Posterior descending artery PT = Pulmonary trunk IVC RV RV PV = Pulmonary vein RCA = Right coronary artery AMA PDA Anterior view Posterior view FAS1_2023_07-Cardio.indd 288 11/22/22 3:48 PM