Embryology of Heart & Lung PDF - Sulaiman Alrajhi University - October 2024

EMBRYOLOGY OF HEART & LUNG Department of Anatomy Faculty of Medicine, SRC October 2024 College of Medicine – World class education in a local environment 10/27/2024...

EMBRYOLOGY OF HEART & LUNG Department of Anatomy Faculty of Medicine, SRC October 2024 College of Medicine – World class education in a local environment 10/27/2024 1  Learning Objectives 1. Heart development Looping of the heart Development & positioning of the compartments Septation 2. Fetal circulation 3. Lung development Stages Maturation Congenital anomalies College of Medicine – World class education in a local environment 10/27/2024 2  Recap early embryo College of Medicine – World class education in a local environment 10/27/2024 3  Early EARLY Embryology EMBRYOLOGY Beginning of the 2nd week of IUL The inner cell mass (embryoblast) differentiates into : epiblast (ectoderm) hypoblast (endoderm) Bilaminar germ disc is formed. College of Medicine – World class education in a local environment 10/27/2024 4  Early EARLY Embryology EMBRYOLOGY During the 3rd week of IUL The epiblast cells invaginate through the primitive streak and primitive node. They lie between the two germ layers as intraembryonic mesoderm (IEM). During the 3rd week of IUL, trilaminar germ disc is formed. College of Medicine – World class education in a local environment 10/27/2024 5  Intraembryonic Mesoderm INTRAEMBRYONIC MESODERM IEM differentiates into: paraxial mesoderm intermediate mesoderm lateral plate mesoderm The lateral plate mesoderm splits into: somatopleuric mesoderm splanchnopleuric mesoderm College of Medicine – World class education in a local environment 10/27/2024 6  EMBRYOLOGY OF HEART College of Medicine – World class education in a local environment 10/27/2024 7  Timing Of Development Of The Heart Embryonic age: Week 3: formation of the primitive heart tube Week 4: looping Week 4-6: formation of compartments Week 6-10: septation, valves, aorta/pulmonary trunk College of Medicine – World class education in a local environment 10/27/2024 8  Development of Heart 1st major system to appear in middle of 3rd week. Derived mainly from splanchnopleuric mesoderm Cardiac progenitor cells College of Medicine – World class education in a local environment 10/27/2024 9  Steps: 1. Establishment of cardiogenic field 2. Formation and position of the heart tube 3. Formation of cardiac loop (looping) 4. Formation of cardiac septa (septation) College of Medicine – World class education in a local environment 10/27/2024 10  1. Establishment of Cardiogenic Field Horseshoe-shaped cardiogenic field Located in front of buccopharyngeal membrane & neural plate Consists of cardiac myoblasts & blood islands (will form blood cells and vessels) called as angioblastic cords College of Medicine – World class education in a local environment 10/27/2024 11  2. Formation Of Single Heart Tube Longitudinal/Cephalocaudal folding Cardiogenic field lies anterior to the buccopharyngel membrane & neural plate  thoracic region College of Medicine – World class education in a local environment 10/27/2024 12  Formation Of Single Heart Tube The growth of brain and cephalic folding of embryo causes: Buccopharyngeal membrane pulled forward Heart & pericardial cavity move to thorax College of Medicine – World class education in a local environment 10/27/2024 13  Formation Of Single Heart Tube Lateral folding As the embryo folds cephalocaudally, it also folds laterally Results in: Caudal region of the paired cardiac primordia  merge to form continuous tube except the caudal-most end. College of Medicine – World class education in a local environment 10/27/2024 14  Results of Folding Heart located in the thoracic cavity Single expanded tube Lined by inner endothelial lining and outer myocardial layer Receive venous drainage at caudal pole Pumps blood at cranial pole Day 21-22 Day 23 Day 24 College of Medicine – World class education in a local environment 10/27/2024 15  Results of Folding College of Medicine – World class education in a local environment 10/27/2024 16   With further development, heart is covered by 3 layers: epicardium, myocardium and endocardium College of Medicine – World class education in a local environment 10/27/2024 17  3. Formation of Cardiac Loop(Looping) Heart tube continues to elongate and bend on day 23. Cephalic portion bends ventrally, caudally and to the right. Caudal (atrial) portion bends to dorsally, cranially and to the left. Complete by day 28 College of Medicine – World class education in a local environment 10/27/2024 18  Formation Of Heart Compartments While cardiac loop is forming, local expansions become visible. Sinus venosus, atrium, ventricle, bulbus cordis (conus cordis), truncus arteriosus Bulbus cordis - Trabeculated part Conus cordis of right ventricle - Outflow tract of both Bulboventricular junction ventricles - Primary interventricular foramen Ventricle Atrioventricular junction - Atrioventricular canal Atrium Located in the pericardial cavity Sinus venosus College of Medicine – World class education in a local environment 10/27/2024 19  Fate of Sinus venosus College of Medicine – World class education in a local environment 10/27/2024 20  Fate of Bulbus Cordis The bulbus cordis elongates and forms three parts- the proximal part forms the trabeculated portion of the right ventricle, the middle part forms conus cordis which is the outflow tract and the truncus arteriosus which forms the ascending aorta and pulmonary trunk. College of Medicine – World class education in a local environment 10/27/2024 21  Abnormalities Of Cardiac Looping Dextrocardia Heart lies in the right side of thorax College of Medicine – World class education in a local environment 10/27/2024 22  4. Formation Of Cardiac Septa (Septation) Formation of cardiac septa Common atrium, atrioventricular canal, truncus arteriosus, conus cordis & ventricle Major septa of heart formed between days 27-37 College of Medicine – World class education in a local environment 10/27/2024 23  Formation Of Cardiac Septa Cells in the heart tube proliferate to form the endocardial cushions The endocardial cushions are located at the I. Atrioventricular junction (between the atrium and the ventricle) II. Truncoconal junction (between the conus part and the trunk) College of Medicine – World class education in a local environment 10/27/2024 24  Formation Of Cardiac Septa  The endocardial cushion at the atrioventricular junction will develop into: interatrial septum atrioventricular canal membranous part of the interventricular septum.  The endocardial cushion at the truncoconal junction will develop into: aortic and pulmonary channels. College of Medicine – World class education in a local environment 10/27/2024 25  Formation Of Interatrial Septum 1. Endocardial cushions at atrioventricular junction proliferate 2. Septum primum (sickel-shaped crest) grows from the roof of the atria 3. The opening between the septum primum and endocardial cushion is called ostium (foramen) primum College of Medicine – World class education in a local environment 10/27/2024 26  Formation Of Interatrial Septum 4. Septum primum and endocardial cushion grow and close the ostium (foramen) primum 5. However, some cells in the septum primum die and form the opening called ostium (foramen) secundum 6. These foramina allow free blood flow from right to left (because the left atrial pressure is low). College of Medicine – World class education in a local environment 10/27/2024 27  Formation Of Interatrial Septum 7. A new crescent-shaped fold appears on the right side of the septum primum, called septum secundum 8. The septum secundum grows down and overlap the ostium (foramen) secundum (it does not close the ostium secundum) 9. Ostium secundum is now called as foramen ovale (oval foramen). College of Medicine – World class education in a local environment 10/27/2024 28  Formation Of Interatrial Septum 10. After birth, the left atrium pressure increases (as oxygenated blood returns from the lungs to the left atrium). The septum primum presses on the septum secundum from the left side Foramen ovale is closed and fossa ovalis is formed Floor of the fossa ovalis is formed by septum primum and Limbus (margin) of fossa ovalis is formed by the lower margin of septum secundum. College of Medicine – World class education in a local environment 10/27/2024 29  Formation Of Interatrial Septum Free edge of Anulus of septum fossa ovalis secundum Fossa Septum ovalis primum College of Medicine – World class education in a local environment 10/27/2024 30  Atrial Septal Defect 6.4/10,000 births, : prevalence is 3:1 College of Medicine – World class education in a local environment 10/27/2024 31  Formation of Interventricular Septum Interventricular septum consists of: i. muscular part ii. membranous part Image result for parts of interventricular septum College of Medicine – World class education in a local environment 10/27/2024 32  Formation Of Muscular Part Of Interventricular Septum Future Future The primitive ventricle (future left ventricle) and the lower part of bulbus cordis (future right ventricle) expand and their adjacent walls merged; which form the muscular part of interventricular septum It is an incomplete septum Above it is a gap called interventricular foramen College of Medicine – World class education in a local environment 10/27/2024 33  Formation Of Membranous Part Of Interventricular Septum  Growth of the endocardial cushions at the atrioventricular junction forms the membranous part of interventricular septum.  Some neural crest cells share in formation of this part. College of Medicine – World class education in a local environment 10/27/2024 34  Ventricular Septal Defect Most common cardiac malformation Involved membranous part of interventricular septum, 12/10,000 births Associated with conotruncal abnormalities College of Medicine – World class education in a local environment 10/27/2024 35  Formation of aorticopulmonary septum A spiral aorticopulmonary septum develops in the truncus arteriosus leading to the formation of separate aortic and pulmonary channels. Formed by the neural crest cells. Failure in the septation process can lead to a congenital defect known as Persistent Truncus Arteriosus (PTA). TGA occurs when the aorticopulmonary septum fails to spiral. College of Medicine – World class education in a local environment 10/27/2024 36 College of Medicine – World class education in a local environment 10/27/2024 37 College of Medicine – World class education in a local environment 10/27/2024 38  Congenital Heart Disease Septal Defects – Atrial and Ventricular Septal defects Endocardial cushion defects Aorticopulmonary defects PDA (Patent Ductus arteriosus) Last Slide College of Medicine – World class education in a local environment 10/27/2024 39 College of Medicine – World class education in a local environment 10/27/2024 40  FETAL CIRCULATION College of Medicine – World class education in a local environment 10/27/2024 41  Fetal Circulation The pattern of blood circulation in the fetus is an excellent example of economizing the limited amount of blood and yet most affective. During fetal life: The essential organs (brain & heart) receive well-oxygenated blood less essential organs receive relatively deoxygenated blood in partially functional organ (liver) and non-functional organs (lungs), the blood by-passes by flowing through the shunts (ducts). College of Medicine – World class education in a local environment 10/27/2024 42  Fetal Oxygenated blood from the placenta Circulation which is about 80% saturated with oxygen returns to the fetus via umbilical vein. From umbilical vein and through the ductus venosus passes into the inferior vena cava, [short-circuiting the liver]. In the inferior vena cava, the placental blood mixes with deoxygenated blood returning from the lower limbs and enters into the right atrium. It is directed to the foramen ovale and the blood passes into the left atrium. From the left atrium, the blood enters into the left ventricle and then into the aorta. College of Medicine – World class education in a local environment 10/27/2024 43  Fetal Circulation The deoxygenated blood from the superior vena cava enters into the right atrium and directed into the right ventricle and then into the pulmonary trunk. From the pulmonary trunk, the blood enters into the aorta through the ductus arteriosus and mixed with oxygenated blood of the aorta (short- circuiting the lungs). The mixed blood through the descending aorta flows toward the placenta through the umbilical arteries; which consists of approximately 58% oxygen saturation. College of Medicine – World class education in a local environment 10/27/2024 44  Changes After Birth As soon as new born infant takes its first breath, major changes begin to convert the foetal circulation to the adult pattern. The goals of changing pattern are: to open the pulmonary circulation for oxygenation to close the umbilical vein and arteries to close the ductus arteriosum and ductus venosum to close the foramen ovale to supply the liver with nutrient- rich blood from the gastrointestinal tract. College of Medicine – World class education in a local environment 10/27/2024 45  CHANGES AFTER BIRTH Cessation of the placenta blood flow and the beginning of respiration. Many blood vessels obliterate and become ligaments. i. Umbilical vein becomes ligamentum teres (round ligament of liver) ii. Ductus venosus becomes ligamentum venosus. iii. Ductus arteriosus becomes ligamentum arteriosus. iv. Foramen ovale closes and becomes fossa ovalis. v. Umbilical arteries become medial umbilical ligaments. College of Medicine – World class education in a local environment 10/27/2024 46  EMBRYOLOGY OF LUNG College of Medicine – World class education in a local environment 10/27/2024 47  Formation of the Lung When the embryo is approximately 4 weeks old, the respiratory diverticulum (lung bud) start to appear. College of Medicine – World class education in a local environment 10/27/2024 48  Respiratory Diverticulum and Tracheoesophageal septum Separation of respiratory diverticulum: 2 longitudinal ridges, the tracheoesophageal ridges; separate it from the foregut. When these ridges fuse, it forms tracheoesophageal septum Tracheoesophageal septum separates: Trachea & lung buds ventrally Esophagus dorsally College of Medicine – World class education in a local environment 10/27/2024 49  Branching of Lung Buds Divisions of lung buds: a. Right: 3 main bronchi b. Left: 2 main bronchi Bronchi continue to divide. By 6 months: 17 generations of subdivisions After birth: 23 generations of subdivisions College of Medicine – World class education in a local environment 10/27/2024 50  Maturation of the Lung Phase Week Events Pseudoglandular period 5-18 weeks Branching has continued to form terminal bronchiole. No respiratory bronchioles or alveoli are present Canalicular period 16-26 weeks Each terminal bronchiole divides into 2 or more respiratory bronchioles, which in turn divide into 3-6 alveolar ducts Terminal sac period 24-38 weeks Terminal sac (primitive alveoli) form, & capillaries establish close contact Alveolar period 36 weeks to Mature alveoli have well-developed epithelial endothelial childhood (capillary) contacts College of Medicine – World class education in a local environment 10/27/2024 51  A. Pseudoglandular phase B. Canalicular phase C. Saccular phase D. Alveolar phase College of Medicine – World class education in a local environment 10/27/2024 52  Milestone of Lung Development College of Medicine – World class education in a local environment 10/27/2024 53  Developmental Anomalies of Respiratory System Esophageal Artesia Tracheo-Esophageal Fistula Respiratory Distress Syndrome Pulmonary Hypoplasia Congenital Diaphragmatic Hernia College of Medicine – World class education in a local environment 10/27/2024 54  Esophageal Atresia Esophageal atresia is a congenital defect which affects the alimentary tract. It causes the esophagus to end in a blind-ended pouch rather than connecting normally to the stomach. College of Medicine – World class education in a local environment 10/27/2024 55  Congenital Tracheo-Esophageal Fistula(TEF) A tracheoesophageal fistula (TEF) is an abnormal connection between your esophagus and trachea. The condition is often congenital, which means it happened during fetal development. College of Medicine – World class education in a local environment 10/27/2024 56  Respiratory Distress Syndrome ( RDS ) Respiratory distress syndrome (RDS) is a breathing problem that sometimes affects babies born six weeks or more before their due dates. Their lungs aren't developed enough to make surfactant, a liquid that coats the inside of the lungs and keeps them open so that the baby can breathe in air once he or she is born. 50 % due to surfactant deficiency Glucocorticoids stimulate surfactant production. Routinely used for prevention of RDS. College of Medicine – World class education in a local environment 10/27/2024 57  Pulmonary Hypoplasia Pulmonary hypoplasia is a condition characterized by small, underdeveloped lungs that can affect not only breathing but also heart function, ability to feed, hearing and overall development Pulmonary hypoplasia results when lungs are compressed by abnormally positioned abdominal viscera and cannot develop normally or expand at birth. It is commonly caused by congenital posterolateral diaphragmatic hernia. College of Medicine – World class education in a local environment 10/27/2024 58  Congenital Diaphragmatic Hernia Failure of the pleuroperitoneal foramen (foramen of Bochdalek) to close allows viscera into thorax. Intestine, stomach or spleen can enter the pleural cavity, compressing the lung. College of Medicine – World class education in a local environment 10/27/2024 59  THANK YOU College of Medicine – World class education in a local environment 10/27/2024 60