Heart and lung development
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This document summarizes the embryology of the human heart and lungs. It describes how the heart develops from two endocardial tubes that merge to form the primitive heart tube by the 22nd day. Septa then form to separate the atria and ventricles. The lungs develop from endoderm and mesoderm, with lung buds forming by week 5 and descending into the pleural cavities. Over several months, the lungs continue developing alveoli and surfactant production to prepare for respiration outside the womb.
Heart and lung development
- 1. SUBJECT: MEDICAL SURGICAL NURSING (Cardio-Thoracic Nursing). PRESENTED BY: HARMEET KAUR M.SC (N) IIND YEAR COLLEGE OF NURSING, AIMS, SRI MUKTSAR SAHIB.
- 2. EMBRYOLOGY OF HUMAN HEART Heart development refers to development of the human heart. This begins with the formation of two endocardial tubes which merge to form the tubular heart, also called the primitive heart tube, that loops and septates to form the adult, human heart. The heart starts to beat spontaneously by 22nd day of development.
- 3. The tubular heart quickly differentiates into the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus. The heart tube elongates on the right side, looping and becoming the first visual sign of left-right asymmetry of the body. Septa form within the atria and ventricles to separate the left and right sides of the heart.
- 4. PRIMITIVE DEVELOPMENT The heart develop from embryonic mesoderm germ- layer cells that differentiate after gastrulation into: mesothelium, endothelium, and myocardium.
- 5. Endocardial tubes At around 18 to 19 days after fertilisation, the heart begins to form. starts to beat and pump blood at around day 21 or 22. The heart begins to develop near the head of the embryo in the cardiogenic area that lies anterior to the buccopharyngeal membrane and neural tube. Develop from splanchnopleuric mesenchyme
- 6. Two strands or cords begin to form in the cardiogenic region A lumen develops within them, at which point, they are referred to as endocardial tubes. By day 19, an endocardial tube begins to develop and by the 22nd day (third week) they converged towards each other to merge together From head to tail, these are the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus.
- 7. Initially, all venous blood flows into the sinus venosus, and contractions propel the blood from tail to head, or from the sinus venosus to the truncus arteriosus. The truncus arteriosus will divide to form the aorta and pulmonary artery; the bulbus cordis will develop into the right ventricle; the primitive ventricle will form the left ventricle; the primitive atrium will become the front parts of the left and right atria and their appendages, and the sinus venous will develop into the posterior part of the right atrium, the sinoatrial node and the coronary sinus.
- 9. Heart tube position The central part of cardiogenic area is in front of the oropharyngeal membrane and the neural plate. The growth of the brain and the cephalic folds push the oropharyngeal membrane forward, while the heart and the pericardial cavity move first to the cervical region and then into the chest. The curved portion of the horseshoe-shaped area expands to form the future ventricular infundibulum and the ventricular regions, as the heart tube continues to expand.
- 10. Cardiac looping The heart tube continues stretching and by day 23, in a process called morphogenesis, cardiac looping begins. The cephalic portion curves in a frontal clockwise direction. The atrial portion starts moving in a cephalically and then moves to the left from its original position. This curved shape approaches the heart and finishes its growth on day 28. The tube is divided into cardiac regions along its craniocaudal axis: the primitive ventricle, called primitive left ventricle, and the trabecular proximal arterial bulb, called the primitive right ventricle.
- 11. Formation of heart chambers Sinus venosus In the middle of the fourth week, the sinus receives venous blood from the poles of right and left sinus. Each pole receives blood from three major veins: the vitelline vein, the umbilical vein and the common cardinal vein. The sinus opening moves clockwise.
- 12. Left common cardinal vein disappears in the tenth week. Only the oblique vein of the left atrium and the coronary sinus remains patent. The right pole joins the right atrium to form the wall portion of the right atrium. The right and left venous valves fuse and form a peak known as the septum spurium. At the beginning, these valves are large but the left venous valve and the septum spurium fuse with the developing atrial septum. The upper right venous valve disappearing. The bottom evolves into: the inferior valve of the vena cava and the coronary sinus valve.
- 13. Heart wall The main walls of the heart are formed between day 27 and 37 of the development of the early embryo. The growth consists of two tissue masses actively growing that approach one another until they merge and split light into two separate conduits. Tissue masses called endocardial cushions develop into atrioventricular and conotroncal regions. In these places, the cushions will help in the formation of auricular septum, ventricular conduits, atrio- ventricular valves and aortic and pulmonary channels.
- 14. Atria and Ventricle At the end of the fourth week, a crest grows that leaves the cephalic part. This crest is the first part of the septum primum. The opening between the bottom edge of the septum primum and endocardial cushions is the ostium primum (first opening).
- 16. Coalescence of these perforations will form the ostium secundum (second opening) When the right of the atrium expands new fold appears, called the septum secundum. A free opening will then appear, called the foramen ovale. The remains of the upper septum primum, will become the valves of the foramen ovale. The passage between the two atrial chambers consists of a long oblique slit through which blood flows from the right atrium to the left. As with the developing left and right atrium, part of the initial atrioventricular canal becomes incorporated into the mitral and tricuspid valve simultaneously by 8th week.
- 17. Initially, a single pulmonary vein develops in the form of a bulge in the back wall of the left atrium. This vein will connect with the veins of the developing lung buds. As development proceeds the pulmonary vein and its branches are incorporated into the left atrium and they both form the smooth wall of the atrium. At the end of the fourth week, two atrioventricular endocardial cushions appear. Initially the atrioventricular canal gives access to the primitive left ventricle, and is separated from arterial bulb by the edge of the ventricular bulb.
- 18. Because of this, blood can access both the left primitive ventricle and the right primitive ventricle. As the anterior and posterior pads project inwardly, they merge to form a right and left atrioventricular orifice. When forming intra-atrial septa, atrio-ventricular valves will begin to grow. An intra-muscular ventricular septum begins to grow from the common ventricle to the atrio-ventricular endocardial cushions. Eventually the interventricular foramen disappears. This closure is achieved by further growth muscular interventricular septum.
- 19. Development of the pacemaker and conduction system The rhythmic electrical depolarization waves that trigger myocardial contraction is myogenic, which means that they begin in the heart muscle spontaneously and are then responsible for transmitting signals from cell to cell. Primitive ventricle acts as initial pacemaker. But this pacemaker activity is actually made by a group of cells that derive from the sinoatrial right venous sinus. These cells form an ovoid sinoatrial node (SAN), on the left venous valve. After the development of the SAN, the superior endocardial cushions begin to form a pacemaker as known as the atrioventricular node.
- 20. With the development of the SAN, a band of specialized conducting cells start to form creating the bundle of His that sends a branch to the right ventricle and one to the left ventricle. The human embryonic heart begins beating approximately 21 days after conception.
- 21. EMBRYOLOGY OF LUNG INTRODUCTION: Lung development refers to development of the lungs. Lung develops from: o Endoderm - tubular ventral growth from foregut pharynx. o Mesoderm - mesenchyme of lung buds. o Intraembryonic coelom - pleural cavities elongated spaces connecting pericardial and peritoneal spaces. The development of lungs starts after the 4th week of fertilization and continue to grow along with the heart.
- 23. Week 4 - laryngotracheal groove forms on floor foregut. Week 5 - left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)
- 24. Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes. Week 7 - enlargement of liver stops descent of heart and lungs.
- 25. Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant. Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and sacs.