Cardiovascular system-Embryology 2.pdf

Cardiovascular System Assist. Prof. Rasha Noori AL-shammary 1 Objectives 1. Describe Gross Anatomy of Heart 2. Establishment of the Cardiogenic Field 3. Describe Folding of the embryo 4-Formation and position of the heart tube 5. Describe Formation of the...

Cardiovascular System Assist. Prof. Rasha Noori AL-shammary 1 Objectives 1. Describe Gross Anatomy of Heart 2. Establishment of the Cardiogenic Field 3. Describe Folding of the embryo 4-Formation and position of the heart tube 5. Describe Formation of the Cardiac loop 6-DescribeFormation of the Cardiac Septa 7. Describe of Atrial system development 2 Cardiovascular System 3  Start beat at 4 week Beat about 100,000 / day It is the heart The blood pump 4  Located in the thoracic cavity between the lungs (mediastinum) The base is behind the sternum The apex just above the diaphragm to the left of the midline 5 Gross Anatomy of Heart 6 7 8 9 Establishment of the Cardiogenic Field 10  The vascular system appears in the middle of the third week, when the embryo is no longer able to satisfy its nutritional requirements by diffusion alone Cardiac progenitor cells lie in the epiblast, immediately lateral to the primitive streak. They migrate through the streak. The cells proceed toward the cranium and position themselves rostral to the oropharyngeal membrane and neural folds to form 11 cardiac myoblasts 12  Cardiogenic field Blood islands also appear in this mesoderm, where they will form blood cells and vessels by the process of vasculogenesis. With time, the islands unite and form a horseshoe-shaped endothelial-lined tube surrounded by myoblasts. This region is known as the cardiogenic field; the intraembryonic cavity over it later develops into the pericardial cavity. 13 14 15  Cephalocaudal folding As a result of cephalocaudal folding of the embryo, the heart and pericardial cavity moves to the thorax.  LATERAL FOLDING by the 22nd day of development, the two tubes fuses and form a single, heart tube consisting of an inner endocardial tube and an outer myocardial mantle HEART BEATS AT DAY 22 17  Formation and position of the heart tube Embryo folded cephalocaudally and laterally. Thus, the heart tube consisting of an inner endothelial lining and an outer myocardial layer. The tube remains attached to the dorsal side of the pericardial cavity by a fold of mesodermal tissue, the dorsal mesocardium. With further development, the dorsal mesocardium disappears, creating the transverse pericardial sinus, which connects both sides of the pericardial cavity. 18 19 20  Formation of the cardiac loop The heart tube continues to elongate and bend on day 23. The cephalic portion of the tube bends ventrally, caudally, and to the right. The atrial (caudal) portion shifts dorsocranially and to the left creates the cardiac loop. It is complete by day 28. While the cardiac loop is forming, local expansions become visible throughout the length of the tube. The atrial portion, initially a paired structure outside the pericardial cavity, forms a common atrium and is incorporated into the pericardial cavity. 21  The bulbus cordis (portion of tube that will form the trabeculated part of the right ventricle) is narrow except for its proximal third. The midportion, the conus cordis, will form the outflow tracts of both ventricles. The distal part of the bulbus, the truncus arteriosus, will form the roots and proximal portion of the aorta and pulmonary artery. 22  At the end of loop formation, the primitive ventricle, which is now trabeculated, is called the primitive left ventricle. The trabeculated proximal third of the bulbus cordis may be called the primitive right ventricle. The conotruncal portion of the heart tube (part of bulbus cordis), initially on the right side of the pericardial cavity, shifts gradually to a more medial position. This change in position is the result of formation of two transverse dilations of the atrium, bulging on each side of the bulbus cordis. 25 26 27  Formation of the Cardiac Septa The major septa of the heart are formed between the 27th and 37th days of development. Two actively growing masses of tissue that approach each other until they fuse, dividing the lumen into two separate canals. Or by active growth of a single tissue mass that continues to expand until it reaches the opposite side of the lumen. 28  The masses, known as endocardial cushions, develop in the atrioventricular and conotruncal regions. In these locations they assist in formation of the atrial and ventricular (membranous portion) septa, the atrioventricular canals and valves, and the aortic and pulmonary channels. 29 30  The other manner in which a septum is formed does not involve endocardial cushions. A narrow strip of tissue in the wall of the atrium or ventricle should fail to grow while areas on each side of it expand rapidly, a narrow ridge forms between the two expanding portions. When growth of the expanding portions continues on either side of the narrow portion, the two walls approach each other and eventually merge, forming a septum. 31  Such a septum never completely divides the original lumen but leaves a narrow communicating canal between the two expanded sections. It is usually closed secondarily by tissue contributed by neighboring proliferating tissues. Such a septum partially divides the atria and ventricles. 32 33  Septum formation in the common atrium At the end of the 4th week, a crest grows from the roof of the common atrium into the lumen. This crest is the first portion of the septum primum. The septum extend toward the endocardial cushions in the atrioventricular canal. The opening between the lower rim of the septum primum and the endocardial cushions is the ostium primum. 34  With further development, extensions of the superior and inferior endocardial cushions grow along the edge of the septum primum, closing the ostium primum. Before closure is complete, cell death produces perforations in the upper portion of the septum primum. And this forms the ostium secundum, ensuring free blood flow from the right to the left primitive atrium. 36 37  When the lumen of the right atrium expands as a result of incorporation of the sinus horn, a new crescent-shaped fold appears. This new fold, the septum secundum, never forms a complete partition in the atrial cavity. Its anterior limb extends downward to the septum in the atrioventricular canal. When the left venous valve and the septum spurium (in Sinus Venosus) fuse with the right side of the septum secundum, the free concave edge of the septum secundum begins to overlap the ostium secundum. 38 39  The opening left by the septum secundum is called the oval foramen (foramen ovale). When the upper part of the septum primum gradually disappears, the remaining part becomes the valve of the oval foramen. The passage between the two atrial cavities consists of an oblique elongated cleft through which blood from the right atrium flows to the left side. After birth, when lung circulation begins and pressure in the left atrium increases, the valve of the oval foramen is pressed against the septum secundum, obliterating the oval foramen and separating the right and left atria. 40 41  In about 20% of cases, fusion of the septum primum and septum secundum is incomplete, and a narrow oblique cleft remains between the two atria. This condition is called probe patency of the oval foramen. 42  Septum formation in the atrioventricular canal At the end of the fourth week, two mesenchymal cushions, the atrioventricular endocardial cushions, appear at the superior and inferior borders of the atrioventricular canal. And two lateral atrioventricular cushions appear on the right and left borders of the canal. The superior and inferior cushions, in the meantime, project further into the lumen and fuse, resulting in a complete division of the canal into right and left atrioventricular orifices by the end of the fifth week. 43 44  Atrial septal defect (ASD) Complete absence of the atrial septum or inadequate development of the septum secundum Failure of closure of ostium primum or secundum. 45  Vascular Development Arterial system Aortic Arches The aortic arches, arise from the aortic sac, the most distal part of the truncus arteriosus and they related to pharyngeal arches. 46 47  The aortic sac contributes a branch to each pharyngeal arch as it forms, giving rise to a total of five pairs of arteries. The five arches are numbered I, II, III, IV, and VI. During further development, this arterial pattern becomes modified, and some vessels regress completely. 48  By day 27 most of the first aortic arch has disappeared, although a small portion persists to form the maxillary artery. The second aortic arch soon disappears and the remaining portions of this arch are the hyoid and stapedial arteries. The third arch is large; the fourth and sixth arches are in the process of formation. The sixth arch is not completed, the primitive pulmonary artery is already present as a major branch. 49 50  In a 29-day. The first and second aortic arches have disappeared. The third, fourth, and sixth arches are large. The truncoaortic sac has divided so that the sixth arches are now continuous with the pulmonary trunk. 51  Vitelline and Umbilical Arteries The vitelline arteries, initially a number of paired vessels supplying the yolk sac, gradually fuse and form the arteries in the dorsal mesentery of the gut. The umbilical arteries, initially paired ventral branches of the dorsal aorta, course to the placenta in close association with the allantois. 52 53  Venous system In the fifth week, three pairs of major veins can be distinguished: 1. The vitelline veins, carrying blood from the yolk sac to the sinus venosus. 2. The umbilical veins, originating in the chorionic villi and carrying oxygenated blood to the embryo. 3. The cardinal veins, draining the body of the embryo proper. 54 Thanks 55