Hello! Welcome to my channel Today we are going to talk about the Embryology of the Cardiovascular System First part in this video we are going to touch the referred topics to the formation of the heart, your partition and the origin of its driving system. All these topics, based on the book of Embryology Langman 14th Edition We start!
As the embryo grows during the third week It reaches a size that no longer allows the simple diffusion mechanism distribute oxygen and nutrients to all your cells or may dispose of waste products. The initial development of the heart and the circulatory system is an embryonic adaptation allowing rapid growth of the embryo by constituting an effective mechanism for the distribution of nutrients. Progenitor heart cells are located in the epiblast, adjacent to the cranial end of the primitive line.
From there they migrate along the line and inland of the visceral layer of the mesoderm of the lateral plate, where they form a horseshoe-shaped cell group which is called the primary cardiogenic field (CPC). These cells form certain regions of the atria and the entire left ventricle. The right ventricle and the outflow tract (which are the arterial cone and arterial trunk) derive from the secondary cardiogenic field (CCS) which also provides cells for integration of the atria and the caudal end of the heart.
Once the cells establish the Primary Cardiogenic Field are induced by the underlying pharyngeal endoderm to form cardiac myoblasts and blood islets, that will give rise to blood cells and vessels through the vasculogenesis process With the passage of time the islets unite and they form a horseshoe tube lined by endothelium and surrounded by myoblasts. This region is known as the cardiogenic region and intraembryonic coelom which is located on it then becomes the Pericardial Cavity CARDIAC TUBE Initially, the central portion of the cardiogenic region is located in a previous region to the oropharyngeal membrane already the neural plate However, with the closure of the neural tube and the formation of brain vesicles, the Central Nervous System grows cranially so quickly that extends over the central cardiogenic region and the future Pericardial cavity As a consequence of brain growth and the cephalic folding of the embryo, the Oropharyngeal Membrane suffers traction in the ventral direction while the Heart and Pericardial Cavity they are located first at the cervical level and finally at the thoracic level As the embryo grows and it folds in the cephalocaudal direction, it also does it laterally Consequently, the medial and caudal regions of the two cardiac primordia they fuse except at their most caudal end. Simultaneously the central horseshoe-shaped region dilates to form the future exit tract and the ventricular regions Thus the heart becomes in a continuous dilated tube consisting of an internal endothelial lining and an external myocardial layer At its caudal pole it receives venous drainage and it starts pumping blood from the first aortic arch towards the dorsal aorta at its cranial pole The developing heart tube bulges more and more in the direction of the pericardial cavity However, at the beginning it remains united to the dorsal region of the pericardial cavity by means of a fold of mesodermal tissue which is called the dorsal mesocardium derived from the Secondary Cardiogenic Field.
As development continues, the mid region of the dorsal mesocardium degenerates and gives rise to the transverse pericardial sinus, connecting both sides of the pericardial cavity The heart is then suspended in that cavity through the blood vessels at its cranial and caudal ends As these events occur, the myocardium thickens and secretes an extracellular matrix layer rich in hyaluronic acid called cardiac jelly Furthermore, the formation of the proepicardial organ occurs in mesenchymal cells located on the caudal border of the dorsal mesocardium The cells of this structure proliferate and migrate over the surface of the myocardium to form the epicardial layer of the heart Thus, the heart tube is made up of three layers 1- The Endocardium which forms the endothelial lining inner heart 2- The Myocardium what constitutes the muscular wall 3- The Epicardium or Visceral Pericardium covering the outside of the tube The outer layer is responsible for the formation of the coronary arteries and the endothelial layer forms the smooth muscle layer Now we go with the FORMATION OF THE CARDIAC HAND The heart tube continues to increase in size while adding CCS cells at its cranial end This growth process is essential for normal integration of the right ventricle, the region of the outflow tract and for the folding process As the exit tract continues to lengthen, the heart tube begins to curve on day 23 The cephalic portion of the tube performs this action ventrally, caudally, and to the right, in both the atrial or caudal portion moves dorsally, cranially and to the left This folding is what causes the cardiac loop His training is completed on day 28 While the heart loop is forming localized expansions are observed at the entire length of the tube. The auricular portion constitutes a common atrium and later it will be incorporated into the pericardial cavity The atrioventricular junction does not expand and gives rise to the atrioventricular duct, connecting the common atrium with the early embryonic ventricle. The arterial bulb is narrow, except in its proximal third This region will give rise to the portion trabeculate of the right ventricle The middle region where the arterial cone is, will constitute the outflow tracts of the two ventricles The distal portion of the bulb located in the arterial trunk will form the roots and proximal segments of the aorta and pulmonary artery.
The junction between the ventricle and the arterial bulb remains narrow and is called primary interventricular foramen Thus, the heart tube is organized by region following its cranio-caudal axis in this way: 1- Trunk Region 2- Right Ventricle 3- Left Ventricle 4 - Atrial Region When the folding is complete smooth-walled heart tube begins to develop primitive trabeculae in two well-defined areas just proximal and distal to the primary interventricular foramen The bulb retains its smooth walls for some time The Primitive Ventricle that now has trabeculae, is called the Primitive Left Ventricle Similarly, the proximal third trabeculate of the heart bulb Primitive Right Ventricle is named. The truncated cone region of the heart tube that initially on the right side of the pericardial cavity, moves gradually until reaching a more medial position This change of position is a consequence of the formation of two dilations transverse in the atrium, protruding on either side of the heart bulb DEVELOPMENT OF THE VENOUS SINUS In the middle of the fourth week the venous sinus receives venous blood coming from the antlers of the right and left breasts. Each pole receives blood from three important veins: 1- The yolk or omphalomesenteric vein, 2- The umbilical vein 3- The common cardinal vein At the beginning, communication between the sinus and the atrium is wide Despite this, in a short time the entrance to the breast scrolls to the right This displacement is due above all in the presence of short circuits left-right blood that are observed in the venous system during the fourth and fifth week of development With obliteration of the right umbilical vein and the left yolk vein during the fifth week the horn of the left sinus of the venous sinus quickly loses its importance When at 10 weeks it is obliterated the left common cardinal vein the only thing left of the left breast shaft is the oblique vein of the left atrium and the coronary sinus As a consequence of short circuits left-right blood the horn and veins of the right breast increase its dimensions considerably The right pole, which now constitutes the only communication between the original venous sinus and the atrium, joins the right atrium to give rise to the smooth portion from the wall of that cavity Your site of entry, the Sinoauricular Orifice it is flanked by a valve fold Right and left Venous Valves In your dorsocranial region valves fuse and conform a ridge known as Septo Espurio At the beginning the valves are big, but when the horn of the right breast is incorporated into the wall of the atrium, the Left Venous Valve and Spurious Septum merge with the developing Atrial Septum The upper portion of the right venous valve completely disappears and its lower segment grows to form two structures: 1- The Inferior Vena Cava Valve 2- The Coronary Sinus Valve Terminal Ridge creates the dividing line between the original trabeculated portion of the right atrium and its smooth wall that originates from the Right Sinus Pole TRAINING OF THE CARDIAC SEPARATORS The main partitions of the heart form between days 27 and 37 of development, when the embryo length increases by 5 mm a 16 - 17 mm approximately A mechanism by which a partition can be formed involves the active growth of two masses approaching each other until merging, so that they divide the cavity in two independent ducts these masses are called Endocardial Pads or Bearings Such a partition can also be formed by active growth single tissue mass that expands until it reaches the opposite side of the cavity These endocardial prominences develop in the regions atrioventricular and truncus and on these sites they facilitate training of the atrial and ventricular septa what are the ducts and the atrioventricular valves and the aortic and pulmonary ducts SEPARATE IN THE COMMON HEADSET At the end of the fourth week, a crescent-shaped ridge grows from the roof of the common atrium towards its cavity This ridge is the first portion of the septum primum The two ends of this partition expand towards the endocardial pads in the atrioventricular canal The hole that persists between the lower edge of the septum primum and the endocardial pads is the Ostium Primum Next, extensions of the upper and lower endocardial pads they grow along the edge of the septum primum, thereby closing the ostium primum However before the closing ends a process of programmed cell death (apoptosis) which ends up producing perforations in the upper region of the septum primum The coalescence of these areas gives rise to the Ostium Secundum which ensures the free passage of blood from the right primitive atrium to the left When the right atrial cavity expands as a consequence of incorporation of the horn of the venous sinus a new fold appears crescent shaped This new fold is the Septum Secundum Its anterior end extends downward in the direction of the septum in the atrioventricular canal When the left venous valve and spurious septum merge with the right side of the septum secundum the free concave edge of this last structure begins to overlap the ostium secundum The opening left by the septum secundum it is called foramen ovale When the upper portion of the septum primum gradually disappears the remaining portion becomes at the valve of the foramen ovale The pathway between the two atrial cavities is made up of an elongated oblique cleft laying the blood from the right atrium flows to the left side AURICULOVENTRICULAR SEPARATION Finishing the fourth week, four endocardial pads appear atrioventricular two sides, one on the dorsal or upper edge atrioventricular duct and one on the lower or ventral edge With the end of the 5th week, dorsal and ventral pads project to a greater extent towards the cavity and fuse, giving rise to a complete division of the duct in left and right atrioventricular orifices SEPARATION OF THE ARTERIAL TRUNK AND THE ARTERIAL CONE During the fifth week of life, Flank walls appear on the trunk, facing each other on opposite walls These flanges are called of arterial trunk ridges and they are located in the upper right region of the wall and in the lower left region of the wall the first one is called Upper right ridge of arterial trunk and the second Lower Left Crest of arterial trunk The upper right ridge of the trunk grows distally and to the left, in both the lower left grows distally and clockwise In this way as they lengthen in the direction of the aortic sac the ridges spiral, what gives rise to position of the aortic and pulmonary arteries After its complete merger, the ridges give rise to the aortopulmonary septum, which results in the position of the aorta and the lung When these ridges appear on the trunk, similar ridges develop along of the right dorsal walls and left ventral of the arterial cone Trunk cone ridges now grow towards each other and distally to join the septum of the trunk When the two frustoconal ridges merge, the septum divides the cone into an anterolateral canal for the right ventricular outflow tract and one posteromedial for the left ventricular outflow tract And the last partition that we are going to talk about is in the ventricles By the end of the fourth week, the two Primitive Ventricles start to expand This is accomplished by continuous growth of the myocardium in the outer region and the continuous generation of diverticula and trabeculae in the internal The medial walls of the expanding ventricles gradually add and merge to constitute the muscular portion interventricular septum The interventricular foramen, located above the muscular portion interventricular septum will obliterate once it is completed cone septum formation In the septum formation membranous ventricle intervene the muscular septum and the growths of the truncal ridges and the endocardial pads Tissue growth of the anterior endocardial pad along the top of the interventricular muscular septum close the hole And the complete closure of the ventricular foramen gives rise to the membranous portion interventricular septum And the last topic of this video is the CARDIAC CONDUCTION SYSTEM Initially all myocardial cells in the heart tube have pacemaker activity and the heart begins to beat around 21 days of gestation Soon after, the cardiac pacemaker is restricted to left caudal region of heart tube Later, the venous sinus assumes this function.
and while it is incorporated into the right atrium, pacemaker tissue is arranged near the superior vena cava drainage hole This is how the Sinoauricular Node (SA) is formed The Auriculoventricular (AV) Node begins its formation from a group of cells distributed around the atrioventricular duct, which coalesce to constitute the AV node Except for nerve fibers sympathetic and parasympathetic that end at the Sinoauricular Node (SA), the rest of the cells of the cardiac conduction system derived from cardiac myocytes that differ in Node Cells, the Beam Branches and the Purkinje Fibers. And well up to here with the end of the video, Hope it has fit If you liked it please give it LIKE SUBSCRIBE and don't forget to activate the BELL for upcoming Embryology videos Greetings and Success in your exams!
