Embryology L 2.2 Early Development of the Cardiovascular System PDF

# Embryology L 2.2 ## Early Development of the Cardiovascular System-1 ### Dr. Saadi Saleh Mohammed Barwari ### 21st January 2025 ## Objectives By the end of this lecture and after appropriate self-learning you should be able to: 1. Explain the formation and regions of the developing heart 2. Descr...

# Embryology L 2.2 ## Early Development of the Cardiovascular System-1 ### Dr. Saadi Saleh Mohammed Barwari ### 21st January 2025 ## Objectives By the end of this lecture and after appropriate self-learning you should be able to: 1. Explain the formation and regions of the developing heart 2. Describe the formation and looping of the primitive heart tube 3. Relate the anatomy of the adult heart to embryonic structures 4. Describe in brief the development of the great vessels. ## LO 1 ### Formation and Position of Heart tube #### Cardiogenic field Blood islands form in the visceral (splanchnic) layer of lateral plate mesoderm cranial to the oropharyngeal membrane and neural fold "developing brain". A horseshoe-shaped endothelial tube (endocardial tubes fusing into a single primitive heart tube) develops as these blood islands coalesce. In the presomite stage, they are induced by underlying pharyngeal endoderm to form cardiac myoblast. The intraembryonic cavity over it later develops into pericardial cavity. **Blood islands** also appear in this mesoderm, where they - will form blood cells and vessels by vasculogenesis - Other blood islands appear bilaterally, parallel & close to the midline of the embryonic shield. These islands form a pair of longitudinal vessels, the dorsal aorta. ### What does folding of the embryo do to the developing heart? - **Lateral folding**: Creates a heart tube - **Cephalocaudal folding**: Brings the heart tube into the thoracic region ### Folding By the 22nd day of development, the two tubes fuse and form a single, heart tube consisting of an: - Inner endocardial tube - Outer myocardial mantle **HEART BEATS AT DAY 22** The developing heart tube bulges more and more into the pericardial cavity. Initially, however, the tube remains attached to the dorsal side of the pericardial cavity by a fold of mesodermal tissue, the dorsal mesocardium. No ventral mesocardium is ever formed. With further development, the dorsal mesocardium disappears, creating the transverse pericardial sinus, which connect both sides of the pericardial cavity. The heart is now suspended in the cavity by blood vessels at its cranial and caudal poles. ### Lateral Folding - During these events, the myocardium thickens and secretes a layer of extracellular matrix, rich in hyaluronic acid called cardiac jelly, which separates it from the endothelium. - In addition, formation of the proepicardial organ occurs in mesenchymal cells located at the caudal border of the dorsal mesocardium. Cells from this structure proliferate and migrate over the surface of the myocardium to form the epicardial layer (epicardium) of the heart. - Thus, the heart tube consists of three layers: (1) the endocardium, forming the internal endothelial lining of the heart; (2) the myocardium, forming the muscular wall; and (3) the epicardium or visceral pericardium, covering the outside of the tube. - This outer layer is responsible for formation of the coronary arteries, including their endothelial lining and smooth muscle. ### The circulatory system is the first organ in operation. ### Development of the Heart - **Head:** Cardiogenic area, Primitive blood vessels - **Tail:** 18 days **Blood Flow:** - 20 days: Endocardial tubes - 21 days: Fusion into primitive heart tube - 22 days: Truncus arteriosus, Bulbus cordis, Primitive ventricle, Primitive atrium - 23 days: Truncus arteriosus, Bulbus cordis, Ventricle, Atrium, Sinus venosus - 24 days: Right atrium, Ventricle, Atrium, Sinus venosus - 35 days: Aortic arch arteries, Truncus arteriosus, Left atrium, Ventricle ### Partitioning of the Heart into Four Chambers - 28 days: Septum primum, Atrium, Ventricle, Interventricular septum - 8 weeks: Atrioventricular canals, Dorsal endocardial cushion, Right atrium, Tricuspid valve, Right ventricle, Foramen ovale, Left atrium, Mitral valve, Left ventricle ### Dorsal folding As a result of cephalocaudal folding of the embryo, the heart and pericardial cavity moves to the thorax. ### Primitive Heart Tube - Aortic Roots - Truncus arteriosus - Bulbus cordis - Ventricle - Atrium - Sinus venosus ### 22nd Day of Development - Atrium - Left and right horns of sinus venosus - Truncus arteriosus - Bulbus cordis - Ventricle ### SEM of Heart Tube - Diagram is of a Heart Tube ### 23-28 Cardiac Looping - **Cardiac Loop**: The heart tube continues to elongate and bend. - **On day 23**: The cephalic position of the heart tube bends ventrocaudally, and to the right and the atrial "caudal" portion of the tube shifts dorsocranially and to the left. - This bending, which may be due to cell shape changes, creates the Cardiac Loop. - **It is completed 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.** ### SEM of Cardiac Looping Day 23-28 - Diagram is of a Heart Tube **LO 2** ### The Result of Cardiac The different parts of the heart tube develop in the following pattern: 1. The atrioventricular junction remains narrow and forms the atrioventricular canal, which connects the common atrium and the early embryonic ventricle. 2. The bulbus cordis is narrow except for its proximal third. This portion will form the trabeculated part of the right ventricle. - 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 (ascending aorta) and pulmonary trunk. 3. The ventricle form the left ventricle. 4. The junction between the ventricle (LV) and the bulbus cordis (RV), remains narrow. It is called the primary interventricular foramen, externally indicated by the bulboventricular sulcus. Thus, the cardiac tube is organized by regions along its craniocaudal axis from the conotruncus to the right ventricle to the left ventricle to the atrial region, respectively. The bulbus cordis is divided into the truncus arteriosus, conus cordis, and trabeculated part of the right ventricle. ### Development of the Sinus Venosus In the middle of the 4th week, the sinus venosus receives venous blood from the right and left sinus horns. Each horn receives blood from 3 important veins: - The vitelline or omphalomesenteric vein - The umbilical vein - The common cardinal vein With obliteration of the right umbilical vein and the left vitelline vein during the 5th week, the left sinus horn rapidly loses its importance. When the left common cardinal vein is obliterated at 10 weeks, all that remains of the left sinus horn is the coronary sinus. As a result of left to right shunts of blood the right sinus horn and veins enlarge greatly. The right sinus horn (which now forms the only communication between the original sinus venosus and the atrium) is incorporated into the wall of the right atrium to form the smooth-walled part "sinus venarum’’, also forms SA node. **LO 3** While pumping, the tube differentiates into five regions (from output to input): 1. **Truncus arteriosus** - becomes ascending aorta and pulmonary trunk of the adult 2. **Bulbus cordis** - an enlargement that becomes right ventricle, including conus arteriosus. 3. **Ventricle** - an enlargement that becomes the left ventricle. 4. **Atrium** - a compartment that becomes adult right and left atriums, and 5. **Sinus venosus** - a paired region into which veins drain; the right becomes incorporated into the adult atrial wall, the left becomes coronary sinus **LO 4** ### The Venous Pole of the Heart is Anchored in the Septum Transversum - Closing cranial neural fold - Anterior cardinal vein - Aortic arches (II and III) - Internal carotid artery - Septum transversum - Anterior intestinal portal - Lateral body wall fold - Posterior intestinal portal - Hindgut - Common cardinal vein - Dorsal aorta - Posterior cardinal vein - Heart - Aortic sac - Vitelline vein - Vitelline artery - Umbilical vein and artery - Placenta ### Each Pharyngeal Arch Contains An Aortic Arch - Lens placode - Otic placode - Pharyngeal arches - Heart bulge - Vitelline duct - Umbilical cord - Allantois - Umbilical ring - Aortic arches (I-VI) - Dorsal aorta - Right dorsal aorta - Left dorsal aorta - Fused right and left dorsal aortae - Aortic sac - Limb ridge - 28 Days **Aortic Arches**: When pharyngeal arches form during the 4th & 5th weeks of development, each arch receives it's own cranial nerve and it's own artery. **These arteries** the aor-tic arches, arise from the aortic sac, the most distal part of the truncus arteriosus. The aortic arches are embedded in mesenchyme of the pharyngeal arches and ter-minate in the right and left dorsal aortae. (In the region of the arches, the dorsal aortae remain paired, but caudal to this region, they fuse to form a single vessel.) ### Each Pharyngeal Arch Contains an Aortic Arch Continued... - Anterior cardinal vein - Common cardinal vein - Dorsal aorta - Posterior cardinal vein - Aortic arches (II and III) - Internal carotid artery - Heart - Aortic sac - Vitelline vein - Vitelline artery - Umbilical vein and artery - 4 weeks - Placenta The pharyngeal arches and their vessels appear in a cranial-to-caudal sequence, so that they are not all present simultaneously. The aortic sac contributes a branch to each new arch as it forms, giving rise to a total of 5 pairs of arteries. (The 5th arch either never forms or forms incompletely, then regresses. Consequently, the five arches are numbered I, II, III, IV, & VI). During further development, this arterial pattern becomes modified, and some vessels regress completely. **Neural crest cells in each pharyngeal arch contribute the coverings (smooth muscle and connective tissue) of the arch vessels and also regulate patterning of these vessels. Signals from endoderm and ectoderm lining the arches provide interactive signals to crest cells to regulate the patterning process.** ### Regression Patterns of the Aortic Arches - Dorsal aorta - Aortic arches (I-VI) - Internal carotid artery - Right vagus nerve - Left vagus nerve - Common carotid artery - Right subclavian artery - Right recurrent nerve - 7th intersegmental artery - Aortic sac - Right dorsal aorta - Left dorsal aorta - Fused right and left dorsal aortae - Day 29 - Arch of aorta - Left recurrent nerve - Ductus arteriosus - Pulmonary artery In the 29 day embryo, the first and second aortic arches have disappeared. The third, fourth, and sixth arches are large. The conotruncal region has divided so that the sixth arches are now continuous with the pulmonary trunk. ### Derivatives of the Aortic Arches - Arch 1: By day 27, most of it has disappeared except a small portion to form Maxillary arteries. - Arch 2: Similarly soon disappears. The remaining portions are the Hyoid & stapedial arteries. - Arch 3: Common carotid and first part of the internal carotid arteries (a) - Arch 4: Left side: part of the arch of the aorta, **between** the left common carotid to the left subclavian arteries (b). - Arch 4: Right side: Right subclavian artery (proximal portion) (c). - Arch 6: Left Side- Left Pulmonary artery and ductus arteriosus. - Arch 6: Right side: The proximal part becomes proximal segment of Right pulmonary artery. The distal part loses it's connection with the dorsal aorta and disappears. (a) Remainder of the internal carotid arteries are derived from the dorsal aorta; the external carotid arteries sprout from the 3rd aortic arch. (b) the proximal portion of the aortic arch is derived from the left horn of the aortic sac; the right horn of this sac forms the brachiocephalic artery. (c) The distal portion of the right subclavian artery “as well as the left subclavian artery” is formed by a portion of the right dorsal aorta and from the seventh intersegmental arteries on their respective sides. ### Postnatal Arrangement of the Aortic Arch- Derived Vessels - Common carotid artery - Right subclavian artery - Internal carotid artery - External carotid artery - Arch of aorta - Ductus arteriosus - Right external carotid artery - Right subclavian artery - Brachiocephalic artery - Ascending aorta - Pulmonary artery - Left internal carotid artery - Left common carotid artery - Left subclavian artery - Ligamentum arteriosum - Pulmonary artery - Descending aorta ### Any Question? - thank you! ### Select the ONE Best Answer 1. The vascular system appears in - a) the middle of the third week 2. On what day does the heart start to beat? - a) 22 3. What structure does the proximal third of the bulbus cordis become? - a) Right Ventricle 4. What structure does the middle third (conus cordis) of the bulbus cordis become? - c) Ventricular Outflow Tracts 5. What structure does the distal third (truncus arteriosus) of the bulbus cordis become? - d) Aorta & Pulmonary Artery 6. What major structure is formed by. the sinus venosus? - e) Right Atrium 7. During cardiac loop, which of the following is wrong? - e) It is complete by day 33.