Embryology Lecture Notes PDF

LECTURE #1 1 EMBRYOLOGY 2 By the end of the lecture, you should be able to: 3  Describe the Formation, Site, Union, Division of the 5 heart tube. 6  Describe the formation and fate of the...

LECTURE #1 1 EMBRYOLOGY 2 By the end of the lecture, you should be able to: 3  Describe the Formation, Site, Union, Division of the 5 heart tube. 6  Describe the formation and fate of the (Sinus 7 Venosus).  Describe the formation of the interatrial and the 11 interventricular septae. 12  Describe the formation of the two atria and the two 15 ventricles. 16  Describe the partitioning of the Truncus arteriosus and formation of the aorta and pulmonary trunk. 17  List the most common cardiac anomalies. 2 EMBRYOLOGY It’s the first functional organ to develop. Origin: cardiogenic area of splanchnic mesoderm The heart primordium can be seen at 18 days as an angioplastic cords which will be canalized to form the 2 heart tubes. It begins cranial to the developing mouth & nervous system and ventral to the developing pericardial sac (as in A) , after the head fold completed the developing heart tubes lie in the ventral aspect of the embryo dorsal to the developing pericardial sac. (as in C) cranial Ventral Dorsa l It begins to beat at 22 to 23 days. Blood flow begins during the beginning of the fourth week. can be visualized by Ultrasound Doppler 3  EMBRYOLOGY the 2 heart tubes approach each other After lateral folding of the embryo and fuse to form a single endocardial heart tube within the pericardial sac. The fusing occurs in a craniocaudal direction. The heart tube grows faster than the pericardial sac, so it shows 5 alternate dilations separated by 4 constrictions: * Sinus venosus, the venous end * Truncus Arteriosus, the Arterial end * Common Ventricle. * Common Atrium. U-Shaped heart tube S-Shaped heart tube * Bulbus Cordis. (the smooth part of the ventricles) The U-shaped heart tube (bulboventricular loop) forms as a result of Bulbus cordis and ventricle growing faster than other regions. As the heart tube more develops it bends upon itself so the atrium and sinus venous become dorsal to the truncus arteriosus, bulbus cordis, and ventricle, and this is called Loop formation Or S- Shaped Heart Tube. 4 EMBRYOLOGY By this stage the sinus venosus has developed 2 lateral expansions, (Horns) : right and left horns (each horn will receive 3 veins ) Left common Left horn Right horn cardinal vein and body  Each sinus venosus' horn receives 3 veins: 1) The Cardinal vein from the fetal body. Forms the Forms the Atrophy and smooth 2) The Vitelline vein from the yolk sac. oblique vein form the posterior of the left coronary wall of the atrium sinus 3) The Umbilical vein from the placenta. right atrium 5 EMBRYOLOGY Rough Smooth Trabeculated posterior part of anterior part the right atrium (musculi pectanti) Form the Right Derived from the horn of the primordial common sinus venosus atrium  Smooth part:  These two parts are demarcated by the crista Derived from the absorbed Pulmonary Veins terminalis ( internally ) , and sulcus terminalis ( externally ).  Rough Trabeculated part: 6 Derived from the common primordial atrium. EMBRYOLOGY  The partitioning begins by the middle of 4th week. It is completed by the end of 5th week. It occurs to 4 different structures : 1) Atrioventricular canal. 2) Common atrium. 3) Common ventricle. 4) Truncus arteriosus & Bulbus cordis. 7 EMBRYOLOGY Two endocardial cushions are formed on the dorsal and ventral walls of the AV canal. The AV endocardial cushions approach each other and fuse to form the septum intermedium. Dividing the AV canal into right & left canals (2 Arrows). These canals partially separate the primordial atrium from the ventricle.  Septum Primum: -It is sickle- shaped septum that grows from the roof of the common atrium towards the fusing endocardial cushions (septum intermedium). - it divides the common atrium into right & left halves. 8 EMBRYOLOGY  Ostium Primum: Ostium: an opening into a vessel or cavity of the body. -The two ends of septum primum reach to the growing endocardial cushions before its central part. -Now the septum primum bounds (surrounds) a foramen called ostium primum. -Function of this foramen: It serves as a shunt, enabling the oxygenated blood to pass from right to left atrium. -Fate of ostium primum: It become smaller and disappears as the septum primum fuses completely with the septum intermedium to form the AV septum.  Septum Secundum: -On the upper part of septum primum , a small openings are seen and fuse together to form an opening called Ostium secundum. This foramen has a specific septum called septum secundum. -It forms an incomplete partition between the two atria. - Consequently a valvular oval foramen forms, (foramen ovale).  Fate of foramen Ovale: -At birth when the lung circulation begins, the pressure in the left atrium increases. - The valve of the foramen ovale is pressed against the septum secundum and obliterates the foramen ovale. -Its site is represented by the Fossa Ovalis -Its floor represents the persistent part of the septum primum. 9 -Its limbus (anulus) is the lower edge of the septum secundum EMBRYOLOGY The interventricular is divided into The Muscular part The Membranous part Division of the primordial ventricle is first It is derived from 3 parts : indicated by a median muscular ridge, the primordial interventricular septum. 1) A tissue extension from the right side of the endocardial cushion.  It is a thick crescentic fold which has a concave upper free edge. 2) Aorticopulmonary septum.  This septum bounds a temporary 3) Thick muscular part of the IV connection between the two ventricles septum. called Interventricular foramen (Because the muscular part can't reach to the cushions). 10 EMBRYOLOGY The bulbus cordis forms the smooth upper part of the two ventricles. : In the left In the right ventricle: Ventricle: It forms the aortic It forms the Conus Vestibule which Arteriosus or -A spiral septum develops in the truncus leads to the aorta. (Infundibulum) which leads to the arteriosus dividing it into aorta and pulmonary trunk. pulmonary trunk (that’s why it is called Aorticopulmonary septum).  The septum divides the upper and lower part vertically (Right & Left).  It deviates in the middle part Horizontally (dividing aorta and pulmonary trunk into anterior & posterior parts). 11 EMBRYOLOGY 1) Atrial septal defects (ASD): a)  Excessive resorption of common atrium. septum primum b) Excessive resorption of (Large foramen ovale) septum primum c) Patent foramen ovale d) Absence of septum secundum ( causes mixture of blood between the two atrium)  Patent foramen ovale No closing of foramen ovale It can be Asymptomatic. 12 EMBRYOLOGY 2) VENTRICULAR SEPTAL DEFECT (VSD): Roger’s disease Absence of the membranous part of interventricular septum. Usually accompanied by other ((Blue baby)) cardiac defects. 3)TETRALOGY OF FALLOT: 1. Pulmonary stenosis. 2. Right ventricular hypertrophy. 3- VSD (absent of membrane IV septum) 4-Overriding of the aorta 13 EMBRYOLOGY 4) (TGA) OR TRANSPOSITION OF GREAT ARTERIES: TGA is due to abnormal rotation or malformation of the aorticopulmonary septum, so the right ventricle joins the aorta, while the left ventricle joins the pulmonary artery. It is one of the most common cause of cyanotic heart disease in the newborn. Often associated with ASD or VSD. 5)Persistent Truncus Arteriosus: It is due to failure of the development of the aorticopulmonary (spiral) septum. It is usually accompanied with VSD. 14 EMBRYOLOGY Heart primordium. 18th Day Heart start to beat 22-33 Days Begins: Partitioning of: middle of 4th week 1. Atrioventricular canal 2.Common atrium 3. Common ventricle 4.Truncus Complete: arteriosus & Bulbus cordis End of 5th week Fate of foramen Ovale. At birth 15 EMBRYOLOGY 1. First heart beat starts at: 4. Which of the follow is NOT part of a. Fourth Week. TETRALOGY OF FALLOT: b. 18th Day. a. Pulmonary stenosis c. At 22 to 23th day. b. Overriding of the aorta d. Begins at the middle of the 4th week. c. Thicked right ventricle wall d. ASD 2. The right horn of sinus venosus forms : a. The Rough Anterior wall of the right atrium. b. The smooth Posterior wall of the right atrium. c. Atrophy and forms coronary sinus d. The oblique vein D 4. C 3. 3. The Bulbus cordis: B 2. a. Begins by the 3rd week and completed by 5th week. C 1. b. Begins by the 3rd week and completed by 4th week. c. Begins by the 4th week and completed by 5th week. d. Begins by the 4th week and completed by 6th week. 16 EMBRYOLOGY  Heart embryology video: http://www.youtube.com/watch?v=5DIUk9IXUaI  Development of heart: http://www.youtube.com/watch?v=OArR67aFze0  Easy Ways to Remember Heart Embryology derivatives: http://www.youtube.com/watch?v=YxPp67XluQA  Development of the heart: http://www.onlineexambuilder.com/development-of-the-heart/exam-19456 17 EMBRYOLOGY TEAM 434 [email protected] 18