Embryo - Cardiovascular system Flashcards
Explain the role of cephalo-caudal and lateral embryonic folding in positioning of the heart field and heart tube.
Events at gastrulation position the mesenchymal cells that will give rise to the cardiogenic field ahead of the oropharyngeal membrane and the neural plate. Angiogenic cells migrate from the primitive streak to the anterior lateral plate
Explain the roles of left-right sidedness and primary & secondary heart fields in heart development. What structures in the heart are affected by the left-right sidedness of the heart fields? What happens when this process is disrupted on left? on the right?
PHF cells are specified to form atria and left and right ventricles of the heart. They migrate from the cranial end of the primitive streak to the lateral plate mesoderm where they form clusters. Once they establish PHF they are induced by underlying pharyngeal endoderm to form cardiac myoblasts and blood islands. The remainder of the right ventricle and outflow trace are derived from the SHF. The SHF provides cells that lengthen the arterial and venous poles of the heart, which includes part of the right ventricle and the outfiow tract [conus cordis and truncus arteriosus] and atria and sinus venosus, respectively. Disruption of the SHF causes shortening of the outfiow tract región, resulting in outfiow tract defects. As the cells migrate through the primitive streak they are specified by the laterality pathway to become the different parts of the heart. Patterning of the heart cells occurs at the same time that laterality (left-right sidedness) is being established for the entire embryo, and proper positioning of the heart toward the left of the body midline requires the inductive effects of both Nodal/Lefty2/PITX2 on the left side and the additional effects of BMP/Prrx1a on the right side. Cells in the SFH also exhibit laterality such that those on the right side contribute to the left of the outflow tract region and those on the left to the right. The laterality of cells in the SFH explains the spiraling nature of the pulmonary artery and aorta and ensures the the aorta exits from the left ventricle and the pulmonary artery from the right ventricle. The laterality pathway. The pathway is expressed in lateral plate mesoderm on the left side and involves a number of signaling molecules, including serotonin (5HT), which results in the expression of the transcription factor PITX2, the master gene for left sidedness. This gene specifies the left side of the body and also programs heart cells in the primary and SHFs. The right side is specified as well, but genes responsible for this patterning have not been completely determined. Disruption of this pathway on the left results in lateral abnormalities, including many heart defects (dextrocardia: right-sided heart, ventricular septal defects, atrial septal defects, double outlet right ventricle, transposition of great vessels, pulmonary stenosis, and more). Disruption of the BMP-Prrx1a signaling on the right side results in a shift of the heart loop towards the midline resulting in mesocardiac.
Describe the fusion of the endocardial tubes to form the single heart tube.
(17-23 days) The yolk sac endoderm plays a critical role in inducing the adjacent cell clusters to begin differentiating into the paired tubes. During gastrulation, heart fields move medially and merge. Primitive heart fields also rotate inferiorly from “head” region to “thorax”. As the heart fields merge the tubes also merge to form the primitive heart tube in the pericardial cavity. (Day23-25) The fused heart tube grows rapidly producing a large tortuous tube. This tube is subdivided into the Aortic roots, Bulbis cordis, future ventricles, Atrium, sinus venosus.
Identify the regions along the heart tube that will contribute to the inflow tracts, atria, ventricles, and outflow tracts
The growth of the heart tube is so rapid it causes the heart tube to start curling up on itself. The future left atrium then moves posteriorly and the ventricles move anteriorly. The Bulbus cordis becomes subdivided into the conus cordis and the truncus arteriosis which become the aortic trunk.
As the Future ventricle starts to expand and the atrium moves posteriorly the heart begins to beat, starting at the sinus venosus - this helps move the floor along.
Inflow tracts: two sets of sinus venosus
6 sets of veins start degenerating and growing together:
Cardinal veins coming from the embryo
Umbilical veins bringing oxygenated blood from the placenta
Vitelline veins coming from the yolk sac area.
Azygous vein grows and joins the superior vena cava. Brachiocephalic vein comes across and joins the superior vena cava. Umbilical and vitelline vein become the inferior vena cava.
The paired veins on left and right gradually consolidate and shift the entrance of the sinus venosis into the back of the atrium on the right side. The original pacemaker region of the heart tube is in the sinus venosis, and as the veins shift to the right atrium, the pacemaker/sinuatrial node moves with them.
The original veins on the left remain only as the coronory sinus, while the veins on the right coalesce into superior and inferior vena cava.
Identify the bulbus cordis, conus cordis, and truncus arteriosus, and name their derivatives.
Bulbus cordis: subdivided into the conus cordis and the truncus arteriosis as the heart rapidly expands.
Conus cordis: Pulmonary trunk
Truncus arteriosus: Aortic trunk to supple the various arches
Derivatives of the primitive aortic arches:
- The third arches: common carotids, internal carotids.
- The fourth arches: right subclavian artery and a small part of the arch of the aorta. (Left vagus and left recurrent laryngeal nerve)
- The sixth arches: proximal parts right and left pulmonary ducts. Also ductus arteriosus.
Describe the roles of cardiac looping, endocardial cushions, and spiral septum in dividing the single heart tube into the four-chambered heart.
Cardiac looping to the right begins as soon as the tubes fuse. Looping shifts the atria towards the “top” of the pericardial cavity and behind the ventricles as seen from the front.
Get right and left atrioventricular canal: The interior of the heart has outgrowth of tissue: endocardial cushions. These cushions grow toward the center and meet creating two separate blood flow tracts each with an atria and a ventricle.
Also have to have swelling of truncus and conus by cells which migrate in from the neural crest - one goes to pulmonary system and the other goes to the pulmonary system.
Atrial separation (seperation): Begins with the outgrowth of the septum priumum (right atrium) that produces an opening called the ostium primum. Continues with the growth of the septum secundum (left atrium) that produces a second opening; ostium secundum. Before birth, blood flows from right atrium to the left atrium through the foramen ovale in the atrial wall.
At birth when the right atrium becomes low pressure and the left atrium becomes high pressure the blood in the left atrium hits the septum secundum causing it to grow together and fuse slightly creating an interatrial septum.
Aorticopulmonary separation (spiral septum): Occurs when neural crest cells migrate to the conus ocrdis and the truncus arteriosus forming two pairs of swellings; these grow along the midline to form one septum that divides the outflow tract. The swellings from the truncus arteriosus twist as they develop forming a spiral outflow pathway. Aortic blood comes up posterior then comes out anterior at the top.
Outline the changes in venous, atrial, and arterial circulation at birth.
During the fetal stage of development, highly oxygenated blood flows into the fetus via the umbilical veins. At birth, the lungs take over and these fetal circulatory pathways shut off . The formation of serial aortic arch vessels within the pharyngeal arches. These connect the aortic sac with the dorsal aortae.
1. Ductus arteriosus becomes the ligamentum arteriosum (bypass mechanism for fetal blood that goes into the pulmonary trunk)
2. Oval foramen closes (bypass mechanisms for blood to skip pulmonary system)
3. Ductus venosus (to bypass liver in fetus because not eating) becomes the ligamentum venosum.
4. Umbilical vein becomes ligamentum teres hepatis
5. Umbilical arteries close
Pulmonary and arterial systems are no longer mixed after birth and pressure differential where left atrium has higher pressure forms!
What is the general timeline for cardiovascular development?
One of the first systems to develop so can get blood to all other developing systems
