The cardivascular system is the first major system fo fxn in the embryo. When does it appear and when does it begin to fxn? What embryonic layers is it composed of?
1. Appears in the middle of 3rd week of development and starts to fxn at the beginning of week 4. Derived mainly from splanchic mesoderm and paraxial and lateral plate mesoderm.
What is the primordium, position, shape/appearance, and processes of early development of the primitive heart and vessels?
Primordium: Angiogenic cell clusters that coalesce to give rise to vessels.
Position: cranial at first, then in the future thoracic cavtiy anterior to the esophagus.
Shape/appearance: A tube
Processes: fusion of cell clusters to form tubes, foling of embryo to move the primitive heart to its adult location.
Discuss folding of the embryo as it relates to positioning of the heart, esophagus, and aorta.
The heart begins in the cranial-most region and during lateral folding "swings down" to lie in the throax. This area of the foregut will develop into the esophagus. The aorta remains posterior to the foregut.
What is the primitive heart (primordium, position, shape/appearance, processes)? What is formation of the cardiac loop? What are its parts?
The primitive heart is a simple tubular dilation of the cardiovascular system with cardiac muscle cells in the wall. It does not have four chambers. The formation of teh cardiac loop is the name of the porcess of dilation, bending, and folding of the tube.
The developing tubular heart dilates to form chambers, constricts to demarcate the transtion from the chambers to the outflow system and venous return and then rotates to the adult orientation in the thorax.
primordium: simple tubular dilation of the cardiovascular system with cardiovascular muscles in the wall
position: anterior to the developing esophagus in the thorax
shape/appearance: a tube
processes: dilation, bending, and folding of the tube (formation of the cardiac loop)
parts of embryonic structure and their adult structures:
truncus arteriosis: aorta and pulmonary trunk
bulbus cordis: smooth pats of the left and right ventricles
venticle: trabeculated parts (trabeculated carnae) of the left and right ventricles
atrium: trabeculated parts (pectinate muscles) of the left and right atria
sinus venosus: smooth part of right atrium and cornary sinus: short but wide veing lying along the heart's posterior surface btwn the left ventricle and left atrium that collects majority of cardiac venous blood and facilitates its movement into the right atrium
Discuss the directional flow of blood in the primitive heart and after birth.
In the primitive heart, there is unidrectional blood flow into the heart from the sinus venosus and away from the heart through the truncus arteriosis. After birth, multidirectional blood flow is needed into the atria and from the ventricles. see pg 59 of course notes
Discuss the primordium, position, shape/appearance, and processes involved in the endocardial cushions and mitral and tricuspid valves. How many endocardial cushions are there?
Four endocardial cushions surround the atrioventricular canal: anterior, posterior, and 2 lateral (4 total). The opposing cushions fuse to form the right and left atrioventricular canals. The remaining more central part of the cusion tissue then forms the mitral and tricuspid valves.
primordium: endocardial cushions form from neural crest cells and mesenchymal tissue. can have many diseases due to issues with migration of neural crest cells. Mitosis, maturation, migration: delay in any of these processes involving neural crest cells will lead to developmental issues.
position: along the fold btwn the primitive atria and ventricles
shape/appearance: can be thought of as a floor with a hole in each atrium to get to the ventricle
processes: migration of neural crest cells to the area and fusion of the endocardial cushions. purpose of this is to separate the atria and ventricles and form mitral and tricuspid valves.
please see pg 60 of course notes for another pic
What is the primordium, position, shape/appearance, and processes involved in forming a wall btwn the atria? Be specific in detailing all of the processes. What occurs in the atria after birth?
primoridium: one common atrium, roof of the atrium, endocardial cushions
position: a long vertical line that would divide the primitive atria
shape/appearance: can be thought of as a wall with a "one way doggy door" to connect the right and left atria
processes" growth of cells from the roof of the atria and endocardial cushions, programmed cell death in the septum primum to form the foramen secundum
The septum primum is a flexible crescent shaped membrane that grows downward from the roof of the primitive atria and partially divied the atrium leaving a foramen primum (or ostium primum-first opening) allowing blood to flow from the right atrium to the left atrium. As the septum primum grows, the foramen primum gets smaller and eventually closes with the growing up of endocardial cushions (neural crest cells).
Apoptosis then occurs in the septum primum to form the foramen secundum. The rigid septum secundum grows downward and gradually overlaps the foramen secundum forming an incomplete partition btwn the atria called the foramen ovale which is covered by the flap like valve of the foramen ovale (foramen ovale replaces foramen secundum). The primitive atrium is divided into left and right atria first by the septum primum and is replaced by the septum secundum. The flexible septum primum flaps back and forth as blood flows from the high pressure right atria into the lower pressure left atria. After birth, high pressure in the left atria permanently closes the foramen ovale by shutting of the septum primum.
What is the primordium, position, shape/appearance, and processes of the interventricular septum?
The interventricular septum appears in the floor of the common primitive ventricle and grows upward toward the endocardial cushions. As the interventricular septum grows upward, the interventricular foramen closes leaving the membranous portion of the septum behind. The membranous part is commonly where ventricular septal defects occur.
primordium: one common ventricle, floor of the ventricle, endocardial cushions
position: along a vertical line that would divide the primitive ventricles
shape/appearance: can be thought of as a wall
processes: growth of cells from the floor of the ventricles and endocardial cushions
What is the primordium, position, shape/appearance, and processes of the separation of the aorta and pulmonary trunk?
As the interventricular septum divides the right and left ventricles, blood is partitioned to flow into the pulmonary ciruclation from the right ventricle and into the systemic circulation from the left ventricle. This involves the endocardial cushions again which grow toward each other like a spiral staircase so that when the growth ends the pulmonary trunk is in communication with the right ventricle and the aorta with the left ventricle. The ridges formed by the endocardial cushions are called the left and right conotruncal ridges.
primordium: truncus arteriosus
position: along a spiraling line that would divide the truncus arteriosus
shape/appearance: can be thought of as a spiral staircase
processes: growth of endocardial cushion cells along the conotruncal ridges
What 3 bypasses are formed in fetal circulation and what are their purposes?
ductus venosus: connects the umbilical vein with the inferior vena cava bypassing the liver
foramen ovale: connects the right atrium with the left atrium bypassing the lungs
ductus arteriosus: connects the left pulmonary artery with the arch of the aorta bypassing the lungs
the lungs and liver are not needed in the fetus and so they are bypassed.
What happens to the embryonic bypasses after birth and how/why?
ductus venosus constricts to form the ligamentum venosus as blood begins to flow through the liver.
foramen ovale closes to form the fossa ovalis as the blood pressure increases in the left atrium.
ductus arteriosus contricts to from the ligamentum arteriosus due to an increase in oxygen and a decrease in circulating prostaglandins
umbilical arteries and vein constricts (will look at these remnants in the GI block)
What is patent foramen ovale? What is the result? What is the female to male prevalence?
open foramen ovale after birth (type of atrial septal defect-ASD). allows interartrial shunting of blood. 2:1 female to male prevalence.
What are the reasons for ostium (foramen) primum and secundum ASDs and where do they occur in relation to the tricuspid valve?
ostium primum defects occur close to the tricuspid valve and are a result of excessive resportion of septum primum.
ostium secundum defects occur further away from the tricuspid valve. they are caused by failure of development of the septum secundum or excessive resorption of the septum primum.
please see pg 67 of course notes
repair of these two ASDs is different
What is the result of a ventricular septal defect and where in the ventricular septum does the defect typically occur?
Ventricular septal defects are mostly an isolated defect but can occur with others. These defects allow interventricular mixing of blood and are typically a result of a defect in the membranous portion of the interventricular septum.
What is Tetralogy of Fallot and what is the result?
Tetralogy of Fallow is the most common cause of early cyanosis and is the result of multiple defects.
1. pulmonary stenosis:dc blood flow to lungs
2. ventricular septal defect: interventricular mixing of blood
3. overriding aorta: arises above the ventricular septal defect. allows some deoxygenated blood from the right ventricle to flow into the aorta
4. Right ventricular hypertrophy (a manifestation of items 1, 2, and 3). can cause heart to stiffen, become weak, and eventually fail.
What is transposition of the great vessels? What defects is it associated with? What is a result?
right to left shunting of blood which leads to cyanosis
1. aorta rises from right ventricle
2. pulmonary artery arises from left ventricle
3. associated with ASD, VSD, patent ducts arteriosus
What is persistent truncus arteriosus? What defects is it associated with? What is a result?
Right to left shunting results in cyanosis.
1. partial development of AV septum
2. always accompanied by membranous VSD