Cardiovascular System Flashcards
Where do blood vessels first form and haematopoiesis commence in the embryo?
In the developing embryo, blood vessels first form during a process called vasculogenesis. Vasculogenesis begins in the extraembryonic mesoderm, which is the embryonic tissue that lies outside the embryo itself. This process leads to the formation of the primary vascular plexus, which is a primitive network of blood vessels.
Haematopoiesis (formation of blood cells) occurs in the liver, spleen and thymus. Mainly in liver until initiation of bone marrow haematopoiesis near birth.
Name the organs that participate in haematopoiesis in the embryo
Liver, spleen, thymus then eventually bone marrow
What is the difference between the terms vasculogenesis and angiogenesis?
Vasculogenesis is formation of new vascular channels through organisation of angioblasts
Angiogenesis is formation of new vessels by budding and branching of pre-existing channels
What is the difference between the septum primum, septum secundum, foramen primum and foramen secundum in atrial septation in the embryo?
Septum Primum:
The septum primum is the first structure to form during atrial septation.
It originates as a downward, crescent-shaped fold of tissue from the roof of the primitive atrium.
Initially, there is a gap or foramen between the free edge of the septum primum and the endocardial cushions in the developing heart. This gap is referred to as the “foramen primum.”
Foramen Primum:
The foramen primum is the opening that exists initially between the free edge of the septum primum and the endocardial cushions in the atria.
During development, the foramen primum gradually narrows as the septum primum grows downward.
Septum Secundum:
The septum secundum is a second septum that forms after the septum primum.
It originates as a thicker, more muscular structure from the right atrial wall and grows toward the septum primum.
The septum secundum develops a crescent-shaped opening, which is referred to as the “foramen secundum.”
Foramen Secundum:
The foramen secundum is the opening that exists between the septum primum and septum secundum.
It serves as a shunt, allowing blood to pass from the right atrium to the left atrium in the developing fetus while bypassing the non-functional fetal lungs.
There are three vascular shunts in the foetal circulation. For each shunt describe the vessels or chambers of heart the shunt carries blood between
a) ductus venosus:
b) foramen ovale:
c) ductus arteriosus:
a) Ductus Venosus:
Ductus Venosus is a shunt that carries blood between the umbilical vein and the inferior vena cava.
Oxygenated blood from the placenta is transported to the fetus through the umbilical vein.
The ductus venosus allows this oxygen-rich blood to bypass the fetal liver (where it would otherwise be processed) and directly enter the inferior vena cava, which leads to the right atrium of the heart.
b) Foramen Ovale:
The foramen ovale is an opening between the two atria (upper chambers) of the fetal heart.
It carries blood from the right atrium to the left atrium.
This shunt allows oxygenated blood from the placenta to pass from the right atrium to the left atrium and bypass the right ventricle. From the left atrium, the oxygenated blood can then be pumped into the systemic circulation.
c) Ductus Arteriosus:
Ductus arteriosus is a shunt that carries blood between the pulmonary artery and the aorta.
It allows most of the blood pumped by the right ventricle to bypass the non-functional fetal lungs and be directed into the systemic circulation.
As a result, deoxygenated blood from the right ventricle is pumped through the pulmonary artery but is mostly diverted away from the lungs through the ductus arteriosus and into the aorta.
What is the developmental mechanism that results in a left sided aortic arch? Describe how a double aortic arch and right sided aortic arch may occur developmentally
Left-Sided Aortic Arch (Normal):
During normal development, the aortic arch forms from the embryonic pharyngeal arch arteries.
Initially, there are six pairs of pharyngeal arch arteries, but the first two pairs regress.
The third pair of pharyngeal arch arteries, known as the third aortic arches, give rise to the common carotid arteries and the proximal part of the internal carotid arteries.
The left third aortic arch persists and becomes the arch of the aorta, which curves to the left and posteriorly to become the left-sided aortic arch.
Double Aortic Arch:
In the case of a double aortic arch, both the right and left fourth pharyngeal arch arteries persist, rather than just the left one.
This results in the development of two aortic arches, one on the left and one on the right.
These arches encircle the trachea and oesophagus, creating a vascular ring that can compress the airway and the oesophagus, potentially leading to breathing and swallowing difficulties.
Right-Sided Aortic Arch:
A right-sided aortic arch occurs when the left fourth pharyngeal arch artery regresses, and the right fourth pharyngeal arch artery persists.
The right aortic arch crosses the midline to the right side of the trachea and oesophagus.
Depending on the exact embryonic development, this right-sided aortic arch may form in various configurations, such as a mirror image of a normal aortic arch (mirror-image right aortic arch) or as a right aortic arch with an aberrant left subclavian artery.
What is the developmental mechanism that results in a right sided superior vena cava? Describe how a double superior venae cavae may occur developmentally
The typical formation of the SVC involves the following steps:
Formation of the Bilateral Superior Cardinal Veins: During early embryonic development, a pair of venous channels known as the “superior cardinal veins” form on each side of the embryo. These veins are responsible for draining blood from the upper half of the body.
Development of the Right and Left SVC: Normally, the right superior cardinal vein regresses, while the left superior cardinal vein persists and contributes to the formation of the left-sided superior vena cava. This left-sided SVC is the primary vessel that drains deoxygenated blood from the upper body into the right atrium of the heart.
In the case of a double SVC:
Both Superior Cardinal Veins Persist: Both the right and left superior cardinal veins persist without regression. This results in the formation of two superior vena cavae, one on each side.
Variations in Drainage: The double SVC may have different patterns of venous drainage. For instance, the right-sided SVC might drain blood from the upper right portion of the body, while the left-sided SVC drains blood from the upper left portion. These vessels can sometimes join together before entering the right atrium.
Explain the steps of interatrial septation to form the foramen ovale in the embryo.
Early Heart Development:
In the early stages of heart development, the heart is a simple tube-like structure composed of several layers, including an outer muscular layer and an inner endocardial cushion.
Formation of the Atria:
As the heart develops further, it begins to partition into various chambers, including the left and right atria. The interatrial septum will eventually separate these two atria.
Formation of the Septum Primum:
The first step in atrial septation involves the formation of a crescent-shaped structure known as the septum primum. The septum primum grows downward from the roof of the primitive atrium towards the endocardial cushion in the floor of the atrium.
Formation of the Foramen Primum:
As the septum primum grows, it leaves a gap or opening between its free edge and the endocardial cushion. This opening is called the “foramen primum.”
Formation of the Septum Secundum:
Simultaneously, another structure known as the septum secundum starts to develop. The septum secundum grows from the right atrial wall and is thicker and more muscular than the septum primum.
Formation of the Foramen Secundum:
The septum secundum also leaves an opening, called the “foramen secundum,” as it grows. This opening is situated to the right of the foramen primum.
Functional Shunting:
Blood is pumped into the right atrium from the body, but fetal lungs are non-functional at this stage. To ensure that well-oxygenated blood can bypass the fetal lungs and go directly to the left atrium, the septum primum and septum secundum play a crucial role. Blood from the right atrium can pass through the foramen ovale (a temporary functional opening) formed by the septum primum and septum secundum, entering the left atrium.
Fusion and Closure:
After birth, when the baby takes its first breath and the lungs become functional, the higher oxygen levels stimulate changes in the circulatory system. The septum primum and septum secundum eventually fuse and close the foramen ovale. This fusion results in the formation of a solid, fully closed interatrial septum, separating the left and right atria.
Why is it desirable to have a ‘hole in the heart’ before birth but undesirable to have a ‘hole in the heart’ after birth?
In summary, having specific “holes in the heart” before birth is desirable to support the unique circulatory needs of the developing foetus. However, these openings must close after birth to establish the proper separation of oxygenated and deoxygenated blood in the postnatal circulatory system, and the persistence of such holes can lead to medical conditions that may require treatment.
Describe two examples of developmental mechanisms that may result in a patent foramen ovale at birth.
Incomplete Closure of the Foramen Ovale:
During fetal development, the foramen ovale allows oxygenated blood to pass from the right atrium to the left atrium, bypassing the non-functional fetal lungs. This is a crucial adaptation for fetal life.
Normally, the foramen ovale begins to close shortly after birth. The increase in oxygen levels and changes in circulatory pressures prompt the foramen ovale to seal shut. The closure is typically complete within a few months.
However, in some cases, the foramen ovale may not close completely due to developmental factors. This incomplete closure can result in a PFO, where a small opening remains between the atria. The reasons for incomplete closure can be genetic or related to variations in the development of the atrial septum. Such variations can lead to a persistent communication between the atria, allowing blood to shunt between them.=
Elevated Right Atrial Pressure:
Elevated pressure in the right atrium can prevent the normal closure of the foramen ovale after birth.
In some medical conditions, such as pulmonary hypertension or right-sided heart disorders, the right atrial pressure may remain high. When right atrial pressure exceeds left atrial pressure, it can force the flap of the foramen ovale to remain open, creating a persistent communication between the atria.
Conditions that lead to elevated right atrial pressure can include congenital heart defects, chronic lung diseases, or certain acquired heart conditions.
Describe the relationship between the inferior vena cava and abdominal aorta in a typical individual.
IVC lies to right of AA and run parallel to each other
What is the developmental reason for the inferior vena cava being located on the right side of the abdomen?
IVC formed from subcardinal and supracardinal veins. Left subcardinal and right supracardinal veins regress leaving right sided IVC
Identify the location of the ligamentum venosum. What is the significance of this structure?
Adult remnant of ductus venosus where 50% of blood passes through and enters IVC
Describe the appearance and location of the fossa ovalis
Slightly depressed circular tissue in interatrial septum
Name the structures each space/passageway listed below connects:
a) foramen ovale
b) ductus arteriosus
a) bypasses blood through pulmonary circuit (from RA to LA)
b) connects pulmonary trunk to aorta
