hEAR DEVELOPMENT PT 2

01:26

Chamber Maturation

During septation, the atrio-ventricular endothelial cushions play a crucial role in forming the pulmonary and mitral/aortic valves, facilitating the partitioning of the heart's atria and ventricles as well as the outflow tract into the aorta and pulmonary artery. The development of these fused endocardial cushions in the atrio-ventricular canal is essential for the proper growth and organization of the heart's structure. The process of heart and vessel partitioning initiates primarily in the central region, which includes the atrio-ventricular canal.

02:50

Septation Process

The septation process in heart development involves the expansion of endothelial-like cells in the endocardial cushions, leading to the formation of protrusions in the atrioventricular canal. These outgrowths extend towards the atria, contributing to the partitioning into left and right atria as they meet at the top of the ventricle. Additionally, the muscular ventricular septum grows from cardiomyocytes at the ventricle's apex, completing the separation.

04:07

Endocardial Cushions

The valvular region of the heart develops through further divisions, leading to the formation of the aortic and pulmonary outflow tracks. Atrial septation is particularly intricate, involving two septa, with the first being the septum primum formed by growing cardiomyocytes from the dorsal roof of the heart. The process of septation is crucial for defining the distinct chambers of the heart.

05:25

Atrial Septation

In the atrioventricular canal region, the atrium develops towards the endocardial cushions, which simultaneously expand upwards. As the septum primum meets the endocardial cushions, an opening known as the ostium primum is formed, which will eventually close. Additionally, this interaction also leads to the formation of a second opening in the septum.

06:44

Formation of Septum Primum

Apoptosis in the upper region leads to cell death, resulting in the formation of an opening known as the osteum secundum in the septum prum. While the osteum premium closes, the developing septum secundum grows from the anterior face of the atrium towards the endocardial cushions but does not fuse fully with the septum prum or the endocardial cushion.

07:53

Ostium Primum and Secundum

The lack of fusion between the septum primum and septum secundum results in openings at the base around the atrioventricular (AV) canal, known as the Foramen Ovale. Initially, these openings, crucial for blood movement between the right and left atria during development, will not overlap in the final structure. However, it is desired that these openings close after birth to prevent free blood flow between the atria.

09:06

Foramen Ovale

The foramen ovale facilitates the movement of blood between the right and left atrium during development, crucial for proper circulatory function. This process involves the growth of the septum primum from the dorsal atrium towards the endocardial cushions, initially forming an opening (ostium primum) as the septum descends. As development progresses, holes form in the septum primum, allowing blood flow directly between the atria, indicating the presence of both well-oxygenated and poorly oxygenated blood.

11:41

Atrial Septation Overview

The structures responsible for atrial septation, namely the septum primum and septum secundum, are clearly outlined, illustrating the flow of oxygenated and poorly oxygenated blood through the heart. The septum secundum grows from the anterior atrium towards the endocardial cushions, avoiding full fusion with the septum primum, which helps maintain the proper blood flow pattern from the right atrium to the right ventricle. Understanding this alignment is crucial for comprehending the overall development of the heart's structures.

13:02

Formation of Septum Secundum

As the septum primum grows towards the AV Canal, a gap persists that prevents fusion with the endocardial cushions, leaving the ostium secundum open. The closure of the septum primum creates a significant opening known as the foramen ovale, allowing blood to flow from the right atrium to the left atrium. This lack of direct fusion maintains the functional connection necessary for proper blood circulation during development.

14:19

Closure of Ostium Primum

The septum secundum features overlapping partitions that facilitate blood communication between the right and left atria, allowing for movement via the foramen ovale and ostium secundum. These structures do not fuse, enabling blood flow through an oscillating valve that can switch between open and closed states. When closed, the valve prevents blood movement between the heart's chambers.

15:46

Foramen Ovale Function

Blood flows between the right and left atria in the developing fetus, facilitated by the foramen ovale, which allows blood propelled from the right atrium to enter the left atrium. This process is essential for delivering oxygenated blood without fully functioning lungs, as the incoming blood via the superior and inferior vena cavae can also move into the ventricles. The regulation of this flow is critical for fetal development, distinguishing it from adult circulation.

17:01

Blood Flow Regulation

Atrial septation is crucial for proper heart development, involving the growth of the septum primum from the atrium's dorsal roof toward the endocardial cushions. As it forms, an initial opening, the ostium primum, allows blood flow between the two atria, while apoptosis leads to the creation of the ostium secundum. Subsequently, the septum secundum grows, but a gap remains between it and the septum primum, ensuring the correct separation of atrial blood flow.

18:24

Visualizing Atrial Septation

The lack of fusion between the septum primum and the endocardial cushion leads to the formation of the Forin OV Val, which facilitates blood flow between the right and left atria via the osteum secundum. The final structure visually appears as two overlapping partitions with holes. In contrast, the process of ventricular septation is simpler, involving the division of the primitive ventricle into distinct left and right ventricles through an outgrowth of myocardium from the outer curvature region.

19:56

Atrioventricular Septation

The fusion of endocardial cushions with the myocardium towards the septum is crucial for the separation of the heart's ventricles, resulting in a membranous intraventricular septum and a muscular interventricular septum. Additionally, atrioventricular septation involves the division of the primitive atrium from the primitive ventricle, driven by the growth and merging of endocardial cushions, which ultimately leads to the formation of the AV valves.

19:56

Ventricular Septation Process

The myocardium's fusion with the endocardial cushions facilitates the separation of the right and left ventricles, forming both a membranous and muscular region of the interventricular septum. Additionally, atrioventricular septation occurs, dividing the primitive atrium from the primitive ventricle due to the merging of the endocardial cushions, which also leads to the development of the atrioventricular valves.

19:56

Ventricular Septation

The fusion of the endocardial cushions with the myocardium facilitates the separation of the right and left ventricles, resulting in both a membranous and muscular interventricular septum. Additionally, atrioventricular septation occurs through the growth of these cushions, leading to the division of the primitive atrium from the primitive ventricle and the formation of the AV valves by merging superior and inferior endocardial cushions.

21:26

Atrioventricular Septation

The fusion and movement of the endocardial cushions lead to the separation of the atrioventricular canal into left and right components, forming the mitral and tricuspid valves. Following this, atrioventricular septation occurs, allowing for the division of atria from ventricles and the development of the AV valves. Finally, septation of the outflow tract is essential to separate the common outflow region into the aortic and pulmonary arteries, facilitating proper circulation.

22:59

Outflow Tract Septation

In the development of the heart, the bulbous cordis and truncus arteriosus regions feature ridges that grow together in a 180° spiral, leading to the separation of the pulmonary trunk and aorta, crucial for the distinction between pulmonary and systemic circulation. This spiral pattern allows for a unidirectional flow of oxygenated and deoxygenated blood within the heart tube, facilitated by structures like the ductus arteriosus and foramen ovale, which bypass the lungs and liver during fetal development. As the heart matures, the left ventricle pumps oxygenated blood to the body, while the right ventricle routes deoxygenated blood back to the heart, optimizing circulation before birth.

29:50

Ductus Arteriosus

The ductus arteriosus connects the pulmonary artery to the aorta, allowing blood to bypass the lungs before birth. After birth, it closes in response to increased oxygen levels and changes in blood flow, leaving a remnant known as the ligamentum arteriosum. Enhanced venous return from the lungs raises pressure in the left atrium, helping to close the foramen ovale.

31:16

Postnatal Changes

After birth, the ductus arteriosus closes, leaving remnants such as the ligamentum venosum and the ligament arteriosum, which connect the aorta and pulmonary arteries, crucial for neonatal circulation. If the ductus arteriosus remains patent postnatally, it causes abnormal blood flow from the aorta to the pulmonary artery, potentially leading to pulmonary congestion and congestive heart failure due to increased workload on the right heart. Managing this condition is critical to prevent complications associated with excess blood flow to the lungs.

33:58

Patent Ductus Arteriosus

After birth, the pressure in the right atrium decreases as the lungs inflate, prompting the closure of the foramen ovale, which previously facilitated blood flow from the right to the left atrium due to higher fetal right atrial pressures. This pressure change allows the septum primum and septum secundum to fuse, effectively closing the structure that helped bypass lung circulation in utero.

35:17

Closure of Foramen Ovale

After birth, the foramen ovale is expected to close, leaving the fossil ovalis as its remnant. If closure fails, it can lead to shunting of blood from the left atrium to the right atrium, potentially causing complications such as pulmonary hypertension if the defect is large. Understanding these processes is crucial as they play a significant role in heart development and function.

38:00

Heart Development Overview

The process of heart development involves dynamic activation and suppression of secreted proteins and signaling pathways, ultimately influencing gene expression during critical developmental time points. This results in the transformation from cardiac progenitor cells to the formation of a four-chamber heart. Further exploration of these mechanisms will be provided in subsequent videos.