Atria and Ventricles

Fetal Heart

At first, the heart is just two tubes.  Over time, each tube starts to get these two little pouches and a curvature.  This curvature becomes even more pronounced as we get towards something that looks like the adult human heart. This is why heart anatomyThe study of the structure of the human body. is so difficult. While we can draw schematics, visualizing the actual flow of blood is hard. It is especially challenging because it’s a 3D structure, and we’re looking at 2D pictures.

This PowerPoint seems deceptively short, but it actually contains a significant amount of anatomy. We will look at some pictures from the book that use great colors to indicate different parts of the heart. For example, blue represents deoxygenated blood, and red represents oxygenated blood. There are arrows in the diagram. However, when you dissect a sheep heart, it doesn’t have these colors. Instead, it looks like uncooked chicken meat and is all the same glistening color.

Atria

This is the structure of the heart we know: four chambers—two superiorAbove or toward the upper part of the body. and two inferiorBelow or toward the lower part of the body.. Let’s focus on the atria, which are called the receiving chambers. Each atrium receives blood from its designated circuit – the systemic or body circuit or the pulmonary circuitThe circulation of blood between the heart and the lungs, where blood is oxygenated... The right atrium receives blood from the vena cava. You can see two vena cavae here: the superior vena cava and the inferior vena cava. They come together and flow into the right atrium. The pulmonary vein brings oxygenated blood to the left atrium.  You can see two veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge for each lung entering on the posterior side of the hear.

If you start to exercise, the blood in your veins of the systemic circuitThe part of the circulatory system that carries oxygenated blood from the heart to the body and retu begins to move. It moves back toward the heart. This movementA fundamental property of life involving motion of the body or its parts. causes the right atrium to overfill.  Luckily, there are these flaps called auricles that allow the atrium to overflow.  There are auricles on both atria.  On the right atrium, there are these ridges of muscles. They help with pushing blood from the atria into the ventricles.  These are called pectinate muscles.  In the fetal heart, there is a hole between the atria called the foramen ovale.  Upon birth, this hold heals over and is then called the fossa ovalis.  If you suffer from very high, unregulated blood pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. at the end of life, you might pop this hole open.  At that point, it is called a PFO or patent foramen ovale.  This is bad because it allows oxygenated and deoxygenated blood to mix. 

Ventricles

Let’s do the anatomy of the ventricles, which can be called distributing chambers. The right and left ventricle is separated by a thick line of myocardium called in interventricular septum.  We will consider a condition concerning this septum. It is called a VSD or ventricular septal defect. This condition is a hole in this septum. 

Just like the right atrium has pectinate muscles, there are muscles in the ventricle walls called trabeculae carnae.  These trabeculae create a structure that makes the heart rigid and prevents blowouts of the heart muscle itself. Being muscle, they also add to the ability to create force.

The moderator band is neural tissue. It is part of the cardiac conductionThe transmission of nerve impulses along neurons. system. The band is composed of neuronsThe functional cells of the nervous system that transmit signals. that conduct electricity throughout the heart muscle.

The ventricles also contain papillary muscles, which are extensions of the trabeculae carnae. “Papillary” means nipple, and these muscles attach to the strings hanging off the valves, known as heartstrings or chordae tendineae. When the heart contracts, these papillary muscles pull on the chordae tendinae and stabilize the AV valves to stay closed.

The left ventricle pumps oxygenated blood into the aorta, which feeds the systemic circuit.  The right ventricle pumps blood into the pulmonary truck, which then separates into the left and right pulmonary arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr.

Flow through Chambers

Blood in the heart takes a U-turn.  Blood enters from the top of the heart. It flows into atria, then ventricles. Finally, it is pumped out of the heart in an upward push.  It’s always an up and down movement. It’s kinda like painting the fence in whatever Karate Kid movie was made for your generation.  The interventricular septum and the interatrial septum are essential. They should not have holes. These septa prevent blood from moving from side to side. 

We are aware of conditions such as a ventricular septal defect. This condition allows blood to go from side-to-side. It mixes the oxygenated with the deoxygenated.  That is like painting the house and you never want to paint the house.  Despite the differences between the sides of the heart, they pump out the same volume.  The small pulmonary circuit and the huge systemic circuit require different compensations. Each chamber adapts by generating different pressures for the volume leaving them.