We next approach our anatomy lessons using something useful as a framework: vital signs. These are measurements of the fundamental functions of the body, and are: blood pressure, heart rate, respiratory rate, pulse oximetry, and temperature. (The whole “pain is the 5th vital sign” is governmental BS and should be ridiculed.)
We will start with blood pressure, and as such, we need to review the general anatomy of the cardiovascular system. Here you will find a very simple, general overview, and are then referred to the Kaplan book and other resources detailed below for your more detailed assignments. Questions are welcome; indeed, questions are a sign that you are thinking.
The image above shows that the heart is divided into 2 sides, creatively called the “right” and the “left”. Then there are upper and lower chambers: the upper is called the atrium (Latin: central room of a Roman household) and collects blood to pass on to the ventricle (Latin: “little belly”). Typical shorthand is to refer to each chamber as a combination of “R” or “L”, “A” or “V”, so LV is left ventricle, RA is right atrium.
There are valves that separate all these chambers: the RA and RV are divided by the tricuspid valve; the RV and pulmonary artery (leading to the lungs) are divided by the pulmonic valve. The LA and LV are divided by the mitral valve; the LV and aorta (leading to the body) are divided by the aortic valve. It is the opening and closing of these valves during the cardiac cycle that make the familiar “lub-dub” you hear through a stethescope.
Assignment #1: Grok pages 197-201 of the Kaplan anatomy book, to include creative coloring. You should then go to the University of Minnesota’s Atlas of Cardiac Anatomy and look around; especially look at the Visible Heart videos; this is great stuff.
In general, the role of the right side of the heart is to collect blood from the body, and pass it to the lungs (right atrium–> right ventricle–> lungs), and the left side of the heart is to collect that same blood from the lungs, and pump it to the body (lungs–>left atrium–> left ventricle–> body).
Although the jobs sound similar, there could not be a bigger difference between the two sides. The left side of the heart is strong, muscular, and thick-walled, producing the familiar pressures of 120/80 you see on a blood pressure cuff; the right side is weak & puny, almost like a handkerchief draped over the left side, producing pressures of, say, 20/5.
The valves are meant to keep the flow unidirectional; damage or irregularities to these valves cause the heart murmurs heard on physical exam.
Assignment #2: Grok page 193 of the Kaplan anatomy book. Trace the flow of blood with your finger. Ask yourself, what would happen if one of the valves were messed up, and leaky (regurgitation)? What would happen if they were too tight (stenotic)? Hints here.
Once the blood leaves the LV, it enters the aorta. Here we find a rather elegant solution to a daunting physiological problem: the human body requires continuous blood flow to work well, but has a pump that produces intermittent pulses of flow.
The walls of the aorta are muscular and act like elastic, heavy-duty rubber tubing (please see Kaplan book, page 205). When the LV pumps out the blood (called systole), it stretches the aorta like a balloon, and “stores” pressure to compensate for the drop in pressure seen when the left ventricle is between pulses (called diastole). This is directly analogous to the use of a capacitor as part of a circuit to rectify AC to DC current, for the engineers in the group.
Thus, the top number of the blood pressure is due to the pump of the LV; the bottom is due to the release of stored energy from the aorta. If you put a pressure transducer, also called an arterial line, in the aorta, the pressures look like this:
And when watching on monitors, it looks like this. Please note, it’s the red waveform that is the arterial; ignore the others for now.
In real life, we use ultrasound to perform an echocardiogram if we want to know what is going on with the heart or the valves. Please view this video, and this one, to get a feel for what a heart looks like on the inside, when in motion. I put this here, just as show; the anatomy as seen on echocardiograms is well beyond the scope of this post (although if you are motivated I certainly won’t stop you).
Assignment #3: Google “dicrotic notch”, post your findings to comments.
Next post will review the arterial anatomy and pressure points to stop bleeding, as well as a few practical exercises for the learner.