Blood Pressure

∞ generated and posted on 2020.03.15 ∞

There is more to the heart and its function than "just" its more obvious anatomical parts.

This page contains the following terms: Layers of the heart wall, Endocardium, Myocardium, Epicardium, Pericardium, Pericardial cavity, Purkinje fibers, Cardiac output, Coronary arteries, Blood pressure, Pulse, Diastole, Diastolic pressure, Systole, Systolic pressure, Electrocardiogram (ECG or EKG) Angina pectoris, Atherosclerosis, Congestive heart failure, Heart murmur, Hypertension

Layers of the heart wall

Endocardium, myocardium, epicardium, and pericardium.

In greater detail, going from the inside of the heart out, there is the lumen (i.e., where the blood flows), the endocardium, the myocardium, the epicardium = the visceral layer of the (serous) pericardium, the pericardial cavity (which contains serous fluid), the parietal layer of the (serous) pericardium, and the fibrous pericardium. The latter forms the connective tissue wall of the pericardial cavity.

Links to terms of possible interest: Endocardium, Epicardium, Fibrous pericardium, Myocardium, Pericardium, Serous pericardium, Trabeculae,

The above video walks us through the layers of the heart wall.

The above video walks through the gross anatomy and layers of the heart, with some emphasis on pathology.

Endocardium

The interior lining of the heart.

The endocardium consists of epithelial tissue and in fact represents a continuation of the endothelium which lines blood vessels generally. The cardiovascular system thus is lined with endothelium and that which is found within the heart is simply described as endocardium. Inflammation of the endocardium is described as endocarditis, which can lead to damaging of the functioning of the heart as endocarditis can involve the heart valves.

The above video very quickly introduces the endocardium, which is continuous with the endothelium that lines the body's blood vessels.

Myocardium	The muscular layer of the heart.
	The myocardium consists of cardiac muscle and is found between endocardium on the inner side and epicardium to the outer side of the heart wall. The myocardium is the raison d'être of hearts. That is, it is the contraction of the myocardium that makes hearts pump, though important as well is coordination of that contraction.

Links to terms of possible interest: Endocardium, Epicardium, Loose connective tissue, Myocardium, Pericardium, Simple squamous epithelium, Trabeculae carneae, Visceral pericardium,

The above video shows the myocardium, which basically is the bulk of the heart wall, i.e., the layer containing the cardiac muscle.

Epicardium	The tissue membrane associated with the external surface of the heart.
	The epicardium is continuous with the pericardium, forming the outer, encapsulating layer of the heart. To avoid confusion, it is important to keep in mind that the epicardium and the visceral layer of the serous pericardium are identical structures, that is, two different names for what anatomically are exactly the same thing.

Links to terms of possible interest: Endocardium, Epicardium, Fibrous pericardium, Heart wall, Myocardium, Parietal layer of serous pericardium, Pericardial cavity, Pericardium, Serous pericardium, Trabeculae, Visceral layer of serous pericardium

The above video provides a very quick overview of what the epicardium consists of and its relation to the pericardium.

Pericardium

Double-layer connective tissue sack that encloses the heart.

The pericardium consists of a fibrous outer layer (fibrous pericardium) and a serous membrane inner layer (parietal layer of the serous pericardium). The pericardium together with the epicardium (together, the serous pericardium) forms the pericardial cavity, which is filled with fluid that serves to lubricate the outside of the heart relative to the pericardial cavity, in which the heart is found. Inflammation of the pericardium is called pericarditis, which can interfere with normal heart functioning.

Links to terms of possible interest: Parietal pericardium, Pericardial fluid, Pericardium, Visceral pericardium

The above video provides a very quick overview of what the pericardium consists of along with its function.

Pericardial cavity

Volume within animals containing the heart.

The pericardial cavity is found within the thoracic cavity, which in turn is found within the ventral cavity. The pericardial cavity is demarcated by the serous membrane known as the pericardium. The pericardium in turn provides lubrication to the exterior of the heart, allowing beating without friction against the thoracic cavity wall (i.e., the chest wall), and also provides a cushioning against sudden movement (sudden deceleration of your body, e.g., such as following a fall, thus is much less likely to result in damage to your heart). Like the pleura, the pericardium consists of multiple layers together forming the pericardial sac which in turn contains the pericardial cavity.

Links to terms of possible interest: Parietal pericardium, Pericardial cavity, Pericardial fluid, Pericardium, Visceral pericardium

This video provides an overview of the pericardium, which defines the pericardial cavity, with mention of the pericardial cavity itself at 1:54; note mention in the video of pericardial sinuses.

Purkinje fibers

Specialized cardiac muscle cells that conduct action potentials between different parts of the heart to increase the coordination of the heart's contraction.

The Purkinje fibers are just one part of a network of structures that coordinate the contraction of cardiac muscle. This coordination is what allows heartbeats to occur in an organized manner. Witness by contrast what happens when contraction occurs in an uncoordinated manner, which we describe as fibrillation, i.e., that which one employs a defibrillator to reverse. In addition to Purkinje fibers, this coordination is achieved via the action of what are known as the SA node, the AV node, and the AV bundle. The Purkinje fibers branch off of the left and right branches of the AV bundle.

Links to terms of possible interest: Atrioventricular bundle, Atrioventricular node, Purkinje fibers, Sinoatrial node

The above video provides an introduction to cardiac conduction including the brief but important roles of Purkinje fibers more generally.

The above video takes us through the overall process of conduction in the heart, of which the Purkinje fibers represent the final anatomical component.

The above video presents a nice graphic overviewing heart conduction but doesn't really explain how exactly the signals propagate to or through the myocardium.

The above video overviews heart conduction along with diastole and systole.

Cardiac output	Measure of blood flow through the ventricles.
	Cardiac output is a measure of heart functioning and is dependent on the rate of beating (heart rate) and the amount of blood that flows per beat (stroke volume). To increase cardiac output, one must increase one or the other or both, which occurs in the course of going from resting to an exercising state.

Links to terms of possible interest: Cardiac output, End diastolic volume, End systolic volume, Heart rate, Stroke volume

The above video provides a nice introduction to the concept of cardiac output.

The above video provides a quite good overview of cardiac output and its control.

Coronary arteries

The blood vessels that are directly responsible for supplying blood to cardiac muscle.

The coronary arteries begin just above the aortic valve and as a consequence fill particularly during diastole as blood flows backwards within the aorta towards that valve. The result is a closing of the aortic valve and then a pushing of blood under substantial pressure into the coronary arteries. The reason that blockage of coronary arteries is such a problem is that these arteries provide nutrients as well as oxygen to the myocardium, that is, the muscle making up the heart. No blood flow through coronary arteries then no myocardium functioning, which we describe as a myocardial infarction, i.e., a heart attack. That leads to portions of the heart no longer contracting which in turn can result in uncoordinated beating known as arrhythmias, which we then treat using defibrillators. Blockage of coronary arteries can also result, if blockage is severe, in death of heart muscle, as often occurs in the course of a myocardial infarction.

Links to terms of possible interest: Circumflex coronary artery, Left coronary artery Right coronary artery

The above video is very short and has no sound but does provide at least a small sense of how the coronary arteries function.

The above video produces as introduction to the anatomy of the coronary arteries.

Blood pressure

Measure of the extent to which the beating of the heart results in a pushing of the circulating fluid against especially arterial walls.

We tend to think of blood pressure as a bad thing, as in high blood pressure. Blood pressure, however, not only can instead be too low, but indeed blood pressure is absolutely essential to the functioning of the body. A blood pressure of zero, in other words, is achieved, other than in the course of certain medical interventions, only upon death. Indeed, the job of the heart as an organ is the generation and maintenance of blood pressure. Thus, when blood pressure is determined, one of the things that is being measured is the output of the heart. This blood pressure as measured, in turn, can be differentiated into that pressure that is directly due to the functioning of the heart's contraction (the systolic pressure) and that which is present indirectly due to the heart's contraction, i.e., as stored via the elasticity of the arterial walls (the diastolic pressure).

Links to terms of possible interest: Blood pressure, Diastolic pressure, Mean arterial pressure, Pulse pressure, Systolic pressure, Ventricular contraction,

What is blood pressure? This video provides a garden hose analogy.

The above video provides an introduction to blood pressure along with high blood pressure, its causes, and results.

Determining blood pressure including as in an emergency is shown in the above video.

Pulse

Sudden increase in blood pressure associated with systole.

The pulse is measured by monitoring arteries that are sufficiently close to the surface of the body that the pressure differential between that associated with diastole and systole can be easily felt (that is, pulse is the systolic pressure increasing relative to the diastolic pressure). Determination of pulse is used to measure heart rate but also is employed to determine blood pressure in the course of use of a sphygmomanometer.

The above video walks us through the basics of how to take a pulse.

Diastole	Interval over which the chambers in the heart fill with blood.
	It is during diastole that the heart is in a relaxed state, that is, between contractions.

The above, short video is a little funky in terms of its sound but nonetheless does a good job of distinguishing diastole from systole.

Diastolic pressure	Minimum blood pressure recorded over a given interval during blood pressure determination.
	Diastolic blood pressure is that stored within the elastic walls of arteries.

The above video discusses diastolic blood pressure, systolic blood pressure, and high blood pressure.

Systole	Interval over which the heart is actively pumping blood.
	It is during systole that the heart is contracting, that is, pushing blood into the next chamber or artery.

Links to terms of possible interest: Aortic valve, Atrial contraction, Atrioventricular valves, Pulmonary valve, Semilunar valves, Ventricular contraction, Ventricular pressure

Systolic pressure	Maximum blood pressure recorded over a given interval during blood pressure determination.
	Systolic blood pressure is that generated directly by the heart itself. Thus, during a heart's contraction one can detect an increase in blood pressure that peaks at what we describe as systolic pressure, and which we can detect manually, at least qualitatively, as a pulse.

Electrocardiogram (ECG or EKG)

Measure of a time course of the electrical activity of the heart.

An EKG is a noninvasive means by which the activity of the heart can be monitored in detail, that is, by means other than in terms of sound, pulse, or pressure. This can allow the detection of abnormalities in the heart that are due to cardiac tissue damage, resulting in arrhythmias. The EKG is a measure of the activity of what is known as the cardiac conduction system, of which the Purkinje fibers are a component.

The above is a really nice introduction to heart electrical activity.

The above video presents a discussion of the basics of heart electrical activity.

Angina pectoris

Chest pain resulting from inadequate blood flow through coronary arteries.

Angina pectoris, typically described simply as angina, results from reduced coronary artery functioning that is often a consequence of atherosclerosis (an arterial plaque-associated partial blockage of arteries). Angina pectoris is not a heart attack (myocardial infarction) which instead is a consequence of reduction in blood flow through a coronary artery to the point where heart muscle tissue literally starts dying. Angina under certain circumstances, and particularly angina that is worsening, can indicate a prelude to a heart attack, however. Nonetheless, and other than that the pain or other symptoms of angina pectoris are uncomfortable, one can view angina pectoris more as an indication of chronic circulatory problems, particularly involving the heart, rather than a critical disease in and of itself.

The above video walks through both angina and the underlying causes.

Atherosclerosis

Accumulation of deposits of calcium, lipids, and body cells on artery walls.

This depositing, as associated with what are known as arterial plaques, results in a thickening of artery walls, bulging inward and thus reducing the cross sections of arterial lumens. That is, arteries become partially blocked, reducing blood flow, increasing blood pressure (due in part to a loss of elasticity of arterial walls), and increasing the potential for blocks to give rise to a thrombus (detached blood clot). Thrombi that are released in the course of the rupturing of these deposits can block downstream vessels. Atherosclerosis is a form of arteriosclerosis (i.e., "hardening of the arteries") that is specifically due to the deposition of these plaques. There is also the term arteriolosclerosis, which refers to a hardening of arterioles. Note that symptoms of atherosclerosis during its often multi-decade development can be few, resulting in diagnosis only once substantial disease is present. Substantial blockage of vessels that can be a consequence of atherosclerosis results in what are known as infarctions, which is the death of tissues that are otherwise fed by the now blocked vessel. A myocardial infarction, a.k.a., a heart attack, is the consequence of such a blockage of a coronary artery.

The above video provides a moderately detailed computer-generated animation look at arterial plaque formation.

A nice overview of coronary artery disease.

The above video is a brief though incomplete look at myocardial infarctions, i.e., what heart attacks consist of.

Congestive heart failure

Inability of the heart during somewhat normal contraction to adequately pump blood.

The symptoms of heart failure can vary in part depending upon whether it is the left versus the right side (or both) of the heart that is not adequately pumping blood. In left side failure – more strictly "congestive heart failure" versus simply "heart failure" – symptoms can appear that are due to inadequate drainage of blood from the lungs. The result of congestive heart failure is an accumulation of fluid in association with the lungs (pulmonary edema) and hence the use of the qualifier, "congestive". In addition, symptoms result from poor circulation to the body, including to the brain which can result in reduced brain functioning. Right-side failure, that is, simply "heart failure", by contrast results in a buildup of fluids in the body generally, since the heart is not adequately pulling blood from systemic circulation back through it. The result is the noted fluid accumulation throughout the body (edema) other than the lungs. This fluid accumulation, however, can lead to reduced functioning, e.g., of the liver. Note that a failure in heart functioning can also occur more acutely, involving less than normal contraction, i.e., as seen with myocardial infarctions.

The above video provides a nice, short, overview of what congestive heart failure consists of.

Heart murmur	Excessive noise that results from inappropriate blood flow through heart valves.
	Though heart murmurs are a sign of a pathology, the pathology is not necessarily severe enough to require treatment. In any case, the noises associated with heart murmurs are detectable using a stethoscope.

The above video bills itself as "Heart Murmur for Beginners", though by "Beginners" what they mean are beginning medical students!

Hypertension

Chronic high blood pressure.

High blood pressure (chronic) can be defined as a sustained systolic pressure over diastolic pressure of 140/90. This is in units of millimeters of mercury, i.e., a column of mercury that is 140 mm or higher and/or a column of mercury that is 90 mm or higher (which in turn is a measure of pressure). Normal, non-hypertensive blood pressure, by contrast, is found in the range 100-140 mm mercury over 60 to 90 mm mercury, though even here at the higher end of these ranges the blood pressures are indicative of what can be described as prehypertensive. Chronic high blood pressure leads to a variety of ailments including aneurysms (i.e., rupture of blood vessels), heart disease, stroke (i.e., blockage of the blood supplies to the brain), and also kidney disease as well as reduction in life expectancy in general. Treatments can involve application of drugs and/or dietary modification and increased exercise. Exercise, BTW, can lead to non-chronic increases in blood pressure, which is normal, whereas chronic high blood pressure is not normal.

Links to terms of possible interest: Diastolic pressure, Hypertension, Prehypertension, Systolic Pressure

The above video provides a quick overview with consideration of hypertension.

Consequences of hypertension, with mention of Al Capone.