Heart

∞ generated and posted on 2016.03.26 ∞

The heart consists of four chambers (2 ventricles and 2 atria), four heart valves, and connections with four major blood vessels (2 sets of veins and 2 arteries).

Blood flows through the heart starting with the vena cava, passing through the tricuspid valve (right AV valve) into the right ventricle which forcibly pushes the blood through the pulmonary valve into the pulmonary trunk and from there pulmonary circulation. The blood then flows from the pulmonary veins into the left atrium, through the mitral valve (a.k.a., bicuspid value or left AV valve) and into the left ventricle which forcibly pushes the blood through the aortic value into the aorta and from there systemic circulation.

This page contains the following terms: Heart, Cardiac muscle, Aorta, Vena cava, Superior vena cava, Inferior vena cava, Ventricle (heart), Right ventricle, Left ventricle, Atrium, Right atrium, Left atrium, Heart valves, Atrioventricular valves (AV valves), Bicuspid valve, Tricuspid valve, Semilunar valves



Heart

Organ responsible for pumping blood.
The heart is a muscular organ in which muscle contraction results in a forcible reduction in the volume of one or more chambers—in humans and other mammals there are four such chambers. Just as in veins, the reduction in volume of these chambers forces the blood found within them in a single direction because of the presence of one-way valves. Also just as within veins, the movement of the blood is driven particularly by muscular contraction surrounding chambers that are filled with blood.

Unlike veins, the heart's muscular contraction occurs specifically for the sake of pumping, that is, pushing blood, and also is coordinated across the heart so that contractions are particularly suitable towards pushing blood that is found within the heart's chambers. This pushing is either to a next chamber or instead to the primary arteries feeding either pulmonary circulation or systemic circulation.


Links to terms of possible interest: Aorta, Atrioventricular valve, Brachiocephalic artery, Common carotid artery, Coronary arteries, Heart, Inferior vena cava, Left atrium, Left ventricle, Mitral valve, Pulmonary arteries, Pulmonary veins, Right atrium, Right ventricle, Semilunar valves, Septum, Subclavian artery, Superior vena cava, Tricuspid valve

The above video introduces the heart along with circulation more generally.

The above video does a good job of describing the pathway of movement of blood through the heart.

The above video provides a good introduction to the anatomy of the heart.

The above video provides a densely packed overview of heart anatomy and function.

I'm actually not all that thrilled by the above video, though it does get at bit interesting starting at 2:10.



Cardiac muscle

Primary tissue of which hearts are composed.
Three types of muscle tissue exist, in humans, and these are smooth muscle, skeletal muscle, and cardiac muscle. Cardiac muscle is that of which hearts and only hearts are composed. Like skeletal muscle, cardiac muscle is striated, that is, has microscopic stripes that represent associations of actin and myosin which together give rise to the muscle shortening that is muscle contraction.

Unlike skeletal muscle, cardiac muscle cells are branched in their associations rather than strictly linear and parallel. The muscle cells will rhythmically contract on their own but additionally are attached to one another through what are known as intercalated discs. Carried across these connections between cardiac muscle cells are the signals for contraction (action potentials), thereby contributing to the coordinated contraction and beating of the heart. The cardiac muscle itself is found within a thick layer making up the heart wall known as myocardium.


Links to terms of possible interest: Cardiac muscle, Endocardium, Heart muscle, Heart wall, Intercalated discs, Myocardium, Parietal pericardium, Pericardial cavity, Striated muscle, Visceral pericardium

This video considers both cardiac muscle and smooth muscle.

Some cardiac muscle histology though no mention of intercalated discs.



Aorta

Largest artery in the body, serving to feed systemic circulation.
The aorta is fed by, that is, is found downstream of the left ventricle. It gives rise to the coronary arteries (right and left), the subclavian arteries which ultimately feed the arms (and are so named because they pass under the clavicle), the carotid arteries which feed the neck as well as the head, and the descending aorta, which feeds the rest of the body. See also the aortic valve (found between the aorta and the left ventricle), the ascending aorta, and the aortic arch. The latter is from which the various above-noted arteries flow, including the brachiocephalic artery which gives rise to both right subclavian artery and the right common carotid artery.


Links to terms of possible interest: Aorta, Abdominal aorta, Aortic arch, Ascending aorta, Brachiocephalic artery, Common carotid artery, Coronary artery, Semilunar valve, Subclavian artery, Thoracic aorta

Awesome video discussing the anatomy of the aorta.

Excellent computer-generated visuals of the aorta in this video.



Vena cava

Largest vein in the body, serving to drain systemic circulation.
The vena cava feeds, that is, is found upstream of the right atrium. The vena cava actually consists of what are known as the inferior vena cava and the superior vena cava. The inferior vena cava carries blood from the posterior portion of the body, that is the back or, in humans, the lower part of the body. The inferior vena cava carries blood from the anterior aspects of the body, that is, the front or, in humans, the upper part of the body.


Links to terms of possible interest: Aorta, Aortic valve, Inferior vena cava, Left atrium, Left ventricle, Mitral valve, Pulmonary arteries, Pulmonary veins, Right atrium, Right ventricle, Semilunar valves, Subclavian artery, Superior vena cava, Tricuspid valve

This video talks about a bit more than the vena cava but does start out with discussion of vena cava, and then goes on to the cardiovascularly downstream anatomy; it gets a bit complicated in doing so, however; at 7:32 the video then returns to the vena cava.



Links to terms of possible interest: Aorta, Bladder, Ductus arteriosus, Ductus venosus, Fetal circulation, Foramen ovale, Inferior vena cava, Placenta, Pulmonary trunk, Umbilical artery, Umbilical vein



Superior vena cava

Major vein draining the head and the front limb or arm end of the body.
The vena cava in actuality exists as a combination of the inferior vena cava and superior vena cava. The word superior refers to something that is found higher up, which in humans is the head though in most vertebrates the equivalent to the superior vena cava instead feeds the front of the body, which is the anterior end.


Links to terms of possible interest: Anterior jugular vein, Brachiocephalic vein, External acoustic meatus, External jugular vein, Internal jugular vein, Occipital vein, Subclavian vein, Superior vena cava

The above video provides a remarkably detailed though brief look at the superior vena cava; it make be overwhelming in detail but does provide a good context for gaining even a moderate understanding of what the superior vena cava is all about.



Inferior vena cava

Major vein draining the tail and the rear limb or legs end of the body.
The word inferior refers to something that is found lower down, which in humans is in the opposite direction of the head though in most vertebrates this is instead the back of the body, which is the posterior.


Links to terms of possible interest: Common iliac veins, External iliac veins, Hepatic veins, Inferior vena cava, Internal iliac veins, Lumbar veins, Renal veins

The above video provides a remarkably detailed though brief look at the inferior vena cava; it make be overwhelming in detail but does provide a context for gaining even a moderate understanding of what the inferior vena cava is all about.



Ventricle (heart)

Major pumping chamber of hearts.
The four-chambered heart, a feature of mammals as well as of birds, consists of two ventricles and two atria. Both are heart chambers but the ventricles are by far the more robust and are what are directly responsible for pumping blood out of the heart, that is, to pulmonary circulation or instead to systemic circulation. In fact, key to at least a minimum level of functioning of the heart are the ventricles.

In ourselves the ventricles are found in the lower portion of the heart, though in fact the majority of the heart consists of the chambers and associated muscle of the ventricles. The two ventricles are named for their position relative to the body, with our left ventricle found on the left side of our hearts and the right ventricle found on the right side.

Our hearts are four chambered and thus possess two ventricles whereas three-chambered hearts or two-chambered hearts possess only a single ventricle. Note that the term ventricle is used within various additional contexts within the body, such as the ventricular system of the brain, and generally refers to a hollowness associated with an organ.


Links to terms of possible interest: Atrium, Four-chambered heart, Three-chambered heart, Two-chambered heart, Ventricle



Right ventricle

Major pumping chamber of pulmonary circulation.
The right ventricle is less robust than that of the left ventricle as the right ventricle is responsible for pushing blood through much less tissue, that is, basically limited to circulation to the lungs. Equivalently to the left ventricle, though taking place on the opposite side of the heart, with the right ventricle blood enters from the right atrium, passes through an AV valve – here called the tricuspid valve – into the right ventricle, and then passes through what is known as the pulmonary semilunar valve into what is known as the pulmonary trunk.

The latter is the primary and largest artery of pulmonary circulation. The pulmonary trunk almost immediately splits into the left and right pulmonary arteries, which provide blood to the left and right sides of the lungs, respectively.


Links to terms of possible interest: Heart, Lungs, Pulmonary circulation, Systemic circulation

The above video provides a detailed overview of the anatomy of the right ventricle, including detail of the tricuspid valve and pulmonary valve.

The above video provides a remarkably detailed though brief look at the right ventricle; it make be overwhelming in detail but does provide a context for gaining even a moderate understanding of what the right ventricle is all about.



Left ventricle

Major pumping chamber of systemic circulation.
The left ventricle is the major pump of our body as it is the major pumping chamber of the major pumping side of the heart. This makes good sense as the left ventricle is responsible for providing much of the blood pressure (that this, pumping blood) for much of the body.

The left ventricle is fed, in terms of blood flow, from the pulmonary veins. This blood moves from the pulmonary veins, through the left atrium, into the left ventricle. The left ventricle then pumps the resulting "charge" of blood into the largest the body's arteries, the aorta.

The pathway of blood flow centered on the ventricle thus consists of pumping of blood by the left atrium, through what is known as the bicuspid valve (an AV valve), into the left ventricle. The blood is then pumped out of the left ventricle through the aortic semilunar valve and into the aorta.

Flow goes the blood through the left atrium from the pulmonary veins, contract goes the left atrium, open goes the bicuspid valve, fill goes the left ventricle>, contract goes the left ventricle, closed goes the bicuspid valve open goes the aortic semilunar valve, and flow goes the blood, at peak blood pressure, into and through the aorta.


Links to terms of possible interest: Aorta, Carotid artery, CO2, Digestive tract, Heart, Hepatic portal vein, Hepatic vein, Iliac artery, Iliac vein, Inferior vena cava, Mesenteric arteries, Jugular vein, Kidneys, Liver, Lungs, O2, Pulmonary artery, Pulmonary vein, Renal artery, Renal vein, Subclavian artery, Subclavian vein, Superior vena cava

The above video provides a detailed overview of the anatomy of the left ventricle, including detail of the bicuspid valve/mitral valve and aortic valve.

The above video provides a remarkably detailed though brief look at the left ventricle; it make be overwhelming in detail but does provide a context for gaining even a moderate understanding of what the left ventricle is all about.



Atrium

Initial but less essential pumping chamber of hearts.
An atrium, or atria as the plural, is responsible for supplying an extra "charge" of blood to its associated ventricle. This extra filling appropriately is known as preloading. Particularly during high demand, the contraction of the atria overfill the ventricles, allowing the ventricles to pump that much more blood at a higher pressure to the rest of the body.

This overfilling is particularly an issue during exercise when that extra blood and extra blood pressure is especially important towards effective performance, such as when running down food or running away from becoming food (putting this issues into the context of their utility in our perhaps more distant ancestors). The atria thus are less crucial to the survival of our bodies at rest, but important contributors to our functioning when the body requires more blood than can be supplied solely by increasing the rate at which the ventricles alone contract.



Links to terms of possible interest: Atrioventricular septum, Bicuspid valve, Interatrial septum, Interventricular septum, Left atrium, Left ventricle, Mitral valve, Right atrium, Right ventricle, Tricuspid valve



Right atrium

Initial but less essential pumping chamber of pulmonary circulation.
The right atrium takes blood from systemic circulation, particularly from the vena cava with which it is continuous. Upon contraction the right atrium sends that blood through the tricuspid valve into the right ventricle.

There is no valve preceding the right atrium other than those valves otherwise located within upstream veins. Note that since this blood is that which is returning from the body, it is depleted in oxygen while carrying an excess of carbon dioxide.


Links to terms of possible interest: Aortic arch, Left atrium, Left ventricle Lobar arteries, Pulmonary arteries, Pulmonary circulation, Pulmonary trunk, Pulmonary veins, Right atrium, Right ventricle

This video talks about the right atrium and vena cava; note that this same video I've also presented above under the heading of vena cava.

The above video provides a remarkably detailed though brief look at the right atrium; it make be overwhelming in detail but does provide a good context for gaining even a moderate understanding of what the right atrium is all about.



Left atrium

Initial but less essential pumping chamber of systemic circulation.
The left atrium takes blood from pulmonary circulation, particularly from the major pulmonary veins. Upon contraction, the left atrium sends that blood through the bicuspid valve into the left ventricle. There is no valve preceding the left atrium and there also are no valves otherwise located within the immediately upstream pulmonary veins. Note that since this blood is that which is returning from the lungs, the blood is oxygenated as well as depleted of carbon dioxide.


Links to terms of possible interest: Aortic arch, Left atrium, Left ventricle Lobar arteries, Pulmonary arteries, Pulmonary trunk, Pulmonary veins, Right atrium, Right ventricle, Systemic circulation

The above video walks us through the anatomy and functioning of the left atrium.

The above video provides a remarkably detailed though brief look at the left atrium; it make be overwhelming in detail but does provide a good context for gaining even a moderate understanding of what the left atrium is all about.



Heart valves

Means by which backflow of blood is prevented during the beating of the heart.
In both veins and the heart the contraction of the volume of blood found within chambers causes a squeezing of that blood away from the point of contraction unless a wall blocking that flow impedes its movement. In the heart these walls consist of what are known as heart valves.

They are valves, and specifically one-way valves, because blood flow not only has to be stopped, in one direction, but also needs to flow, in the other direction. The direction of flow of blood through these one-way valves is from the direction of veins to the direction of arteries, i.e., just as blood flows though one-way valves found in veins towards the heart.

Heart valves come in two basic types, the AV or atrioventricular valves, on the one hand, and the semilunar valves on the other. They are open during diastole and closed during systole.


Links to terms of possible interest: Aortic valve, Bicuspid valve, Pulmonary valve, Tricuspid valve

The above video provides a nice introduction to the anatomy of heart valves.



Atrioventricular valves (AV valves)

Means by which backflow is prevented between ventricles and atria.
The atrioventricular valves are the more robust of the heart valves, preventing backward flow of blood out of the ventricles. Catastrophic failure of these valves, known as prolapse where they fail to prevent backflow, is prevented by connective tissue cords that attach the AV valves to the ventricle walls. These cords are called chordae tendineae, which in turn are connected to what are known as papillary muscles, which in turn are connected to the ventricle walls. The AV valves thus can open into the ventricle but cannot fold backwards (prolapse) into the upstream atria. The atrioventricular valves can be differentiated into the bicuspid valve (a.k.a., mitral valve) versus the tricuspid valve.


Links to terms of possible interest: Aortic valve, Atrioventricular valves, Bicuspid valve, Pulmonary valve, Semilunar valves, Tricuspid valve

The above video fits a lot of information into its 35 seconds on the functioning of heart valves, including a nice cutaway representation of blood flow through the heart including through these valves.



Bicuspid valve

Reversible partition between the left ventricle and the left atrium of the heart.
The bicuspid valve, also known as the mitral valve, possesses two flaps versus the three of the tricuspid valve.

The above video provides a good introduction to the mitral valve, a.k.a., the bicuspid value.



Tricuspid valve

Reversible partition between the right ventricle and the right atrium of the heart.
The tricuspid valve possesses three flaps versus the two of the bicuspid valve.

The above video provides a good introduction to the tricuspid valve.



Semilunar valves

Means by which backflow is prevented between ventricles and the major arteries that they feed with blood.
The semilunar valves are differentiated into the aortic valve versus the pulmonary valve. These are found between the left ventricle and aorta and between the right ventricle and the pulmonary trunk, respectively. The semilunar valves are much less robust than the AV valves since the pressure that they hold back is much less than that generated by the ventricles.


Links to terms of possible interest: Aortic semilunar valve, Bicuspid valve, Pulmonary semilunar valve, Tricuspid valve

The above video provides a discussion of heart valve function, damage, and replacement, with focus on the aortic valve, one of the two semilunar valves.

The above video provides a discussion of the aortic semilunar valve.

The above video provides an interesting summary of what the heart is all about, considering its embryology during human fetal development.


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