Cardiology Flashcards
Why is the heart considered a double pump?
The heart, while only a single organ, works as a double pump. It propels blood though the lungs (pulmonary circulation) and the rest of the body (systemic circulation) simultaneously.
How much blood does the heart pump per day?
At rest the heart pumps about 1,800 gallons of blood per day through about 60,000 miles of blood vessels.
Describe the heart’s location
The heart rests on the muscular diaphragm separating the thoracic and abdominal cavities. The thoracic space in which it sits is known as the mediastinum.
apex of the heart
About 2/3 of the heart mass lies to the left of the midline, with its
apex, formed by the tip of the left ventricle, lying 9cm (3.25 inches) from the midline, deep to the 5th intercostal space.
base of the heart
Opposite to the apex is the base of the heart. It lies superior and
posterior in the mediastinum and is formed mostly by the left atrium.
pericardium
The pericardium is a triple-layered bag that surrounds and
protects the heart, confining it to its position within the mediastinum, yet allowing it freedom of movement for contraction. The pericardium consists of two main portions
fibrous pericardium
The outer fibrous pericardium is a tough, inelastic, fibrous
connective tissue attached to the great vessels associated with the heart, the diaphragm, and at the roots of the lungs. It serves to anchor the heart within the mediastinum, prevent over-stretching of the heart during exercise, and offers some degree of protection.
Serous pericardium
The inner serous pericardium is a
thinner and more delicate membrane that forms a double layer around the heart. It is subdivided into to layers
Serous pericardium - parietal layer
The outer portion of the serous pericardium, the
parietal layer, is fused to the inside surface of the fibrous pericardium.
Viseral layer of the serous pericardium
The inner visceral layer of the serous pericardium,
also known as the epicardium or the outer wall of the heart itself, adheres tightly to the surface of the heart muscle (the myocardium).
pericardial cavity
Between the parietal and visceral layers is a small
space called the pericardial cavity. It contains a small amount of pericardial fluid, secreted by the serous pericardium that is used for lubrication to reduce friction as the heart moves.
epicardium
The wall of the heart itself is subdivided into three layers.
The epicardium, the outermost layer, is also known as the visceral layer of the serous pericardium. It is a thin, transparent membrane that imparts a slippery texture to the outer surface of the heart
myocardium
The myocardium, the middle layer, consists of cardiac
muscle cells and is responsible for the pumping action of the heart. The cardiac muscle fibers are involuntary, striated, and branched, swirling diagonally around the heart in interlacing bundles to form two large networks, the atria and the ventricles.
intercalated discs
Each cardiac muscle cell contacts neighboring cells
by transverse thickenings of the sarcolemma called intercalated discs, within which are gap junctions that electrically couple the cells so that they work as a unit (cardiac muscle is a functional syncytium).
cardiac skeleton
The two muscle masses, atria and ventricles, are
separated from each other by the cardiac skeleton, dense fibrous connective tissue in the form of a figure-8 separating the two masses. This fibrous tissue uncouples the electrical activity of the atria from that of the ventricles so that the two can work independently.
endocardium
The innermost layer of the heart wall is the endocardium,
a simple squamous epithelium overlying a thin connective tissue. The endocardium becomes continuous with the endothelium of the blood vessels.
heart chambers
The interior of the heart is divided into four compart-
ments that receive the circulating blood.
The two superior chambers are the right atrium and the left atrium, each of which has an appendage called the auricle that increases the volume of the atrium and is used during exercise.
The two lower chambers are the right ventricle and the left ventricle.
coronary sulcus and interventricular sulci
Externally, the heart cham-
bers are delineated from one another by a series of grooves within which lie the coronary arteries and coronary veins.
The coronary sulcus separates the atria from the ventricles.
The anterior and posterior interventricular sulci separate the two ventricles front and back.
role of cardiac skeleton
The connective tissue of the cardiac skeleton
effectively separates the upper atria from the lower ventricles so that they work independent of one another.
interatrial septum
Internally the chambers of the heart are separated by
muscular walls called septa.
The interatrial septum separates the atria and bears a prominent feature called the fossa ovalis, the remnant of the fetal foramen ovale, an opening that allowed blood to pass from right atrium to left atrium.
interventricular septum
The interventricular septum separates the
ventricles and is divided into two portions: the superior membranous and inferior muscular interventricular septum.
atrial wall thickness
The myocardium of the atria is relatively thin since
it has only to move blood into the ventricles, and therefore needs to generate only a small amount of pressure.
ventricular wall thickness
The myocardium of the ventricles is
considerably thicker since it must move blood to the lungs (right ventricle) or to the rest of the body (left ventricle). The left ventricle wall is thickest since it must generate the largest amount of pressure.
Describe the basic pattern of blood flow from the body through three veins: superior vena cava, inferior vena cava, and the coronary sinus.
The superior vena cava brings blood from most of the upper body to the heart (head, neck, upper extremity, and thorax).
The inferior vena cava brings blood from all parts of the body inferior to the diaphragm.
The coronary sinus receives blood from the coronary veins draining the heart itself and delivers it to the right atrium.
From the right atrium blood moves into the right ventricle, is pumped into the pulmonary trunk, which divides into right and left pulmonary arteries, each of which carries deoxygenated blood to its respective lung.
Oxygenated blood from the lungs passes to the left atrium via 4 pulmonary veins.
Blood then passes from the left atrium into the left ventricle, from which it is pumped into the aorta for distribution throughout the systemic circulation.
What are heart valves?
As each chamber of the heart contracts, it pushes a portion of its blood into a ventricle or into a great artery. To prevent backflow of blood, the heart is equipped with valves, formed from the connective tissue of the cardiac skeleton and covered with endocardium. They open and close by pressure changes.
Describe atrioventricular valves?
Atrioventricular (AV) valves lie between the atria and the ventricles. The tricuspid valve is on the right side, and the bicuspid (mitral) valve is on the left. Each cusp of an AV valve is roughly shaped like a triangle; the base is attached to the heart wall and the apex is pointed down into the ventricle.
What are the chordae tendineae and papillary muscles?
Attached to the apices of the cusps are tendon-like cords of connective tissue called the chordae tendineae, which anchor the valves down inside the ventricle wall by attaching to papillary muscles.
Describe the mechanism by which the atrioventricular valves open and close. Be sure to include the pressure changes that occur?
In order for blood to pass from atrium to ventricle, the AV valve must be open with its pointed ends extending into the ventricular cavity, the papillary muscles relaxed, and the chordae tendineae slackened.
Contraction of the ventricular myocardium increases the pressure within the ventricle, forcing the blood toward the opening between atrium and ventricle.
The pressure change and the force of the blood drive the cusps of the AV valve upward until their edges meet and close the opening, thus preventing backflow of blood into the atrium.
At the same time, the papillary muscles contract, adding further tension to the chordae tendineae, preventing the cusps from everting or swinging upward into the atrium and thus allowing blood to flow back into the atrium.
Describe semilunar valves on location shape and functioning
located in the pulmonary trunk and aorta just as each vessel emerges from its respective ventricle.
shape – Each of these valves consists of three half-moon shaped
cusps that are attached to the artery wall like a pocket is attached to a shirt, with a free upper margin.
functioning – When blood is ejected from the ventricle into the
artery, the cusps are pushed flat against the artery wall, allowing blood to pass. After contraction, when arterial pressure becomes greater then ventricular pressure, blood begins to flow back to the ventricle. As it does so, blood backfills the SL valve cusps, filling the pockets and causing the free margins to bulge outward from the wall of the vessel. When the edges of the three bulging cusps meet each other, the valve is closed and blood cannot return to the heart.
What is coronary circulation?
The myocardium has its own blood supply and does not rely upon diffusion of nutrients from the blood circulating through the chambers to meet its needs. Two coronary arteries branching from the ascending aorta, right and left, are responsible for the total blood flow to the myocardium.
left coronary artery
The left coronary artery emerges from the
aorta to the left of the pulmonary trunk and almost immediately divides into two branches: anterior interventricular artery (left anterior descending or LAD) circumflex artery.
supply area – The left coronary artery, via its branches is
responsible for most of the blood supply to the anterior myocardium of both ventricles and to the left atrium.
right coronary artery
The right coronary artery emerges from the
aorta to the right of the pulmonary trunk and passes in the groove between the right atrium and right ventricle. It gives rise to two arteries: marginal artery and posterior interventri-cular artery.
supply area – The right coronary supplies blood to the right
atrium and the posterior myocardium of the ventricles.
anastomoses of the heart
There are a great many interconnec-
tions (anastomoses) between the branches of the coronary arteries, particularly where the anterior and posterior interventricular arteries meet. Anastomoses provide a number of alternate routes for blood flow should one path become blocked.
great cardiac veins
The great cardiac vein is located in the
anterior interventricular sulcus, alongside the anterior interventricular branch of the left coronary artery. It drains blood from the myocardium of the anterior aspect of the heart.
middle cardiac vein
The middle cardiac vein lies in the posterior
interventricular sulcus, alongside the posterior interventricular branch of the right coronary artery. It drains blood from the myocardium of the posterior aspect of the heart.
small cardiac vein
The small cardiac vein is found in the groove
between the right atrium and right ventricle. It drains blood from the myocardium of both areas.