your heart beats 100,000 times every day? We can learn a lot about heart anatomy by

tracing a drop of blood through the heart. The superior and inferior vena cavae bring

deoxygenated blood from the body to the heart. Blood flows from the vena cavae to a chamber

called the right atrium. Blood flows from the right atrium to a larger

chamber called the right ventricle. The blood flows past a valve called the tricuspid

valve. This one way valve has 3 leaflets or cusps and keeps blood flowing in one direction

toward the ventricle. Blood is then pumped out of the right ventricle

into another vessel called the pulmonary trunk and past a valve called the pulmonary valve

one of 2 semilunar valves. This one-way valve keeps the blood flowing toward the lungs.

Blood flows from the pulmonary trunk to the right and left pulmonary arteries. An interesting

fact is that these are the only arteries in the body that carry deoxygenated blood.

Blood now moves into the lungs for oxygenation. Oxygenated blood returns to the heart via

the right and left pulmonary veins. Most veins carry deoxygenated blood. The pulmonary veins

are an exception. Blood enters the left atrium which is the

receiving chamber on the left side of the heart.

Blood flows from the left atrium to the left ventricle past the bicuspid or mitral valve.

Blood is pumped out of the left ventricle and enters the aorta while flowing past the

aortic valve, another one way semilunar valve. Blood then moves through the arterial system

to the body. The heart is surrounded by a series of membranes

called the pericardium or pericardial membranes. Let's look at the layers of the heart and

pericardium. Looking from the inside out the endocardium

is the innermost lining. It consists of a thin layer of simple squamous cells.

The myocardium is a thick muscular layer consisting of cardiac muscle.

The visceral pericardium or epicaridium is the outermost layer of the heart.

The pericardial cavity is a space filled with a serous fluid called pericardial fluid.

The parietal pericardium is the fibrous outer most layer of the pericardium.

Looking at a bit more detailed diagram of the heart we can see the chordae tendinae

which are tendinous structures attaching the tricuspid and bicuspid valves to the papillary

muscles on the inner walls of the ventricles. The papillary muscles are small muscles that

contract when the ventricles contract to prevent backflow of blood into the atria.

The fossa ovalis is a remnant of fetal circulation. It begins in utero as the foramen ovale. At

birth a tissue flap closes the hole and it eventually permanently adheres and becomes

the fossa ovalis. The trabecular carnae are muscular structures

that line the walls of the ventricles. The atria have similar structures called pectinate

muscles. The interventricular septum is a muscular

wall between the ventricles. The ligamentum arteriosum is another remnant

of fetal circulation. It begins as a tubular structure and after birth eventually becomes

a ligament. The top portion of the heart is known as the

base. The bottom portion is known as the apex.

Let's take a look at the coronary arteries. These arteries supply the heart with blood.

There are 2 coronary arteries, the right and left.

Both originate from the aorta. The right coronary artery supplies the right

atrium and parts of both ventricles. It branches to form the marginal and posterior descending.

The left coronary artery supplies the left atrium, left ventricle and interventricular

septum. It branches to form the circumflex, marginal and anterior descending or interventricular

arteries. We hope you have learned something about heart

anatomy and see you next time.