THE HEART

By: Rhea Chong CN 04 Denise Yang CN 26

The heart is a myogenic muscular organ found in all animals with a circulatory system (including all vertebrate) that is responsible for pumping blood throughout the blood vessel by repeated, rhythmic contractions.

Myogenic contraction refers to a muscle contraction initiated by the myocyte cell itself instead of an outside occurrence or stimulus such as nerve innervation. A myocyte (also known as a muscle cell)

is the type of cell found in muscles. Cardiac myocytes are responsible for

generating the electrical impulses that control the heart rate, among other things.

HOW DOES THE HEART BEAT?

Before each beat, your heart fills with blood. Then its muscle contracts to squirt the blood along. When the heart contracts (becomes smaller), it squeezes — try squeezing your hand into a fist. That's sort of like what your heart does so it can squirt out the blood. Your heart does this all day and all night, all the time.

The vertebrate heart is composed of cardiac muscle, which is an involuntary striated muscle tissue (a form of fibers that are combined into parallel fibers) found only in this organ, and connective tissue.

HUMAN HEART It is enclosed in a double-walled sac called the pericardium. This sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood.

LOCATION

In the human body, the heart is usually situated in the middle of the thorax with the largest part of the heart slightly offset to the left, although sometimes it is on the right, underneath the human sternum. The heart is usually felt to be on the left side because the left heart (left ventricle) is stronger (it pumps to all body parts). The left lung is smaller than the right lung because the heart occupies more of the left hemithorax.

EPICARDIUM The outer wall of the human heart is composed

of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the pericardium.

Its largest constituent is connective tissue and functions as a protective layer. The visceral pericardium apparently produces thepericardial fluid, which lubricates motion between the inner and outer layers of the pericardium.

MYOCARDIUM

The middle layer is called the myocardium(cardiac muscle) and is composed of muscle which contracts.

It is composed of spontaneously contracting cardiac muscle fibers which allows the heart to contract.

It stimulates the heart contractions to pump blood from the ventricles and relaxes the heart to allow the atria to receive blood.

These contractions produce what is known as a heart beat.

ENDOCARDIUM The inner layer is called the endocardium and is in

contact with the blood that the heart pumps.

The endocardium, which is primarily made up of endothelial cells, controls myocardial function.

The cardiac endothelium controls the development of the heart in the embryo as well as in the adult.

Endothelium- thin layer of cells that lines the interior surface of blood vessels, forming an interface between the circulating blood in the lumen and the rest of the vessel wall, it reduces the turbulence of the flow of blood, allowing cells to be pumped further Lumen- inside space of the artery

ENDOCARDIUM Additionally, the contractility and electrophysiological

environment of the cardiomyocyte are regulated by the cardiac endothelium.

Electrophysiolgy- involves measurements of voltage change or electrical current.

The endocardial endothelium may also act as a kind of blood-heart barrier, thus controlling the ionic composition of the extracellular fluid in which the cardiomyocytes bathe.

Ion- atom or a group of atoms with a net electric charge Extracellular- outside the cell

Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves.

CHAMBERS OF THE HEART

The human heart is divided into four main chambers: the the upper chambers are called the left and right atria and two lower chambers are called the right and left ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers. There is a thick wall separating the right and left side of the heart called tyhe septum. Normally with each beat the right ventricle pumps the same ampunt of blood into the lungs that the left ventricle pumps out into the body.

PATHWAYS OF THE HEART

The pathway of blood through the human heart consists of a pulmonary circuit and a systemic circuit.

These pathways include the tricuspid valve the mitral valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valve are classified as the atrioventricular valves.this is because they are found in between the atria and ventricles. The aortic and pulmonary semilunar valves separate the left and right ventricle from the pulmonary artery and the aorta respectively.

Semilunar valves- permit blood to be forced into the arteries, but prevent backflow of blood from the arteries into the ventricles.

FUNCTION (THE RIGHT SIDE)

The right side collects de-oxygenated blood, in the right atrium, from the body(via superior and interior vena cava) and pump it(via the right ventricle) into the lungs so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the passive process of diffusion.

This process is called the pulmonary circulation.

FUNCTION (THE LEFT SIDE)

• The left side of the heart collects oxygenated blood from the lung into the left atrium. From the left atrium the blood moves to the left ventricle, which pumps it out to the body (via the aorta). On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systematic circulation.

• Systematic circulation- carries oxygenated blood away from the heart to the body and returns deoxygenated blood back to the heart

PATH OF BLOOD FLOW

Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here it is pumped out of the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, blood flows back through the aortic semilunar valve to the aorta and to the rest of the body. The deoxygenated blood finally retutns to the heart through the inferior vena cava and superior vena cava, and enters the right atrium where the process begins.

PARTS OF THE HEART

Some cardiac cells are self-excitable, contracting without any signal from the nervous system, even if removed from the heart and placed in culture. Each of these cells have their own intrinsic contraction rhythm. A region of the human heart called the sinoatrial node, or pacemaker, sets the rate and timing at which all cardiac muscle cells contract. It is located in the right atrium of the heart.

TRIVIA1) The term cardiac (as in cardiology) means

"related to the heart" and comes from the Greek language καρδιά, kardia, for "heart".

2) A kitchen faucet would need to be turned on all the way for at least 45 years to equal the amount of blood pumped by the heart in an average lifetime.

3) The volume of blood pumped by the heart can vary over a wide range, from five to 30 liters per minute.

4) Grab a tennis ball and squeeze it tightly: that’s how hard the beating heart works to pump blood.

TRIVIA5) Laughing can be a great workout for your

heart. Whenever you laugh, the blood flow in your heart is increased for up to 45 minutes, which in turn improves your heart health.

6) The human heart can create enough pressure that it could squirt blood at a distance of thirty feet.

7) For men, there is a strange link between the ring finger and the heart. According to scientific studies, the longer a man’s ring finger is, the lower his chance of having a heart attack.

8) Most heart attacks occur between the hours of 8 and 9 AM.

THE END.