The heart
The heart is an organ that is approximately the size of your fist. It pumps blood throughout
the body and is composed of multiple layers of tissue. The heart is at the centre of the
circulatory system, it is a system of organs that include the heart, blood vessels, and blood
which is circulated throughout the entire body of a human and other vertebrates. The
circulatory system also encompasses the cardiovascular system, which consists of the heart
and blood vessels.
The heart has multiple functions, which include: Pumping blood throughout the body,
controlling heart rate, and the maintenance of blood pressure. As the blood pumps blood
around the body it delivers oxygen and nutrients so that organs within the body can continue
to function. The blood also transports glucose C6H12O6 around the body, which is used for
the main source of energy of our cells, and keeps blood sugar levels consistent within the
body. White blood cells, platelets, hormones and proteins are also transported through the
blood. Waste is also removed via blood, such as carbon dioxide which is transported back to
the lungs and other waste products such as bacteria and destroyed viruses.
The electrical system in the heart controls and regulates the frequency and the rhythm of our
heartbeats. The body receives the right amount of blood from a healthy heart. If the heart
was weakened by disease or an injury, the organs within the body would not receive enough
blood to work and function at a normal level. A problem with the electrical system which
regulates your heart rate can make it harder for the heart to pump blood around the body.
The heart is in the centre of the chest, near the lungs. There are four hollow chambers
surrounded by muscle and other heart tissue. Chambers are separated by heart valves
which make sure that the blood flows in the right direction. The two upper chambers of the
heart are called atria and the two lower chambers are called ventricles. Blood flows from the
body and lungs to the atria and from the atria to the ventricles. The ventricles then pump
blood out of the heart to the lungs and other parts within the human body. There is an
internal wall of tissue that divides the right and left sides of the heart. This wall is called the
septum.
The heart is made up of three layers of tissue, this is to provide structure and support to the
heart, the connective tissues serve to provide a separation between the atria and the
ventricles of the heart.
Endocardium is the thin inner lining of the heart chambers and also forms the surface of the
valves. It is the innermost layer of the heart. The endocardium has two layers whereby the
inner layer lines the heart chambers and is made of endothelial cells.
Myocardium is the thick layer of muscle that allows the heart chambers to contract and relax
to pump blood to the body. It is the thickest layer of all three heart layers. The muscle layer
enables heart contractions, so is responsible for contracting and relaxing involuntarily and
keeps the heart pumping blood around the body.
Pericardium is the sac that surrounds the heart. It is made of thin layers of tissue and holds
the heart in place and protects it. There is a small amount of fluid between the layers which
helps to reduce friction between the beating heart and surrounding tissues. There are two
layers to the pericardium: fibrous pericardium which is the outer layer and is made from thick
connective tissue. This layer holds the heart in place in the chest cavity and protects from
infection. The serous pericardium is the inner layer which is further divided into two layers:
visceral and parietal layers. Serous pericardium helps lubricate the heart. The epicardium is
also a layer of thin elastic connective tissue and fat that serves as an additional layer of
, protection from trauma or friction for the heart under the pericardium. Epicardium also
contains the coronary blood vessels which oxygenate the tissues of the heart with a blood
supply from the coronary arteries.
The heart consists of four chambers and two ventricles which operate in a double circulatory
system. The right ventricle pumps oxygen depleted blood back to the lungs, it is located in
the lower right portion of the heart helps the right atrium and opposite the left ventricle.
Deoxygenated blood flows into the right atrium and passes through the tricuspid valve into
the right ventricle, and to the lungs where it is oxygenated. The oxygenated blood returns
from the lungs to the left atrium; it is pushed into the left ventricle and then out along the
main blood vessel of the body, which is the aorta. The chambers are separated by a wall of
tissues and called the septum. Differences in thickness of the heart chamber walls are due
to variations in the myocardium, which reflects the amount of force each chamber is required
to generate.
The cardiac cycle is a series of pressure changes that take place within the heart. These
pressures result in the movement of blood through different chambers of the heart and the
body as a whole. Cardiac diastole is where the heart is relaxed. Both the atria and ventricles
are relaxed, and blood reaches the atria at a low pressure through the veins, pulmonary vein
and vena cava. When blood passes through the atria, blood pressure rises causing the
atrioventricular valves (av) to open, enabling blood to reach the ventricles.
Atrial systole is where the atria contracts when they are 50% empty. This ensures that all of
the blood leaves the atria and enters the ventricles. This causes all the pressure within the
ventricles to rise significantly, closing the AV valves and preventing blood from returning to
the atria. Ventricular systole, in which the ventricles contract upwards from the bottom of the
heart which is also known as the apex of the heart. The pressure in the ventricles now
further increases in the arteries (pulmonary arteries and aorta). Due to this pressure change,
blood can flow out through the semilunar valves and allows the blood to leave.
Effects of stimulants on the heart
Stimulants stimulate the sympathetic nervous system and increase heart rate, blood
pressure, and respiration. They can cause a dangerously high body temperature. Stimulants
are a class of drugs that speed up messages travelling between the brain and the body.
They can make a person feel more awake, alert, confident or energetic. Stimulants are not
limited to illegal drugs but include: caffeine, nicotine, amphetamines and cocaine.
Cardiovascular disease
Cardiovascular disease (CVD) is a general term that describes a disease of the heart or
blood vessels; it is usually associated with a build-up of fatty deposits inside the arteries and
an increased risk of blood clots. CVD is one of the main causes of death and disability in the
UK, but can be prevented by leading a healthy lifestyle. Coronary heart disease occurs when
the flow of oxygen rich blood to the heart is blocked or reduced. This would put an increased
strain on the heart and can lead to angina, which is chest pain caused by restricted blood
flow to the heart muscle. Heart attacks - where blood flow to the heart muscle is suddenly
blinded.
Peripheral arterial disease which occurs when there is a blockage in the arteries to the limbs.
This can cause: dull or cramping leg pain, which is worse when walking, numbness or
weakness in the legs, or persistent open sores in the feet and lungs, etc.
