Pulmonary Artery
This artery branches after leaving the right ventricle, each branch carrying deoxygenated blood to one lung.
Septum
The septum is a thick muscle wall that divides the heart into two distinct hearts.
Myocardium
The hearts interconnected muscle fibers enable it to contract and relax automatically.
Pathway of Blood around the Body
The blood circulates throughout the body. It carries nutrients (food) and oxygen to all the cells of the body, and carries away waste products so that they can be removed from the body. Without access to the blood, cells and body tissues die.
Blood Circulation
Blood circulates the body in two systems (pulmonary and systemic) through interconnecting pathways of arteries, veins and smaller blood vessels. In the pulmonary circulation, deoxygenated blood travels from the heart to the lungs, where it is freshly enriched with oxygen before returning to the heart. The oxygenated blood is then transported by the systemic circulation to all body parts.
Diagram 3 – Diagram of Valves in Veins
Cardiac Cycle
Three different phases make up the sequential beating of the heart. The relaxing the of the muscle and refilling of the chambers with fluid is the first stage, this is then followed by stages when the atria and ventricle contract, sending blood through the heart and out into the arteries. The complete cycle takes approximately four-fiths of a second.
STAGE 1 – DIASTOLE
In the first stage of the cycle, deoxygenated blood enters the right atrium and oxygenated blood enters the left atrium. The blood then flows through the ventricles.
STAGE 2 – ATRIAL SYSTOLE
Impulses from the sinoatrail node initiate the next phase of the cycle, whilst the atria contract. This squeezes any blood in the atria into ventricles.
STAGE 3 – VENTRICULAR SYSTOLE
The ventricles contract valves at the ventricle exit opens and blood is forced out into the pulmonary artery and the aorta, as this stage ends STAGE 1 begins again.
The heart is controlled by the automatic nervous system that has two branches namely the sympathetic nervous system and the parasympathetic nervous system. The two systems act like a brake and accelerator on the heart. The two systems supply a special cluster of cells in the upper part of the right atrium; this is called the Sino- Atrial Node (S-A node) sometimes referred to the ‘pacemaker’. Every few seconds the S-A node sends nerve impulses across the branching network of atrial muscle fibers that causes a contraction. These impulses are caught by another group of cells, these cells form the Atrio-Ventricular Node (A-V Node) and impulses are then relayed to a band of conducting tissue made up from large muscles cells called Purkinje fibers.
Blood Vessels
Arteries
The arteries carry blood away from the heart to different areas of the body. Blood carrier’s oxygen in it and without oxygen all the cells within the body will die. The walls of the arteries are made up of very strong elastically muscles because the arteries have to with stand high pressures of blood as it is pumped out of the heart. Blood will flow quickly around the arteries in pulses.
The walls of the arteries are made up of three layers:
- A thick outer layer of collagen fibers
- A thick elastic layer of muscle fibers are arranged in rings
- A thin lining layer
Veins
Veins carry deoxygenated blood back to the heart. They have thin flexible walls that are a lot thinner than arteries because the pressure of the blood is a great deal lower.
Nevertheless veins are made up of three layers:
- Thin outer layers of collagen fibers
- Thin middle layers containing a few muscle fibers
- Thin lining layer
Blood flows slowly through the veins without any pulse, veins have a system of valves that prevent blood flowing backwards.
Blood has to flow from the arteries into veins, but it can do so directly, therefore arteries branch and branch and become narrower forming smaller vessels called arterioles. Arterioles branch many more times, into tiny blood vessels known as capillaries.
Capillaries
Capillaries are very fine narrow vessels that occur in branching networks throughout body tissue, capillary walls are made up of a single layer of cells.
Valves
Diagram 4 – Diagram of Valves in Veins
There are one-way valves at intervals inside the larger veins. These valves prevent blood flowing back in the wrong direction. When a person stands, there is quite a height of blood between the heart and legs. Gravity tends to pull the blood back down, but is prevented from doing so by the vein valves, and by the normal flow of blood towards the heart.
Heart Related Illnesses
Cardiovascular Disorders
Common heart disorders and diseases include structural defects; damage due to restricted blood supply caused by narrowing of the arteries: disorders of the heart muscle and viral infections. The circulation of blood might be hindered by obstructions such as blood clots or fatty deposits or by weakened arteries or malfunctioning valves.
Heart Attack
A heart attack is medically referred to as a Myocardial Infraction; it is the death of part of the heart muscle. This is caused by the blockage of a coronary artery, therefore depriving an area of the heart of its blood supply. Symptoms of a heart attack include:
- Sever chest pains
- Sweating and nausea
- Shortness of breath
Heart Valve Disorders
If a heart valve isn't working properly, blood flow is thrown into chaos.
The two main problems that occur are:
- Valves that don't shut properly, causing regurgitation of blood back across the valve in the wrong direction (for example, from the aorta back into the heart).
- Valves that won't open properly, known as stenosis of the valve, which means blood flow through the valve is limited.
If the problem is mild, it may go unnoticed. However, it can put excessive strain on the heart, making it swollen, less effective as a pump and more likely to have an abnormal rhythm. It can also result in a backlog of pressure, causing fluid to accumulate in the lungs and lower leg.
Defective heart valves are also more vulnerable to infections from bacteria entering the bloodstream. This is why people with diseased heart valves should always take antibiotics when they have surgery or major dental work.
Aneurysm
An aneurysm is an abnormal bulge or “ballooning” in the wall of an artery. An aneurysm that grows and becomes large enough can burst, causing dangerous, often fatal, bleeding inside the body. Most aneurysms occur in the aorta and are referred to as a thoracic aortic aneurysm. Aneurysms also can occur in arteries in the brain, heart, intestine, neck, spleen, back of the knees and thighs, and in other parts of the body. If an aneurysm in the brain bursts, it causes a stroke. Many cases of ruptured aneurysm can be prevented with early diagnosis and medical treatment.