FUNCTIONS OF HEART

Coronary, pulmonary and systemic circulations are the systems that allow blood to be pumped throughout the body, coronary circulation is the system that allows blood to be pumped through the heart, pulmonary circulation is the system that pumps blood through to the lungs and the systemic circulation which is the system that pumps the blood around the rest of the body and to the remaining organs. As humans we have a closed cardiovascular system which means the blood never leaves the circulation of the blood vessels. The coronary circulation is part of the systemic circulation by definition it supplies blood to muscles- muscles of the heart

 (myocardium), however it is the only system to provide the heart with blood. The blood comes from the aorta and filters through into the right atrium. If the heart didn’t receive the blood supply, it would cause severe tissue damage.

The pulmonary circulation uses the pulmonary artery to take de-oxygenated blood away from the heart through to the lungs which is where the blood is then oxygenated. The de-oxygenated blood enters the right atrium of the heart and flows through the tricuspid valve and then from there it flows into the right ventricle, here it is then pumped through the pulmonary semilunar valve into the pulmonary artery to the lungs. In the lungs is where the gas exchange takes place, where the CO2 is released and the blood then absorbs oxygen. This is the stage when the pulmonary vein returns the freshly oxygenated blood to the heart.

The systemic circulation on the other hand takes the oxygenated blood from the heart and transports it throughout the rest of the body except from the lungs. The system then provides all other organs with the oxygenated blood, the circulation then returns all of the de-oxygenated blood back to the heart for the process to start all over again. The systemic circulation is a much lengthier system than the pulmonary circulation due to transporting blood all over the body.

(1)The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle. The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium is deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the strong left ventricle to be pumped through the aorta to the different organs of the body.

The blood circuit is flows in the shape of a figure of 8. There are two loops to this circuit. The top loop carries the blood from the heart to the lungs and back (the pulmonary circulation). The bottom loop carries the blood from the heart all over the body (systemic circulation).

The 4 main stages of the cardiac cycle are:

Atrial Diastole -which is where the top chamber (atria) relaxes and fills with blood from the veins

Atrial Systole- where the atria contracts and blood is forced into the relaxing bottom chambers which are otherwise known as ventricles

Ventricular systole- which is where the ventricles contract and blood is forced out of the heart in to the arteries.

Ventricular diastole -when the ventricles relax and become ready for the next pump cycle..

The circulatory system also consists of the lymphatic system; this is a non-closed system that carries a clear liquid called lymph towards the heart and allows an average of 20 litres of blood per day through capillary filtration which removes plasma while leaving the erythrocytes. Around 17 litres of filtered plasma get reabsorbed into the blood vessels; however 3 litres are then left behind in the interstitial fluid. The main role of the lymph system is to provide an auxiliary route for the extra 3 litres to return to the blood. (4) The lymphatic system has multiple interrelated functions:

it is responsible for the removal of interstitial fluid from tissues

it absorbs and transports fatty acids and fats as chyle from the digestive system

it transports white blood cells to and from the lymph nodes into the bones

The lymph transports antigen-presenting cells (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated.

There are three main blood vessels in the cardiovascular system, these are the arteries, veins and capillaries; arteries are responsible for carrying the blood away from the heart, they are made up of a thick elastic muscular wall, which is capable of stretching as blood is being pumped through at a high pressure. The muscle walls are able to contract to force the blood along through the arteries

Veins are made up of a much thinner, less muscular wall compared to the arteries. The blood in the veins is under considerably much lower pressure compared to the blood in the arteries, this is because arteries need higher pressure in order to deliver the oxygenated blood to the arterioles, capillaries, other organs and tissues and to also prevent the back flow of blood, veins don’t require this high pressure because the de-oxygenated blood can travel from the tissues to the heart through the veins with the help of the muscle contractions. One of the functions of the veins is to ensure that the blood doesn’t flow back towards the heart, veins contain valves every few centimetres along, this helps them push the blood in one direction. However muscle contraction and relaxation can also occur to help squeeze the walls of the veins to help the blood flow back towards the heart when necessary. You can use a stethoscope to hear pulmonary circulation. The sounds that are audible are the ventricles contracting and the valves closing.

Capillaries are the smallest of all the blood vessels they have a wall that is one cell thick, capillaries connect the arterioles and venules this is where all the exchange of nutrients and gases such as oxygen and carbon dioxide occurs- through the capillary surfaces. Leucocytes are able to leave our capillaries in order to digest any micro-organisms that could be a potential threat or disease.

Arteries, veins and capillaries are all blood vessels of the body and all of them are routes for the blood to pass through to provide their functions. They all contain tunica externa, tunica media and tunica intima.

Blood is carried away from the heart via the arteries and the blood returns to the heart through the veins. Our circulatory system is a transport system the carries our blood, oxygen and waste products to and from our body’s cells in order for our bodies to functions. (2) During systemic circulation, blood passes through the kidneys. This phase of systemic circulation is known as renal circulation. During this phase, the kidneys filter much of the waste from the blood. Blood also passes through the small intestine during systemic circulation. This phase is known as portal circulation. During this phase, the blood from the small intestine collects in the portal vein which passes through the liver. The liver filters sugars from the blood, storing them for later

When it comes to heat regulation in order to keep cool our capillaries are capable of forcing the blood supply to the surface of the skin, this allows the air to reach the blood and to cool it more easily, and sweating is also induced as part of the heart regulation. However when trying to keep warm our capillaries work hard in order to reduce the blood at the skin surface and sweating is also reduced. This is known as vasoconstriction and vasodilation. Heat regulation is one of the key functions of the circulatory system as well as many other functions. Signals along nerves from the hypothalamus control both vasodilation and vasoconstriction. It is necessary for the human body to have vasodilation and vasoconstriction as it regulates the body’s blood pressure, by constricting and releasing the vessels to allow more or less blood through, for example whilst exercising our heart and breathing rates increase and blood vessels in our limbs dilate in order to deliver more oxygenated blood to our working muscle cells. (3) Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels. The process is particularly important in staunching haemorrhage and acute blood loss. When blood vessels constrict, the flow of blood is restricted or decreased, thus, retaining body heat or increasing vascular resistance

Our blood that is carried around in our cardiovascular system is responsible for maintaining its levels in many advance ways. For example haemostasis is a complex chain reaction that produces the blood to clot this is otherwise known as coagulation. The body clots in two different ways, there is the normal clot which is a good formation that stops bleeding, and there is also a thrombus which is bad as it can block the blood vessels.

The endothelium is the cells that create the vessel wall. When the endothelium becomes damaged, for example, when a cut breaks through the wall, collagen fibres then start to appear. These collagen fibres are a protein that is vital for the structure of the vessel wall, these fibres then allow platelets to attach themselves, these are produced from precursor megakaryocytes, it’s these platelets that lead to the formation of blood clots.

The platelets become activated and begin to release a chemical called ‘Thromboxane A2’ which calls on more platelets to the area. Fibrin, which is the insoluble form of the soluble protein fibrinogen, is then converted by thrombin. The fibrin begins to appear and layers on top of the platelets which start to fuse them together. This fibrin helps the clot form as the red blood cells stick to the fibrin. This process then repeats until the clot is fully formed. This process is important for the cardiovascular system, this is because the average human contains around 4.7 to 5.7 litres of blood, if around 30%-40% of this is lost it could prove fatal or cause severe damage.

The blood the is carried around the cardiovascular system, is made of erythrocytes, leucocytes, platelets and plasma which is mainly water, amino acids, proteins, carbohydrates, lipids, hormones, vitamins, electrolytes, dissolved gases, and cellular wastes. Erythrocytes contain a globular protein called haemoglobin which allows oxygen to bind to it; this allows the erythrocytes to transport oxygen throughout the body and organs. The haemoglobin molecule is made up of 4 polypeptide chains, 2 containing 141 amino acids and 2 containing 146, attached to each polypeptide chain is a molecule that contains iron and is known as a ‘haem’, the function of this molecule is to absorb oxygen until it is fully saturated. Carbon dioxide however binds to the amino acids and not the erythrocytes, this means that is binding to the proteins and not the ‘haem

Chambers of the Heart

The heart is a muscular organ about the size of a fist, located just behind and slightly left of the breastbone. The heart pumps blood through the network of arteries and veins called the cardiovascular system.

The heart has four chambers:

• The right atrium receives blood from the veins and pumps it to the right ventricle.
• The right ventricle receives blood from the right atrium and pumps it to the lungs, where it is loaded with oxygen.
• The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle.
• The left ventricle (the strongest chamber) pumps oxygen-rich blood to the rest of the body. The left ventricle’s vigorous contractions create our blood pressure.

The coronary arteries run along the surface of the heart and provide oxygen-rich blood to the heart muscle. A web of nerve tissue also runs through the heart, conducting the complex signals that govern contraction and relaxation. Surrounding the heart is a sac called the pericardium.

Heart Conditions

• Coronary artery disease: Over the years, cholesterol plaques can narrow the arteries supplying blood to the heart. The narrowed arteries are at higher risk for  complete blockage from a sudden blood clot (this blockage is called a heart attack).
• Stable angina pectoris: Narrowed coronary arteries cause predictable chest pain or discomfort with exertion. The blockages prevent the heart from receiving the extra oxygen needed for strenuous activity. Symptoms typically get better with rest.
• Unstable angina pectoris: Chest pain or discomfort that is new, worsening, or occurs at rest. This is an emergency situation as it can precede a heart attack, serious abnormal heart rhythm, or cardiac arrest.
• Myocardial infarction (heart attack): A coronary artery is suddenly blocked. Starved of oxygen, part of the heart muscle dies.
• Arrhythmia (dysrhythmia): An abnormal heart rhythm due to changes in the conduction of electrical impulses through the heart. Some arrhythmias are benign, but others are life-threatening.
• Congestive heart failure: The heart is either too weak or too stiff to effectively pump blood through the body. Shortness of breath and leg swelling are common symptoms.
• Cardiomyopathy: A disease of heart muscle in which the heart is abnormally enlarged, thickened, and/or stiffened. As a result, the heart's ability to pump blood is weakened.
• Myocarditis: Inflammation of the heart muscle, most often due to a viral infection.
• Pericarditis: Inflammation of the lining of the heart (pericardium). Viral infections, kidney failure, and autoimmune conditions are common causes.
• Pericardial effusion: Fluid between the lining of the heart (pericardium) and the heart itself. Often, this is due to pericarditis.
• Atrial fibrillation: Abnormal electrical impulses in the atria cause an irregular heartbeat. Atrial fibrillation is one of the most common arrhythmias.
• Pulmonary embolism: Typically a blood clot  travels through the heart to the lungs. 
• Heart valve disease: There are four heart valves, and each can develop problems. If severe, valve disease can cause congestive heart failure.
• Heart murmur: An abnormal sound heard when listening to the heart with a stethoscope. Some heart murmurs are benign; others suggest heart disease.
• Endocarditis: Inflammation of the inner lining or heart valves of the heart. Usually, endocarditis is due to a serious infection of the heart valves.
• Mitral valve prolapse: The mitral valve is forced backward slightly after blood has passed through the valve. 
• Sudden cardiac death: Death caused by a sudden loss of heart function (cardiac arrest).
• Cardiac arrest: Sudden loss of heart function.

  Heart Tests

  • Electrocardiogram (ECG or EKG): A tracing of the heart’s electrical activity. Electrocardiograms can help diagnose many heart conditions.
  • Echocardiogram: An ultrasound of the heart. An echocardiogram provides direct viewing of any problems with the heart muscle’s pumping ability and heart valves.
  • Cardiac stress test: By using a treadmill or medicines, the heart is stimulated to pump to near-maximum capacity. This may identify people with coronary artery disease.
  • Cardiac catheterization: A catheter is inserted into the femoral artery in the groin and threaded into the coronary arteries. A doctor can then view X-ray images of the coronary arteries or any blockages and perform stenting or other procedures.
  • Holter monitor: If a doctor suspects an arrhythmia, a portable heart monitor can be worn. Called a Holter monitor, it records the heart's rhythm continuously for a 24 hour period.
  • Event monitor: If a doctor suspects an infrequent arrhythmia, a portable heart monitor called an event monitor can be worn. When you develop symptoms, you can push a button to record the heart's electrical rhythm.

    Heart Treatments

    • Exercise: Regular exercise is important for heart health and most heart conditions. Talk to your doctor before starting an exercise program if you have heart problems.
    • Angioplasty: During cardiac catheterization, a doctor inflates a balloon inside a narrowed or blocked coronary artery to widen the artery. A stent is often then placed to keep the artery open.
    • Percutaneous coronary intervention (PCI): Angioplasty is sometimes called a PCI or PTCA (percutaneous transluminal coronary angioplasty) by doctors.
    • Coronary artery stenting: During cardiac catheterization, a doctor expands a wire metal stent inside a narrowed or blocked coronary artery to open up the area. This lets blood flow better and can abort a heart attack or relieve angina (chest pain).
    • Thrombolysis: “Clot-busting” drugs injected into the veins can dissolve a blood clot causing a heart attack. Thrombolysis is generally only done if stenting is not possible.
    • Lipid-lowering agents: Statins and other cholesterol (lipid) lowering drugs reduce the risk for heart attack in high-risk people.
    • Diuretics: Commonly called water pills, diuretics increase urination and fluid loss. This reduces blood volume, improving symptoms of heart failure.
    • Beta-blockers: These medicines reduce strain on the heart and lower heart rate. Beta-blockers are prescribed for many heart conditions, including heart failure and arrhythmias.
    • Angiotensin-converting enzyme inhibitors (ACE inhibitors): These blood pressure medicines also help the heart after some heart attacks or in congestive heart failure.
    • Aspirin: This powerful medicine helps prevent blood clots (the cause of heart attacks). Most people who have had heart attacks should take aspirin.
    • Clopidogrel (Plavix): A clot-preventing medicine that prevents platelets from sticking together to form clots. Clopidogrel is especially important for many people who have had stents placed.
    • Antiarrhythmic medications: Numerous medicines help control the heart’s rate and electrical rhythm. These help prevent or control arrhythmias.
    • AED (automated external defibrillator): If someone has sudden cardiac arrest, an AED can be used to assess the heart rhythm and send an electrical shock to the heart if necessary.
    • ICD (Implantable cardioverter defibrillator): If a doctor suspects you are at risk for a life-threatening arrhythmia, an implantable cardioverter defibrillator may be surgically implanted to monitor your heart rhythm and send an electrical shock to the heart if necessary.
    • Pacemaker: To maintain a stable heart rate, a pacemaker can be implanted. A pacemaker sends electrical signals to the heart when necessary to help it beat properly.