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The Cardiovascular System Essay

The cardiovascular system is made up of the heart, blood vessels and blood. The heart is a myogenic muscle, meaning that it can contract without any nervous supply. It is composed of cardiac muscle which is built up of cells that are connected by cytoplasmic bridges, allowing electrical impulses to cross. The four major functions of the cardiovascular system are:

1. To transport nutrients, gases and waste products around the body
2. To protect the body from infection and blood loss
3. To help the body maintain a constant body temperature (‘thermoregulation’)
4. To help maintain fluid balance within the body

Delivery of Oxygen and Nutrients & Removal of Waste Products: The cardiovascular system works as a transport network, linking all of the body parts via a system of Major routes (arteries and veins), Main routes (arterioles and venules) and Minor routes (capillaries). This network allows a non-stop transportation system, the blood, to add or remove different nutrients, gases, waste products and messages to different parts of the body. Important nutrients such as glucose are added from the digestive system to the major muscles and organs that require them for energy in order to execute their functions. Hormones, chemical messengers, are transported by the cardiovascular system to their target organs, and the many waste products of the body are transported to the lungs or urinary tract to be removed from the body.

The cardiovascular system works in partnership with the respiratory system to deliver the oxygen needed to the tissues of the body and remove unnecessary and harmful carbon dioxide. To be able to do this efficiently and effectively, the cardiovascular system is comprised of two circuits. These circuits are known as the pulmonary circuit and the systemic circuit. The pulmonary circuit consists of the heart, lungs, pulmonary veins and pulmonary arteries. This circuit is responsible for pumping deoxygenated (blue) blood from the heart to the lungs in order for it to be able to be oxygenated (red) and return to the heart. The Pulmonary circuit works out of the right side of the heart and feeds blood back into the left side.

The systemic circuit consists of the heart and all the other arteries, arterioles, capillaries, venules, and veins in the body that aren’t part of the pulmonary circuit. This circuit is responsible for pumping oxygenated (red) blood from the left side of the heart to all the tissues, muscles and organs in the body, to be able to provide them with the nutrients and gases they need to be able to execute their specific functions. After it has delivered the oxygen needed, the systemic circuit is then responsible for picking up the waste carbon dioxide and returning this in the now deoxygenated (blue) blood, back to the lungs, where it will enter the pulmonary circuit to become oxygenated again. Maintenance of constant body temperature (thermoregulation): The average core body temperature range for a healthy adult is expected to be between 36.1°C and 37.8°C, with 37°C being known as ‘normal’ body temperature.

If the body’s temperature drops anywhere below this essential range it is known as hypothermia and if it rises above this essential range it is known as hyperthermia. As the body’s temperature moves further into hypo or hyperthermia they will become life threatening. Because of this, the body works continuously, with the help of the cardiovascular system, to maintain its core temperature within the normal healthy range. This process of temperature regulation is known as thermoregulation and the cardiovascular system plays an important and essential part. Temperature changes that may occur within the body are detected immediately by sensory receptors called thermoreceptors, which in turn communicate information about these changes to the hypothalamus in the brain.

When a substantial change in temperature is recorded, the hypothalamus reacts by initiating certain specific mechanisms in order to return the core temperature back to a safe temperature range. There are four place in the body where these adjustments in temperature can occur, they are: 1. Sweat glands: These glands are instructed to release sweat onto the surface of the skin when either the blood or skin temperature is detected to be well above a normal safe temperature. This allows heat to be lost through evaporation and cools down the skin so that blood that has been sent to the skin can be cooled down.

b. Smooth muscle around arterioles: Large increases in temperature will result in the smooth muscle in the walls of arterioles being triggered to relax, causing vasodilation. This then causes an increase in the volume of blood flow to the skin, allowing cooling to occur.

If however the thermoreceptors detect a cooling of the blood or skin then the hypothalamus reacts by sending a message to the smooth muscle of the arteriole walls causing the arterioles to vasoconstrict, this means reducing the blood flow to the skin and therefore helping to maintain the core body temperature. c. Skeletal muscle: When a drop in blood temperature is recorded the hypothalamus will also react by causing the skeletal muscles to start shivering. Shivering is caused by lots of very fast, small muscular contractions which then produce heat to help warm the blood d. Endocrine glands: The hypothalamus may trigger the release of hormones such as thyroxin, adrenalin and noradrenalin in response to the drops in blood temperature. These hormones all help to increase the body’s metabolic rate, which increases the production of heat.

2. Protection from infection and blood loss
Blood contains three types of cells, these are listed below and shown in the images.
1. Red blood cells
2. White blood cells
3. Platelets

Red blood cells: are solely responsible for transporting oxygen around the body to the important tissues and organs that require it. As oxygen enters the blood stream through the alveoli of the lungs, it binds to a necessary protein in the red blood cells called haemoglobin.

white blood cells: A white blood cells job in the body is to detect foreign bodies or infections and envelop and kill them. When they detect and kill an infection they create antibodies for that particular infection which allows the immune system to act more quickly and efficiently against foreign bodies or infections it has come into contact with previously.

Platelets: are cells which are responsible for clotting the blood, they stick to foreign particles or objects such as the edges of a cut. Platelets become connected with the help of fibrinogen, causing a clump to form which acts like a plug, blocking the hole in the broken blood vessel. On an external wound this would become a scab. If the body has a low level of platelets then blood clotting may not occur and bleeding can continue for long periods of time.

Excessive blood loss can be fatal – this is why people with a condition known as haemophilia need medication else even minor cuts can become fatal as the bleeding will continue without a scab being formed. Alternatively, if platelet levels are excessively high then clotting within blood vessels can occur, leading to a stroke and/or heart attack. This is why many people with a history of cardiac problems are often prescribed medication to keep their blood thin to minimise the risk of clotting within their blood vessels. This medication will be blood thinners such as warfarin.

4. Maintaining fluid balance within the body

The cardiovascular system works in connection with other body systems (nervous and endocrine) to maintain the balance of the body’s fluid levels. Fluid balance is essential in order to make sure that there is sufficient and efficient movement of electrolytes, nutrients and gases through the body’s cells. When the fluid levels in the body do not balance a state of dehydration or hyperhydration can occur, both of which effect normal body function and if left unchecked can become dangerous or even fatal.

Dehydration is the excessive loss of body fluid, usually accompanied by an excessive loss of electrolytes. The symptoms of dehydration include; headaches, cramps, dizziness, fainting and raised blood pressure, the blood becomes thicker as its volume decreases requiring more force to pump it around the body.

Hyperhydration on the other hand results from an excessive intake of water which pushes the normal balance of electrolytes outside of their safe limits. This can occur through long bouts of intensive exercise where electrolytes are not replenished and excessive amounts of water are consumed. This can lead to internal drowning. This can also result in the recently consumed fluid rushing into the body’s cells, causing tissues to swell. If this swelling occurs in the brain it can put excessive pressure on the brain stem that may result in seizures, brain damage, coma or even death. Dehydration or a substantial loss of body fluid results in an increase in the concentration of substances within the blood (blood tonicity) and a decrease in blood volume. Where as hyperhydration or a gain in body fluid (intake of water) usually results in a reduction of blood tonicity and an increase in blood volume.

Any change in blood tonicity and volume is detected by the kidneys and osmoreceptors in the hypothalamus. Osmoreceptors are specialist receptors that detect changes in the dilution of the blood. Basically they detect if we are hydrated (diluted blood) or dehydrated (less diluted blood). In response they release hormones which are transported by the cardiovascular system, through the blood, to act on main tissues such as the kidneys to increase or decrease urine production. Another way the cardiovascular system maintains fluid balance is by either dilating or constricting the blood vessels to increase or decrease the amount of fluid that can be lost through sweat.

Blood Vessels:

Arteries: Arteries are the main blood vessel in the body for carrying oxygenated blood. These vessels have thick walls to be able to withstand the high pressures of the oxygenated blood that they carry. Veins: Veins are the main vessel for carrying deoxygenated blood. These vessels have a large lumen and thinner walls as the blood they carry is not as high pressure. Veins can be categorized into four main types: pulmonary, systemic, superficial, and deep veins. Arterioles: A small branch of an artery that leads to a capillary.

The oxygenated hemoglobin (oxyhemoglobin) makes the blood in arterioles (and arteries) look bright red. Arterioles are smaller in diameter to arteries and are located further away from the heart where blood pressure is lower. Venules: Smaller branches of veins that lead to a capillary. These transport deoxygenated blood like veins but are smaller in size. Capillaries: Capillaries are extremely small vessels located within the tissues of the body that transport blood from the arteries to the veins. Fluid exchange between capillaries and body tissues takes place at capillary beds.

. The Respiratory System

Respiratory System: Oxygen Delivery System

The main function of the respiratory system is to supply the blood with oxygen so that the blood can deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen (O2) and exhale carbon dioxide (CO2). This exchange of gases is the respiratory system’s way of transporting oxygen to the blood. Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the system through the mouth and the nose and then passes through the larynx and the trachea, which is a tube that enters the chest. In the chest, the trachea splits into two slightly smaller tubes called the bronchi. Each bronchus is then divided again, forming the bronchioles.The end of the bronchioles are tiny sacs called alveoli. The average adult will have about 600 million of these spongy, air-filled sacs in their lungs. These sacs are surrounded by capillaries for efficient gas exchange.

This oxygen that has been inhaled passes into the alveoli and then diffuses through the cell walls of the alveoli into the capillaries and thus into the arterial blood. At the same time, the waste-rich blood from the veins releases carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale. The diaphragm’s job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs.

The respiratory system is divided into two main components:

Upper respiratory tract: Composed of the nose, the pharynx, and the larynx, the organs of the upper respiratory tract are located outside the chest cavity. Nasal cavity: Inside the nose, the sticky mucous membrane lining the nasal cavity traps dust particles, and tiny hairs called cilia help move them to the nose to be sneezed or blown out. Sinuses: These air-filled spaces along side the nose help make the skull lighter. Pharynx: Both food and air pass through the pharynx before reaching their appropriate destinations. The pharynx also plays a role in speech. Larynx: The larynx is essential to human speech.

Lower respiratory tract: Composed of the trachea, the lungs, and all segments of the bronchial tree (including the alveoli), the organs of the lower respiratory tract are located inside the chest cavity. Trachea: Located just below the larynx, the trachea is the main airway to the lungs. Lungs: Together the lungs form one of the body’s largest organs. They’re responsible for providing oxygen to capillaries and exhaling carbon dioxide. Bronchi: The bronchi branch from the trachea into each lung and create the network of intricate passages that supply the lungs with air. Diaphragm: The diaphragm is the main respiratory muscle that contracts and relaxes to allow air into the lungs.

Gas Exchange

Gas exchange is the diffusion of Oxygen from the alveoli into the blood flow and the waste Carbon Dioxide (CO2) that is situated in the blood flow passing back into the alveoli to be breathed out. Each tiny alveoli is covered in a network of capillaries which make this process easier.

•We breathe in air, containing 21% Oxygen

•The air reaches the alveoli. Here the Oxygen passes through the alveoli walls and into the surrounding capillaries

•The oxygen then enters the red blood cells where it combines with haemoglobin to form oxyhaemoglobin

•It will now travel around the body to where it is needed, such as our important organs and muscles

•At the same time, Carbon Dioxide, a waste product, is collected from the muscles and organs, into the blood stream

•When back at the lungs the CO2 diffuses out of the blood, into the alveoli to be breathed out

•The cycle continues as more Oxygen is received into the blood flow.

The body uses Oxygen and creates waste Carbon Dioxide because of the volumes of both gases in the air we breath in and out:

Air breathed in
Air breathed out
Carbon Dioxide

This table shows that we use some of the Oxygen we breathe in, as less is breathed out. This is because some oxygen is retained in the lungs as residual volume so that it can be used as an emergency store. It also shows that we produce CO2 as there is more in the air we breathe out.


Breathing in is known as inspiration
Breathing out is known as expiration
The intercostal muscles are positioned inbetween our ribs
The Diaphragm is a sheet of muscle which sits under the ribs and lungs Inspiration
To be able to draw air into our lungs, the volume of the chest, or thoracic cavity must increase. This happens because the Intercostal muscles and the diaphragm contract. The rib cage moves up and out and the diaphragm flattens to increase the space in the thoratic cavity. This decreases the air pressure within our lungs, causing air to rush in from outside.


At the end of a breath, the intercostal muscles and diaphragm will relax, returning to their starting position, which will decrease the size of the thoracic cavity. The decreased space and increased air pressure in the lungs forces air out Lung Capacity

Human lungs will hold varying amount of air, depending on how deeply and quickly we breathe. They are also never empty, even if you breathe out as far as you can. Different terms describe the different volumes of the lungs:

Tidal volume – The amount of air you breathe in or out with each breath Inspiratory capacity – The maximum amount you can breathe in (after a normal breath out) Expiratory reserve volume – After breathing our normally, this is the extra amount you can breathe out Vital capacity – The maximum amount of air you could possibly breathe in or out in one breath Residual volume – The amount of air left in your lungs after you have breathed out as much as possible The more exercise that we undergo, the more our need for Oxygen increases. This means that the amount we breathe in and pump around our bodies in the blood must change to keep up. To do this, we breathe faster and our heart pumps faster. This increased oxygen uptake, is measure by your VO2, or the amount of oxygen your body uses in a minute. This can be used as a prediction of your fitness level. The maximum VO2 is called VO2 Max and the fitter you are the higher this is because your body is more effective at taking in and using oxygen.

Control of Breathing (Neural and Chemical):

There are two ways in which the body controls the ability to breath, Neural and chemical control. These are explained below:

Neural Breathing
Neural breathing control contains two ways of controlling the breathing; voluntary breathing along with automatic breathing also. Mechanoreceptors send messages to the brain when they sense a different movement of joints they access movement and metabolic status.

Chemical Breathing

Chemical mechanisms are those of which detect how much oxygen and carbon dioxide is within the body, if there is too much gases the chemical reactions control this is order for our brain to tell us to breathe faster and quicker. If there is too much carbon dioxide and a shortage of oxygen then this is suited in order for our respiration to speed up.

The Heart:

ATRIUM- There are two atria in the heart. The right atrium receives deoxygenated blood from the vena cava and pumps it through the tricuspid valve into the right ventricle. The left atrium receives oxygenated blood from the pulmonary vein and pumps it through the bicuspid valve into the left ventricle. VENTRICLES- There are two ventricles in the heart. The right ventricle receives deoxygenated blood from the right atrium and pumps it through the pulmonary valve into the pulmonary artery and off to the lungs to be oxygenated. The left ventricle receives oxygenated blood from the left atria and pumps it through the aortic valve into the aorta and off to the body. The left ventricle is slightly thicker walled that the right ventricle as it is required to pump the blood further. AORTA- The aorta is the main artery of the body which feeds the major organs and muscles of the body with oxygenated blood from the left side of the heart. PULMONARY ARTERY- Another main artery of the body, the pulmonary artery transports deoxygenated blood from the right side of the heart to the lungs for it to be oxygenated.

This is the only artery in the body to carry deoxygenated blood. SUPERIOR & INFERIOR VENA CAVA- The superior and inferior vena cava are the two main veins of the body which bring deoxygenated blood from around the body back into the right side of the heart. PULMONARY VEIN- Another main vein of the body, the pulmonary vein transports oxygenated blood from the lungs back into the left side of the heart. This is the only vein in the body to carry oxygenated blood. CHORDAE TENDINAE- The chordae tendinae keep blood from flowing back into the atria after passing into the ventricles. SEPTUM- The septum separates the left and the right sides of the heart and contains the important SA node, used to make the heart beat. BICUSPID VALVE- The bicuspid valve, also known as the atrio-ventricular valve is situated in the left side of the heart between the left atrium and left ventricle. This valve opens when prompted to allow blood to be pumped from the atrium into the ventricle and closes after this process to stop the blood from flowing back on itself.

TRICUSPID VALVE- The Tricuspid valve, also known as the atrio-ventricular valve is situated in the right side of the heart between the right atrium and right ventricle. This valve opens when prompted to allow blood to be pumped from the atrium into the ventricle and closes after this process to stop the blood from flowing back on itself. PULMONARY VALVE- Also known as the semi-lunar valve. Situated between the right ventricle and the pulmonary artery this valve allows blood to be pumped into the artery whilst stopping it from flowing back on itself back into the right ventricle. AORTIC VALVE- Also known as the semi-lunar valve. Situated between the left ventricle and the aorta this valve allows blood to be pumped into the artery whilst stopping it from flowing back on itself back into the left ventricle.

The Lungs:

LARYNX- The larynx (voice box) is part of the respiratory system that holds the vocal cords. It is responsible for producing voice, helping us swallow and breathe. TRACHEA- The trachea (or windpipe) is a wide, hollow tube that connects the larynx (or voice box) to the bronchi of the lungs. It is an integral part of the body’s airway and has the vital function of providing air flow to and from the lungs for respiration. CARTILAGE RINGS- The function of the cartilaginous rings of the trachea is to stabilize the trachea and keep it rigid while allowing the trachea to expand and lengthen when the person breathes. If the trachea was not supported in this way, it would simply collapse because of the pressure of the chest. There are between 16 and 20 cartilaginous rings in an average trachea. The first and last tracheal rings are broader and deeper than the others.

The first ring is just beneath the larynx and the thyroid gland. The last one is just above where the trachea branches off into the bronchi, the two tubes that lead to the lungs. MAIN STEM BRONCHUS- either of the two main branches of the trachea, which contain cartilage within their walls BRINCHI- Smaller branches of the mainstem bronchi which lead to and carry air to the bronchioles. BRONCHIOLES- Smaller branches of the bronchi which lead air to the alveoli for diffusion. LOBES- Lobes are the flaps of tissue that make up each lung. Ach lung is made up of 3 lobes. PLEURA- A thin serous membrane that envelops each lung and folds back to make a lining for the chest cavity.

PLEURAL FLUID- The pleura produces a fluid that acts as a lubricant that helps you to breathe easily, allowing the lungs to move in and out smoothly. This is called pleural fluid. ALVEOLI- The alveoli are tiny air sacs within the lungs where the exchange of oxygen and carbon dioxide takes place. DIAPHRAGM- The diaphragm is the dome-shaped sheet of muscle and tendon that serves as the main muscle of respiration and plays a vital role in the breathing process. PLEURAL MEMBRANE- The pleural membranes enclose a fluid-filled space surrounding the lungs.

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