The respiratory system refers to the set of organs that allows a person to breath (air in and out).

This includes the nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and alveoli.

These organs combine to allow for the exchange of oxygen and carbon-dioxide between the air in a person’s lungs and their blood. It is this exchange that allows not only for movement to occur at various intensities, but also to sustain life.

The respiratory system is connected with the circulatory system and should be considered together. Together they are often called the cardiorespiratory or cardiovascular system. This is because both systems on their own are insufficient to understand movement and in the maintenance of life.

The structure of the respiratory system greatly enhances its ability to achieve its function. 

The function of the system is to enable the transfer of oxygen into the blood and the removal of carbon-dioxide out of the blood.

The respiratory system consists of the following organs: nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and alveoli. These organs combine to allow gas exchange to occur between the lungs and the circulatory system.

The nasal cavity is where air travels through and is warmed, while the small hairs in the cavity remove any small particles, such as dust or bugs.

The pharynx is where the nasal cavity and the oral cavity combine and allows for the movement of both air, food and liquid (the epiglottis is used to close off the airway when swallowing).

The larynx, also known as the voice box, is used to make sound and to talk.

The trachea is the main air pipe that brings air down to the lungs. The trachea then spits into two main bronchi or bronchus, which continue to branch down to bronchioles. These bronchioles then bring the air to the alveoli which have a very large porous surface (it has pores or holes in it for the exchange of gas), which are lined with fluid. Each alveoli is surrounded by a mesh of capillaries to allow for gas exchange into the circulatory system.

Function of the respiratory system

The function of the respiratory system is to allow us to breath and promote gas exchange with the circulatory system. This is achieved by having a large surface area to value ratio caused by the alveoli. 

This large surface area allows for a large area where gas can be exchanged. During gas exchange oxygen is transferred to the circulatory system, while carbon-dioxide is removed.

The respiratory system will increase the depth of breath in response to physical activity. This increases the number of alveoli being used for gas exchange and therefore, increases the amount of oxygen transferred to the blood and carbon-dioxide removed.

The respiratory system will also increase the breathing rate allowing for a faster change of gas inside the lungs, which increases the amount of gas exchange per minute allowing for higher delivery of oxygen to the working muscle. This improves movement efficiency of the muscles.

Lung function is to enable respiration, which is the transfer of cases between the blood and the lungs.

In order to achieve this the lungs must use inspiration and expiration. For inspiration (inhale) to occur, many muscles are contracted, such as the diaphragm, intercostals and pectorals causing a decrease in air pressure within the lungs. This then forces air from the atmosphere to move into the lungs to balance the pressure. As the air comes into the body it is warmed by the blood vessels close to the surface in the respiratory system and moistened by the mucus lining the walls. This helps to increase gas exchange and makes breathing more comfortable.

Another aspect of lung function is expiration (exhale). Expiration requires that the body increases the pressure in the lungs in order to push air out of the lungs, although complete emptying of the lungs does not happen as this would cause a suction to occur, which would make it difficult to inspire again. The trachea, bronchi and bronchioles are also kept open by cartilage to ensure the airway does not close, but remains open to make breathing easier. Expiration is achieved through the elastic properties of the lungs and thoracic cage, as well as contraction of the intercostal muscles. This increases the air pressure in the lungs pushing the air out into the atmosphere.

During exercise or physical activity, the lung function is to increase the respiratory rate in order to increase the volume of air moving in and out of the lungs per minute. The volume of air inspired and expired also increases in response to physical activity in order to increase the oxygen absorbed through the alveoli and carbon-dioxide expelled from the body.

The respiratory system is set up in order to promote the exchange of gases between the air and blood. This exchange of gases between the blood and lungs is called respiration. The external exchange of gases occurs between the alveoli and the capillaries that encase them. Deoxygenated (no oxygen) blood travels in the capillaries to the alveoli, where carbon-dioxide diffuses out of the blood and into the alveoli. At the same time, oxygen that has been brought into the alveoli through inspiration diffuses across the alveoli membrane and into the capillaries. This is external respiration. This results in oxygenated blood being taken away from the lungs, back to the heart where it gets pumped around the body for use, while the carbon-dioxide is expelled into the atmosphere. 

The internal exchange of gases occurs between the capillaries that encase cells, for us particularly muscle cells and the cell itself. Here the oxygenated blood is brought to the muscle, where oxygen is taken out of the blood and transferred to the muscle tissue, while at the same time carbon-dioxide is taken out of the muscle cell and brought into the blood. Oxygen is transported through the blood attached to haemoglobin and travels in the muscle attached to myoglobin. The exchange of gases across the membranes of the capillary and the muscle is referred to as diffusion and is known as internal respiration. The carbon-dioxide is then taken to the lungs via the heart in order to remove the carbon-dioxide and receive oxygen again (external respiration). 

The circulatory system is seen to comprise two separate systems the cardiovascular system and the lymphatic system. Usually, people only think of the circulatory system as the cardiovascular system, which includes: the heart, arteries, veins and capillaries, however, this is incorrect. The cardiovascular system is responsible for the movement of blood around the body. Blood carries energy, hormones, nutrients, heat, gases and much more through the body and has a large influence on movement efficiency and performance. This is because of its connection to the respiratory system and the exchange of gases in the body. 

The lymphatic system is responsible for the movement of lymph (collection of interstitial fluid) back to the cardiovascular system via the lymph, nodes, organs and ducts. The main function of the lymph system is the cleaning of lymph by the immune system.

The components of blood can be broken up into two sections plasma and cells.

Blood makes up 7% of the human body at around 5 litres in the average human being.

The components of blood include erythrocytes, leukocytes, thrombocytes and plasma.

Erythrocytes 

Erythrocytes are the first of the components of blood and account for 45% of blood volume. They are better known as red blood cells and contain haemoglobin, the molecule responsible for binding with oxygen and transporting it around the body. This is particularly important for aerobic activity, where oxygen is needed in order to sustain performance. Erythrocytes do not have a nucleus or organelles, but do contain the protein that gives an individual their blood type.

Leukocytes

Leukocytes are the second of the components of blood and account for less than 0.7% of blood volume. They are better known as white blood cells and are part of the body's immune system. Leukocytes destroy and remove unwanted cells, because they are old, broken or foreign (infections such as bacteria or virus).

Thrombocytes

Thrombocytes are another component of blood and also account for less than 0.7% of blood volume. They are better known as platelets and are responsible for the clotting of blood to stop bleeding.

Plasma

Plasma is the last of the components of blood and accounts for 54.3% of blood volume. Plasma is 92% water and 8% protein giving it a yellow colour. Plasma is responsible for the transport and delivery of nutrients such as glucose, amino acids, fatty acids, electrolytes (dissolved minerals) and vitamins. This is particularly important for movement as the delivery of extra glucose to the muscle allows for higher intensities to be produced. Plasma is also responsible for the removal of waste products such as carbon dioxide, lactic acid and urea. Carbon dioxide removal is particularly important for aerobic performances, while lactic acid removal is important for anaerobic performance.

The structure and function of the heart, arteries, veins and capillaries is vital for the circulatory system to work. The overall function of the circulatory system is to transport blood and lymph around the body. In doing so it delivers oxygen and nutrients to the body, removes waste products from the body, is involved in the regulation of body temperature and helps to fight against infection. 

The main function of the heart is to pump blood around the body. It does this through regular and rhythmical contractions of its muscular walls, particularly the muscles around the left and right ventricles. The right ventricle is responsible for pumping blood through the pulmonary circulation (to the lungs) using the pulmonary artery. On the other side, the left ventricle is responsible for pumping blood around the systemic circulation (to the body) via the aorta. Above each ventricle is an atrium, which fills with blood ready to transfer into the ventricles. The right atrium fills with deoxygenated blood from the vena cava, returning from the body, while the left atrium fills with oxygenated blood from the pulmonary vein bringing blood back from the lungs. Between the various structures there are four main valves, which ensure blood only flows in the direction it is meant to. These are the mitral valve, the aortic valve, the pulmonary valve and the tricuspid valve.

Structure and function of arteries

Arteries provide the tubing to take blood away from the heart (regardless of oxygenation) and also help the heart to pump the blood. Therefore, arteries require elastic walls to cope with the pressure caused when the ventricles contract and muscle to provide a further contraction to help move the blood. The muscles also help dilate (open) the artery to increase blood flow. Arteries have high pressure and fast blood flow.

Structure and function of veins

In direct contrast to arteries, veins provide the tubing to take blood back to the heart. Veins have a thinner wall because they do not have to deal with constant changes in blood pressure with heart contractions and the blood moves more slowly through them. They contain valves, which help to prevent blood flowing in the wrong direction. This is needed especially in veins that are bringing blood up-wards against gravity. Veins are often blue in colour and sit closer to the skin than arteries, making them visible to the naked eye.

Capillaries exist between arteries and veins and allow for nutrient and waste exchange between tissue and the blood. Therefore, capillaries are very thin and have permeable membranes to allow for the movement of nutrients, waste products and gases. There are three different types of capillaries continuous, fenestrated and sinusoid.

Myocytes (muscle cells) have a large density of continuous capillaries around them to allow for this exchange to occur. Type 1 (slow twitch or aerobic) myocytes have more capillaries than type 2 (fast twitch or anaerobic) myocytes.

Pulmonary and systemic circulation

The cardiovascular division of the circulatory system is further broken into two, the pulmonary and systemic circulation. The pulmonary and systemic circulation make up the two major branches of the cardiovascular system and are connected to either side of the heart. 

The Pulmonary Circulation

Pulmonary circulation begins at the right side of the heart as the right ventricle pumps blood into the pulmonary artery. The pulmonary artery then carries the deoxygenated blood to the lungs, where it spreads out into the capillaries that surround the alveoli of the lungs. The blood is then oxygenated, while at the same time carbon-dioxide is removed into the lungs and the blood then travels back to the heart through the pulmonary artery, which empties into the left atrium.

Systemic circulation is connected to the left side of the heart and carries blood to the rest of the body in order to deliver oxygenated blood (along with all the other nutrients). This blood travels out of the left ventricle through the aorta, which breaks into various arteries and then down to capillaries. The capillaries then deliver the oxygenated blood and other nutrients to the cells of the body, including myocytes (muscle cells) and remove carbon-dioxide. The blood then continues to travel through the veins and back to the right atrium via the vena cava (the largest vein).

Blood Pressure 

Blood pressure is used as a measure of health and fitness and measures the pressure exerted by the blood onto the artery walls. This measure is taken using a sphygmomanometer together with a stethoscope or an electronic blood pressure monitor. Blood pressure is measured in mmHg and consists of two numbers systolic pressure and diastolic pressure. Systolic is the blood pressure in the arteries during a contraction of the heart, while diastolic is the blood pressure during the relaxation and filling of the heart. Optimum blood pressure is under 120/80 mmHg, and between this and 139/89 mmHg is considered normal. Any higher than this is high blood pressure. Hypertension is a disease when a person has consistently high blood pressure. Hypertension can cause damage to the blood vessels, heart, brain and other important organs.

Blood pressure during exercise

Blood pressure changes during exercise, since during exercise a person’s ventricles contract more forcefully. This causes an increase in systolic pressure during exercise, which continues to increase according to the intensity of the workload. Diastolic pressure decreases because arterial walls dilate (relax) to allow greater flow of blood.

The cardiovascular system's efficiency is crucial for overall health and performance. Several factors can significantly impact its function. To recall these, you might like to use the acronym H.A.H.A.H.

Health behaviours (Physical activity, diet, stress, smoking)

Regular exercise: Improves heart health, strengthens the heart muscle and increases blood vessel efficiency.

Sedentary lifestyle: Can lead to decreased cardiovascular fitness, increased risk of heart disease and reduced blood flow.

Exercise intensity and duration: The type, intensity and duration of physical activity can influence cardiovascular benefits.

Healthy diet: A diet rich in fruits, vegetables, whole grains, lean proteins and healthy fats can support heart health.

Unhealthy diet: A diet high in saturated and trans fats, sodium and processed foods can increase the risk of cardiovascular disease.

Specific nutrients: Nutrients like omega-3 fatty acids, antioxidants and fibre can have beneficial effects on cardiovascular health.

Chronic stress: Can lead to increased blood pressure, heart rate and the risk of cardiovascular disease.

Stress management techniques: Relaxation techniques like meditation, yoga or deep breathing can help manage stress and improve cardiovascular health.

Tobacco smoke: Damages blood vessels, increases blood pressure, and raises the risk of heart disease, stroke and lung cancer.

Quitting vaping and/or smoking: Can significantly improve cardiovascular health over time.

Age

Ageing: The risk of cardiovascular disease increases with age.

Lifestyle factors: Maintaining a healthy lifestyle can help reduce the effects of ageing on cardiovascular health.

Health conditions such as vascular disease

Atherosclerosis: The build-up of plaque in the arteries can narrow blood vessels and restrict blood flow.

Other vascular diseases: Conditions like peripheral artery disease and varicose veins can affect blood circulation and cardiovascular health.

Family history: A family history of cardiovascular disease can increase an individual's risk.

Genetic factors: Certain genetic factors can predispose individuals to heart problems.

Certain medications: Some medications can affect blood pressure, heart rate or blood clotting, impacting cardiovascular health.

Proper use: It's essential to use medications as prescribed and consult with a healthcare professional.

Altitude

High altitude: Living or training at high altitudes can increase the body's demand for oxygen leading  to adaptations in the cardiovascular system.

Acclimatisation: The body can adapt to high altitude by increasing red blood cell production and improving blood flow to the tissues.

Haemoglobin Levels

Haemoglobin: A protein in red blood cells that carries oxygen.

Low haemoglobin levels: Can lead to anaemia and reduced oxygen delivery to tissues, affecting cardiovascular function.

High haemoglobin levels: While beneficial for athletes in high-altitude environments, excessively high levels can increase the risk of blood clotting.

Sources:

American Heart Association. (2023). Heart Disease Facts. 

https://www.heart.org/en/about-us/heart-and-stroke-association-statistics1.professional.heart.orgprofessional.heart.org

Centers for Disease Control and Prevention (CDC). (2023). Heart Disease.

https://www.cdc.gov/heart-disease/about/index.html

World Health Organization (WHO). (2023). Cardiovascular Diseases.

https://www.who.int/health-topics/cardiovascular-diseases