1.6 - The Heart & Cardiovascular System
Functions of the cardiovascular system
The cardiovascular system's primary function is to move blood around the body. It plays a vital role in supporting physical activity by ensuring the body receives what it needs to function effectively.
Key functions
- Transport of substances - The system carries oxygen from the lungs to muscles, delivers nutrients such as glucose for energy release, and removes waste products like carbon dioxide back to the lungs.
- Temperature control - During prolonged exercise, the system redirects more blood towards the skin's surface. This allows heat to escape, helping to cool the body and prevent overheating.
Components of the cardiovascular system
The cardiovascular system is made up of interconnected parts that work as a team to circulate blood effectively.
Main components
- Heart - A muscular organ that acts as a pump, pushing blood around the body through rhythmic contractions.
- Blood - A fluid that carries gases, nutrients, and waste products, serving as the transport medium within the system.
- Blood vessels - A network of tubes that form pathways for blood to travel, connecting the heart to all parts of the body.
The double-circulatory system
The cardiovascular system operates as a double-circulatory system, which means blood travels through two separate loops or circuits before completing a full cycle.
The two circuits
- Pulmonary circuit - This loop connects the heart to the lungs. Deoxygenated blood travels from the heart to the lungs to release carbon dioxide and collect oxygen.
- Systemic circuit - This loop connects the heart to the rest of the body. Oxygenated blood is pumped from the heart to tissues and organs, delivering oxygen and nutrients while collecting waste products.
Blood flow through the heart
Blood follows a specific path through the heart, passing through chambers and valves to ensure one-way movement.
Path of deoxygenated blood
- Deoxygenated blood returns from the body and enters the right atrium through the vena cava.
- It passes through the tricuspid valve into the right ventricle.
- The right ventricle contracts, pushing blood through the pulmonary valve into the pulmonary artery.
- The pulmonary artery carries blood to the lungs to be oxygenated.
Path of oxygenated blood
- Oxygenated blood returns from the lungs and enters the left atrium through the pulmonary veins.
- It passes through the bicuspid valve into the left ventricle.
- The left ventricle contracts, pushing blood through the aortic valve into the aorta.
- The aorta carries oxygenated blood to the rest of the body, including muscles. After oxygen is used, blood becomes deoxygenated and returns via the right atrium through the vena cava.
Types and functions of blood vessels
Blood vessels are tubes that carry blood throughout the body. They all have a hollow centre called the lumen, which allows blood to pass through smoothly.
Arteries
Arteries carry blood away from the heart and carry oxygenated blood (except for the pulmonary artery). Arteries have thick, muscular walls to withstand and maintain high pressure.
Veins
Veins carry blood towards the heart and typically at low pressure. They transport deoxygenated blood (except for the pulmonary veins) and have valves to prevent blood from flowing backwards. Veins have thinner walls with less muscle than arteries.
Capillaries
Capillaries form a network that connects arteries and veins, allowing exchange of gases and nutrients at tissue level. They have very thin walls so substances like oxygen and carbon dioxide can diffuse easily. Capillaries are narrow with a large surface area, and blood flows slowly through them, giving more time for efficient exchange.
Heart rate, stroke volume, and cardiac output
During physical activity, the heart adjusts its performance to meet higher oxygen needs. Several measurements help track these changes, providing insight into cardiovascular efficiency.
Key measurements
- Heart rate - The number of times the heart beats per minute, often measured in beats per minute (bpm). A typical adult resting heart rate is 60-80 bpm.
- Stroke volume - The amount of blood pumped out by each ventricle with every contraction.
- Cardiac output - The total volume of blood pumped by a ventricle per minute.
Formula for cardiac output
Where:
- Q = Cardiac output (in litres per minute)
- Heart rate = Beats per minute (bpm)
- Stroke volume = Volume of blood per beat (in litres)
The role of blood in transport during physical activity
Blood is essential for transporting substances that support energy production and waste removal, making it critical for performance in sports. Its components are specialised for these tasks.
Key components and functions
- Red blood cells - These cells are the most vital for physical activity as they carry oxygen from the lungs to muscles and transport carbon dioxide back to the lungs for exhalation.
- Haemoglobin - A protein found in red blood cells that binds to oxygen and carbon dioxide, storing and releasing them as needed.