Functions of the circulatory system

The circulatory system acts as the body's transport network. It relies on the heart to pump blood through a series of vessels.

Key components and their roles

• Heart - A muscular organ that acts as a pump, expanding to fill with blood and contracting to push it out through vessels.
• Blood vessels - These include arteries (which carry blood away from the heart), veins (which return blood to the heart), and capillaries.
• Blood types - Oxygenated blood and deoxygenated blood are circulated to meet the body's needs.

Double circulation and its circuits

Double circulation refers to the heart's system of pumping blood through two separate loops, allowing blood to pass through the heart twice in each complete cycle. It consists of two main circuits that work together.

Pulmonary circuit

This circuit handles the exchange of gases in the lungs. Blood is pumped from the heart to the lungs, then returns to the heart.

Systemic circuit

This circuit supplies the rest of the body with oxygenated blood. Blood is pumped from the heart to all body tissues, then returns to the heart.

Structure of the heart

The heart is divided into four chambers, which work together to pump blood efficiently.

Chambers of the heart

• Atria (singular: atrium) - The two upper chambers.
• Ventricles - The two lower chambers.

Additional structural features

• Septum - A thick muscular wall that divides the left and right sides of the heart, preventing oxygenated and deoxygenated blood from mixing.
• Valves - Flap-like structures located where blood enters and exits the heart; they open to allow forward flow and close to prevent backward movement.

The right side of the heart manages deoxygenated blood, while the left side handles oxygenated blood. A helpful acronym is LORD: Left Oxygenated, Right Deoxygenated.

Blood vessels connected to the heart

Several major blood vessels connect directly to the heart, facilitating the entry and exit of blood in the circulatory system.

Key blood vessels

• Vena cava - A large vein that brings deoxygenated blood from the upper and lower body back to the right atrium.
• Pulmonary artery - An artery that carries deoxygenated blood from the right ventricle to the lungs.
• Pulmonary veins - Veins that return oxygenated blood from the lungs to the left atrium.
• Aorta - The largest artery, which transports oxygenated blood from the left ventricle to all parts of the body.

Sequence of blood flow through the heart

Blood follows a specific path through the heart, involving coordinated contractions of the chambers. Both atria contract simultaneously, then both ventricles contract simultaneously. This pattern allows blood to pass through the heart twice per cycle, maintaining high pressure for efficient delivery.

Flow of deoxygenated blood

• Deoxygenated blood enters the right atrium via the vena cava.
• The right atrium contracts, forcing blood past a valve into the right ventricle.
• The right ventricle contracts, pushing blood through the pulmonary artery to the lungs.

Flow of oxygenated blood

• Oxygenated blood enters the left atrium via the pulmonary veins.
• The left atrium contracts, forcing blood past a valve into the left ventricle.
• The left ventricle contracts, pushing blood through the aorta to the body tissues.