Blood and Lymphatic Vessels

Blood Vessels

Arteries: These are thick-walled, muscular vessels that carry blood away from the heart. They contain a layer of muscle and elastic fibres allowing them to withstand high pressure and stretch with each heartbeat.
Arterioles: Arteries divide into smaller vessels known as arterioles. They help regulate blood pressure by contracting or dilating.
Capillaries: The arterioles divide into tiny blood vessels called capillaries. Their walls are one cell thick, facilitating efficient exchange of substances between the blood and body tissues.
Venules: These are small, thin vessels that carry blood from capillaries towards veins.
Veins: These vessels carry blood back towards the heart. Their walls are less muscular and elastic than arteries. They contain valves to prevent backflow of blood.

Structure and Function of Blood Vessels

Arterial System: High-pressure system designed to deliver oxygenated blood (except in the pulmonary artery) to body tissues. Arteries lack valves as the high pressure prevents backflow.
Venous System: Low-pressure system responsible for returning deoxygenated blood (except in the pulmonary veins) to the heart. Veins have valves to prevent the backflow of blood.
Capillaries: Network of vessels that allows for exchange of substances (oxygen, nutrients, waste) with body tissues. Designed to maximise surface area, allowing efficient diffusion.

The Lymphatic System

Lymph vessels: These are a network of tiny, thin-walled vessels distributed throughout the body. They carry lymph, a colourless fluid containing white blood cells that protect against infection.
Lymph nodes: These are small, bean-shaped structures located along the lymphatic vessels. They filter the lymph and remove harmful substances.
Function of the Lymphatic System: Important for immune defence, it filters and removes harmful substances, and returns leaked plasma proteins and excess interstitial fluid back to the bloodstream.

Comparison between Blood and Lymphatic Vessels

Blood vessels transport blood throughout the body, delivering oxygen and nutrients to tissues, and removing waste products.
Lymphatic vessels, on the other hand, transport lymph, returning excess tissue fluid to the blood and defending the body against disease.

Roles of the Lymphatic System

It complements the cardiovascular system by returning excess fluid and proteins from tissues back to the bloodstream.
It serves as a pathway for the transport of fats from the digestive system to the bloodstream.
It plays a vital role in the body’s defence mechanisms, including the production and circulation of lymphocytes, a type of white blood cell.