Circulatory System Overview

Circulation Overview

• The circulatory system involves the heart, blood vessels, and blood.
• Its function includes supplying nutrients, removing waste, regulating body temperature, and aiding the immune system.

Closed Circulatory System

• Humans have a closed circulatory system, where blood is confined to vessels.
• This differs from an open system, where blood mixes with interstitial fluid.

Functions of Circulation

• Delivering nutrients to tissues.
• Removing waste products of metabolism.
• Controlling blood flow to regulate heat loss.
• Supporting the body's defense mechanisms by delivering antibodies, platelets, and leukocytes to affected areas.

Blood Distribution

• Most blood (64%) is in systemic veins and venules, acting as a reservoir.
• Venoconstriction reduces blood volume in these vessels.
• A smaller portion (9%) of blood is in pulmonary vessels.
• About 7% of blood is in the heart.

Systemic and Pulmonary Circulation

• Pulmonary circulation: The blood flow between the heart and lungs.
  • Low-pressure system.
• Systemic circulation: The blood flow between the heart and the rest of the body.

Blood Vessel Types

• Arteries: Responsible for carrying oxygenated blood away from the heart.
  • Elastic arteries (conducting): Large arteries that act as pressure reservoirs.
  • Muscular arteries (distributing): Medium-sized arteries that regulate blood flow.
• Arterioles: Small arteries that regulate blood flow into capillaries.
• Thick muscle coat, less elastic fiber.
• Capillaries: Microscopic vessels where gas and nutrient exchange occurs.
  • Thin walls for efficient exchange.
• Only 25% patent at rest.
  • Continuous, fenestrated, or sinusoidal types.
• Venules: Small veins that collect blood from capillaries.
• Veins: Return deoxygenated blood to the heart.
• Large lumen, thin walls, no elastic layers, and valves.
• Capacitance vessels: Veins that accommodate large volumes of blood without substantial pressure change.
• Valves in veins prevent backflow of blood.

Blood Vessel Structure

• Tunica intima: Innermost layer of a blood vessel.
• Tunica media: Middle layer of a blood vessel, composed of smooth muscles.
• Tunica externa: Outermost layer of a blood vessel, composed of connective tissue.

Physiological Classification of Blood Vessels

• Windkessel vessels: Aorta and large arteries that act as pressure reservoirs.
• Resistance vessels: Arterioles, metarterioles, and precapillary sphincters regulate blood flow.
• Exchange vessels: Capillaries support gas and nutrient exchange.
• Capacitance vessels: Veins that accommodate blood volume.

Special Features of Veins

• Valves: Prevent backflow.
• Muscular contractions: Aid blood returning to the heart.
• Sympathetic tone: Influences blood vessel diameter.

Varicose Veins

• A condition where veins become enlarged and twisted, causing symptoms like aching and edema, and an unsightly appearance.

Shunt Vessels (Anastomoses)

• Arteriovenous anastomoses: Bypass capillaries, connect metarterioles to venules.
• Regulate blood flow in skin, lips, and other locations. Important in temperature regulation.

End Arteries

• Arteries that provide blood supply with no alternate route (lack of anastomoses).
• Examples: Central retinal artery, splenic artery, renal artery, and metaphyses of long bones.

Explore the intricacies of the circulatory system, including its components such as the heart, blood vessels, and blood. Understand how this closed system functions to supply nutrients, remove waste, and support immunity. Dive into the roles of systemic and pulmonary circulation and blood distribution.