Cardiovascular System: Structure and Function

Organisation of the Cardiovascular System

Overview of Circulatory Pathways

The cardiovascular system is responsible for the transport of blood, nutrients, gases, and waste products throughout the body. It consists of two main circulatory loops and a central pump, the heart.

• Pulmonary Circulation: This pathway carries deoxygenated blood from the right side of the heart to the lungs for oxygenation, and returns oxygenated blood to the left side of the heart.

• Systemic Circulation: This pathway distributes oxygenated blood from the left side of the heart to all body tissues and returns deoxygenated blood to the right side of the heart.

• Heart (Pump): The heart is a muscular organ that maintains blood flow through rhythmic contractions.

Key Terms

• Arteries: Vessels that carry blood away from the heart.

• Veins: Vessels that carry blood toward the heart.

• Capillaries: Microscopic vessels where exchange of gases, nutrients, and waste occurs.

Diagram Description

The provided diagram illustrates the flow of blood through the pulmonary and systemic circuits, highlighting the heart's central role.

Blood Vessels

Classification and Structure

Blood vessels are classified based on their function and structure. They form a continuous network for blood transport.

• Arteries: Thick-walled vessels that transport blood from the heart under high pressure.

• Arterioles: Small branches of arteries that regulate blood flow into capillary beds.

• Capillaries: The smallest blood vessels, facilitating exchange between blood and tissues.

• Postcapillary Venules: Small veins that collect blood from capillaries.

• Veins: Vessels with thinner walls that return blood to the heart under lower pressure.

Microcirculation

• The term microcirculation refers to the network of arterioles, capillaries, and postcapillary venules where exchange processes occur.

Portal Systems

A portal system is a unique vascular arrangement in which blood passes through two consecutive capillary beds before returning to the heart.

• Venous Portal Systems: Found in the liver (via the portal vein) and pituitary gland.

• Arterial Portal System: Found in the kidney.

Table: Types of Portal Systems

Type	Location	Function
Venous Portal System	Liver, Pituitary Gland	Allows processing of substances before entering systemic circulation
Arterial Portal System	Kidney	Facilitates filtration and reabsorption

Additional info:

• The cardiovascular system is essential for maintaining homeostasis, delivering oxygen and nutrients, and removing metabolic waste.

• Portal systems are critical for specialized functions such as hormone regulation (pituitary) and detoxification (liver).