Cardiovascular System: Structure and Function

Overview of the Cardiovascular System

Major Circuits of Blood Flow

The cardiovascular system consists of two main circuits that transport blood throughout the body: the pulmonary circuit and the systemic circuit.

• Pulmonary Circuit: Carries blood between the heart and lungs. Pulmonary arteries transport deoxygenated blood from the right ventricle to the lungs, while pulmonary veins return oxygenated blood to the left atrium.

• Systemic Circuit: Delivers oxygenated blood from the left ventricle to the rest of the body via systemic arteries, and returns deoxygenated blood to the right atrium through systemic veins.

Pulmonary Circuit	Systemic Circuit
Pulmonary arteries (deoxygenated blood)	Systemic arteries (oxygenated blood)
Pulmonary veins (oxygenated blood)	Systemic veins (deoxygenated blood)

Distribution of Capillaries

• Capillaries in lungs: Site of gas exchange between blood and air.

• Capillaries in head, neck, upper limbs: Supply tissues with oxygen and nutrients, remove waste.

• Capillaries in trunk and lower limbs: Serve the body's core and extremities.

Types of Blood Vessels

Classification and Function

Blood vessels are classified into three main types, each with distinct roles in circulation:

1. Arteries: Carry blood away from the heart. Typically transport oxygenated blood, except in the pulmonary circuit.

2. Veins: Carry blood to the heart. Usually transport deoxygenated blood, except for pulmonary veins.

3. Capillaries: Form networks between arteries and veins, facilitating exchange of materials.

Capillaries: Exchange Vessels

Capillaries are also known as exchange vessels because they allow the transfer of substances between blood and tissues.

• Materials exchanged: Dissolved gases (O2, CO2), nutrients (glucose, amino acids), and waste products (urea, carbon dioxide).

• Structure: Thin walls permit efficient diffusion.

Chambers of the Heart

Functional Anatomy

The heart contains four chambers, each with a specific role in the circulation of blood:

1. Right Atrium: Collects deoxygenated blood from the systemic circuit.

2. Right Ventricle: Pumps blood into the pulmonary circuit for oxygenation.

3. Left Atrium: Receives oxygenated blood from the pulmonary circuit.

4. Left Ventricle: Pumps oxygenated blood into the systemic circuit.

Anatomy of the Heart

External Features

The heart is a muscular organ with distinct anatomical landmarks:

• Base: Location of great veins and arteries.

• Apex: Pointed tip of the heart, directed downward and to the left.

• Pericardial Sac: A double-walled sac that surrounds and protects the heart.

• Mediastinum: The central compartment of the thoracic cavity, where the heart is situated between the two pleural cavities (lungs).

Key Terms

• Apex: The pointed end of the heart, important for orientation in anatomical studies.

• Mediastinum: The region in the thorax between the lungs, containing the heart, esophagus, trachea, and major blood vessels.

Summary Table: Heart Chambers and Circuits

Chamber	Receives Blood From	Pumps Blood To	Circuit
Right Atrium	Systemic veins	Right ventricle	Systemic
Right Ventricle	Right atrium	Pulmonary arteries	Pulmonary
Left Atrium	Pulmonary veins	Left ventricle	Pulmonary
Left Ventricle	Left atrium	Systemic arteries	Systemic

Additional info:

• The pulmonary circuit is responsible for gas exchange, while the systemic circuit delivers nutrients and removes waste from tissues throughout the body.

• Capillaries are the only blood vessels where exchange of gases, nutrients, and waste occurs due to their thin walls and extensive surface area.