Understanding the Cardiovascular System

• Also known as the Circulatory System
• Composed of the heart, blood vessels, and blood
• Transports essential substances to cells and removes waste products
• Facilitates the movement of materials throughout the body via the blood
• Transports cells responsible for fighting disease-causing microorganisms

Blood Vessels

• Reach the entire body
• Arteries are represented in red and carry oxygen-rich blood
• Veins are represented in blue and carry oxygen-poor blood

Heart

• Described as a hollow, muscular organ
• Responsible for pumping blood throughout the body
• It is about the size of one's fist
• Located in the center of the chest

Heart Structure

• The heart is divided into two sides, right and left, separated by a wall of tissue
• Each side contains two chambers: an upper chamber (atrium) and a lower chamber (ventricle)

Atrium

• The atria are separated from the ventricles by valves
• Valves are flaps of tissue that prevent the backflow of blood
• The atria receive blood as it enters the heart

Ventricles

• Situated in the lower portion of the heart
• Responsible for pumping blood out of the heart

Heart Function

• Consists of two main phases
• The heart muscles relax, allowing the atria to fill with blood
• The atria contract, filling the ventricles, which in turn contract to pump blood forward
• This pumping action produces the sound of a heartbeat
• The entire process occurs in less than one second

Valve Function

• The valve is a flap of tissue
• Prevents the backflow of blood

Pacemaker

• A group of cells situated in the right atrium
• Continuously receives signals regarding the body's oxygen requirements
• Adjusts the heart rate to meet those needs

Two Loops

• The body's blood vessels consist of arteries, capillaries, and veins
• Arteries -- carry blood away from the heart
• Capillaries -- facilitate the exchange of substances between blood and body cells
• Veins -- carry blood back to the heart

Two Loops (cont.)

• Blood circulates through the body in a figure-eight pattern
• The heart is at the center, where the two loops intersect

Loop One

• Blood travels from the heart to the lungs and then back to the heart
• Blood entering the right atrium from the body is oxygen-poor, with low oxygen and high carbon dioxide levels
• Oxygen-poor blood appears dark red (often depicted as blue in diagrams)
• Blood flows from the right atrium to the right ventricle, then through arteries to the lungs
• In capillaries near the lungs, blood picks up oxygen, becoming oxygen-rich, and releases carbon dioxide
• The now bright red, oxygen-rich blood flows to the left side of the heart to be pumped through loop two

Loop Two

• Blood flows to the body and back to the heart
• The left atrium fills with oxygen-rich blood from the lungs
• Blood flows from the left atrium to the left ventricle, then into the aorta, the body's largest artery
• From the aorta, blood flows into branching arteries and tiny capillaries in different parts of the body
• Oxygen moves out of the blood and into the body cells, while carbon dioxide passes from the body cells into the blood
• Blood flows back to the right atrium through veins