1. Objectives 33.1 The Circulatory System
-Identify the functions of the human circulatory system.
-Describe the structure of the heart and how it pumps blood through the body.
-Name three types of blood vessels in the circulatory system.

2. Vocabulary Word Definition Myocardium
Thick middle muscle layer of the heart
Atrium
Upper chamber of the heart that receives blood from the rest of the body
Ventricle
Lower chamber of the heart that pumps blood out of the heart to the rest of the body
Valve
Flap of connective tissue located between an atrium and a ventricle, or in a vein, that prevents backflow of blood
Pulmonary circulation
Path of circulation between the heart and lungs
Systemic circulation
Path of circulation between the heart and the rest of the body
Pacemaker
Small group of cardiac muscle fibers that maintains the heart's pumping rhythm by setting the rate at which the heart contracts; the sinoatrial (SA) node
Artery
Large blood vessel that carries blood away from the heart to the tissues of the body
Capillary
Smallest blood vessel, brings nutrients and oxygen to the tissues and absorbs carbon dioxide and waste products

3. What does the Circulatory System do?
The circulatory system transports oxygen, nutrients and other substances throughout the body, and removes wastes from tissues.

4. Heart Structure
Your heart is composed almost entirely of a muscle layer called myocardium. The heart begins beating 18 days after conception and stops only when you die.
An adult’s heart beats an average 72x a minute, pumping about 70 milliliters (about 2.5 cups) of blood with each contraction.

5. Heart Structure The heart is divided into four chambers.
Two upper chambers called atria (singular: atrium);
Two lower chambers called ventricles.
A wall called the septum separates the right side of the heart from the left side.

6. Blood Flow Through the Heart
Flaps of tissue called valves are located between the atria and the ventricles; as well as, at the exits of each ventricle.
Valves prevent the back flow of blood.

7. The Heart’s Blood Supply
The heart muscle needs a constant supply of oxygen and nutrients.
A pair of blood vessels called coronary arteries supply blood to the heart muscle.

8. Circulation The heart functions as two pumps.
1. The right side of the heart pumps blood to the lungs; pulmonary circulation.
The left side pumps blood to the rest of the body; systemic circulation.

9. The “Pacemaker”
Each contraction begins in a small group of muscle fibers called the SA node, located in the right atrium.
The SA node “sets the pace” for the heart, so it is referred to as the pacemaker.

10. Blood Vessels
Blood flows through three types of vessels — arteries, capillaries, and veins.

11. Arteries
Arteries are large vessels that carry blood away from the heart to the rest of the body.
Arteries have thick elastic walls that help them withstand the powerful pressure produced when the heart contracts.

12. Capillaries
The smallest blood vessels are the capillaries. Most capillaries are so narrow that blood cells pass through them in single file.
The extremely thin walls allow O2, nutrients , CO2 and waste to diffuse across their walls.

13. Veins
After blood passes through the capillaries, it returns to the heart through veins.
Veins also contain valves that close to ensure blood does not flow backward.

14. Blood Pressure
Blood pressure is measured with the following two numbers:
1. Systolic pressure — the force in the arteries when the ventricles contract.
2. Diastolic pressure — the force in the arteries when the ventricles relax.
* A typical blood pressure reading for a healthy teen or adult is below 120/80.