Circulatory System

Circulatory System

Middle School

​

Learning Objectives

• Describe the main function and components of the circulatory system.

• Explain the structure of the heart and the path of blood circulation.

• Differentiate between the structure and function of arteries, veins, and capillaries.

• Identify the components of blood and describe their important functions.

• Recognize common cardiovascular diseases and ways to maintain a healthy heart.

Key Vocabulary

​

Artery

A type of blood vessel that carries blood away from the heart to the lungs or body.

​

Vein

A type of blood vessel that brings blood toward the heart from the lungs or the body.

​

The smallest blood vessel, connecting small arteries and veins found throughout the body.

​

Blood Pressure

The force that is exerted by circulating blood on the walls of the blood vessels.

​

Pulmonary Circulation

The part of the circulatory system carrying deoxygenated blood between the heart and the lungs.

​

Systemic Circulation

The part of the circulatory system carrying oxygenated blood between the heart and the body.

Capillary

​

​

The Heart

• The heart is a muscular, fist-sized organ that pumps blood throughout the body.

• It has four chambers: two upper atria and two lower ventricles.

• Valves ensure one-way blood flow; their closing creates the heartbeat sound.

• The pacemaker, in the right atrium, sends electrical signals to regulate the heartbeat.

​

Multiple Choice

What is the main function of the valves in the heart?

• To pump blood out of the heart.

• To prevent blood from flowing backward.

• To separate the atria from the ventricles.

• To generate the electrical signals for the heartbeat.

The Three Major Types of Blood Vessels

​

Arteries

• ​Carry blood away from the heart to the body.

• ​​Have thick, muscular walls to handle high blood pressure.

• ​Transport blood that is typically rich in oxygen.

​

Veins

• ​Carry blood from the body back toward the heart.

• ​​Their walls are thinner and less muscular than arteries.

• ​Transport blood that is typically low in oxygen.

​

Capillaries

• ​Are the smallest and most numerous blood vessels.

• ​​Connect arteries and veins, forming vast networks.

• ​Allow exchange of oxygen, nutrients, and waste products.

​

Multiple Choice

What is the key difference between arteries and veins?

• Arteries carry oxygenated blood, while veins carry deoxygenated blood.

• Arteries carry blood away from the heart, while veins carry blood toward the heart.

• Arteries are smaller than veins.

• Arteries have valves, while veins do not.

​

​

Components of Blood

• Plasma is the golden-yellow fluid part of blood that carries other blood cells.

• Red blood cells contain hemoglobin, a protein that carries oxygen throughout the body.

• White blood cells are part of the immune system and fight against pathogens.

• Platelets are small cell fragments that help your blood to clot after an injury.

​

Multiple Choice

Which component of blood is responsible for transporting oxygen?

• Plasma

• Red Blood Cells

• White Blood Cells

• Platelets

​

​

Path of Blood Flow

Pulmonary Circuit

• Carries oxygen-poor blood from the heart to the lungs to pick up oxygen.

• Blood flows from the right atrium to the right ventricle and then to the lungs.

• In the lungs, blood drops off carbon dioxide and collects a fresh supply of oxygen.

Systemic Circuit

• Carries oxygen-rich blood from the heart to all other parts of the body.

• Blood flows from the left atrium to the left ventricle and out through the aorta.

• After delivering oxygen, the blood returns to the heart to start the cycle again.

Multiple Choice

What is the main purpose of the pulmonary circuit?

• To pump oxygen-rich blood to the entire body.

• To filter waste products from the blood.

• To carry blood to the lungs to pick up oxygen.

• To deliver nutrients to the heart muscle.

​

​

Cardiovascular Health

• Cardiovascular disease (CVD) affects the heart and blood vessels.

• Atherosclerosis is when plaque builds up in arteries, reducing blood flow.

• Hypertension, or high blood pressure, puts extra force on artery walls.

• Regular exercise and a healthy diet help keep your heart strong.

​

Multiple Choice

What is atherosclerosis?

• A term for high blood pressure.

• The buildup of plaque in the arteries.

• A genetic heart condition.

• A disease of the heart valves.

​

Common Misconceptions

Misconception	Correction
Arteries carry oxygen-rich blood, and veins carry oxygen-poor blood.	Arteries carry blood away from the heart; veins carry blood to the heart.
The brain must constantly send signals to the heart to make it beat.	The heart has an internal pacemaker that automatically controls its beat.
Any blood type can be safely given to any person.	A person must receive a compatible blood type to avoid a dangerous reaction.

Multiple Choice

Why do arteries need to have thicker, more muscular walls than veins?

• Because they have to carry blood a longer distance.

• To withstand the higher pressure of blood being pumped directly from the heart.

• To prevent the backflow of blood.

• Because they are wider in diameter than veins.

Multiple Choice

If a red blood cell is in the right ventricle, what is its next main destination and why is it going there?

• The aorta, to deliver oxygen to the body.

• The left atrium, to be pumped out to the body.

• The lungs, to pick up oxygen.

• The right atrium, to finish the circuit.

Multiple Choice

A person develops a condition that narrows their arteries. Based on what you've learned, what is a likely and direct consequence of this?

• An increase in the number of white blood cells.

• A decrease in the heart rate.

• An increase in blood pressure (hypertension).

• A decrease in the amount of plasma in the blood.

Multiple Choice

How does a diet high in unhealthy fats and salt contribute to poor cardiovascular health?

• It can decrease the amount of hemoglobin in red blood cells.

• It can lead to plaque buildup (atherosclerosis) and high blood pressure (hypertension).

• It weakens the signals sent by the pacemaker.

• It damages the valves between the atria and ventricles.

​

Summary

• The circulatory system transports oxygen, nutrients, and waste through the body.

• The heart pumps blood through the pulmonary circuit to the lungs and the systemic circuit to the body.

• Arteries carry blood away from the heart, veins return it, and capillaries connect them.

• A healthy lifestyle with a balanced diet and exercise is crucial for heart health.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4