Circulatory and Respiratory System
Science

Tiny, thin-walled sacs in the lungs where oxygen and carbon dioxide are exchanged between air and the blood
Alveolus
Tiny, thin-walled sacs in the lungs where oxygen and carbon dioxide are exchanged between air and the blood. Alveolus. An alveolus is a small air sac in the lungs that allows for gas exchange with the blood.

The respiratory organ that absorbs oxygen from the air and removes carbon dioxide from the blood
Lung
The respiratory organ that absorbs oxygen from the air and removes carbon dioxide from the blood. Lung. The lung is a vital organ that helps you breathe by exchanging oxygen and carbon dioxide with the environment.

A clear tissue fluid that moves between the blood and the lymph vessels, it transports fats and aids the immune system
Lymph
A clear tissue fluid that moves between the blood and the lymph vessels, it transports fats and aids the immune system. Lymph is a fluid in the body that helps fight infections and removes waste.

The group of cells in the right atrium of the heart that “set the pace” for the heartrate, the sinoatrial node
Pacemaker
The group of cells in the right atrium of the heart that set the pace for the heart rate, the sinoatrial node. Pacemaker. A pacemaker is a small device that helps regulate the heartbeat by sending electrical signals to the heart.

The flow of blood between the heart and all parts of the body, except the lungs
Systemic circulation
The flow of blood between the heart and all parts of the body, except the lungs, is called systemic circulation. Systemic circulation is the process by which oxygen-rich blood is carried from the heart to the body and then returns oxygen-poor blood back to the heart.