Human Body Systems: Respiratory, Excretory, and Circulatory

Lesson 4: Human Body Systems

Respiratory Apparatus

Function: The exchange of gases. It takes in oxygen and releases carbon dioxide.

Phases of Respiration

• Inhalation: Air passes through the nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles.
• Gas Exchange: Takes place in the alveoli, which are in contact with blood vessels. Oxygen passes from the alveoli to the capillaries, while carbon dioxide passes from the capillaries to the alveoli.
• Exhalation: Air travels from the alveoli through the bronchioles and respiratory paths to the outside.

Note: Inspiration is when air enters the lungs; expiration is when air leaves the lungs.

Diseases of the Respiratory System

Common conditions include respiratory tumors, colds, inflammation, pneumonia, asthma, and allergic rhinitis.

Excretory Apparatus

As a result of the nutrition process, our body cells produce waste substances. If these accumulated, they would be toxic; therefore, the body must expel them.

Circulatory Apparatus

The blood, heart, and blood vessels make up the circulatory system. It transports oxygen from the lungs to the cells and digested food from the small intestine to the cells. It also removes waste chemicals like carbon dioxide from cells to the lungs and other wastes to the kidneys. Additionally, it transports hormones, antibodies, and blood proteins.

Blood Circulation

The heart acts as a pump that circulates blood through the blood vessels.

Double Circulation

The heart is divided into two halves: right and left, separated by a thick muscle wall called the septum.

• The right side pumps blood to the lungs and back to the heart.
• The left side pumps blood to the rest of the body and back to the heart.

Cardiac Cycle:

• Diastole: The heart muscles are relaxed.
• Systole: The heart muscles contract.

The Three Blood Vessels

• Arteries: Have thick muscular and elastic walls to withstand high blood pressure.
• Veins: Have thin walls with less muscle and elastic tissue; blood pressure here is low.
• Capillaries: Have walls that are only one cell thick, allowing substances to pass easily in and out of the blood in body tissues.