The Major Body Systems COS 9 Identify major body systems and their functions, including the circulatory system, respiratory system, excretory system, and reproductive system.

The Circulatory System The circulatory system is made up of the vessels and the muscles that control the flow of the blood around the body. This process is called circulation. The main parts of the system are the heart, arteries, capillaries, and veins.

As blood begins to circulate, it leaves the heart from the left ventricle and goes into the aorta. The aorta is the largest artery in the body. The blood leaving the aorta is full of oxygen. This is important for the cells in the brain and the body to do their work. The oxygen- rich blood travels throughout the body in its system of arteries.

On its way back to the heart, the blood travels through a system of veins. As it reaches the lungs, the carbon dioxide (a waste product) is removed from the blood and replace with fresh oxygen that we have inhaled through the lungs.

What is Blood? Blood is thicker than water and has a slightly salty taste. In an adult’s body there is 10.6 pints of blood circulating around. In their blood there are billions of living blood cells floating in a liquid called plasma. The red blood cells are the heavier, more solid parts. The plasma is lighter.

The Respiratory System The primary function of the respiratory system is to supply the blood with oxygen to be delivered to all parts of the body.

Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose.

The oxygen then passes through the larynx (where speech sounds are produced) and the trachea which is a tube that enters the chest cavity.

In the chest cavity, the trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again forming the bronchial tubes.

The bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli.

The diaphragm's job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs.

There are many diseases that can harm and even destroy the respiratory system. Asthma is an increasingly common disease that causes coughing and makes it hard to breathe. Lung cancer is a major cause of death particularly among smokers. Tuberculosis is a disease caused by bacteria that can destroy the lungs.

The Excretory System The excretory system regulates the chemical composition of body fluids by removing wastes and retaining the proper amounts of water, salts, and nutrients. Components of this system include the kidneys, liver, lungs, and skin.

The kidneys are organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. Cross section of a kidney

The kidneys funnel the urine into the bladder along two separate tubes called ureters.

The bladder stores the urine until muscular contractions force the urine out of the body through the urethra.

The liver acts as a filter for the blood. As blood passes through the liver, it removes amino acids that do not need to be in your body.

The other excretory organ is the skin. The skin can sometimes be thought as the largest organ of the human body.

The Reproductive System The major function of the reproductive system is to ensure survival of the species.

A female's internal reproductive organs are the vagina, uterus, the fallopian tubes, and ovaries. They are all located entirely within the pelvis.

Unlike the female, whose sex organs are located entirely within the pelvis, the male has reproductive organs, or genitals, that are both inside and outside the pelvis. The male genitals include the testicles, the duct system, the accessory glands, and the penis.

Within the context of producing offspring, the reproductive system has four functions: To produce egg and sperm cells To transport and sustain these cells To nurture the developing offspring To produce hormones