Chapter A1.2 Human Body Systems

The Circulatory System The circulatory system transports oxygen, nutrients, and wastes through the body in the blood. The liquid part of the blood, called plasma, is mostly water. Plasma also contains dissolved nutrients and waste products. The waste product in blood is what we call carbon dioxide.

continued The solid part of blood contains red blood cells and white blood cells. Red blood cells absorb oxygen and deliver it to the organs. White blood cells help the body fight infection. They attack and destroy the germs and viruses and bacteria that enter the body.

continued Blood also contains platelets– tiny pieces of blood cells inside membranes. Platelets cause blood cells to clot when a cut or open wound occurs. They also repair damage to your blood vessels. The heart pumps blood through blood vessels. The oxygen rich blood flows through the body through arteries, and returns to the heart and lungs through veins.

continued Capillaries- are blood vessels so small that the red blood cells have to travel through single file. There are capillaries throughout the body so that oxygen can reach every part of your body.

The Respiratory System When you breathe, you draw air into your lungs. The air is filtered by tiny hairs inside your nose and warmed by capillaries. The warmed air then travels down your trachea, or windpipe. The trachea branches into smaller tubes called bronchi.

continued Each bronchi tube leads to one of the lungs. In the lungs, the tubes divide smaller and smaller. At the end of the smallest tubes, there are tiny air sacs called alveoli. The walls of the alveoli are only one cell thick. The blood coming from the heart contains much carbon dioxide.

continued Carbon dioxide diffuses through the walls of the alveoli and then into the air you will breathe out. When you breathe in, the air diffuses through the alveoli and into the red blood cells. The oxygen rich blood then flows back to the heart. The heart then pumps the “oxygenated” blood throughout your body.

The Digestive System Digestion starts as soon as you chew your food. Your chewing breaks the food into smaller pieces and mixes with your saliva. Saliva moistens the food and begins to break down the starchy foods into sugars. When you swallow, food goes through your esophagus, a long tube from your mouth to your stomach.

continued Juices in your stomach containing acid and other chemicals break down the proteins. After several hours in your stomach, the digested food moves into your small intestine. In the small intestine, more chemicals break down the food. Nutrients from the food are now able to diffuse through the villi, tiny finger like structures, into the blood.

continued Undigested food then travels to the large intestine, where water and minerals pass into the blood, and non-needed material are removed from the body. Two other organs aid in digestion. The liver produces bile, which is stored in the gallbladder until you need it. The pancreas produces a fluid that calms stomach acid and other chemicals that help complete digestion.

The Excretory System The waste left over from the circulatory system must be removed from the blood. The food material not used by the body must be removed from the intestine. This is the job of the excretory system. Cell wastes include carbon dioxide and ammonia. Ammonia travels to the liver where it is converted into urea.

continued The urea then travels by way of the blood to the kidneys. The urea, water and other wastes then form urine and it flows from the kidney to the bladder through tubes called ureters. You empty the bladder when it is full through a tube called the urethra.

continued The body gets rid of wastes in other ways too. When you exercise you get warm and sweat. Sweat is a salty liquid that cools your body when it evaporates.