The circulatory system includes a network of about 100,000 kilometers of blood vessels. End to end, they would encircle Earth two and a half times! These vessels supply the trillion cells in your body with nutrients and oxygen, and removes carbon dioxide and other waste products.

Organs of the Circulatory System Your cells require a constant supply of nutrients and oxygen. If diffusion were the only method of transportation, it would take a long time for these chemicals to travel from your small intestine to the cells in your brain. Our bodies have a more efficient distribution system—the circulatory system.

The circulatory system is responsible for delivering nutrients and oxygen to cells, transporting hormones throughout your body and carries wastes away from cells. The circulatory system also plays important roles in repairing tissue and protecting the body from infection.

The three primary components of the circulatory system are the blood, the heart, and the blood vessels. Blood is a type of connective tissue made up of cells and liquid. Solid part is: Red blood Cells (RBC), White Blood Cells (WBC) platelets and fluid part is the plasma Blood is pumped through the body by the heart, a multi-chambered, muscular organ. The overall flow of blood is from the heart to tissues throughout the body and back to the heart then to the lungs and back to the heart.

Three types of blood vessels: Arteries (Artery) – largest Veins – smaller and has one way valves inside Capillaries – smallest (only about 1 red blood cell can pass through at a time)

Blood flows throughout your body via blood vessels, tubes that form a closed pipeline within the body. Your body contains about 5 liters of blood. Under normal activity, it takes about one minute for all that blood to make a complete circuit through the body. Normal Heart rate: 60 – 100 BPM

Chemical Exchange Between Blood and Body Tissues Capillaries are in close contact with the cells of your body. Most cells in your body are no farther than 10 micrometers (µm) from a capillary and the blood inside it..

Cells in body tissues are surrounded by interstitial fluid. The substances in capillaries do not enter tissue cells directly. First these substances must enter the interstitial fluid, then enter the cells.

The exchange of substances between blood and the interstitial fluid such as oxygen and carbon dioxide, diffuse across membranes or pass through gaps between the epithelial cells of the capillary wall.

Blood pressure also forces fluid through the capillary wall. At the artery end of a capillary, blood pressure forces water, small solutes, and some dissolved proteins through the gaps between cells .

Blood cells and larger proteins are too large to pass easily through these openings, so they remain in the capillary. The vein end of the capillary is hypertonic compared to the surrounding interstitial fluid.

So, water tends to reenter the vein end of the capillary via osmosis. Blood pressure is very low at the vein end of the capillary, so it does not oppose the flow of fluid back into the capillary. 85 percent of the fluid that leaves the artery end of the capillary reenters at the vein end.

The Lymphatic System Your blood loses about 4 liters of fluid into the interstitial fluid each day. The lymphatic system collects and returns most of this fluid to the circulatory system. Like the circulatory system, the lymphatic system consists of capillaries and larger vessels (Figure 30-4). Once inside the lymphatic vessels, this collected fluid is called lymph.

Like veins, lymphatic vessels are embedded in muscle tissue Like veins, lymphatic vessels are embedded in muscle tissue. Also like veins, lymphatic vessels have valves that prevent lymph from flowing back toward the capillaries. The combination of muscle contractions squeezing the vessels and the one-way valves helps fluid move through the lymphatic system. Eventually, lymph drains into the circulatory system near the heart, allowing the fluid to be reused.

Located at juncture points throughout the lymphatic system are enlargements in the lymph tissue called lymph nodes. Lymph nodes help defend the body against infection. The nodes contain cells that destroy some bacteria and viruses that may enter the body. Have you ever had "swollen lymph glands" in your neck when you've had a cold or the flu? These "glands" are actually groupings of lymph nodes, swollen with infection-fighting cells. In Chapter 31 you will read more about the lymphatic system's role in fighting disease.