Internal Environment, Circulation, Blood & Heart Health

Internal Environment and the Circulatory System

1.) Internal environment: Refers to the fluids that surround the cells in the body. Conditions of the internal environment, like temperature or the composition of the fluid, must be stable for cells to work properly. This stable internal environment, called homeostasis, is maintained by the organ systems of the body.

• The internal environment consists of:
• Interstitial fluid (tissue fluid): It surrounds and bathes the cells.
• Blood and lymph: They collect and distribute substances the cells need, and eliminate waste from the cells through the circulatory system.

The lymphatic system:

• Transport absorbed fat from the small intestine to the blood.
• Defend the body as part of the immune system.

Lymphatic System

2.) Lymphatic system:

• Lymph capillaries: They collect excess interstitial fluid.
• Lymph nodes (glands): They contain defence cells that locate and fight microorganisms that could cause infection.
• Lymphatic vessels: They return the excess lymph to the circulatory system.
• Lymph: Consists of interstitial fluid that flows into the lymphatic vessels.

Blood

3.) Blood: Blood is a thick red liquid that flows inside the blood vessels.

Blood is made up of:

• Blood plasma: A yellowish liquid that makes up about 55% of blood. It consists of water and dissolved substances.
• Blood cells: Red blood cells, white blood cells and platelets make up the remaining ~45% of blood. They are formed in the red bone marrow located inside some bones, such as the femur.

The Heart

5.) The heart: The heart is made up of four chambers: two atria at the top and two ventricles below them. The right and the left sides of the heart are separated by a partition; however, the chambers on the same side are connected.

Parts and Processes of the Heart

1. Deoxygenated blood enters the right atrium through the superior vena cava and the inferior vena cava. Then it passes to the right ventricle.
2. Oxygenated blood leaves the lungs through the pulmonary veins (two from each lung) and enters the left atrium.
3. Deoxygenated blood leaves the right ventricle and enters the lungs through the pulmonary artery. This artery has two branches, one for each lung. The pulmonary semilunar valve prevents blood from flowing backwards.
4. Oxygenated blood leaves the left ventricle through the aorta. The aortic semilunar valve prevents blood from flowing backwards.
5. The coronary arteries supply blood to the muscle tissue of the heart.

The Cardiac Cycle

Atrial Systole

Both atria contract, pushing blood through the tricuspid and mitral valves into the ventricles. Both ventricles fill with blood.

Ventricular Systole

Both ventricles contract. The pulmonary and the aortic valves open, and the blood is pushed through the pulmonary artery and the aorta.

Diastole

The atria and the ventricles relax. The aortic and the pulmonary valves are closed. The atria fill with blood.