The Internal Environment and Circulatory System
The Internal Environment and the Circulatory System
The internal environment is the fluid surrounding the cells of an organism. Cells extract nutrients and oxygen, and necessary substances are discharged as waste and carbon dioxide. It is made up of:
- Interstitial plasma: A liquid between the cells that functions in nutrition and defense. It originates from blood that has been filtered through the thin walls of blood capillaries.
- Blood and lymph: Lymph is a liquid formed from interstitial plasma that circulates through lymphatic vessels.
The Circulatory System
The circulatory system distributes nutrients and oxygen around the body, while collecting waste products of cellular metabolism. It includes:
- Blood vessels: Conduits through which blood circulates to all parts of the body. There are three types:
- Arteries: Carry blood from the heart to all other organs.
- Veins: Carry blood from various organs to the heart. Their walls are thinner and less elastic than arteries.
- Capillaries: Microscopic vessels where arteries connect with the beginning of veins.
Blood: The Transport Medium
Blood is a viscous, red, salty liquid that circulates inside the blood vessels. Blood is involved in the following functions:
- Nutrition: Transports nutrients from the digestive system to all cells of the body.
- Respiration: Carries oxygen from the lungs to the cells and carbon dioxide produced by the cells in reverse.
- Excretion: Collects waste produced by the cells and carries it to the excretory system to remove it from the body.
- Thermal regulation: Involved in regulating body temperature by heating or cooling the body.
Blood Composition
- Plasma: A yellowish liquid constituted 90% by water. It contains a variety of substances such as proteins, glucose, lipids, minerals, and gases.
- Blood cells: Erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (thrombocytes).
The Heart
The heart is a muscular organ about the size of a fist, responsible for propelling blood through blood vessels. It is located in the central part of the chest between the two lungs.
- Mitral valve: Connects the left atrium and left ventricle. It consists of two thin flaps.
- Tricuspid valve: Connects the right atrium and right ventricle. It consists of three thin flaps.
Heart Function
It consists basically of two types of coordinated movements that take place in the atria and ventricles: a contraction movement called systole, and a relaxation movement called diastole.
- Atrial systole: When the atria are full of blood, they contract. This contraction causes the opening of the mitral and tricuspid valves, and the passage of blood to the ventricles.
- Ventricular systole: Almost immediately after atrial systole, the contraction of the ventricles occurs.
- Diastole: When ventricular systole ends, the ventricles relax, and the lowering of ventricular blood pressure causes the semilunar valves to close.
Circulation
Circulation is double and complete because the blood passes twice through the heart, and the oxygen-rich blood is not mixed with blood rich in carbon dioxide.
- Pulmonary circuit: Established between the heart and lungs.
- Systemic circuit: Established between the heart and various organs of the body.
The Lymphatic System
The lymphatic system is in charge of collecting the fluid between the cells and returning it to the blood. It also transports fats absorbed in the intestine.
- Lymphatic capillaries: Small, blind-ended vessels distributed throughout all tissues. They are responsible for collecting interstitial fluid.
- Lymphatic vessels: Vessels that have a structure similar to veins. They are the result of the confluence of lymphatic capillaries.
- Lymph nodes: Small enlargements that occur along lymphatic vessels. They filter and eliminate foreign substances and microorganisms before they enter the bloodstream.
Diseases of the Circulatory System
- Atherosclerosis: The hardening of the arteries. It is produced by the deposit of fat and cholesterol on the inner wall of the arteries, making the inside diameter decrease and hindering the passage of blood.
- Myocardial infarction: The process by which thrombosis occurs in a coronary artery, blood flow is interrupted, and the muscle cells nourished by it die as a result.
Cardiovascular Health
Cardiovascular diseases can be avoided by exercising, eating a healthy diet, and not smoking.