Understanding Homeostasis and Blood Circulation

The Internal Environment and Homeostasis

The internal environment is the set of fluids surrounding the cells of the body. From this environment, cells extract nutrients and oxygen, and into it, they discharge metabolic waste and CO₂.

Components of the Internal Environment

In humans, the internal environment consists of:

• Blood: A fluid that acts as a transport for various substances and travels through the blood vessels.
• Interstitial Fluid: A fluid with defensive and nutritive functions that lies between the cells. It arises from blood filtered by the capillaries.
• Lymph: The fluid found in the lymphatic vessels, which originates from interstitial plasma.

System Organization and Regulation

The operation and organization of the body depend on homeostasis, which is the maintenance of constant properties within the internal environment. This process is managed by the body's systems. The circulatory system can be divided into two parts: the blood circulatory system and the lymphatic circulatory system.

The Blood Circulatory System

Features and Functions

The blood circulatory system distributes nutrients and O₂ throughout the body. It also collects waste from metabolism and leads it to urinary excretion. It is composed of:

Blood Vessels

• Arteries: These carry blood from the heart to various organs. They have thick walls and elastic resistance due to the high pressures affecting them.
• Veins: These carry blood from the organs back to the heart. Their walls are thinner and less elastic because they support less pressure. They have valves that prevent the backflow of blood.
• Capillaries: These are microscopic vessels that connect arteries and veins. Through their walls, there is a continuous exchange of O₂, CO₂, nutrients, and wastes with every cell in the body.

Blood and Plasma

Blood is a viscous, red liquid with a salty taste that circulates in the blood vessels. Its functions include respiration, nutrition, excretion, defense, and temperature regulation.

Plasma is a yellowish liquid consisting of 90% water and 10% carbohydrates, fats, and other substances.

Blood Cells

• Red blood cells: Biconcave cells without nuclei. They are elastic and deformable, allowing them to pass through the capillaries. They contain hemoglobin, the protein that carries oxygen and CO₂.
• White blood cells: These are large cells with a nucleus that defend the body against infections.
• Platelets: Cell fragments without nuclei involved in blood clotting.

The Heart

The heart is the central organ of the circulatory system responsible for pumping blood throughout the body.