Circulatory System: Structure, Function and Components of Blood

Circulatory System

Circulation is a continuous movement of fluids through the body. The movements that allow us to transport the nutrients and oxygen we inhale to be distributed to the cells of our organism so they can carry out reactions with metabolic substances that allow us to maintain our vital activity.

The Heart

Heart: The heart is an organ and a muscle that beats. It is an important pump that receives blood from the veins and sends it to the lungs and the rest of the body to be properly oxygenated.

Heart sounds (HS): A special piece of muscle tissue in the right auricle, close to the opening of the vena cava, sets in motion the impulse that triggers cardiac contraction.

Heart Movements (Cardiac Cycle)

• Atrial systole: The atria contract and push blood through the atrioventricular valves into the ventricles.
• Ventricular systole: The ventricles contract and push the blood they contain into the pulmonary artery and aorta, opening the semilunar (sigmoid) valves.
• Diastole: The heart relaxes and receives blood from the vena cava and pulmonary veins. The blood cannot return to the atria, and the semilunar valves close.

Lymph

Lymph: Lymph is a fluid that travels through the lymphatic vessels. It is a plasma-like liquid, sometimes with a yellowish tint, that contains white blood cells and a large number of cells. It is classified as a liquid connective tissue.

Blood Vessels

Blood vessels: Blood vessels are hollow, tubular structures through which blood flows, driven by the heart throughout the body. They are classified as follows:

• Arteries: Carry blood away from the heart to the organs, transporting oxygen and nutrients. They have thick, elastic walls and a high internal pressure.
• Veins: Carry blood from the organs and tissues back to the heart and to the lungs, where carbon dioxide is exchanged for oxygen from inhaled air. They have thinner walls than arteries.
• Capillaries: These are the smallest vessels, with very thin walls, where the exchange of substances between blood and tissues takes place.

Components of Blood

Plasma, red blood cells, phagocytes, lymphocytes:

• Blood plasma: The acellular fluid fraction of blood. It is composed of about 90% water and multiple dissolved substances, with an abundance of proteins. Among the multiple substances are sodium (Na), potassium (K), urea, hormones, and more.
• Red blood cells: These are the most numerous formed elements of blood. Hemoglobin is one of its main components, and its objective is to transport oxygen to the different tissues of the body.
• Phagocytes: These are cells capable of engulfing and digesting microorganisms, substances, cells, aged cells, and cellular debris. They engulf them using pseudopods and then digest them in the cytoplasm.
• Lymphocytes: A type of leukocyte belonging to the agranulocytes. They are small cells with a large, rounded nucleus.