Blood

From ArticleWorld

Blood is the fluid-like body tissue that is the substrate in which many molecules and cells are transported throughout the body. It is composed of a fluid component, called serum or plasma, and a relatively solid component that contains the various cells normally found in our bloodstream.

Physiology

Blood is a complicated mixture of nutrients such as oxygen, glucose (sugar), proteins, waste products, such as carbon dioxide and urea, products of metabolism, cell messengers (hormones), enzymes and the building blocks necessary to create or heal tissue. The blood is also the substrate in which blood cells such as leukocytes, erythrocytes and platelets travel and perform their various functions.

The cellular components of blood are made in the bone marrow and released into the blood whenever needed. Other components of the blood are made elsewhere. For example, several glands in the body release hormones that act as messengers to deliver signals to distant parts of the body. Many of the proteins in the blood are produced in the liver. Still other molecules are nutrients absorbed from the digestive system or are released in a nutrient form by the liver, which stores some nutrients but does not actually make them.

Blood has the important function of carrying hemoglobin inside red blood cells. It is the hemoglobin which picks up oxygen in the lungs to a saturation of between 96-97%. The oxygen is allowed to diffuse into the tissues until it leaves the tissues at an oxygen saturation level of 75%. Carbon dioxide, a byproduct of metabolism, is also carried by the blood from the tissues until it can diffuse into the air sacs of the lungs, where it is exhaled from the body in the act of respiration.

Anatomy

Blood has solid components (cells) that make up 45% of the total volume and liquid components that make up the remainder. The liquid part of blood is called “plasma” when it contains clotting factors in it and “serum” when the clotting factors have been removed. The average adult human carries approximately 5 liters in total blood volume.

Of the solid components of the blood, the erythrocytes (red blood cells) are important in the transportation of oxygen in the blood. Leukocytes (white blood cells) come in several different types but, in general, are important in fighting infections. Some leukocytes become active in the process of the allergic response; others are used in fighting cancer cells; others create the process of inflammation in arthritis, trauma or immune diseases. Platelets are very small cells that aid in the process of blood clotting.

Blood plasma is mostly (96%) water and is the liquid in which many proteins, sugars, enzymes, hormones and electrolytes (like salt) travel throughout the body.