LESSON 1
BLOOD
1-1.
INTRODUCTION
Blood is a complex and unique fluid of variable composition circulating through
the heart, arteries, capillaries, and veins, known as the vascular system of the body. It
is a tissue in which cellular constituents are suspended in a liquid medium performing
specialized functions. The prime function of blood is to carry oxygen from the lungs to
the body tissues and carbon dioxide from the tissues to the lungs. Blood carries fluid to
and from the tissues, thus maintaining proper fluid balance throughout the body
(explained later in this paragraph). The average pH value of blood is 7.40. Blood also
carries nutrients or food supplies from the digestive system to the body cells or tissues
and transports waste products for the tissues to the kidneys and bowel for excretion to
prevent accumulation. In response to trauma or infection, blood cells and antibodies
are carried in the blood to a point protection against the causative agents of disease, or
to transport blood-clotting substances to a break in a blood vessel to promote the
clotting process when injury is caused by bleeding or hemorrhage. The blood also
carries hormones from the endrocrine glands to the target organs, and it assists in the
regulation of the body temperature by carrying excess heat from the interior of the body
to the surface layers of the skin, where the heat is dissipated to the surrounding air. To
perform these complex functions, blood is complex and is composed of two main parts.
One part is composed of blood cells, the particles suspended in the plasma, making up
approximately 45 percent of total blood volume and including erythrocytes (red blood
cells), leukocytes (white blood cells), and thrombocytes (platelets). The red and white
blood cells are known as corpuscles. The other part is plasma, the fluid portion of the
blood, which consists primarily of water in which are dissolved proteins and many
inorganic and organic substances carried by the blood to and from the tissues. Plasma
makes up 55 percent of the blood.
1-2.
GENERAL CELLULAR STRUCTURE
a. A typical cell is composed of a single nucleus embedded in cytoplasm. The
living substance of the cell is a grayish, viscous liquid called protoplasm. Protoplasm is
enclosed in the cell interfaces by a cell membrane that selectively regulates the
interchange of materials between the cell and its environment. A typical cell tree is
diagramed in figure 1-1, however, all cells and forms or development of cells are not
depicted.
b. The nucleus is a spherical oval body surrounded by a thin membrane (nuclear
membrane). Contained in the nucleus is a sphere called the nucleolus. The nucleus is
thought to be an organizing center for the cell and can have the capacity for cell
production. The absence of nuclei signifies the end of cell development. Also found
MD0853
1-2