Biology & Physiology

==Blood the Fluid of Life==

CHARACTERISTICS OF BLOOD - Blood has distinctive physical characteristics: An average person has 5 to 5.5 liters (13 pints) of blood, proportionate to body size. Of the total blood volume in the human body, 38% to 48% is composed of the various blood cells also called “formed elements”. The remaining 52% to 62% of the blood volume is the plasma or the liquid portion of the blood. Color-yeah… of course it's red. Arterial blood is bright red because it contains high levels of oxygen. Venous blood has given up much of its oxygen in tissues and has a darker, dull red color. This may be important in the assessment of the source of bleeding. PH-the normal pH range of blood is 7.35-7.45, which is slightly alkaline. Viscosity-this means the thickness or the resistance to flow. Blood is about 3 to 5 times thicker than water. Viscosity is increased by the presence of blood cells and the plasma proteins, and this thickness contributes to normal blood pressure.

There are four different blood types. Also there are Rh factors which make every person's blood type even more unique. Therefore, blood from a donor must match exactly that of the recipient. A little known fact about blood is that it falls under the category of a connective tissue. Technically blood is a liquid connective tissue accounting for about 8% of human body weight.

COMPOSITION OF BLOOD - When a sample of blood is spun in a centrifuge, the cells and cell fragments are separated from the liquid. Because the formed elements are heavier than the liquid matrix, they are packed in the bottom of the tube by the centrifugal force. The straw colored liquid on the top is the plasma. The three classes of formed elements are: Erythrocytes or red blood cells Leukocytes or white blood cells Thrombocytes or platelets

A given volume of blood is 55% plasma and 45% formed cells. Plasma is the liquid portion of blood, and it is about 90% water. The remaining portion consists of more than 100 different organic and inorganic solutes that are dissolved in water. Because plasma is a transport medium, its solutes are continuously changing as substances are added or removed by the cells.

BLOOD FUNCTIONS as the body's transport medium providing cells with nutrients and oxygen and for the removal of metabolic wastes. It also has roles in temperature regulation, fluid and electrolyte balance, ph regulation, prevention of fluid loss, nourishment and disease prevention. These roles overlap and interact as the blood carries out its role in providing suitable conditions for cellular function. One drop of blood (1mm cubed) contains 4 thousand to 10 thousand white blood cells, about 250 thousand platelets, and 4.5 million red blood cells. Blood gets around the body in about 60 seconds. Three fifths of the blood is in the veins and arteries, one fifth is in the lungs being oxygenated, the other fifth is scattered in various places like the muscles, lymphatics, liver, kidneys etc. One cell makes 45 thousand journeys in the body in a lifetime. The primary role of blood is an oxygen carrier - a life carrier.

An page on the anatomy of blood circulation can be found Here.