Blood: The Essential Fluid to Fuel the Life by Abdullah Al Moinee

Blood: The Essential Fluid to Fuel the Life 

Abdullah Al Moinee 

Life is a fusion of organized organic systems which are webbed and fueled by means of the blood circulation. Blood is the fluid that transports energy, nutrients, metabolic waste, and essential biomolecules to all tissues and circulates in the heart, capillaries, arteries and veins carrying oxygen to and carbon dioxide from the tissues of the body. 

Medical terms regarding blood often start with hemo which is derived from the Greek word αἷμα (haima) for "blood". In terms of anatomy and histology, blood is considered as a specialized form of connective tissue, given its origin in the bones and the presence of potential molecular fibers in the form of fibrinogen. 

In ancient time humans must have realized how blood signifies life. They must have observed that the loss of blood usually leads to death. So, the transfer of blood from one person to another is an ancient idea. In 1492, the first reported blood transfusion occurred. The transfusion was done on Pope Innocent VII in Rome. His doctors advised to transfuse blood from three healthy individuals as a therapeutic measure for his illness. However, the outcome of this blood transfusion was not successful and the Pope died soon after. William Harvey, an English physician discovered how blood circulated around the body, with the heart pumping blood into the body through the arteries, and the blood returning back to the heart through the veins in 1628. Later, in 1665, the first successful blood transfusion was recorded. Experiments were done by an English physician, Richard Lower, who transfused blood from one dog to another. Most of the dogs survived the transfusion. 

Blood is circulated around the body through blood vessels by the pumping action of the heart. In animals with lungs, arterial blood carries oxygen from inhaled air to the tissues of the body, and venous blood carries carbon dioxide, a waste product of metabolism produced by cells, from the tissues to the lungs to be exhaled. Blood is composed of blood cells suspended in blood plasma in vertebrates,. Plasma, which constitutes 55% of blood fluid, of which approximately 92% is water. Blood plasma also consists of hormones, glucose, proteins, gases, electrolytes, nutrients, blood cells themselves. The blood cells are mainly red blood cells (RBCs) or erythrocytes, white blood cells (WBCs) or leukocytes, and platelets or thrombocytes. Red blood cells perform many important functions within the body. RBCs fuel the supply of nutrients such as glucose, amino acids, and fatty acids and removal of waste such as carbon dioxide, urea, and lactic acid. The immunological functions and detection of foreign material by antibodies are bolstered by the white blood cells. The defensive system is thus formed by the WBCs. White blood cells are responsible for fighting viruses, bacteria and other infectious diseases. They also fight cancer cells and other unwanted material that enter human body. Platelets are completely different and are responsible for blood clotting whenever bleeding occurs because of a cut. Platelets functions on coagulation as the response to a broken blood vessel for the conversion of blood from a liquid to a semisolid gel to stop bleeding.

Hemoglobin is the principal determinant of the color of blood in vertebrates which is contained by RBCs. Hemoglobin is an iron-containing protein, which facilitates oxygen transport by reversibly binding to this respiratory gas and greatly increasing its solubility in blood. In contrast, carbon dioxide is mostly transported extracellularly as bicarbonate ion transported in plasma. Each molecule of hemoglobin has four heme groups, and their interaction with various molecules alters the exact color. In vertebrates and other hemoglobin-using creatures, arterial blood and capillary blood are bright red, as oxygen imparts a strong red color to the heme group. Deoxygenated blood is a darker shade of red; this is present in veins, and can be seen during blood donation and when venous blood samples are taken . 

Blood contributes for 7% of the human body weight, with an average density around 1060 kg/m3, very close to pure water's density of 1000 kg/m3. The average adult has a blood volume of roughly 5 litres, which is composed of plasma and several kinds of cells. It has to be noted that An adult body has 100,000 kilometers or 60,000 miles of blood vessels running throughout the body. The only place where blood cannot be found in human body is the cornea (eye) because cornea is capable of directly extracting oxygen from air. Scientists have come up with a method that can be used to send oxygen directly to blood without using the lungs. More than 400 gallons of blood are filtered by our kidneys every single day. Kidneys are actually responsible for regulating the production of red blood cells in human body. Kidneys are responsible for producing erythropoietin hormone (EPO) that binds with the receptors in stem cell walls in bone marrow and after a complex set of events, the DNA of stem cells are transformed into red blood cells. Kidneys will release EPO only when it finds that oxygen levels in blood have gone below normal. In other words, kidneys are responsible for measuring levels of oxygen in blood. People suffering with kidney failure generally become anemic because kidneys fail to produce enough EPO that can stimulate the production of red blood cells in bone marrow. This however never means that all anemic patients have failed kidneys. 

In a healthy human breathing, air at sea-level pressure is chemically combined with the hemoglobin constituting about 98.5% of the oxygen In a sample of arterial blood. The hemoglobin molecule is the primary transporter of oxygen in mammals and many other species Hemoglobin has an oxygen binding capacity between 1.36 and 1.40 ml O2 per gram hemoglobin which increases the total blood oxygen capacity seventyfold, compared to if oxygen solely were carried by its solubility of 0.03 ml O2 per liter blood per mm Hg partial pressure of oxygen. On the other hand, CO2 is carried in blood in three different ways. 70% of the CO2 is converted into bicarbonate ion by dint of the enzyme named carbonic anhydrase in the red blood cells (CO2 + H2O → H2CO3 → H+ + HCO− ). Besides, about 7% of the carbon dioxide is dissolved in the plasma and about 23% of it is bound to hemoglobin as carbamino compounds. Hemoglobin, the main oxygen-carrying molecule in red blood cells, carries both oxygen and carbon dioxide. However, the CO2 bound to hemoglobin does not bind to the same site as oxygen. Instead, it combines with the N-terminal groups on the four globin chains. 

Blood pressure (BP) is the pressure of circulating blood that exerts on the walls of blood vessels. It usually refers to the pressure in large arteries of the systemic circulation. Blood pressure is usually expressed in terms of the systolic pressure (maximum during one heart beat) over diastolic pressure (minimum in between two heart beats) and is measured in millimeters of mercury (mm-Hg), above the surrounding atmospheric pressure. Blood pressure is one of the vital signs, along with respiratory rate, heart rate, oxygen saturation, and body temperature. Normal resting blood pressure in an adult is approximately 120 millimetres of mercury (16 kPa) systolic, and 80 millimetres of mercury (11 kPa) diastolic, abbreviated "120/80 mmHg". 

Blood accounts for transfusion is obtained from human donors by blood donation and stored in a blood bank. There are many different blood types in humans, the ABO blood group system, and the Rhesus blood group system being the most important. Transfusion of blood of an incompatible blood group may cause severe, often fatal, complications, so cross matching is done to ensure that a compatible blood product is transfused. The ABO blood group system was discovered in the year 1900 by Karl Landsteiner. Jan Janský is credited with the first classification of blood into the four types (A, B, AB, and O) in 1907, which remains in use today. In 1907 the first blood transfusion was performed that used the ABO system to predict compatibility. Though we are familiar with common blood types A, B, AB and O, which is a part of simplified ABO system, there are actually around 30 different recognized blood groups or blood types on which researches are going on.