Blood: The Vehicle of the Life Force

The blood is a vital fluid composed of cellular components and liquid substance called plasma. The cellular components or blood corpuscles float in the plasma. About 40 to 45% of the volume is made up of blood cells and about 55-60% volume is fluid. The volume of cellular components is determined by hematocrit technique. The total volume of blood is about ¹/₁₂th to ¹/₁₃th of our body weight. The vital energy of the body is generated by metabolic processes through oxidation and enzymatic actions. The blood carries oxygen from the lungs and distributes the same to all organs and tissues. Infact, blood is a vehicle of life force.

Composition of Plasma of Blood: The blood plasma contains the following substances:

• Water: 91 - 92%
• Protein: 7 - 8% (Albumin, globulin and coagulation factors)
• Salts: 0.9% (Sodium chloride, potassium chloride, sodium bicarbonate, salts of calcium, magnesium, phosphorus, iron and trace metals).

In addition to above there are small amounts of organic materials like glucose, cholesterol, urea, uric acid, creatinine and amino acids along with hormones, enzymes and antigens.

Cellular Components: There are three types of cells present on blood:

• Red blood cells (RBCs) or erythrocytes.
• White blood cells (WBCs) or leucocytes.
• Platelets or thrombocytes.

Erythrocytes are circular, bi-concave disc like cells and originate in bone marrow. They are pale buff colored when seen singly, but in masses appear red and give the red color to blood , hence called red blood cells. They contain the vital substance hemoglobin. The amount of hemoglobin present in normal blood is about 15 g/dl. The normal count of RBCs in blood is about 5,000,000 (5 x 10⁶) per microlitre of blood. The average life of red blood cell is about 115 days. Hemoglobin is a complex protein rich in iron. It has an affinity for oxygen and combines with it to form oxy-hemoglobin in RBCs. By means of this function oxygen is carried to the tissues from the lungs. A balanced diet rich in iron and proteins is necessary for the replacement of worn out RBCs. Women require more iron as some is lost in the menstrual flow; in pregnancy the requirements are greater to supply iron for the developing fetus.

Blood Groups: Erythrocytes or RBCs carry at their surface the blood group antigens and there are antibodies in the plasma against the antigen absent at the surface of erythrocytes. There are two antigens: A-antigen and B-antigen. Depending upon the presence and absence of these antigens at the surface of RBCs, there are 4 blood groups:

• Blood group A: Antigen A present at the surface of erythrocytes.
• Blood group B: Antigen B present at the surface of erythrocytes.
• Blood group AB: Antigen A and B present at the surface of erythrocytes.
• Blood group O: No antigen present at the surface of erythrocytes.

In addition to above blood groups, there are a number of sub-groups. Sub-groups and Rhesus factor (Rh factor) in blood is important to be determined by agglutination procedures during compatibility testing. Rhesus factor of fetus is also important in Rh-factor negative mothers.

The white blood cells (WBCs) or leucocytes are transparent and not colored cells. The normal count of WBCs is 4000 to 11000 per microlitre of blood. There are five groups of WBCs:

• Granulocytes or polymorphonuclear cells or neutrophils form about 70 - 75% of total leucocytes' count in blood and provide first line of defence against infectious organisms by phagocytic function.
• Lymphocytes form about 20 - 25% of total leucocytes' count in blood. These cells are called immuno-competent cells and provide active immunity and defence against infectious organisms and tumors. There are further types sub-types of these cells like T-lymphocytes and B-lymphocytes; T-helper and T-suppressor lymphocytes etc.
• Monocytes also provide defence against infectious organisms through phagocytic function. They constitute about 5% of total leucocytes' count in blood.
• Eosinophils are the leucocytes which have active affinity for acidic staining material called eosin and appear red in a blood film after staining. These cells are associated with defence against allergic disorders. Normally they count about 2 - 3% of total leucocytes' count in blood.
• Basophils are the cells which stain with basic dyes and look blue in a stained blood film with blue granules in their cytoplasm. These cells count less than 1% of total leucocytes' count in blood and are associated with allergic disorders.

Platelets or thrombocytes are very small cells, about one third of the size of an erythrocyte. Their normal count is 150,000 to 300,000 per microlitre of blood. They play a vital role in the control of bleeding from an injury and in the clotting of blood.

The blood act as a vehicle or transport system of our body carrying all the cellular components, chemical substance, oxygen and nutrients for the nourishment and defence of body in order to maintain its normal function and preservation of life. Red blood cells convey oxygen to the tissues and remove carbon dioxide. Plasma distributes proteins needed for tissue formation and repair. Blood also carries waste products of metabolism for elimination through excretion by kidneys. Internal secretions, hormones and enzymes are also conveyed by blood from organ to organ or target site by the blood. In nutshell the blood is a vehicle of the life force.

Human Anatomy & Physiology: Introduction

Anatomy: The study of the structure of the human body and the relationship of its constituent parts to each other or one or the other is called general anatomy. In regional anatomy, a geographical study is made and each region e.g. arms, legs, head, ears, eyes. nose, trunk, genitalia etc., is being studied in terms of its components. Different regions of human body do have some common structures such as bones muscles, nerves and blood vessels. An anatomical region performing a particular function is called a system. There are a variety of systems in human body. The systematic study of these systems is called the systematic anatomy. The functional relationship of different parts or organs of the body is called the functional anatomy. The anatomical features of our body which could be appreciated by naked eye are covered under the macroscopic anatomy and the finer structures which could be revealed with the help of a microscope are termed as microscopic anatomy. Closely allied to the anatomy are histology and cytology, the study of tissues and cells respectively. Human body is studied from the erect position with the arms by the sides and the palms of the hands facing forwards, the head erect and eyes looking straight in front. This is the universal description of anatomical position. Various parts of the body are described in relation to certain imaginary lines or planes. The median plane runs through the center of the body. Any structure which lies nearer to the median plane of the body is said to be medial to the other. For example the inner side of the thigh is described as the medial aspect and the outer as the lateral aspect. The terms internal and external are used to describe the relative distance of an organ or structure from the center of a cavity. The ribs for example have an internal and external surface. The terms superficial and deep are used to denote relative distance from the surface of the body. The terms superior and inferior are used to denote the positions relatively high or low in relation to trunk and the terms proximal and distal are employed to describe nearness to or distance from a given point particularly in relation to limbs. For example the proximal phalanges are nearer to the wrist and the distal ones are the farthest away. When three structures are running from the medial plane of the body outwards, they are described as being placed in medial, intermediate and lateral position. The terms anterior and posterior are synonymous with ventral and dorsal. These terms are only adapted to man in the erect attitude or anatomical position. For example the anterior and posterior tibial arteries lie in front and back in the leg. In describing hand the terms palmar and dorsal are used instead of anterior and posterior and in describing foot the terms plantar and dorsal are employed. Many parts of the body are symmetrically arranged. For example left and right limbs are similar. The eyes, ears lungs and kidneys too are left and right and symmetrically arranged. There is also a good deal of asymmetry in the arrangement of the body. The spleen lies entirely on the left side; the pancreas lies partly on each side and the larger part of the liver lies on the right side. Physiology: It is the study of the internal functions of the normal human body and closely linked to the study of internal functions of all the living creatures in the subject of biology. The body is made up of many tissues and organs each having its own particular function to perform. The cell is the smallest unit of the body of which all the body parts are comprised. The cells and/or organs are adapted to perform the special functions in a system. The cells of the nervous system and muscle are very specialized. Other cells such as those in the connective tissue are not so highly developed as compared to muscle and nerve cells. Bioenergetic pathways, cellular interactions and their biochemical products such as enzymes and hormones are at the core of the physiology.