Human Immunity and Blood

Human blood has three main types of cells: erythrocytes (red blood cells that carry oxygen), leucocytes (white blood cells that fight infection), and thrombocytes (platelets that help with blood clotting). Option B correctly lists all three types. Granulocytes are actually a subtype of leucocytes, not a separate category.

The ABO system classifies blood into four main groups based on the presence or absence of A and B antigens on red blood cells. This is fundamental to blood transfusion compatibility.

Haematology is the branch of medicine concerned with the study of blood, blood-forming organs, and blood diseases. It covers red and white blood cells, platelets, bone marrow, and conditions like anemia, leukemia, and clotting disorders.

White blood cells (leukocytes) typically make up about 1% of total blood volume by count. The vast majority of blood cells are red blood cells (erythrocytes), which make up about 40-45% of blood volume, with the remainder being plasma and platelets.

Red blood cells (erythrocytes) are produced in the bone marrow through a process called erythropoiesis. In adults, this primarily occurs in the flat bones like the sternum, ribs, and pelvis. The liver produces red blood cells only during fetal development, while the spleen filters and stores old red blood cells rather than producing them.

TB is the standard medical abbreviation for Tuberculosis, an infectious disease caused by Mycobacterium tuberculosis bacteria. It primarily affects the lungs (pulmonary TB) but can affect other organs (extrapulmonary TB). Options A, B, and D incorrectly add anatomical terms - TB is not specific to body parts or blood.

AB blood group individuals lack anti-A and anti-B antibodies, so they can receive blood from any group (A, B, AB, or O) without antibody-mediated rejection. They are called universal recipients.

Leukemia is a cancer of the body's blood-forming tissues, including the bone marrow and the lymphatic system. It involves the overproduction of abnormal white blood cells that crowd out healthy blood cells.

Lymph glands (lymph nodes) produce and store white blood cells, particularly lymphocytes, which are crucial for immune function. They filter lymph fluid and help fight infections. Lacrimal glands produce tears, mucous glands produce mucus, and Weber's glands are minor salivary glands - none produce white blood cells.

Monocytes are the largest type of white blood cell and are characterized by a large, eccentric, kidney-shaped or bean-shaped nucleus. Eosinophils usually have bilobed nuclei, and lymphocytes have large, round nuclei that fill most of the cell.

White blood cells (leukocytes) are the primary components of the immune system responsible for defending the body against infectious diseases and foreign materials. Red blood cells carry oxygen, and platelets are responsible for blood clotting.

Platelets (thrombocytes) are cell fragments that clump together to form a plug when a blood vessel is damaged. White blood cells and neutrophils are part of the immune system, while red blood cells transport oxygen.

O positive (O+) is the most common blood type in the global population, found in approximately 37-40% of people. O negative is the universal donor but is much rarer, while A and B types are less frequent than O+.