Haematopoiesis is the process of formation of all blood cells (RBCs, WBCs, platelets) from stem cells in the red bone marrow. Specific terms: Erythropoiesis = formation of RBCs, Leukopoiesis = formation of WBCs, Thrombopoiesis = formation of platelets. All blood cells originate from a common precursor called Haematopoietic Stem Cell (HSC).

Leukaemia is a type of cancer of the blood or bone marrow characterized by the uncontrolled production of abnormal WBCs. These abnormal cells crowd out normal blood cells (RBCs, normal WBCs, platelets), leading to anaemia, infections, and bleeding. Types include Acute/Chronic Lymphocytic Leukaemia (ALL/CLL) and Acute/Chronic Myeloid Leukaemia (AML/CML). Treatment includes chemotherapy, radiation, and bone marrow transplant.

In adults, RBCs are produced in the Red Bone Marrow - a process called Erythropoiesis. Red bone marrow is found in flat bones like the sternum, ribs, skull, pelvis, and vertebrae. In the fetus, RBCs are initially produced in the yolk sac, liver, and spleen. The hormone Erythropoietin (EPO), produced by the kidneys, stimulates RBC production.

Blood group O (O negative / O-) is called the Universal Donor because it lacks A and B antigens on RBCs, so it can be donated to people of any blood group without causing an immune reaction. Blood group AB is the Universal Recipient because people with AB blood have both A and B antigens and can receive blood from any group. Blood group system was discovered by Karl Landsteiner (Nobel Prize 1930).

Complete blood flow sequence: Body > Superior/Inferior Vena Cava > Right Atrium > Tricuspid Valve > Right Ventricle > Pulmonary Valve > Pulmonary Artery > Lungs (oxygenation) > Pulmonary Veins > Left Atrium > Mitral Valve > Left Ventricle > Aortic Valve > Aorta > Body. This is the complete double circulation in humans.

Haemoglobin (Hb) is the iron-containing protein in RBCs that binds oxygen and transports it from lungs to tissues. Normal haemoglobin levels: Men: 13.5-17.5 g/dL, Women: 12-15.5 g/dL. Haemoglobin also transports about 20% of CO2 from tissues to lungs. Low haemoglobin = Anaemia. Haemoglobin bound to oxygen is called Oxyhaemoglobin (bright red), and without oxygen is Deoxyhaemoglobin (dark red).

Blood group AB is the Universal Recipient because individuals with AB blood have both A and B antigens on their RBCs and no anti-A or anti-B antibodies in their plasma. Therefore, they can receive blood from A, B, AB, or O groups without an immune reaction. However, AB positive (AB+) is the true universal recipient as it also lacks anti-Rh antibodies.

The Coronary Arteries are the blood vessels that supply oxygenated blood to the heart muscle (myocardium) itself. They arise from the base of the Aorta (just above the aortic valve). There are two main coronary arteries: Left Coronary Artery (LCA) supplying most of the left ventricle, and Right Coronary Artery (RCA) supplying the right ventricle and SA/AV nodes. Blockage of coronary arteries causes Heart Attack (Myocardial Infarction).

White Blood Cells (WBCs / Leucocytes) are the immune cells of the blood that defend the body against infections, bacteria, viruses, and foreign substances. Normal WBC count: 4,000-11,000 per mm3 of blood. WBCs are of several types: Neutrophils (most common, 60-70%), Lymphocytes, Monocytes, Eosinophils, and Basophils. A high WBC count (Leucocytosis) may indicate infection.

Karl Landsteiner, an Austrian biologist, discovered the ABO blood group system in 1901. He was awarded the Nobel Prize in Physiology or Medicine in 1930 for this discovery. He later also co-discovered the Rh (Rhesus) factor in 1940 along with Alexander Wiener. The discovery of blood groups made safe blood transfusions possible and revolutionized modern medicine and surgery.