Tachycardia = heart rate above 100 bpm (too fast). Bradycardia = heart rate below 60 bpm (too slow). Arrhythmia = any irregular heart rhythm. Fibrillation = rapid, chaotic, uncoordinated contractions (Atrial or Ventricular Fibrillation). Tachycardia can be caused by fever, anxiety, exercise, anaemia, hyperthyroidism, or heart disease. Sustained ventricular tachycardia is a medical emergency.

Hypertension is the medical term for persistently high blood pressure - defined as blood pressure consistently >=140/90 mmHg. It is called the Silent Killer because it usually has no symptoms but causes serious damage to arteries, heart, kidneys, and brain over time. Risk factors include excess salt intake, obesity, stress, smoking, and family history. Treatment includes lifestyle changes and antihypertensive medications.

Iron is the essential mineral required for haemoglobin synthesis. Iron is part of the heme group in haemoglobin - each haemoglobin molecule contains 4 heme groups, each with one iron (Fe2+) atom that binds one oxygen molecule. A total of 4 oxygen molecules are carried per haemoglobin. Iron deficiency leads to Iron Deficiency Anaemia - the most common nutritional deficiency worldwide.

Blood composition: Plasma = 55% (liquid component) and Formed elements = 45% (RBCs, WBCs, platelets). Within the formed elements, RBCs (Red Blood Cells) make up the vast majority (~99%). The percentage of RBCs in total blood is called the Haematocrit (PCV - Packed Cell Volume), which is normally 40-45%.

Systemic Circulation is the circulation of oxygenated blood from the heart to all body tissues (except lungs) and return of deoxygenated blood back to the heart: Left Ventricle > Aorta > Body Tissues > Superior/Inferior Vena Cava > Right Atrium. This is the larger circuit of the double circulation. The systemic circuit supplies oxygen and nutrients to all organs and removes CO2 and waste products.

Haematology (Greek: haema = blood) is the branch of medicine that deals with the study of blood, blood-forming tissues, and blood disorders. A haematologist diagnoses and treats conditions like anaemia, leukaemia, lymphoma, haemophilia, thalassaemia, and clotting disorders. Cardiology deals with the heart, Nephrology with kidneys, and Oncology with cancer.

Red Blood Cells (RBCs / Erythrocytes) carry oxygen due to the presence of Haemoglobin - an iron-containing protein that binds to oxygen. Each RBC contains approximately 270 million haemoglobin molecules. RBCs are biconcave disc-shaped, lack a nucleus (in mature form), and have a lifespan of approximately 120 days. They are produced in the red bone marrow.

A Sphygmomanometer is the instrument used to measure blood pressure. It consists of an inflatable cuff, pressure gauge, and valve. Blood pressure is measured in mmHg (millimetres of mercury). A Stethoscope is used to listen to heart and lung sounds. An ECG (Electrocardiogram) records the electrical activity of the heart.

Anaemia is a condition where the blood has a lower than normal number of RBCs or insufficient haemoglobin, resulting in reduced oxygen-carrying capacity. Symptoms: fatigue, pale skin, shortness of breath, dizziness. Types: Iron Deficiency Anaemia (most common), Pernicious Anaemia (Vitamin B12 deficiency), Sickle Cell Anaemia (genetic), Aplastic Anaemia (bone marrow failure), and Haemolytic Anaemia (RBC destruction).

Red Blood Cells (RBCs) have a lifespan of approximately 120 days. After this period, old RBCs are destroyed in the spleen (called the graveyard of RBCs) and liver. The haemoglobin is broken down - the iron is recycled for new RBC production (in bone marrow) and the remaining portion is converted into bilirubin (excreted as bile).