Thrombus is a blood clot that forms inside a blood vessel and remains at the site of formation. Embolus is a clot (or other material like fat or air) that breaks off and travels through the bloodstream, potentially blocking a distant vessel. Pulmonary Embolism = embolus blocks pulmonary artery (from DVT). Cerebral Embolism = embolus blocks brain artery (causes stroke). Plaque = fatty deposit on artery wall (atherosclerosis). Fibrin = protein forming the clot mesh.

Arterioles are small branches of arteries that connect arteries to capillaries. They are the primary site of peripheral vascular resistance and play a crucial role in regulating blood pressure and blood flow distribution. Arterioles have well-developed smooth muscle walls that can constrict (vasoconstriction) or dilate (vasodilation) to control the amount of blood entering capillary beds. This helps direct blood to active tissues during exercise or stress.

The ABO blood group system is based on: Antigens (agglutinogens) present on the surface of RBCs and Antibodies (agglutinins) present in blood plasma. Blood Group A: Antigen A on RBC, Anti-B antibody in plasma. Blood Group B: Antigen B on RBC, Anti-A antibody in plasma. Blood Group AB: Both A and B antigens, no antibodies. Blood Group O: No antigens, both Anti-A and Anti-B antibodies.

Coronary Circulation is the circulation that supplies oxygenated blood to the myocardium (heart muscle) itself. The heart cannot rely on the blood passing through its chambers for its own oxygen supply. The coronary arteries arise from the aorta just above the aortic valve. Coronary Artery Disease (CAD) occurs when these arteries are narrowed by atherosclerosis, leading to angina or heart attack.

Pericarditis is the inflammation of the pericardium (the protective sac around the heart). Symptoms include sharp chest pain that improves when leaning forward, pericardial friction rub (characteristic scratching sound heard with stethoscope), fever and fatigue. Causes: viral infections (most common - Coxsackievirus), bacterial infections, autoimmune conditions, and post-heart attack. Can lead to Cardiac Tamponade if fluid accumulates. Treatment: anti-inflammatory drugs (NSAIDs, colchicine).

Monocytes (3-8% of WBCs) are the largest WBCs. They perform phagocytosis - engulfing and digesting bacteria, dead cells, and cellular debris. When monocytes migrate from the blood into tissues, they differentiate into Macrophages, which are powerful phagocytic cells that form the first line of defence in tissues. Macrophages also present antigens to lymphocytes, linking innate and adaptive immunity.

Portal Circulation (Hepatic Portal System) is a special circulation where blood from the digestive organs (intestines, stomach, spleen, pancreas) flows to the liver via the Hepatic Portal Vein before entering the general circulation. This allows the liver to process absorbed nutrients (glucose, amino acids), detoxify harmful substances, and metabolize drugs (First Pass Effect). This is why the liver is the first organ exposed to absorbed nutrients and drugs.

The Cardiac Cycle has two phases: Systole is the phase of heart contraction - ventricles contract and eject blood into arteries (~0.3 seconds). Diastole is the phase of heart relaxation - heart fills with blood (~0.5 seconds). During diastole, the mitral and tricuspid valves open, allowing blood to flow from atria into ventricles. A normal cardiac cycle (one complete heartbeat) takes approximately 0.8 seconds at 75 bpm.

Eosinophils (1-4% of WBCs) are granulocytes that combat parasitic infections (worms/helminths) by releasing toxic proteins that kill parasites, and modulate allergic reactions - involved in allergic and asthmatic responses. High eosinophil count (Eosinophilia) indicates parasitic infection or allergic conditions like asthma and hay fever. They contain granules that stain with eosin dye (hence the name). Basophils release histamine during allergic reactions.

The Left Ventricle has the thickest muscular walls (~1.1-1.3 cm) because it must generate enough pressure to pump blood through the entire systemic circulation (the entire body). Right Ventricle has thinner walls (~0.3-0.5 cm) and pumps only to the lungs (short distance, low resistance). Right Atrium receives deoxygenated blood from the body. Left Atrium receives oxygenated blood FROM the lungs (does not pump to lungs).