Biology : Body Fluid and Circulation

Explore the circulatory system as the delivery system for nutrients, gases, hormones, and wastes, powered by the heart and circulating through blood vessels with blood, lymph, plasma, and cells.

Explain the composition of human blood, detailing plasma as 55% and its contents, and red blood cells comprising 45%, with hemoglobin driving oxygen transport and buffering.

Explore white blood cells and platelets: colorless, nucleated leukocytes with diapedesis, and platelets from megakaryocytes that clot at injury sites to prevent hemorrhage.

Explore granulocytes, including neutrophils, eosinophils, and basophils, their red bone marrow origin, staining differences, nucleus shapes, and roles in infection, allergies, and anticoagulation.

This lecture explains agranulocytes, focusing on lymphocytes and monocytes, their 30% and 1–3% white blood cell presence, and their roles in antibodies, humoral immunity, and phagocytosis.

Platelets form a platelet plug at injury sites; they are small, non-nuclear cellular fragments produced in the bone marrow, and secrete serotonin to cause vasoconstriction, aiding blood clotting.

Injury triggers release of substances that initiate a cascade converting liquid blood to a semi-solid clot. Thrombin activates fibrinogen into insoluble fibrin, which, with platelets, seals the leak.

Explore the heart in the mediastinum, slightly tilted left in the thoracic cavity; a hollow muscular cone with atria and ventricles, plus its size, weight, and wall layers.

Explore the heart's three-layer wall—pericardium, myocardium, and no guardian—covering the fibrous and inner pericardium, the pericardial space with fluid, and the rhythmic contraction of cardiac muscle.

Describe the external heart structure, detailing the four chambers (atria and ventricles) and vessels such as the superior and inferior vena cava, coronary sinus, pulmonary veins, and systemic aorta.

Identify atrioventricular valves, including tricuspid on the right and mitral (bicuspid) on the left, and semilunar valves between ventricles and arteries that open during contractions to prevent backflow.

Explore the heartbeat and pulse, defining 72 bpm as normal heart rate, tachycardia above 100, bradycardia below 60, and cardiac output from heart rate times stroke volume.

Explore the heart's intrinsic conduction system, from the sinoatrial node pacemaker to the atrioventricular node, bundle of His, and Purkinje fibers that coordinate atrial and ventricular contractions.

Describes veins and capillaries and their roles in blood circulation. Shows how veins return blood to the heart under low pressure, and capillaries enable gas, nutrient, and waste exchange.

Explore double circulation by outlining pulmonary, systemic, and coronary pathways, showing blood moving from the right ventricle to the lungs, to the left atrium, then to the body and back.

Explore how blood pressure is the pressure on arterial walls during ventricular systole and diastole, measured with a cuff, sphygmomanometer, and stethoscope on the brachial artery.

Hypertension is a persistent high blood pressure, above 150 mm Hg systolic and 90 mm Hg diastolic, linked to high salt and fat intake, stress, and obesity.