Tukuk-OSYour heart is two pumps sharing a wall: the right side sends spent blood through the lungs to reload oxygen (low pressure — lungs are delicate), the left side drives that blood to everything else at many times the pressure. It moves about five litres a minute at rest, roughly 7,500 litres a day, and beats close to 100,000 times a day — around 2.5 billion in an average lifetime — starting before you were born, from a single looping tube squeezed by its own pacemaker cluster, the sinus node, which fires the electrical wave every beat. That wave is what an ECG reads: the muscle is electrically driven, chemically tuned and mechanically executed.
Blood pressure numbers are push and rest: 120/80 mmHg means the artery peaks at 120 during a squeeze and never falls below 80 between beats. Sustained high pressure is dangerous not for the number itself but what it does — it wounds artery walls, and those wounds are where cholesterol lodges: atherosclerosis is largely an injury-repair response at the sites where pressure and turbulence damage the lining. The vicious loop is real: stiffer arteries raise the top number, which stiffens them further.
The system’s engineering elegance shows in capillaries: blood-vessel walls one cell thick, so narrow that red cells fold single-file and spend under a second in contact with tissue, delivering oxygen via haemoglobin — the iron-containing molecule that grips oxygen loosely and releases it where acidity and CO₂ are high, precisely where working muscle needs it. Resting muscles get about a fifth of output; the brain alone, at 2% of body mass, bills about 20% of the energy — an expensive tenant the plumbing exists to serve.