Thorax
Heart
How to spot it. A cone-shaped muscular organ in the middle of the chest, tilted so its apex points down and to the left.
What it does. Pumps blood through two circuits: the right side to the lungs, the left side to the rest of the body.
Where it sits. Sits between the lungs, above the diaphragm; its great vessels lead to the lungs and the systemic circulation.
NEET points
Class 11 · Unit V · Human Physiology · Body Fluids and Circulation
- Four chambers: two atria above, two ventricles below, divided by the interatrial and interventricular septa.
- The tricuspid valve guards the right atrioventricular opening, the bicuspid or mitral valve the left, and semilunar valves the openings of the pulmonary artery and the aorta. All of them open one way only.
- The sinoatrial node in the upper wall of the right atrium sets the rhythm and is therefore called the pacemaker; the atrioventricular node, the bundle of His and the Purkinje fibres carry it to the ventricles.
- Cardiac output = stroke volume × heart rate. About 70 mL × 72 beats a minute ≈ 5 litres a minute in a healthy adult.
- Double circulation: blood passes through the heart twice in one complete circuit, which is why oxygenated and deoxygenated blood never mix in an adult.
Chapter numbering moved when NCERT rationalised its books in 2023 and the NTA has revised the NEET syllabus since, so this maps by unit and title. It is a study aid, not a syllabus.