The heart
Inside the heart
- The heart is a bag of muscle that never stops.
- A wall, the septum, splits it into a left side and a right side.
- Each side has an upper atrium and a lower ventricle.
The four chambers
- Atria (top) receive blood and push it into the ventricles below.
- Ventricles (bottom) pump blood out into arteries.
- Valves between the chambers stop blood flowing backwards.
- The heart muscle is fed by the coronary arteries.
- The septum keeps oxygenated blood (left) apart from deoxygenated blood (right) — they never mix.
Practice
Blood is pumped OUT of the heart into arteries by the:
The ventricles (lower chambers) pump blood out; the atria (upper) push blood into the ventricles.
Practice
The septum:
The septum is the dividing wall that stops the two sides' blood from mixing.
A thicker left side (Supplement)
- The left ventricle wall is thicker — it pumps blood all round the body.
- The right side only pumps to the nearby lungs, so its wall is thinner.
- Atria have thin walls — they only push blood to the ventricle just below.
- Valves: atrioventricular (atrium↔ventricle) and semilunar (at the ventricle exits).
Practice
Why is the left ventricle wall thicker than the right?
The left ventricle pumps to the whole body (high pressure); the right side only reaches the nearby lungs.
Heartbeat, exercise, disease
- Beat: atria contract → ventricles contract (valves snap shut) → muscle relaxes and refills.
- During exercise the heart rate rises, so muscles get oxygen and glucose faster.
- Coronary heart disease: coronary arteries narrow/block, starving the heart muscle of oxygen. Risks: fatty diet, lack of exercise, smoking, stress, genetics, age.
Practice
Coronary heart disease happens when:
Narrowed/blocked coronary arteries cut the heart muscle's oxygen supply.
You've got it
Key idea
- heart = muscle, split by the septum; each side has an atrium (top) + ventricle (bottom)
- the left ventricle wall is thickest (pumps to the whole body); the septum keeps oxygenated/deoxygenated blood apart
- exercise raises heart rate; blocked coronary arteries cause coronary heart disease