The skeleton and muscles
- The skeleton supports the body, protects organs (the skull protects the brain; the ribs protect the heart and lungs), helps us move and makes blood cells in the bone marrow.
- Joints are where bones meet. Ligaments join bone to bone, and cartilage cushions the ends of bones. Hinge joints (elbow, knee) move one way; ball and socket joints (hip, shoulder) move in many directions; some joints, such as those in the skull, are fixed.
- Tendons join muscles to bones. Muscles can only pull (contract), so they work in antagonistic pairs.
- To bend the arm, the biceps contracts and the triceps relaxes. To straighten it, the triceps contracts and the biceps relaxes.
Breathing
- Air passes through the nose or mouth, down the trachea (windpipe, kept open by rings of cartilage), into the bronchi, then the bronchioles, and finally the alveoli (tiny air sacs).
- Breathing in: the intercostal muscles contract, moving the ribs up and out; the diaphragm contracts and flattens. The volume of the chest increases, the pressure falls, and air is drawn in.
- Breathing out: the muscles relax, the ribs move down and in, and the diaphragm domes upwards. The volume decreases, the pressure rises, and air is pushed out.
Gas exchange
- In the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses out of the blood.
- Alveoli are adapted for this: a huge surface area, thin walls (one cell thick), a good blood supply and a moist lining.
Drugs and organ donation
- A drug is a substance that changes the way the body works. Medicinal drugs treat illness (paracetamol for pain, antibiotics for bacterial infections). Recreational drugs are taken for enjoyment (caffeine, alcohol, nicotine) and some are illegal.
- Drugs can have side effects and can be addictive.
- Smoking: tar causes cancer and damages the alveoli; nicotine is addictive; carbon monoxide reduces the oxygen the blood can carry; the smoke damages the cilia that clean the airways.
- Alcohol slows reaction times and can damage the liver and brain.
- Organ donation: in an opt-in system, people register if they want to donate; in an opt-out system, everyone is a donor unless they say no. People debate consent, religious beliefs and the shortage of organs.
Key terms
- Skeleton
- The bones that support and protect the body and help it move.
- Joint
- A place where two bones meet.
- Ligament
- Joins bone to bone at a joint.
- Tendon
- Joins a muscle to a bone.
- Antagonistic muscles
- A pair of muscles that pull in opposite directions.
- Trachea
- The windpipe, which carries air to the lungs.
- Bronchi
- The two tubes that branch off the trachea into the lungs.
- Alveoli
- Tiny air sacs in the lungs where gas exchange happens.
- Diaphragm
- A sheet of muscle below the lungs that helps with breathing.
- Intercostal muscles
- Muscles between the ribs.
- Gas exchange
- Oxygen entering the blood and carbon dioxide leaving it.
- Drug
- A substance that changes the way the body works.
- Addiction
- Needing a drug and finding it hard to stop taking it.