Human organ systems
The human body is built of cells; cells form tissues (epithelial, connective, muscle, nervous), tissues form organs (heart, lung), and organs form organ systems; the systems together form the whole organism. The book describes seven systems. 1) The supporting and movement system – skeleton and muscles; the skull protects the brain, the rib cage protects the heart and lungs, and blood cells form in bone marrow. To bend the arm, the biceps on the upper arm contracts and the triceps relaxes; to straighten it, the reverse. 2) The circulatory system – the four-chambered heart works as a pump; an artery carries blood away from the heart, a vein brings blood to the heart, and capillaries are tiny vessels among the tissues; blood stays inside vessels (a closed system) and flows in two loops. 3) The digestive system – mouth, pharynx, oesophagus, stomach, intestine. 4) The nervous system – central (brain in the skull, spinal cord in the vertebral canal) and peripheral parts. 5) The respiratory system – nasal cavity, pharynx, trachea, bronchi, alveoli and lungs; gases are exchanged between the alveoli and capillaries. 6) The lymphatic system – lymph nodes, vessels, lymph and the spleen; nodes trap bacteria and viruses and support immunity. 7) The endocrine system – endocrine glands (pituitary, pineal, thyroid, thymus, adrenal glands) that release hormones into the blood. For example, when you are frightened the adrenal gland releases adrenaline, which strengthens the defence reaction. If one system fails, the others are affected too.
Pulse measuring (in pairs): find the pulse with two fingers on the inner wrist on the thumb side, count for 30 seconds and multiply by 2; count again after 10 squats. Record the result in a table. Safety: take the pulse only at the wrist, do not press on the neck; pupils with a heart or breathing condition skip the exercise and only count; stop and sit if dizzy; the teacher supervises.