Biology: Structure and Function of the Human Body
Human body questions are diagram-driven, but every diagram reduces to one idea: structure matches function.
Digestion and absorption
- だ液アミラーゼ: デンプン → 麦芽糖, fastest near 37 °C, inactivated by boiling.
- ペプシン (stomach, acidic) and トリプシン (pancreas): proteins → peptides → amino acids.
- 胆汁 is made in the liver and stored in the 胆のう; it emulsifies fat but is not an enzyme.
- Absorption occurs through the 小腸の柔毛: glucose and amino acids pass into blood, fats first into lymph.
Respiration and circulation
- 肺胞 is thin-walled and wrapped in capillaries for gas exchange; 細胞呼吸 uses oxygen and glucose to release energy.
- The heart has four chambers; the left ventricle wall is thickest because it pumps blood around the whole body.
- 肺循環: right ventricle → lungs → left atrium. 体循環: left ventricle → body → right atrium.
- 動脈 carries blood away from the heart, so 肺動脈 carries oxygen-poor blood; 'artery = oxygen-rich' is false.
Excretion and control
The liver converts ammonia into urea and the kidneys filter it out. Reflexes are handled by the spinal cord without waiting for the brain.
Worked example. Blood leaving the left ventricle carries about 20 cm³ O₂ per 100 cm³; blood returning to the right atrium carries about 15 cm³. The 5 cm³ difference was delivered to tissues, which is why the left ventricle needs the thickest muscle.
Traps. Saying 胆汁 digests fat; starting 肺循環 from the left ventricle; forgetting 血小板 and 血しょう in blood composition; defining 動脈 and 静脈 by oxygen content instead of direction of flow.