Biology (university) · Part 09
Animal physiology
How the body keeps conditions steady, sends signals, moves blood and gases, and fights infection.
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- HomeostasisKeeping the internal conditions of the body within a narrow range, such as temperature, blood sugar and water level. Most of it uses negative feedback: a change triggers a response that reverses the change.
- Action potentialA brief electrical signal travelling along a neuron. At rest, the inside is negative (about -70 millivolts). A stimulus opens sodium channels, sodium rushes in and the cell depolarises. Then potassium channels open, potassium leaves and the neuron resets.
- SynapseThe gap between two neurons. When the signal arrives, calcium enters the sending cell and vesicles release neurotransmitter, which crosses the gap and binds receptors on the next cell, starting a new signal.
- HormoneA chemical messenger made by an endocrine gland, carried in the blood, and acting on target cells with the right receptors. Hormone effects are slower but last longer than nerve signals.
- Double circulationMammals pump blood through two loops. The right side sends blood to the lungs to pick up oxygen. The left side sends oxygen-rich blood to the body. The heart has four chambers to keep the two kinds of blood apart.
- Oxygen transportHaemoglobin in red blood cells binds oxygen in the lungs, where oxygen is plentiful, and releases it in tissues, where oxygen is low. Each haemoglobin carries up to four oxygen molecules. More acidic, warmer tissues make it release oxygen more readily.
- NephronThe working unit of the kidney. Blood is filtered in the glomerulus, then the tubule takes back useful substances (water, glucose, salts) and leaves wastes such as urea in urine. Antidiuretic hormone (ADH) controls how much water is taken back.
- Adaptive immunityThe part of the immune system that learns. B cells make antibodies that bind specific antigens. T cells kill infected cells or help other cells. Memory cells remain after infection, so a second infection is met quickly.
- Innate immunityThe body's fast, general defences present from birth: skin and mucus barriers, inflammation, and cells such as phagocytes that engulf germs. It reacts the same way each time and has no memory.