11.3.1 Identify Major Organs Involved in Homeostasis
The major organs involved in human homeostasis are:
- Skin: Regulates body temperature and water loss.
- Lungs: Maintain oxygen and carbon dioxide levels in the blood.
- Kidneys: Regulate water, electrolyte balance, and blood composition.
11.3.2 Relate the Structure of Skin with Its Function to Regulate Body Temperature
Structure:
- Epidermis: Outer layer with dead cells and keratin, providing a barrier.
- Dermis: Contains sweat glands, blood vessels, and nerve endings.
- Hypodermis: Fat layer for insulation.
Function in Temperature Regulation:
- Sweating: Sweat glands produce sweat, which evaporates to cool the body during overheating.
- Vasodilation/Vasoconstriction: Blood vessels in the dermis dilate (to release heat) or constrict (to conserve heat) based on external temperature.
- Insulation: Hypodermal fat reduces heat loss in cold conditions.
- Hair: Erector pili muscles cause goosebumps, trapping air for insulation in cold weather.
11.3.3 Describe Role of Lungs in Keeping the Carbon Dioxide Concentration Down to a Certain Level
Lungs regulate blood carbon dioxide (CO₂) levels through respiration. During exhalation, CO₂ (a waste product of cellular respiration) is expelled from the blood via alveoli in the lungs. Chemoreceptors in the brain and blood vessels monitor CO₂ levels (and pH). High CO₂ increases blood acidity, triggering faster breathing to expel more CO₂. This maintains blood pH (7.35–7.45) and prevents respiratory acidosis or alkalosis.
Example: During exercise, increased CO₂ production prompts faster breathing to restore normal levels.
11.3.4 Describe Role of Kidneys in Keeping the Blood Composition Constant
Kidneys regulate water, electrolytes, and waste levels in the blood.
Mechanism:
- Filtration: Nephrons filter blood to remove waste (e.g., urea) and excess ions.
- Reabsorption: Essential substances (e.g., glucose, water, sodium) are reabsorbed into the blood.
- Secretion: Excess ions (e.g., H⁺, K⁺) or toxins are secreted into urine.
- Hormonal Regulation: Kidneys produce erythropoietin (for red blood cell production) and renin (for blood pressure regulation) and respond to antidiuretic hormone (ADH) and aldosterone to control water and sodium balance.
- Outcome: Maintains blood pH, osmolarity, and volume, ensuring stable blood composition.