Overview
This lecture explains how the kidneys regulate waste products, ions, and water in the body, focusing on kidney structure and the role of ADH in water balance.
Kidney Functions
- Kidneys filter blood to remove waste and maintain balance of ions and water.
- The main waste product removed is urea, formed in the liver during deamination of excess amino acids.
- Kidneys help maintain correct levels of sodium and potassium ions, which are vital for cell function.
- Ion levels are mainly regulated by kidneys, not through sweating.
Water Regulation and Homeostasis
- Water is gained from food and drink; lost through sweat, breathing, and mainly urine.
- Proper water balance is necessary to prevent cells from swelling (too much water) or shrinking (too little water) due to osmosis.
- Most water loss occurs via urine, regulated by the kidneys.
Kidney Structure and Processes
- Kidneys contain about a million nephrons, each with tubules for filtering blood.
- Filtration: small molecules like water, glucose, amino acids, and urea are filtered; large proteins and cells are not.
- Selective reabsorption: necessary substances (e.g., all glucose, some water) are reabsorbed; urea is not.
Hormonal Control of Water Levels (ADH)
- The hypothalamus in the brain detects water concentration in blood.
- When water levels are low, hypothalamus signals pituitary gland to release ADH (antidiuretic hormone).
- ADH makes kidney tubules reabsorb more water, increasing blood water and reducing urine output.
- If water levels are high, less ADH is released, so less water is reabsorbed and more urine is produced.
Negative Feedback in Water Regulation
- Water regulation by ADH is a negative feedback loop: changes in water levels trigger hormone release that restores balance.
Key Terms & Definitions
- Urea — waste product formed from amino acids in the liver.
- Deamination — process of removing the amino group from amino acids.
- Nephron — functional unit of the kidney that filters blood.
- Filtration — process by which small molecules are separated from the blood in the kidneys.
- Selective Reabsorption — reuptake of useful substances from kidney tubules back into the blood.
- ADH (Antidiuretic Hormone) — hormone that increases water reabsorption in the kidneys.
- Negative Feedback — regulatory mechanism where a change triggers a response that restores balance.
Action Items / Next Steps
- Review kidney structure and nephron function.
- Study the role of hormones, especially ADH, in homeostasis.
- Prepare definitions of key terms for future quizzes.