Biology: The Excretory System: Kidneys, Filtration, and Homeostasis
How kidneys filter blood and help maintain internal balance
Biology: The Excretory System: Kidneys, Filtration, and Homeostasis
How kidneys filter blood and help maintain internal balance
Biology - Grade 9-12
- 1
Describe the main functions of the excretory system in humans. Include at least three functions in your answer.
Think about what must stay balanced in the blood for cells to function properly.
The excretory system removes metabolic wastes such as urea, helps regulate water balance, controls salt and ion levels, helps maintain blood pH, and contributes to blood pressure regulation. - 2
A nephron is the functional unit of the kidney. Identify the main job of the nephron and explain why kidneys contain so many nephrons.
A nephron filters blood and forms urine by filtration, reabsorption, and secretion. Kidneys contain many nephrons to provide a large surface area for efficient filtering and precise regulation of blood composition. - 3
Explain what happens during filtration in the glomerulus and Bowman's capsule.
Focus on size and pressure as the reasons substances move or stay behind.
During filtration, blood pressure forces water and small dissolved substances out of the glomerulus and into Bowman's capsule. Blood cells and most large proteins remain in the blood because they are too large to pass through the filtration membrane. - 4
A blood test shows protein in a patient's urine. Explain why this may suggest damage to the kidney's filtration membrane.
Protein in urine may suggest damage to the filtration membrane because healthy glomeruli usually prevent large proteins from leaving the blood. If the membrane is damaged, proteins can leak into the filtrate and appear in urine. - 5
Compare filtration and reabsorption in the nephron. Describe where materials move during each process.
Filtration starts urine formation, while reabsorption helps keep useful materials in the body.
Filtration moves water and small solutes from the blood into Bowman's capsule to form filtrate. Reabsorption moves needed substances such as water, glucose, amino acids, and ions from the nephron tubule back into the blood. - 6
A diagram shows glucose entering the nephron filtrate and then leaving the tubule to return to the blood. Name this process and explain why it is important.
This process is reabsorption. It is important because glucose is a useful nutrient for cellular respiration, so the body normally returns it to the blood instead of losing it in urine. - 7
Explain how secretion differs from reabsorption in urine formation.
Pay attention to the direction materials move between the blood and the nephron tubule.
Secretion moves certain substances from the blood into the nephron tubule, while reabsorption moves needed substances from the tubule back into the blood. Secretion helps remove extra wastes, drugs, hydrogen ions, and excess potassium ions. - 8
A student drinks a large amount of water. Predict how this will affect urine volume and urine concentration if the kidneys are functioning normally. Explain your reasoning.
The student will likely produce a larger volume of more dilute urine. The kidneys remove excess water from the blood to help maintain water balance and keep the internal environment stable. - 9
Antidiuretic hormone, or ADH, increases water reabsorption in the collecting ducts. Predict what happens to urine volume and concentration when ADH levels rise.
ADH helps the body conserve water.
When ADH levels rise, the collecting ducts reabsorb more water into the blood. Urine volume decreases, and the urine becomes more concentrated. - 10
During dehydration, the body must maintain homeostasis. Explain how the kidneys help respond to dehydration.
During dehydration, the kidneys conserve water by increasing water reabsorption, often under the influence of ADH. This produces a smaller amount of more concentrated urine and helps maintain blood volume and cell function. - 11
The table shows two urine samples. Sample A is pale yellow with low solute concentration. Sample B is dark yellow with high solute concentration. Which sample is more likely from a dehydrated person, and why?
Concentrated urine contains less water compared with the amount of dissolved waste.
Sample B is more likely from a dehydrated person because it has a high solute concentration and less water. Dark, concentrated urine often indicates that the kidneys are conserving water. - 12
Urea is a nitrogen-containing waste made when proteins are broken down. Explain how urea travels through the body and leaves it.
Urea is produced mainly in the liver when excess amino acids are broken down. It travels in the blood to the kidneys, where it is filtered into the nephron and eventually leaves the body in urine.