THE FUNCTION OF THE KIDNEY The diagram below represents blood entering and leaving a nephron, the functional unit of the kidney. Area A shows the blood entering the kidney, Area B shows the blood after filtration. Area C shows the blood after re-absorption. Area E shows the location of the formation of urine and secretion. Some of the contents of the blood and the filtrate are indicated in the key. Study the function of the kidney using the following guiding questions: The movement of materials from the glomerulus (A) to Bowman’s capsule (C) is called filtration. What substances are found in the filtrate (fluid in the capsule)? What substances do not pass out of the blood? Why do some substances pass and some do not pass to the Bowman’s capsule? Re-absorption of useful materials occurs in the tubules (area D) . What substances are reabsorbed back into the blood by the tubules? (Guidance: you can find them also by comparing the content of the filtrate and the resulting urine). What substances are found in the resulting urine? For each of the substances you mentioned in 5 – what is the purpose of that substance being in the urine?

Reabsorption of water occurs as the filtrate passes through the collecting tubule. Antidiuretic hormone (ADH), released into the blood by the posterior gland, makes the collecting tubule more permeable to water. As the level of ADH in the blood increases, more water is released from the collecting tubule back into the blood. 7. Which of the diagrams above shows the collecting tubule under the influence of a high level of ADH? Copy that diagram next to your answer. 8. In which circumstances would you expect ADH to be high in the blood? Caffeine inhibits (blocks) the effect of ADH and is therefore considered a diuretic. A diuretic causes the production of a large volume of urine. 9. Which diagram shows the effects of a high-level of caffeine in the blood? Copy that diagram next to your answer. The tubule of the nephron is capable of reabsorbing from the filtrate a maximum of 375 milligram of glucose per minute. If more glucose is present in the filtrate than can be reabsorbed, the glucose will remain in the filtrate. People with untreated diabetes mellitus may have a high glucose level in their blood. 10. Which diagram illustrates the urine of a patient is diabetic? Copy it next to your answer. One of the effects of Alcohol is to reduce the release of ADH in the brain (which would explain why you have a larger urine volume when you drink alcohol). 11. Which diagram illustrates the urine of a person that drank alcohol? Copy it next to your answer.