Chapter 16 Answers: Excretory System

16.2 Organs of Excretion: Review Questions and Answers

  1. What is excretion, and what is its significance? Excretion is the process of removing wastes and excess water from the body. It is an essential process in all living things and a major way the human body maintains homeostasis.
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  3. Describe the excretory functions of the liver. The liver detoxifies and breaks down many substances in the blood including toxins. The liver also excretes bilirubin, a waste product of hemoglobin catabolism, in bile, which is eventually excreted in feces by the large intestine.
  4. What are the main excretory functions of the large intestine? The main excretory function of the large intestine is to eliminate solid waste that remains after food is digested and water is extracted from the indigestible matter.
  5. List organs of the urinary system. Organs of the urinary system include the kidneys, ureters, urinary bladder, and urethra.
  6. Describe the physical states in which the wastes from the human body are excreted. Wastes excreted from the human body include solids, liquids, and gases.
  7. Give one example of why ridding the body of excess water is important. Answers may vary. Sample answer: One example of why it is important to rid the body of excess water is that the correct volume of extracellular fluid needs to be maintained, which is important for homeostasis throughout the body.
  8. What gives feces its brown colour? Why is that substance produced?Bilirubin, which is produced from the breakdown of hemoglobin from dead red blood cells.

    16.3 Introduction to the Urinary System: Review Questions and Answers

    1. Self-marking
    2. State the main function of the urinary system. The main function of the urinary system is to eliminate the waste products of metabolism from the body by forming and excreting urine.
    3. What are nephrons? Nephrons are the tiny structural and functional units of the kidneys that filter blood, reabsorb needed materials, and form urine. There are at least a million nephrons in each kidney.
    4. Other than the elimination of waste products, identify functions of the urinary system. Besides the elimination of waste products, functions of the urinary system include maintaining homeostasis of mineral ions in extracellular fluid, regulating acid-base balance in the blood, regulating the volume of extracellular fluids, and controlling blood pressure.
    5. How is the formation of urine regulated? The formation of urine is regulated by endocrine hormones, including antidiuretic hormone from the posterior pituitary gland, parathyroid hormone from the parathyroid glands, and aldosterone from the adrenal glands.
    6. Explain why it is important to have voluntary control over the sphincter at the end of the urethra. It is important to have voluntary control over the sphincter at the end of the urethra, because it allows us to control when and where we urinate. You know, so we don’t pee our pants.
    7. In terms of how they affect the kidneys, compare aldosterone to antidiuretic hormone. Both aldosterone and antidiuretic hormone cause the kidneys to excrete less water in urine. Aldosterone additionally causes less sodium to be excreted as well.
    8. If your body needed to retain more calcium, which of the hormones described in this concept is most likely to increase? Explain your reasoning. Parathyroid hormone, because it causes less calcium to be excreted in urine and therefore more is retained by the body.

      16.4 Kidneys: Review Questions and Answers

      1. Self-marking
      2. Contrast the renal artery and renal vein. A renal artery connects each kidney with the aorta and transports unfiltered blood to the kidney. A renal vein connects each kidney with the inferior vena cava and transports filtered blood back to the circulation.
      3. Identify the functions of a nephron. Describe in detail what happens to fluids (blood, filtrate, and urine) as they pass through the parts of a nephron. The functions of a nephron are filtering materials out of the blood, allowing needed materials to be absorbed back into the blood, and secreting additional materials from the blood to form urine. As blood passes through capillaries in the glomerulus, substances are filtered out of blood and pass into Bowman’s capsule and then the renal tubule. The filtered substances form a fluid called filtrate. As filtrate passes through the renal tubule, some substances are reabsorbed into the blood from the filtrate, and other substances are secreted from the blood into the filtrate, forming urine.
      4. Identify two endocrine hormones secreted by the kidneys, along with the functions they control. The kidneys secrete the endocrine hormones calcitriol, which helps control the blood calcium level; and erythropoietin, which stimulates the bone marrow to produce of red blood cells.
      5. Name two regions in the kidney where water is reabsorbed. Two regions in the kidney where water is reabsorbed are: from the renal tubule into the peritubular capillaries and from the collecting ducts.
      6. Is the blood in the glomerular capillaries more or less filtered than the blood in the peritubular capillaries? Explain your answer. Blood in the glomerular capillaries is less filtered than blood in the peritubular capillaries because it is just starting to be filtered in the glomerular capsule. Blood in the peritubular capillaries comes in large part from filtered blood that is reabsorbed from the renal tubule.
      7. What do you think would happen if blood flow to the kidneys is blocked? Answers will vary. Sample answer: If blood flow to the kidneys is blocked, I think that wastes would build up in the blood, as well as excess water and ions. This would be very dangerous and potentially deadly.

        16.5 Ureters, Urinary Bladder, and Urethra: Review Questions and Answers

        1. What are ureters?  Describe the location of the ureters relative to other urinary tract organs. Ureters are tube-like structures that are part of the urinary system.
        2. Identify layers in the walls of a ureter. How do they contribute to the ureter’s function? The walls of the ureter contain smooth muscle that can contract to push urine through the ureter by peristalsis. They are lined with transitional epithelium that can expand and stretch to allow urine to pass through.
        3. Describe the urinary bladder. What is the function of the urinary bladder? The urinary bladder is a hollow, muscular organ that rests on the pelvic floor. It is lined with transitional epithelium. The function of the urinary bladder is to collect and store urine from the kidneys before the urine is eliminated through urination.
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        5. How does the nervous system control the urinary bladder? As the urinary bladder fills with urine, the autonomic nervous system causes the detrusor muscle in the bladder wall to relax so the bladder can hold more urine. Once the bladder is about half full, it triggers the sensation of needing to urinate. When the individual is ready to void, conscious control by the somatic nervous system causes the detrusor muscle to relax and the bladder sphincter to contract and open. This forces urine out of the bladder and allows it to flow into the urethra.
        6. What is the urethra? The urethra is a tube that connects the urinary bladder to the external urethral orifice.
        7. How does the nervous system control urination? Somatic nerves control the sphincter at the distal end of the urethra. This allows the opening of the sphincter for urination to be under voluntary control.
        8. Identify the sphincters that are located along the pathway from the ureters to the external urethral orifice. The first sphincter is at the entrance of the bladder. Next, the internal urethral sphincter is at the base of the bladder and allows urine to flow into the urethra when open. Finally the external urethral sphincter controls the flow of urine out of the body.
        9. What are two differences between the male and female urethra? The male urethra is longer than the female urethra because it travels through the penis. The male urethra also carries semen in addition to urine.
        10. When the bladder muscle contracts, the smooth muscle in the walls of the urethra relax.

          16.6 Disorders of the Urinary System: Review Questions and Answers

          1. Self-marking
          2. Define kidney failure. Kidney failure is a condition that may be caused by diabetic nephropathy, PKD, or chronic hypertension in which the kidneys are no longer able to adequately filter metabolic wastes from the blood.
          3. When kidney function drops below the level needed to sustain life, what are potential treatments for kidney failure? Potential treatments for kidney failure when kidney function drops below the level needed to sustain life include kidney transplantation or repeated, frequent hemodialysis.
          4. Describe hemodialysis. Hemodialysis is a medical procedure in which a patient’s blood is filtered artificially through a machine and then returned to the patient’s circulation.
          5. How may a large kidney stone be removed from the body? A large kidney stone may be shattered with high-intensity ultrasound into pieces small enough to pass through the urinary tract, or it may be removed surgically.
          6. How are bladder infections usually treated? A bladder infection is generally caused by bacteria, so treatment usually includes antibiotic drugs.
          7. Why are bladder infections much more common in females than in males? Bladder infections are much more common in females than in males because the female urethra is much shorter and closer to the anus.
          8. Compare and contrast stress incontinence and urge incontinence. Stress incontinence is caused by stretching of pelvic floor muscles during childbirth. It involves leakage of small amounts of urine when coughing, sneezing, or lifting. Urge incontinence is caused by an “overactive bladder” that empties without warning. It involves leakage of large amounts of urine while experiencing a sudden urge to urinate.
          9. Why is the presence of a protein(such as albumin) in the urine a cause for concern? Proteins such as albumin are not usually filtered out of the blood in the glomeruli of the kidneys. When the glomerular capillaries are damaged, it allows albumin to leak into the filtrate from the blood. As a result, albumin ends up being excreted in the urine. Therefore, the presence of proteins such as albumin in the urine is a cause for concern because it may indicate that there is a problem with kidney function.
          10. Patients undergoing hemodialysis usually have to do this procedure a few times a week. Why does it need to be done so frequently? Answers may vary. Sample answer: Hemodialysis artificially filters the blood when kidney function is significantly impaired. It needs to be done frequently because wastes build up continually in the blood as the body carries out its functions. Therefore, these wastes need to be removed frequently to avoid health problems or even death.

            16.7 Case Study Conclusion and Chapter Summary: Review Questions and Answers

            1. Self-marking
            2. In what ways can the alveoli of the lungs be considered analogous to the nephrons of the kidney? Answers may vary. Sample answer: Both the alveoli and the nephrons are tiny functional units within a larger organ that take wastes from the blood and excrete them. The alveoli are in the lungs and excrete waste gases, while the nephrons are in the kidneys and excrete wastes in urine.
            3. What is urea? Where is urea produced, and what is it produced from? How is urea excreted from the body? Urea is a waste product produced by the body as a result of protein catabolism. Urea is produced in the liver from ammonia, which is a by-product of protein catabolism. Urea is mainly excreted in the urine after being filtered out from the blood by the kidney, but small amounts are also excreted in sweat.
            4. If a person has a large kidney stone preventing urine that has left the kidney from reaching the bladder, where do you think this kidney stone is located? Explain your answer. The kidney stone is located in a ureter because the ureters connect the kidney to the bladder.
            5. As it relates to urine production, explain what is meant by “Excretion = Filtration – Reabsorption + Secretion. “Excretion = Filtration – Reabsorption + Secretion” means that what is excreted from the kidney in the form of urine is the product of what is filtered out by the nephron (filtrate), minus what is reabsorbed back into the body from the filtrate, plus what is secreted from the blood into the filtrate.
            6. Which disease discussed in the chapter specifically affects the glomerular capillaries of the kidneys? Where are the glomerular capillaries located within the kidneys, and what is their function? Diabetic nephropathy. The glomerular capillaries are located in the nephrons of the kidney. Their function is to filter substances out of the blood and into the Bowman’s capsule.
            7. Describe one way in which the excretory system helps maintain homeostasis in the body. Answers will vary. Sample answer: One way in which the excretory system helps maintain homeostasis in the body is by regulating water and salt balance through the function of the kidneys.
            8. High blood pressure can both contribute to the development of kidney disorders and be a symptom of kidney disorders. What is a kidney disorder that can be caused by high blood pressure? Kidney failure. What is a kidney disorder that has high blood pressure as a symptom? Polycystic kidney disease. How does blood pressure generally relate to the function of the kidney? The kidneys help regulate blood pressure by regulating the amount of water and salts in the blood. Because blood flows into the kidney to be filtered, changes in blood pressure (such as hypertension) can affect the functioning of the kidney itself.
            9. If the body is dehydrated, what do the kidneys do? What does this do to the appearance of the urine produced? If the body is dehydrated, the kidneys retain more water, releasing less into the urine. This causes the urine to appear darker and more concentrated.
            10. Identify three risk factors for the development of kidney stones. Answers will vary. Sample answer: Three risk factors for the development of kidney stones are: high consumption of cola soft drinks, not drinking enough fluids, and being overweight.


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            Human Biology by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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