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Fundamentals · chapter 26 · Urinary Elimination

Functions of the Urinary System

The 14 things this section of the textbook says that you are most likely to be asked about — quoted word for word, not retold. Then 6 practice questions with the reasoning.

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Key points

  1. Kidneys excrete waste

    The kidneys play a pivotal role in filtering the bloodstream to selectively excrete these waste substances.

  2. Urea and ammonia

    The liver converts ammonia into urea, which is less toxic and more water soluble, making it easier for the kidneys to filter and eliminate from the body (Mayo Clinic, 2023).

  3. Creatinine and kidney function

    Like urea, creatinine is filtered by the kidneys and excreted in urine, and creatinine levels in the blood and urine serve as important indicators of kidney function.

  4. Elevated creatinine meaning

    Elevated creatinine levels may suggest impaired kidney function, as the kidneys may be struggling to effectively filter and eliminate this waste product.

  5. Uric acid complications

    This heightened concentration can lead to the formation of urate crystals.

  6. Fluid electrolyte acid-base balance

    The urinary system contributes significantly to overall physiological stability as a pivotal regulator of the body’s fluid, electrolyte, and acid-base balance.

  7. Urine composition processes

    These processes collectively determine the composition of urine, allowing for the precise regulation of electrolyte levels and fluid volume and the removal of metabolic waste.

  8. Renal pH regulation

    Through selective processes in the renal tubules, acidic hydrogen ions and alkaline bicarbonate ions are regulated to help control the body’s pH.

  9. Tubular reabsorption role

    In subsequent tubular reabsorption, the kidneys selectively reclaim crucial substances, including sodium, potassium, and water, redirecting them back into the bloodstream to prevent excessive loss (Preminger, 2022).

  10. Kidneys regulate physiologic parameters

    Importantly, this dynamic interplay contributes significantly to the body’s ability to regulate key physiological parameters such as blood volume, blood pressure, and electrolyte concentrations (Preminger, 2022).

  11. Acid-base ion control

    The kidneys play a pivotal role in regulating acid-base balance by selectively excreting hydrogen ions (H +) and reabsorbing bicarbonate ions (HCO 3 –) in the renal tubules.

  12. Renin release trigger

    When the kidneys detect reduced blood flow or low blood pressure, they release the enzyme renin.

  13. Angiotensin II effects

    Notably, angiotensin II exerts a potent vasoconstrictor effect, causing the narrowing of blood vessels, thereby elevating blood pressure (Fountain et al., 2023).

  14. Erythropoietin and RBCs

    Erythropoietin then travels to the bone marrow, where RBCs are formed, and stimulates an increase in the production of RBCs.

Terms to know

urea
As you learned in the previous section, urea is a nitrogenous waste product that forms in the liver during the breakdown of proteins and amino acids.
creatinine
Another waste product, creatinine, results from the breakdown of creatine phosphate, which is used as an energy source in muscle cells.
uric acid
A chemical compound, uric acid is generated as a by-product during the breakdown of a compound called a purine, which is a naturally occurring substance found in the body’s cells and in specific foods, such as organ meats, seafood, and certain vegetables.
urate crystal
A urate crystal is a solid structure that has the potential to accumulate in joints and other tissues, giving rise to conditions such as gout, a type of arthritis characterized by intense pain, swelling, and tenderness in the joints, often affecting the big toe (El Ridi Tallima, 2017).
RAAS
RAAS is a complex hormonal cascade that plays a crucial role in regulating blood pressure, electrolyte balance, and fluid volume within the body.
renin
An enzyme synthesized and discharged by specialized juxtaglomerular cells in the kidneys, renin is a key player in the intricate regulatory system known as the renin-angiotensin-aldosterone system (RAAS).
erythropoiesis
This regulatory mechanism, known as erythropoiesis, is vital for maintaining the oxygen-carrying capacity of the blood and ensuring homeostasis within the circulatory system.
erythropoietin (EPO)
A glycoprotein hormone, erythropoietin (EPO) plays a crucial role in the regulation of RBC production.

Practice questions

Stuck on select-all-that-apply? How to take them one option at a time.

The graded version needs JavaScript. Every question is below anyway, with the answer and why.

Every question here, with the answer

  1. A nurse reviews a patient’s laboratory trends and notes an elevated creatinine level. Which interpretation is most appropriate based on the urinary system’s function?

    1. The liver is failing to convert ammonia into urea.
    2. The bladder is unable to store urine before controlled release.
    3. The patient is producing too many red blood cells in response to hypoxia.
    4. The kidneys may be struggling to filter and eliminate this waste product effectively.

    Answer: The kidneys may be struggling to filter and eliminate this waste product effectively.

    Creatinine is filtered by the kidneys and excreted in urine, so elevated levels can indicate impaired kidney filtration. The other options relate to urea formation, red blood cell production, or urine storage rather than the meaning of elevated creatinine.

  2. A nurse is planning care for a patient with a kidney condition affecting fluid and electrolyte balance. Which actions align with the QSEN principles described in this section? Select all that apply.

    1. Focus only on urine output and ignore risks from fluid or electrolyte imbalances.
    2. Tailor interventions to the patient’s individualized kidney-function needs.
    3. Participate in evaluating and improving protocols related to kidney care.
    4. Use evidence-based information when assessing and managing the patient.
    5. Manage the patient’s kidney-related needs without involving other healthcare team members.

    Answer: Tailor interventions to the patient’s individualized kidney-function needs., Participate in evaluating and improving protocols related to kidney care., Use evidence-based information when assessing and managing the patient.

    The section connects urinary-system regulation with patient-centered care, evidence-based practice, quality improvement, teamwork, and patient safety. Working in isolation or ignoring imbalance-related complications conflicts with those QSEN principles.

  3. A patient asks how the urinary system helps prevent harmful shifts in body pH. Which explanation should the nurse give?

    1. The kidneys increase red blood cell production to directly correct alkalosis.
    2. The kidneys form urate crystals to remove excess bases from the blood.
    3. The bladder selectively filters electrolytes before urine leaves the body.
    4. The kidneys regulate hydrogen ions and bicarbonate ions to help control blood pH.

    Answer: The kidneys regulate hydrogen ions and bicarbonate ions to help control blood pH.

    The section states that the kidneys help maintain acid-base balance by selectively excreting hydrogen ions and reabsorbing bicarbonate ions. Urate crystals are related to uric acid and gout, while bladder storage and RBC production are not the described acid-base mechanism.

  4. A nurse is teaching a student how the kidneys refine urine composition to support fluid and electrolyte balance. Which processes should the nurse include? Select all that apply.

    1. Erythropoietin release
    2. Urate crystal accumulation
    3. Glomerular filtration
    4. Tubular secretion
    5. Tubular reabsorption

    Answer: Glomerular filtration, Tubular secretion, Tubular reabsorption

    The section identifies filtration, reabsorption, and secretion as the coordinated kidney processes that refine urine composition. Erythropoietin release relates to RBC production, and urate crystal accumulation is a complication of elevated uric acid, not a normal urine-refining process.

  5. A patient has reduced blood flow to the kidneys and low blood pressure. Which kidney response is expected as part of blood pressure regulation?

    1. Form urate crystals to stimulate aldosterone release.
    2. Release renin to begin a cascade that can increase blood pressure.
    3. Convert ammonia into urea to increase blood volume.
    4. Release erythropoietin to narrow blood vessels immediately.

    Answer: Release renin to begin a cascade that can increase blood pressure.

    When the kidneys detect reduced blood flow or low blood pressure, they release renin, which initiates the RAAS pathway. Erythropoietin is related to RBC production, ammonia conversion occurs in the liver, and urate crystals are associated with gout.

  6. A nurse is explaining erythropoietin to a patient with low oxygen levels in the blood. Which statements are accurate? Select all that apply.

    1. Erythropoietin stimulates the bone marrow to produce and release more RBCs.
    2. Erythropoietin causes urate crystals to accumulate in joints.
    3. Erythropoietin is produced primarily by the kidneys.
    4. Low oxygen levels in the blood can trigger erythropoietin release.
    5. Erythropoietin directly filters urea, creatinine, and uric acid from the blood.

    Answer: Erythropoietin stimulates the bone marrow to produce and release more RBCs., Erythropoietin is produced primarily by the kidneys., Low oxygen levels in the blood can trigger erythropoietin release.

    Erythropoietin is mainly produced by the kidneys in response to low oxygen levels and stimulates the bone marrow to increase RBC production. Filtering waste products and urate crystal formation are separate urinary-system topics, not functions of erythropoietin.

Where every quote comes from

Section 26.2 Functions of the Urinary System of Fundamentals of Nursing by Christy Bowen, Lindsay Draper, Heather Moore, OpenStax, 2024. Read the whole section free at openstax.org.

The textbook is licensed under CC BY-NC-SA 4.0. This page quotes it word for word and adds the headings, the order and the practice questions; references to the book's figures and stray spaces left by its formatting are removed. The page is shared under the same licence. Nothing here is sold.