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Ch. 24 The Urinary System
Amerman - Human Anatomy & Physiology 2nd Edition
Amerman2nd EditionHuman Anatomy & PhysiologyISBN: 9780136873822Not the one you use?Change textbook
All textbooksAmerman 2nd EditionCh. 24 The Urinary SystemProblem 13
Chapter 24, Problem 13

Which of the following conditions does not contribute to the creation and/or maintenance of the medullary osmotic gradient?
a. The countercurrent exchanger of the vasa recta
b. The countercurrent multiplier of the nephron loops of cortical nephrons
c. The countercurrent multiplier of the nephron loops of juxtamedullary nephrons
d. The permeability of the medullary collecting system to urea and other ions

Verified step by step guidance
1
Understand the medullary osmotic gradient: The medullary osmotic gradient is a concentration gradient in the kidney's medulla that allows for water reabsorption and urine concentration. It is primarily established and maintained by the countercurrent mechanisms and urea recycling.
Review the role of the countercurrent multiplier: The countercurrent multiplier occurs in the nephron loops of juxtamedullary nephrons. These loops actively transport ions (e.g., Na+ and Cl−) out of the ascending limb, creating a gradient that concentrates the medulla.
Analyze the role of the countercurrent exchanger: The countercurrent exchanger occurs in the vasa recta, the capillaries surrounding the nephron loops. It helps preserve the medullary osmotic gradient by allowing water and solutes to move passively, preventing washout of the gradient.
Evaluate the permeability of the medullary collecting system: The medullary collecting ducts are permeable to urea and other ions under the influence of antidiuretic hormone (ADH). This permeability contributes to the recycling of urea, which further enhances the medullary osmotic gradient.
Identify the incorrect option: The nephron loops of cortical nephrons do not significantly contribute to the medullary osmotic gradient because they are shorter and do not extend deep into the medulla. Therefore, the countercurrent multiplier of cortical nephrons is not involved in creating or maintaining the gradient.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Medullary Osmotic Gradient

The medullary osmotic gradient is a crucial physiological feature of the kidney that allows for the concentration of urine. It is established by the differential permeability of the nephron segments and the countercurrent mechanisms, which create a gradient of osmolarity in the renal medulla. This gradient is essential for the reabsorption of water and solutes, enabling the body to maintain fluid balance.
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Countercurrent Multiplier

The countercurrent multiplier is a mechanism in the nephron, particularly in the loops of Henle, that enhances the osmotic gradient in the renal medulla. It involves the flow of filtrate in opposite directions through the descending and ascending limbs, allowing for the active transport of ions and the passive movement of water. This process is vital for producing concentrated urine and is more pronounced in juxtamedullary nephrons compared to cortical nephrons.
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Vasa Recta

The vasa recta are specialized capillaries that run parallel to the nephron loops and play a key role in maintaining the medullary osmotic gradient. They function as a countercurrent exchanger, allowing for the exchange of water and solutes without dissipating the osmotic gradient established by the nephron. This mechanism ensures that the blood supply to the kidney does not interfere with the concentration of urine, preserving the gradient necessary for effective water reabsorption.
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Related Practice
Textbook Question

Glomerular hydrostatic pressure _____ filtration; colloid osmotic pressure and capsular hydrostatic pressure_____ filtration.

a. Favors; favor

b. Opposes; oppose

c. Favors; oppose

d. Opposes; favor

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Textbook Question

Dilute urine is produced when decreased levels of______ are secreted.

a. Aldosterone

b. Atrial natriuretic peptide

c. ADH

d. None of the above

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Textbook Question

The kidneys produce _____ urine when the osmolarity of the body's fluids increases. They produce _____ urine when the osmolarity of the body's fluids decreases.

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Textbook Question

Normal urine should have which of the following properties? Circle all that apply.

a. Translucency

b. Yellowish pigment

c. Cloudy appearance

d. pH less than 4.5

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Textbook Question

The GFR may be estimated by measuring the rate at which certain substances are removed from the blood, which is known as:

a. Renal clearance

b. Plasma creatinine

c. Glomerular hydrostatic pressure

d. Inulin estimation

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Textbook Question

The route by which substances are reabsorbed by crossing through the cells of the renal tubule and collecting system is known as the:

a. Paracellular route

b. Transcellular route

c. Primary active transport route

d. Facultative route

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