Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

25. The Urinary System

The Kidneys

Anatomy & Physiology

25. The Urinary System

The Kidneys

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Problem 24

Textbook Question

Describe two functions of countercurrent multiplication in the kidney.

Verified step by step guidance

Understand the concept of countercurrent multiplication: Countercurrent multiplication is a mechanism in the kidney that helps concentrate urine and maintain water and electrolyte balance. It occurs in the loop of Henle, where the descending and ascending limbs interact to create a gradient of solute concentration in the medulla.

Identify the first function: Countercurrent multiplication helps establish a concentration gradient in the renal medulla. This gradient is essential for the kidney's ability to reabsorb water from the collecting ducts, especially under the influence of antidiuretic hormone (ADH).

Identify the second function: Countercurrent multiplication facilitates the reabsorption of sodium and chloride ions in the ascending limb of the loop of Henle. This process contributes to the osmotic gradient and helps regulate electrolyte balance in the body.

Relate the functions to physiological importance: The concentration gradient created by countercurrent multiplication is crucial for producing concentrated urine, which prevents excessive water loss and maintains homeostasis in the body.

Summarize the mechanism: Countercurrent multiplication relies on the permeability differences between the descending limb (permeable to water but not solutes) and the ascending limb (impermeable to water but actively transports solutes). This interaction amplifies the medullary concentration gradient, supporting the kidney's role in water and solute regulation.

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Key Concepts

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

Countercurrent Multiplication

Countercurrent multiplication is a mechanism in the kidney that enhances the concentration of urine. It involves the interaction between the descending and ascending limbs of the loop of Henle, where the flow of filtrate in opposite directions creates a gradient that allows for the reabsorption of water and solutes, ultimately concentrating urine.

Osmotic Gradient

The osmotic gradient is the difference in solute concentration across the renal medulla, which is crucial for water reabsorption. As the filtrate moves through the loop of Henle, the ascending limb actively transports sodium and chloride ions out, creating a high osmolarity in the surrounding interstitial fluid, which draws water out of the descending limb and collecting ducts.

Urine Concentration

Urine concentration refers to the kidney's ability to produce urine with varying levels of solute concentration, depending on the body's hydration status. Countercurrent multiplication plays a vital role in this process by allowing the kidneys to conserve water and excrete waste efficiently, thus maintaining homeostasis and regulating blood osmolarity.