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

Renal Physiology Step 1: Glomerular Filtration

Anatomy & Physiology

25. The Urinary System

Renal Physiology Step 1: Glomerular Filtration

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Problem 23

Textbook Question

What primary changes occur in the composition and concentration of filtrate as a result of activity in the proximal convoluted tubule?

Verified step by step guidance

Understand the role of the proximal convoluted tubule (PCT) in the nephron: The PCT is responsible for reabsorbing essential substances from the filtrate back into the bloodstream and secreting waste products into the filtrate.

Identify the substances reabsorbed in the PCT: Approximately 65-70% of water, sodium ions (Na⁺), chloride ions (Cl⁻), glucose, amino acids, and bicarbonate (HCO₃⁻) are reabsorbed here. This process reduces the concentration of these substances in the filtrate.

Recognize the secretion of waste products: The PCT actively secretes hydrogen ions (H⁺), ammonia (NH₃), and certain drugs or toxins into the filtrate, increasing their concentration in the filtrate.

Understand the mechanism of reabsorption: Reabsorption in the PCT occurs through active transport (e.g., sodium-potassium pumps for Na⁺), facilitated diffusion (e.g., glucose transporters), and osmosis (for water). This ensures the filtrate composition changes significantly as it moves through the PCT.

Summarize the changes in filtrate composition: By the end of the PCT, the filtrate is significantly reduced in volume due to water reabsorption, has lower concentrations of nutrients and ions like Na⁺ and Cl⁻, and has higher concentrations of waste products like H⁺ and NH₃.

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Key Concepts

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

Proximal Convoluted Tubule (PCT)

The proximal convoluted tubule is a segment of the nephron in the kidney responsible for the reabsorption of water, ions, and nutrients from the filtrate back into the bloodstream. It plays a crucial role in maintaining homeostasis by adjusting the composition of the filtrate, ensuring that essential substances are retained while waste products are excreted.

Filtrate Composition

Filtrate composition refers to the mixture of substances that pass through the glomerulus into the nephron. Initially, it contains water, electrolytes, glucose, amino acids, and waste products. As the filtrate moves through the PCT, significant reabsorption occurs, altering its composition by reducing the concentration of valuable substances while concentrating waste.

Reabsorption Mechanisms

Reabsorption mechanisms in the PCT involve both passive and active transport processes that facilitate the movement of substances from the filtrate back into the blood. This includes the use of transport proteins and channels for ions and nutrients, as well as osmotic gradients that drive water reabsorption, ultimately affecting the concentration and composition of the filtrate.

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