Textbook Question
Name and define the three distinct processes involved in the production of urine.
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Ch. 26 The Urinary System
Martini, Nath, Bartholomew11th EditionFundamentals of Anatomy & PhysiologyISBN: 9780136874089
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Table of contents
- Ch. 1 An Introduction to Anatomy and Physiology26
- Ch. 2 The Chemical Level of Organization34
- Ch. 3 The Cellular Level of Organization30
- Ch. 4 The Tissue Level of Organization24
- Ch. 5 The Integumentary System17
- Ch. 6 Bones and Bone Structure36
- Ch. 7 The Axial Skeleton11
- Ch. 8 The Appendicular Skeleton17
- Ch. 9 Joints13
- Ch. 10 Muscle Tissue12
- Ch. 11 The Muscular System28
- Ch. 12 Nervous Tissue18
- Ch. 13 The Spinal Cord, Spinal Nerves, and Spinal Reflexes22
- Ch. 14 The Brain and Cranial Nerves20
- Ch. 15 Sensory Pathways and the Somatic Nervous System17
- Ch. 16 The Autonomic Nervous System and Higher-Order Functions30
- Ch. 17 The Special Senses16
- Ch. 18 The Endocrine System20
- Ch. 19 Blood31
- Ch. 20 The Heart31
- Ch. 21 Blood Vessels and Circulation29
- Ch. 22 The Lymphatic System and Immunity31
- Ch. 23 The Respiratory System12
- Ch. 24 The Digestive System18
- Ch. 26 The Urinary System31
- Ch. 27 Fluids & Electrolytes32
- Ch. 28 The Reproductive System12
- Ch. 29 Development and Inheritance23
Martini, Nath, Bartholomew11th EditionFundamentals of Anatomy & PhysiologyISBN: 9780136874089Not the one you use?Change textbook
Chapter 25, Problem 16
When the renal threshold for a substance exceeds its tubular maximum:
(a) More of the substance will be filtered
(b) More of the substance will be reabsorbed
(c) More of the substance will be secreted
(d) The amount of the substance that exceeds the tubular maximum will be found in the urine
(e) Both a and d occur
Verified step by step guidance1
Step 1: Understand the key terms involved in the problem. The 'renal threshold' is the plasma concentration level at which a substance begins to appear in the urine because the kidneys cannot reabsorb it all. The 'tubular maximum' (Tm) is the maximum rate at which the renal tubules can reabsorb a substance.
Step 2: Recognize that when the plasma concentration of a substance exceeds the renal threshold, the filtered load of that substance surpasses the tubular maximum reabsorption capacity.
Step 3: Since the tubular maximum is exceeded, the tubules cannot reabsorb all of the filtered substance, so the excess amount remains in the tubular fluid and is excreted in the urine.
Step 4: Analyze the answer choices in this context: (a) More of the substance will be filtered — filtration depends on plasma concentration and glomerular filtration rate, so if plasma concentration increases, filtered load increases; (d) The amount exceeding the tubular maximum will appear in urine because it cannot be reabsorbed.
Step 5: Conclude that the correct understanding is that both more of the substance is filtered (due to higher plasma concentration) and the excess beyond the tubular maximum appears in urine, which corresponds to answer (e).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Renal Threshold
The renal threshold is the plasma concentration level of a substance at which the kidneys begin to excrete it into the urine because reabsorption mechanisms are saturated. Below this threshold, the substance is mostly reabsorbed; above it, excess amounts appear in urine.
Recommended video:
4:35
Transport Maximum (TM) & Renal Threshold
Tubular Maximum (Tm)
Tubular maximum refers to the highest rate at which a substance can be reabsorbed or secreted by the renal tubules. When the filtered load exceeds this maximum, the excess substance cannot be reabsorbed and is excreted in urine.
Recommended video:
4:35Transport Maximum (TM) & Renal Threshold
Relationship Between Renal Threshold and Tubular Maximum
If the renal threshold exceeds the tubular maximum, it means the plasma concentration is high enough that the filtered load surpasses the reabsorption capacity. Consequently, the surplus substance appears in urine, indicating saturation of reabsorption.
Recommended video:
4:35Transport Maximum (TM) & Renal Threshold
Related Practice
Textbook Question
What are the primary effects of angiotensin II on kidney function and regulation?
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Textbook Question
Which structures of the urinary system are responsible for the transport, storage, and elimination of urine?
Textbook Question
Sympathetic activation of nerve fibers in the nephron causes
(a) the regulation of glomerular blood flow and pressure,
(b) the stimulation of renin release from the juxtaglomerular complex,
(c) the direct stimulation of water and Na+ reabsorption,
(d) all of these.
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Textbook Question
When ADH levels rise,
(a) The amount of water reabsorbed increases.
(b) The DCT becomes impermeable to water.
(c) The amount of water reabsorbed decreases.
(d) Sodium ions are exchanged for potassium ions.
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Textbook Question
Sodium reabsorption in the DCT and in the cortical portion of the collecting system is accelerated by the secretion of
(a) ADH
(b) Renin
(c) Aldosterone
(d) Erythropoietin
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