The correct option is
D. nephron.
Detailed Explanation:
- Understanding the Structure of the Kidney:
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The mammalian kidney is a complex organ responsible for filtering blood, removing waste, and regulating water and electrolyte balance. It consists of various structures, but the functional unit is the nephron.
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What is a Nephron?:
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A nephron is the basic structural and functional unit of the kidney. Each kidney contains approximately one million nephrons. Each nephron is responsible for the processes of filtration, reabsorption, secretion, and excretion.
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Components of a Nephron:
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A nephron consists of several key parts:
- Renal Corpuscle: This includes the glomerulus (a network of capillaries) and the Bowman's capsule (the cup-like structure that encases the glomerulus).
- Renal Tubule: This is divided into three segments: the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule. Each segment has specific functions in reabsorbing water, ions, and nutrients back into the bloodstream.
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Function of the Nephron:
- The nephron filters blood to form urine. The process begins in the glomerulus, where blood pressure forces water and solutes out of the blood and into the Bowman's capsule. This filtrate then travels through the renal tubule, where essential substances are reabsorbed, and waste products are secreted into the filtrate, ultimately forming urine.
Why the Other Options are Incorrect:
- A. Urethra:
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The urethra is a tube that carries urine from the bladder to the outside of the body. It is not involved in the filtration or processing of blood; therefore, it is not a functional unit of the kidney.
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B. Malpighian Capsule:
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The term "Malpighian capsule" is often confused with the Bowman's capsule. However, it is not a commonly used term in mammalian biology. The correct term is Bowman's capsule, which is part of the nephron but not the entire functional unit. Thus, this option is misleading.
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C. Glomerulus:
- The glomerulus is a crucial part of the nephron, specifically involved in the filtration of blood. However, it is only one component of the nephron and does not represent the entire functional unit. The nephron includes both the glomerulus and the renal tubule, making it the correct answer.
Summary of Key Points:
- The nephron is the functional unit of the mammalian kidney, responsible for filtering blood and forming urine.
- Each nephron consists of a renal corpuscle (glomerulus and Bowman's capsule) and a renal tubule (proximal tubule, loop of Henle, distal tubule).
- The urethra is a passage for urine, not a functional unit; the glomerulus is part of the nephron, not the whole unit; and "Malpighian capsule" is not a standard term in this context.
- Understanding the structure and function of the nephron is essential for grasping kidney physiology and its role in homeostasis.