Questions and Answers
Which of the following is a function of the kidneys? (Select all that apply)
What is the basic functional unit of the kidney?
Nephron
What percentage of nephrons are cortical nephrons?
Juxtamedullary nephrons are located in the outer part of the cortex.
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What hormone is produced by the juxtaglomerular cells?
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The ______ is the process of emptying the urinary bladder.
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Match the following types of nephrons with their descriptions:
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What is the typical volume that triggers the micturition reflex?
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What is one function of erythropoietin secreted by the kidneys?
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The renal circulation constitutes a small percentage of cardiac output.
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Study Notes
Kidney Function
- Regulates water and inorganic ion balance in the body.
- Excretes metabolic waste products to maintain homeostasis.
- Eliminates foreign chemicals through urine production.
- Secretes hormones such as:
- Erythropoietin: Stimulates red blood cell production.
- Renin: Secreted by juxtaglomerular cells to regulate angiotensin formation.
- 1,25-dihydroxyvitamin D3: Affects calcium balance.
Anatomical Characteristics of the Kidney
- Composed of three main structures: renal cortex, renal medulla, and renal pelvis.
- Functional unit is the nephron, with approximately 1 million per kidney.
- Each nephron consists of:
- Renal corpuscle (glomerulus and Bowman’s capsule).
- Renal tubule (proximal convoluted tubule, loop of Henle, distal convoluted tubule).
Types of Nephrons
- Cortical nephrons:
- Make up ~85% of all nephrons.
- Located primarily in the cortex.
- Juxtamedullary nephrons:
- Found closer to the medulla.
- Characterized by longer loops of Henle that extend deep into renal pyramids.
Differences Between Cortical and Juxtamedullary Nephrons
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Location:
- Cortical: Outer cortex.
- Juxtamedullary: Inner cortex near medulla.
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Glomerulus Size:
- Cortical: Smaller.
- Juxtamedullary: Larger.
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Loop of Henle Length:
- Cortical: Short.
- Juxtamedullary: Longer.
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Efferent Arteriole:
- Cortical: Forms peritubular capillary.
- Juxtamedullary: Forms vasa recta.
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Sympathetic Nerve Innervation:
- Cortical: Rich.
- Juxtamedullary: Poor.
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Renin Concentration:
- Cortical: High.
- Juxtamedullary: Almost none.
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Functions:
- Cortical: Reabsorption and secretion.
- Juxtamedullary: Concentration and dilution of urine.
Juxtaglomerular Apparatus (JGA)
- Comprises macula densa, juxtaglomerular cells (JGC), and mesangial cells.
- Macula densa detects Na+, K+, and Cl- in tubular fluid, signaling changes.
- JGC, located in afferent arterioles, secretes renin to manage blood pressure and filtration.
Renal Blood Circulation
- Renal blood flow is significant: 1200 ml/min, constituting 1/5 - 1/4 of cardiac output.
- Blood distribution: Cortex receives ~94%, outer medulla 5-6%, and inner medulla 1-2%.
- Daily urine volume varies, reflecting fluid and electrolyte loss.
Micturition and Urinary System Function
- Urine travels from the ureters to the bladder via smooth muscle contractions.
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Micturition Process:
- Bladder fills until pressure exceeds 400-500 ml.
- Initiated by the micturition reflex, which empties the bladder.
- Bladder capacity ranges: 250-400 ml.
- Stretching of bladder walls activates the spinal reflex for urination, involving:
- Parasympathetic stimulation, leading to bladder contraction.
- Opening of the internal and external sphincters.
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Description
Test your understanding of kidney functions including water regulation, metabolic waste excretion, and hormone secretion such as erythropoietin and renin. This quiz covers the key physiological roles of the kidneys in maintaining homeostasis and balanced bodily functions.
