Questions and Answers
Which part of the nephron is primarily responsible for making the urine hypertonic?
What is the defining characteristic of the thick ascending part of the loop of Henle?
What type of epithelial tissue lines the thin ascending part of the loop of Henle?
Which of the following features is NOT associated with the distal convoluted tubules?
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Which structure is hypothesized to actively reabsorb sodium in the kidney?
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What is the primary function of the renal pelvis in the urinary system?
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How are the cells in the distal convoluted tubules described histologically?
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What property of the collecting tubules allows for urine concentration?
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What is the main function of the collecting tubules?
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Which type of epithelium lines the larger collecting tubules?
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What distinguishes the collecting tubules from other parts of the nephron?
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How do extraglomerular mesangial cells function in relation to the renal blood supply?
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What is the structural feature of the collecting tubules as observed under electron microscopy?
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What is the pathway through which urine travels after leaving the collecting tubule?
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What role do chloride ions play in the function of certain renal cells?
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What structural feature characterizes the lumen of collecting tubules?
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What is the primary function of the proximal convoluted tubule in the renal system?
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Which structural characteristic of the proximal convoluted tubule's cells aids in reabsorption?
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What type of cells predominantly line the proximal convoluted tubule?
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What is the average length of the proximal convoluted tubule?
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How does the proximal convoluted tubule primarily absorb water?
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What is the primary appearance of cells in the proximal convoluted tubule when viewed under light microscopy?
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Which product is NOT reabsorbed by the proximal convoluted tubule?
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What characterizes the tubular structure under electron microscopy?
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Study Notes
Renal Structural Components
- Cells display numerous microvilli and a Golgi apparatus positioned infranulearly.
- Lack of a basement membrane is notable.
- Macula densa cells are sensitive to chloride ion content and regulate glomerular filtration by constricting the glomerular afferent arteriole.
- Extraglomerular mesangial cells (also known as Lacis cells) are located between the afferent and efferent arterioles, potentially serving a phagocytic role.
Collecting Tubules
- Collecting tubules are distinct from the nephron and arise from the medullary rays through the union of distal convoluted tubules.
- They integrate into the medullary pyramid, leading to the formation of the straight papillary duct (duct of Bellini), which opens into the minor calyx.
- Minor calyces combine to form major calyces, which lead into the renal pelvis.
- Histological characteristics include:
- Lined with simple cuboidal epithelium in smaller tubules and simple columnar epithelium in larger ones.
- Pale acidophilic cytoplasm, clear cell borders, wide lumen, and centrally located dark nuclei.
- Ultrastructure reveals minimal organelles, few microvilli, and basal infoldings.
- Functionally, the collecting tubules are responsible for water reabsorption regulated by antidiuretic hormone, which concentrates urine before it enters the calyces and ureter.
Efferent Arteriole and Capillary Plexus
- Efferent arterioles connect two capillary beds.
- The first capillary network consists of glomerular capillaries, divided into four segments:
- Thick Descending Limb: Extends from the cortex into the medulla, resembling proximal convoluted tubule structure and function.
- Thin Descending Limb: Located in the medulla, lined with simple squamous epithelium, highly permeable to water and impermeable to sodium, making urine hypertonic.
- Thin Ascending Limb: Also in the medulla, lined with simple squamous epithelium.
- Thick Ascending Limb: Moves from the medulla to cortex, similar in function to the distal convoluted tubule, permeable to sodium but impermeable to water, resulting in hypotonic urine.
Distal Convoluted Tubules
- Continuation from the thick ascending loop of Henle, connecting with collecting tubules in the cortex.
- Histological features include:
- Wide lumen with 5-8 cuboidal cells, less acidophilic than proximal convoluted tubules.
- Rounded nuclei located near the apical surface, no brush border, and distinct cell boundaries.
- Ultrastructure:
- Few short microvilli on the apical surface.
- Basal region contains mitochondria and basal infoldings.
- Functions include preventing molecule passage through filtration slits based on their electrostatic charges.
Proximal Convoluted Tubules
- Begin at the cortex at the urinary pole of the renal corpuscle, highly convoluted before straightening into the loop of Henle.
- Cross-section dimensions: ~60µm in diameter and 14mm in length, with a small lumen.
- Histological features:
- Narrow lumen formed by 4-5 pyramidal cells, strongly acidophilic.
- Rounded nuclei centrally located, pronounced brush border on the apical surface, and indistinct cell boundaries.
- Ultrastructural highlights:
- Apical surface adorned with numerous long microvilli, basal striation from infoldings, and abundant mitochondria aiding in acidophilia.
- Key functions:
- Actively reabsorbs 85% of sodium and water, entirely reabsorbs glucose and amino acids, and uptakes low molecular weight proteins through pinocytosis for conversion to amino acids.
- Excretes specific metabolites, dyes, and drugs while eliminating waste products like urea and uric acid, resulting in isotonic filtrate.
Loop of Henle
- U-shaped structure primarily located in the medulla, critical for urine concentration.
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Description
This quiz explores the characteristics and functions of extraglomerular mesangial cells, including their role in regulating glomerular filtrate through sensitivity to chloride ion content. It also covers the structural aspects of these cells and their location between afferent and efferent arterioles. Test your knowledge on this important subject in renal physiology.
