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What is the basic functional unit of the kidney?
What is the basic functional unit of the kidney?
Nephron
What is the process of removing waste products from the blood and forming urine?
What is the process of removing waste products from the blood and forming urine?
Urine production
What are the three basic processes involved in urine production?
What are the three basic processes involved in urine production?
Filtration, reabsorption, and secretion
Which of the following are types of nephrons?
Which of the following are types of nephrons?
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Which process occurs in the glomerulus?
Which process occurs in the glomerulus?
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The filtrate formed in the glomerulus contains blood cells and proteins.
The filtrate formed in the glomerulus contains blood cells and proteins.
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What is the primary function of the proximal convoluted tubule (PCT)?
What is the primary function of the proximal convoluted tubule (PCT)?
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The loop of Henle is impermeable to water.
The loop of Henle is impermeable to water.
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What is the main function of the loop of Henle?
What is the main function of the loop of Henle?
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Which hormone regulates water reabsorption in the collecting duct?
Which hormone regulates water reabsorption in the collecting duct?
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What is the primary role of the distal convoluted tubule (DCT)?
What is the primary role of the distal convoluted tubule (DCT)?
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Which cell type in the DCT is responsible for acid-base balance?
Which cell type in the DCT is responsible for acid-base balance?
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Urea is a waste product that is completely reabsorbed in the nephron.
Urea is a waste product that is completely reabsorbed in the nephron.
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What is the role of the vasa recta in the countercurrent multiplication process?
What is the role of the vasa recta in the countercurrent multiplication process?
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Which of the following is NOT a way that the kidneys regulate blood pressure?
Which of the following is NOT a way that the kidneys regulate blood pressure?
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What is the main component of urine by weight?
What is the main component of urine by weight?
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What is the average daily urine volume for an adult?
What is the average daily urine volume for an adult?
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The kidneys play a vital role in maintaining fluid balance and electrolyte balance in the body.
The kidneys play a vital role in maintaining fluid balance and electrolyte balance in the body.
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What are the two main types of cells found in the collecting duct?
What are the two main types of cells found in the collecting duct?
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Which of the following is NOT a hormone that influences urine production?
Which of the following is NOT a hormone that influences urine production?
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Study Notes
Renal Physiology II: Urine Production
- Urine production involves solute and water transport along the nephron.
- The nephron is the basic functional unit of the kidney.
- There are approximately one million nephrons in each kidney.
- Nephrons are highly organized structures involved in filtering blood.
- The kidney has two main types of nephrons: cortical and juxtamedullary.
- Cortical nephrons have shorter loops of Henle.
- Juxtamedullary nephrons have longer loops of Henle.
Learning Outcomes
- Students should understand the role of nephron segments.
- The process of reabsorption and secretion across renal epithelial membranes should be described.
- Students are expected to explain how and why the loop of Henle generates a hyperosmotic medulla.
Nephron Overview
- The nephron is the fundamental functional unit of the kidney.
- It filters blood, controlling water and solute reabsorption.
- The nephron includes a large number of specialized structures.
- It processes about 180 liters of filtrate per day.
Nephron: Cell Types
- Epithelial cells form the tubule.
- Podocytes are glomerular epithelial cells involved in filtration.
- Brush border cells are in the proximal tubule and are responsible for absorption.
- Cells in the renal tubules express different channels and transporters that carry out reabsorption and secretion.
- Different regions of the nephron have unique structural and functional characteristics.
Nephron: Three Basic Processes
- The nephron segment by segment processes filtered substances through filtration, reabsorption and secretion.
- Filtration, the initial step, removes substances from the blood.
- Reabsorption recovers essential materials from the filtrate.
- Secretion actively moves substances from the blood to the filtrate.
- These processes regulate fluid balance, pH, and blood composition
Glomerular Filtration
- The glomerular filtration membrane filters blood without cells or proteins.
- It contains water, glucose, amino acids, and ions.
- Glomerular filtration rate (GFR) is usually constant despite blood pressure changes.
- The glomerular filtration membrane is intrinsic and regulated by several factors such as myogenic activity and the tubuloglomerular feedback mechanism (JGA), hormonal and nervous control.
Tubule Organisation
- Filtration, reabsorption, and secretion are major functions of the nephron.
- Filtration involves the movement of fluids and solutes into the nephron from the blood.
- Reabsorption involves materials moving from the nephron back into the blood.
- Secretion is the movement of substances from the blood into the nephron.
Proximal Reabsorption
- The proximal tubule is highly efficient at reabsorbing substances.
- It reabsorbs about 65% of filtered water and a varying amount of solutes that are important.
- Sodium reabsorption drives the reabsorption of glucose and amino acids.
- Reabsorption in the Proximal tubules, surface area is increased due to abundant microvilli.
- Cells contain abundant mitochondria, the main energy source for the active transport processes.
Loop of Henle
- The loop of Henle is a critical segment in the nephron for water and sodium reabsorption.
- This creates an osmotic gradient and concentration of urine.
- The loop has a descending limb (permeable to water) and an ascending limb (impermeable to water).
- The descending limb concentrates solutes because water moves out into the surrounding tissues.
- The ascending limb actively transports salt ions out of the tubule and concentrates solutes in the medulla
Countercurrent Multiplier
- The loop of Henle creates a hypertonic environment by actively transporting salts.
- This mechanism, called the countercurrent multiplier, maintains a high concentration of solutes in the renal medulla.
- The flow of filtrate in the descending and ascending limbs is in opposite directions, maintaining the concentration gradient.
- Water reabsorption is stimulated by the ADH hormone.
Counter Current Multiplier: The Vasa Recta
- Blood flows in the opposite direction to the filtrate in the loop of Henle.
- The vasa recta capillaries help to maintain the established concentration gradient by reabsorbing water.
- The kidney capillaries do not remove the urea and sodium needed for the counter current system.
Urea Recycling
- Urea recycling is the process of urea reabsorption.
- It's a major contributor to osmolarity in the renal medulla, a critical process for concentrating urine.
- About 40–50% of the filtered urea is reabsorbed in the collecting tubule.
Distal Convoluted Tubule and Collecting Duct
- Final adjustments of urine composition, including water and salt reabsorption, occur in the distal tubule and collecting duct.
- Fine tuning urine composition is controlled by different hormones.
Urine Composition
- Urine contains water, ions, and metabolic waste products.
- The composition of the urine varies depending on the body fluid balance.
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