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Questions and Answers
What are the intrinsic mechanisms that help control blood pressure?
What are the intrinsic mechanisms that help control blood pressure?
Autoregulation and the Renin-Angiotensin-Aldosterone (RAA) system.
What do juxtaglomerular cells detect to activate the RAA system?
What do juxtaglomerular cells detect to activate the RAA system?
A drop in blood pressure or salt concentration.
The sympathetic nervous system increases glomerular filtration rate (GFR) to decrease blood pressure.
The sympathetic nervous system increases glomerular filtration rate (GFR) to decrease blood pressure.
False
What is the primary action of aldosterone in the kidneys?
What is the primary action of aldosterone in the kidneys?
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What is the effect of ADH on the concentrating ability of urine?
What is the effect of ADH on the concentrating ability of urine?
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The ____ of Henle sets up a steep osmotic gradient in the kidney.
The ____ of Henle sets up a steep osmotic gradient in the kidney.
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What happens to urine volume in the presence of ADH during dehydration?
What happens to urine volume in the presence of ADH during dehydration?
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The collecting ducts are normally permeable to water.
The collecting ducts are normally permeable to water.
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What does the counter-current multiplier mechanism help establish?
What does the counter-current multiplier mechanism help establish?
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What is the typical range of normal urine production per day?
What is the typical range of normal urine production per day?
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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Study Notes
Renal Control of Blood Pressure
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Kidneys regulate blood pressure by modifying extracellular fluid (ECF) volume and plasma composition.
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Intrinsic Mechanisms:
- Autoregulation: Protects kidneys from fluctuations in systemic blood pressure.
- Renin-Angiotensin-Aldosterone (RAA) system: Juxtaglomerular cells sense blood pressure in afferent arterioles and release renin to restore blood pressure, reliant on the juxtaglomerular apparatus (JGA).
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Extrinsic Mechanisms:
- Sympathetic nervous system reduces glomerular filtration rate (GFR) to elevate blood pressure when necessary.
Juxtaglomerular Apparatus
- Composed of:
- Juxtaglomerular (JG) cells: Specialized muscle cells releasing renin in response to low blood pressure or decreased sodium concentration.
- Macula densa cells: Located in the distal convoluted tubule, these cells recognize changes in sodium levels in the filtrate, stimulating renin release.
Renin-Angiotensin-Aldosterone System (RAAS)
- Monitors blood pressure in afferent arterioles; a decrease triggers renin release.
- Renin initiates a cascade involving angiotensin I and II, antidiuretic hormone (ADH), and aldosterone to modulate blood pressure and fluid balance.
Effect of Aldosterone
- Produced by adrenal cortex, it enhances sodium reabsorption in distal convoluted tubules and collecting ducts.
- Stimulates the synthesis of Na+/K+ transport proteins via DNA coding for mRNA.
- In the absence of aldosterone, significant salt loss (up to 20g/day) occurs; with aldosterone, salt loss is minimal.
Regulation of Urine Volume
- Achieved by kidneys managing urine output through Counter-Current Multiplier Mechanism (CCMM).
- The anatomical structure of juxtamedullary nephrons and vasa recta enables this mechanism, with varying permeability in different segments.
Counter-Current Multiplier Mechanism
- Counter-current: Filtrate flows in opposite directions in the loop of Henle compared to blood in vasa recta.
- Multiplier mechanism: Ion movement occurs in incremental steps, resulting in significant osmotic changes.
Osmotic Gradient Creation
- The loop of Henle establishes an osmotic gradient from cortex (300 mOsm/L) to medulla (1200 mOsm/L) via:
- Water and ion movement from filtrate to blood in the vasa recta.
- Variances in tubular cell permeabilities between descending and ascending limbs.
Mechanism of Osmotic Gradient
- Descending limb: Permeable to water but not to Na+ and Cl-; water exits by osmosis, collected by vasa recta.
- Ascending limb: Impermeable to water, permeable to Na+ and Cl-; “salt pumps” reduce filtrate osmolarity to 100 mOsm/L as salts are retained by vasa recta.
Reabsorption in Collecting Ducts
- Collecting ducts are typically impermeable to water but can change permeability through ADH modulation.
Antidiuretic Hormone (ADH)
- Controls urine concentration based on body hydration states.
- Osmoreceptors in the hypothalamus detect plasma osmolality and prompt ADH release during water deficits.
- ADH increases water reabsorption in distal convoluted tubule (DCT) and collecting ducts.
Effect of ADH on Urine Volume
- Presence of ADH: In dehydration, ADH causes collecting ducts to become permeable to water, resulting in concentrated urine (~500 ml/day, <1200 mOsm/L).
- Absence of ADH: Collecting ducts remain impermeable to water, leading to dilute urine (~>100 mOsm/L, larger volumes).
Summary of Loop of Henle Functionality
- Adjusts osmotic gradients essential for urine concentration, playing a crucial role in renal function and fluid balance.
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Description
This quiz explores the intricate relationship between renal function and blood pressure regulation. Learn about intrinsic mechanisms such as autoregulation and the renin-angiotensin-aldosterone (RAA) system that aid in blood pressure control. Test your knowledge on how kidneys manage extracellular fluid volume and composition.
