Kidney Functions and Nephrons
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Questions and Answers

What is one of the primary functions of the kidneys related to fluid balance?

  • Control respiratory rate
  • Regulate blood glucose levels
  • Produce digestive enzymes
  • Regulate body fluid osmolarity and electrolyte levels (correct)

    • Which part of the nephron is primarily responsible for the filtration process?

  • Glomerulus (correct)
  • Distal convoluted tubule
  • Collecting duct
  • Proximal convoluted tubule

    • In which kidney region does the renal pelvis reside?

  • Cortex
  • Peritoneum
  • Medulla
  • Pelvis (correct)

    • What distinguishes juxtamedullary nephrons from cortical nephrons?

    <p>They extend deep into the medulla with long loops of Henle</p> Signup and view all the answers

    Which step in urine formation involves moving substances from blood into the filtrate?

    <p>Secretion</p> Signup and view all the answers

    What is the role of erythropoietin secreted by the kidneys?

    <p>Stimulate red blood cell production</p> Signup and view all the answers

    Which of the following components returns reabsorbed substances back to the blood?

    <p>Peritubular capillaries</p> Signup and view all the answers

    Which statement correctly contrasts cortical and juxtamedullary nephrons?

    <p>Cortical nephrons are primarily involved in standard filtration and reabsorption.</p> Signup and view all the answers

    What is the primary role of the descending limb of the loop of Henle?

    <p>Permits water reabsorption</p> Signup and view all the answers

    Which mechanism is responsible for maintaining the osmotic gradient in the renal medulla?

    <p>Countercurrent exchanger</p> Signup and view all the answers

    How does antidiuretic hormone (ADH) affect urine concentration?

    <p>Increases water reabsorption</p> Signup and view all the answers

    What are the common causes of intrinsic acute kidney injury (AKI)?

    <p>Ischemia and toxins</p> Signup and view all the answers

    Which part of the nephron is primarily responsible for secreting organic ions?

    <p>Proximal tubule</p> Signup and view all the answers

    What occurs in the ascending limb of the loop of Henle?

    <p>NaCl is reabsorbed but is impermeable to water</p> Signup and view all the answers

    Which condition is characterized by a SCr increase of 0.3 mg/dL within 48 hours?

    <p>Acute kidney injury (AKI)</p> Signup and view all the answers

    What is a characteristic of dilute urine formation?

    <p>Low levels of ADH result in increased water loss</p> Signup and view all the answers

    Which factors can lead to volume depletion related to prerenal acute kidney injury?

    <p>Heart failure</p> Signup and view all the answers

    What is the main function of tubular secretion in the kidneys?

    <p>Regulating acid-base balance and waste removal</p> Signup and view all the answers

    Which structure is primarily responsible for filtering blood plasma and producing protein-free filtrate?

    <p>Glomerulus</p> Signup and view all the answers

    What is the primary function of mesangial cells in the glomerulus?

    <p>Support filtration surface area</p> Signup and view all the answers

    Which of the following pressures typically opposes filtration in the glomerulus?

    <p>Glomerular capillary oncotic pressure</p> Signup and view all the answers

    What physiological response occurs when there is an increase in blood pressure in the afferent arteriole?

    <p>Constriction of smooth muscle cells in the afferent arteriole</p> Signup and view all the answers

    Which blood pressure regulation mechanism is intrinsic to the kidney?

    <p>Myogenic response</p> Signup and view all the answers

    What effect does a rise in capillary oncotic pressure have on urine formation?

    <p>Decreases urine formation</p> Signup and view all the answers

    Which component of the filtration membrane prevents the passage of medium-to-large anions?

    <p>Podocyte layer</p> Signup and view all the answers

    How does angiotensin II primarily affect blood pressure regulation?

    <p>Causes systemic vasoconstriction</p> Signup and view all the answers

    Which structure is primarily involved in the reabsorption of water, ions, and nutrients in the nephron?

    <p>Proximal tubule</p> Signup and view all the answers

    Which factor does not affect glomerular filtration rate (GFR)?

    <p>Filtrate color</p> Signup and view all the answers

    What primarily triggers renin release from granular cells in the kidney?

    <p>Low blood pressure</p> Signup and view all the answers

    What is the primary result of aldosterone action in the nephron?

    <p>Increases Na+ reabsorption</p> Signup and view all the answers

    Which route is primarily responsible for the passage of substances between renal tubule cells?

    <p>Transcellular route</p> Signup and view all the answers

    How does tubular reabsorption relate to the high volume of filtrate produced by the kidneys?

    <p>It prevents massive fluid loss</p> Signup and view all the answers

    What pressure primarily opposes fluid movement into Bowman’s capsule during glomerular filtration?

    <p>Bowman’s space hydrostatic pressure</p> Signup and view all the answers

    Which component of the juxtaglomerular apparatus is responsible for detecting sodium chloride levels in the filtrate?

    <p>Macula densa cells</p> Signup and view all the answers

    What is the main action of aldosterone in the nephron?

    <p>Promotes sodium reabsorption</p> Signup and view all the answers

    What is the typical normal glomerular filtration rate (GFR) range in adults?

    <p>120-125 mL/min</p> Signup and view all the answers

    What role do mesangial cells serve in the renal glomerulus?

    <p>They provide structural support and regulate surface area</p> Signup and view all the answers

    What mechanism is primarily used by the peritubular capillaries to assist in the reabsorption of solutes?

    <p>Active transport</p> Signup and view all the answers

    What effect does sympathetic nervous system activation have on glomerular filtration rate?

    <p>Reduces GFR by constricting afferent arterioles</p> Signup and view all the answers

    Which layer of the filtration membrane primarily prevents the passage of large proteins?

    <p>Basement membrane</p> Signup and view all the answers

    What is the primary mechanism by which the renin-angiotensin-aldosterone system (RAAS) increases blood volume?

    <p>Enhanced sodium and water reabsorption</p> Signup and view all the answers

    What effect does an increase in capillary hydrostatic pressure have on urine formation?

    <p>Increases urine through enhanced filtrate flow</p> Signup and view all the answers

    What is primarily responsible for the reabsorption of sodium in the nephron?

    <p>Na+/K+ pumps in the proximal tubule</p> Signup and view all the answers

    Which of the following statements correctly describes the role of the countercurrent multiplier in the nephron?

    <p>It generates an osmotic gradient allowing water reabsorption in the loop of Henle.</p> Signup and view all the answers

    In which part of the nephron is potassium secreted through Na+/K+ pumps?

    <p>Distal tubule</p> Signup and view all the answers

    Which factor is primarily responsible for the urine concentration under high levels of antidiuretic hormone (ADH)?

    <p>Enhanced water reabsorption in the collecting ducts.</p> Signup and view all the answers

    What primarily happens to the osmotic gradient created by the loop of Henle?

    <p>It maintains equilibrium in the vasa recta.</p> Signup and view all the answers

    Which condition can lead to acute kidney injury (AKI) classified as intrinsic?

    <p>Ischemic damage to kidney tissue</p> Signup and view all the answers

    How do epithelial cells in the nephron primarily become injured in toxic environments?

    <p>Due to their high metabolic rates and reabsorption activities.</p> Signup and view all the answers

    Which response accurately depicts the process of tubular secretion?

    <p>It transports ions and organic anions into the filtrate.</p> Signup and view all the answers

    Which mechanism helps maintain the renal medullary osmotic gradient in the kidney?

    <p>Countercurrent exchange in the vasa recta.</p> Signup and view all the answers

    What primarily contributes to the formation of dilute urine?

    <p>Low levels of ADH allowing for water loss.</p> Signup and view all the answers

    What is the primary role of calcitriol produced by the kidneys?

    <p>Maintaining calcium homeostasis</p> Signup and view all the answers

    Which structure within the nephron is involved in the process of reabsorption?

    <p>Loop of Henle</p> Signup and view all the answers

    What distinguishes juxtamedullary nephrons from cortical nephrons?

    <p>They are primarily involved in urine concentration.</p> Signup and view all the answers

    Which part of the renal vasculature pathway carries blood away from the glomerulus?

    <p>Efferent arteriole</p> Signup and view all the answers

    What is the primary function of the proximal convoluted tubule?

    <p>Reabsorption of nutrients and water</p> Signup and view all the answers

    Which region of the kidney is immediately adjacent to the renal cortex?

    <p>Medulla</p> Signup and view all the answers

    What type of pressure typically opposes the process of filtration in the glomerulus?

    <p>Oncotic pressure</p> Signup and view all the answers

    In what way does the renal pelvis serve the urinary system?

    <p>It collects urine before it enters the ureter.</p> Signup and view all the answers

    Which process primarily occurs in the glomerulus?

    <p>Filtration of blood</p> Signup and view all the answers

    What is the effect of tubular secretion in the renal system?

    <p>To eliminate waste products from the blood</p> Signup and view all the answers

    What is the main purpose of tubular reabsorption in relation to GFR?

    <p>Prevents excessive water and solute loss</p> Signup and view all the answers

    Approximately what percentage of filtrate is reabsorbed in healthy kidneys?

    <p>99%</p> Signup and view all the answers

    Which nephron segment is primarily involved in the removal of excess hydrogen ions?

    <p>Distal tubule</p> Signup and view all the answers

    Which substance is not effectively reabsorbed by the nephron?

    <p>Creatinine</p> Signup and view all the answers

    Which nephron segment is responsible for the majority of nutrient reabsorption, including glucose?

    <p>Proximal tubule</p> Signup and view all the answers

    In which part of the nephron does most tubular secretion primarily occur?

    <p>Proximal tubule</p> Signup and view all the answers

    Which hormone is responsible for increasing the water permeability of the collecting duct?

    <p>Antidiuretic hormone (ADH)</p> Signup and view all the answers

    What effect does sodium reabsorption in the proximal tubule have on the nephron?

    <p>Facilitates glucose reabsorption</p> Signup and view all the answers

    What feature primarily characterizes the ascending limb of the loop of Henle?

    <p>It actively transports sodium and chloride.</p> Signup and view all the answers

    What is the primary reason proximal tubule cells are particularly vulnerable to toxins?

    <p>They have high metabolic activity and reabsorptive demands.</p> Signup and view all the answers

    Which statement describes the role of ADH in urine formation?

    <p>It enhances water reabsorption by increasing aquaporin channels.</p> Signup and view all the answers

    What is the clinical significance of the Cockcroft-Gault equation?

    <p>It estimates creatinine clearance (CrCl).</p> Signup and view all the answers

    Which of the following accurately defines oliguria as a symptom of AKI?

    <p>Urine output less than 400 mL/day.</p> Signup and view all the answers

    Which immune cells play a role in the repair of ischemic tubular necrosis?

    <p>Macrophages</p> Signup and view all the answers

    At which location is the medullary osmotic gradient at its peak?

    <p>At the tip of the loop of Henle.</p> Signup and view all the answers

    What condition primarily causes postrenal AKI?

    <p>Obstruction in the urinary tract</p> Signup and view all the answers

    Which type of AKI is most commonly classified as prerenal?

    <p>Volume depletion or reduced renal perfusion</p> Signup and view all the answers

    Which structure is referred to as the countercurrent exchanger in renal physiology?

    <p>Vasa recta</p> Signup and view all the answers

    Study Notes

    Kidney Functions

    • Functions of the Kidneys:
      • Regulate fluid and electrolyte balance
      • Maintain acid-base balance
      • Produce hormones (renin, calcitriol, erythropoietin)
      • Filter and remove waste products

    The Nephron

    • Nephron: The functional unit of the kidney; responsible for urine formation
      • Filtration: Occurs in the glomerulus; plasma is filtered, creating filtrate resembling blood plasma
      • Reabsorption: Water and solutes are reabsorbed from filtrate back into the bloodstream
      • Secretion: Substances are moved from blood into filtrate for removal

    Kidney Anatomy

    • Internal Kidney Anatomy:
      • Cortex: Outermost layer, lighter in color
      • Medulla: Contains renal pyramids, each draining urine into a minor calyx
      • Pelvis: Innermost collecting area, major calyces drain into the renal pelvis, leading urine to the ureter

    Nephron Types

    • Cortical Nephrons: Primarily located in the renal cortex, shorter loops of Henle
    • Juxtamedullary Nephrons: Extend deep into the medulla, long loops of Henle enabling urine concentration

    Renal Vasculature

    • Renal Vasculature Pathway:
      • Afferent Arteriole: Brings blood to the glomerulus
      • Glomerular Capillaries: Site of filtration
      • Efferent Arteriole: Exits the glomerulus, leading to peritubular capillaries or vasa recta
      • Peritubular Capillaries/Vasa Recta: Surround nephron tubules, facilitating solute and water exchange

    Osmolarity

    • Osmolarity Calculation:
      • Uses molarity of dissolved salts, considering ion dissociation

    Glomerulus & Peritubular Capillaries

    • Glomerulus: High-pressure capillary bed; filters blood
    • Peritubular Capillaries/Vasa Recta: Low-pressure capillaries surrounding renal tubules, aiding in reabsorption

    Filtration Membrane

    • Filtration Membrane:
      • Fenestrated Endothelium: Allows passage of most plasma components, not blood cells
      • Basement Membrane: Blocks large proteins due to negative charges
      • Podocyte Layer with Filtration Slits: Prevents filtration of medium-to-large anions

    Mesangial Cells

    • Mesangial Cells:
      • Location: Surround glomerular capillaries
      • Role: Provide structural support, clear trapped molecules, regulate filtration surface area

    Glomerular Filtration Pressures

    • pressures governing capillary fluid exchange in glomerular filtration:
      • Glomerular Capillary Hydrostatic Pressure (PGC): Pushes fluid out of the capillary
      • Bowman’s Space Hydrostatic Pressure (PBS): Pushes fluid into the capillary
      • Glomerular Capillary Oncotic Pressure (πGC): Pulls fluid back into the capillary
      • Bowman’s Space Oncotic Pressure (πBS): Typically negligible, but would pull fluid into Bowman's capsule if present

    Net Filtration Pressure (NFP):

    • NFP = PGC - PBS - πGC + πBS

    Fluid Movement & Urine Formation

    • Increased PGC = more fluid into Bowman's capsule = increased urine formation.
    • Increased πGC = more fluid into glomerular capillaries = decreased urine formation.

    Glomerular Filtration Rate (GFR)

    • GFR: Volume of filtrate produced per minute by all nephrons (normal GFR = 120-125 mL/min).
    • Factors affecting GFR: Blood pressure, glomerular surface area, and filtration membrane permeability.

    GFR Regulation

    • Intrinsic Mechanisms: Myogenic response and tubuloglomerular feedback
    • Extrinsic Mechanisms: Neural (sympathetic activation) and hormonal control (RAAS)

    Myogenic Mechanism

    • Myogenic Mechanism: Smooth muscle in the afferent arteriole responds to pressure changes:
      • Increased BP = constriction = reduced blood flow = stabilized GFR
      • Decreased BP = dilation = increased blood flow = increased GFR

    Juxtaglomerular Apparatus (JGA)

    • JGA: Composed of:
      • Granular Cells: Produce renin in response to blood pressure changes
      • Macula Densa Cells: Detect NaCl levels in filtrate and signal adjustments
      • Juxtaglomerular Cells: Regulate blood pressure and GFR through renin release and arteriole constriction/dilation

    Neural Regulation of GFR

    • Sympathetic Input: Constricts afferent arterioles, reducing GFR during stress, conserving water and ions.

    Renin-Angiotensin-Aldosterone System (RAAS)

    • RAAS Steps:
      • Low blood pressure triggers renin release.
      • Renin converts angiotensinogen to angiotensin I.
      • Angiotensin I converts to angiotensin II via ACE (angiotensin-converting enzyme).
      • Angiotensin II raises blood pressure through vasoconstriction and stimulates aldosterone release for sodium reabsorption.

    RAAS & Blood Pressure Regulation

    • Increases blood volume & pressure: Retains sodium and water, raising total blood volume and systemic resistance.

    Renin Release Triggers

    • Reduced stretch in granular cells (low BP).
    • Low NaCl levels detected by macula densa cells.
    • Sympathetic nervous activation.

    Angiotensin II Actions

    • Angiotensin II Functions:
      • Causes systemic vasoconstriction.
      • Stimulates aldosterone release.
      • Promotes ADH secretion, thirst, and fluid reabsorption.
      • Constricts the efferent arteriole, maintaining GFR.

    Aldosterone & Urine Formation

    • Aldosterone: Increases Na+ reabsorption and K+ secretion, influencing fluid balance and blood pressure regulation.

    Tubular Reabsorption

    • Importance: Essential to prevent massive fluid loss and maintain homeostasis, as GFR produces 180 liters of filtrate daily.

    Reabsorption Routes

    • Transcellular Route: Transport through tubule cells using active or passive mechanisms.
    • Paracellular Route: Substances pass between cells, driven by gradients.

    Tubular Segment Contribution to Reabsorption

    • Proximal Tubule: Major reabsorption site for water, ions, and nutrients.
    • Loop of Henle: Concentrates filtrate.
    • Distal tubule and collecting duct: Fine-tune reabsorption based on hormonal regulation.

    Renal Tubule Segment Reabsorption Capabilities

    • Proximal Tubule: Major reabsorption site for water, ions, and nutrients.
    • Loop of Henle: Primarily reabsorbs NaCl.
    • Distal Tubule: Reabsorbs water and Na+ (regulated by aldosterone).
    • Collecting Duct: Fine-tunes water reabsorption (regulated by ADH).

    Sodium Reabsorption & Cotransport

    • Sodium Reabsorption: Creates an electrochemical gradient, facilitating reabsorption of water, ions, and nutrients.
    • Cotransport: Movement of one substance coupled with movement of another.

    Non-Reabsorbed Molecules

    • Urea and creatinine: Partially or not reabsorbed, are eliminated as waste due to lack of transporters.

    Tubular Secretion

    • Tubular Secretion: Moves hydrogen ions, potassium, organic anions, and cations into the filtrate to regulate acid-base balance and remove waste.

    Potassium and Organic Secretion

    • Potassium Secretion: Occurs in the distal tubule and collecting ducts through Na+/K+ pumps.
    • Organic Ion Secretion: Occurs in the proximal tubule using specific transporters.

    Urine Concentration

    • Urine Concentration Components:
      • Countercurrent Multiplier in the loop of Henle.
      • Countercurrent Exchanger in vasa recta.
      • ADH to adjust water reabsorption.

    Medullary Osmotic Gradient & Loop of Henle

    • Loop of Henle: Establishes an osmotic gradient, enabling urine concentration by allowing water reabsorption.

    Loop of Henle Functions

    • Descending Limb: Permits water reabsorption.
    • Ascending Limb: Reabsorbs NaCl but is impermeable to water, contributing to osmotic gradient creation.

    Countercurrent Exchanger

    • Vasa Recta: Maintains the osmotic gradient by equilibrating solutes and water in the renal medulla, supporting concentration.

    Dilute vs. Concentrated Urine

    • Dilute Urine: Formed with low ADH, allowing water loss.
    • Concentrated Urine: Formed with high ADH, promoting water reabsorption.

    Antidiuretic Hormone (ADH)

    • ADH Function: Enhances water reabsorption in the collecting ducts, increasing urine concentration.

    Cockcroft-Gault Equation for Creatinine Clearance

    • Creatinine Clearance Calculation:
      • For Men: (140-age) x weight (kg) / (72 x creatinine (mg/dL))
      • For Women: (140-age) x weight (kg) / (72 x creatinine (mg/dL)) x 0.85

    Acute Kidney Injury (AKI)

    • AKI Diagnostic Criteria:
      • SCr increase of 0.3 mg/dL within 48 hours OR
      • 50-100% increase in baseline SCr within 48 hours OR
      • Oliguria for 6+ hours.

    AKI Classifications

    • Prerenal: Reduced blood flow to the kidneys.
    • Intrinsic: Kidney damage.
    • Postrenal: Obstruction in the urinary tract. (Prerenal is the most common classification.)

    AKI Causes

    • Prerenal: Volume depletion, heart failure.
    • Intrinsic: Toxins, ischemia.
    • Postrenal: Obstructions (BPH, stones).

    Ischemia & Tubular Necrosis

    • Ischemia: Reduces oxygen, causing necrosis, especially in the proximal tubule and thick ascending loop of Henle.

    Cell Role in Tubular Necrosis Repair

    • Ischemic tubular cells and immune cells: Repair through proliferation and differentiation if injury is reversible.

    Tubular Epithelial Cell Injury Predisposition

    • Epithelial cells: Vulnerable to toxins due to high metabolic rate, reabsorption activity, and oxygen consumption; the proximal tubule is most affected.

    Kidney Functions

    • Regulate blood volume, osmolarity, and electrolyte levels
    • Maintain acid-base balance
    • Produce hormones like renin, calcitriol, and erythropoietin
    • Remove metabolic waste and foreign substances

    Nephron Functions

    • Urine formation through three steps:
      • Filtration: In the glomerulus; plasma is filtered to create a filtrate similar to blood plasma
      • Reabsorption: Water and solutes are removed from filtrate and returned to the blood
      • Secretion: Substances are moved from blood into the filtrate for waste removal

    Kidney Anatomy

    • Three main regions:
      • Cortex: Outermost region; lighter in color
      • Medulla: Contains renal pyramids, each draining urine into a minor calyx
      • Pelvis: Innermost region; collects urine from major calyces, leading to the ureter
    • The nephron includes the renal corpuscle, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct, all involved in urine processing

    Nephron Types

    • Cortical nephrons: Located in the cortex; have shorter loops of Henle and are more involved in standard filtration and reabsorption
    • Juxtamedullary nephrons: Extend deep into the medulla; have long loops of Henle, enabling urine concentration for water conservation

    Renal Vasculature

    • Blood flow pathway within the kidneys:
      • Afferent arteriole: Carries blood to the glomerulus
      • Glomerular capillaries: Site of filtration
      • Efferent arteriole: Exits glomerulus, leading to the peritubular capillaries or vasa recta
      • Peritubular capillaries/vasa recta: Surround nephron tubules and facilitate solute and water exchange

    Osmolarity

    • Calculated by considering the molarity of dissolved salts and dissociation into ions

    Glomerulus and Peritubular/Vasa Recta Capillaries

    • Glomerulus: High-pressure capillary bed for filtration, producing protein-free filtrate
    • Peritubular capillaries/Vasa Recta: Low-pressure capillaries surrounding the renal tubules (peritubular in cortical nephrons, vasa recta in juxtamedullary nephrons) reabsorb water and solutes from the filtrate to maintain the medullary osmotic gradient

    Filtration Membrane

    • Three layers:
      • Fenestrated endothelium: Allows passage of most plasma components, but not blood cells
      • Basement membrane: Blocks larger proteins due to negative charges on glycoproteins
      • Podocyte layer with filtration slits: Prevents filtration of medium-to-large anions and regulates filtrate composition

    Mesangial Cells

    • Surround glomerular capillaries
    • Provide structural support, clear trapped molecules, and regulate filtration surface area by contracting to reduce glomerular surface availability

    Glomerular Filtration Pressure

    • Four pressures govern fluid exchange during filtration:
      • Glomerular capillary hydrostatic pressure (PGC): Pushes fluid out of the capillary
      • Bowman’s space hydrostatic pressure (PBS): Pushes fluid into the capillary
      • Glomerular capillary oncotic pressure (πGC): Pulls fluid back into the capillary
      • Bowman’s space oncotic pressure (πBS): Typically negligible

    Net Filtration Pressure (NFP)

    • NFP = PGC - PBS - πGC
    • Increased NFP increases urine formation
    • Decreased NFP decreases urine formation

    Glomerular Filtration Rate (GFR)

    • Represents the volume of filtrate produced per minute by all nephrons
    • Normal GFR in adults is approximately 120-125 mL/min
    • Influenced by blood pressure, glomerular surface area, and permeability of the filtration membrane

    GFR Regulation

    • Intrinsic Mechanisms:
      • Myogenic response: Smooth muscle cells in the afferent arteriole respond to pressure changes
      • Tubuloglomerular feedback: Macula densa cells in the JGA detect NaCl levels in the filtrate and signal adjustments
    • Extrinsic Mechanisms:
      • Neural: Sympathetic activation
      • Hormonal: Renin-angiotensin-aldosterone system (RAAS)

    Myogenic Mechanism

    • Increased blood pressure constricts afferent arterioles, reducing blood flow and stabilizing GFR
    • Reduced pressure dilates afferent arterioles, increasing blood flow and GFR

    Juxtaglomerular Apparatus (JGA)

    • Granular cells: Produce renin in response to blood pressure changes
    • Macula densa cells: Detect NaCl levels in filtrate and signal adjustments
    • Juxtaglomerular cells: Regulate blood pressure and GFR through renin release and arteriole constriction/dilation

    Neural Regulation of GFR

    • Sympathetic input constricts afferent arterioles, reducing GFR during stress to conserve water and ions

    Renin-Angiotensin-Aldosterone System (RAAS)

    • Steps:
      • Low blood pressure triggers renin release
      • Renin converts angiotensinogen to angiotensin I
      • Angiotensin I converts to angiotensin II via ACE (angiotensin-converting enzyme)
      • Angiotensin II raises blood pressure through vasoconstriction and stimulates aldosterone release for sodium reabsorption

    RAAS and Blood Pressure Regulation

    • RAAS increases blood volume and pressure by retaining sodium and water, raising total blood volume and systemic resistance

    Renin Release Triggers

    • Reduced stretch in granular cells (low blood pressure)
    • Low NaCl levels detected by macula densa cells
    • Sympathetic nervous activation

    Angiotensin II Actions

    • Causes systemic vasoconstriction
    • Stimulates aldosterone release
    • Promotes ADH secretion, thirst, and fluid reabsorption
    • Constrict's the efferent arteriole, maintaining GFR

    Aldosterone Role in Urine Formation

    • Increases Na+ reabsorption and K+ secretion, influencing fluid balance and blood pressure regulation

    Importance of Tubular Reabsorption

    • Reabsorption prevents significant fluid loss and maintains homeostasis since GFR produces around 180 liters of filtrate per day

    Reabsorption Routes

    • Transcellular Route: Transport through tubule cells using active or passive mechanisms
    • Paracellular Route: Substances pass between cells, driven by gradients

    Tubule Segment Contributions to Reabsorption

    • Each tubule segment contributes differently; the proximal tubule reabsorbs the majority of water, ions, and nutrients

    Renal Tubule Reabsorption Capabilities

    • Proximal tubule: Major reabsorption site for water, ions, and nutrients
    • Loop of Henle: Concentrates filtrate
    • Distal tubule and collecting duct: Fine-tune reabsorption based on hormonal regulation

    Sodium Reabsorption

    • Creates an electrochemical gradient, facilitating reabsorption of water, ions, and nutrients

    Non-Reabsorbed Molecules

    • Urea and creatinine are partially or not reabsorbed due to lack of transporters and serve as waste products

    Tubular Secretion

    • Moves hydrogen ions, potassium, organic anions, and cations into the filtrate to regulate acid-base balance and remove waste

    Potassium and Organic Secretion

    • Potassium is secreted in the distal tubule and collecting ducts through Na+/K+ pumps
    • Organic ions are secreted in the proximal tubule using specific transporters

    Urine Concentration

    • Requires:
      • Countercurrent multiplier in the loop of Henle
      • Countercurrent exchanger in the vasa recta
      • ADH to adjust water reabsorption

    Renal Medullary Osmotic Gradient and Loop of Henle

    • The loop of Henle establishes an osmotic gradient, allowing the kidney to concentrate urine by enabling water reabsorption

    Functions of Descending and Ascending Loop Limbs

    • Descending limb: Permits water reabsorption
    • Ascending limb: Reabsorbs NaCl but is impermeable to water, aiding in osmotic gradient creation

    Countercurrent Exchanger Role

    • The vasa recta maintains the osmotic gradient by equilibrating solutes and water in the renal medulla, supporting concentration

    Dilute vs. Concentrated Urine

    • Dilute urine: Formed with low ADH, allowing water loss
    • Concentrated urine: Formed with high ADH, promoting water reabsorption

    Antidiuretic Hormone (ADH) Function

    • Enhances water reabsorption in the collecting ducts, increasing urine concentration

    Cockcroft-Gault Equation for Creatinine Clearance

    • Calculates creatinine clearance:
      • Creatinine Clearance = (140 - Age) x (Weight in kg)/ (72 x Serum Creatinine)
      • For females, multiply the result by 0.85
      • Uses serum creatinine levels to estimate glomerular filtration rate (GFR)

    AKI Diagnostic Criteria

    • AKI is diagnosed by:
      • Serum creatinine (SCr) increase of 0.3 mg/dL within 48 hours or
      • 50-100% increase in baseline SCr within 48 hours or
      • Oliguria for 6+ hours

    AKI Classifications

    • Three major types:
      • Prerenal: Reduced blood flow to the kidneys
      • Intrinsic: Kidney damage
      • Postrenal: Obstruction in the urinary tract
      • Prerenal is the most common type

    Common Causes of AKI

    • Prerenal: Volume depletion, heart failure
    • Intrinsic: Toxins, ischemia
    • Postrenal: Obstructions (BPH, stones)

    Ischemia and Tubular Necrosis

    • Ischemia (reduced oxygen) causes necrosis in the proximal tubule and thick ascending loop of Henle

    Tubular Necrosis Repair

    • Ischemic tubular cells and immune cells repair through proliferation and differentiation if the injury is reversible

    Tubular Epithelial Cell Injury Predisposition

    • Epithelial cells are vulnerable to toxins due to high metabolic rates, reabsorption activity, and oxygen consumption, with the proximal tubule being most affected

    Tubular Reabsorption and GFR

    • Tubular reabsorption returns water and solutes to the bloodstream, preventing excessive loss.
    • In normal conditions, approximately 99% of filtered fluid is reabsorbed daily.

    Transcellular vs. Paracellular Reabsorption

    • Transcellular route is when substances reabsorb through epithelial cells.
    • Paracellular pathway is when substances move between adjacent cells.

    Contributions of Tubule Segments to Reabsorption

    • The proximal convoluted tubule is responsible for the majority of reabsorption.
    • The distal convoluted tubule fine-tunes solute concentrations.

    Reabsorption Capabilities of Renal Tubule Segments

    • The ascending limb of the loop of Henle is impermeable to water but reabsorbs NaCl.
    • The proximal tubule primarily reabsorbs glucose.

    Sodium Reabsorption and Cotransport

    • Sodium reabsorption in the proximal tubule drives water reabsorption through osmosis.
    • Glucose is reabsorbed via sodium-dependent cotransport.

    Non-Reabsorbed Molecules

    • Creatinine is not effectively reabsorbed by the nephron due to lacking specific transporters.

    Tubular Secretion

    • Tubular secretion removes excess hydrogen and potassium ions.
    • Most tubular secretion occurs in the proximal tubule.

    Potassium and Organic Secretion

    • Potassium secretion is regulated in the distal tubule and collecting duct.
    • Organic anion secretion primarily happens in the proximal tubule.

    Components Supporting Urine Concentration

    • The loop of Henle creates the medullary osmotic gradient.
    • Antidiuretic hormone (ADH) increases the permeability of the collecting duct to water.

    Medullary Osmotic Gradient and Loops of Henle

    • The descending limb of the loop of Henle is permeable to water but not solutes.
    • The medullary osmotic gradient is highest at the tip of the loop of Henle.

    Descending vs. Ascending Limbs of the Loop of Henle

    • The ascending limb of the loop of Henle actively reabsorbs Na+ and Cl-.
    • The descending limb's primary function is to reabsorb water.

    Countercurrent Exchanger

    • The vasa recta acts as a countercurrent exchanger.
    • This maintains the medullary osmotic gradient.

    Mechanisms of Dilute vs. Concentrated Urine

    • In the absence of ADH, the kidneys produce dilute urine.
    • ADH is crucial for forming concentrated urine.

    Antidiuretic Hormone (ADH) Function

    • ADH increases water reabsorption in the distal tubule and collecting duct.
    • ADH increases aquaporin numbers in the collecting duct.

    Cockcroft-Gault Equation

    • The Cockcroft-Gault equation estimates creatinine clearance (CrCl).
    • For female patients, the result is multiplied by 0.85.

    AKI Diagnostic Criteria

    • AKI is diagnosed by an increase in serum creatinine by 0.3 mg/dL within 48 hours.
    • Oliguria in AKI is defined as urine output less than 400 mL/day.

    Major Classifications of AKI

    • Prerenal AKI is the most common classification.
    • Postrenal AKI is primarily caused by urinary tract obstruction.

    Common Causes of AKI Classifications

    • Hypovolemia is a common cause of prerenal AKI.
    • Acute tubular necrosis is a frequent cause of intrinsic AKI.

    Ischemia and Tubular Necrosis

    • Proximal tubule and thick ascending limb of Henle are most susceptible to ischemia.
    • Ischemic injury to the tubules leads to tubular necrosis.

    Repair of Reversible Tubular Necrosis

    • Tubular epithelial cells repair by proliferating and differentiating.
    • Macrophages are involved in the repair process.

    Tubular Epithelial Cell Vulnerability

    • Proximal tubule cells have high metabolic activity and reabsorptive demands, making them vulnerable to toxins.
    • The proximal tubule has the highest risk of injury from nephrotoxic substances.

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    Description

    This quiz covers the essential functions of the kidneys, the role of nephrons in urine formation, and the internal anatomy of the kidneys. Test your knowledge on renal physiology and how the kidneys maintain homeostasis in the body.

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