Renal Physiology Quiz
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Questions and Answers

Which structure is NOT part of the cortical medullary ray?

  • Distal convoluted tubule (correct)
  • Proximal convoluted tubule
  • Thick ascending limb
  • Cortical collecting duct

    • What is the primary role of secretion in renal handling of substances?

  • Concentration of urine
  • Increased reabsorption of nutrients
  • Regulation of waste product elimination (correct)
  • Filtration of plasma proteins

    • Which substance is freely filtered and entirely reabsorbed by the kidneys?

  • Chloride ions
  • Glucose (correct)
  • Sodium ions
  • Urea

    • How many times per day is the plasma volume filtered through the kidneys at a typical GFR?

    <p>60 times</p> Signup and view all the answers

    What is a common waste product formed from the breakdown of nucleic acids?

    <p>Uric acid</p> Signup and view all the answers

    Which ion is indicated to be highly reabsorbed by the kidneys?

    <p>Sodium ions</p> Signup and view all the answers

    What is the mechanism of filtration primarily responsible for?

    <p>Excretion of metabolic products</p> Signup and view all the answers

    What is the function of the macula densa in the kidney?

    <p>Detect sodium chloride concentration</p> Signup and view all the answers

    What is the primary function of the kidneys related to metabolic waste?

    <p>Excretion of metabolic waste products</p> Signup and view all the answers

    How frequently is the plasma volume filtered by the kidneys each day?

    <p>60 times</p> Signup and view all the answers

    Which of the following substances is NOT regulated by the kidneys?

    <p>O2</p> Signup and view all the answers

    What is the maximal concentration of urine that a typical healthy person can achieve?

    <p>1200 mOsm</p> Signup and view all the answers

    What task do different regions of the nephron perform?

    <p>Performing specific modifications to fluid</p> Signup and view all the answers

    To maintain homeostasis, what is primarily regulated by the kidneys in relation to blood pressure?

    <p>Blood volume and cardiac output</p> Signup and view all the answers

    What is the minimal amount of fluid that must be eliminated daily to maintain waste excretion?

    <p>0.5 L</p> Signup and view all the answers

    Which of the following best describes the final product of renal processing?

    <p>Urine containing substances for homeostatic balance</p> Signup and view all the answers

    Which electrolyte's concentration is primarily manipulated by the kidneys to regulate osmolarity?

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

    What role does the kidney play in the production of red blood cells?

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

    Where is ADH synthesized in the body?

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

    What happens to osmoreceptor cells in the anterior hypothalamus when the osmolarity of the extracellular fluid increases?

    <p>They shrink</p> Signup and view all the answers

    What is the primary effect of ADH on the renal tubules?

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

    How does ADH affect aquaporin-2 channels in renal tubules?

    <p>Stimulates their translocation to the membrane</p> Signup and view all the answers

    What is the mechanism for forming dilute urine in the kidneys?

    <p>Decreased ADH release</p> Signup and view all the answers

    What is the effect of high ADH levels on urine concentration?

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

    What happens to the interstitial osmolarity during the formation of dilute urine?

    <p>It decreases from 600 mOsm/L to 300 mOsm/L</p> Signup and view all the answers

    Which function is NOT a role of ADH in kidney water regulation?

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

    What is the primary action of aldosterone in the kidneys?

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

    Which mechanism is responsible for the rapid constriction of peripheral blood vessels?

    <p>Angiotensin II action</p> Signup and view all the answers

    What effect does angiotensin II have on renal arterioles?

    <p>Constricts efferent arteriole</p> Signup and view all the answers

    How does aldosterone affect potassium levels in the body?

    <p>Promotes K+ secretion</p> Signup and view all the answers

    What regulates water and sodium excretion in the body?

    <p>Renin-angiotensin-aldosterone (RAAS) system</p> Signup and view all the answers

    What is the effect of ADH on urine concentration?

    <p>Increases urine concentration</p> Signup and view all the answers

    Which enzyme's activity is stimulated by aldosterone in the basolateral membrane?

    <p>Na-K ATPase</p> Signup and view all the answers

    What does increased tubular reabsorption of Na+ lead to in the body?

    <p>Increased blood pressure over time</p> Signup and view all the answers

    Which of the following is not a major action of aldosterone?

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

    What is the primary role of the macula densa in response to increased glomerular filtration rate (GFR)?

    <p>It increases the resistance of the afferent arteriole by constriction.</p> Signup and view all the answers

    Which substance is released by the macula densa when NaCl and flow rate are low?

    <p>Nitric oxide</p> Signup and view all the answers

    What action does increased NaCl concentration in the macula densa lead to?

    <p>Increased intracellular Ca2+ in smooth muscle cells.</p> Signup and view all the answers

    How does the tubuloglomerular feedback mechanism help to autoregulate GFR during changes in arterial pressure?

    <p>By influencing afferent arteriolar resistance based on NaCl and flow.</p> Signup and view all the answers

    What occurs when the GFR is decreased?

    <p>Decreased NaCl concentration sensed by the macula densa.</p> Signup and view all the answers

    What role does angiotensin II play when GFR is low?

    <p>It constricts the efferent arterioles.</p> Signup and view all the answers

    Which process occurs when NaCl and flow rates are high in the renal system?

    <p>Decreased renin secretion.</p> Signup and view all the answers

    What is the effect of ATP and adenosine released from the macula densa after sensing increased NaCl?

    <p>They increase smooth muscle contraction in the afferent arterioles.</p> Signup and view all the answers

    How does the constriction of the afferent arteriole affect GFR?

    <p>Decreases GFR due to reduced blood flow</p> Signup and view all the answers

    What effect does strong sympathetic nervous system activation have on GFR?

    <p>Decreases GFR by constricting renal arterioles</p> Signup and view all the answers

    Which mechanisms help maintain a consistent renal blood flow and GFR?

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

    What occurs during strong constriction of the efferent arteriole?

    <p>Decreased GFR due to reduced renal blood flow</p> Signup and view all the answers

    What mechanism primarily prevents large changes in GFR with variations in blood pressure?

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

    How is the macula densa feedback mechanism divided?

    <p>Afferent and efferent arteriole feedback mechanisms</p> Signup and view all the answers

    What happens to urine production if GFR increases significantly without autoregulation?

    <p>Urine production increases significantly</p> Signup and view all the answers

    What role does norepinephrine and epinephrine play in regulating GFR?

    <p>They constrict both afferent and efferent arterioles</p> Signup and view all the answers

    What primary factor determines glomerular hydrostatic pressure?

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

    What effect does myogenic response to increased arterial pressure have on renal vasculature?

    <p>Contracts smooth muscle cells in arterioles</p> Signup and view all the answers

    Study Notes

    Course Information

    • Course name: CBM 103 Normal Processes and Regulation
    • Course part: 1
    • Instructor: Tom Kovala
    • Contact Information:

    References

    • Guyton, Textbook of Medical Physiology:
      • Chapter 19: Renin-angiotensin, Hypertension (pages 220-226)
      • Chapter 25: Fluid compartments, edema
      • Chapter 26: Reabsorption and secretion
      • Chapter 27: Glomerular filtration
      • Chapter 28: Tubular filtration and secretion
      • Chapter 29: Urine concentration-dilution, ECF, and Na, K+, Ca++, PO4− and Mg+ regulation
      • Chapter 32: Diuretics
    • Vander's Renal Physiology, 9th Ed.
    • Baynes, Medical Biochemistry: Chapter 35, Water and electrolyte homeostasis
    • Waller, Medical Pharmacology and Therapeutics: Chapter 14, Diuretics
    • Renal Pathophysiology, The Essentials 5th Ed. by H.G. Rennke and B.M. Denker

    Renal Functions

    • Excretion of metabolic waste products and foreign chemicals
    • Regulation of water and electrolyte balance (body fluid osmolarity and electrolyte composition)
    • Regulation of systemic blood pressure and extracellular fluid volume
    • Secretion, metabolism, and excretion of hormones
    • Regulation of acid-base balance
    • Regulation of red blood cell production
    • Regulation of vitamin D production and calcium and phosphate balance
    • Gluconeogenesis

    Maintenance of Body Fluid Composition

    • The kidney regulates fluid volume (cardiac output and blood pressure)
    • osmolarity (largely through Na and Cl)
    • electrolyte content and concentration (Na+, K+, Cl−, Ca²+, PO₄³, Mg²+)
    • pH (looking at regulation of H+ concentration)

    Renal Basics

    • A large volume of blood passes through the kidneys each day
    • About 20% of that volume is filtered (about 180 L filtered per day)
    • As the plasma volume is 3 L, the plasma is filtered ~60 times per day
    • This allows most metabolic waste products to be rapidly removed and eliminated in the urine
    • Most of the fluid and selected substances are reabsorbed to preserve them
    • Some substances are secreted into the filtrate
    • Different regions of the nephron carry out different tasks, depending on the cells present in that region
    • The tubules are like an assembly line, each segment accepts the fluid coming into them, performs specific modifications, and sends the fluid on to the next segment
    • The final product (urine) contains the amounts of substances required to maintain homeostatic balance

    Urine Production

    • A typical healthy 70 kg person has to excrete about 600 mOsm of solutes per day
    • The maximal concentration of urine is about 1200 mOsm
    • Requires the minimal elimination of 0.5 L of fluid per day
    • Necessary to eliminate waste products

    Nephron Structure

    • Diagram showing parts, and associated osmolarity values

    Corticopapillary Osmotic Gradient

    • The thick ascending limb actively pumps NaCl into the medullary interstitium to create an osmotic gradient.
    • Detailed processes and descriptions

    Short-Looped and Long-Looped Nephrons

    • Diagram showing the different nephrons

    Substances in the Plasma

    • Filtration, reabsorption, secretion, and excretion rates for different substances
    • Excretion rate (4) of a substance is determined by filtration (1), reabsorption (2), and secretion (3).

    Renal Handling of Substances

    • Substance A: Filtration only (e.g., creatinine)
    • Substance B: Freely filtered but partially reabsorbed (e.g., electrolytes, Na+, Cl−)
    • Substance C: Freely filtered, but entirely reabsorbed (e.g., amino acids, glucose)
    • Substance D: Freely filtered, additional amounts secreted

    Substances to be Cleared from the Blood

    • Especially metabolic byproducts such as urea, creatinine, uric acid, and urates are poorly reabsorbed
    • Nutritional substances, such as glucose, and amino acids are completely reabsorbed
    • Electrolytes, including Na+, Cl−, and bicarbonate are highly reabsorbed

    Common Waste Products

    • Urea: Ammonia released by deamination of amino acids in the liver, is converted into urea by combining 2 ammonia molecules with 1 CO₂ molecule
    • Creatinine: A waste product produced from the breakdown of protein in muscle tissue and from digestion of protein in food
    • Uric acid: Synthesized in the liver, intestines and vascular endothelium by the degradation of nucleic acids

    Why Filter Large Amounts of Solutes then Reabsorb Them

    • Entire plasma volume is ~3 L
    • GFR is about ~180 L/day
    • Plasma is filtered about 60 times a day
    • High glomerular filtration rate (GFR) allows rapid removal of waste products
    • High GFR allows the kidney to precisely and rapidly regulate the volume and composition of the body fluids

    Effects of Changes in Resistance on GFR

    • Diagram showing the relationships and effects

    GFR Regulation

    • Diagram showing pressure, and effects on GFR

    Physiological Control of GFR and Renal Blood Flow

    • Strong sympathetic nervous system activation decreases GFR
    • Essential all renal blood vessels innervated by sympathetic nerve fibers
    • Mild or moderate sympathetic activation has little or no effect on GFR
    • Seems to be important if severe, acute disturbances (defense reaction, brain ischemia, severe hemorrhage)

    Sympathetic Nervous System Activation Increases Na Reabsorption

    • Strong SNS activation required to constrict renal arterioles, reducing GFR
    • Independent of GFR
    • Low levels of SNS activation can decrease Na and water excretion in the proximal tubule, LoH, and more distal segments of the tubule
    • Results in activation of α-adrenergic receptors in tubular epithelial cells

    Physiological Control of GFR and Renal Blood Flow

    • Norepinephrine and epinephrine constrict afferent and efferent arterioles, reducing GFR
    • Parallel sympathetic nerve activity has effects only under severe conditions
    • Endothelin, released by damaged endothelial cells, constricts afferent and efferent arterioles, reducing GFR. Roles not completely understood

    Myogenic Autoregulation of Renal Blood Flow and GFR

    • "Myogenic mechanism" contributes to maintaining a consistent renal blood flow and GFR
    • Individual blood vessels resist stretching with increased arterial pressure
    • Stretch of the vessel wall increases influx of Ca²⁺ from the ECF into smooth muscle cells
    • Ca²⁺ induces smooth muscle cell contraction, preventing increases in renal blood flow and GFR

    Autoregulation of Renal Blood Flow and GFR

    • Diagram showing relationship between GFR and blood pressure

    Macula Densa Feedback Mechanism

    • Two components:
      • Afferent arteriole feedback mechanism
      • Efferent arteriole feedback mechanism
    • Both dependent on the juxtaglomerular complex

    Macula Densa Feedback

    • Increase in GFR increases NaCl concentration in tubule fluid in the loop of Henle
    • Senses by the macula densa, converted into a signal
    • Increases resistance of the afferent arteriole by constriction, which decreases GFR
    • Decrease in GFR has opposite effects

    Macula Densa Feedback Mechanism

    • Diagram showing the interactions and feedback loops

    Macula Densa Senses

    • (a) Reduced NaCl as the filtrate leaves the thick ascending limb of the loop of Henle and enters the distal tubule
    • (b) Reduced flow sensed by epithelial microvilli (sense flow of fluid)
    • Low NaCl and flow indicates the GFR is low—initiates release of nitric oxide (NO) and prostaglandin (PGE₂) which dilates afferent arteriole smooth muscle, increase release of renin, renin cleaves angiotensinogen to angiotensin II (ACE to Ang II), angiotensin II constricts the efferent arteriole, restores flow rate and pressure, increase GFR to normal
    • High NaCl and flow rate indicates GFR is high—Na-K-2Cl cotransporters increase intracellular NaCl concentration, macula densa (MD) cells release ATP/adenosine
    • ATP/adenosine bind to purinergic receptors of afferent arterioles, increasing Ca²⁺ which induces constriction, reduces renin secretion, reduces flow rate and pressure, dropping GFR to normal

    Mechanism by which increase in Na in NaCl at macula densa induces vasoconstriction

    • Increasing GFR elevates the [NaCl] in the tubule at the MD, enhancing NaCl uptake of MD cells through the Na-K-2CI symporter (NKCC2)
    • Increase ATP and adenosine (ADO) release
    • ATP binds to P2X receptors, adenosine binds to adenosine A1 receptors in smooth muscle cells surrounding the afferent arteriole, increase intracellular [Ca²⁺]
    • Rise in [Ca²⁺] induces vasoconstriction of the afferent arteriole, returning GFR to normal levels

    ATP and Adenosine Inhibition of Renin and GFR Regulation

    • [NaCl] decreases, reduces NaCl uptake by MD densa cells
    • Reduces ATP/Adenosine release, which decreases intracellular [Ca²⁺] in smooth muscle cells
    • Increase GFR and stimulate renin release
    • Decrease in NaCl entry into macula densa cells increases production of prostaglandin E₂ (stimulating renin secretion by granular cells)
    • Increases in GFR—NaCl delivery to macula densa increases; renin release decreases; which reduces plasma angiotensin II, a hormone that enhances NaCl and water retention

    Regulation of Renin Secretion

    • Perfusion pressure: Afferent arteriole acts as a high-pressure baroreceptor. Decreased BP, renin is secreted; increased BP, renin secretion is suppressed
    • Sympathetic nerve activity: Activation of sympathetic nerves increases renin secretion
    • NaCl delivery to Macula densa: High NaCl inhibits renin secretion; low NaCl increases renin secretion

    Angiotensinogen

    • Synthesized in the liver
    • 400 amino acids glycoprotein
    • Angiotensin I: 10 amino acids cleaved off by renin
    • Angiotensin II: 8 amino acids cleaved off by angiotensin converting enzyme (ACE)

    Angiotensin II Raises Blood Pressure

    • Direct effects of Angiotensin II -Constriction of peripheral blood vessels (rapid) -Constricts renal arterioles, reducing blood flow and filtration rates -Slower blood flow reduces pressure in peritubular capillaries, increasing reabsorption from the tubules -Increases tubular reabsorption of Na and water in proximal tubule, thick ascending Loop of Henle, distal tubule, collecting tubule
    • Indirect effects of Angiotensin II -Release of aldosterone from the adrenal cortex, which promotes reabsorption of Na+ and H₂O in the distal convoluted tubule and increases K+ secretion -Na+ and water reabsorption increase ECF and arterial pressure.

    Angiotensin II Increases Na and Water Reabsorption

    • Stimulates Na reabsorption in the proximal tubule, LoH, distal tubule, and the collecting ducts
    • Stimulates Na-K ATPase in the basolateral membrane
    • Na-H exchanger (NHE) in the luminal membrane (more Na absorbed and H+ secreted)
    • Na-bicarbonate co-transporter in the basolateral membrane

    Aldosterone

    • Major mineralocorticoid produced in the adrenal cortex
    • Primary site of action is the principal cells of the cortical collecting tube
    • Regulates ECF volume (increases reabsorption of Na+, therefore increases water reabsorption)
    • Controls potassium homeostasis (Increases secretion of K+)

    Aldosterone Increases Na Reabsorption and K Secretion

    • Major site for aldosterone action is the principal cells of the cortical collecting tube
    • Activates the Na-K ATPase in the basolateral membrane
    • Increase Na permeability on the luminal membrane
    • Aldosterone increases ECF volume and arterial pressure but has only a small effect on plasma Na concentrations (balanced by water uptake)

    Blood Pressure Regulation by the Renin-Angiotensin-Aldosterone Pathway (RAAS)

    • Diagram of the pathway, explaining the effect of blood pressure on renin release and subsequent effects

    Regulation

    • Renal feedback mechanisms: -Control sodium and water excretion -ECF sodium concentration and osmolarity
    • Eliminate excess water: Producing a dilute urine
    • Conserve water: Producing a concentrated urine
    • Mechanisms that regulate water and sodium appetite

    Antidiuretic Hormone (ADH)

    • ADH = vasopressin = arginine vasopressin (AVP)
    • Alters renal excretion of water independent of solute excretion
    • Feedback system to regulate urine concentration

    ADH Synthesis

    • ADH synthesized in supraoptic and paraventricular neurons
    • Osmoreceptor cells in the anterior hypothalamus shrink when the osmolarity of the ECF increases
    • Osmoreceptor cell sends signal to nerve cells
    • ADH released into the bloodstream from the posterior pituitary

    Summary of Regional Tubule Functions

    • Diagram showing the relationship between ADH and water permeability in distal tubules and collecting ducts

    ADH Increases Water Permeability via Aquaporin-2 Channels

    • Vasopressin-induced increase in the water permeability of the collecting duct
    • Rapid effect translocation of aquaporin-2 to the membrane
    • Long term effect, increase production of aquaporin-2

    Formation of a Dilute Urine

    • Continue electrolyte reabsorption
    • Decrease water reabsorption
    • Mechanism: Decreased ADH release and reduced water permeability in distal and collecting tubules

    Formation of a Concentrated Urine when ADH Levels are High

    • Continue electrolyte reabsorption
    • Increase water reabsorption
    • Increased ADH
    • High osmolarity of renal medulla (countercurrent multiplier)

    Changes in Osmolarity of the Renal Tubular Fluid

    • Diagram showing changes in osmolarity

    Note on Interstitial Osmolarity Gradients

    • In dilute urine formation, interstitial osmolarity goes from 300 mOsm/L in the cortex to 600 mOsm/L
    • In dilute urine formation, interstitial osmolarity goes from 200 mOsm/L to 1200 mOsm/L in the medullary interstitium

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    Test your knowledge on renal physiology with this quiz. Questions cover key concepts such as filtration, reabsorption, secretion, and the functions of different nephron regions. Ideal for students studying human biology or medical courses.

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