Renal Physiology and Angiotensin II Effects
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What role does angiotensin II play in the regulation of mean arterial pressure (MAP)?

  • It has no significant effect on MAP.
  • It decreases MAP by stimulating the release of natriuretic peptides.
  • It increases MAP by constricting arteriolar smooth muscle. (correct)
  • It decreases MAP by dilating blood vessels.

    • Which of the following effects is directly related to aldosterone release triggered by angiotensin II?

  • Increase in blood volume due to sodium reabsorption. (correct)
  • Promotion of glucose reabsorption in the kidneys.
  • Decrease in renal blood flow.
  • Stimulation of urine output.

    • Which condition triggers the release of renin from granular cells?

  • Higher mean arterial pressure (MAP).
  • MAP falling below 80 mm Hg. (correct)
  • Increased sodium concentration in the blood.
  • Increased stretching of granular cells.

    • How does angiotensin II affect renal function?

    <p>By decreasing surface area available for filtration through contraction of mesangial cells.</p> Signup and view all the answers

    What is the relationship between angiotensin II and the hypothalamus?

    <p>Angiotensin II stimulates the hypothalamus to release ADH and activates the thirst center.</p> Signup and view all the answers

    What is the primary function of the countercurrent mechanisms in the kidneys?

    <p>To establish and maintain an osmotic gradient</p> Signup and view all the answers

    Which segment of the Loop of Henle is impermeable to water?

    <p>Ascending limb</p> Signup and view all the answers

    What happens to the osmolality of the filtrate as it passes through the descending limb of the Loop of Henle?

    <p>It increases to approximately 1200 mOsm</p> Signup and view all the answers

    Which ion is actively reabsorbed in the thick segment of the ascending limb of the Loop of Henle?

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

    What is the osmolality range that the kidneys establish from the renal cortex to the medulla?

    <p>300 mOsm to 1200 mOsm</p> Signup and view all the answers

    What is the average Glomerular Filtration Rate (GFR) in healthy kidneys?

    <p>120–125 ml/min</p> Signup and view all the answers

    Which structure allows filtrate to pass into the capsular space?

    <p>Filtration slits</p> Signup and view all the answers

    What primarily governs the Glomerular Filtration Rate?

    <p>Total surface area available for filtration</p> Signup and view all the answers

    Which type of control mechanism acts locally within the kidney to regulate GFR?

    <p>Intrinsic controls</p> Signup and view all the answers

    What type of epithelium comprises the parietal layer of the glomerular capsule?

    <p>Simple squamous epithelium</p> Signup and view all the answers

    What is the significance of the net filtration pressure (NFP) in kidney function?

    <p>It dictates the amount of filtrate produced.</p> Signup and view all the answers

    Which of the following pressures contributes to the net filtration pressure (NFP)?

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

    What are the extensions of visceral layer podocytes called that cling to the basement membrane?

    <p>Foot processes</p> Signup and view all the answers

    What is the primary function of the myogenic mechanism in intrinsic controls?

    <p>To maintain a constant GFR when MAP is between 80-180 mm Hg</p> Signup and view all the answers

    How do macula densa cells respond when GFR increases?

    <p>They release a vasoconstricting chemical that acts on the afferent arteriole.</p> Signup and view all the answers

    What happens to the afferent arterioles during extreme stress conditions?

    <p>They constrict due to norepinephrine and epinephrine release.</p> Signup and view all the answers

    What is the role of the tubuloglomerular feedback mechanism?

    <p>To adjust GFR based on sodium chloride concentration in the filtrate.</p> Signup and view all the answers

    What is the range of mean arterial pressure (MAP) for which intrinsic controls effectively maintain GFR?

    <p>80-180 mm Hg</p> Signup and view all the answers

    Which of the following occurs when GFR decreases?

    <p>The afferent arterioles dilate to restore GFR.</p> Signup and view all the answers

    What protects the glomeruli from high blood pressure damage?

    <p>Myogenic mechanism constriction of afferent arterioles</p> Signup and view all the answers

    Which mechanism is flow-dependent and directed by macula densa cells?

    <p>Tubuloglomerular feedback mechanism</p> Signup and view all the answers

    What happens to the filtrate as it moves through the ascending loop of Henle?

    <p>It is diluted.</p> Signup and view all the answers

    What occurs in the renal pelvis when there is no ADH present?

    <p>Dilute urine is formed.</p> Signup and view all the answers

    To what minimum osmolality can the filtrate decrease in the distal convoluted tubule and collecting duct?

    <p>50 mOsm</p> Signup and view all the answers

    What role does Na+ play in the formation of dilute urine?

    <p>It may be selectively removed from the filtrate.</p> Signup and view all the answers

    Which of the following describes the effect of ADH on urine concentration?

    <p>ADH leads to the formation of concentrated urine.</p> Signup and view all the answers

    During which process is water primarily reabsorbed in the nephron?

    <p>Passive transport in the descending limb of Henle</p> Signup and view all the answers

    In which part of the nephron is the filtrate first diluted?

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

    What is the effect of removing Na+ from the filtrate in the DCT and collecting duct?

    <p>Decreased osmolality of excreted urine</p> Signup and view all the answers

    What type of connective tissue primarily composes the outer adventitia of the urinary bladder?

    <p>Fibrous connective tissue</p> Signup and view all the answers

    Which muscle type is primarily responsible for the contraction of the detrusor muscle during urination?

    <p>Smooth muscle</p> Signup and view all the answers

    Where do kidney stones typically form?

    <p>In the renal pelvis</p> Signup and view all the answers

    What is the primary role of the internal urethral sphincter?

    <p>To prevent urine leakage during filling</p> Signup and view all the answers

    Which layer of the bladder wall is composed of transitional epithelial mucosa?

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

    Which of the following factors is NOT associated with the formation of renal calculi?

    <p>High urine output</p> Signup and view all the answers

    What initiates the process of micturition?

    <p>Contraction of the bladder wall</p> Signup and view all the answers

    What type of epithelium primarily lines the urethra?

    <p>Pseudostratified columnar epithelium</p> Signup and view all the answers

    Study Notes

    Excretory System Jokes

    • Jokes about the excretory system are not very funny.

    Urinary System Organs

    • Kidneys are major excretory organs.
    • Urinary bladder is the temporary storage reservoir for urine.
    • Ureters transport urine from the kidneys to the bladder.
    • Urethra transports urine out of the body.

    Kidney Functions

    • Removal of toxins, metabolic wastes, and excess ions from the blood.
    • Regulation of blood volume, chemical composition, and pH.
    • Gluconeogenesis during prolonged fasting
    • Endocrine functions
    • Renin: regulation of blood pressure and kidney function
    • Erythropoietin: regulation of RBC production
    • Activation of vitamin D

    Nephrons

    • Structural and functional units that form urine.
    • Approximately 1 million per kidney.
    • Two main parts:
      • Glomerulus: a tuft of capillaries
      • Renal tubule: begins as a cup-shaped glomerular (Bowman's) capsule surrounding the glomerulus.

    Renal Corpuscle

    • Glomerular capsule
    • Glomerulus

    Renal Tubule

    • Proximal convoluted tubule
    • Loop of Henle (Descending limb and Ascending limb)
    • Distal convoluted tubule
    • Collecting duct

    Glomerular Filtration

    • Passive mechanical process driven by hydrostatic pressure.
    • The glomerulus is a very efficient filter because its filtration membrane is very permeable and it has a large surface area.
    • Glomerular blood pressure is higher (55 mm Hg) than other capillaries.
    • Molecules >5 nm are not filtered (e.g., plasma proteins) and function to maintain colloid osmotic pressure of the blood.
    • Filtration membrane has three parts:
      • Capillary endothelium
      • Basement membrane
      • Foot processes of podocytes of glomerular capsule

    Glomerular Filtration Rate (GFR)

    • Volume of filtrate formed per minute by the kidneys (120-125 ml/min).
    • Governed by (and directly proportional to):
      • Total surface area available for filtration
      • Filtration membrane permeability
      • Net filtration pressure

    Regulation of Glomerular Filtration

    • GFR is tightly controlled by two types of mechanisms:
      • Intrinsic controls (renal autoregulation): Act locally within the kidney
      • Extrinsic controls: Nervous and endocrine mechanisms that maintain blood pressure, but affect kidney function

    Intrinsic Controls: Myogenic Mechanism

    • BP constriction of afferent arterioles
    • Helps maintain normal GFR
    • Protects glomeruli from damaging high BP
    • BP dilation of afferent arterioles
    • Helps maintain normal GFR

    Intrinsic Controls: Tubuloglomerular Feedback Mechanism

    • Flow-dependent mechanism directed by the macula densa cells.
    • If GFR increases, filtrate flow rate increases in the tubule.
    • Filtrate NaCl concentration will be high because of insufficient time for reabsorption.
    • Macula densa cells of the JGA respond to NaCl by releasing a vasoconstricting chemical that acts on the afferent arteriole; GFR.
    • The opposite occurs if GFR decreases.

    Extrinsic Controls: Sympathetic Nervous System

    • Under normal conditions at rest: renal blood vessels are dilated; renal autoregulation mechanisms prevail.
    • Under extreme stress: norepinephrine is released by the sympathetic nervous system; epinephrine is released by the adrenal medulla; both cause constriction of afferent arterioles, inhibiting filtration and triggering the release of renin.

    Extrinsic Controls: Renin-Angiotensin Mechanism

    • Triggered when the granular cells of the JGA release renin.
    • Angiotensinogen (a plasma globulin), renin, angiotensin I, angiotensin-converting enzyme (ACE), angiotensin II

    Effects of Angiotensin II

      1. Constrict arteriolar smooth muscle, causing MAP to rise.
      1. Stimulates the reabsorption of Na+.
      1. Acts directly on the renal tubules; triggers adrenal cortex to release aldosterone
      1. Stimulates the hypothalamus to release ADH and activates the thirst center
    • Constrict efferent arterioles; decreasing peritubular capillary hydrostatic pressure and increasing fluid reabsorption
    • Causes glomerular mesangial cells to contract; decreasing the surface area available for filtration

    Triggers for renin release by granular cells

    • Reduced stretch of granular cells (MAP below 80 mm Hg)
    • Stimulation of the granular cells by activated macula densa cells
    • Direct stimulation of granular cells via 1-adrenergic receptors by renal nerves

    Other Factors Affecting GFR

    • Prostaglandin E2: Vasodilator that counteracts vasoconstriction by norepinephrine and angiotensin II; prevents renal damage when peripheral resistance is increased.
    • Intrarenal angiotensin II: Reinforces the effects of hormonal angiotensin II
    • Adenosine: A vasoconstrictor of renal vasculature

    Tubular Reabsorption

    • A selective transepithelial process.
    • All organic nutrients are reabsorbed.
    • Water and ion reabsorption are hormonally regulated.
    • Includes active and passive processes
    • Two routes:
      • Transcellular
      • Paracellular

    Paracellular Route

    • Between cells.
    • Limited to water movement and reabsorption of Ca2+, Mg2+, K+, and some Na+ in the PCT where tight junctions are leaky.

    Transcellular Route

    • Luminal membranes of tubule cells
    • Cytosol of tubule cells
    • Basolateral membranes of tubule cells
    • Endothelium of peritubular capillaries

    Sodium Reabsorption

    • Na+ (most abundant cation in filtrate)
    • Primary active transport out of the tubule cell
    • Na+-K+ ATPase in the basolateral membrane
    • Na+ passes in through the luminal membrane by secondary active transport or facilitated diffusion mechanisms

    Reabsorption of Nutrients, Water, and lons

    • Na+ reabsorption provides energy and means for reabsorbing most other substances.
    • Organic nutrients are reabsorbed by secondary active transport.
    • Transport maximum (Tm) reflects the number of carriers in the renal tubules available.
    • When carriers are saturated, excess of that substance is excreted.
    • Water is reabsorbed by osmosis (obligatory water reabsorption), aided by water-filled pores called aquaporins.
    • Cations and fat-soluble substances follow by diffusion.

    Reabsorptive Capabilities of Renal Tubules and Collecting Ducts

    • PCT: Site of most reabsorption (65% of Na+ and water, all nutrients, ions, small proteins)
    • Loop of Henle:
      • Descending limb: H2O
      • Ascending limb: Na+, K+, Cl-
    • DCT and collecting duct: Reabsorption is hormonally regulated; Ca2+ (PTH), Water (ADH), Na+ (aldosterone and ANP)
    • Mechanism of aldosterone: Targets collecting ducts (principal cells) and distal DCT; promotes synthesis of luminal Na+ and K+ channels; promotes synthesis of basolateral Na+-K+ ATPases

    Tubular Secretion

    • Reabsorption in reverse.
    • K+, H+, NH4+, creatinine, and organic acids move from peritubular capillaries or tubule cells into filtrate.
    • Disposes of substances that are bound to plasma proteins.
    • Eliminates undesirable substances that have been passively reabsorbed (e.g., urea and uric acid).
    • Rids the body of excess K+.
    • Controls blood pH by altering amounts of H+ or HCO3- in urine.

    Regulation of Urine Concentration and Volume

    • Osmolality: Number of solute particles in 1 kg of H2O; reflects ability to cause osmosis
    • Osmolality of body fluids: Expressed in milliosmols (mOsm); The kidneys maintain osmolality of plasma at ~300 mOsm, using countercurrent mechanisms

    Countercurrent Mechanism

    • Occurs when fluid flows in opposite directions in two adjacent segments of the same tube.
    • Filtrate flow in the loop of Henle (countercurrent multiplier).
    • Blood flow in the vasa recta (countercurrent exchanger).
    • Role of countercurrent mechanisms: Establish and maintain an osmotic gradient (300 mOsm to 1200 mOsm) from renal cortex through the medulla; Allow the kidneys to vary urine concentration.
    • Countercurrent Multiplier: Loop of Henle
      • Descending limb: Freely permeable to H2O, which passes out of the filtrate into the hyperosmotic medullary interstitial fluid; Filtrate osmolality increases to ~1200 mOsm
      • Ascending limb: Impermeable to H2O, Selectively permeable to solutes (Na+ and Cl- are passively reabsorbed in the thin segment, Actively reabsorbed in the thick segment); Filtrate osmolality decreases to 100 mOsm
    • Countercurrent Exchanger: Vasa Recta
      • Maintain the osmotic gradient
      • Deliver blood to the medullary tissues
      • Protect the medullary osmotic gradient by preventing rapid removal of salt, and by removing reabsorbed H2O

    Formation of Dilute Urine

    • Filtrate is diluted in the ascending loop of Henle.
    • In the absence of ADH, dilute filtrate continues into the renal pelvis as dilute urine.
    • Na+ and other ions may be selectively removed in the DCT and collecting duct, decreasing osmolality to as low as 50 mOsm.

    Formation of Concentrated Urine

    • Depends on the medullary osmotic gradient and ADH.
    • ADH triggers reabsorption of H2O in the collecting ducts.
    • Facultative water reabsorption occurs in the presence of ADH so that 99% of H2O in filtrate is reabsorbed.

    Diuretics

    • Chemicals that enhance the urinary output.
    • Osmotic diuretics: Substances not reabsorbed (e.g., high glucose in a diabetic patient).
    • ADH inhibitors such as alcohol.
    • Substances that inhibit Na+ reabsorption and obligatory H2O reabsorption such as caffeine and many drugs

    Renal Clearance

    • Volume of plasma cleared of a particular substance in a given time.
    • Renal clearance tests are used to
      • Determine GFR
      • Detect glomerular damage
      • Follow the progress of renal disease.
    • RC = UV/P
      • RC = renal clearance rate (ml/min)
      • U = concentration (mg/ml) of the substance in urine
      • V = flow rate of urine formation (ml/min)
      • P = concentration of the same substance in plasma

    Renal Clearance (continued)

    • For any substance freely filtered and neither reabsorbed nor secreted, RC = GFR = 125 ml/min.
    • If RC < 125 ml/min, the substance is reabsorbed.
    • If RC = 0, the substance is completely reabsorbed.
    • If RC > 125 ml/min, the substance is secreted (most drug metabolites)

    Physical Characteristics of Urine

    • Color and transparency: Clear, pale to deep yellow (due to urochrome); Drugs, vitamin supplements, and diet can alter the color; cloudy urine may indicate a urinary tract infection.
    • Odor: Slightly aromatic when fresh; develops ammonia odor upon standing; may be altered by some drugs and vegetables.
    • pH: Slightly acidic (~pH 6, with a range of 4.5 to 8.0); Diet, prolonged vomiting, or urinary tract infections may alter pH; Specific gravity: 1.001 to 1.035, dependent on solute concentration.
    • Chemical Composition of Urine
      • 95% water and 5% solutes.
      • Nitrogenous wastes: urea, uric acid, and creatinine
      • Other normal solutes: Na+, K+, PO43–, SO42-, Ca2+, Mg2+, HCO3-
      • Abnormally high concentrations of any constituent may indicate pathology

    Ureters

    • Convey urine from kidneys to bladder.
    • Retroperitoneal.
    • Enter the base of the bladder through the posterior wall.
    • As bladder pressure increases, distal ends of the ureters close, preventing backflow of urine
    • Three layers of wall of ureter:
        1. Lining of transitional epithelium
        1. Smooth muscle muscularis (contracts in response to stretch)
        1. Outer adventitia of fibrous connective tissue

    Renal Calculi

    • Kidney stones form in renal pelvis.
    • Crystallized calcium, magnesium, or uric acid salts .
    • Larger stones block ureter; cause pressure and pain in kidneys.
    • May be due to chronic bacterial infection, urine retention, Ca2+ in blood, pH of urine.

    Urinary Bladder

    • Muscular sac for temporary storage of urine.
    • Retroperitoneal, on pelvic floor posterior to pubic symphysis.
    • Males-prostate gland surrounds the neck inferiorly.
    • Females-anterior to the vagina and uterus.
    • Layers of the bladder wall:
      • 1 Transitional epithelial mucosa
      • 2 Thick detrusor muscle (three layers of smooth muscle).
      • 3 Fibrous adventitia (peritoneum on superior surface only).
    • Collapses when empty; rugae appear
    • Expands and rises superiorly during filling without significant rise in internal pressure

    Urethra

    • Muscular tube
    • Lining epithelium: Mostly pseudostratified columnar epithelium, except Transitional epithelium near bladder, Stratified squamous epithelium near external urethral orifice
    • Sphincters:
      • Internal urethral sphincter (involuntary, smooth muscle at bladder-urethra junction)
      • External urethral sphincter (voluntary, skeletal muscle surrounding the urethra as it passes through the pelvic floor)

    Micturition

    • Urination or voiding
    • Three simultaneous events:
      • 1 Contraction of detrusor muscle by ANS
      • 2 Opening of internal urethral sphincter by ANS
      • 3 Opening of external urethral sphincter by somatic nervous system
    • Pontine control centers mature between ages 2 and 3.
        1. Pontine storage center inhibits micturition: Inhibits parasympathetic pathways; Excites sympathetic and somatic efferent pathways.
        1. Pontine micturition center promotes micturition: Excites parasympathetic pathways; Inhibits sympathetic and somatic efferent pathways

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    Description

    This quiz explores the crucial role of angiotensin II in regulating mean arterial pressure and its various effects on renal function. Test your knowledge on key concepts such as the relationship between angiotensin II and aldosterone, renal countercurrent mechanisms, and the Loop of Henle's structure. Understand how these factors contribute to kidney function and homeostasis.

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