Kidney Function and Body Fluids
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Questions and Answers

What is the primary function of the kidneys in maintaining homeostasis?

  • Maintaining the concentration of most of the constituents of body fluids (correct)
  • Regulating the concentration of oxygen in the body
  • Filtering out waste products from the digestive system
  • Producing hormones to regulate blood pressure

    • What is the functional unit of the kidney?

  • Bowman's capsule
  • Glomerulus
  • Renal tubule
  • Nephron (correct)

    • What is the function of the proximal convoluted tubule?

  • Filtration of plasma
  • Regulation of blood pressure
  • Reabsorption of glucose, Na+, K+, HCO3, and H2O (correct)
  • Secretion of K+ and H+

    • What is the function of the loop of Henle?

    <p>Regulation of sodium and water balance</p> Signup and view all the answers

    What is the function of the distal convoluted tubule?

    <p>Secretion of potassium and hydrogen ions</p> Signup and view all the answers

    What percentage of the cardiac output is received by the kidneys?

    <p>20-25%</p> Signup and view all the answers

    What is the term for the renal plasma flow that becomes glomerular filtrate?

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

    What is the function of the juxtaglomerular apparatus?

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

    What is the main function of secretion in the glomerular filtration process?

    <p>Transfer of substances from the blood to the lumen</p> Signup and view all the answers

    What is the glomerular filtration rate (GFR) in milliliters per minute?

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

    What is the effect of an increase in osmotic pressure of Bowman's capsule on GFR?

    <p>Increases GFR</p> Signup and view all the answers

    What is the composition of the glomerular filtrate?

    <p>Plasma minus plasma proteins</p> Signup and view all the answers

    Why does an increase in ABP have little effect on GFR?

    <p>Due to autoregulation of GFR</p> Signup and view all the answers

    What is the function of the basement membrane in the glomerular capillary membrane?

    <p>Decreases diffusion of albumin due to repulsion with proteoglycan</p> Signup and view all the answers

    What are the two forces that help filtration in the glomerular capillary membrane?

    <p>Glomerular capillary pressure and osmotic pressure of proteins in Bowman's capsule</p> Signup and view all the answers

    What is the primary mechanism of active reabsorption in the proximal tubule?

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

    What is the net filtration pressure in the glomerular capillary membrane?

    <p>10 mmHg</p> Signup and view all the answers

    What is the normal fasting blood glucose level?

    <p>70-110 mg/100 ml blood</p> Signup and view all the answers

    What is the effect of an increase in glomerular hydrostatic pressure on the glomerular filtration rate?

    <p>Increases GFR</p> Signup and view all the answers

    What is the renal threshold for glucose?

    <p>180 mg/100 ml blood</p> Signup and view all the answers

    What is the effect of a decrease in plasma proteins on the glomerular filtration rate?

    <p>Increases GFR</p> Signup and view all the answers

    What is the term for the abnormal excretion of glucose in the urine?

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

    What is the primary mechanism of sodium reabsorption and excretion in the kidneys?

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

    What is the result of a decrease in GFR on urea excretion?

    <p>Decreases urea excretion</p> Signup and view all the answers

    What is the primary function of a chemical buffer system?

    <p>To maintain a constant pH level in the body</p> Signup and view all the answers

    Which buffer system is considered the strongest due to its huge amount?

    <p>Protein buffer system</p> Signup and view all the answers

    How does the respiratory system control pH in the blood?

    <p>By controlling CO2 tension</p> Signup and view all the answers

    What is the primary mechanism of water reabsorption in proximal tubules?

    <p>Obligatory reabsorption</p> Signup and view all the answers

    What is the effect of aldosterone on sodium retention?

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

    What is the response of the respiratory system in case of acidosis?

    <p>It increases CO2 washout</p> Signup and view all the answers

    What is the normal daily intake of potassium in an adult?

    <p>100 mEq/day</p> Signup and view all the answers

    How do the kidneys regulate pH in the body?

    <p>By controlling HCO3 absorption and formation</p> Signup and view all the answers

    What are the two types of acidosis and alkalosis?

    <p>Respiratory and metabolic</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

    What is the primary source of hydrogen ions in the body?

    <p>Not specified in the text</p> Signup and view all the answers

    What is the effect of diabetes insipidus on water balance?

    <p>Water loss</p> Signup and view all the answers

    What is the primary mechanism of regulating H+ concentration in the body?

    <p>All of the above</p> Signup and view all the answers

    What is the effect of osmotic diuretics on sodium reabsorption?

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

    Study Notes

    Kidney Function

    • The kidneys perform two major functions: excreting end products of body metabolism (e.g., urea, uric acid) and maintaining the concentration of body fluid constituents (e.g., volume, ions, osmotic pressure).
    • The kidneys play a crucial role in homeostasis.
    • The kidneys produce renin and prostaglandins, which affect blood pressure.
    • The kidneys produce renal erythropoietin, which helps synthesize red blood cells.

    Functional Anatomy of the Kidney

    • The functional unit of the kidney is the nephron, which consists of:
    • Glomerulus (tuft of capillaries between two arterioles, embedded in Bowman's capsule) + Function: Filtration of plasma
    • Renal tubule: - Proximal convoluted tubule: brush luminal border (microvilli), mitochondria for energy for active transport - Function: Reabsorption of glucose, Na+, K+, HCO3, H2O, and amino acids - Loop of Henle: - Descending and ascending limbs - Distal convoluted tubule >> collecting tubules >> renal pelvis - Function: + Reabsorption of Na+ (aldosterone), H2O (ADH) + Secretion of K+ (aldosterone) and H+

    Blood Supply

    • Each kidney contains about 1.3 million nephrons.
    • The kidneys receive 20-25% of the cardiac output.
    • The renal artery (a direct branch from the abdominal aorta) supplies blood to the kidney.
    • The efferent arteriole gives rise to peritubular capillaries.

    Formation of Urine

    • Glomerular filtration: Plasma is filtered through the glomerular capillary membrane into the space of Bowman's capsule.
    • Reabsorption: Transfer of substances from the lumen to the blood.
    • Secretion: Transfer of substances from the blood to the lumen.
    • Glomerular filtrate: Plasma minus plasma proteins.
    • Glomerular filtration rate (GFR) = 125 ml/min = 180 L/day.

    Glomerular Capillary Membrane

    • Three layers: endothelial layer with pores (Fenestra), podocytes, and the basement membrane.
    • 1% of albumin passes the membrane, which is cigar-shaped and negatively charged, decreasing diffusion.

    Filtration Forces

    • Two forces help filtration:
      • Glomerular capillary pressure = 60 mmHg
      • Osmotic pressure of proteins in Bowman's capsule = 0
    • Two forces oppose filtration:
      • Osmotic pressure of proteins in glomerulus = 32 mmHg
      • Hydrostatic pressure in Bowman's capsule = 18 mmHg

    Factors Affecting Glomerular Filtration

    • Changes in filtration coefficient (Kf)
    • Increases in glomerular hydrostatic pressure (e.g., increased blood pressure, dilation of afferent arteriole)
    • Increases in hydrostatic pressure of Bowman's capsule (e.g., urine flow obstruction)
    • Decreases in osmotic pressure of glomerular capillaries (e.g., decreased plasma proteins)
    • Increases in osmotic pressure of Bowman's capsule (e.g., nephrotic syndrome)

    Tubular Reabsorption

    • Active reabsorption: Against concentration gradient, needs energy (e.g., Na+, K+, glucose, amino acids)
    • Passive reabsorption: With concentration gradient, no energy required (e.g., glucose, amino acids, proteins, vitamins)

    Glucose Reabsorption

    • Completely reabsorbed by an active process in the proximal tubule
    • Glucose level in blood: 70-110 mg/100 ml (fasting), 140 mg/100 ml (2 hours postprandial)
    • Renal threshold for glucose: 180 mg/100 ml (above which glucose appears in urine)

    Amino Acid Reabsorption

    • Active reabsorption in the proximal convoluted tubule

    Sodium Reabsorption and Excretion

    • Mainly regulated by aldosterone
    • 99% of Na+ filtered is reabsorbed in renal tubules
    • Diuretics inhibit tubular sodium and water reabsorption

    Potassium Regulation

    • Normal plasma level: 3.5-5 mEq/L
    • Daily intake: 100 mEq, excreted in urine (90 mEq) and feces (10 mEq)
    • Factors increasing renal potassium excretion:
      • High potassium diet
      • Aldosterone in the distal convoluted tubule
    • Renal failure leads to increased potassium levels in blood

    Water Reabsorption and Excretion

    • Obligatory water reabsorption in the proximal tubules
    • Facultative water reabsorption in the late distal and collecting tubules, regulated by ADH
    • Diabetes insipidus: Deficiency of ADH (pituitary) or failure of the kidney to respond to ADH (nephrogenic)

    Regulation of H+ Concentration (Acid-Base Balance)

    • Hydrogen ion concentration is kept constant (pH = 7.4)
    • Sources of hydrogen ions in the body: metabolic processes
    • Mechanism of acid-base balance:
      1. Rapidly acting (chemical buffers): seconds to minutes
      2. Intermediate acting (respiratory regulation): minutes to hours
      3. Slowly acting (renal regulation): hours to days

    Chemical Buffers

    • Buffer systems: Weak acids + salts of their conjugate base (e.g., H2CO3 + NaHCO3)
    • Bicarbonate-carbonic acid system: Not a powerful buffer
    • Protein buffer system: Plasma proteins (7 gm/100 cc) and hemoglobin (15 gm/100 cc) act as weak acids

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    Learn about the kidney's role in excreting waste products, maintaining body fluid balance, and producing hormones that affect blood pressure and red blood cell synthesis.

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