Renal System

• What are the learning outcomes related to the kidneys?

  Identify organs associated with kidneys, outline gross structure, describe nephron structure, explain urine formation, maintain body water and electrolyte balance, and be aware of kidney disorders.
• At what week do kidneys develop in human embryos?

  By the 10th week.
• What embryonic structure do the kidneys replace during development?

  The mesonephros.
• What is the anatomical position of the kidneys?

  • Lie on the posterior abdominal wall
  • One on each side of the vertebral column
  • Below the diaphragm
  • Behind the peritoneum
  • Retroperitoneal
  • Extend from the 12th thoracic vertebra to the 3rd lumbar vertebra
  • Protected by the lower ribcage
• How long, wide, and thick are the kidneys?

  About 11 cm long, 6 cm wide, and 3 cm thick.
• Why is the right kidney usually slightly lower than the left?

  Due to the space occupied by the liver.
• What is the average weight of the kidneys?

  Around 150 g.
• What encloses the kidneys and holds them in position?

  A sheath of fibrous connective tissue called the renal fascia.
• What structures enter and leave the kidney via the hilum?

  • Renal blood vessels
  • Lymph vessels
  • Ureter
  • Nerves
• Describe the urine drainage system from the kidney.

  1. Urine formed in the kidney passes through renal papilla into minor calyx
  2. Several minor calyces merge into a major calyx
  3. Major calyces combine to form the renal pelvis
  4. Renal pelvis narrows to become the ureter
• What type of epithelium lines the walls of the calyces and renal pelvis?

  Transitional epithelium.
• What propels urine through the calyces, renal pelvis, and ureter?

  Peristalsis.
• What percentage of cardiac output do the kidneys receive?

  About 20%.
• What is the blood supply to the kidneys?

  Via the renal artery.
• What are the main components of the nephron?

  • Glomerular (Bowman’s) capsule
  • Glomerulus
  • Proximal convoluted tubule
  • Medullary loop (loop of Henle)
  • Distal convoluted tubule
  • Collecting duct
• How many nephrons does the kidney contain?

  1–2 million nephrons.
• What is the function of the collecting ducts in the kidneys?

  Transport urine through the pyramids to the calyces.
• What is the role of mesangial cells in the kidneys?

  They protect the kidneys from invading microorganisms.
• What happens to blood after it leaves the glomerulus?


  It leaves in the efferent arteriole.
• Why does the afferent arteriole have a larger diameter than the efferent arteriole?

  To increase blood pressure inside the glomerular capillaries.
• What is the fluid that has left the blood and entered the glomerular capsule called?

  Filtrate.
• What are the three processes involved in urine formation?

  1. Filtration
  2. Selective reabsorption
  3. Secretion
• What is the composition of the filtrate compared to plasma?

  Very similar, but without blood cells, plasma proteins, and large molecules.
• What causes filtration to occur in the glomerulus?

  A difference in blood pressure between the glomerulus and the filtrate in the glomerular capsule.
• What is the glomerular filtration rate (GFR) in a healthy adult?

  About 125 mL/min.
• How much filtrate is formed by the two kidneys each day?

  About 180 litres.
• What is the formula for determining eGFR in children?


  eGFR = k x (height in cm) ÷ serum Cr.
• What is the renal threshold?

  The kidneys’ maximum capacity for reabsorption of a substance.
• What hormones influence selective reabsorption in the kidneys?

  • Parathyroid hormone
  • Antidiuretic hormone (ADH)
  • Aldosterone
  • Atrial natriuretic peptide (ANP)
• What is the role of antidiuretic hormone (ADH) in the kidneys?

  It increases the permeability of the distal convoluted tubules and collecting ducts to water.
• What does aldosterone do in the kidneys?

  It increases the reabsorption of sodium and water, and the excretion of potassium.
• What is the function of atrial natriuretic peptide (ANP)?

  It decreases reabsorption of sodium and water, increasing urinary volume.
• What is the importance of tubular secretion of hydrogen ions (H + )?

  It is important in maintaining normal blood pH.
• What are the main constituents of urine?

  • Water (96%)
  • Urea (2%)
  • Uric acid
  • Creatinine
  • Ammonia
  • Sodium
  • Potassium
  • Chlorides
  • Phosphates
  • Sulphates
  • Oxalates
• What percentage of urine is water?

  96%.
• What is the typical concentration of urea in urine?

  1. 3 g/L.
• What is the range of uric acid excretion in urine over 24 hours?

  1. 48 to 4.43 mmol/24 hours.
• What is the typical concentration of creatinine in urine?

  0.67 g/L.
• What is the range of ammonia concentration in urine?

  10 to 80 mcg/100 mL.
• What is the typical concentration of sodium in urine?

  1. 17 g/L.