bsci202 exam 3 - urinary system

• what are the functions of the urinary system?

  • filters blood to allow toxins, waste to leave the body and help monitor acid-base balance of body (maintain internal environment)
  • produce renin, erythropoietin
  • metabolism of vitamin D into active form to absorb more calcium
• list the organs of the urinary system and discuss their functions:

  • 2 kidneys: produce urine
  • 2 ureters: transport urine from kidneys to urinary bladder
  • 1 urinary bladder: stores urine before urination
  • urethra: carries urine to surface of body
• what is the structure and function of nephrons?

  function: filter blood to manufacture urine (filtration, reabsorption, secretion)

  structure: glomerus, glomerular capsule (bowman's), PCT, loop of henle. DCT, CD

  • the glomerus and glomerular capsule together is the renal corpuscle
• what are cortical nephrons?

  the glomerus is in the cortex, has peritubular capillaries that reabsorb and secrete, and has a SHORT loop of henle
• what are juxtamedullary nephrons?

  glomerus at the cortex-medulla boundary, vasa recta creates the osmotic gradient, has a LONG loop of henle, and concentrates urine
• what is glomerular filtration?


  materials are filtered from the blood of glomerus to the lumen of the glomerular which is driven my glomerular pressure

  • when glomerular hydrostatic pressure exceeds luminal hydrostatic pressure in the bowmans capsule
• what is tubular reabsorption?

  substances are reabsorbed into the peritubular capillaries in the PCT
• what is tubular secretion?

  transfer of molecules from the peritubular capillaries to the lumen of the renal tubule to be excreted from the body
• what is the structure of the filtration membrane of the renal corpuscle?

  capillary endothelium, basement membrane, podocyte of visceral layer of glomerular capsule
• what is the function of the filtration membrane?

  allows smaller molecules in the plasma to leak into tubule to create filtrate (plasma - large proteins)
• what is net filtration pressure?

  pressure that acts as the driving force for filtration (usually positive) and initiates urine formation
• what is glomerular filtration rate?

  amount of fluid filtered into glomerular capsule per unit time
• how do you calculate net filtration rate?

  NFP = GBHP - (CHP + BCOP) --> 10 mmHg

  GBHP - glomerular blood hydrostatic pressure (55)

  CHP - capsular hydrostatic pressure (15)

  BCOP - blood colloid osmotic pressure (30)
• why is there a regulation of GFR?

  1. protects glomerulus during times of high blood pressure
  2. maintain GFR during times of low pressure
• what is the myogenic response of autoregulation when maintaining GFR?

  stimulant: increased pressure in the afferent arteriole

  1. stretch sensitive ion channels open
  2. arteriolar smooth muscle contracts, reducing blood flow
  3. NFP and GFR decrease
• what is the juxtaglomerular complex made up of and what is its function?

  includes modified ascending tubule and afferent arteriole having granular, macula dense, and mesangial cells

  function: help regulate GFR and systemic blood pressure
• where are granular cells located and what are there function?

  location: around afferent arteriole

  function: they are modified smooth muscle cells that are mechanoreceptors that sense BP and respond by secreting renin
• where are macula densa cells located and what are there function?

  location: cells in the ascending limb of loop of henle

  function: act as chemoreceptors for filtrate
• where are extraglomerular mesangial cells located and what are there function?

  location: outside of the renal corpuscle

  function: pass paracrine hormones from macula densa cells to granular cells
• where are the glomerular mesangial cells located and what are there function?

  location: inside of the renal corpuscle

  function: contract and alter glomerular surface area
• what is the tubuloglomerular feedback mechanism?

  renal tubule (containing macular densa cells) provides feedback to the glomerulus to regulate GFR

  • the NaCl in filtrate depends on GFR
  • the NaCl in filtrate is sense by the macula densa cells
• tubuloglomerular feedback mechanism: if GFR is too low, then

  1. macula densa cells detect reduced osmolarity
  2. macula densa cells relase vasodilators onto the afferent arteriole
  3. increased blood flow into the glomerulus
  4. NFP and GFR increase
• tubuloglomerular feedback mechanism: if GFR is too high, then

  1. macula densa cells detect increased osmolarity
  2. vasoconstricting chemicals are released and afferent arteriole constricts, reducing blood flow to glomerular capillaries
  3. GFR decreases
• what two systems are in the extrinsic control of regulating GFR?

  nervous system and endocrine system (renin-angiotensin-aldosterone mechanism)
• what is the stimulus for the extrinsic control of regulating GFR?

  decreased blood pressure
• how do the nervous and endocrine system increase blood pressure?

  1. stretch/mechanoreceptors
  2. reduced stretch in afferent arteriole stimulation of renin secretion (granular cells)
  3. 2. sympathetic nervous system nerves
  4. B. sympathetic stimulation of renin secretion (granular cells)
  5. 3. macula densa cells detect reduced [NaCl] stimulates renin secretion
• what does renin do for the extrinsic control of GFR to increase blood pressure?

  makes angiotensin II which is a powerful vasoconstrictor
• what substances are secreted into the filtrate by tubule cells during tubular secretion?

  drugs, urea, uric acic, excess K+, H+
• how is the acidification of urine used to control the pH of body fluids?

  the secretion of H+ and reabsorption of HCO3- controls blood pH in kidneys

  • this can also adjust the acidity of urine
• how is the collecting duct used to regulate the concentration of body fluids ?

  it uses ADH (antidiuretic hormone): it causes cells in CD to insert aquaporins into membrane which allows for high water reabsorption, leading to small urine volume

  • high ADH levels --> small volume of concentrated urine
  • low ADH levels --> large volume of dilute urine
• what is the normal composition of urine?

  1 -2 L per day, pH average of 6 (range of 4.5 - 8) pale to deep yellow (urochrome: pigment derived from bilirubin), 1.001 - 1.035 specific gravity, slightly aromatic
• what is the term for abnormally low urine output?

  oligouria
• what is the term for abnormally high urine output?

  polyuria
• what is the intracellular fluid compartment?

  2/3 of total body water (located inside the body cells)

  • 25 L, K+ and HCO3-, some protein and Mg2+
• what is the extracellular fluid compartment?

  1/3 of total body water (located outside of the body cells)

  • 15 L, Na+ and Cl-, and some HCO3-
• what makes up the extracellular fluid compartment?

  • interstitial fluid: 80% of ECF (12 L, Na+ and Cl-, some HCO3-)
  • plasma volume: 20% of ECF (3 L, Na+ and Cl-, some HCO3-)
• what are the functions and regulation of sodium (Na+)?

  functions: externs significant osmotic pressure in ECF, needed for normal neuromuscular function, renal acid-base mechanisms are coupled to Na+ transport, primary/secondary active transport molecules in nephron and digestive tract, etc.

  regulation: aldosterone promotes Na+ reabsorption at DCT, atrial natriuretic peptide promotes Na+ secretion at DCT and CD
• what are the functions and regulation of potassium (K+)?

  functions: needed for normal neuromuscular function, needed for protein synthesis, has an impact on acid-base balance

  regulation: aldosterone promotes K+ secretion (blood to filtrate/urine), pH driven shifts in K+ balance
• what are the functions and regulation of calcium (Ca2+)?

  functions: provides strength in skeleton, used for blood clotting, neurotransmitter release and other cellular secretion, important second messenger, muscle contraction

  regulation: parathyroid hormone causes reabsorption at DCT and absorption in small intestine elevates plasma Ca2+
• what are the functions and regulation of magnesium (Mg2+)?

  activates coenzymes in cells used for carbohydrate and protein metabolism, needed for neural and muscular function

  regulation: PTH inhibits renal reabsorption