physiological Function of kidneys

• What is the osmolarity of isotonic ECF?

  300 milliOsmols/Litre
• What does hypotonic ECF mean?

  It is too dilute, less than 300 mOsm/L
• What does hypertonic ECF mean?

  It is too concentrated, greater than 300 mOsm/L
• What is the role of volume regulation in ECF?

  To maintain blood pressure
• How is osmolarity regulated in the body?

  To prevent swelling or shrinking of cells
• What are the sources of water intake and loss in the body?

  • Intake:
  • Food and drink (variable)
  • Metabolically produced (~350 mL/day)
  • Loss:
  • Faeces (variable)
  • Sweat (variable)
  • Lungs (H2O only)
  • Urine (regulated)
• What is the balance equation for salt and water?

  Intake = loss
• What type of transport occurs at the luminal membrane of tubule epithelial cells for Na+?

  Passive transport via Na+ channels and co-transporters

  
• What type of transport occurs at the basolateral membrane of tubule epithelial cells for Na+?

  Active transport via Na+-K+ ATPase pump

  
• How does Na+ enter the blood plasma from the tubule epithelial cells?

  By diffusion down the concentration gradient
• What percentage of total Na+ is reabsorbed in the distal and collecting tubules?

  8%

  
• What happens when Na+ levels are too high in the body?

  Increased blood volume leads to high blood pressure
• What happens when Na+ levels are too low in the body?

  Most/all filtered Na+ is reabsorbed
• What are the components of the Renin-Angiotensin-Aldosterone System (RAAS)?

  • Juxtaglomerular complex
  • Increases Na+ retention
  • Activates in response to low ECF volume, NaCl levels, or arterial blood pressure

  
• What do natriuretic peptides/hormones do?

  Inhibit Na+ reabsorption

  
• What is the role of vasopressin/ADH in the body?

  Increases water retention

  
• What triggers the secretion of renin from granular cells?

  Fall in ECF volume, NaCl levels, or arterial blood pressure
• What are the three ways the body detects changes that trigger renin secretion?

  Intrarenal baroreceptors, macula densa cells, sympathetic NS innervation
• What is the pathway of renin in the RAAS?

  1. Renin converts angiotensinogen to angiotensin I
  2. Angiotensin I is converted to angiotensin II by ACE in lungs
  3. Angiotensin II stimulates aldosterone secretion from adrenal cortex

  
• What is the effect of aldosterone on Na+ and K+ in the distal and collecting tubules?

  Increases Na+ reabsorption and K+ secretion

  
• How does aldosterone affect Na+ channels and Na+-K+ pumps?

  Promotes insertion of Na+ channels and Na+-K+ pumps
• What is the net result of RAAS activation?

  Increased Na+, water retention, blood volume, and blood pressure

  
• What are the functions of natriuretic peptides/hormones?

  • Induce Na+ excretion
  • Inhibit Na+ reabsorption
  • Inhibit renin and aldosterone secretion
  • Increase GFR
  • Inhibit sympathetic NS activity
• What is required for adjustable water reabsorption in the collecting duct?

  Presence of ADH and hypertonic interstitium

  
• What does "hypertonic" interstitium mean?

  Osmolarity is greater than 300 mOsm/L
• What is the osmolarity gradient in the renal medulla?

  • Renal cortex: isotonic at 300 mOsm/L
  • Renal medulla: increases to 1200 mOsm/L
  • Enables urine production of varying concentrations (100-1200 mOsm/L)

  
• What triggers the release of vasopressin/ADH?

  When ECF is too hypertonic
• What is the role of AQP-2 channels in the presence of vasopressin/ADH?

  Promotes water reabsorption into blood

  
• What is the minimal urine output during H2O deficit?

  0.5 L/day

  
• What is the importance of the vertical osmotic gradient in the medulla?

  Enables urine concentration variation

  
• What is the normal blood pH range?

  7.35 to 7.45

  
• What is acidosis?

  Blood pH below 7.35
• What is alkalosis?

  Blood pH above 7.45
• What are the three lines of defense against H+ in the body?

  1. Chemical buffer systems
  2. Respiratory mechanism
  3. Renal mechanism
• How do chemical buffer systems maintain pH?

  By binding free H+ to neutralize
• What is the role of the respiratory mechanism in pH control?

  Eliminates H+ by blowing off CO2
• What is the renal mechanism of pH control?

  Secretes H+ into urine and reabsorbs HCO3-

  
• What is the bicarbonate buffering system's primary function?

  Buffers against pH changes in ECF
• How is bicarbonate reabsorbed in the kidneys?

  Filtered HCO3- is reabsorbed, H+ is secreted

  
• What is the primary active transport mechanism for H+ secretion in the proximal tubule?

  H+ ATPase pumps