Overview of Renal Physiology

Question 1

Main physiologic fxn of the kidneys

Answer 1

• maintenance of composition and volume of extracellular fluid

Question 2

Size of (standard=70kg) bodily fluid compartments

Answer 2

• Intracellular fluid = contained w/in body cells
  
  • non-circulating = 24L
  • blood cells = 3L
  • total = 27L
• extracellular fluid = remaining fluid outside of cells
  
  • interstitial fluid = 12L
  • plasma = 3L
  • total = 15L

Question 3

Daily water balance volumes (inputs & outputs for 70kg persn)

Answer 3

• Inputs:
  
  • ingestion in fluid/food = 2L
  • metabolic processes = 0.5L
  • total = 2.5L
• Output
  
  • sweat and feces = 0.1L
  • Respiration, skin “leaks” = 0.9L
  • urine = 1.5L
  • total = 2.5L

Question 4

Main mechanism for regulation of composition of ECF

Answer 4

• for any given substance, ingestion is generally in excess of incidental loss
• ECF constancy is acheved b regulating urinary output

Question 5

Nephron characteristics

Answer 5

• =basic structural unit of the kidney
• =blood supply + epithelial tube (aka “tubule”)
  
  • blood supply = 2 capillary beds in serious ==> glomerular & peritubular capillaries

Question 6

Major fxnl processes of nephron

Answer 6

1. glomerular filtration = filter plasma into initial part of tubule (“filtration) ==> allows water, solutes to pass but retains larger mlx
2. tubular reabsorption = recapture filtered components via membrane transporters ==> just enough ECF components returned to plasma
3. excretion = regulated substances in excess pass through tubule and are excreted
   
   1. secretion = blood ==> tubule to achieve balance

Question 7

Renal blood flow (RBF) =

Renal plasma flow (RPF) =

Answer 7

• RBF = ~1.3L (25% of CO)
• RPF (hematocrit=50%) = .65L

Question 8

Filtration fraction =

Glomerular filtration rate (GFR) =

Answer 8

• FF = 20% = .2
• GFR = .2 x 650 ml/min = 130 ml/min
  
  • =50 gallons/day

Question 9

Renin-angiotensis axis characteristics

Answer 9

• angiotensin = potent vasopressor hormone
• decrease in BP ==> increase renal secretion of renin ==> converts agiotensinogen into angiotensin I (AgI) ==> angiotensin converting enzyme converts AgI ==> Angiontensin II (AgII)
• AgII ==> constriction of arteriolar smooth muscle ==> peripheral resistance ==> increased blood pressure
• **Renin = rate-limiting for the production of AgII = determines axis activity

Question 10

Approximations of normal values for plasma constituents

Answer 10

• Bicarb = 22
• Cl^- = 100
• Creatinine = 1
• Osmolality = 290
• K⁺ = 4
• Protein = 7
• Na⁺ = 140
• BUN = 12