1. Functions of the Kidney...

    As a Homeostatic Organ:
    Intake = Output

    • Excretion of Metabolic Wastes
    • Regulation of Volume and Composition of ECF
    • Regulation of Acid-Base Balance
  2. Function of Kidney...

    As an Endocrine Organ
    Production of:

    EPO- reg. RBC production

    Calcitriol- (1,25(OH)2 - Vit. D3 - Reg. Ca and Phosphate metabolism

    Renin, Bradykinins, Prostaglandins- reg. systemic and local (renal) hemodynamics- key factors in arterial hypertension
  3. Metabolic fxns of Kindey
    Key site for glycolysis, gluconeogenesis, proteolysis
  4. Renal Blood supply is normally
    20% of Cardiac Output; 99% blood flow goes to Cortex, 1% goes to Medulla
  5. Fxnal and Structural unit of the Kidney, composed of a and its b.

    a = Glomerulus

    b = Tubule
  6. Outer part of the Kidney

    Most nephrons reside here
  7. Inner part of Kidney

    specialized nephrons within the Juxtamedullary have a greater concentrating ability
  8. Filtration Occurs in the a, resorption of water mainly occurs in b.
    a= Cortex

    b= Medulla
  9. Urine flows to a under pressure, where it is collected and transmitted to b via c, which are smooth muscle tubes.
    a = renal pelvis

    b = urinal bladder

    c = ureters
  10. Backflow of urine is prevented by a functional valve at a.

    The Neck of the bladder has b at the conjunction with the urethra.
    a = Uretero- vesicular junction

    b = internal sphincter
  11. Types of nephrons

  12. Capillary beds in the kidney
    Glomerular - under high pressure for filtering

    Peritubular - situated around the tubule at low pressure

    Permits large volumes of fluid to be filtered and reabsorbed
  13. Renal Circulation
    Renal A -> Interlobar Aa --> Arcuate aa --> Interlobular aa--> Afferent Arterioles --> Glomerular capillaries --> Efferent arterioles --> Vasa Recta --> Peritubular capillaries
  14. JG Apparatus
    Aff. Arterioles + Efferent + JG cells + Macula Densa
  15. Filtration
    Conversion of Blood plasma into primary tubular fluid- glomerular filtrate

    Occurs in the Glomerulus, through semipermeable walls of glom- caps.
  16. Arterial Pressure provides the a necessary for filtration. It is controlled by b.
    a = driving hydrostatic pressure

    b = Afferent and Efferent Arterioles
  17. Structure of Glomerular capillary wall

    Creates barrier to forces favoring and opposing filtration
    Capillary endothelium- single cell layer forming multiple fenestrae

    Glomerular basement membrane- acellular; arranged in 3 layers

    Visceral endothelium- podocytes
  18. Forces of Filtration
    Hydrostatic and Oncotic Pressure
  19. GFR =
    Kf x [( PGC - PBS) - (∏GC - ∏BS)]

    • ([ ] = Net Filtration Pressure)
    • Kf = Coefficient of ultrafiltration

    PBS = Hydrostatic Pressure in Bowman's Space

    PGC = Hydrostatic P in Glomerular Cap

    GC = Oncotic Pressure in Glomerular Capillary

    BS = Oncotic Pressure in Bowman's Space
  20. PGC
    Mostly determines rate of filtration as well as tubular flow to renal pelvis

    It is determined by the blood input from afferent arterioles and the tonus of efferents

    Primary Target for mechanisms that control GFR
  21. Plasma Oncotic Pressure increases significantly along the capillary bed due to what?

    How does this affect rate of filtration?
    Most of the plasma proteins are retained in the capillary lumen
  22. Sieve Function
    Coefficient of Ultrafiltration, Kf
  23. Selectivity of Filtration
    Conferred by the selective permeability of glomerular capillary wall.
  24. Freely Filtered
    • Water
    • small Cations (Na, K)
    • small Anions (Cl)
    • Glucose
  25. Poorly Filtered
  26. Factors affecting permeability of polypeptides
    Size - Smaller > Larger

    Charge - Cationic polypeptides filtered more efficiently than Anionic

    Shape - long, flexible proteins filtered more efficiently than Globular proteins
  27. Regulation of GFR
    Maintained within physiologic parameters by

    Systemic Factors - renal modulation of systemic BP and intravascular volume

    Intrinsic Factors - control of renal blood flow, PGC, and Kf.
  28. Systemic Factors of GFR regulation
    Mostly Humoral

    Renin- Angiotensin- Aldosterone system
  29. Renin
    Produced by JG cells in afferent arteriole

    Release is stimulated by decrease in Renal Perfusion (usually from systemic hypotension)

    Renin Catalyzes Angiotensinogen --> Angiotensin I
  30. Angiotensin II
    Converted from Ag-I via ACE

    Ag-II is a potent vasoconstrictor acts

    Directly - constr. arterial blood vessels to increase systemic BP and renal perfusion pressure

    Indirectly - stimulates release of Aldosterone and ADH; both retain electrolytes and water from excretion
  31. Negative feedback of Renin Actions
    improvement of renal perfusion, and high levels of Ag-II inhibit renin release by JG cells.

    Ag-II also stimulates production of Prostaglandins (PgE2 PgI2) which are vasodilators and counteract the effects of Ag-II on renal vasculature
  32. Intrinsic factors of GFR regulation
    directly control glomerular capillary perfusion

    • Myogenic Reflex - Glomerular arterioles respond to changes in arteriolar wall tension; increase in tension - > constriction; decrease -> dilation
    • changes regulate the resistance to blood flow in Afferent Arteriole
    • reflex is independent of renal innervation

    Tubulo-glomerular Feedback - Macula Densa (b/w afferent and efferent arterioles, and adjacent to JG cells) sense increases in Tubular Flow Rate, which leads to decrease in filtration rate of glomerulus (in same nephron)
  33. Cx= (Ux x V)/ Px
    Determination of GFR by rate of clearance of substance X from plasma

    • Cx = Volume of plasma cleared cleared of substance X per unit time
    • Ux = urine concentration
    • V = volume urine collected over time period of collection
    • Px = Plasma conc. of substance X
  34. Inulin is indicator substance of choice because...
    freely filtered by glomeruli, but neither absorbed nor secreted

    it is a xenobiotic, the rate of disappearance strictly dependent on GFR
  35. In clinical practice, most widely used indicator substance (for mammals) is...?
  36. Filtration Fraction (FF)
    Fraction of Renal Plasma Flow (RPF) that is actually filtered by glomeruli

    FF = GFR/RPF
  37. Fractional Excretion (FE)
    Rate of Excretion of substance X / its rate of filtration

    FEx = (Ux x V) / (Px x GFR)

    Used to evaluate net secretion/ reabsorption

    • FE > 1, there is net secretion of indicator substance by the tubule
    • FE < 1, there is net reabsorption of substance by the tubule
  38. Renal Tubule function is assessed by determining what parameters?
    FER - fractional excretion rate

    FAR - fractional reabsorption rate
  39. % of a filtered substance that is ultimately excreted in urine
    FER - net result of tubular reabsorption and secretion
  40. Proportion of filtered substance X reabsorbed by the tubule
    FAR = 100% - FER
  41. Part of Tubule Responsible for reabsorption of bulk of filtered solutes
    Proximal Tubule - at least 60% of all solutes are reabsorbed here
  42. Transport Pathways from Tubule into bloodstream

  43. Transcellular Pathway
    substances are taken up from tubular lumen by cells through apical membranes (brush border creates large surface area)

    Active transport across cell to basolateral membrane and passed into capillaries of peritubular capillary plexus
  44. Paracellular Pathway
    Substances are move from tubular fluid, across Zonula Occludens, into lateral intercellular space.

    Then move from here into peritubular capillaries

    Substances transported via passive diffusion along [ ] gradient or by Solvent Drag.
  45. Movement in Paracellular pathway is driven by a.
    a - Starling's forces

    Blood in peritubular capillaries has High Oncotic Pressure (due to loss of volume and increase [protein] ), and Low Hydrostatic Pressure (due to low resistance of their walls)
  46. Much of the transport of substances is driven through Active Transport of Sodium mediated by...?
    Na+/K+ ATPase pump in the basolateral plasma membrane.

    pumps out 3 Na into Interstitial fluid and takes up 2 K into cell
Card Set
Renal Phys, Respiration, Water Balance