1. STRUCTURE & FUNCTION OF THE RENAL SYSTEM AND RENAL DIAGNOSTIC PROCEDURES

3. Kidneys (Fig. 28-1) –Paired, encapsulated At hilus –Renal artery enters, renal vein exits –Approx. 25% cardiac output to kidney Two main functions of kidney: Filtration –Removes metabolic wastes Esp. urea, other N- containing wastes Regulation –Electrolytes –Intravascular volume –Blood pH

5. Renal blood flow from cortex to medulla –Medulla has high metabolic rate Prone to hypoxia if ischemia –Medulla arranged in wedges (Fig.28-2) Renal pyramids Columns –Between pyramids from cortex through medulla Apices –Extend to: Minor calyces –Cup-shaped cavities; join  major calyces  –Renal pelvis

7. Ureter (Fig.28-1) –Tube from kidney that carries waste fluid to the: Bladder –Urine storage site; attached to urethra  outside body

9. Nephron Anatomic unit of kidney function (Fig.28-3) –Approx. 10 6 nephrons/kidney –Two anatomical regions: Glomerulus –Tuft of capillaries loop into circular capsule –In cortex of kidney – Blood filtration site Renal tubule –Begins as end of glomerulus –Traverses cortex, medulla –Site where water, solutes reclaimed following filtration

11. Renal tubule – cont’d –Anatomical areas: –Proximal, convoluted tubule »Impt to reabsorption of water, electrolytes –Loop of Henle »Hairpin loop »Impt to urine concentration –Distal tubule »Both straight and convoluted »Impt to reabsorption in response to hormonal signals –Collecting ducts »Impt to Afine tuning@ of water, electrolytes

12. Renal Tubule Summary Anatomical areas: –Proximal, convoluted tubule Impt to reabsorption of water, electrolytes –Loop of Henle Hairpin loop Impt to urine concentration –Distal tubule Both straight and convoluted Impt to reabsorption responding to hormonal signals –Collecting ducts Impt to fine tuning of water, electrolytes

13. Renal corpuscle Bowman's capsule + glomerular capillary tuft (Fig.28-6) Bowman's capsule –Circular –Space inside = Bowman’s space –Narrows to form proximal tubule Glomerular capillaries arranged in loops

15. Glomerular capillary membranes (Fig.28-6) –Blood components from artery filtered here –Glomerular capillary tuft -- three membrane layers Different than most other capillaries in body –Cells of membrane layers -- unique w/ unique structures in each layer Inner capillary endothelium Basement membrane Epithelium –Primary urine forms as result of filtration

16. Glomerular filtration –Glomerulus permeable to Water Electrolytes Small organic molecules (ex: glucose, urea, creatinine) –Not permeable to Rbc’s Wbc;s Molecules w/ MW > 70,000 (so most proteins) –Leave glomerulus (still in blood) through the efferent arteriole –Size and charge of molecules impt to whether molecule will be filtered or not

17. –Capillary pressures important (Fig.28-11, Table 28-1) Hydrostatic Pressure forces fluids through filter –What is the filter? Forces opposing BHP: –Colloid osmotic P »Due to blood cells, proteins, as in “regular” capillaries –Hydrostatic P of fluid already in Bowman=s space Net filtration P = (forces favoring filtration) ‑ (forces opposing filtration)(Table28-1) –Positive or negative net filtration in a healthy system?

18. –Glomerular filtration rate (GFR) Volume of plasma filtered at glomerulus per unit time Approx. 180 L/day = 120 mL/min –BUT only 1-2 L/day excreted »About 99% of filtrate reabs’d in tubule GFR depends on factors affecting fluid pressures in nephron and vasculature –Arteriolar resistance changes capillary hydrostatic P in glomerulus –Decr’d blood flow to kidney from systemic circulation decr’s GFR –Obstruction to urine outflow may incr back pressure at Bowman’s capsule, so decr GFR –Loss of protein ‑ free fluid alters COP, so alters net filtration –Renal disease

19. Hormonal Regulation of GFR Through renin  changes in renal blood flow, so changes in GFR –Occur and regulated locally (at kidney tissue) and systemically Two impt hormones affect GFR: –Aldosterone (regulates Na+) –ADH (regulates water)

20. Specialized cells sensitive to specific hormones –Juxtaglomerular aparatus Juxtaglomerular cells –Lie around afferent arteriole Macula densa –Portion of renal distal tubule »Loops back up toward Bowman’s capsule »Butts up against glomerulus –Located in space between afferent and efferent arterioles

22. –Together juxtaglomerular cells + macula densa cells (or juxtaglomerular apparatus) control: Blood flow into nephron at glomerulus, so –Glomerular filtration Renal secretion –Because sensitive to hormones such as aldosterone and ADH

24. Renal Tubule Physiology Extend from Bowman’s capsule Receive and process filtrate from capsule Processing of fluid by two major forces: tubular reabsorption and secretion –Reabsorption Occurs through minute pores in tubules Compounds reabsorbed from tubule  peritubular capillaries (surround the tubules)  blood

25. –Secretion Opposite of reabsorption Compounds secreted go from blood capillaries  renal tubule  filtrate –By the end of the proximal tubule Water, Na+ –60-70% reabsorbed back into blood K+, glucose, bicarb, Ca+2, amino acids, uric acid –Approx 90% reabsorbed back into blood

27. –Loop of Henle Mostly Na+, Cl-, H 2 O move to adjust concentration of fluid in tubule Loop has ascending, descending regions –Cells in some regions permeable to water »Here water can move out of tubule –Cells in other regions not permeable to water »Here water trapped in the tubule –Cells in some regions permeable to Na+ »Here Na+ can move out of the tubule –Cells in other regions not permeable to Na+ »Here Na+ is trapped in the tubule

29. Resulting fluid through loop goes from isotonic to hypertonic to hypotonic –Due to differences in kidney cells from cortex to medulla and different permeabilities of tubule to different molecules –As the fluid leaves loop of Henle, it is hypotonic (so dilute, compared to other body fluids)

30. –Distal tubule ‑ final regulation of water, and acid ‑ base balance Water, Na+, bicarb –Reabsorbed here when ADH present K+, urea, H+, ammonia –Secreted Hormones important to regulation here –ADH (antidiuretic hormone) »  incr’d water reabsorption –Aldosterone »  incr’d Na+ reabsorption –Parathyroid hormone (PTH) »  incr’d Ca+2 reabsorption

31. –Collecting duct Final urine concentration adjusted Final pH balance adjusted Final product = urine low in volume (compared to what was filtered), and high in osmotic concentration (the body rids itself of unwanted molecules)

32. Renal diagnostic procedures (Table 28-3 p.804) Urinalysis –Non ‑ invasive, inexpensive –Normal urine properties well-known, easily measured Specific gravity –Solute concentration in urine –Correlates w/ osmolality in normal urine –Normal value: 1.025-1.032 –Usually describes ADH Because ADH controls water reabsorption What ADH problem might you expect if specific gravity were high? Low?

33. Urine sediment can be examined microscopically –Red blood cells Hematuria = large number rbcs in the urine –Should be few/none –Why? What keeps rbc’s in the body? –Casts Precipitates from cells lining the renal tubules –Red cells suggest tubule bleeding –White cells suggest tubule inflammation –Epithelial cells suggest degeneration, necrosis of tubule cells

34. –Crystals May form as urine cools Observed microscopically Indications –Inflammation –Infection –Stones –White blood cells (pyuria) From urinary tract infection –Bacteria Infection

35. Clearance tests –Determine how much of substance can be cleared from blood by kidney per unit time Indirect measure of GFR, tubular reabs’n/secr’n, renal blood flow –GFR Best estimate of overall kidney health Decreases w/ lost or damaged nephrons Use creatinine clinically –Biochem prod’d by muscle, released to blood at constant rate –Freely filtered at the glomerulus –Neither reabs=d nor secr=d as it progresses through the tubule, so: Amount creatinine excreted = amount creatinine filtered –Can be calculated: »Amount creatinine in urine over time = (vol. urine/time) x (urine concentration of creatinine)

36. Blood tests –Plasma creatinine concentration (P cr ) Normal levels = 0.7-1.5 mg/dL Use same biochem described for clearance test, but measured in blood instead of in urine Again, creatinine filtered at glomerulus; neither reabs’d nor secr’d; and amount creatinine filtered = amount excreted Get increased Pcr if chronic disease affecting GFR –When GFR decr’d, get decr’d filtration of creatinine out of blood (and into urine), so –Blood (plasma) creatinine increases Useful: –To monitor changes in chronic renal function BUT P cr increases with trauma, muscle tissue breakdown

37. –Blood Urea Nitrogen (BUN) Urea prod’d constantly as cells metabolize proteins Measurement of BUN reflects both GFR and urine concentrating ability Normal levels 10-20 mg/dL Urea filtered at glomerulus Urea reabsorbed back into blood at tubules –If decr’d GFR, get incr’d BUN –OR if decr’d blood flow to kidney, get incr’d BUN –Incr’d BUN or Pcr = increase in nitrogenous substances in blood = azotemia