The kidneys are paired organs located retroperitoneally that are responsible for filtering blood and regulating homeostasis. Each kidney contains millions of nephrons, the functional units that filter blood to form urine via glomerular filtration. Urine passes from the nephrons through the renal medulla and pelvis into the ureters. Hormones and pressure differences influence filtration and reabsorption of water and solutes along the nephron tubules to produce concentrated urine. Urinalysis can detect abnormalities in kidney function by measuring properties like pH, specific gravity, and microscopic constituents. Blood tests also evaluate renal function by analyzing creatinine, BUN, and clearance rates.

1. Renal Structure and Function
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2. Kidneys
• Paired
• Retroperitoneal
• Partially protected by the 11th and 12th ribs
• Right slightly lower due to liver
• Surrounded by renal capsule
• Adipose capsule
• Renal fascia
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5. Anatomy
• Hilum (hilus)
• Renal artery and vein
• Cortex
• Medulla
• Renal pyramids and renal papillae
• Major and minor calyces
• Renal Pelvis
• Ureters
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7. • Ureters connect kidneys to urinary bladder
• Urethra leads from bladder outside the
body
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9. • Kidneys make up 1 % of body mass, but
receive about 25% of cardiac output.
• Kidney has two major functions:
1. Filtration of blood
• Removes metabolic wastes from the body,
esp. those containing nitrogen
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10. 2. Regulation:
Blood volume and composition
Electrolytes
Blood pH
Blood pressure
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11. Nephron
• Functional unit of the kidney
• Filtration, tubular reabsorption, tubular
secretion
• Renal corpuscle:
– Glomerulus – capillaries
– Glomerular or Bowman’s capsule
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12. • Bowman’s capsule
– Receives filtrate
• Proximal convoluted tubule
– Reabsorption of water and solutes
• Nephron loop or Loop of Henle
– Regulates concentration of urine
• Distal convoluted tubule and Collecting
duct
• Reabsorption of water and electrolytes
– ADH, aldosterone, ANP
– Tubular secretion
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17. Filtration
• Renal corpuscle
• Filtration membrane
– Fenestrated endothelium of capillaries
– Basement membrane of glomerulus
– Slit membrane between pedicels of podocytes
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18. Forces that influence filtration
• Glomerular blood hydrostatic pressure
• Opposing forces:
– Plasma colloid osmotic pressure
– Capsular hydrostatic pressure
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20. Glomerular Filtration Rate
• Volume of plasma filtered / unit time
• Approx. 180 L /day
• Urine output is about 1- 2 L /day
• About 99% of filtrate is reabsorbed
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22. GFR influenced by:
• Blood pressure and blood flow
• Obstruction to urine outflow
• Loss of protein-free fluid
• Hormonal regulation
– Renin – angiotensin
– Aldosterone
– ADH
– ANP
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23. Juxtaglomerular apparatus
• Juxtaglomerular cells lie in the wall of
afferent arteriole
• Macula densa in final portion of loop of
Henle – monitor Na+ and Cl- conc. and
water
• Control blood flow into the glomerulus
• Control glomerular filtration
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26. Tubular reabsorption
• Water, glucose, amino acids, urea, ions
• Sodium diffuses into cell; actively pumped
out – drawing water with it
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29. • In addition to reabsorption, also have
tubular secretion – substances move from
peritubular capillaries into tubules – a
second chance to remove substances
from blood.
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31. • By end of proximal tubule have
reabsorbed:
• 60- 70% of water and sodium
• about 100% of glucose and amino acids
• 90 % of K+, bicarb, Ca++, uric acid
• Transport maximum – maximum amount
of a substance that can be absorbed per
unit time
• Renal threshold – plasma conc. of a
substance at which it exceeds Tm.
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32. Loop of Henle
• Responsible for producing a concentrated
urine by forming a concentration gradient
within the medulla of kidney.
• When ADH is present, water is
reabsorbed and urine is concentrated.
• Counter-current multiplier
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34. Distal convoluted tubule and
collecting ducts
• What happens here depends on ADH
• Aldosterone affects Na+ and K+
• ADH – facultative water reabsorption
• Parathyroid hormone – increases Ca++
reabsorption
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36. Distal convoluted tubule and
collecting ducts
• Tubular secretion to rid body of
substances: K+, H+, urea, ammonia,
creatinine and certain drugs
• Secretion of H+ helps maintain blood pH
(can also reabsorb bicarb and generate
new bicarb)
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38. Renal diagnostic procedures
• Urinalysis is non-invasive and inexpensive
• Normal properties are well known and
easily measured
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39. pH
• Normally 4.8 – 8.0
• Higher in alkalosis, lower in acidosis
• Diabetes and starvation ↓ pH
• Urinary infections ↑ pH
– Proteus and pseudomonas are urea splitters
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40. Specific gravity
• Normal values 1.025 -1.032
• High specific gravity can cause
precipitation of solutes and formation of
kidney stones
• When tubules are damaged, urine specific
gravity approaches that of glomerular
filtrate – 1.010 – remains fixed = 2/3 of
nephron mass has been lost
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41. • Diabetes insipidus = 1.003
• Diabetes mellitus = 1. 030
• Emesis or fever = 1.040
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42. Microscopic analysis
• Red blood cells – should be few or none
– Hematuria – large numbers of rbc’s in urine
– Catheterization
– Menstruation
– Inflamed prostate gland
– Cystitis or bladder stones
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43. • Casts – precipitate from cells lining the
renal tubules
– Red cells – tubule bleeding
– White cells – tubule inflammation
– Epithelial cells – degeneration, necrosis of
tubule cells
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44. • Crystals –
– Infection
– Inflammation
– stones
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45. • White blood cells
– Pyuria
– Urinary tract infection
• Bacteria
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46. Substances not normally present in
urine
• Acetone
• Bile, bilirubin
• Glucose
• Protein – albumin
– Renal disease involving glomerulus
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47. Blood Urea Nitrogen BUN
• Urea produced by breakdown of amino
acids - influenced by diet, dehydration,
and hemolysis
• Normal range 10-20 mg/ dL
• If the GFR decreases due to renal disease
or blockage, or decreased blood flow to
kidney - BUN increases
• General screen for abnormal renal
function
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48. Creatinine clearance
• Creatinine is an end product of muscle
metabolism
• Muscle mass is constant; creatinine is
constant
• Normal 0.7 – 1.5 mg/ dL in plasma
• Can then be compared to creatinine in
urine over 24 hour period to determine
clearance
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49. • Creatinine clearance is an indirect
measure of GFR and renal blood flow
• Creatinine is neither reabsorbed nor
secreted, just freely filtered.
• Amount excreted = amount filtered
• Useful to monitor changes in chronic renal
function
• Increases with trauma with massive
muscle breakdown
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50. Diagnostic testing
• Inulin clearance - not absorbed or
secreted = GFR
• PAH – para-aminohippuric acid – not
absorbed ; actively secreted = renal
plasma flow
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