The document provides information on the urinary system and urinalysis. It describes the structures of the urinary system including the kidneys, ureters, bladder, and urethra. It then discusses the functions of the kidneys including production of urine, regulation of fluid balance and acid-base balance, and hormone production. Microscopic anatomy of the nephron is explained along with terms like osmosis, diffusion, reabsorption, and secretion. Physiology concepts such as urine concentration and regulation of volume are summarized. Finally, some common urinary conditions and what they indicate in urinalysis are briefly mentioned.

1. Urinary System &
Urinalysis
VTT 250 Anatomy & Pathology Lab

2. Structures
Kidneys
Ureters
Bladder
Urethra

3. Kidneys

4. Function
Production of urine which is the fluid that
facilitates the elimination of metabolic waste
materials from the body.
Helps maintain homeostasis by manipulating
the composition of blood plasma.
Regulation of the acid-base balance and fluid
electrolyte balance.
Blood filtration, reabsorption, and secretion.

5. Function…
Fluid Balance Regulation-
The amount of urine produced helps ensure that
the body contains the right amount of water.
If the body has excess water and needs to get rid
of it, more urine is formed (diuresis).
If the body needs to conserve water, less urine will
be produced.
Much of this function is under the control of
antidiuretic hormone (ADH) and aldosterone.

6. Function…
Acid-Base Balance Regulation-
Enabled by the ability to remove hydrogen and
bicarbonate ions from the blood and excrete them in the
urine.
Hormone Production-
The kidneys have a close association with the endocrine
system.
They can influence the rate of release of ADH and
aldosterone.
They also produce erythropoietin and some
prostaglandins.

7. Gross Anatomy
Bean shaped and
covered by a fibrous
capsule.
The indented area is
called a hilus.
Renal pelvis- a urine
collection chamber that
forms the beginning of
the ureter

8. Gross Anatomy
Renal cortex- outer
portion.
Renal medulla-
surrounds the renal
pelvis and has a smooth
appearance.

9. Microscopic Anatomy
The Nephron-
The basic functional unit of
the kidney.
Each nephron is composed
of a:
Renal corpuscle
Proximal Convoluted
Tubule (PCT)
Loop of Henle
Distal Convoluted Tubule
(DCT)

10. Terms to
Remember…
Osmosis- the passage of water across a semi-
permeable membrane from a weaker to a stronger
solution.
Diffusion- the passage of a substance from an area
of high concentration to an area of low concentration.
Reabsorption- the passage of chemical substances
from the lumen of the renal tubules into the renal
capillaries, back into the body.
Secretion- the passage of chemical substances from
the renal capillaries into the lumen of the renal
tubules, out of the body, into the urine.

11. Microscopic
Anatomy…
Renal corpuscle- located in the cortex of
the kidney.
Made up of the glomerulus (a tuft of capillaries)
and Bowman’s capsule.
The function is to filter blood in the first stage of
urine production.
The blood pressure within each glomerulus is high
because the blood comes directly from the renal
artery and the aorta.
The walls of the efferent arteriole of the
glomerulus are able to constrict under the
influence of renin.

12. Microscopic
Anatomy…
High pressure forces fluid and small
molecules out through the pores and into the
lumen of the glomerular capsule.
This process of ultrafiltration results in the
formation of glomerular filtrate.
It is very dilute and consists of 99% water and
1% chemical solutes and is isotonic with
plasma.

13. Microscopic
Anatomy…
PCT- a continuation of Bowman’s capsule.
The longest part of the nephron.
Functions-
Reabsorption of glucose, water, and sodium from the
filtrate.
Secretion of toxins and certain drugs (penicillin).
Concentration of nitrogenous waste- mainly urea
produced as a result of protein metabolism.

14. Microscopic
Anatomy…
Loop of Henle-
Function: to concentrate or dilute the filtrate
according to the status of the blood plasma and
the rest of the extracellular fluid.
Occurs in 2 stages:
Descending loop- water is drawn out of the filtrate by
sodium ions and is reabsorbed by the capillaries.
Ascending loop- sodium is pumped out of the filtrate
into the medullary tissue.

15. Microscopic
Anatomy…
Loop of Henle…
Na+ and Cl- are pumped out of the ascending loop into
the tissue of the surrounding medulla.
Normally, water would follow Na+ by osmosis but the
walls of the ascending loop are impermeable to water
so this does not occur.
The walls of the descending loop are permeable to
water, so water is drawn out by osmosis.

16. Microscopic
Anatomy…
The resulting filtrate, now referred to as urine,
is more concentrated and is reduced in
volume.

17. Microscopic
DCT-
Anatomy…
Function: to make final adjustments to the chemical make-
up of urine in response to the status of blood plasma.
Under the control of aldosterone.
Reabsorption of sodium ions.
Excretion of potassium ions.
Regulation of the acid-base balance (pH) of the blood by the
excretion of hydrogen ions.
In this part of the tubule, water is not reabsorbed in any
great quantity.

18. Microscopic
Anatomy…
Collecting Ducts-
Carry tubular filtrate through the medulla and
eventually empty into the renal pelvis.
Function: make final adjustments to the water
content of urine.
This change occurs by altering the permeability of
the duct walls.
Under the control of antidiuretic hormone (ADH).

20. Physiology…
Reabsorption- Sodium
The glomerular filtrate Potassium
contains the waste
products that need to be Calcium
removed from the body. Chloride
That filtrate also contains Magnesium
substances found in
plasma that need to be Glucose
reabsorbed to maintain Amino acids
homeostasis.
Bicarbonate
Water

21. Physiology…
Reabsorption-
Some substances make this movement passively through
osmosis or diffusion.
Others have to be actively transported across cell
membranes.
About 65% of all tubular reabsorption takes place in the
PCT.
About 80% of the water, sodium, chloride, & bicarbonate are
reabsorbed.
100% of the glucose and amino acids are reabsorbed.

22. Glucose Threshold
(p . 3 1 2 )
The limit of the amount of glucose that can be
reabsorbed
Dogs: 180 mg/dl
Cats: 240 mg/ml

23. Physiology…
Secretion-
Many waste products are not filtered from the
blood in sufficient amounts from the glomerular
capillaries.
The “left over” substances are removed by tubular
secretion.
Most tubular secretion occurs in the DCT.
Hydrogen, potassium, & ammonia are some of
the substances eliminated by secretion.

24. Urine Volume
Regulation
ADH & aldosterone are responsible for the
majority of urine volume regulation.

25. Urine Volume
Regulation
ADH acts on the DCT & collecting ducts to
promote water reabsorption.
Aldosterone increases the reabsorption of sodium
into the bloodstream.
This causes an osmotic imbalance that
encourages water to follow sodium.
Water cannot move out of the DCT unless
sufficient ADH control is present.

26. Ureters
The tubes that exit the kidney at the hilus and
connect to the bladder.
They continuously move urine from the
kidneys to the bladder.
The smooth muscle layer propels the urine
through the ureter by peristaltic contractions.

27. Bladder
Stores urine as it is produced and releases it
from the body.
Lined with transitional epithelium that
stretches as the bladder fills.
The wall contains smooth muscle.
When it contracts, urine is expelled.

28. Urethra
A continuation of the neck of the bladder that
runs through the pelvic canal.
Carries urine from the bladder to the external
environment.

29. Pathology

30. Acute Renal Failure
An abrupt decrease in glomerular filtration.
Usually the result of hypoperfusion or
nephrotoxic injury to the kidney, which
causes damage to the nephron.
Nephrotoxins- ethylene glycol, gentamicin,
sulfonamides…
Azotemia- a build-up of toxins within the
body.

31. Chronic Renal Failure
“CRF”
A common disease of older pets.
An irreversible and progressive decline in renal
function caused by destruction of the nephron units.
Main coon, Abyssinian, Russian Blue, and Burmese
breeds seem to be predisposed.
Irreversible destruction of the nephron results in
uremia.
BUN,  Creatinine, & isothenuria specific
gravity=water

32. Ethylene Glycol
Toxicity
Most dangerous form of antifreeze.
Most commercial antifreeze products contain
between 95-97% ethylene glycol.
Minimum lethal dose of undiluted ethylene glycol
antifreeze is 4.4-6.6ml/kg in dogs and 1.4ml/kg in
cats.
Causes metabolic acidosis and acute renal tubular
necrosis.
Peak levels of ethylene glycol are reached within 1-4
hours post ingestion.

33. Ethylene Glycol
Toxicity…
Clinical Signs:
Vomiting is seen within the first few hours
progressing to depression, ataxia, weakness,
tachypnea, polyuria, and polydipsia (1-6
hours)
18-36 hours acute renal failure occurs.

34. Diabetes Insipidus
(p . 3 1 2 )
Insipid means tasteless***
A decrease in the pituitary release of ADH
(antidiuretic hormone)
ADH is responsible for regulating urine
volume
The collecting ducts do not reabsorb
adequate amounts of water which causes
PU/PD

35. FLUTD/FUS & Urolithiasis
Colville p. 317
“Feline Lower Urinary Tract Disease” or “Feline Urologic
Syndrome”
Presence of mineral precipitates
Urolith’s are the most common cause
Calcium oxylate is the most common mineral found (urine is too
acidic)
Signs- hematuria, dysuria
Detected by urinalysis, radiographs or ultrasound.
Urolith’s that remain in the bladder can damage the bladder
lining, resulting in secondary bacterial infections and hematuria.

36. Different Types of
Bladder Stones
(Urolith’s)

37. URINALYSIS

38. Physical Properties
Include all observations that can be made
without the aid of a microscope or chemical
reagents.

39. Color
Normal is light yellow to amber and is a result
of pigments called urochromes.
The magnitude of color depends on the
degree of urine concentration or dilution.

40. Color…
Colorless-
Low specific gravity.
Associated with polyuria.
Dark yellow-
High specific gravity.
Associated with oliguria.(less urine than norm)
Yellow-brown or green- is likely to contain
bile pigments.

41. Color…
Red or reddish-brown- indicates the
presence of red cells (hematuria) or
hemoglobin (hemoglobinuria).
Brown- may contain myoglobin, which is
excreted during conditions that cause muscle
cell lysis, such as rhabdomyolysis.

42. Clarity (Transparency)
Normal is clear/transparent.
Urine may become cloudy while standing
because of bacterial multiplication or crystal
formation.

43. Odor
Samples standing at room temperature may
develop an ammonia odor as a result of
bacterial growth.
Sweet or fruity odor indicates the presence of
ketones.

44. Urine Specific Gravity
(USG)
Defined as the weight (density) of a liquid compared
to that of distilled water.
May be determined before or after centrifugation.
USG yields information on the hydration status and
the ability of the kidney to concentrate or dilute urine.
Only the refractometer should be used to determine
USG.

45. Urine Specific Gravity
(USG)…
Causes of  USG-
 water intake
 fluid loss
Acute renal failure
Dehydration
Shock

46. Urine Specific Gravity
(USG)…
Causes of  USG-
Water re-absorption problems
 fluid intake
Excessive fluid administration
Pyometra
Diabetes insipidus
Diuretic therapy

47. Urine Specific Gravity
(USG)…
Isothenuria “Fixed USG”-
1.008-1.012
Occurs when the USG approaches that of
glomerular filtrate.
Urine in this range has not been concentrated or
diluted by the kidneys.
The closer the USG is to isothenuric, the greater
the amount of kidney function has been lost
(~75%).

48. CHEMICAL ANALYSIS

51. pH
Expresses the hydrogen ion (H+) concentration.
A measure of the degree of acidity or alkalinity of
urine.
A pH >7.0 is alkaline, <7.0 is acidic.
Urine left standing open at room temperature
tends to increase in pH resulting from a loss
of carbon dioxide.
The pH of urine is largely dependant on diet.

52. pH…
Decreased pH-
Fever, starvation, high protein diet, acidosis, excessive
muscular activity.
Increased pH-
Alkalosis, high fiber diets, urethral obstruction, bladder
paralysis (urine retention).
An abnormal pH can result in crystal or urolith
formation.
The pH can be corrected by manipulating the diet to
help dissolve the solids or prevent uroliths from
forming.

53. Protein
Usually absent or present in trace amounts of
normal urine.
Urine dip sticks allow semi-quantitative
measurements by progressive color changes
on the reagent pad.
Reagent strips commonly detect albumin and
are not very sensitive to globulins (proteins
insoluble in water).

54. Protein…
Urine Protein : Creatinine Ratio-
This test is used to confirm significant amounts of
protein in the urine.
Used to determine the degree of protein loss in
chronic renal disease.
See page 161

55. Protein…
Protein interpretation-
Very dilute urine may yield a false negative because
the protein concentration may be below the sensitivity
of the testing method.
Transient Proteinuria- may result from a
temporary increase in glomerular permiability.
This condition is caused by increased pressure in the
glomerular capillaries and may be found in muscle exertion,
emotional stress, or convulsions.

56. Protein…
Protein interpretation-
Proteinuria indicates disease of the urinary
tract, especially the kidneys.
Both acute and chronic renal disease lead to
proteinuria.
Acute nephritis is characterized by marked
proteinuria with WBC’s and casts in the urine.

57. Glucose
The presence of glucose in the urine is known as
glucosuria.
Glucose is filtered through the glomerulus and
reabsorbed by the tubules.
Glucosuria usually does not occur unless the blood
glucose level exceeds the renal threshold.
At this concentration, tubular reabsorption cannot
keep up with the glomerular filtration of glucose, and
glucose passes into the urine.

58. Glucose…
Glucosuria occurs in diabetes mellitus as a
result of a deficiency of insulin or an inability
of insulin to function.
Transient glucosuria- a release of
epinepherine causes glucose levels to rise for
energy.
Causes: fear, excitement, restraint.

59. Ketones
Includes: acetone, acetoacetic acid, and β-
hydroxybutyric acid.
Ketone bodies are formed during incomplete
catabolism of fatty acids.
When fatty acid metabolism is not
accompanied by sufficient carbohydrate
metabolism, excess ketones are present in
the urine.
A condition known as ketonuria.

60. Ketones…
Ketonuria frequently occurs in animals with diabetes
mellitus.
Because the animal lacks the insulin necessary for
carbohydrate metabolism, fat is broken down to meet
the animal’s energy needs and excess ketones are
excreted in the urine.
Ketones are toxic, causing CNS depression and
acidosis.
Hence- ketoacidosis or acidosis resulting from ketonuria.

61. Ketones…
Transient ketonuria- can occur with starvation
or prolonged anorexia.
 ketones can suggest diabetes mellitus.

62. Bile Pigments
Bilirubin and urobilinogen.
Only conjugated (water soluble) bilirubin is
found in urine.
Bilirubinuria can be seen with bile duct
obstructions, liver disease, and hemolytic
anemia.

63. Bile Pigments…
 Bilirubin (bilirubinuria) suggests:
Excessive hemolysis of RBC’s.
Hepatobiliary obstruction
Liver disease

64. Blood
Tests for blood in the urine detect:
Hematuria- usually a sign of disease causing
bleeding somewhere in the urogenital tract.
Hemoglobinuria- usually the result of
intravascular hemolysis.
Myoglobinuria-
Myoglobin is a protein found in muscle.
Severe muscle damage causes myoglobin to leak from
muscle cells into the blood.

65. Blood…
Causes of hematuria-
Inflammation (cystitis)
Urolithiasis
Bladder tumors- transitional cell carcinoma
Iatrogenic trauma- catheter placement,
cystocentesis.
Causes of hemoglobinuria-
Excessive lysis of RBC’s (hemoglobinemia)
IMHA
Mismatched blood transfusion
RBC parasites

66. Blood…
Causes of myoglobinuria-
Muscle cell lysis
Excessive exercise
Electrical shock
Heat stroke
Snake venoms

67. Leukocytes
You can believe a positive reaction but never
believe a negative reaction.
Always examine the sediment for
confirmation.
Presence usually indicates a bacterial
infection in the urogenital tract.
A positive nitrate reaction occurs with a
large quantity of bacteria in the urine.

68. Microscopic Examination
of Urine
The 5 “C’s”
Cells, Casts, Crystals, Critters, & Crap

69. Page 165

70. Cells
Erythrocytes- may have
several different
appearances depending on
the urine concentration, pH,
and time elapsed between
collection and examination.
May be confused with fat
globules or yeast.
Indicates bleeding
somewhere in the urogenital
tract.

71. Cells…
Leukocytes-
Larger than RBC’s.
Finding more than 2-3/hpf
indicates an inflammatory
process in the urogenital
tract.
Pyuria is indicative of
nephritis, cystitis, or
urethritis.
Urine with pyuria should
always be cultured for
bacteria.

72. Cells…
Squamous Epithelial
Cells-
Their presence usually is
not considered
significant.
They often have straight
edges and distinct
corners which sometimes
curl or fold.
They contain a small,
round nucleus.

73. Cells…
Transitional Cells-
Come from the bladder,
ureters, renal pelvis, and
proximal urethra.
Usually round, may be
pear-shaped or caudate.
Small nucleus.
Increased numbers
suggest cystitis or
pyelonepheritis.

74. Cells…
Renal Epithelial Cells-
The smallest epithelial cells
observed in urine.
Originate in the renal
tubules.
Often confused with WBC’s.
Generally round with a large
nucleus.
Increased numbers occur in
diseases of the renal
parenchyma.

75. Casts
Formed in the lumen of the distal and collecting
tubules of the kidney.
Where the concentration and acidity of urine is the greatest.
In the renal tubules, secreted protein precipitates in
acidic conditions and forms casts shaped like the
tubules.
All casts are cylindrical structures, with parallel sides.
Their ends may be tapered or round.
Casts dissolve in alkaline urine.
Larger numbers may indicate a lesion in the renal
tubules.

76. Cast Formation

77. Casts…
Hyaline Casts-
Clear, colorless, and
somewhat transparent
structures.
Composed only of protein.
Usually only identified in dim
light.
Numbers are increased with
renal irritation, fever, poor
renal profusion, or general
anesthesia.

78. Casts…
Granular Casts-
Hyaline casts containing
granules.
Most common type of
cast.
May be coarse or fine.
Seen with acute
nepheritis.

79. Casts…
Leukocyte Casts-
The presence of
leukocyte casts indicates
inflammation in the renal
tubules.

80. Casts…
Erythrocyte Casts-
Indicate renal bleeding.

81. Casts…
Waxy Casts-
Usually wider, with
square ends.
Highly refractile.
Indicates chronic, severe
degeneration of the renal
tubules.

82. Casts…
Fatty Casts-
Contain many small droplets
of fat that appears as
refractile bodies.
Frequently seen in cats with
renal disease because they
have lipid in their renal
parenchyma.
Suggestive of degeneration
of the renal tubules.

83. Crystals
“Crystalluria”
Some crystals form as a consequence of
metabolic diseases.
Conditions that lead to crystal formation (diet)
may also cause formation of urinary calculi.
The type of crystal depends on the urine pH,
concentration, and temperature.

84. Crystals…
Triple Phosphate-
Alkaline urine.
“Coffin lids”

85. Crystals…
Amorphous
phosphates-
Found in alkaline urine.
Amorphous urates-
Found in acidic urine.

86. Crystals…
Ammonium biurate-
Yellow
Dumbbell or sheaves of
needles.
Spheres with spicules-
“Thorn apples”

87. Crystals…
Calcium Oxylate-
Acidic urine.
Monohydrate-
“Picket fence”
Common in ethylene
glycol toxicity.
Dihydrate-
“Envelopes”

88. Crystals…
Uric Acid-
Acidic urine.
Yellow or brown.
Normal in which
species?
Dalmations

89. Crystals…
Leucine-
Acidic urine.
Yellow or brown
Highly refractive

90. Crystals…
Tyrosine-
Acidic urine
Fine needles grouped in
clusters.
Bilirubin-
Acidic urine.
Yellow needles.

91. Crystals…
Cystine-
Acidic urine
Colorless and highly
refractive.
Hexagonal plates.

92. Crystals…
Calcium Carbonate

93. “Critters”
Capillaria plica- bladder
worm of dogs
Dirofilaria
Dioctophyma renale-
kidney worm of dogs

94. “Critters”
Spermatozoa-
Presence of sperm
indicates that the urine
has been mixed with
semen.
Sperm may be found in
intact males when urine
is collected by
cystocentesis.

95. “Critters”…
Bacteria-
Small and consistent in
shape.
Rods or cocci.
Usually accompanied by
leukocytes.
Beware of contamination!

96. “Critters”…
Fungal Hyphae-
Colorless.
Usually contaminants of
a urine sample.

97. “Crap”
Mucus Threads-
Long, narrow, wavy
strands.
Originate from mucous
surfaces.
Normal in small numbers.
Greatly increased with
irritation of any kind.

98. “Crap”

99. Serum Chemistries
(Review)
BUN- evaluates the kidneys ability to remove
urea from the blood.
Creatinine- formed from creatine, found in
skeletal muscle, also evaluates the kidneys
filtering ability.
Glucose- useful to evaluate the renal
threshold and diabetes.

100. Electrolyte Assays
(Review)
Sodium- evaluates filtration and
reabsorption.
Chloride- evaluates water distribution and
osmotic pressure.
CO2/Bicarbonate- evaluates excretion and
reabsorption.

101. Send Out Tests
(Usually)
Urine Culture and Sensitivity (C&S)
Creatinine : Cortisol Ratio
Protein : Creatinine Ratio

102. The End!!