GP- kidneys and ureters

what are the functions of the urinary system?

-maintenance of water, electrolytes, acid/base balance

-clearance of waste products

-conservation of nutrients

-erythropoietin production

-hormone degradation and excretion

-enzyme degradation

what are the 3 steps in urine formation?

1. glomerular filtration

2. tubular reabsorption

3. tubular secretion

the glomerular filtration rate (GFR) depends on:

capillary hydrostatic pressure- blood enters through the afferent arteriole and exits via the efferent tubule. the hydrostatic pressure ↓ when the afferent tubule constricts. the hydrostatic pressure ↑ when the efferent tubule constricts. this is controlled by the juxtoglomerular apparatus

bowman's space fluid oncotic pressue

how does the GFR change with changes in the capillary hydrostatic pressure? how is the hydrostatic pressure changed?

↑ hydrostatic pressure = ↑ GFR

this happens when the efferent arteriole constricts

↓ hydrostatic pressure = ↓ GFR

this happens when the afferent arteriole constricts

the constrictions of the arterioles are controlled by the juxtaglomerular apparatus

what does the juxtaglomerular apparatus do?

controls renal blood flow, and therefore glomerular filtration

it controls the constriction of the afferent/efferent arterioles, which causes a change in hydrostatic pressure, and therefore in the GFR

how does the constriction of the efferent arteriole affect the GFR?

↑ GFR

because it ↑ the hydrostatic pressure

how does the constriction of the afferent arteriole affects the GFR?

↓ GFR

because it ↓ the hydrostatic pressure

what substances are reabsorbed in the proximal tubule?

glucose (100%)

amino acids (100%)

proteins

H2O

Na+ (65%)

HCO3 (80-90%)

Ca2+ (60%)

P (85%)

K+ (60-70%)

where in the nephron is glucose reabsorbed?

proximal tubule

where in the nephron are amino acids reabsorbed?

proximal tubule

is glucose reabsorbed or secreted?

reabsorbed (100% in the proximal tubule)

are amino acids reabsorbed or secreted?

reabsorbed (100% in the proximal tubule)

what substances are reabsorbed in the loop of henle?

NaCl (25%)

H2O (15%)

Mg (15%)

where is H2O reabsorbed in the nephron?

proximal tubule, loop of henle, distal tubule, collecting duct

(throughout the entire nephron)

where is NaCl reabsorbed in the nephron?

loop of henle

is NaCl reabsorbed or secreted?

25% reabsorbed in the loop of henle

what substances are reabsorbed in the distal and collecting tubules?

Na+ (5%)

H2O

is Mg reabsorbed or secreted?

15% reabsorbed in the loop of henle

what hormone regulates the secretion of H2O in the distal tubule and collecting duct?

ADH

what waste products are secreted by the nephron, composing the urine?

ammonia

uric acid

H+

K+

creatinine

(all of these will intoxicate the animal if not secreted)

if the animal has renal failure and cannot secrete the waste products, what happens?

the animal will be intoxicated by the waste products, and will most likely die from ammonia intoxication

what is diuresis?

urine production

what is the normal diuresis quantity of dogs, cats, and horses?

dogs: 20-40ml/kg/day

(or 1-2ml/kg/hr)

cats: 28 ml/kg/day

horses: 15-30 ml/kg/day

these values are measured by putting an intraurethral catheter and collecting the urine

what is polyuria?

what can cause this?

↑ production of urine

causes:

↑ water intake

stress

diuretics

↑ urine osmolarity (DM, CRF, HAC)

diabetes insipida

sepsis

what physiological changes cause polyuria?

↑ water intake

stress

what can cause polyuria?

physiological:

↑ water intake

stress

pharmacological:

diuretics

mannitol

pathological:

↑ urine osmolarity (DM, CRF, HAC)

diabetes insipida

sepsis

diabetes insipida has what main urinary related clinical sign?

polyuria, due to ADH deficit

diabetes mellitus has what main urinary related clinical sign?

polyuria, due to increased urine osmolarity

polydipsia due to polyuria

chronic renal failure will lead to _____uria (oly/poly)

polyuria

cushing's disease will lead to _____uria (olig/poly)

polyuria

what is oliguria? what can cause this?

↓ urine production (<0.25 ml/kg/hr)

causes:

↓ water intake

↓ GFR (due to glomerular disease, heart failure, shock, etc)

partial urinary tract obstruction

an animal producing 0.08-0.25 ml/kg/hr of urine has ______uria

oliguria

an animal producing <0.08ml/kg/hr of urine has ______uria

anuria

what pathologies lead to a ↓ GFR, which causes oliguria?

heart failure

glomerular disease

shock

what pathological reasons might an animal have oliguria?

↓ GFR, due to heart failure, glomerular disease, shock, etc

partial urinary tract obstruction

what is anuria? what cause cause this?

no urination (<0.08 ml/kg/hr)

causes:

dehydration

severe hemorrhage

acute tubular necrosis

acute renal failure

calculi

tumors

what are the different etiologies of anuria?

pre-renal:

dehydration

severe hemorrhage

renal:

acute tubular necrosis

acute renal failure

post-renal:

calculi

tumors

what is polaquiuria?

↑ frequency of urination with ↓ urine quantity

usually due to pain

↑ frequency of urination with ↓ urine quantity is called...

polaquiuria

if an animal is urinating <0.08ml/kg/hr, we call this ______uria

anuria

dehydration can cause _____uria

oliguria or anuria

pain commonly causes ____uria

polaquiuria

calculi or tumors in the urinary tract can cause...

polaquiuria (if painful), anuria (if completely obstructing), or oliguria (if partially obstructing)

acute tubular necrosis will cause ______uria

anuria

what is dysuria?

difficulty urinating

incomplete/painful urination due to a lower urinary tract pathology

the incomplete/painful urination due to a lower urinary tract pathology is called ______

dysuria

dysuria results from a problem where?

lower urinary tract

what is vesical tenesmus?

feeling of incomplete emptying of the urinary bladder after urination

the feeling of incomplete emptying of the urinary bladder after urination is called.....

vesical tenesmus

what is urinary incontinence?

lack of control over urination

an animal that cannot control its urination has ______

urinary incontinence

what can cause urinary incontinence?

hormonal:

↓ testosterone/ estrogen (due to early castration)

mechanical:

bladder tumors

calculi

prostate disease

neurological:

CNS lesions

peripheral nerve lesions

if we castrate a puppy/kitten too early, this inhibits the secretion of testosterone and estrogen, which will commonly lead to what urinary problem?

urinary incontinence

what neurological problems may cause urinary incontinence?

CNS lesions

peripheral nerve lesions

what mechanical problems can cause urinary incontinence?

bladder tumors

calculi

prostatic disease

how can we perform a clinical evaluation of the urinary system?

1. hematology and biochemistry profile

2. urinalysis and urine sediment exam

3. xrays

4. ultrasound of kidney, bladder, and urethra

5. biopsy

if performing a biochemistry test to assess the urinary system, what values do we check?

BUN (urea)

serum creatinine

these can tell us the functionality of the GFR

if performing a urinalysis to assess the urinary system, what values do we check?

to check tubular function:

concentration/dilution

electrolytes

glucose

protein

casts

to check glomerular function:

urine protein (albumin, creatinine)

RBCs

if we want to assess the # of functional nephrons, what do we want to assess?

the GFR.

we do this by performing a biochemistry exam and looking at BUN and serum creatinine

if substances that should be excreted in the urine are present or ↑ in the blood, this indicates_______

inadequate GFR (which can indicate ↓ functional nephrons)

what is BUN?

urea

final product of protein catabolism

excreted by the kidneys and GI

if ↑ in the blood, most likely due to a kidney disorder (also possibly ↑ protein diet or GI hemorrhage)

↑ BUN means:

kidney disorder

↑ protein diet

GI hemorrhage

what is serum creatinine?

a product of muscle metabolism (muscular animals have more creatinine)

removed almost 100% by glomerular filtration

which, BUN or serum creatinine can be due to a kidney problem, hydration status, or diet?

BUN

serum creatinine is only affected by the kidneys

which, BUN or creatinine, is a better parameter for GFR measurement, because it is only affected by glomerular filtration?

serum creatinine

(BUN can also be affected by a GI hemorrhage or ↑ protein diet)

what is azotemia?

↑ BUN and ↑ creatinine

there are 3 types:

1. pre-renal

2. renal

3. post-renal

↑ BUN and ↑ creatinine is called...

azotemia

what is prerenal azotemia?

hemodynamic azotemia, due to dehydration and hypovolemia.

-↓ renal blood flow

-↓ perfusion pressure

-↑ vascular resistance

easy to treat, but can lead to ARF

hallmarks:

-mild azotemia

-↑ urine specific gravity

-↓ urine Na+

increased BUN and creatinine in the blood due to dehydration/hypovolemia is called.....

pre-renal azotemia

if an animal with ↑ BUN and creatinine also has a high specific gravity and ↓ Na+ in the urine, what do we call this?

pre-renal azotemia

(due to dehydration/ hypovolemia)

what is renal azotemia?

↑ BUN and creatinine due to acute renal failure, which leads to irreversible parenchymal damage.

it is caused by ischemic, toxic, or inflammatory insult

↑ BUN and creatinine caused by Acute renal failure is called....

renal azotemia

what can cause renal azotemia?

acute renal failure, due to ischemic, toxic, or inflammatory insult

what is post-renal azotemia?

↑ BUN and creatinine due to obstruction of the urine flow and retention of these products within the body

these are caused by obstructions of the lower urinary tract, such a uroliths, mucous plugs, blood clots, and masses (intra or extra luminal)

↑ urea and BUN caused by lower urinary tract obstruction is called...

post renal azotemia

what may cause a lower urinary tract obstruction? this can lead to what abnormal values in a biochemistry test?

uroliths

mucous plugs (cats)

blood clots

intra/extra luminal masses

azotemia (↑ BUN and creatinine)

the sudden loss of renal function is called....

acute renal failure

is acute renal failure reversible?

potentially, if it is diagnosed and treated quickly

there are ____ clinical stages of acute renal failure.

3:

induction

maintenance

recovery

is acute renal failure a serious condition?

yes

______% of acute renal failure is pre-renal

60-70

25% of acute renal failure is due to a problem with the _______

kidneys (tubules, interstitium, or glomeruli)

___% of acute renal failure is caused by obstruction of outflow of urine (post renal)

5%

what is the most common cause of acute renal failure?

↓ renal perfusion (without renal cell injury)- pre-renal acute renal failure. this can be caused by diarrhea/vomiting, cardiac failure, hemorrhage, dehydration, hypoalbuminemia, thrombosis in renal arteries, or septic shock

this makes up 60-70% of acute renal failure cases

pre-renal acute renal failure will appear with what abnormal values on the blood and urine test?

↑ ↑ BUN : creatinine ratio

↓ urine Na+

↑ urine osmolarity

a very high BUN and low creatinine (↑ BUN:creatinine) indicates what type of renal failure?

pre-renal acute renal failure

what type of renal failure can diarrhea/vomiting, dehydration, cardiac failure, hemorrhage, thrombosis, septic shock, and hypoalbuinemia cause?

pre-renal acute renal failure

because they will cause a decrease in renal perfusion

we see these results in the blood and urine tests:

↑ BUN : creatinine

↓ urine Na+

↑ urine osmolarity

what can we suspect is the diagnosis?

pre-renal acute renal failure

(due to ↓ renal perfusion)

what problems in the kidneys can cause acute renal failure?

acute renal nephritis- caused by allergy, autoimmune, embolism, ascending infection

glomerulonephritis- caused by inflammation, immune-mediated, neoplasia, or diabetes

amyloidosis- this is progressive and irreversible

amyloidosis can cause what type of renal failure?

acute renal failure, because it accumulated between the renal cells and compresses them

this is progressive and irreversible

what are possible causes of acute renal nephritis?

allergy

autoimmune

embolism

ascending infection

what might cause glomerulonephritis?

inflammation

immune mediated

neoplasia

diabetes

what can cause post-renal acute renal failure?

obstructions

uroliths, neoplasia, tumors, adhesions, bladder displacement

trauma

how does acute renal failure appear in a blood and urine test if it is due to a problem within the kidney?

↑ BUN and creatinine

presence of renal tubular epithelial cells, RBCs, WBCs, or casts in the urine sediment

proteinuria

if we perform a blood and urine test on an animal and see:

↑ BUN and creatinine

presence of renal tubular epithelial cells, RBCs, WBCs, or casts in the urine sediment

proteinuria

what is most likely the cause?

intrinsic acute renal failure (caused by acute renal nephritis, glomerulonephritis, or amyloidosis)

what abnormalities are present in the blood and urine tests of an animal with post renal acute renal failure?

↑ BUN and creatinine

obstruction shown in imaging

hematuria

what are the 3 stages of acute renal failure?

1. induction

renal insult, cellular damage

2. maintenance

loss of nephron function, oliguria (bc cannot reabsorb H2O)

3. recovery (not always)

return to normal tubular function, resolution of azotemia, polyuria → normal diuresis, nephron repair

if in the recovery stage of acute renal failure the nephrons become fibrotic, what happens?

development of chronic renal failure

what are the clinical signs of acute renal failure?

uremic syndrome (due to acidosis- ↑ H+)

-vomiting and diarrhea

-lethargy

-anorexia

-depression

-coma

-oral cavity ulceration

-halitosis

-oliguria → polyuria

what is uremic syndrome?

a set of clinical signs associated to severe kidney failure or post renal obstruction due to accumulation of uremic toxins in the blood

-vomiting/diarrhea

-lethargy

-anorexia

-depression

-coma

-oral cavity ulceration

-halitosis