Introduction and clinical approach to urinary tract medicine Flashcards
Where does ultrafiltration of plasma occur in the kidney?
At the glomerulus - through pores in the capillary wall into the Bowman’s capsule and the filtrate then enters the PCT
Which structures act to control blood flow to the glomerulus and GFR?
Sphincters on the afferent and efferent arterioles
What substances are retained in the capillary following ultrafiltration?
Large proteins
Negatively charged proteins e.g. albumin
Most of the filtered Na is absorbed where in the nephron?
PCT
What is the role of the loop of Henle?
Acts as a counter current multiplier and generates medullary hypertonicity
What happens at the DCT?
Selective reabsorption of various solutes and secretion of substances occurs to regulate the final excretory product
What is the function of ADH?
Controls permeability of the DCT and CDs to water - allows movement of water into the hypertonic interstitium and concentration of urine
Give examples of the functions of the kideny
- Excretion of waste
- Control of body fluid balance
- Endocrine: renin, erythropoietin, calcium metabolism, phosphorus balance
Define azotaemia
An abnormal conc of urea, creatinine and other nitrogenous compounds in the blood
What is the cause of pre-renal azotaemia?
- Decreased GFR due to decreased renal perfusion
- Dehydration, hypovolaemia, heart failure
What is the cause of renal azotaemia?
- Renal parenchymal disease
- When enough nephrons are non-functional
What is the cause of post-renal azotaemia?
- Interference with urine excretion
- Urethral obstruction, urinary tract rupture
Define chronic kidney disease
Structural or functional abnormalities of one or both kidneys that have been there for 3 months or longer
What is an acute kidney injury, give examples
- Rapid loss of kidney function, a sudden inability to maintain fluid, acid-base and electrolyte balance
- Leptospirosis, ethylene glycol, NSAID toxicity
What causes PU/PD?
- increased filtered load per surviving nephron
- disruption of normal counter-current system
- impaired response to ADH
- Dehydration
Why does nausea and vomiting occur following reduced kidney function?
Uraemia toxins act on chemoreceptor trigger zone
Why does anorexia occur following reduced kidney function?
- Oral pain: urea diffuses into salvia causing ulceration and pain
- Nausea
- Gastritis
- Acidosis
- Hypokalaemia
Why does anaemia occur following reduced kidney function?
Relative deficiency in erythropoietin
- GI blood loss
- Excessive blood sampling
Compare azotaemia and uraemia
Azotaemia = an abnormal concentration of urea, creatinine and other nitrogenous compounds in the blood
Uraemia = clinical syndrome that results from loss of kidney function, involving multiple metabolic derangements
- Urine in the blood = severe kidney disease
Give examples of different urinary changes that can occur with urinary tract disease
Pollakiuria – increased frequency
Stranguria – straining
Dysuria – difficulty urinating
Incontinence – unaware they are urinating/loss of control
Haematuria seen throughout urination indicates disease at which point of the urinary tract?
Upper UT
Haematuria seen at the end of urination indicates disease at which point of the urinary tract?
Lower UT
What are the two most common urinary changes seen with cystitis?
- Pollakiuria (increased frequency)
- Stranguria (Straining): frequent, small amounts of urine
What are the core lab tests to consider when dealing with a urinary tract disease?
- Haematology may be useful – e.g. raised WBC in inflammatory process such as pyelonephritis
- Biochemistry
- Urinalysis
- Urine culture
What is the most important point to note when dealing with renal azotaemia?
Renal azotaemia implies loss of at least 75% of functioning nephrons
Where is urea made?
In the liver from catabolised proteins and ammonia
Describe reabsorption/excretion of urea by the kidneys
- Filtered by glomerulus, some reabsorbed in PCT
- Proportion of urea that is reabsorbed depends on body fluid balance: dehydration => slower flow through tubules and more urea reabsorbed; high fluid flow through tubules => more excreted
Serum urea is affected by which factors?
- GFR
- Dietary protein
- Body energy balance
- Fluid status
Describe reabsorption/excretion of creatinine by the kidney
- Filtered by glomerulus, Not reabsorbed in PCT
- It is excreted almost exclusively by the kidney
Serum creatinine is affected by which factors?
Muscle mass
GFR
When would low albumin levels be seen?
Protein losing nephropathy (deterioration of kidney function => failure)
Which substance, that is usually excreted by the kidneys is seen to increase during kidney failure?
Phosphorus (only when approx 85% of nephrons are non-functional)
What is symmetric dimethyl arginine (SDMA)?
Now being offered by some laboratories. Released into circulation from cells and eliminated by kidneys. Correlates well with GFR (better than creatinine in some studies, probably because it is affected by fewer non-renal factors). Early reports in dogs and cats suggest it MAY be useful for early detection of CKD in dogs and cats, but it’s not perfect
A needle placed into the bladder to remove urine is called?
Cystocentesis
Which methods of sampling urine are sterile and non-sterile?
Sterile = cystocentesis Non-sterile = free catch midstream and catheterisation
Why must a urine sample be sampled when it is fresh?
Delays allow crystal precipitation and bacterial growth
What do the following urine colours indicate:
- Pale yellow-amber
- Red to brown
- Dark yellow/brown
- Normal
- Haematuria or haemoglobinuria
- Bilirubinuria
What does cloudy urine indicate?
Increased cells, crystals, bacteria, mucus, lipids, casts, sperm
Protein sediment analysis alongside dipstick analysis would provide what suggestion for these findings:
- No sediment
- Active sediment
No sediment- suggests renal proteinuria
Active sediment- suggests bladder or genital tract problem
What is used to measure specific gravity?
Refractometer
What is specific gravity?
A measure of kidneys’ ability to dilute or concentrate the urine. Urine specific gravity is important in assessing azotaemia and interpreting other urine parameters
What are normal specific gravities for dogs and cats?
S.G. > 1.030 in dogs
S.G. > 1.035 in cats
Define Hyposthenuria
Excretion of urine of low specific gravity due to an inability of the tubules of the kidneys to produce concentrated urine
- Kidney is actively diluting the urine (e.g. diabetes insipidus, psychogenic PD and occasionally hyperadrenocorticism)
What is the specific gravity range for Hyposthenuria?
S.G. 1.001 - 1.007 - less then plasma
Define isosthenuria
Urine has same osmolality as plasma, kidney is nether concentrating nor diluting the urine
What is the specific gravity range for isosthenuria?
S.G. 1.008 - 1.012 (= plasma)
What are the intermittent ranges (slightly concentrated) for USG of dogs and cats?
S.G. 1.013 - 1.029 (dog)
S.G. 1.013 - 1.034 (cat)
What can be examined in a urine sediment analysis?
- Cells: increased in inflammation or infection
- Crystals: may be incidental but may be associated with urolithiasis
- Culture and sensitivity: bacteria
Give some bacterial examples of species commonly involved in UTIs
- Streptococcus
- Staphylococcus
- E.coli
Describe the appearance of calcium oxalate dihydrate crystals and struvite crystals
Calcium oxalate = octahedral (like two pyramids put together)
Struvite = rectangular
What are urine casts and what does their presence suggest?
- Casts: Cylindrical moulds of stuff from kidney tubules
- Seeing occasional casts is normal
- Increased numbers suggest renal disease.
Which parts of the urinary tract can be seen on an ultrasound?
- Kidneys
- Bladder
- Ureters (if distended)
- Prostate
What are the four end organs affected by high blood pressure?
Eyes – retinas
Kidneys
Brain – CNS
Heart
Which acid/base metabolic disturbance is most common in CKD?
Metabolic kidney disease
If a dog has urea levels of 45mmol/L (high) and creatinine levels of 670umol/L (high), does it have CKD?
No – severe kidney problem but it is acute
A male dog has a urethral obstruction, is straining to urinate, but no urine comes out, what is the term for this?
Dysuria
3yo Labrador that is vomiting with increased levels of urea and creatinine and a USG of 1.045, is the azotaemia pre-renal, renal or post-renal?
Pre-renal
A different dog is also vomiting, with high levels or urea and creatinine, but this time the USG is 1.011, is the azotaemia pre-renal, renal or post-renal?
Renal
