Chapter 114: Kidneys Flashcards
Where is the macula densa and what is its function?
Macula densa – between glomerulus and afferent arterioles
Maintain autoregulation of renal blood flow
What is the vein following the nephron called?
Vasa recta
What is the arterial circle in relation to the kidney?
Small capsular arteries enter kidney from capsular surface – secondary arteries anastomose to primary renal arteries and create a renal “arterial circle” – can permit blood flow to kidney if renal artery is obstructed
- Most commonly arise from phrenicoabdominal and adrenal arteries
- More prominent in diseased kidneys
what % of dogs and cats have a multiple renal arteries?
In which kidney is it more common?
13% dogs
10% cats
left is more common
Which renal vein do the ovarian/testicular veins drain into?
Left
where is blood flow highest in the kidney?
Cortical blood flow is the highest
- Cortical 4ml/min/g of tissue
- Outer medulla 0.7ml/min/g
- Internal medulla 0.1ml/min/g
How do you calculate renal blood flow?
Renal blood flow = Renal perfusion pressure / renal vascular resistance
The glomerular filtration rate is what % of plasma flow rate?
20%
Based on radiographs, the normal kidney of a dog is how many times the length of the L2 vertebrae? For a cat?
Normal dog kidney is 2.5-3.5 times length of L2 vertebrae
Normal cat kidney is 2-3 times L2 vertebrae
Name phases of IVU?
Renal angiographic phase
renal blush (nephrogram)
excretory phase (pyelogram)
What is a normal resistive index for a dog?
How do you calculate?
- Normal dog: 0.63 +/-0.05
RI = Peak systolic velocity – end diastolic velocity / peak systolic velocity
If the kidney absent but ureter present is it renal agenesis of dysgenesis?
Dysgenesis (agenesis implies lac of ureter)
What breed of dog is most likely to develop polycystic kidneys?
Bull terrier
most common renal tumour in dog
renal cell carcinoma
What dog breed gets renal cystadenocarcinoma?
GSD
Often combined with Nodular dermatofibrosis +/- uterine leiomyoma
What is the role of the vasa recta capillaries?
- Extend alongside the nephron from the cortex into the medulla, reabsorbing water from the collecting ducts and returning it back to systemic circulation
- Help to maintain hypertonicity of the renal medulla
What structure helps to maintain renal autoregulation of blood flow?
Macula densa (between glomerulus and afferent arterioles)
What cells within the glomerulus are responsible for filtration?
What size particles can pass through the slits?
Podocytes - rest on glomerular basement membrane (negatively charged) and create filtration slits between cells.
<60,000 daltons
What is the normal amount of urine production?
20-45ml/kg/day
What is the osmolality of the glomerular filtrate and of the medullary interstitial fluid?
Glomerular filtrate: 300mOs/L
Medullary interstitial fluid: 1200-1400mOs/L
What is normal renal blood flow?
- Approximately 25% of cardiac output
- 4ml/min/g of renal tissue (in cortex)
Calculated as renal perfusion/renal vascular resistance
What determines the concentrating ability of the kidney?
Renal medullary hyperosmolarity which is maintained by the vasa recta through a counter-current mechanism
What can cause decreased concentrating ability of the kidney?
Increased blood flow through vasa recta (increased pressures, vasodilation, fluid volume)
Decreased urea (malnutrition, PSS)
What (2) mechanisms create medullary interstitial hyperosmolarity?
- Facilitated diffusion of urea into interstitium (40-50%)
- Active transport of Na, K, Cl in proximal loop of Henle
