Chapter 114: Kidneys

Question 1

Where is the macula densa and what is its function?

Answer 1

Macula densa – between glomerulus and afferent arterioles

Maintain autoregulation of renal blood flow

Question 2

What is the vein following the nephron called?

Answer 2

Vasa recta

Question 3

What is the arterial circle in relation to the kidney?

Answer 3

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

Question 4

what % of dogs and cats have a multiple renal arteries?
In which kidney is it more common?

Answer 4

13% dogs
10% cats
left is more common

Question 5

Which renal vein do the ovarian/testicular veins drain into?

Answer 5

Left

Question 6

where is blood flow highest in the kidney?

Answer 6

Cortical blood flow is the highest

• Cortical 4ml/min/g of tissue
• Outer medulla 0.7ml/min/g
• Internal medulla 0.1ml/min/g

Question 7

How do you calculate renal blood flow?

Answer 7

Renal blood flow = Renal perfusion pressure / renal vascular resistance

Question 8

The glomerular filtration rate is what % of plasma flow rate?

Answer 8

20%

Question 9

Based on radiographs, the normal kidney of a dog is how many times the length of the L2 vertebrae? For a cat?

Answer 9

Normal dog kidney is 2.5-3.5 times length of L2 vertebrae
Normal cat kidney is 2-3 times L2 vertebrae

Question 10

Name phases of IVU?

Answer 10

Renal angiographic phase
renal blush (nephrogram)
excretory phase (pyelogram)

Question 11

What is a normal resistive index for a dog?

How do you calculate?

Answer 11

• Normal dog: 0.63 +/-0.05

RI = Peak systolic velocity – end diastolic velocity / peak systolic velocity

Question 12

If the kidney absent but ureter present is it renal agenesis of dysgenesis?

Answer 12

Dysgenesis (agenesis implies lac of ureter)

Question 13

What breed of dog is most likely to develop polycystic kidneys?

Answer 13

Bull terrier

Question 14

most common renal tumour in dog

Answer 14

renal cell carcinoma

Question 15

What dog breed gets renal cystadenocarcinoma?

Answer 15

GSD

Often combined with Nodular dermatofibrosis +/- uterine leiomyoma

Question 16

What is the role of the vasa recta capillaries?

Answer 16

• 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

Question 17

What structure helps to maintain renal autoregulation of blood flow?

Answer 17

Macula densa (between glomerulus and afferent arterioles)

Question 18

What cells within the glomerulus are responsible for filtration?

What size particles can pass through the slits?

Answer 18

Podocytes - rest on glomerular basement membrane (negatively charged) and create filtration slits between cells.

<60,000 daltons

Question 19

What is the normal amount of urine production?

Answer 19

20-45ml/kg/day

Question 20

What is the osmolality of the glomerular filtrate and of the medullary interstitial fluid?

Answer 20

Glomerular filtrate: 300mOs/L

Medullary interstitial fluid: 1200-1400mOs/L

Question 21

What is normal renal blood flow?

Answer 21

• Approximately 25% of cardiac output
• 4ml/min/g of renal tissue (in cortex)

Calculated as renal perfusion/renal vascular resistance

Question 22

What determines the concentrating ability of the kidney?

Answer 22

Renal medullary hyperosmolarity which is maintained by the vasa recta through a counter-current mechanism

Question 23

What can cause decreased concentrating ability of the kidney?

Answer 23

Increased blood flow through vasa recta (increased pressures, vasodilation, fluid volume)
Decreased urea (malnutrition, PSS)

Question 24

What (2) mechanisms create medullary interstitial hyperosmolarity?

Answer 24

• Facilitated diffusion of urea into interstitium (40-50%)
• Active transport of Na, K, Cl in proximal loop of Henle

Question 25

What is the concave surface of the kidney called?

Answer 25

The hilus

Question 26

What are the layers of the kidney?

Answer 26

Fibrous capsule
Outer cortex (glomeruli here)
Inner medulla
Renal pelvis (continuous with ureter)

Question 27

What vessel do the renal arteries come off of?

Answer 27

The aorta

Question 28

Describe the arterial blood flow through the kidneys:

Answer 28

Renal a. -> dorsal/ventral branches -> 3-7 interlobar aa. -> arcuate aa. -> interlobular aa. -> afferent glomerular arterioles -> glomerulus -> efferent arterioles -> intertubular capillaries -> venous system

Question 29

Describe the venous drainage of the kidneys:

Answer 29

The deep and superficial renal veins are in the outer cortex. They drain the capsule -> stellate v. -> interlobular v. -> arcurate v. -> renal v. -> vena cava

Question 30

What innervates the kidneys?

Answer 30

The sympathetic ganglion and the vagus trunks.

Question 31

How many nephrons are in each kidney?

Answer 31

50,000

Question 32

Trace the tubule system:

Answer 32

Proximal convoluted tubule -> descending loop -> ascending loop -> distal convoluted tubule -> collecting tubule -> papillary duct -> collecting system (pelvis)

Question 33

True or false? Renal perfusion pressure is equal to MAP

Answer 33

True

Question 34

What is the normal orientation of renal vessels?

Answer 34

Renal vein is ventral to renal artery

Question 35

What is the renal crest?

Answer 35

The center of kidney/collecting system.