Anatomy, Embryology, and Imaging of the Kidney

Question 0

Average length of a human kidney?

How does the left vary from the right?

Answer 0

Average length is about 11cm, but depends on the size of the person.
The right kidney is a little “squashed” by the liver.

Question 1

What are the top, bottom, left, and right sides of the kidney called?

Answer 1

The superior and inferior poles.

The lateral and medial borders.

Question 2

About how much kidney function must a person lose before symptoms appear?
(How does this affect determining acute vs. chronic kidney injury?)

Answer 2

About 90%.
(Because both acute and chronic injury can have a rapid onset of symptoms, it can be difficult to determine acute vs. chronic from timeline alone.)

Question 3

How does chronic kidney injury often change the size of the kidneys?

Answer 3

Chronically injured kidneys are often smaller with scarring/fibrosis.

Question 4

How can the cortex appear altered on ultrasound of a chronically injured kidney?

Answer 4

The cortex of a chronically injured kidney will often have more areas of echodensity.

Question 5

What vertebral levels do the kidneys typically span?

Answer 5

T12 - L3

Question 6

If you were biopsy-ing a kidney, would you go from the front?

Answer 6

Nope, there’s lots of stuff to hit. Better to go from the back, hitting the part of the kidney not protected by the ribs. (though there are still a few splanchnic nerves one could hit…)

Question 7

What are the renal “papilla”?

Answer 7

Each pyramid, composed of medulla, ends in a papilla draining into a minor calyx.

Question 8

Where are the renal sinuses?

Answer 8

Between the minor calyces.

they’re often filled with fat and have blood vessels running through them

Question 9

What are the renal columns?

Answer 9

Extensions of the cortex between the pyramids. Not much action there.

Question 10

What are the medullary rays?

Answer 10

A number of structures, but notably, collecting ducts that drain down into larger ducts. (more on these next lecture)

Question 11

What’s downstream of the minor calyces?

Answer 11

Minor calyces -> major calyces -> renal pelvis -> ureter.

Question 12

Should you be able to see the renal calices on normal x-ray? What if you do?

Answer 12

No. If you do, it suggests a problem like a big “staghorn” kidney stone.

Question 13

What does a ureter / other renal outflow obstruction look like on ultrasound? What is this process called?

Answer 13

Dilated renal pelvis/calyces (which are echo-lucent).

This is called hydronephrosis.

Question 14

How many major branches does each renal artery give off? What’s the term for the arteries at this level?

Answer 14

Each renal artery gives off 5 “segmental” arteries - 4 anterior and 1 posterior.

Question 15

About how much kidney function will be lost if one segmental artery is completely occluded?

Answer 15

20%

Question 16

What are the names of the “levels” of arteries after segmental arteries?

Answer 16

Segmental -> interlobar arteries -> arcuate arteries -> interlobular arterioles.

Question 17

How would you treat a severe kidney bleed (eg. from trauma)?

Answer 17

Coil embolization of the segmental artery upstream of the bleed.

Question 18

3 layers of the ureter wall?

Answer 18

Fibrous
Muscular
Mucuous coat

Question 19

How does the ureter opening into the bladder help prevent reflux?

Answer 19

The superior part of the ureter extends into the lumen of the bladder, such that when the bladder is distended it compresses and closes the opening to the ureter.

Question 20

Anatomy review: What is the name of the structure in the bladder where the ureters enter?

Answer 20

The trigone.

Question 21

3 causes of obstruction of the ureter “from within”?

Answer 21

Kidney stones.
Blood clots.
Tumors.

Question 22

Can lots of things cause an external obstruction of a ureter?

Answer 22

Yep.

He highlighted iliac artery aneurysm as an example.

Question 23

3 portions of the male urethra?

Answer 23

Prostatic
Membranous
Cavernous

Question 24

What germ layer, and what part of it, gives rise to the kidneys?

Answer 24

Intermediate mesoderm.

Question 25

What are the excretory organs that exist in humans from week 3-5?

Answer 25

Pronephros - don’t worry about them.

Question 26

What’s the second excretory organ to develop in the embryo?

Answer 26

The mesonephros.

these become testes/etc. in males, regress in females

Question 27

What embryonic structure gives rise to final, adult nephrons?

Answer 27

The metanephrons.

Question 28

When does metanephron development cease?

Answer 28

Week 36 -thus some premature babies will have underdeveloped kidneys.

Question 29

How do the metanephric blastema and the mesonephric duct talk to eachother to form a kidney?

Answer 29

Metanephric blastema induces ureteric bud.
Ureteric bud promotes blastema differentiation into glomeruli and tubules (mesenchymal -> epithelial transformation).
The ureteric tips and cap mesenchyme are special…

Question 30

A lot of branching and budding happens when forming the calyces and inducing the million future nephrons.

Answer 30

Okay.

Question 31

What might happen if a ureteric bud branches before penetrating the metanephric blastema?

Answer 31

It can give rise to a second ureter for that kidney, or a whole new third kidney.

Question 32

What’s the syndrome that results from in utero kidney dysfunction?
What’s the primary deficit that drives the defects?

Answer 32

Potter’s syndrome: kidney dysfunction -> oligohydramnios, i.e. not enough amniotic fluid.
(forehead, ears, nose, fingers, lungs are adversely affected)
(injecting saline to take the place of missing amniotic fluid has yielded promising results, but the kids will still need kidney transplants)

Question 33

Does the arterial supply change as the kidneys ascend to their final position?

Answer 33

Yes. They stimulate new vessel budding from the aorta as they travel up, eventually getting to the renal aa.

Question 34

What’s a horseshoe kidney? Why doesn’t it ascend all the way?

Answer 34

Left and right kidney are fused at the inferior pole.

It can’t ascend all the way because it gets stuck on the inferior mesenteric artery.

Question 35

How can supernumerary renal arteries cause a problem?

Answer 35

They can cause external obstruction of the ureter.

And if a surgeon doesn’t realize that it’s there, it can be a problem.