ICL 1.0: Embryology and Anatomy of the Kidney

Question 1

which structures are located next to the kidneys anatomically?

Answer 1

the adrenal glands sit right on top of the kidneys!

the inferior vena cava and abdominal aorta run right inbetween the two kidneys

the kidneys are right at the level of the 11th and 12th ribs –> the right kidney is slightly lower than the left because the liver is on the right side and pushes that kidney down a little

psoas, quadratus lumborum and transversus abdominis muscles surround them as well

Question 2

what kind of organ is the kidney? how big is it?

Answer 2

it’s a retroperitoneum organ

grossly, the kidneys are 2 organs in the posterior side of the body

150 g male/130 g female

12x10x3 cm each = based on the size, you can predict the function because a small kidney will have less nephrons so less function! also when you’re matching kidney donors, the size matters too

Question 3

what are the relevant anatomical associations of the right kidney?

Answer 3

1. liver
2. adrenal gland
3. duodenum
4. small intestine
5. colon

superiorly, there’s the hepatorenal ligament which attaches the right kidney to the liver –> so some injuries to the liver or kidney can shear this attachment and cause significant bleeding

medially, there’s part of the duodenum which is associated with the hilar structures of the kidney – Kocher maneuver moves the duodenum off the kidney so you can see it

the colon is also associated with the kidney so you’d also have to reflect that off – part of the small intestine may or may not be too based on the person

the right adrenal gland sits on top of the kidney

Question 4

what are the relevant anatomical associations of the left kidney?

Answer 4

1. spleen
2. stomach
3. adrenal gland
4. pancreas
5. colon

superiorly the left kidney is bordered by the tail of the pancreas and splenic vessels that run posterior to the pancreas

so if someone is getting a left nephrectomy you have to counsel the patient they could get pancreatitis or adrenal injury or splenic injury or even the stomach

Question 5

what is the gerota fascia?

Answer 5

aka perirenal fascia

it encases the kidney and protects the kidney from infections that could come from other organs

it also limits the invasion of tumors from the kidney or to the kidney

inferiorly, the gerota fascia isn’t closed; so if the kidney has a deep laceration, the blood will pool inferiorly because of this – that also means perinephric fluid collections can track inferiorly into the pelvis without violating gerota fascia

it crosses the midline and fuses with the gerota fascia of the other kidney

Question 6

what is the renal artery?

Answer 6

they’re inferior to the superior mesenteric artery and originate off the descending aorta

the renal arteries are end arteries so there are no collateral arteries! they end at the parenchyma of the kidneys

the kidney then splits into 5 branches = segmental arteries –> posterior, apical, upper, middle and lower segmental arteries

the renal vein is anterior to the renal artery – then the renal pelvis and ureter are located posterior to both of these vascular structures

Question 7

what is the most important segmental artery of the renal artery ?

Answer 7

posterior segmental branch

typically the first branch of the renal artery and it passes posterior to the renal pelvis while the rest of the segmental arteries pass anterior to the renal pelvis – sometimes there are anomalies where the posterior segmental branch where it’s anterior and this causes compression of the renal pelvis which would cause a ureteropelvic junction obstruction with a lot of pain and renal function could be compromised

any occlusion of it would cause infarct of that area of the kidney and it’ll become necrotic because there’s no collaterals!!

each segmental artery supplies a distinct portion of the kidney with no collateral circulation between them so occlusion or injury to a segmental branch will cause segmental renal infarction

Question 8

48 year old presents to the emergency room with sudden onset of severe abdominal pain, 10/10, associated with nausea & vomiting. Patient is afebrile, Bp 85/60, HR 109, RR 28, she is alert and oriented. Reports a history of asthma, depression and kidney problem.

what do you do next?

what type of tumor does she most likely have?

Answer 8

resuscitate and give fluids and get CT scan

CT scan shows bleeding tumor! angiomyolypoma

AML is a benign tumor composed of blood vessels, smooth muscles and fat and they are the most common benign mesenchymal renal tumors!!

the kidney is supplied by end arteries so you can go in and embolize the arteries causing the bleeding; this would treat the tumor!

Question 9

what is the flow of oxygenated blood through the kidney?

Answer 9

the renal artery originates from the abdominal aorta and becomes the segmental artery which then becomes the lobar artery

then blood goes into the interlobar arteries –> arcuate artery –> interlobular arteries –> afferent arteriole –> glomerulus –> efferent arteriole

go look at the picture; it’s very important!

Question 10

what is the venous system of the kidney?

Answer 10

the veins have collateral flow unlike the arterial supply, the venous drainage communicates freely through venous collars around the infundibula, providing for extensive collateral circulation in the venous drainage of the kidney

this means that occlusion of the renal vein has little or no effect on renal outflow

the renal vein originates from the abdominal inferior vena cava

the left renal vein receives the left adrenal vein superiorly, lumbar vein posteriorly, and left gonadal vein inferiorly while the right renal vein typically does not receive any branches so the right gonadal and adrenal vein comes off the IVC itself on the right

the right renal vein is shorter which makes sense because the IVC is on the right side of the body so the left renal vein has to travel a little more to get to it

right renal vein doesn’t usually have branches so the gonadal vein on the right side comes right off the IVC

Question 11

32 year old female presents to your clinic with complaint of gross hematuria. She reports that she started an intensive exercise regimen with 3o pound weight loss during the “covid lockdown”. She feels well overall, except for occasional left flank discomfort and blood in her urine.

what’s wrong?

Answer 11

Nutcracker syndrome = left renal vein compression

superior mesenteric artery originates from the aorta just above the left renal vein - usually there’s a fat pad that separates these two structures but patients who have lost a lot of weight lose this and they get compression of the renal vein! so the SMA is compressing the renal vein between the SMA and the thoracic aorta!

this can cause DVTs!!!

overtime, this blood needs to leave and get back to the heart but if it’s compressed, it’ll go through the collateral veins like the lumbar, gonadal etc. so the collateral veins get very distended

it takes time for these collaterals to develop though so in the meantime you’ll get hemorrhage which shows up as blood in the urine! there’s also distention of the capsule of the kidney which leads to flank pain

Question 12

what is the renal lymphatic system?

Answer 12

on the left, primary lymphatic drainage is into the left lateral para-aortic lymph nodes including nodes anterior and posterior to the aorta between the inferior mesenteric artery and the diaphragm

occasionally, there will be additional drainage from the left kidney into the retrocrural nodes or directly into the thoracic duct above the diaphragm

on the right, drainage is into the right interaortocaval and right paracaval lymph nodes including nodes located anterior and posterior to the vena cava, from the common iliac vessels to the diaphragm. Occasionally, there will be additional drainage from the right kidney into the retrocrural nodes or the left lateral para-aortic lymph nodes.

Question 13

how common are anatomic variations in the renal vasculature?

Answer 13

common…

up to 25-40% of kidneys

this is important because lower pole arteries on the right tend to cross anterior to the IVC, whereas lower pole arteries on either side can cross anterior to the collecting system, causing a ureteropelvic junction obstruction

the artery of the right kidney runs posteriorly but if you have an extra artery they’ll run anterior to the IVC which causes a problem because arteries are muscular structures and can cause compression of other structures like the ureter (like with Nutcracker syndrome)

Question 14

where does the renal collecting system originate from?

Answer 14

the renal collecting system originates in the renal cortex at the glomerulus as filtrate enters into Bowman capsule

Question 15

what is the innervation of the kidney?

Answer 15

sympathetic preganglionic nerves originate from the eighth thoracic through first lumbar spinal segments and then travel to the celiac and aorticorenal ganglia

parasympathetic fibers originate from the vagus nerve and travel with the sympathetic fibers to the autonomic plexus along the renal artery

the primary function of the renal autonomic innervation is vasomotor, with the sympathetic inducing vasoconstriction and the parasympathetic causing vasodilation

the nerves run along the arteries

so sometimes people with uncontrolled BP get a kidney removed and it helps their BP!

Question 16

how does the position of the kidney change?

Answer 16

the exactpositionof the kidney within the retroperitoneum varies during different phases of respiration, body position, and presence of anatomic anomalies.

for example, the kidneys move inferiorly approximately 3 cm (one vertebral body) during inspiration and during changing body position from supine to the erect position

because of the inferior displacement of the right kidney by the liver, the right kidney sits 1 to 2 cm lower than the left kidney

therefore the right kidney resides in the space between the top of the 1st lumbar vertebra to the bottom of the 3rd lumbar vertebra, whereas the left kidney occupies a space between the 12th thoracic vertebra and the 3rd lumbar vertebra

Question 17

what is the ureter?

Answer 17

bilateral tubular structures responsible for transporting urine from the renal pelvis to the bladder

begins at the renal-pelvic junction posterior tot he renal artery and vein; then progresses inferiorly along the anterior border of the psoas muscle

anteriorly, the right ureter is related to the ascending colon, cecum, colonic mesentery, and appendix

the left ureter is closely related to the descending and sigmoid colon and their accompanying mesenteries

approximately a third of the way to the bladder the ureter is crossed anteriorly by the gonadal vessels. As it enters the pelvis the ureter crosses anterior to the iliac vessels. This crossover point is usually at the bifurcation of the common iliac into the internal and external iliac arteries, thus making this a useful landmark for pelvic procedures

Question 18

what are the different segments of the ureter?

Answer 18

the ureter can be divided into upper, middle, and lower segments

the upper ureter extends from the renal pelvis to the upper border of the sacrum

the middle ureter comprises the segment from the upper to the lower border of the sacrum

the lower (distal or pelvic) ureter extends from the lower border of the sacrum to the bladder

Question 19

what is the blood supply of the ureter?

Answer 19

it’s segmental

the upper part is from the renal artery and gonadal artery and the aorta itself; these are usually posterior and medial

the middle to lower ureter is all medial supply from the common, internal and external lilac arteries!

if there was a uretopelvic junction obstruction from stricture, you can use a scope and go into the ureter and make an incision to try and open up the ureter!

Question 20

what are come normal variations in uretal caliber?

Answer 20

1. UPJ
2. the iliac vessels
3. ureterovesical junction

so the ureter has sites of normal functional/ anatomic narrowing at the ureteropelvic junction (UPJ), the iliac vessels, and the ureterovesical junction (UVJ)

there’s also the anterior displacement and angulation of the ureter over the iliac vessels

Question 21

where does kidney pain present?

Answer 21

anterior pain of the kidney can radiate to the groin

posteriorly it’s in the flank

Question 22

how is the ureter anatomically related to the male anatomy?

Answer 22

as the ureter enters the bladder it crosses anterior to common ilac artery and dives into the deep pelvis to the bladder

it enters posteriorly to the vas deferens

so when you’re approaching the prostate, you have to be careful not to damage the ureter˜

Question 23

how is the ureter anatomically related to the female anatomy?

Answer 23

hysterectomy meas uterine artery has to be ligated and the ureter runs right next to it and it could potentially get ligated too! so you have to be careful

Question 24

summary of kidney anatomy?

Answer 24

The kidney is divided into cortex and medulla. The medullary areas are pyramidal, more centrally located, and separated by sections of cortex. These segments of cortex are called the columns of Bertin.

Orientation of the kidney is greatly affected by the structures around it. Thus the upper poles are situated more medially and posteriorly than the lower poles. Also, the medial aspect of the kidney is more anterior than the lateral aspect.

Gerota fascia envelops the kidney on all aspects except inferiorly, where it is not closed but instead remains an open potential space.

From anterior to posterior, the renal hilar structures are the renal vein, renal artery, and collecting system.

The renal artery splits into segmental branches. Typically, the first branch is the posterior segmental artery, which passes posterior to the collecting system. There are generally three to four anterior segmental branches that pass anteriorly to supply the anterior kidney.

The progression of arterial supply to the kidney is as follows: renal artery → segmental artery → interlobar artery → arcuate artery → interlobular artery → afferent artery.

The venous system anastomoses freely throughout the kidney. The arterial supply does not. Thus occlusion of a segmental artery leads to parenchymal infarction, but occlusion of a segmental vein is not problematic because there are many alternate drainage routes.

Anatomic variations in the renal vasculature are common, occurring in 25% to 40% of kidneys.

Each renal pyramid terminates centrally in a papilla. Each papilla is cupped by a minor calyx. A group of minor calyces join to form a major calyx. The major calyces combine to form the renal pelvis.

There is great variation in the number of calyces, calyceal size, and renal pelvis size. The only way to determine pathologic from normal is by evidence of dysfunction.

Question 25

what does the kidney come from embryologically?

Answer 25

the intermediate mesoderm gives rise to paired, segmentally organized nephrotomes from the cervical to sacral region; cervical nephrotomes are formed early during the fourth week and are collectively referred to as Pronephros

human develop three kidneys in the course of intrauterine life – the embryonic kidneys are in order of their appearance, the pronephros, the mesonephros, and the metanephros –> all three kidneys develop from the intermediate mesoderm.

Question 26

what is the pronephros?

Answer 26

pronephros is a transitory, nonfunctional kidney seen in the third week

it degenerates by the start of the fifth week

development of the pronephric tubules starts at the cranial end of the nephrogenic cord and progresses caudally

Question 27

what is the metanephros?

Answer 27

the definitive kidney, or the metanephros, forms in the sacral region as a pair of new structures, called the ureteric buds, sprout from the distal portion of the nephric duct and come in contact with the condensing blastema of metanephric mesenchyme at about the 28th day

the outgrowth of the ureteric bud from the nephric duct and its invasion into the condensing blastema of metanephric mesenchyme is a crucial initiating event in the development of the adult kidney

the ureteric bud and metanephric mesenchyme exert RECIPROCAL INDUCTIVE effects toward each other, and the proper differentiation of these primordial structures depends on these inductive signals

Question 28

what is the mesonephros?

Answer 28

the second kidney, the mesonephros is also transient

serves as an excretory organ for the embryo

there is a gradual transition from the pronephros to the mesonephros at

Question 29

what is a nephron? what does it arise from embryologically? how about the collecting duct?

Answer 29

the nephron, which consists of the glomerulus, proximal tubule, loop of Henle, and distal tubule is thought to derive from the metanephric mesenchyme

however, the collecting system, consisting of collecting ducts, calyces, pelvis and ureter, is formed from the ureteric bud

Question 30

what is developing at the same time as the kidney embryologically?

Answer 30

the kidney and ureter are developing at the same time as the reproductive system

Question 31

what are the stages of kidney development embryologically?

Answer 31

normal embryologic development of the kidney occurs in three stages; pronephros, mesonephros, and metanephros. The last stage, the metanephros forms the permanent kidney and is first detected at five to six weeks of gestation. The metanephros is composed of the metanephric mesenchyme and ureteral bud (caudal portion of the mesonephric duct).

the metanephros is initially positioned in the pelvis opposite the sacral somites. Rapid caudal growth results in the migration of the developing kidney from the pelvis to the retroperitoneal renal fossa, which lies on either side of the spine opposite the second lumbar vertebra. As each kidney ascends, it rotates through 90 degrees such that the renal hilum is directed medially as the kidney reaches its final position. Migration and rotation are completed by the eighth week of gestation

the ascending kidney derives its vascular supply locally from neighboring vessels. As the kidneys reach their permanent position, renal arteries and veins develop and provide vascular support. As a result, ectopic kidneys usually contain numerous small vessels and reflect the continuous changes in blood supply of the developing kidneys during the course of renal ascent

Question 32

what is the ascent of the kidneys?

Answer 32

the metanephros normally ascends from the sacral region to its definitive lumbar location between the sixth and ninth weeks; the precise mechanism responsible for renal ascent is not known, but it is speculated that the differential growth of the lumbar and sacral regions of the embryo plays a major role –> these arteries do not elongate to follow the ascending kidneys but instead degenerate and are replaced by successive new arteries

the final pair of arteries forms in the upper lumbar region and becomes the definitive renal arteries; at times, a more inferior pair of arteries persists as accessory lower pole arteries

the renal maturation continues to take place post- natally, nephrogenesis is completed before birth at around 32 to 34 weeks of gestation

Question 33

what are some of the anomalies of kidney development?

Answer 33

1. renal ectopy (doesn’t ascend)
2. renal fusion (horseshoe kidney)

positional (ectopy) and fusion anomalies occur when this normal embryogenic migration is disrupted

ectopic kidney can be associated with other nonrenal anomalies (adrenal, cardiac, and skeletal abnormalities) and as a clinical feature in syndromes such as CHARGE syndrome (coloboma, heart disease, atresia choanae, retarded growth and development, genital hypoplasia, and ear anomalies) and VACTERL syndrome (vertebral, anal, cardiac, tracheal, esophageal, renal, limb anomalies). Thoracic kidneys are often associated with congenital diaphragmatic hernia.

Question 34

what are ectopic kidneys?

Answer 34

kidney that do not ascend above the pelvic brim are commonly called pelvic kidneys

rarely, the ectopic kidney is found in the thorax

fused crossed ectopic kidney: ectopic kidney moves across the midline and fuses to the lower pole of the normally positioned contralateral kidney

nonfused crossed ectopic kidney: ectopic kidney moves across the midline without fusion and is positioned at the rim of the pelvis below the normal kidney

bilateral crossed ectopic kidneys: both kidneys are ectopic and cross the midline with the ureters maintaining their normal bladder insertions

Question 35

what is a horseshoe kidney?

Answer 35

the most common fusion anomaly is the horseshoe kidney, which occurs with fusion of one pole of each kidney

it’s usually trapped by the inferior mesenteric artery

the inferior poles of the kidneys may also fuse, forming a horseshoe kidney that crosses over the ventral side of the aorta –> during ascent the fused lower pole becomes trapped under the inferior mesenteric artery and thus does not reach its normal site

rarely, the kidney fuses to the contralateral one and ascends to the opposite side, resulting in a cross-fused ectopy

associated with kidney stones

Question 36

kidney embryology summary?

Answer 36

the genitourinary system develops from three embryonic sources: intermediate mesoderm, mesothelium of coelomic (future peritoneum) cavity, and endoderm of the urogenital sinus

the urinary system begins its development before the genital system development becomes evident. With the formation of nephric ducts, embryonic kidneys develop sequentially in the order of pronephros, mesonephros, and metanephros

the permanent kidney, the metanephros, develops as a result of inductive interactions involving ureteric bud (an outgrowth of nephric duct), condensing blastema of meta- nephric mesenchyme, and stromal cells

the renal tubulo- genesis occurs via mesenchymal-epithelial conversion, whereas dichotomous branching of the ureteric bud leads to the formation of the collecting system

Question 37

the fetal kidneys develop from which of the following embryonic structures?

A. paraxial (somite) mesoderm

B. intermediate mesoderm

C. neural tube

D. lateral mesoderm

Answer 37

B. intermediate mesoderm

Question 38

at what gestational time point does the metanephros development begin?

A. 20th day

B. 24th day

C. 28th day

D. 32nd day

Answer 38

B. 24th day

Question 39

the fused lower pole of the horseshoe kidney is trapped by which of the following structures during the ascent?

A. inferior mesenteric artery

B. superior mesenteric artery

C. celiac artery

D. common iliac artery

Answer 39

A. inferior mesenteric artery

the inferior poles of the kidneys may fuse, forming a horseshoe kidney that crosses over the ventral side of the aorta

during ascent, the fused lower pole becomes trapped under the inferior mesenteric artery and thus does not reach its normal site

Question 40

the exact position of the kidney within the retroperitoneum varies during:

A. different phases of respiration

B. presence of anatomic anomalies

C. body position

D. a, b, and c

E. a and c

Answer 40

D. a, b, and c

Question 41

the gerota fascia envelops the kidney and the adrenal gland on all aspects but remains open:

A. inferiorly

B. laterally

C. medially

D. interiorly and laterally

E. interiorly and medially

Answer 41

A. inferiorly

Question 42

You are a 4th year medical student on urology rotation, the chief resident is performing a partial nephrectomy on the right kidney for a 5cm tumor. You are assisting with the procedure. She encounters the right renal vein as it emerges from the inferior vena cava. Which of the following statements is accurate about renal veins?

ligation of segmental renal vein will cause:

A. no pathologic conditions

B. opening of the collateral circulation

C. segmental renal infarction

D. an effect that depends on the availability of collaterals

E. renal atrophy

Answer 42

A. no pathologic conditions

because you have collaterals!!

Question 43

occlusions or injury to a segmental renal artery will cause:

A. no pathologic conditions

B. opening of the collateral circulation

C. segmental renal infarction

D. an effect that depends on the availability of the collaterals

E. renal atrophy

Answer 43

C. segmental renal infarction

Question 44

a 55 year old man with no significant history presents with left flank pain and progressive fatigue. his PE is unremarkable. urinalysis is clean. serum creatinine is normal with GFR > 80. on cross sectional imagining he is four to have a 15 cm tumor. surgical intervention is planned. you recall that the white line of Toldt is the lateral reflection of posterior parietal peritoneum that convers:

A. the ascending colon

B. the descending colon

C. the transverse colon

D. the ascending and descending colons

E. the ascending and transverse colon

Answer 44

B. the descending colon