Kidneys and Clinical Considerations of the Kidney

 THE KIDNEYS

Synonyms

The kidneys are also called renes from which we have

the derivative renal; and nephros from which we have

the terms nephron, nephritis, etc.

● The kidneys are retroperitoneal organs that lie on the ventral surface of the quadratus lumborum

muscle and lateral to the psoas muscle and vertebral column.

● The kidneys are directly covered by a fibrous capsule called the renal capsule (or true capsule)

which can be readily stripped from the surface of the kidney except in some pathologic conditions

where it is strongly adherent due to scarring.

● The kidneys are further surrounded by the perirenal fascia of Gerota (or false capsule) which is

important in staging renal cell carcinoma. The perirenal fascia of Gerota defines the perirenal space

that contains the kidney, adrenal gland, ureter, gonadal artery and vein, and perirenal fat.

● Any fat located outside the perirenal space is called pararenal fat which is most abundant postero-

laterally.

● At the concave medial margin of each kidney is a vertical cleft called the renal hilum where the fol-

lowing anatomical structures are arranged in an anterior to posterior direction: Renal vein (most

anterior) → renal artery → renal pelvis (most posterior).

● The renal hilum is continuous with a space called the renal sinus that contains the renal pelvis,

major and minor calyces, renal blood vessels, nerves, lymphatics, and a variable amount of fat.

A. Left Kidney

● The upper pole of the left kidney is located at about vertebral level T11. The left kidney is higher

than the right kidney.

● The left kidney is related to rib 11 and rib 12.

● The renal hilum of the left kidney lies 5 cm from the median plane along the transpyloric plane

(which passes through vertebral level L1).

B. Right Kidney

● The upper pole of the right kidney is located at about vertebral level T12. The right kidney is

lower than the left kidney due to the presence of the liver on the right side.

● The right kidney is related to rib 12.

● The renal hilum of the right kidney lies 5 cm from the median plane just below the transpyloric plane

(which passes through vertebral level L1).

DISSECTION

Remove the fat and fascia from the anterior surface of

the left and right kidneys and suprarenal glands. Find

the left suprarenal vein and the left testicular or

ovarian vein and trace both to the left renal vein.

Follow this vein from the left kidney to the inferior

vena cava and note its tributaries. Displace the vein

and expose the left renal artery, follow its branches to

the left suprarenal gland and ureter. Follow the ureter

in the abdomen.

Identify the structures related to the anterior surface

of both the kidneys. Turn the left kidney medially to

expose its posterior surface and that of its vessels and

the ureter and identify the muscles, vessels and nerves

which are posterior to them. Carry out the same

dissection on the right side. Note that the right

testicular or ovarian and suprarenal veins drain directly

into the inferior vena cava. Cut through the convex

border of the kidney till the hilus. Look at its interior.

Identify the cortex, pyramids, calyces. Follow the

ureters in the renal pelvis, in the abdomen, in the

pelvic cavity and finally through the wall of urinary

bladder.

Definition of kidney

The kidneys are a pair of excretory organs situated on the

posterior abdominal wall, one on each side of the

vertebral column, behind the peritoneum. They remove

waste products of metabolism and excess ofwater and

salts from the blood, and maintain its pH.

External Features

Each kidney is bean-shaped. It has upper and lower

poles, medial and lateral borders, and anterior and

posterior surfaces.

The kidneys are paired organs that lie behind the peri-

toneum high up on the posterior abdominal wall on either

side of the vertebral column . The right kidney is

slightly lower than the left kidney because of the large size

of the right lobe of the liver. With contraction of the di-

aphragm during respiration, both kidneys move by as much

as 1 in. (2.5 cm) downward in a vertical direction. On the

medial concave border of each kidney is the hilus, which

extends into a large cavity (the renal sinus). The hilus

transmits the renal pelvis, the renal artery, the renal vein,

and the sympathetic nerve fibers. The kidneys have the

following coverings:

Two Poles of the Kidney

The upper pole is broad and is in close contact with the

corresponding suprarenal gland. The lower pole is

pointed.

Two Surfaces

The anterior surface is said to be irregular and the

posterior surface flat, but it is often difficult to recognize

the anterior and posterior aspects of the kidney by

looking at the surfaces. 

Two Borders

The lateral border is convex. The medial border is

concave. Its middle part shows a depression, the hilus or

hilum.

Hilum

What are The following structures are seen in the hilum from

anterior to posterior side?

(1) The renal vein (2) the renal

artery, and (3) the renal pelvis, which is the expanded

upper end of the ureter. Examination of these structures

enables the anterior and posterior aspects of the kidney to

be distinguished from each other. As the pelvis is

continuous, inferiorly, with the ureter the superior and

inferior poles of the kidney can also be distinguished by

examining the hilum. So it is possible to determine the

side to which a kidney belongs by examining the

structures in the hilum. Commonly, one of the branches

of the renal artery enters the hilus behind the renal pelvis,

and a tributary of the renal vein may be found in the same

plane.

Location

The kidneys occupy the epigastric, hypochondriac,

lumbar and umbilical regions  Vertically they

extend from the upper border of twelfth thoracic vertebra

to the centre of the body of third lumbar vertebra. The

right kidney is slightly lower than the left, and the left

kidney is a little nearer to the median plane than the right.

The transpyloric plane passes through the upper part

of the hilus of the right kidney, and through the lower

part of the hilus of the left kidney.

The long axis of the kidney is directed downwards and

laterally, so that the upper poles are nearer to J the

median plane than the lower poles. The transverse axis is

directed laterally and backwards.

In the foetus the kidney is lobulated and is made up

of about 12 lobules. After birth the lobules gradually

fuse, so that in adults the kidney is uniformly smooth.

However, the evidence of foetal lobulation may

persist.

Stations of the Kidneys

I The kidneys are retroperitoneal organs and are only

partly covered by peritoneum anteriorly.

Relations Common to the Two Kidneys

1. The upper pole of each kidney is related to the

corresponding suprarenal gland. The lower poles lie

about 2.5 cm above the iliac crests.

2. The medial border of each kidney is related to (1)

the suprarenal gland, above the hilus, and (if) to the

ureter below the hilus 

3. Posterior relations: The posterior surfaces of both

kidneys are related to the following: (1) The diaphragm;

(2) the medial and lateral arcuate ligaments; (3) the

psoas major; (4) the quadratus lumborum; (5) the

transversus abdominis; (6) the subcostal vessels; and (7)

the subcostal, iliohypogastric and ilioinguinal nerves

. In addition, the right kidney is related to

twelfth rib, and the left kidney to eleventh and twelfth

rib

: Vertical section through the posterior abdominal wall

showing the relationship of the pleura to the kidney.

4. The structures related to the hilum have been

described earlier.

Other Relations of the Right Kidney

Anterior Relations

(1) Right suprarenal gland, (2) liver, (3) second part of

duodenum, (4) hepatic flexure of colon, and (5) small

intestine. Out of these the hepatic and intestinal surfaces

are covered by peritoneum.

The lateral border of the right kidney is related to the

right lobe of the liver and to the hepatic flexure of the

colon (Fig. 24.3).

Other Relations of the Left Kidney

Anterior Relations

(1) Left suprarenal gland, (2) spleen, (3) stomach, (4)

pancreas, (5) splenic vessels, (6) splenic flexure and

descending colon, and (7) jejunum. Out of these the

gastric, splenic and jejunal surfaces are covered by

peritoneum.

The lateral border of the left kidney is related to the

spleen and to the descending colon.

Capsules or Coverings of Kidney

1. The fibrous capsule: This is a thin membrane

which closely invests the kidney and lines the renal

sinus. Normally it can be easily stripped off from the

kidney, but in certain diseases it becomes adherent and

cannot be stripped (Fig. 24.6).

2. Perirenal or perinephric fat: This is a layer of

adipose tissue lying outside the fibrous capsule. It is

thickest at the borders of the kidney and fills up the extra

space in the renal sinus.

3. Renal fascia: 

Superiorly, the two layers of the renal fascia first

enclose the suprarenal gland in a separate compartment,

and then fuse with each other. They finally become

continuous with the fascia covering the undersurface of

the diaphragm 

Inferiorly, the two layers remain separate, enclosing

the ureter. The anterior layer merges with the

extraperitoneal connective tissue of the iliac fossa, while

the posterior layer blends with the fascia iliaca 

Laterally, the two layers get fused and become

continuous with the fascia transversalis.

Medially, the anterior layer passes in front of the renal

vessels and merges with the connective tissue around the

aorta and the inferior vena cava. The posterior layer gets

fused to the fascia covering the quadratus lumborum and

the psoas major; and to the vertebrae and intervertebral

discs. At the medial border of the kidney, the fascia

forms a septum which is pierced by the renal vessels.

Because of the septum, perirenal effusions cannot cross

to the opposite side.

4. Pararenalor paranephric body [fat): It consists of a

variable amount of fat lying outside the renal fascia. It is

more abundant posteriorly and towards the lower pole of

the kidney. It fills up the paravertebral gutter and forms a

cushion for the kidney.

Structure

1. Naked eye examination of a coronal section of the

kidney shows: (a) an outer, reddish brown cortex; (b) an

inner, pale medulla; and (c) a space, the renal sinus 

The renal medulla is made up of about 10 conical

masses, called the renal pyramids. Their apices form the

renal papillae which indent the minor calices.

The renal cortex is divisible into two parts: (a)

cortical arches^or cortical lobules, which form caps

over the bases of the pyramids; and (b) renal columns,

which dip in between the pyramids.

Each pyramid along with the overlying cortical

arch forms a lobe of the kidney.

The renal sinus is a space that extends into the I

kidney from the hilus. It contains (a) branches of the

renal artery; (b) tributaries of the renal vein; and (c) the

renal pelvis. The pelvis divides into 2 to 3 major calices,

and these in their turn divide into 7 to 13 ■ minor

calices. Each minor calyx (kalyx= cup of a flower) ends

in an expansion which is indented by one to three renal

papillae.

2. Histologically, each kidney is composed of one to

three million uriniferous tubules. Each tubuljH consists

of two parts which are embryologically distinct from

each other. These are as follows.

A. The secretory part, called the nephron, which

elaborates urine. Nephron is the functional unit of

the kidney, and comprises: (a) the renal corpuscle or

Malpighian corpuscle, (for filtration of substances

from the plasma) made up of glomerulus (a tuft of

capillaries) and Bowman's capsule; and (b) the renal

tubule, (for selective resorption of substances from

the glomerular filtrate) made up of the proximal

convoluted tubule, loop of Henle with its descending

and ascending limbs, and the distal convoluted

tubule 

B. The collecting tubule begins as a junctional

tubule from the distal convoluted tubule. Many tubules

unite together to form the ducts of Bellini which open

into the minor calices through the renal papillae.

C. Juxtaglomerular apparatus is formed at the

vascular pole of glomerulus which is intimately

related to its own ascending limb of the Henle's loop

near the distal convoluted tubule.

I of the tubule; (b) juxtaglomerular cells, formed by the

epitheloid cells in the media of the afferent arteriole;

and (c) Some agranular cells between macula densa and

the glomerulus proper.

Arterial Supply

Usually there is one renal artery on each side, arising

from the abdominal aorta. Accessory renal arteries are

present in 30% of individuals; they arise commonly

from the aorta, run parallel to the renal artery, and enter

the kidney either at the hilus or at one of its poles.

At or near the hilus the renal artery divides into

anterior and posterior divisions. Further branching of

these divisions gives rise to segmental arteries each of

which supplies one vascular segment. Five such

segments are described. These are: (1) Apical, (2) upper,

(3) middle, (4) lower, and (5) posterior (Fig. 24.9). The

segmental arteries are end arteries, so that the vascular

segments are independent units.

Each segmental artery divides into lobar arteries,

usually one for each pyramid. Each lobar artery divides

into 2-3 interlobar arteries which run on each side of the

pyramid. At the corticomedullary junction, the interlobar

arteries divide dichotomously into arcuate arteries

which arch over the bases of the pyramids, at right angles

to the interlobar arteries. The arcuate arteries give off

interlobular arteries which run radially into the cortical

substance at right angles to the arcuate arteries. The

arcuate arteries do not anastomose with their neighbours

but finally turn up into the cortex as additional

interlobular arteries. The interlobular arteries do not

anastomose with their neighbours, and therefore are end

arteries. However, small branches from

interlobular arteries perforate the fibrous capsule of the

kidney to anastomose with a capsular plexus through

which the renal vessels may anastomose with suprarenal,

phrenic, testicular or ovarian, or even lumbar vessels.

This anastomosis may sometimes establish a limited

collateral circulation.

Afferent glomerular arterioles are derived mostly as

side branches from interlobular arteries, but some may

arise directly from the arcuate or even interlobar arteries.

The efferent glomerular arteriole, from most of the

glomeruli, divides soon to form the peritubular capillary

plexus around the proximal and distal convoluted

tubules. Since blood passes through two sets of

capillaries, glomerulus and peritubular plexus, it forms

the renal portal circulation.

Arterial supply of the medulla is derived mostly from

the efferent arterioles of the juxtamedullary glomeruli,

and partly from a number of aglomerular arterioles.

Each arteriole dips into renal pyramid, breaks up into 1-2

dozen of descending vasa recta

which run into the outer part of medulla. These break up

to form capillary plexus in the inner part of pyramids,

closely related to the loops of Henle

300 Abdomer

and the collecting ducts. At the venous end the plexus

gives rise to ascending vasa recta which return blood to

interlobular or arcuate veins. In the outer part of medulla,

the close relation between the descending vasa recta, the

venules, and the medullary portion of renal tubules and

ducts provides the structural basis for the countercurrent

exchange and multiplier system.

It appears there are two main patterns of renal

circulation: (1) The free circulation is essentially

glomerular in the cortex. This is probably the normal

pattern. (2) The restricted circulation is essentially

medullary where the cortical glomeruli are bypassed, and

the blood is shunted through the juxtamedullary

glomeruli and the vasa rectae. The medullary circulation

is more rapid than cortical.

Venous Drainage

The venous end of the peritubular capillary plexus gives

rise to interlobular veins which run along the

corresponding arteries. The interlobular veins drain into

the arcuate veins, which in their turn open into the

interlobar veins. These emerge at the renal sinus and join

to form the renal vein which drains into the inferior vena

cava.

The venous end of the capillary plexus along the vasa

recta gives rise to veins which drain into the arcuate

veins.

● The venous drainage of the kidney is to the interlobular veins → arcuate veins → interlobar veins →

renal vein → IVC.

● The arcuate veins drain into interlobar veins which anastomose and converge to form several renal

veins that unite in a variable fashion to form the renal vein

● The veins draining the kidney have no segmental organization like the arterial supply.

● The renal veins lie anterior to the renal arteries at the renal hilum.

● The longer left renal vein passes anterior to the aorta on its path to the IVC. The renal veins ultimately

drain into the IVC.

Lymphatic Drainage

The lymphatics of the kidney drain into the lateral aortic

nodes located at the level of origin of the renal arteries

(L2).

Nerve Supply

The kidney is supplied by the renal plexus, an offshoot

of the coeliac plexus. It contains sympathetic (T10-L1)

fibres which are chiefly vasomotor. The afferent nerves

of the kidney belong to segments T10 toT12.

Exposure of the Kidney from Behind

In exposing the kidney from behind, the following layers

have to be reflected one by one.

(1) Skin; (2) superficial fascia; (3) posterior layer of

thoracolumbar fascia with latissimus dorsi and serratus

posterior inferior; (4) erector spinae, which can be

removed for convenience; (5) middle layer of

thoracolumbar fascia; (6) quadratus lumborum; and (7)

anterior layer of thoracolumbar fascia in which the

related nerves are embedded (Fig. 24.11).

_________________ HISTOLOGY________________

The cortex of kidney shows cut sections of glomeruli,

many sections of proximal convoluted tubule, some

sections of distal convoluted tubule few collecting

ducts. Section through the pyramid of the medulla

shows light staining collecting ducts, sections of loop

of Henle, thick and thin segments of descending and

ascending limbs, capillaries and connective tissue.

Clinical Considerations of the Kidney

A. Rotation of the Kidney. During the relative ascent of the kidneys in fetal development, the

kidneys rotate 90 degrees medially so that the renal hilus is normally orientated in a medial direction.

B. Ascent of the Kidney. The fetal metanephros is located in the sacral region, whereas the adult

kidneys are normally located at vertebral levels T12-L3. The change in location (i.e., ascent) results from

a disproportionate growth of the fetus caudal to the metanephros.

C. Horseshoe Kidney occurs when the inferior poles of both kidneys fuse during fetal development.

The horseshoe kidney gets trapped behind the inferior mesenteric artery as the kidney attempts to

ascend toward the normal adult location.

D. Kidney Trauma. Kidney trauma should be suspected in the following situations: Fracture of the

lower ribs, fracture of the transverse processes of lumbar vertebrae, gunshot or knife wound over the

lower rib cage, after a car accident where seat belt marks are present. Right kidney trauma is associated

with liver trauma whereas left kidney trauma is associated with spleen trauma. Clinical findings include

flank mass and/or tenderness, flank ecchymosis, hypotension, hematuria. One of the absolute indica-

tions for renal exploration is the presence of a pulsatile or expanding retroperitoneal hematoma

found at laparotomy.

E. Surgical Approach to the Kidney. An incision is made below and parallel to the 12th rib in

order to prevent inadvertent entry into the pleural space. The incision may be extended to the front of

the abdomen by traveling parallel to the inguinal ligament.