Relative Spatial Relationships

The kidneys have:

• • superior and inferior poles

  • medial and lateral borders

  • anterior and posterior surfaces

Kidneys are located high in the abdomen on the posterior wall inferior to the diaphragm in the region of the lower ribs. The left kidney is located slightly higher than the right kidney – roughly from T11-L2 vertebral level, while the right kidney spans T12-L3 vertebral levels. The superior 1/3 of the posterior surface of the kidney lies against the diaphragm. The remaining 2/3 is inferior to the diaphragm, and is adjacent to the quadratus lumborum muscle. The subcostal nerve (T12) and vessels run posterior to the kidneys. And the 11th and 12th ribs run behind the upper portion of both kidneys. At rest, the hila of the kidneys coincide with the transpyloric plane, the midpoint between the jugular notch and the pubic symphysis, which corresponds to where the pyloric part of the stomach meets the duodenum (approximately at the L1 vertebral level).

The anterior relationships are different on each side, except that both kidneys are capped superomedially by a suprarenal (adrenal) gland. The right kidney contacts the descending (2nd) portion of the duodenum, the right lobe of the liver, the right colic (hepatic) flexure, and some coils of jejunum. The left kidney contacts the pancreas, the stomach, the spleen, the left colic (splenic) flexure, and some coils of jejunum.

The medial border of the kidney contains the hilum – the space into which the renal arteries and veins pass and the renal pelvis and ureter emerge. The kidneys do not sit with their borders and surfaces in a strict anatomical position. For example, the medial borders of the kidneys are oriented anteromedially, and the lateral borders are oriented posterolaterally.

Ureters pass retroperitoneally through the abdomen, and enter into the pelvis adjacent to the bifurcation of the common iliac aa. Ureters enter into the base/fundus of the bladder.

2. Describe and identify the internal gross anatomy of the kidneys.

The kidney is one of several organs in the body whose parenchyma is organized into a cortex surrounding a medulla.

The renal medulla is divided into discrete structures called renal (medullary) pyramids, conical masses of tissue that primarily contain the collecting ducts and nephron loops (of Henle). The apex of the renal pyramids, or renal papilla, points toward the center of the kidney. At the renal papilla, the collecting ducts conduct urine into minor calices (calyces), which coalesce to form major calices, and finally converge into a renal pelvis. The renal pelvis is the proximal, dilated portion of the ureter.

The renal cortex is organized in two parts: arches and columns. The cortex is surrounded by a fibrous renal capsule. Between the renal capsule and the bases of the renal pyramids are the cortical arches. Surrounding and interleaving between sides of renal pyramids are the cortical columns.

3.  Describe the flow of blood to and through the kidney. Understand left renal vein entrapment syndrome and the relationships of the vessels that contribute to this susceptibility. 

Each kidney is supplied with blood from a renal artery which branches directly from the abdominal aorta, slightly inferior to the origin of the superior mesenteric artery. Renal arteries travel relatively posterior to the ipsilateral renal vein. Renal veins drain directly into the IVC. Because the aorta runs slightly to the left of midline, and the IVC is significantly right of midline, the arteries and veins have different lengths depending on if they are associated with the right or left kidney. Notably, the left renal v. is relatively long.

Renal Segments, Lobes, and Lobules

Each kidney consists of five surgically resectable renal segments, each supplied with blood from a separate segmental artery.

The five renal segments are:

• Apical

• Anterosuperior

• Anterio-inferior

• Posterior

• Inferior

Another functional way of subdividing a kidney is by renal lobes. Renal lobes consist of a single renal pyramid, the cortical arch associated with that pyramid, and portions of the cortical columns (containing the nephrons) associated with that pyramid. Renal lobes may be subdivided into renal lobules. A renal lobule is a collection of cortex containing all the nephrons associated with a single medullary ray and a single collecting duct.

Each renal artery typically hosts five segmental arteries. Segmental arteries give rise to interlobar aa., which transition into arcuate aa. as the vessels move from the lateral surfaces of renal pyramids to the bases of renal pyramids. Both interlobar and arcuate aa. give rise to cortical radiate aa. (interlobular aa.), and cortical radiate aa. give rise to afferent arterioles, which feed glomeruli. Glomeruli are drained by efferent arterioles, which feed into peritubular capillaries and vasa recta.

The veins follow a similar pattern, with multiple tributaries coming out of the hilum of the kidney to coalesce to form the renal vein.

As the left renal v. is approximately 3x longer than the right renal v., a variety of veins draining structures on the left side of the body frequently drain into the left renal v. These include the:

• L. inferior phrenic v.

• L. suprarenal v.

• L. gonadal v.

The left renal v. occupies a narrow space, posterior to the superior mesenteric a. (SMA) and anterior to the abdominal aorta. An aneurysm in either artery (typically in the wall of the aorta) may compress the left renal v., jeopardizing the return of blood from the left kidney, suprarenal gland, gonad, and inferior hemidiaphragm. This is known as left renal vein entrapment syndrome (aka nutcracker syndrome).

To summarize:

4. List the structures of the excretory pathway.

Distal convoluted tubules of nephrons → collecting ducts → Minor calices (calyces) @ renal papillae* → Major calices* → Renal pelvis* → Ureter* → Urinary bladder* → Urethra*

*Grossly visible

Minor calices

There are typically 3-4 minor calices for each major calyx.

Each minor calyx has a renal papilla, an indentation of the apex of the renal pyramid, where urine is excreted.

Major calices

There are typically 2-3 major calices in a kidney, which receive urine from the minor calices, and drains into the renal pelvis.

Renal pelvis

The renal pelvis is the superior expansion of the ureter which receives urine from the major calices.

Ureters

The ureter is a muscular duct that connects the kidney to the bladder and transmits urine.

There are 3 parts of the ureter:

• Abdominal part: crossed by gonadal vessels and crosses over bifurcation of the common iliac a.

  • Retroperitoneal

• Pelvic part: traverses the pelvic cavity retro- and then subperitoneally

• Intramural part: contained within the wall of the base of the urinary bladder

Urinary bladder

The urinary bladder is a distensible, urine-storing, subperitoneal organ.

The apex of the urinary bladder is supero-posterior to the superior portion of the pubic symphysis.

Inferior from the apex is the anterior surface of the bladder, which lies adjacent to the pubic symphysis.

Posterior to the apex is the superior surface of the bladder. The superior surface is covered by peritoneum.

The base/fundus of the bladder is the posterior-most wall (opposite the apex). It may be closely associated with either the vagina (women), or the rectum (men).

The wall of the base contains the intramural parts of the ureters, which open into the lumen of the bladder via ureteric orifices.

The neck is the inferior-most portion of the bladder, and contains the internal urethral meatus. In males, the neck of the bladder is superiorly adjacent to the prostate gland, and in females, the neck is very closely associated with vagina. The neck is held in place anteriorly and anterolaterally by the pubovesical ligament (women) / puboprostatic ligament (men).

The triangular space defined by the ureteric orifices and the internal urethral meatus is called the trigone.

Urethra

The urinary bladder voids urine to the external environment through the urethra. The urethra is substantially sexually polymorphic.

The typical female urethra begins at the internal urethral meatus, travels anteroinferiorly between the pubic symphysis and vagina, and terminates in the external urethral meatus. The external urethral meatus is typically found in the vestibule of the vagina between the glans clitoris and the opening of the vagina.

The typical male urethra is tripartite, its parts including:

• • intramural (preprostatic) part: neck of bladder to prostate

  • prostatic part: begins at the internal urethral meatus, traverses the prostate gland, where it receives secretions of the prostate as well as from the ejaculatory ducts (this is the point of entry of semen into the urethra)

  • membranous part: traverses the pelvic diaphragm

  • spongy/penile part: traverses the corpus spongiosum of the penis; ends in the external urethral meatus on the distal ventral portion of the glans penis.

The urinary bladder is served by the superior and inferior vesical aa. of the internal iliac (aka hypogastric) a. Sex is on a continuum, arterial branches are named for their pelvic targets (eg the uterine a. supplies the uterus, vesical aa. supply the bladder, etc.).

The urinary bladder is innervated by the vesical plexus, a mixed autonomic plexus supplied by anterior brs. of the inferior hypogastric plexus. The inferior hypogastric plexus will be reviewed in more detail in the reproductive sessions to come, but the major inputs include:

• Pelvic splanchnic nn.,

  • Parasymp. fibers from S2-4 

• Sacral splanchnic nn., &

  • Sacral sympathetic ganglia (S1-2)

• Hypogastric nn. (mixed).

  • Superior hypogastric plexus (mixed)

5. Describe the basics of the autonomics serving the kidneys and ureters.

The kidneys are served by both sympathetics and parasympathetics through the renal plexus, which surrounds the renal aa.

The sympathetics are derived from thoracic splanchnic nn., particularly the least splanchnic n., if present. Additional sympathetic innervation comes from the 1st lumbar splanchnic n. And the aortic plexus.

The parasympathetics are derived from fibers of the posterior vagal trunk.

The ureters are served by both sympathetics and parasympathetics through fibers of various plexuses, such as intermesenteric (aortic), renal, and superior & inferior hypogastric plexuses.

The visceral afferents travel with sympathetics and are typically referred to cutaneous areas innervated by T11-L2 spinal nerves. This includes the inferior quadrants and extending towards the external genitalia; thus, the mnemonic ‘from the loin to the groin’ for ureteric referred pain.

The urinary bladder is served by the vesical plexus, which is an autonomic plexus supplied by the inferior hypogastric plexuses. Each inferior hypogastric plexus lies laterally to the pelvic viscera, and is supplied by pelvic splanchnic nn. (preganglionic parasympathetic fibers from S2,3,4), sacral splanchnic nn. (postganglionic sympathetic fibers from sacral sympathetic ganglia), and hypogastric nn. (mixed fibers running between the superior hypogastric plexus and the inferior hypogastric plexuses).