Dissector Answers - Urinary System

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Demonstrate the relationships of the kidneys and suprarenal glands to adipose and fascial coverings, lower ribs and other abdominal organs.
  2. Describe the basic internal gross anatomy of the kidney.
  3. Define the blood supply and drainage of the kidneys and suprarenal glands.
  4. Describe the general organization of the urinary and endocrine systems.
  5. Describe the routes and relationships of the ureters from the kidneys to the urinary bladder.
  6. Recognize the urinary bladder in either its expanded or contracted position, and determine the extent of its peritoneal covering.
  7. Identify the internal orifices of the bladder and differentiate the trigone region from the rest of the bladder lining.
  8. Describe the relationships of the bladder to other pelvic organs in both sexes.
  9. Differentiate between male and female urethrae.

Learning Objectives and Explanations:

1. Demonstrate the relationships of the kidneys and suprarenal glands to adipose and fascial coverings, lower ribs and other abdominal organs. (W&B 489-493, N 273,329,330,354 or TG 5-30, 5-31, 5-42)

The kidneys do not lie in the coronal plane as is often shown in atlases. Since they lie against the psoas muscle (which lies against the vertebral column), their posterior surfaces face somewhat medial as well, while their anterior surfaces face laterally. The convex lateral border (the outside of the "bean") is also posterior, and the medial border, with the hilum, is also anterior.

The kidneys are retroperitoneal. Unlike other GI organs that begin development with a mesentery then fuse to the body wall, the kidneys are stuck there from the beginning. Besides their peritoneal covering, each is embedded in two layers of fat, with a membrane, the renal fascia, in between the layers. Inside the renal fascia is the perirenal fat, while outside the membrane is the pararenal fat. (The perirenal layer is inside, while the pararenal layer is around the renal fascia.)

With regard to the relationships of the kidneys to other structures, we can think about the posterior and the anterior surfaces. The superior 1/3 of the posterior surface lies against the diaphragm. The remaining 2/3 is inferior to the diaphragm, and therefore contacts the quadratus lumborum muscle. The subcostal nerve and vessels run posterior to the kidneys on either side. (The kidney is somewhat protected by the twelfth rib.)

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.

2. Describe the basic internal gross anatomy of the kidney. (W&B 491-493, N 334A, 334B or TG 5-32A, 5-32B).

The kidney is one of several organs in the body that has some sort of cortex (Latin, cortex = bark) around the outside, surrounding an inner medulla. The renal medulla is divided into renal (medullary) pyramids, with renal columns, made of cortical tissue, between them. The renal pyramids have their apex, or renal papilla, pointed toward the center of the kidney. Here the tubules dump into first minor calicies, which then join with others to form major calicies, and finally the renal pelvis. The renal pelvis is the proximal, dilated portion of the ureter.

3. Define the blood supply and drainage of the kidneys and suprarenal glands. (N 332,335 or TG 5-31, 5-32)

Both kidneys are supplied by renal arteries, both of which branch directly from the abdominal aorta slightly inferior to the branching point of the SMA. The renal arteries travel to each kidney, each one posterior to its respective renal vein, which 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. The right artery is a little longer than the left, passing behind the IVC and the point of junction of the right renal vein and the IVC. The right vein is very short. On the left side, the left artery, which is a bit shorter than the right, emerges from the aorta and runs posterior to the left vein. The left vein has a very long trip back over to the right side and the IVC.) On both sides the arteries branch multiple times, into segmental arteries, before entering the hilum of the kidney both anterior and posterior to the renal pelvis. 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 far as circulation within the kidney goes, know that the segmental arteries run in the renal columns, and that there are no anastomoses between them. (See W&B 492-493 or a histology text for the somewhat complicated pattern of vessels that branch from there.)

The suprarenal (adrenal) glands are extremely vascular. (According to W&B, relative to size, more blood flows through them than any other organ, with the possible exception of the thyroid gland.) They receive blood from three sources, all of which branch into varying numbers of twigs before entering the gland.

Most of the venous drainage, which is important since it carries all of the goodies made by the gland, is via the suprarenal (central suprarenal) veins. The left one drains into the left renal vein while the right one drains directly into the IVC.

Note: The renal arterial supply is extremely variable. In fact, the "Illustrated Encyclopedia of Human Anatomic Variation" suggests that "it is not only ludicrous but dangerous to suggest that the kidneys each receive only a single artery."

For more than you ever wanted to know about anatomical variation, the University of Iowa has a great site, an "Illustrated Encyclopedia of Human Anatomic Variation". Here is a quick and dirty link to the section on renal arteries.
4. Describe the general organization of the urinary and endocrine systems. (W&B 493, N 341 or TG5-30)

The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The kidneys filter the blood, then collect and concentrate the waste products. This waste water travels in the ureters from the kidney to the urinary bladder, where it is stored until it is excreted at a convenient time. The bladder pushes its contents out of the body via the urethra. In females it is a short trip to the outside of the body, while in males, the urethra must travel through the penis. (Latin, urinari = to dive)

The endocrine system is a collection of ductless glands that are scattered about the body. They make chemical signals, or hormones, in response to internal or external stimuli. These hormones are usually released into the blood, where they traverse the entire circulation to reach their target. The suprarenal (adrenal) glands are very important in that they regulate water/ion balance, various aspects of metabolism, part of sexual development, and the "fight or flight" response.

5. Describe the routes and relationships of the ureters from the kidneys to the urinary bladder. (N 332, 349, 362, 363, TG5-30B, TG5-39, TG6-07A, TG6-07B, TG6-09A, TG6-09B)

The ureter begins below the renal hilum as the renal pelvis narrows. Ureter descends roughly vertically on the anterior surface of the psoas major muscle. It lies a few centimeters lateral to the inferior vena cava on the right side and the abdominal aorta on the left. At the pelvic brim, the ureter leaves the psoas major to cross over the bifurcation of the common iliac arteries into the external and internal iliac arteries. It lies within this bifurcation as it passes into the pelvis. It runs anteroinferiorly beneath the pelvic peritoneum on the lateral pelvic wall, creating a ureteric fold. The fossa above the ureteric fold is the ovarian fossa, and serves as a bed for the ovary on the lateral pelvic wall. The ureter passes forward under the broad ligament (female) or peritoneum (male) to reach the posterolateral surface of the urinary bladder and enter it in a glancing anteromedial direction. The ureteric orifices appear within the posterior wall of the bladder as slit-like openings at either end of an interureteric crest.

6. Recognize the urinary bladder in either its expanded or contracted position, and determine the extent of its peritoneal covering. (W&B 538-539, 541 (fig), 545 (fig), N 360, 361, 362, 366, 402, 403, 406, 407, 408, 410, TG 6-07A, 6-07B, 6-08A, 6-08B, 6-10A, 6-10B, 6-17A, 6-17B, 6-19A, 6-19B, 6-33, 6-34)

The superior surface of the bladder is covered by peritoneum as well as the uppermost one or two centimeters of the posterior aspect. The rest of it is extraperitoneal, actually below the lowest extent of the peritoneum.

7. Identify the internal orifices of the bladder and differentiate the trigone region from the rest of the bladder lining. (W&B 539-540, N 360, 361, 362, 366, 402, 403, 406, 407, 408, 410, TG 6-10A, 6-10B)

There is an "orifice of the ureter" for each ureter, in addition to an internal urethral orifice, for a total of three. These orifices mark the apices of an equilateral triangle, the vesicle trigone, made of smooth mucous membrane. In an undistended bladder, the ureteric orifices lie about three centimeters apart, with the internal urethral orifice between and inferior to them.

8. Describe the relationships of the bladder to other pelvic organs in both sexes. (W&B 533-534, N 360, 361, 362, 366, 402, 403, 406, 407, 408, 410, TG 6-07A, 6-07B, 6-08A, 6-08B)

The bladder lies in the anterior half of the pelvis, bounded anteriorly and laterally by the pubic symphysis. Posterior to it we have:

Inferior to the bladder we find the pelvic diaphragm (in females) or the prostate gland (in males).

9. Differentiate between male and female urethrae. (W&B 542-543, N 369, 379, 384, 385, TG 6-08A, 6-08B, 6-09A, 6-09B, 6-10A, 6-10B)

The female urethra is about four centimeters long and is entirely "membranous urethra". The male urethra is longer than the female urethra, and is divided into three parts: membranous, prostatic, and penile (spongy) urethra. (See Pelvis & Pelvic Viscera Dissector Answers.)

Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless.

The Kidneys - The Ureters - The Suprarenal Glands - Nerves - More Nerves - Still More Nerves - Last one (I promise) - The Portal System of Veins - The Abdominal Aorta - Surface Anatomy of the Abdomen - Surface Markings of the Abdomen

Questions and Answers:

1. What is the vertebral level of an imaginary horizontal line drawn between the right and left iliac crests? (N 248 or TG 5-03)
The line between the iliac crests is at the level of L4.
2. What are the structures that enter and leave the kidney along the medial border and can be elevated with it? (N 334A, 334B,332 or TG 5-31)
The renal veins, renal arteries, and the ureters enter and leave the kidney along the medial border and can be elevated with it.
3. What are the anterior visceral relations of the kidneys? (N 329 or TG 5-31,342A, 342B,349 or TG 5-42) (See #1 above)
4. What are the differences between the left and right renal veins? (N 332 or TG 5-31) (See #3 above)
The left renal vein is longer than the right renal vein since the inferior vena cava is on the right side of the body. There are also differences in the veins connecting to the renal veins, but this will be addressed later.
5. How is the left renal vein related to the aorta, the superior mesenteric artery, and the left renal artery? (N 332 or TG 5-31)
The left renal vein crosses anterior to the aorta and posterior to the superior mesenteric at a level just below the branch point of the superior mesenteric from the aorta. It runs anterior to the left renal artery.
6. Where on the aorta are the origins of the renal arteries? (N 264 or TG 5-34,332 or TG 5-31)
The renal arteries originate from the aorta approximately an inch below the celiac trunk, slightly inferior to the origin of the superior mesenteric artery. This is the upper L2 vertebral level.
7. What is the developmental significance of the supernumerary (extra) renal arteries? (N 333)
The kidneys develop within the pelvis and then ascend to their adult levels. As they travel up the posterior abdominal wall, the arterial supply actually remodels itself, to achieve a higher origin from the aorta. Supernumerary renal arteries are remnants of the earlier blood supply, and consequently they most commonly enter the inferior pole of the kidney. (See #3 above.)
8. Describe the level of origin, variations, course, relations, and branches of the gonadal arteries and veins. (N 341 or TG 5-30,400, 401)
The gonadal arteries originate from the anterior aspect of the aorta, below the renal arteries, at the lower L2 vertebral level. They have ureteric branches and descend obliquely (crossing over the ureters) either to the ovaries (as "ovarian arteries") or the deep inguinal canal (as "testicular arteries"). The gonadal veins follow the same path back from the respective organs, but end differently. The right gonadal vein drains into the inferior vena cava at the same level as the right gonadal artery originates from the aorta, and the left gonadal vein drains into the left renal vein.
9. What is the relationship of the ureter to the gonadal vessels, the left colic vessels, and the root of the mesentery? (N 340,341,401 or TG 5-30, 5-30)
The ureter passes posterior to the gonadal vessels, the left colic vessels, and the root of mesentery.
10. What is the relationship between the renal artery, the renal vein, and the renal pelvis at the hilum of the kidney? (N 334A, 334B,335 or TG 5-32)
The renal vein is anterior to the renal artery and pelvis. The renal artery mainly is anterior to the renal pelvis but a few of the branches enter the kidney posterior to the pelvis.
11. What are the differences between the right and left suprarenal glands in terms of shape and relationship to the kidney? (N 332,341 or TG 5-31, 5-30)
Both glands lie on top of the kidney and slightly medially. The right suprarenal gland is triangular and smaller than the left gland. The left gland is semilunar in shape.
12. What is the relationship of the right suprarenal gland to the inferior vena cava? (N 341 or TG 5-30)
The right gland makes contact medially with the inferior vena cava.
13. Besides the inferior phrenic vein and the suprarenal vein, what other veins drain into the left renal vein? (N 332,341 or TG 5-31, 5-30)
The left gonadal vein drains into the left renal vein, and the left 2nd lumbar vein drains into its posterior aspect. (See #19)
14. Where are the postganglionic neurons of the suprarenal glands located? (N 348 or TG 5-39)
The suprarenal medulla is directly innervated by preganglionic sympathetic fibers, causing a systemic sympathetic response. (The suprarenal (adrenal) medulla is modified nerve tissue. Activation of it causes the release of norepinephrine and/or epinephrine, which enter the blood stream and cause the systemic response.) However, postganglionic neurons from the celiac ganglion reach the cortical tissue of the suprarenal glands to innervate the suprarenal blood vessels.
15. Locate a ureter. Note its relation to uterine artery. Trace it to the bladder and posteriorly to the brim of the pelvis, noting course, relation to peritoneum, and blood supply. (N 400, TG 6-11B, 6-17)

The ureter passes over the pelvic brim just medial to the ovarian vessels, usually at the bifurcation of the common iliac artery. The ureter then descends and passes anteriorly within the pelvis. It is crossed superiorly by the uterine artery ("bridge over water") before it turns medially to enter the posterior wall of the bladder.

15a. Explore the female urethra, noting length, sphincter muscle, and relation to vagina. Note specifically the relation of the orifice to the anterior vaginal wall. What is the significance? (W&B 549, N 383, 379, TG 6-08, 6-10)

The urethra is about four centimeters long. It is homologous to male prostatic/membranous urethra. Its orifice is within the vestibule of the vagina, immediately in front of the vaginal orifice.

16. Define the ampulla of the ductus deferens. Is it covered by peritoneum? (N 361A, 361B, 384A, 384B, TG 6-14)

The ductus deferens is covered by peritoneum, but its ampulla is not. The upper end of the seminal vesicle may contact peritoneum, otherwise it is inferior to the peritoneum lining the rectovesical pouch.

17. What is the rectovesical pouch? (N 361A, 361B, TG 6-08)

The rectovesical pouch is the reflection of peritoneum between the rectum and the bladder. This of course only occurs in males.

18. Locate the anterior division of the internal iliac artery and note how it terminates by dividing into the inferior gluteal and the internal pudendal arteries. These exit the pelvis below the lower border of the piriformis muscle. What are other relations? (N 402, 403A, 403B, 502, TG 3-29, 6-17A, 6-17B)
The internal pudendal and inferior gluteal (the larger of the two) arteries are terminals of the anterior division of the internal iliac artery. They arise from a common trunk either within or outside the pelvis. The internal pudendal artery exits the greater sciatic foramen between the piriformis and coccygeus muscles, crosses the iliac spine to pass through the lesser sciatic foramen, and enters the pudendal canal. The inferior gluteal artery passes between the second and third sacral nerves to leave the pelvis below the piriformis muscle.
19. Do you have an "aberrant obturator artery", which arises from the inferior epigastric artery and accompanies the obturator nerve?
An aberrant obturator artery takes its origin from the inferior epigastric or, rarely, from the external iliac itself. It would descend along the brim of the pelvis to the obturator foramen.
20. Locate the sympathetic trunk entering the pelvis along the medial border of the pelvic sacral foramina. Note number of ganglia, gray rami communcantes, and sacral splanchnic nerves. (N 410, 412, TG 8-18, 8-20)
Both sympathetic trunks descend on the anterior surface of the sacrum in the extraperitoneal connective tissue. There are usually four ganglia in the sacral region, one opposite the upper three sacral segments and one beneath the fourth and fifth segments of the sacrum. The two trunks typically unite over the coccyx to form the "ganglion impar". Sacral splanchnic nerves are slender fibers leaving the anterior surface of the sacral sympathetic trunk ganglia to enter the inferior hypogastric plexus on the sides of the rectum. Gray rami communicantes also leave the lateral side of the sacral sympathetic trunk to reach the sacral ventral primary rami as they emerge from the anterior sacral foramina.
21. How many pelvic splanchnic nerves are there? (N 410, 412, TG 8-19, 8-21)
The pelvic splanchnic nerves represent the sacral portion of the craniosacral outflow or parasympathetic portion of the autonomic nervous system. The pelvic splanchnic nerves spring from the ventral rami of the second, third, and fourth sacral nerves. The contribution from the third sacral nerve is usually the largest. From three to ten strands of nerves pass forward and become incorporated into the inferior hypogastric plexus.
22. What is the puborectalis muscle? What is its significance? (N 367A, 367B, 368, 369, 370, TG 6-21A, 6-21B, 6-22, 6-23A, 6-23B)
The puborectalis muscle is the most medial portion of the levator ani muscle. It passes around the terminal rectum to form the puborectal sling, which kinks the anorectal junction forward to assist in maintaining fecal continence. This muscle marks the transition from rectum to anus.
23. Define the urogenital hiatus. What does it transmit? (N 367A, 367B, 368, 369, 370, TG 6-21A, 6-21B, 6-22, 6-23A, 6-23B)
The passage (transmission) of the urethra/vagina and anus through the pelvis requires a separation of the two halves of the pelvic diaphragm in front of the rectum. This is the urogenital hiatus.