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Lab 8 - Inguinal Region & Gonads

Please refer to this pre-lab exercise regarding the anatomy of the pelvis

Pre-lab Exercise: Surface Anatomy of the Inguinal Region

Primary Lab Objectives and Goals:

In a cadaver with testes:

  1. Remove the skin of the inguinal region and the upper thigh. Understand the relationship between the inguinal region and the bones of the pelvis. Locate the inguinal ligament and the superficial inguinal ring. Understand that this is the exit point of the inguinal canal and the passage way for structures passing into the scrotum and of all inguinal hernias.
  2. Locate the cremater muscle in the spermatic cord and understand its origin at the internal oblique muscle.

  3. Open the scrotum and examine its layers.

  4. Examine the external anatomy of the testis and identify the epididymus, ductus deferens, and testicular vein and artery. Trace the ductus deferens through the inguinal canal and into the pelvis. Examine the internal anatomy of the testis.

In a cadaver with ovaries:

  1. Trace the course of the ovarian vessels to the ovary and the round ligament of the uterus to the deep inguinal ring and understand the anatomical relationships of these structures to each other.

  2. Remove the skin of the inguinal region and the upper thigh. Understand the relationship between the inguinal region and the bones of the pelvis.
  3. Locate the inguinal ligament and the superficial inguinal ring. Understand that this is the exit point of the inguinal canal and the passage way for the round ligament of the uterus to the labia majora and of all inguinal hernias.

  4. Expose and examine an ovary and understand the ligaments that stabilize it.

If you have a cadaver with testes, proceed with the dissection immediately below. If you have a cadaver with ovaries, refer to the pertinent section that follows. Make sure that you read the descriptions for both the cadavers with testes and with ovaries that all members of your group see both types of cadavers.

Click here to view a video summarizing the dissection of the inguinal canal (courtesy of UMich)

 

INGUINAL CANAL DISSECTION IN A CADAVER WITH TESTES

1. INGUINAL REGION

  1. Complete the skinning of the inguinal region, extending your cut into the upper thigh.
  2. Clean the aponeurosis of the external abdominal oblique muscle.
  3. Identify and palpate the superficial inguinal ring and the spermatic cord as it exits the ring.
  4. Clean and examine the ilioinguinal nerve as it emerges from the superficial inguinal ring, anterior to the spermatic cord.
  5. Medial to the superficial inguinal ring, locate the specialized fascia that forms the suspensory ligament of the penis.

Atlas Images:

 

 

 

 

 

 2. CREMASTER MUSCLE

  1. Cut and reflect the aponeurosis of the external oblique muscle by making an incision upward from the superficial ring at an angle toward the anterior superior iliac spine, cutting through only this external layer.
  2. As you separate the external oblique muscle from the internal oblique muscle, look for two nerves. The ilioinguinal nerve should be exposed as it travels through the inguinal canal. The iliohypogastric nerve runs parallel and is just superior to the ilioinguinal nerve.
  3. Remove the fascia covering the spermatic cord.
  4. Locate fibers of the cremaster muscle arising from the internal oblique muscle.

Atlas Images:

 

FUNCTIONAL ANATOMY: 

The cremaster muscle, innervated by the genital branch of the genitofemoral nerve, helps regulate the temperature of the testes. When the temperature is cold is contracts, pulling the testes up and closer to the body to retain heat. It also contracts reflexively when the inside of the thigh is touched.

 

 

3. SCROTUM

  1. Make an incision through the skin of the scrotum and expose the rest of the spermatic cord and testis.
  2. Trace the continuity of the layers of the scrotum with the corresponding layers of the body wall. When you are done examining the scrotal layers, you can remove the skin.

The fascia enclosing the contents of the spermatic cord consists of three layers; the external spermatic fascia is derived from the external oblique muscle, the cremaster muscle and fascia is derived from the internal oblique, and the internal spermatic fascia is derived from the transversalis fascia.

Atlas Images:

FUNCTIONAL ANATOMY:

The duct that conducts spermatozoa from the testis to the ejaculatory duct and urethra is attached at the cranial end of the testis. From that point, it passes caudally on the dorsolateral surface of the testis, and then runs back up cranially from the bottom of the testis to enter the inguinal canal. The first part that lies against the side of the testis is called the epididymis, and is the site of sperm maturation and storage.  From here the duct continues cranially and is called the ductus deferens (also known as the deferent duct, or vas deferens). A vasectomy consists of cutting the vas deferens so sperm can no longer reach the ejaculatory duct. The vas deferens travels through the inguinal canal into the pelvis where it is joined by the seminal vesicle to form the ejaculatory duct, which passes through the prostate into the urethra.

 

4. TESTIS AND DUCTUS DEFERENS

  1. Incise and open the tunica vaginalis, the celomic sac (derived from peritoneum) wrapped around the testis.
  2. Distinguish and examine the epididymis and the ductus deferens.
  3. Trace the duct back through the inguinal canal to the pelvic rim.
  4. Remove the peritoneal ‘roof’ of the pelvis to expose the adherent ureters and ductus deferens.
  5. Retrace the embryologic descent of the testis by following the testicular artery from the aorta down to the deep inguinal ring.
  6. Trace the ductus deferens medially to where it joins with the duct from the seminal vesicle to form the ejaculatory duct. The ejaculatory ducts then enter the prostate gland to empty into the prostatic urethra.

 

Atlas Images:

Transect the testis from its superior pole to its inferior pole (along its anterior surface, opposite the epididymis).
  1. Identify its major components: the tunica albuginea, efferent ductules, seminiferous tubules, and rete testis.
  2. Use a fine-tipped probe to tease out some of the seminiferous tubules of one lobule.

Atlas images:

 

 

INGUINAL CANAL DISSECTION IN A CADAVER WITH OVARIES

FUNCTIONAL ANATOMY:

Because the ovaries do not descend into the labia majora (except as a rare congenital defect), the components of the inguinal canal are poorly marked. There is no equivalent of the spermatic cord. The only structures traversing the inguinal canal are (a) the round ligament of the uterus (the equivalent of the gubernaculum testis), (b) its companion artery (equivalent to the cremaster artery) and (c) the genital branch of the genitofemoral nerve.

1. ROUND LIGAMENT OF THE UTERUS

  1. Trace the course of the ovarian arteries from the aorta to the ovaries. The ovarian vessels are contained within the suspensory ligament of the ovary (known by clinicians as the infudibulopelvic or IP ligament).
  1. Remove the peritoneal ‘roof’ of the pelvis.
  2. Locate the round ligament of the uterus and and trace it from uterus (medially) to the deep inguinal ring (laterally).

HINT: The round ligament of the uterus can be found along the interior side of the anterior body wall by locating the inferior epigastric vessels. The round ligament loops around these vessels (laterally) before entering the deep inguinal canal. The round ligament contains the Sampson artery.

Atlas Images:

 

 

 

2. INGUINAL REGION

  1. Complete the skinning of the inguinal region, extending your cut into the upper thigh.
  2. Clean the aponeurosis of the external abdominal oblique muscle.
  3. Identify the superficial inguinal ring and the round ligament of the uterus as it exits through the ring. 

NOTE: It is very difficult to locate the round ligament as it exits through the superficial inguinal ring. It is much reduced at this point and there may only be thin fibrous remnants that are difficult to distinguish from the surrounding tissue.

Atlas Images:

 

 

3. INGUINAL RING

  1. Cut and reflect the aponeurosis of the external oblique muscle by making an incision upward from the superficial ring at an angle toward the anterior superior iliac spine, cutting through only this external layer.
  2. As you separate the external oblique muscle from the internal oblique muscle, you should look for two nerves. More of the ilioinguinal nerve should be exposed as it travels through the inguinal canal. The iliohypogastric nerve runs parallel and just superior to the ilioinguinal nerve.
  3. Attempt to trace the round ligament through the canal, out through the superficial ring, and down to its attachment to the labia majora.

Atlas Images:

 

 

 

4. OVARY

  1. On one side, dissect away the peritoneum enclosing the ovary.
  2. Identify the ovarian ligament which connects the ovary to the uterus.

Atlas Images:

FUNCTIONAL ANATOMY:

On the gross anatomical level, the ovary is much less complicated than the testis. Because the ova simply rise to the surface of the ovary and burst out of a ripe follicle into the celom, the ovary has no duct system like the testis.

  1. Examine a cross-section of the ovary.
  2. Identify the follicles, corpus albicans, and corpus luteum (if present).
 

 Clinical Notes

1. Round Ligament
As the uterus enlarges during pregnancy it can stretch the round ligament may cause lower abdominal, inguinal, and or groin pain.

2. Vasectomy
To perform a vasectomy, the ductus deferens is isolated on each side and transected or a small section is removed. Sperms can no longer pass to the urethra. They degenerate in the epididymis and the proximal end of the ductus deferens. Secretion of the auxiliary genital glands (seminal gland, bulbourethral gland, and prostate) can still be ejaculated. The testes continue to function as an endocrine gland for the production of testosterone.

3. Testicular cancer
Because the testes descend from the dorsal abdominal wall into the scrotum during fetal development, their lymphatic drainage differs from that of the scrotum, which is an out-pouching of the antero-lateral abdominal skin. Therefore:

Cancer of the testis: metastasizes initially to the lumbar lymph nodes
Cancer of the scrotum: metastasizes initially to the superficial inguinal lymph nodes

4. Ectopic pregnancy
An ectopic pregnancy occurs when the blastocyst implants somewhere outside the uterine cavity. This typically happens as the result of slow transit of the fertilized ovum through the uterine tube, but ectopic pregnancies are also possible when the embryo implants on the cervix, ovary, peritoneum (abdominal lining), etc.

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