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Lab 7 - Inguinal Region & Gonads

Suggested reading:
Ch. 4: pp. 260-261, 282-291, clinical case 5

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

Primary Lab Objectives and Goals:

In the MALE:

  1. Examine the surface anatomy of the male inguinal region. Remove the skin of the inguinal region and the upper thigh. Understand the relationship between the inguinal region and the bones of the pelvis.

  2. Trace the course of the ureters and ductus deferens in the pelvis, and understand the anatomical relationships of these structures to each other.

  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 structures passing into the scrotum and of all inguinal hernias.

  4. Open the inguinal canal and examine its contents. Note and understand the relationship between the canal and the external abdominal oblique muscle, the contents of the canal, and the location of the deep inguinal ring.

  5. Open the scrotum and examine the testis and identify the location of sperm production, and the relationship between the veins and arteries.

In the FEMALE:

  1. Examine the surface anatomy of the inguinal region. Remove the skin of the inguinal region and the upper thigh. Understand the relationship between the inguinal region and the bones of the pelvis.

  2. Trace the course of the ureters and the round ligament of the uterus in the pelvis, and understand the anatomical relationships of these structures to each other.

  3. Locate the inguinal ligament and thesuperficial 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. Open the inguinal canal and examine its contents. Note and understand the relationship between the canal and the external abdominal oblique muscle, the contents of the canal, and the location of the deep inguinal ring.

  5. Expose and examine an ovary, and understand the several ligaments that stabilize it.

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

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

 

DISSECTION OF THE MALE INGUINAL CANAL

1. DUCTUS DEFERENS

  1. Retrace the descent of the testis by following the testicular artery down to the internal opening of the inguinal canal; the deep inguinal ring.
  2. Remove the peritoneal ‘roof’ of the pelvis, dissecting out the adherent ureters and ductus deferens as you do so.
  3. Trace the ductus deferens laterally to the opening of the inguinal canal.
  4. 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:

FUNCTIONAL ANATOMY:

The ductus deferens empty into the urethra at the midline of the body, having been pulled sideways away from the midline by the descending testes. From the testis, each ductus deferens runs laterally through the inguinal canal and then medially back towards the urethra. It therefore hooks around the inferior epigastric artery.

 

 

2. INGUINAL REGION

  1. Complete the skinning of the inguinal region, extending your efforts a short way into the thigh.
  2. Clean the aponeurosis of the external abdominal oblique muscle.
  3. As you are clearing away the subcutaneous fat, look for three sets of superficial cutaneous vessels: the superficial epigastric, superficial circumflex iliac, and external pudendal arteries.
  4. Identify and palpate the superficial inguinal ring and the spermatic cord as it exits the ring.
  5. Clean and examine the ilioinguinal nerve as it emerges from the superficial inguinal ring, anterior to the spermatic cord.
  6. Medially locate the specialized fascia that forms the suspensory ligament of the penis.

Atlas Images:

 

 

 

 3. CREMASTER MUSCLE

  1. Cut and reflect the aponeurosis of the external oblique muscle by making a slit 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 part of the fascia covering the spermatic cord.
  4. Locate some of the 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.

 

 

4. SCROTUM

  1. Make an incision through the skin of the scrotum and expose the spermatic cord and testis.
  2. Trace the continuity of the layers of the scrotum with the corresponding layers of the body wall.

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 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.

 

5. TESTIS

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

Atlas images:

 

 

DISSECTION OF THE FEMALE INGUINAL CANAL

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 in human females. There is no female 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. Locate the round ligament of the uterus as it enters the deep ring of the inguinal canal.

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. It will loop around these vessels (laterally) before entering the inguinal canal.

  1. Trace the course of the ovarian arteries from the ovaries to the aorta.
  2. Remove the peritoneal ‘roof’ of the pelvis.
  3. Dissect out the round ligament and follow it back to the uterus.

Atlas Images:

 

 

 

2. INGUINAL REGION

  1. Complete the skinning of the inguinal region, extending your efforts a short way into the thigh.
  2. Clean the aponeurosis of the external abdominal oblique muscle.
  3. As you are clearing away the subcutaneous fat look for three sets of superficial cutaneous vessels: the superficial epigastric, superficial circumflex iliac, and external pudendal.
  4. Identify the superficial inguinal ring and the round ligament of the uterus as it exits through the ring. 
  5. Clean and examine the ilioinguinal nerve as it emerges from the superficial inguinal ring. 

NOTE: In the female, 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 a slit 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. LIGAMENTS OF THE OVARY

  1. On one side, dissect away the peritoneum enclosing the ovary.
  2. Expose the ovary, the vessels, and the ligaments on either side of it.
  3. Identify the ovarian ligament which connects the ovary to the uterus.
  4. Identify the suspensory ligament of the ovary. This is a fold of peritoneum covering the ovarian vessels, that connect to the lateral side of the ovary.

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.

 

 

5. OVARY

  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 its pull on the round ligament may cause inguinal 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
When a fertilized ovum turns around and exits the oviduct to enter the peritoneal cavity, the result may be an abdominal extopic pregnancy in which the embryo implants on the broad ligament, bowel mesentery, loop of bowel, or parietal peritoneum.

 

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