Descent of the Testes

The testes begin development near the kidneys. How do they end up in the scrotum, and why? In the embryo, a cord of muscle and connective tissue called the gubernac-ulum9 (GOO-bur-NACK-you-lum) extends from the gonad to the floor of the abdominopelvic cavity. It shortens as the fetus grows and guides the testis through a passageway in the groin called the inguinal canal. This descent of the testes (fig. 27.5) begins in weeks 6 to 10; by 28 weeks, the testes enter the scrotum. As they descend, they are accompanied by ever-elongating testicular arteries and veins and by lymphatic vessels, nerves, sperm ducts, and extensions of the internal abdominal oblique muscle.

8phallo = penis

9gubern = rudder, to steer, guide

Saladin: Anatomy & I 27. The Male Reproductive I Text I © The McGraw-Hill

Physiology: The Unity of System Companies, 2003 Form and Function, Third Edition

1022 Part Five Reproduction and Development

Developing glans

Glans of penis

Scrotum

Genital tubercle

Urogenital fold

Labioscrotal fold

Genital tubercle

Urogenital fold

Labioscrotal fold

Glans

Tail

-Phallus

Urogenital fold Labioscrotal fold

Developing glans

Glans of penis

Scrotum

Perineal Raphe

Urethral groove

Anus

Prepuce Urethral orifice

Perineal raphe

Anus

Perineal Descent Pictures

Developing glans

Labia minora

Labia majora

Clitoral Glans Developer

Glans of clitoris

Vaginal orifice

Glans of clitoris

Vaginal orifice

Figure 27.4 Development of the External Genitalia. (a) By 6 weeks, the embryo has three primordial structures—the phallus, urogenital folds, and labioscrotal folds—that will become the male or female genitalia. (b) At 8 weeks these structures have grown, but the sexes are still indistinguishable. (c) Slight sexual differentiation is noticeable at 10 weeks. (d) The sexes are fully distinguishable by 12 weeks. Matching colors identify homologous structures of the male and female.

Saladin: Anatomy & I 27. The Male Reproductive I Text I © The McGraw-Hill

Physiology: The Unity of System Companies, 2003 Form and Function, Third Edition

Chapter 27 The Male Reproductive System 1023

7-month fetus

8-month fetus

1-month-old infant

7-month fetus

— Parietal peritoneum Epididymis Testis

Ductus deferens Pubis

Vaginal process Gubernaculum Scrotal swelling

Muscular wall of abdomen

Inguinal canal

8-month fetus

Muscular wall of abdomen

Inguinal canal

Vaginal process

Penis

Infant Inguinal Canal

Vaginal process

Penis

1-month-old infant

Processes Vaginalis

Closed proximal portion of vaginal process

Spermatic cord Tunica vaginalis Scrotum Gubernaculum

Closed proximal portion of vaginal process

Spermatic cord Tunica vaginalis Scrotum Gubernaculum

Figure 27.5 Descent of the Testis. Note that the testis and spermatic ducts are retroperitoneal. An extension of the peritoneum called the vaginal process follows the testis through the inguinal canal and becomes the tunica vaginalis. Why is this structure of male anatomy called the tunica vaginalis?

In the scrotum, the testes are kept at a temperature of about 35°C, which is 2°C cooler than in the pelvic cavity. This is essential for sperm production. About 3% of boys are born with undescended testes, or cryptorchidism (see table 27.2).

Before You Go On

Answer the following questions to test your understanding of the preceding section:

3. What are mesonephric and paramesonephric ducts? What factors determine which one develops and which one regresses in the fetus?

4. What male structures develop from the phallus and labioscrotal folds?

5. Define the gubernaculum and describe its function.

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Responses

  • aryan
    Where is the perineal raphe?
    8 years ago
  • rayyan
    Why is the structure of male antomy called tunica vaginalis?
    6 years ago

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