Scrotum

The testes are contained in a pendulous pouch, the scro-tum17 (fig. 27.10). The left testis is usually suspended lower than the right so the two are not compressed against each other between the thighs. The skin of the scrotum has sebaceous glands, sparse hair, rich sensory innervation, and somewhat darker pigmentation than skin elsewhere. The scrotum is divided into right and left compartments by an internal median septum, which protects each testis from infections of the other one. The location of the septum is externally marked by a seam called the perineal raphe18 (RAY-fee), which also extends anteriorly along the ventral side of the penis and posteriorly as far as the margin of the anus (see fig. 27.6).

The spermatic cord is a cord of connective tissue that passes upward behind the testis, across the anterior side of the pubis, and into an opening called the inguinal ring in the muscles of the groin. From there, it travels about 4 cm through the inguinal canal and emerges into the pelvic cavity. It contains the ductus deferens (a sperm duct), blood and lymphatic vessels, and testicular nerves—structures that followed the testis as it descended through the canal. The cord is easily palpated through the skin of the scrotum.

The original reason that a scrotum evolved has long been a subject of debate among reproductive biologists and still has no universally accepted answer. Now that human testes reside in the scrotum, however, they have

17scrotum = bag

18 raphe = seam

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

Reproductive System Functions

Figure 27.7 The Male Reproductive System. (a) Median section of the pelvic cavity viewed from the left. (b) Posterior view of the reproductive organs.

Why does enlargement of the prostate interfere with urination?

Figure 27.7 The Male Reproductive System. (a) Median section of the pelvic cavity viewed from the left. (b) Posterior view of the reproductive organs.

Why does enlargement of the prostate interfere with urination?

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

1026 Part Five Reproduction and Development

Function Tunica Albuginea

Spermatic cord

Blood vessels and nerves

Seminiferous tubule

-Septum -Lobule

Tunica vaginalis

Tunica albuginea

Spermatic cord

Blood vessels and nerves

Seminiferous tubule

-Septum -Lobule

Tunica vaginalis

Tunica albuginea

Tunica Vaginalis Epididymis

Spermatic cord Ductus deferens

Head of epididymis

Testis, covered by tunica albuginea

Tail of epididymis

- Scrotum (folded down)

Spermatic cord Ductus deferens

Head of epididymis

Testis, covered by tunica albuginea

Tail of epididymis

- Scrotum (folded down)

Figure 27.8 The Testis and Associated Structures. (a) Anatomy of the testis, epididymis, and spermatic cord. (b) The testis and associated structures dissected free of the scrotum, shown life size.

Interstitial cells

Blood vessel Germ cells

Sustentacular cell

Tails of spermatozoa

Sustentacular cell

Tails of spermatozoa

The Testis And Associated Structure

Figure 27.9 Histology of the Testis. (a) Scanning electron micrograph; (b) light micrograph. Figure b is from a region of the tubule that did not have mature sperm at the time. (a) From R. G. Kessel and R. H. Kardon, Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy (W. H. Freeman, 1979).

Tunica Vaginalis Microscopically

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 1027

Chapter 27 The Male Reproductive System 1027

Male External Reproductive Organ
Figure 27.10 Anatomy of the Male Inguinal Region and External Genitalia.

adapted to this cooler environment and cannot produce sperm at the core body temperature of 37°C. The scrotum has three mechanisms for regulating the temperature of the testes:

1. The cremaster19 muscle consists of strips of the internal abdominal oblique muscle that enmesh the spermatic cord. When it is cold, the cremaster contracts and draws the testes closer to the body to keep them warm. When it is warm, the cremaster relaxes and the testes are suspended farther from the body.

2. The dartos20 muscle (tunica dartos) is a subcutaneous layer of smooth muscle. It, too, contracts when it is cold, and the scrotum becomes taut and wrinkled. The tautness of the scrotum helps to hold the testes snugly against the warm body and it reduces the surface area of the scrotum, thus reducing heat loss.

3. The pampiniform21 plexus is an extensive network of veins from the testis that surround the testicular artery in the spermatic cord. As they pass through the inguinal canal, these veins converge to form the testicular vein, which emerges from the canal into the pelvic cavity. Without the pampiniform plexus, warm arterial blood would heat the testis and inhibit spermatogenesis. The pampiniform plexus, however, prevents this by acting as a countercurrent heat exchanger (fig. 27.11). Imagine that a house had uninsulated hot and cold water pipes running close to each other. Much of the heat from the hot water pipe would be absorbed by the cold water pipe next to it—especially if the water flowed in opposite directions so the cold water carried the heat away. In the spermatic cord, such a mechanism removes heat from the descending arterial blood, so by the time it reaches the testis this blood is 1.5° to 2.5°C cooler than the core body temperature.

21 pampin = tendril + form = shape

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

1028 Part Five Reproduction and Development

1028 Part Five Reproduction and Development

Scrotum Warm And Cold

Figure 27.11 The Countercurrent Heat Exchange Mechanism of the Pampiniform Plexus. Warm blood flowing down the testicular artery loses some of its heat to the cooler blood flowing in the opposite direction through the pampiniform plexus of veins (represented as a single vessel for simplicity). Arterial blood is about 2°C cooler by the time it reaches the testis.

Figure 27.11 The Countercurrent Heat Exchange Mechanism of the Pampiniform Plexus. Warm blood flowing down the testicular artery loses some of its heat to the cooler blood flowing in the opposite direction through the pampiniform plexus of veins (represented as a single vessel for simplicity). Arterial blood is about 2°C cooler by the time it reaches the testis.

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  • Lachlan Murphy
    What are the external organ of a male?
    4 years ago
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    What is tunical albuginea?
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    What are the external organs of male?
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