Anatomy Of Penis

The penis25 serves to deposit semen in the vagina. Half of it is an internal root and half is the externally visible shaft

Chapter 27 The Male Reproductive System 1029

and glans26 (see figs. 27.7 and 27.12). The external portion is about 8 to 10 cm (3-4 in.) long and 3 cm in diameter when flaccid (nonerect); the typical dimensions of an erect penis are 13 to 18 cm (5-7 in.) long and 4 cm in diameter. The glans is the expanded head at the distal end of the penis with the external urinary meatus at its tip.

The skin is very loosely attached to the shaft, allowing for expansion during erection. It continues over the glans as the prepuce, or foreskin, which is often removed by circumcision. A ventral fold of tissue called the frenu-lum attaches the skin to the glans. The skin of the glans itself is thinner and firmly attached to the underlying erectile tissue. The glans and facing surface of the prepuce have sebaceous glands that produce a waxy secretion called smegma.27

The penis consists mainly of three cylindrical bodies called erectile tissues, which fill with blood during sexual arousal and account for its enlargement and erection. A single erectile body, the corpus spongiosum, passes along the ventral side of the penis and encloses the penile urethra. It expands at the distal end to fill the entire glans. The dorsal side of the penis, proximal to the glans, has a corpus cavernosum (plural, corpora cavernosa) on each side. Each is ensheathed in a fibrous tunica albuginea, and they are separated from each other by a median septum. (Note that the testes also have a tunica albuginea and the scrotum also has a median septum.)

All three cylinders of erectile tissue are spongy in appearance and contain numerous tiny blood sinuses called lacunae. The partitions between lacunae, called trabeculae, are composed of connective tissue and smooth trabecular muscle. In the flaccid penis, trabecular muscle tone collapses the lacunae, which appear as tiny slits in the tissue.

At the body surface, the penis turns 90° dorsally and continues inward as the root. The corpus spongiosum terminates internally as a dilated bulb, which is ensheathed in the bulbospongiosus muscle and attached to the lower surface of the perineal membrane within the urogenital triangle (see p. 350). The corpora cavernosa diverge like the arms of a Y. Each arm, called a crus (cruss; plural, crura), attaches the penis to the pubic arch (ischiopubic ramus) and perineal membrane on its respective side. Each crus is enveloped by an ischiocavernosus muscle. The innervation and blood supply to the penis are discussed later in connection with the mechanism of erection.

Before You Go On

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

6. State the names and locations of two muscles that help regulate the temperature of the testes.

24William Cowper (1666-1709), British anatomist

25penis = tail

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

1030 Part Five Reproduction and Development

Skin

Superficial fascia

Deep fascia

Skin

Superficial fascia

Deep fascia

Erect Penis Name Anatomy

Corpus cavernosum Corpus spongiosum

External urethral orifice (a)

Figure 27.12 Anatomy of the Penis. (a) Dissection in lateral view. (b) Cross section.

During erection, why is it important that the corpus spongiosum remain less engorged with blood than the corpora cavernosa?

Corpus cavernosum Corpus spongiosum

External urethral orifice (a)

Dorsal vein Dorsal nerve

Dorsal artery Deep artery

Corpora cavernosa

-Prepuce

Urethra Corpus spongiosum Glans of penis

Cavernosa Dan Corpus Spongiosum

Median septum

Tunica albuginea

Lacunae Skin

Superficial fascia

Median septum

Tunica albuginea

Lacunae Skin

Superficial fascia

Deep fascia

Figure 27.12 Anatomy of the Penis. (a) Dissection in lateral view. (b) Cross section.

During erection, why is it important that the corpus spongiosum remain less engorged with blood than the corpora cavernosa?

7. Name three types of cells in the testis, and describe their locations and functions.

8. Name all the ducts that the sperm follow, in order, from the time they form in the testis to the time of ejaculation.

9. Describe the locations and functions of the seminal vesicles, prostate, and bulbourethral glands.

10. Name the erectile tissues of the penis, and describe their locations relative to each other.

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