Biology Today — January 2018

External Genitalia : Penis

It is the male copulatory organ and serves both as a reproductive organ and urinal duct. Unlike other species, human penis has
no baculum or erectile bone and is larger than that of any other primate, in relation to proportion of body mass. It is made up
of three columns of tissue.

Urinary bladder

Root

Body of penis

Composed of three

columns of erectile

tissue.

Glans penis

Bulbous end of

penis formed by

corpus spongiosum.

Highly sensitive.

Prostate gland

Prostatic urethra

Bulbourethral gland

Membranous urethra

Spongy urethra

(Longest part)

Corpora cavernosa

Two posterior, yellow fibrous

ligamentous tissue, present

next to each other on dorsal

side.

Corpus spongiosum

Ventral, highly vascular and

spongy tissue that surrounds

the urinogenital canal.

Prepuce

The loose fold of skin

covering the glans penis.

Urethral meatus

External urethral orifice.

Fig.: L.S. of penis showing its parts and urethra traversing through it

Subcutaneous and

deep dorsal vein Dorsal artery

Corpus cavernosa

Deep artery

Corpus spongiosum

Fascia of buck

Urethra

Skin

Fig.: T.S. of penis showing arrangement of three column of tissues

Function : Penis helps in sexual intercourse and insemination. This involves following three phases:

Erection of penis

An erection refers to the stiffening and rising of the penis that is often associated with sexual arousal. It occurs due to the
autonomic dilation of arteries supplying blood to the penis. This allows more blood to fill the three spongy erectile tissue chambers
in the penis, causing it to lengthen and stiffen. The engorged erectile tissue presses against and constricts the veins that carry
blood away from the penis. More blood enters than leaves the penis until an equilibrium is reached where an equal volume
of blood flows into the dilated arteries and out of the constricted veins; a constant erectile size is achieved at this equilibrium.

(a) Penile venules
(uncompressed)
Deep dorsal vein
Corpora cavernosa
Cavernosal arteries
Spongy urethra

Corpus spongiosum

Flaccid : Transverse view

(b)

Erect : Transverse view

Cavernosal arteries dilate,

engorging corporal tissue

with blood

Engorged corporal tissue compresses penile

veins venules, maintaining erection