Anatomy of the Penis
- Anatomy of the Penis (1/2): gross appearance, vascular supply, innvervation, histology.
- Anatomy of the Penis (2/2): phases of erection, neural control, molecular signaling.
References: (Benninghoff, 1993 ).
Gross Anatomy of the Penis
Transverse section of the penis. Figure modified from Gray's Anatomy, Lea and Febinger 1918, Philadelphia, USA.
Corpora of the Penis
The penis is composed of two corpora cavernosa and one unpaired corpus spongiosum. The corpora contain oddly shaped cavities, which are lined with endothelium. Smooth muscle runs through the walls and septa of the corpora. The afferent arteries are notable for their strong smooth muscle wall.
Corpora cavernosa penis:
each corpora cavernosa begins at the inferior ramus of the pubic bone (crura penis) and extends through the penis to the glans. Two Mm.
ischiocavernosi surround the corpora cavernosa.
Corpus spongiosum penis:
the unpaired corpus spongiosum surrounds the urethra and begins between the two crura penis as a thickening (Bulbus penis). At the tip of the penis, the corpus spongiosum forms the glans penis. Connective tissue fibers provide a strong connection to the corpora cavernosa. The M. bulbocavernosus surrounds the bulb of the penis.
conical shaped end of the corpus spongiosum. The urethra ends with the external urethral orifice or meatus urethrae externus at the tip of the glans. The Corona glandis forms a sulcus and marks the transition from corpus spongiosum to the corpus cavernosum.
Tunica albuginea of the penis:
a strong 1 mm thick fascial sheath surrounds the outside of the two corpora cavernosa and forms a septum in between (Septum pectiniforme penis).
Fascia and Ligaments of the Penis
The Penis (tunica albuginea of the corpora cavernosa) is circularly surrounded by the Buck's fascia (Fascia penis profunda). The fascia penis superficialis lies above the Buck's fascia and is endorsed with smooth muscle from the tunica dartos [Figure: transverse section of the penis]. The fascia penis superficialis connects caudal to the superficial perineal fascia (Colles' fascia) and cranial to the Scarpa's fascia. The above-mentioned attachments of the fascia penis superficialis restrict penile haematomas to the area between the inguinal ligament, the fascia lata and ventral of the central tendinon of the pelvic floor.
The penile ligaments attach the penis to the symphysis and the linea alba of the rectus sheath (fundiform ligament and suspensory ligament).
The prepuce (foreskin) consists of an inner and outer leaf and covers the glans of the flaccid penis. The foreskin serves as reserve skin during erection. The two skin sheets are movable against each other. The frenulum is located at the ventral side of the glans and attaches the prepuce to the glans [fig. uncircumcised penis]. The smegma is a whitish pollution of the glans and prepuce and arises due to a bacterial colonization of the desquamated epithelium.
The male urethra can be divided in the following sections.
3–5 cm long. The colliculus seminalis is located in the middle of the prostatic urethra. At the colliculus seminalis, also called verumontanum, end the ejaculatory ducts and pass into the urethra. The prostatic utricle is a relic of the embryonic period (Müllerian duct) in the midline of the prostatic urethra.
part of the urethra, which runs through the pelvic floor and is enclosed by the external urethral sphincter (M. sphincter urethrae externum).
consists of the bulbar and penile urethra. The Cowper's glands flow into the proximal spongy urethra. The urethral glands (Littre's glands) open on the entire length of the urethra.
increase in diameter of urethra while transversing the glans.
Vascular Supply of the Penis
Arteries of the penis:
all of the penile arteries arise from the internal pudendal artery from the internal iliac artery [Fig. Arteries of the penis]. The internal pudendal artery reaches the ischiorectal fossa by the Alcock's canal.
Dorsal artery of penis (A. dorsalis penis):
located on the dorsum of the corpus cavernosum and supplies the glans, the prepuce and penile skin.
Deep artery of penis (A. profunda penis):
located in the center of the corpus cavernosum and emits many Aa. helicinae (helicine arteries) which flow into the caverns of the corpus cavernosa.
Bulbourethral artery (A. bulbi penis):
supplies the corpus spongiosum and the urethra.
Veins of the penis:
the veins of the penis break through the tunica albuginea and open via the circumflex veins in the unpaired deep dorsal vein, which empties into the venous plexus of Santorini. The superficial dorsal vein lies external to Buck's fascia.
Lymphatic vessels of the penis:
flow into the superficial inguinal and subinguinal lymph nodes. The proximal urethra drains into the pelvic lymph nodes (internal iliac and common iliac lymph nodes).
Innervation of the Penis
the processing of sensory stimuli in the limbic system and hypothalamus stimulates the spinal autonomic centers of the erection. The main centers in the hypothalamus are the paraventricular nucleus and the medial area praeoptica. The neurotransmitters of these first neurons are Oxytocin, melanocortin and dopamine.
Spinal autonomic centers:
cortical and peripheral stimuli activate spinal centers and cause the erection. The Nucleus intermediolateralis (S2–S4) is the parasympathetic spinal center, the sympathetic spinal center is located T12–L2.
Inferior hypogastric plexus:
gets nerve fibers from the above mentioned centers. The inferior hypogastric plexus sends nerve fibers to the pelvic organs.
Cavernous nerves of the penis:
autonomic nerve fibers for the penis from the inferior hypogastric plexus, located posterolateral to the seminal vesicles and pass lateral to the prostate (mainly located between 5 to 7 o'clock). In the membranous portion of the urethra, the nerve fibers are located at 3 and 9 o'clock, at the distal bulb of penis they are located at 1 and 11 o'clock, where they enter into the penis. In addition, nerve fibers accompany the arteries or sensory nerves. The autonomic nerve fibers innervate the helicine arteries. The cholinergic nerve endings stimulate the NO-synthase and therefore the release of NO (nitric oxide). The exact mechanism is explained in the section physiology of erection.
Motor neuron innervation:
the pudendal nerve (S2-4) innervates the M. bulbocavernosus and M. ischiocavernosus.
afferent nerve fibers to move from the receptors via the dorsal penile nerve and pudendal nerve into the spinal cord. Next steps are either the medial lemniscus or spinothalamic tract.
Histology of the Penis
Histology of the male urethra:
the wall of the urethra consists of a mucosa with varying epitheliums (prostatic urethra with transitional epithelium, spongy urethra with stratified columnar epithelium, fossa navicularis with squamous epithelium), a submucosa with connective tissue and glands, and a very thin muscularis.
Histology of the Glans and prepuce:
keratinized squamous epithelium.
Histology of the erectile tissue:
the corpora contain septa of smooth muscle, which form bizarrely shaped cavities. Vascular endothelium lines the septa and cavities. The afferent arteries for the erectile tissue possess a strong muscularis.
Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
References anatomy of the penis
Benninghoff 1993 BENNINGHOFF, A.:
- Makroskopische Anatomie, Embryologie und Histologie des
München; Wien; Baltimore : Urban und Schwarzenberg, 1993
Porst 2004 PORST, H.:
- Tadalafil, Therapiestrategien bei erektiler Dysfunktion.
Linkenheim-Hochstetten : Aesopus Verlag, 2004