Penis & scrotum

General

Anatomy & histology-male urethra

Authors: Jesus Adrian Chavez, M.D., Debra L. Zynger, M.D.

Topic Completed: 1 August 2016

Minor changes: 26 October 2020

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed search: urethra anatomy [title] normal male

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Table of Contents

Cite this page: Chavez J. Anatomy & histology-male urethra. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/prostateurethramalenormal.html. Accessed October 28th, 2021.

Definition / general

Fibromuscular tube lined by urothelium, columnar epithelium and nonkeratinizing squamous epithelium that takes urine from the urinary bladder to the exterior through the external urethral meatus (Ross: Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 7th Edition, 2015, Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014)
Subepithelium composed of loose fibroelastic tissue, glands and abundant vessels
Muscle layers include smooth muscle and exterior skeletal muscle
Size, structure and function differ in males and females

Clinical features

Functions as the terminal duct for both the genital and urinary system
Measures 15 to 20 cm in length
Epithelium is derived from the urogenital sinus which forms from the ventral portion of the endodermal cloaca after its division (Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014)
Urethral sphincter surrounds the urethra
- Extends from the bladder neck to the inferior fascia of the urogenital diaphragm (Int Urol Nephrol 2014;46:1469)
- Controls urination and discharge of semen into urethra
- Composed of smooth and striated muscle
Divided into prostatic, membranous and penile urethra (Ross: Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 7th Edition, 2015, Gartner: Color Textbook of Histology, 3rd Edition, 2006)
- Prostatic urethra:
  - Extends from the bladder neck through the prostate gland (3 to 4 cm)
  - Lined by urothelium
  - Ejaculatory ducts enter at the posterior wall
  - Most prostatic ducts empty into the posterior and lateral walls (Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014)
  - Verumontanum (Müllerian vestige) is posterior to the mid prostatic in which the ejaculatory ducts empty and subsequently joins to the prostatic urethra (Ross: Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 7th Edition, 2015)
- Membranous urethra:
  - Extends from the apex of the prostate to the bulb of the penis (1 cm, Ross: Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 2015, 7th Edition, 2015, Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014)
  - Lined by stratified / pseudostratified columnar epithelium (similar to urothelium but lack umbrella cells)
  - Passes through the urogenital diaphragm as it enters the perineum
  - Surrounded by external voluntary sphincter formed by skeletal muscle of the urogenital diaphragm
- Penile (spongy) urethra:
  - Extends through the penis to the urethral meatus opening in the glans (15 cm, Ross: Histology: A Text and Atlas: With Correlated Cell and Molecular Biology, 7th Edition, 2015, Bostwick: Urologic Surgical Pathology, 3rd Edition, 2014)
  - Divided into 3 regions
    - Bulbar urethra: spans the bulb of the penis, lined by stratified / pseudostratified columnar epithelium
    - Pendulous urethra: spans the pendulous penis (shaft), lined by stratified / pseudostratified columnar epithelium
    - Fossa navicularis: dilated portion in the glans, lined by non-keratinizing squamous epithelium
  - Surrounded by the corpus spongiosum
  - Bulbourethral (Cowper) glands, glands of Littré (mucous glands) and intraepithelial (juxtaepithelial) glands empty in the penile urethra

Diagrams / tables

Images hosted on other servers:

Embryology and anatomy

Gross images

Contributed by Jesus Adrian Chavez, M.D. and Debra L. Zynger, M.D.

Dissected male urethra, longitudinal section

Penectomy, cross section

Microscopic (histologic) description

Urothelium
- Basal layers composed of either low columnar or cuboidal cells, followed by several layers of polyhedral cells
- Most superficial composed of round, dome shaped umbrella cells that are occasionally multinucleated and flattened according to amount of distention
Stratified / pseudostratified columnar epithelium
- Multiple cell layers of polyhedral cells; the most superficial are columnar
- Stratified / pseudostratified; in the pseudostratified layer, all cells are in contact with the basal layer
Nonkeratinizing squamous epithelium
- Composed of multiple layers
- Divided in zones according to cell shapes; cuboidal (deepest), polymorphous (middle), squamous / flattened (superficial)
Urethral / periurethral glands
- Bulbourethral (Cowper) glands: mucous-acinous glands in the bulbous and membranous urethra with uniform pale cytoplasm and basal, compressed nuclei
- Littré glands: tubuloacinar-mucinous glands with uniform, pale eosinophilic to clear cytoplasm and basally flattened nuclei in penile urethra (Mills: Histology for Pathologists, 4th Edition, 2012)
- Intraepithelial (juxtaepithelial) glands: nests of cells with eosinophilic to flocculent cytoplasm with basally placed nucleus located at the junction of the epithelium and subepithelium