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The human male urethra laid open on its anterior (upper) surface. In the human male, the urethra is on average 18 to 20 centimeters (7 to 8 inches) long and opens at the end of the external urethral meatus. [10] The urethra is divided into four parts in men, named after the location: [10]
The distal section of the urethra allows a human male to direct the stream of urine by holding the penis. This flexibility allows the male to choose the posture in which to urinate. In cultures where more than a minimum of clothing is worn, the penis allows the male to urinate while standing without removing much of the clothing.
Inside the penis is the urethra, which is used to ejaculate semen and to excrete urine. Both substances exit through the meatus. When a male becomes sexually aroused, erection occurs because sinuses within the erectile tissues of the penis (corpora cavernosa and corpus spongiosum) become filled with blood.
The human urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites , and regulate blood pH .
Bilateral to the urethral fold, genital swellings become prominent. These structures are the future scrotum and labia majora in males and females, respectively. The genital tubercles of an eight-week-old embryo of either sex are identical.
In males, the internal urethral sphincter has the additional function of preventing the flow of semen into the male bladder during ejaculation. [3] Females do have a more elaborate external sphincter muscle than males as it is made up of three parts: the sphincter urethrae, the urethrovaginal muscle, and the compressor urethrae.
The membranous urethra or intermediate part of male urethra is the shortest, least dilatable, and, with the exception of the urinary meatus, the narrowest part of the urethra. [citation needed] It extends from the apex of the prostate proximally to the bulb of urethra distally. It measures some 12 mm in length. It traverses the pelvic floor.
The urethral crest is an anatomical feature present in the urinary system of both males and females. In males, the urethral crest is known as the crista urethralis masculinae , or the crista phallica , and is a longitudinal fold on the posterior wall of the urethra extending from the uvula of the bladder through the prostatic urethra . [ 1 ]