The urethra is a relatively thin-walled, muscular tube that conveys urine from the urinary bladder to outside the body.
Urethra
The urethra is a relatively thin-walled, muscular tube that
conveys urine from the urinary bladder to outside the body. It is lined with mucous
membrane known as pseudostratified columnar epithelium and a thick layer of
smooth muscle tissue. The portions of the ure-thra nearer the urinary bladder
become transitional epithelium. The wall of the urethra has many mucous glands,
also called urethral glands, which
secrete mucus into the urethral canal. In females, the urethra is only about
3–4 cm or 1.5 inches long, opening via the external
urethral orifice or urinary meatus.
In males, the urethra is about 20 cm or 8 inches long. It
functions as part of both the urinary and repro-ductive systems, extending from
the bladder to the tip of the penis. In both males and females, the portion of
the urethra near the external opening becomes protective stratified squamous
epithelium. There are three regions of the urethra in males: the prostatic, membranous, and spongy urethra. The prostatic
urethra is inside the prostate gland and is about 2.5 cm or 1 inch in length. The membranous urethra is its intermediate portion,
located inside the urogenital diaphragm. It extends from the prostate for about
2 cm to the beginning of the penis. The spongy urethra is about 15 cm in length,
continu-ing throughout the penis up to its opening at the tip.
The detrusor muscle
originating in the bladder becomes thicker, forming the internal urethral sphincter at
the junction of the urethra and the blad-der. This sphincter is involuntary and
is controlled by the autonomic nervous system to prevent leaking of urine. As
the urethra passes through the urogenital diaphragm, it is surrounded by
the external urethral sphincter.
This sphincter is voluntarily controlled.
Another muscle, the levator ani,
helps in voluntary constriction of the urethra.
1. Describe the structures needed for urination.
2. What is the amount of urine in the bladder that usually
triggers the urge to urinate?
3. Contrast
the female and male urethra.
TH 2019 - 2023 pharmacy180.com; Developed by Therithal info.