Urethra plays a very vital role in human excretory system. It is prone to several diseases. In this article on urethra facts we are going to learn about this important organ and also learn how it differs between males and females. Pay attention as it may become a bit confusing. Let’s begin…
Urethra Facts: 1-5
2. Urethra is different in males and females. In males, the urethra carries both semen and urine. In females, the urethra carries only urine. The opening of the urethra or the urinary meatus is present above vagina.
3. There is sphincter1 known as external urethral sphincter (made of striated muscles, hence under voluntary control) which controls the passage of urine.
4. In females it is present at the distal (far) end of the urinary bladder whereas in males it is located below the prostate gland2.
5. Males have another sphincter known as internal urethral sphincter. This internal urethral sphincter is absent in females. In males it is present at the junction of urinary bladder and urethra. It is made of smooth muscles, hence under involuntary control. In males, during ejaculation, the internal urethral sphincter contracts so that the semen doesn’t enter the urinary bladder.
Urethra Facts: 6-10
6. Males have longer urethra compared to females. On an average, the urethra of men is about 20 centimeters or 8 inches. Urethra in males has been divided into four parts and are named based on the location.
The four parts of male urethra are (points 7 to 15):
7. Pre-prostatic urethra – It is the intramural part of the urethra3. It consists of transitional epithelium. Depending on whether the bladder is empty or full, the length of the urethra can be 0.5 centimeters to 1.5 centimeters.
8. Prostatic urethra – It moves through the prostate gland. It also consists of transitional epithelium.
9. Ejaculatory duct4 opens into the urethra which receives sperms from vas deferens5 and fluid from the seminal vesicle6.
10. Many of the prostate ducts also open in to the urethra and contain the ejaculate secreted by the prostate gland. An indentation (dent or cavity) known as prostate utricle is also seen. All these openings together are called Verumontanum.
Urethra Facts: 11-15
11. Membranous urethra – This part of the urethra passes through the external urethral sphincter. Its length is 1-2 centimeters and is the urethra’s narrowest part. The bulbourethral gland or the Cowper’s glands are present posterior to the membranous urethra.
12. Membranous urethra is located in the deep perineal pouch7. It consists of pseudostratified epithelium.
13. Spongy urethra – Longest part of the urethra. It is present all across the length of the penis. It is surrounded by corpus spongiosum (a spongy tissue). Urethral gland or gland of Litte duct opens into urethra here. Cowper’s glands duct also opens into spongy urethra.
14. The proximal end of the spongy urethra consists of pseudostratified columnar epithelium and the distal end consists of squamous epithelium.
15. Lumen8 of the urethra is parallel to the lumen of the penis except at one point – the external urethral opening where it runs vertical. It is because of this arrangement of the lumen that urine ejects as spiral stream and helps in cleaning the external urethral opening. This kind of mechanism is absent in females and this is the reason for females have greater chances of contracting UTI (Urinary Tract Infections) compared to males.
Urethra Facts: 16-20
16. In females, the urethra is about 2 inches or 5 centimeters long. The opening of the urethra is present between the clitoris and vagina. The urethra is embedded in the wall of the vagina.
17. The proximal end of urethra in females consists of transitional epithelium and the distal end consists stratified squamous epithelium. In females, only external urethral sphincter is present. There are three layers of urethra – muscular, erectile and mucous.
18. The external urethral sphincter of the females consists of three parts – sphincter urethrae (which covers only the urethra), urethrovaginal muscle (wraps both urethra and vagina, so when the muscle contracts, both the vagina and urethra gets contracted) and compressor urethrae (wraps around the urethra anteriorly so that when contracted, urethra presses against the vagina).
19. When we urinate, the urinary bladder releases urine with force and to accommodate this, the urethra relaxes and allows the passage of the urine and expels the urine in streams. After urination, the urethra contracts and urinary bladder relaxes.
20. In males, there is another function of urethra. Like urine, semen also exits the body through urethra.
Urethra Facts: 21-25
21. There are many diseases related to the urethra. Hypospadias is a condition where the opening of urethra is on the penis’ underside and Epispadias is a condition where the meatus is above than where it should have been. Both of these occur only in males.
22. Urethra’s infection is known as urethritis. As said earlier, females are much more prone to such diseases compared to males. The common cause of Dysuria9 is urethritis.
23. Urethral stricture is a condition where the urethra narrows down due to injuries, infections etc. One of the reasons for urethral strictures is kidney stones passage to the urethra. There is something called Urethral Syndrome – where the symptoms are present but there is no infection.
24. Other diseases are injuries to urethra, cancer of urethra and infections due to the insertion of the foreign bodies in the urethra (rare). Retrograde urethrogram is a radiological procedure used to detect any injuries of the urethra.
25. Catheter10 is inserted to remove urine from the urinary bladder when a person is hospitalized. Urinary catheterization is difficult in men than in females because there is a bend at the start of the spongy urethra.
Glossary of terms
Sphincter1: A circular muscle which controls the passage of some material.
Prostate Gland2: One of the glands of the male reproductive system which secretes 30% of the semen.
Intramural part of the urethra3: The pre-prostatic urethra is so called because it passes nearly vertically through urinary bladder’s wall before entering into prostate gland.
Ejaculatory duct4: Duct formed by vas deferens and duct of seminal vesicle.
Vas deferens5: Tube like structures which transport sperm from epididymis† to ejaculatory duct.
Epididymis†: Epididymis is a convoluted duct which transports sperm from testis to vas deferens.
Seminal vesicle6: Also known as seminal glands are those vesicles or glands whose secretion contains some semen.
Perineal pouch7: It is the anatomical space which is partly covered by the perineum*.
Perineum*: It is the space present between anus and scrotumǂ in males and anus and vulva‼ in females
Scrotumǂ: It is a pouch of skin containing the testicles in males.
Vulva‼: It is the external opening of the vagina in females.
Lumen8: It is the central cavity present in hollow structures or tubular structures in an organism or a cell.
Dysuria9: It is the pain experienced while urinating.
Catheter10: It is a flexible tube used in medical science for inserting it into a narrow opening in human body cavity. Usually it is inserted into the bladder for fluid removal.