þvagrásin

The urethra, known as þvagrásin in Icelandic, is a tube that connects the bladder to the outside of the body. Its primary function in both males and females is to expel urine from the bladder during urination. The length and structure of the urethra differ significantly between the sexes.

In females, the urethra is relatively short, measuring about 4 centimeters (1.6 inches) in length. It originates from the internal urethral orifice of the bladder and terminates at the external urethral meatus, located between the clitoris and the vagina. Due to its short length and proximity to the anus, women are more susceptible to urinary tract infections.

In males, the urethra is considerably longer, approximately 20 centimeters (7.9 inches). It begins at the internal urethral orifice of the bladder and passes through the prostate gland, the pelvic diaphragm, and finally through the penis to the external urethral orifice at the tip of the glans. In males, the urethra serves a dual role, also acting as a passageway for semen during ejaculation. The prostatic urethra, the membranous urethra, and the penile (spongy) urethra are its distinct parts.

The lining of the urethra is composed of stratified squamous epithelium, which changes to pseudostratified columnar epithelium in some sections. Several small glands called urethral glands secrete mucus, which helps to lubricate the passage and protect its lining. The expulsion of urine is controlled by two sphincters: the internal urethral sphincter, made of smooth muscle and involuntary, and the external urethral sphincter, made of skeletal muscle and under voluntary control.