Urethra

Epithelial Cells

Urethras can vary in length depending on the placement of the bladderA muscular organ that stores urine before excretion. and other pelvic organs. Toward the trigoneA triangular area in the bladder between the ureter openings and the urethra, important for directin of the bladder, the urethraThe tube that carries urine from the bladder to the outside of the body. is made of transitional epithelial tissue. This tissue has characteristic cuboidal cellsThe basic structural and functional units of life. with a dome shape on the apical surface. As the urethra approaches the external urethral orifice, it transitions into stratified squamous tissue. This then seamlessly turns into the cutaneous membrane. As with many orifices, the stratified squamous cells allow some to be lost as urineThe liquid waste excreted by the kidneys. exits with no consequences.

Longer Lengths

Short urethras are pretty straighforward in their transition from bladder connection to external urethral orifice. Urethras that involve a penis have more sections to them, usually named for the surrounding tissue. For example, the prostatic urethra runs through the prostate gland, located around the trigone of the bladder. The prostatic urethra collects output from the ureterThe tube that carries urine from the kidney to the bladder. and the ejaculatory duct (an extension of the vas deferns). When it exits the prostate, it becomes the membranous urethra for a very short segment. Then it dips into the erectile tissue of the penis. There, it becomes the spongy urethra and is surrounded by the corpus spongiosum, one of three erectile bodies.