Where does urine come from

Human beings cannot live without eating, drinking, defecating and urinating. Once we are separated from these, human beings will no longer exist. After eating every day, we will definitely excrete, which is our metabolic process. For example, when we drink water, we will feel the urge to urinate after a while. Urinating is part of our normal metabolic process. So why does the water we drink turn into urine? Where does our urine come from?

Urine comes from the urethra. The urethra is the tube that leads from the bladder to the outside of the body. The male urethra is slender, about 18 cm long, starting from the internal urethral opening of the bladder and ending at the external urethral opening. It passes through the prostate, membranous part and corpus cavernosum of the penis. The male urethra has both urination and ejaculation functions. The female urethra is thick and short, about 5 cm long. It starts from the internal urethra, passes through the front of the vagina, and opens into the vaginal vestibule. The male urethra has a sphincter composed of circular striated muscle in the membranous part of the urethra, called the external urethral sphincter, which is controlled by consciousness. When the female urethra passes through the urogenital diaphragm at the perineum, it is surrounded by the urethrovaginal sphincter, which is a striated muscle and is also controlled by the will.

The male urethra has a dual function of both urination and ejaculation.

The male urethra is about 16-22 cm long, from the urethral opening at the bladder neck to the external urethral opening. The average tube diameter is 5 to 7 mm. It can be divided into the penile part (cavernous part), bulb part, membranous part and prostatic part. Clinically, the prostatic part and the membranous part are called the posterior urethra.

The anterior urethra starts from the urethral opening and ends at the bulb. It is about 15 cm long and is covered with the corpus spongiosum of the urethra. It is attached to the two shallow grooves of the corpus spongiosum of the penis. This section of urethra is mobile and therefore not easily injured. The two ends of the anterior urethra are enlarged, one is located at the urethral opening, called the navicular fossa, and the other is located at the bulbar urethra.

The posterior urethra starts from the membranous urethra and ends at the bladder neck, and is about 4 cm long. The membranous urethra is the shortest, only about 1 cm, and is located between the two layers of triangular ligaments. It is surrounded by striated muscle, namely the external sphincter, and is the most fixed and weakest section. Improper use of urethral instruments can easily lead to injury, and the perineum is also the most vulnerable part when it is violently squeezed. The urethral prostate is about 3 cm long, starting from the triangular ligament, passing through the entire gland to the bladder neck. It is the widest part of the entire urethra. In the center of the posterior wall of this section of urethra, there is a bulge called the urethral ridge or the seminal vestibule, and there is a recess in the middle of it. There are openings of the ejaculatory ducts on both sides of the crypt, and the prostatic ductules open in the grooves on both sides of the seminal colliculus.

The female urethra is very short, only 2.5-5 cm long, with an average of 3.5 cm, and a diameter of about 8 mm. It is easy to expand and can reach 10-13 mm. It has no bends and starts from the bladder neck and runs downward and forward to the urethral opening behind the pubic symphysis in front of the vagina. The female urethra can be divided into three parts: upper, middle and lower: the tissue structure of the upper part is consistent with the bladder neck. The circular muscle of the bladder neck is continuous with the circular muscle of the upper urethra and is particularly thickened at the neck, which is different from the sphincter of the male bladder neck, which is composed of the left and right middle and outer layer muscle fibers crossing each other.