The prostatic or membranous urethra
Urethra has three regions in males, the prostatic urethra, membranous urethra, and the spongy urethra.
membranous urethra
the membranous part of urethra
prostatic portion membranous portion cavernous portion
There is no defined region of urethra: it begins a at the bladder and ends at the head of the penis. The external urethra, the area that you can see, is called the meatus.
The prostatic portion of the urethra collects seminal fluids from the prostate during ejaculation as well as providing a duct through which urine and semen can be eliminated from the body.
The male urethra is divided into threesegments.The prostatic urethra passes through the prostate gland, the urogenital diaphragm and the bulb of the urethra.The membranous urethra has the shortest length and is found between the prostatic urethra and the spongy urethra. It extends downward between the apex of the prostate and the bulb of the urethra.The spongy urethra is the longest part of the male urethra and it passes through the length of the penis, more specifically through the corpus spongiosum penis (a mass of spongy tissue surrounding the male urethra within the penis), and the glans.
Semineferous tubules, straight tubules, rete testes, efferent ducts, ductus deferens (vas deferens), ejaculatory duct, prostatis urethra, membranous urethra, spongy urethra, external urethral orifice.Testes (Testis) -> Epididymis -> Vas Deferens -> Urethra.
The three regions/sections of the male urethra are:Prostatic UrethraThe prostatic urethra begins at the neck of the bladder and includes all of the section that passes through the prostrate gland. It is the widest and most dilatable part of the male urethral canal.Membranous UrethraThe membranous urethra is the shortest and narrowest part of the male urethra. This section measures approx. 0.5 - 0.75 inches (12 - 19 mm) in length and is the section of the urethra that passes through the male urogenital diaphragm.The external urethral sphincter (muscle) is located in the urogenital diaphragm (as for the female urethra). This muscle is referred to as the "compressor urethrae muscle" in some older textbooks.The passage of urine along the urethra through the urogenital diaphragm is controlled by the external urethral sphincter, which is a circular muscle under voluntary control (that is, it is innervated by the somatic nervous system, SNS).See the page about micturation for more about control of these structures by the nervous system.Spongy UrethraThe spongy urethra is the longest of the three sections. It is approx. 6 inches (150 mm) in length and is contained in the corpus spongiosum that extends from the end of the membranous portion, passes through the penis, and terminates at theexternal orifice of the urethra - which is the point at which the urine leaves the body.
It is a membranous organ in the inner ear.
A membranous sac is, as it says, a sac with a membrane. What it is specifically varies. Bronchi in the lungs are membranous sacs and the amniotic sac on a baby is membranous.