Stereocilia (epididymis)
Encyclopedia
The stereocilia of the epididymis
are structures which aid in absorption. They are long cytoplasmic projections but have no motility.
Unlike the stereocilia
of the ear
, those in the epididymis are more like long microvilli that cover the open surface of the epididymis. These extensions increase the surface area of the cell allowing for greater absorption and secretion.
The stereocilia have no internal microtubule
structure and unlike true cilia, are non-motile. The internal actin network increases the surface area just like microvilli. Because sperm
are initially nonmotile as they leave the seminiferous tubules
, large volumes of fluid are secreted to propulse the spermatozoa, along with the cilia of the pathway to the epididymus. The core function of the stereocilia is to resorb this large volume of fluid (90% of fluid volume), as the spermatozoa start to become motile here. They do not reach full motility (hypermotility) until they reach the vagina
where the alkaline pH is neutralized by acidic vaginal fluids.
Epididymis
The epididymis is part of the male reproductive system and is present in all male amniotes. It is a narrow, tightly-coiled tube connecting the efferent ducts from the rear of each testicle to its vas deferens. A similar, but probably non-homologous, structure is found in cartilaginous...
are structures which aid in absorption. They are long cytoplasmic projections but have no motility.
Unlike the stereocilia
Stereocilia
In the inner ear, stereocilia are the mechanosensing organelles of hair cells, which respond to fluid motion in numerous types of animals for various functions, including hearing and balance. They are about 10–50 micrometers in length and share some similar features of microvilli...
of the ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
, those in the epididymis are more like long microvilli that cover the open surface of the epididymis. These extensions increase the surface area of the cell allowing for greater absorption and secretion.
The stereocilia have no internal microtubule
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...
structure and unlike true cilia, are non-motile. The internal actin network increases the surface area just like microvilli. Because sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
are initially nonmotile as they leave the seminiferous tubules
Seminiferous tubules
Seminiferous tubules are located in the testes, and are the specific location of meiosis, and the subsequent creation of gametes, namely spermatozoa....
, large volumes of fluid are secreted to propulse the spermatozoa, along with the cilia of the pathway to the epididymus. The core function of the stereocilia is to resorb this large volume of fluid (90% of fluid volume), as the spermatozoa start to become motile here. They do not reach full motility (hypermotility) until they reach the vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
where the alkaline pH is neutralized by acidic vaginal fluids.