Seminal vesicles

The seminal vesicles (also called vesicular glands<ref Name="Wilke">Template:Cite book</ref> or seminal glands) are a pair of convoluted tubular accessory glands that lie behind the urinary bladder of male mammals. They secrete fluid that largely composes the semen.

The vesicles are 5–10 cm in size, 3–5 cm in diameter, and are located between the bladder and the rectum. They have multiple outpouchings, which contain secretory glands, which join together with the vasa deferentia at the ejaculatory ducts. They receive blood from the vesiculodeferential artery, and drain into the vesiculodeferential veins. The glands are lined with column-shaped and cuboidal cells. The vesicles are present in many groups of mammals, but not marsupials, monotremes or carnivores.

Inflammation of the seminal vesicles is called seminal vesiculitis and most often is due to bacterial infection as a result of a sexually transmitted infection or following a surgical procedure. Seminal vesiculitis can cause pain in the lower abdomen, scrotum, penis or peritoneum, painful ejaculation, and blood in the semen. It is usually treated with antibiotics, although may require surgical drainage in complicated cases. Other conditions may affect the vesicles, including congenital abnormalities such as failure or incomplete formation, and, uncommonly, tumours.

The seminal vesicles have been described as early as the second century AD by Galen, although the vesicles only received their name much later, as they were initially described using the term from which the word prostate is derived.

Structure

The human seminal vesicles are a pair of glands in males that are positioned below the urinary bladder and at the end of the vasa deferentia, where they enter the prostate. Each vesicle is a coiled and folded tube, with occasional outpouchings termed diverticula in its wall.<ref name=HistologyText>Template:Cite book</ref> The lower part of the tube ends as a straight tube called the excretory duct, which joins with the vas deferens of that side of the body to form an ejaculatory duct. The ejaculatory ducts pass through the prostate gland before opening separately into the verumontanum of the prostatic urethra.<ref name="HistologyText" /> The vesicles are between 5–10 cm in size, 3–5 cm in diameter, and have a volume of around 13 mL.<ref name="Grays2016">Template:Cite book</ref>

The vesicles receive blood supply from the vesiculodeferential artery, and also from the inferior vesical artery. The vesiculodeferential artery arises from the umbilical arteries, which branch directly from the internal iliac arteries.<ref name="Grays2016" /> Blood is drained into the vesiculodeferential veins and the inferior vesical plexus, which drain into the internal iliac veins.<ref name="Grays2016" /> Lymphatic drainage occurs along the venous routes, draining into the internal iliac nodes.<ref name="Grays2016" />

The vesicles lie behind the bladder at the end of the vasa deferentia. They lie in the space between the bladder and the rectum; the bladder and prostate lie in front, the tip of the ureter as it enters the bladder above, and Denonvilliers' fascia and the rectum behind.<ref name="Grays2016" />

Development

Template:Further In the developing embryo, at the hind end lies a cloaca. This, over the fourth to the seventh week, divides into a urogenital sinus and the beginnings of the anal canal, with a wall forming between these two inpouchings called the urorectal septum.<ref name=Langman2019>Template:Cite book</ref> Two ducts form next to each other that connect to the urogenital sinus; the mesonephric duct and the paramesonephric duct, which go on to form the reproductive tracts of the male and female respectively.<ref name=Langman2019 />

In the male, under the influence of testosterone, the mesonephric ducts proliferate, forming the epididymis, ductus deferens and, via a small outpouching near the developing prostate, the seminal vesicles.<ref name=Langman2019 /> Sertoli cells secrete anti-Müllerian hormone, which causes the paramesonephric ducts to regress.<ref name=Langman2019 />

The development and maintenance of the seminal vesicles, as well as their secretion and size/weight, are highly dependent on androgens.<ref name="FeyHeni2012">Template:Cite book</ref><ref name="pmid11753468">Template:Cite journal</ref> The seminal vesicles contain 5α-reductase, which metabolizes testosterone into its much more potent metabolite, dihydrotestosterone (DHT).<ref name="pmid11753468" /> The seminal vesicles have also been found to contain luteinizing hormone receptors, and hence may also be regulated by the ligand of this receptor, luteinizing hormone.<ref name="pmid11753468" />

Microanatomy

File:Histology of seminal vesicle glands on H&E stain.jpg

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The inner lining of the seminal vesicles (the epithelium) is made of a lining of interspersed column-shaped and cube-shaped cells.<ref name=Wheaters2013 /> There are varying descriptions of the lining as being pseudostratified and consisting of column-shaped cells only.<ref name=Smiths2019>Template:Cite book</ref> When viewed under a microscope, the cells are seen to have large bubbles in their interior. This is because their interior, called cytoplasm, contains lipid droplets involved in secretion during ejaculation.<ref name=Wheaters2013>Template:Cite book</ref> The tissue of the seminal vesicles is full of glands, spaced irregularly.<ref name=Wheaters2013 /> As well as glands, the seminal vesicles contain smooth muscle and connective tissue.<ref name=Wheaters2013 /> This fibrous and muscular tissue surrounds the glands, helping to expel their contents.<ref name="Grays2016" /> The outer surface of the glands is covered in peritoneum.<ref name="Grays2016" />

• Seminal vesicle low mag.jpg

  Low magnification micrograph of seminal vesicle. H&E stain.

• Seminal vesicle high mag.jpg

  High magnification micrograph of seminal vesicle. H&E stain.

Function

The seminal vesicles secrete a significant proportion of the fluid that ultimately becomes semen.<ref name=GH2016>Template:Cite book</ref> Fluid is secreted from the ejaculatory ducts of the vesicles into the vas deferens and ejaculated through the urethra during the male sexual response.<ref name="Smiths2019" />

About 70-85% of the seminal fluid in humans originates from the seminal vesicles.<ref name=kierszenbaum558>Template:Cite book</ref> The fluid consists of nutrients including fructose and citric acid, prostaglandins, and fibrinogen.<ref name=GH2016 /> Fructose is not produced anywhere else in the body except in the seminal vesicles. It provides a forensic test in rape cases.

Nutrients help support sperm until fertilisation occurs; prostaglandins may also assist by softening mucus of the cervix, and by causing reverse contractions of parts of the female reproductive tract such as the fallopian tubes, to ensure that sperm are less likely to be expelled.<ref name="GH2016" />

Clinical significance

Disease

Diseases of the seminal vesicles as opposed to that of prostate gland are extremely rare and are infrequently reported in the medical literature.<ref>Dagur G, Warren K, Suh Y, Singh N, Khan SA. Detecting diseases of neglected seminal vesicles using imaging modalities: A review of current literature. Int J Reprod Biomed. 2016;14(5):293-302.</ref>

Congenital anomalies associated with the seminal vesicles include failure to develop, either completely (agenesis) or partially (hypoplasia), and cysts.<ref name="smiths" /><ref name="causes" /> Failure of the vesicles to form is often associated with absent vas deferens, or an abnormal connection between the vas deferens and the ureter.<ref name="Grays2016" /> The seminal vesicles may also be affected by cysts, amyloidosis, and stones.<ref name="smiths" /><ref name="causes" /> Stones or cysts that become infected, or obstruct the vas deferens or seminal vesicles, may require surgical intervention.<ref name="Smiths2019" />

Seminal vesiculitis (also known as spermatocystitis) is an inflammation of the seminal vesicles, most often caused by bacterial infection.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Symptoms can include vague back or lower abdominal pain; pain of the penis, scrotum or peritoneum; painful ejaculation; blood in the semen on ejaculation; irritative and obstructive voiding symptoms; and impotence.<ref>Template:Cite book</ref> Infection may be due to sexually transmitted infections, as a complication of a procedure such as prostate biopsy.<ref name="Smiths2019" /> It is usually treated with antibiotics. If a person experiences ongoing discomfort, transurethral seminal vesiculoscopy may be considered.<ref name="pmid21696400">Template:Cite journal</ref><ref name="pmid24391141">Template:Cite journal</ref> Intervention in the form of drainage through the skin or surgery may also be required if the infection becomes an abscess.<ref name="Smiths2019" /> The seminal vesicles may also be affected by tuberculosis, schistosomiasis and hydatid disease.<ref name="smiths">Template:Cite book</ref><ref name="causes">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> These diseases are investigated, diagnosed and treated according to the underlying disease.<ref name="Smiths2019" />

Benign tumours of the seminal vesicles are rare.<ref name="Smiths2019" /> When they do occur, they are usually papillary adenomata and cystadenomata. They do not cause elevation of tumour markers and are usually diagnosed based on examination of tissue that has been removed after surgery.<ref name="Smiths2019" /> Primary adenocarcinoma, although rare, constitutes the most common malignant tumour of the seminal vesicles;<ref name=":0" /> that said, malignant involvement of the vesicles is typically the result of local invasion from an extra-vesicular lesion.<ref name="Smiths2019" /> When adenocarcinoma occurs, it can cause blood in the urine, blood in the semen, painful urination, urinary retention, or even urinary obstruction.<ref name="Smiths2019" /> Adenocarcinomata are usually diagnosed after they are excised, based on tissue diagnosis.<ref name="Smiths2019" /> Some produce the tumour marker Ca-125, which can be used to monitor for reoccurence afterwards.<ref name="Smiths2019" /> Even rarer neoplasms include sarcoma, squamous cell carcinoma, yolk sac tumour, neuroendocrine carcinoma, paraganglioma, epithelial stromal tumours and lymphoma.<ref name=":0">Template:Cite journal</ref>

Investigations

Symptoms due to diseases of the seminal vesicles may be vague and not able to be specifically attributable to the vesicles themselves; additionally, some conditions such as tumours or cysts may not cause any symptoms at all.<ref name="Smiths2019" /> When diseases is suspected, such as due to pain on ejaculation, blood in the urine, infertility, due to urinary tract obstruction, further investigations may be conducted.<ref name="Smiths2019" />

A digital rectal examination, which involves a finger inserted by a medical practitioner through the anus, may cause greater than usual tenderness of the prostate gland, or may reveal a large seminal vesicle.<ref name="Smiths2019" /> Palpation is dependent on the length of index finger as seminal vesicles are located above the prostate gland and retrovesical (behind the bladder).

A urine specimen may be collected, and is likely to demonstrate blood within the urine.<ref name="Smiths2019" /> Laboratory examination of seminal vesicle fluid requires a semen sample, e.g. for semen culture or semen analysis. Fructose levels provide a measure of seminal vesicle function and, if absent, bilateral agenesis or obstruction is suspected.<ref name="smiths" />

Imaging of the vesicles is provided by medical imaging; either by transrectal ultrasound, CT or MRI scans.<ref name="Smiths2019" /> An examination using cystoscopy, where a flexible tube is inserted in the urethra, may show disease of the vesicles because of changes in the normal appearance of the nearby bladder trigone, or prostatic urethra.<ref name="Smiths2019" />

Other animals

The evolution of seminal vesicles may have been influenced by sexual selection.<ref name=":1" /> They occur in birds and reptiles<ref>Template:Cite book</ref> and many groups of mammals,<ref name="Kardong2019" /> but are absent in marsupials,<ref>Template:Cite book</ref><ref>Template:Cite book</ref> monotremes, and carnivorans.<ref name="Marx2009" /><ref name=":1">Dixson, Alan F. "Sexual selection and evolution of the seminal vesicles in primates." Folia Primatologica 69.5 (1998): 300-306.</ref> The function is similar in all mammals they are present in, which is to secrete a fluid as part of semen that is ejaculated during the sexual response.<ref name=Kardong2019>Template:Cite book</ref>

History

The action of the seminal vesicles has been described as early the second century AD by Galen, as "glandular bodies" that secrete substances alongside semen during reproduction.<ref name=Marx2009>Template:Cite journal</ref> By the time of Herophilus the presence of the glands and associated ducts had been described.<ref name="Marx2009" /> Around the time of the early 17th century the word used to describe the vesicles, parastatai, eventually and unambiguously was used to refer to the prostate gland, rather than the vesicles.<ref name="Marx2009" /> The first time the prostate was portrayed in an individual drawing was by Reiner De Graaf in 1678.<ref name="Marx2009" />

The first described use of laparoscopic surgery on the vesicles was described in 1993; this is now the preferred approach because of decreased pain, complications, and a shorter hospital stay.<ref name="Smiths2019" />

Additional images

• Pelvic MRI T1FSE T2frFSE T2FSfrFSE 11.jpg

  Seminal vesicles seen on an MRI scan through the pelvis. The large cyan-coloured area is the bladder, and the lobulated smaller structures below it are the vesicles.

• Seminal vesicles.jpg

  Seminal vesicles seen in a cadaveric specimen from on top, with the bladder to the bottom of the image, and the rectum at the top. Their position near the vas deferentia can be seen.

• Gray1152.png

  Fundus of the bladder with the vesiculae seminales.

See also

• Male accessory gland infection (MAGI)
• Ejaculatory duct
• Urethra
• Prostate
• List of distinct cell types in the adult human body

External links

• Template:BUHistology - "Male Reproductive System: prostate, seminal vesicle"
• Template:SUNYAnatomyLabs - "The Male Pelvis: The Urinary Bladder"
• Template:SUNYAnatomyLabs - "The Male Pelvis: Structures Located Posterior to the Urinary Bladder"

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