Each tube is a muscularhollow organ[3] that is on average between 10 and 14 cm (3.9 and 5.5 in) in length, with an external diameter of 1 cm (0.39 in).[4] It has four described parts: the intramural part, isthmus, ampulla, and infundibulum with associated fimbriae. Each tube has two openings: a proximal opening nearest to the uterus, and a distal opening nearest to the ovary. The fallopian tubes are held in place by themesosalpinx, a part of thebroad ligamentmesentery that wraps around the tubes. Another part of the broad ligament, themesovarium suspends the ovaries in place.[5]
Almost a third of cases ofinfertility are caused by fallopian tube pathologies. These includeinflammation, andtubal obstructions. A number of tubal pathologies cause damage to the cilia of the tube, which can impede movement of the sperm or egg.[7]
Each fallopian tube leaves the uterus at an opening at theuterine horns known as theproximal tubal opening orproximal ostium.[9] The tubes have an average length of 10–14 centimeters (3.9–5.5 in)[4] that includes the intramural part of the tube. The tubes extend to near the ovaries where they open into the abdomen at thedistal tubal openings. In othermammals, the fallopian tube is called theoviduct, which may also be used in reference to the fallopian tube in thehuman.[10][11] The fallopian tubes are held in place by themesosalpinx a part of thebroad ligamentmesentery that wraps around the tubes. Another part of the broad ligament, themesovarium suspends the ovaries in place.[5]
Each tube is composed of four parts: from inside the proximal tubal opening the intramural or interstitial part, that links to the narrow isthmus, the isthmus connects to the larger ampulla, which connects with the infundibulum and its associated fimbriae that opens into theperitoneal cavity from the distal tubal opening.[12]
The intramural part or interstitial part of the fallopian tube lies in themyometrium, the muscular wall of the uterus. This is the narrowest part of the tube that crosses the uterus wall to connect with the isthmus. The intramural part is 0.7 mm wide and 1 cm long.[12]
The narrow isthmus links the tube to the uterus, and connects to the ampulla. The isthmus is a rounded, and firm muscular part of the tube. The isthmus is 1–5 mm wide, and 3 cm long.[12] The isthmus contains a large number of secretory cells.[10]
The ampulla is the major part of the fallopian tube. The ampulla is the widest part of the tube with a maximal luminal diameter of 1 cm, and a length of 5 cm. It curves over the ovary, and is the primary site of fertilization.[12] The ampulla contains a large number of ciliated epithelial cells.[10] It is thin walled with a much folded luminal surface, and opens into the infundibulum.[12]
The infundibulum opens into the abdomen at the distal tubal opening and rests above the ovary. Most cells here are ciliated epithelial cells.[10] The opening is surrounded byfimbriae, which help in the collection of the oocyte after ovulation.[4] The fimbriae (singular fimbria) is a fringe of densely ciliated tissue projections of approximately 1 mm in width around the distal tubal opening, oriented towards the ovary.[12] They are attached to the ends of the infundibulum, extending from its inner circumference, and muscular wall.[12] The cilia beat towards the fallopian tube.[12] Of all the fimbriae, one fimbria known as theovarian fimbria (orfimbria ovarica) is long enough to reach and make contact with the near part of the ovary during ovulation.[13][14][12] The fimbriae have a higher density of blood vessels than the other parts of the tube, and the ovarian fimbria is seen to have an even higher density.[8]
An ovary is not directly connected to its adjacent fallopian tube. When ovulation is about to occur, thesex hormones activate the fimbriae,[citation needed] causing them to swell with blood, extend, and hit the ovary in a gentle, sweeping motion. An oocyte is released from the ovary into the peritoneal cavity and the cilia of the fimbriae sweep it into the fallopian tube.[citation needed]
The outermost covering layer ofserous membrane is known as the serosa.[6] The serosa is derived from the visceralperitoneum.[14]
The muscularis mucosae consists of an outer ring ofsmooth muscle arranged longitudinally, and a thick inner circular ring of smooth muscle.[6] This layer is responsible for the rhythmicperistaltic contractions of the fallopian tubes, that with the cilia move the egg cell towards the uterus.[14]
The innermost mucosa is made up of a layer of luminal epithelium, and an underlying thin layer ofloose connective tissue thelamina propria.[16] There are three different cell types in the epithelium. Around 25% of the cells are ciliated columnar cells; around 60% are secretory cells, and the rest arepeg cells thought to be a secretory cell variant.[4] The ciliated cells are most numerous in the infundibulum, and the ampulla.Estrogen increases the formation of cilia on these cells. Peg cells are shorter, have surfacemicrovilli, and are located between the other epithelial cells.[6] The presence ofimmune cells in the mucosa has also been reported with the main type beingCD8+ T-cells. Other cells found areB lymphocytes,macrophages,NK cells, anddendritic cells.[16]
The histological features of tube vary along its length. The mucosa of the ampulla contains an extensive array of complex folds, whereas the relatively narrow isthmus has a thick muscular coat and simple mucosal folds.[14]
Stages of development of theparamesonephric ducts (Müllerian ducts), and their normal and abnormal development
Embryos develop agenital ridge that forms at their tail end and eventually forms the basis for theurinary system andreproductive tracts. Either side and to the front of this tract, around the sixth week develops a duct called theparamesonephric duct, also called the Müllerian duct.[17] A second duct, themesonephric duct, develops adjacent to this. Both ducts become longer over the next two weeks, and the paramesonephric ducts around the eighth week cross to meet in the midline and fuse.[17] One duct then regresses, with this depending on whether the embryo is geneticallyfemale ormale. In females, the paramesonephric duct remains, and eventually forms the female reproductive tract.[17] The portions of the paramesonephric duct, which are morecranial—that is, further from the tail-end, end up forming the fallopian tubes.[17] In males, because of the presence of the Y sexchromosome,anti-Müllerian hormone is produced. This leads to the degeneration of the paramesonephric duct.[17]
As the uterus develops, the part of the fallopian tubes closer to the uterus, the ampulla, becomes larger. Extensions from the fallopian tubes, the fimbriae, develop over time. Cell markers have been identified in the fimbriae, which suggests that their embryonic origin is different from that of the other tube segments.[8]
Apart from the presence of sex chromosomes, specific genes associated with the development of the fallopian tubes include theWnt andHox groups of genes,Lim1,Pax2, andEmx2.[17]
Embryos have two pairs of ducts that will letgametes out of the body when they are adults; the paramesonephric ducts develop in females into the fallopian tubes, uterus, andvagina.
Afterovulation, the egg (oocyte) passes from the ovary (left) through the fallopian tube to the uterus (right).
The fallopian tube allows the passage of an egg from the ovary to the uterus. When anoocyte is developing in an ovary, it is surrounded by a spherical collection of cells known as anovarian follicle. Just before ovulation, the primary oocyte completesmeiosis I to form the firstpolar body and a secondary oocyte, which is arrested inmetaphase ofmeiosis II.
At the time ofovulation in themenstrual cycle, the secondary oocyte is released from the ovary. The follicle and the ovary's wall rupture, allowing the secondary oocyte to escape. The secondary oocyte is caught by the fimbriated end of the fallopian tube and travels to the ampulla. Here, the egg is able to become fertilized with sperm. The ampulla is typically where the sperm are met and fertilization occurs; meiosis II is promptly completed. After fertilization, the ovum is now called azygote and travels toward the uterus with the aid of the hairlikecilia and the activity of the muscle of the fallopian tube. The early embryo requires critical development in the fallopian tube.[10] After about five days, the newembryo enters theuterine cavity and, on about the sixth day, begins toimplant on the wall of the uterus.
The release of an oocyte does not alternate between the two ovaries and seems to be random. After removal of an ovary, the remaining one produces an egg every month.[18]
Almost a third of cases ofinfertility are caused due to fallopian tube pathologies. These include inflammation, andtubal obstructions. A number of tubal pathologies cause damage to the cilia of the tube, which can impede movement of the sperm or egg. A number ofsexually transmitted infections can lead to infertility.[7]
If ablocked fallopian tube has affected fertility, its repair where possible may increase the chances of becoming pregnant.[20] Tubal obstruction can beproximal, distal or mid-segmental. Tubal obstruction is a major cause of infertility but full testing of tubal functions is not possible. However, the testing of patency – whether or not the tubes are open can be carried out usinghysterosalpingography,laparoscopy and dye, orhystero contrast sonography (HyCoSy). During surgery, the condition of the tubes may be inspected and a dye such asmethylene blue can be injected into the uterus and shown to pass through the tubes when thecervix is occluded. As tubal disease is often related toChlamydia infection, testing forChlamydia antibodies has become a cost-effective screening device for tubal pathology.[21]
Occasionally the embryoimplants outside of the uterus, creating anectopic pregnancy. Most ectopic pregnancies occur in the fallopian tube, and are commonly known astubal pregnancies.[22]
Example and location of some surgical procedures performed on the fallopian tubes
The surgical removal of a fallopian tube is called asalpingectomy. To remove both tubes is a bilateral salpingectomy. An operation that combines the removal of a fallopian tube with the removal of at least one ovary is asalpingo-oophorectomy. An operation to remove a fallopian tube obstruction is called atuboplasty. A surgical procedure topermanently prevent conception istubal ligation.
Fallopian tube cancer, which typically arises from theepithelial lining of the fallopian tube, has historically been considered to be a very rare malignancy. Evidence suggests it probably represents a significant portion of what has previously been classified asovarian cancer, as much as 80 per cent. These are classed asserous carcinomas, and are usually located in the fimbriated distal tube.[23]
In rare cases, a fallopian tube mayprolapse into the vaginal canal following ahysterectomy. The swollen fimbriae can have the appearance of anadenocarcinoma.[24]
The Greek doctor Herophilus, in his treatise on midwifery, points out the existence of the two ducts that he supposed transported "female semen". Then Galen, already in the modern era, described that the paired ducts indicated by Herophilus were connected to the uterus.
In 1561, the Renaissance doctorGabriele Falloppio published his bookObservationes Anatomicae. Its contribution is a detailed description of the "tubal" of the uterus and its different portions, with its farthest (distal) end open towards the abdomen, and the other (proximal) connected to the uterus.[25][26]
Though the nameFallopian tube iseponymous, it is often spelt with a lower casef from the assumption that the adjectivefallopian has been absorbed into modern English as thede facto name for the structure.Merriam-Webster dictionary for example listsfallopian tube, often speltFallopian tube.[27] Falloppio called the organ "tuba uteri" because of its physical similarity to atrumpet.[28]
^abcdefghiStandring, Susan (2016).Gray's anatomy : the anatomical basis of clinical practice (Forty-first ed.). [Philadelphia]. p. 1301.ISBN9780702052309.{{cite book}}: CS1 maint: location missing publisher (link)
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