1) General Zoological Data
Lowland gorillas are an African species. There are local differences in phenotype and genetic makeup that subdivide Eastern and Western gorillas into subspecies, with perhaps additional subspecies. The larger Mountain gorilla placenta has not been studied and none of this endangered species are in captivity. Numerous gorillas have bred in captivity, in various zoos (Cousins, 1976). The largest colony exists in Aspinall's Howletts and Port Lympne Parks, Kent, UK (Aspinall, 1982). In Africa, the principal predator of gorillas is the leopard. Osteomyelitis from such an apparent attack has been reported by Tutin & Benirschke (1991).
term gorilla placenta, maternal surface at left.
Note the long umbilical cord with few twists. Note also the circummarginate insertion of the membranes on the right.
2) General Gestational Data
Adult females weigh from 70-140 kg (Nowak & Paradiso, 1983). Newborns weigh around 2 kg and have closed skull sutures with thick skull bones. The estrous cycle is 31 days; usually one young is born after 251-295 days of gestation. Twins are uncommon and are usually stillborn or aborted (Rosen, 1972). The newborn weight is about 1.6 to 2 kg at term. Sexual maturity of females is reached at 8 years, and at 11 years in males. In captivity, the lifespan is over 50 years. The placental weight, at term (excluding membranes and cord), is around 350 g. The average placental disk measures approximately 15 x 13 x 2 cm. The membranes (chorion laeve) attach marginally or in a circummarginate fashion. The organ bears great similarity to human placentas, except for its smaller size and the longer umbilical cord. The most recently studied placenta from the "Safari Center" at San Diego Zoo Global was 15 cm in diameter and weighed 225 g. It had the cord knot to be described below.
Wislocki (1932) has described the anatomy and histology of the female reproductive tract, including placentation, in great detail.
|Gorilla group at the Wild Animal Park of the Zoological Society of San Diego.|
|Mother and neonate gorilla at San Diego's Wild Animal Park.|
As is true of the human placenta, the gorilla placenta implants "interstitially", with decidua surrounding the entire implanted blastocyst. Once the membranes "herniate" into the uterine cavity, the peripheral villi, those on the membrane surface, atrophy. Implantation of the blastocyst onto the other endometrial surface does not occur. Thus, a single discoid organ forms with membranes like those in humans. The placenta is anterior or posterior in its location. A wide margin of membranes separates it from the endocervical canal.
4) General Characterization of the Placenta
Other than for their smaller size, the discoid shape and appearance of the gorilla placenta are very similar to those of human placentas. It is cotyledonary with few, relatively indistinct cotyledonary subdivisions seen on the maternal surface. There are much basal calcification and a considerable amount of fibrinoid material. The barrier is identical to that of humans, it is hemochorial and there is moderately extensive trophoblastic invasion of the endometrium and probably also invasion of the superficial myometrium. Vascular trophoblastic invasion occurs in the decidua basalis. There are large deposits of extravillous trophoblast ("X-cells") and some have cystic centers. The same cells infiltrate into the decidua basalis.
|Cyst of extravillous trophoblast ("X-cells")|
|Term gorilla placental villus. It is much like the human.|
5) Details of fetal/maternal barrier
The surface area of villous structures was determined by Baur (1970). It is similar to that of other ape placentas and humans. The surface is composed of syncytiotrophoblast with underlying cytotrophoblast. The syncytium has brush (microvillous) borders.
|Placental floor, villi below, much fibrinoid and mild calcification|
|More term villi of gorilla placenta.|
7) Uteroplacental circulation
This is essentially the same as in human gestations, except that the maternal decidual arterioles usually have thicker walls.
|Membranes with chorion at left and decidua at right. Note the thick, hyalinized arterioles.|
8) Extraplacental membranes
Wislocki (1932) and others have shown the presence of a decidua capsularis with remnants of villi in the chorion laeve. The amnion is identical to the human placental amnion, and there is no allantoic membrane.
|Membranes with atrophied villus in between decidua (right) and chorion (left), within trophoblast layer.|
9) Trophoblast external to barrier
There are extensive islands of "X-cells" and there is invasion by extravillous trophoblast into the decidua basalis and into the maternal vessels. Whether it also extends into the myometrium, as is true in humans, is unknown.
placentae with green and yellow
discoloration at left; at right is the underlying
infarct (From Benirschke, 1980).
|Term gorilla placental villi with focal necrosis and hemosiderin deposition in villus. The cause is unknown; in human placentas this would be suspicious of former hemorrhage or CMV infection.|
16) Physiological data
Whereas alkaline phosphatase, (the most abundant enzyme of human placentas), is present in placentas of chimpanzees and orangutans, it is extremely low or absent in gorilla placentas (Doellgast et al., 1979, 1981). Information on blood groups and many other physiological data can be found in Benirschke, 1986.
Sonographic estimation of birth size has been advanced by Yeager et al. (1981).
Other features of interest
abortus with hydatid villi lacking
vessels and degenerating decidua. This is essentially
similar to a human spontaneous abortus
due to chromosomal error.
|This is another view of the aborted pregnancy. The villi are significantly enlarged (swollen, "hydatid"), but there is still a floor of decidua basalis. Villi contain no vessels and are comparable to what in human pregnancies might be a "partial mole" due to triploidy. No trophoblastic proliferation.|
|Another, similar spontaneous abortus.|
|A very young spontaneous abortus with defective embryo in the center of a blood-filled chorion.|
of mature placenta with live infant
Decidual necrosis is on top.
|Histologic appearance of the infarcted placental tissue.|
|Gorilla placenta with fetal vascular latex injection- note marginal cord and one-to-one correspondence of fetal blood vessels.|
|Knot in umbilical cord of gorilla placenta, at right.|
|Five year-old male gorilla with growth retardation, presumably due to a large deletion of a portion of one chromosome # 3.|
|Stillborn gorilla male. Fetal death because of abruptio placentae.|
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