The ovarian bursa and infundibulum

Key words: canine, ovary, pyometra, infundibulum, corpora lutea

This image shows an opened ovarian bursa taken from the reproductive tract of a seven year old bitch during the luteal phase, two weeks after ovulation.

Image size: 3500x1985px

The normal, small opening to the peritoneal cavity was cut extended to show the ovary and bursa. This ovary contained 10 corpora lutea. The contralateral ovary contained several more corpora lutea and collectively they were supporting pyometra in this bitch. Her reproductive tract is shown elsewhere.

The infundibulum is usually difficult to delineate, being similar in color to the internal surface of the bursa and rather amorphous in appearance. However, when these structures are submerged in water, the infundibulim, its ostium and folded structure become obvious. The uterine tube runs within the wall of the bursa and due to the presence of large deposits of adipose tissue in this area, it is almost impossible to demonstrate without careful dissection.

Note: Humans and anthropoid apes do not have ovarian bursae but the majority of animals do. In most domestic animals, ovarian bursae are sac-like and lie adjacent to their ovaries. In other animals, canids and rodents included, the ovarian bursae cover the ovaries far more completely. In an animal with an ovarian bursa, the uterine tube (fallopian tube) runs within the wall of the bursa, connecting the infundibulim to the uterine lumen. 

In bitches, the bursa surrounds the ovary almost completely and only a small slit-like opening allows communication between the peritoneal cavity and the inside of the bursa. It is therefore, possible to ovariectomize thousands of bitches, yet never to see an ovary! Indeed, only a small section of the ovary can be seen through the opening of the ovarian bursa.

Interestingly, the purpose of ovarian bursae is not clear. They are not essential for capture of oocytes because the ovarian bursae have been surgically removed in mice but conception was still possible. Bear in mind too, that humans do not have ovarian bursae yet the world struggles with overpopulation! It is however, clear that the infundibulum plays an essential role in the capture of oocytes at the time of ovulation. Through increased turgidity and changes in cilliary action during estrus, the folds and villi of the infundibulum trap oocytes and guide them into the ampullae of the uterine tube. This is a source of amazement  because the infundibulum does not cover the ovary in any animal known to the author and in many cases lies some distance from a site of ovulation.

The macroscopic appearance of the infundibulae of various species are variable, some being folded and lace-like as in cattle and others, having thicker folds as seen here, in bitches.

References.

G.L.Kelly. 1939 Effect of opening the ovarian bursa on fecundity in the albino rat. The Anatomical Record. 73: 401–405

Knoll, B. and Talbot P. 1998. Cigarette smoke inhibits oocyte cumulus complex pick-up by the oviduct in vitro independent of ciliary beat frequency. Reproductive toxicology. 12: 57-68

Lyons, R.A. et al 2002. Fallopian tube ciliary beat frequency in relation to the stage of menstrual cycle and anatomical site. Human Reprod. 17:584-588

The  exocelom (exocoelom) of the canine feto-placental unit

Keywords: anatomy, canine, placenta, exocelom, cord

Figure 1. A fetus estimated to be approximately 46-48 days of age. Image size: 1772 x 1635 px.

The inset image has been re-used with permission from Rutgers University Press*

When one examines the canine placentation closely (or even fleetingly as fetuses are extracted from the uterus during cesarean section!) it is evident that there is no clearly delineated extra-amnionic cord. However, the extra-amnionic cord is indeed present. It is just obscured within a wide swath of tissue that bridges the gap between the amnion and the chorion. That transparent swath of tissue can be seen here, attached to the ventral aspect of the amnion along its length. Along the lower length of that swath, it is attached to the inner surface of the chorion, within the thick zonary band.

In this image, the intra-amnionic cord is obvious.

As mentioned, the canine fetus has an umbilical cord with both intra-and extra-amnionic segments, like that of an equine fetus, a convenient species for comparison. When an equine fetus is born, the extra-amnionic cord is obvious; a distinct and separate entity. Yet, this is not the case in dogs. Why? This is because there is a large, seemingly empty cavity that surrounds the extra-amnionic cord in the canine fetal-placental unit. In embryological terms, this cavity is known as the exocelom (literally: "out-of-the-body-cavity" ). 

The exocelom is colored green in the inset image.  In the main image, the tips of the forceps lie in the exocelom. In horses this cavity exits only in early pregnancy but the space has diminished so much by about 65 days of gestation that there is no longer an obvious space around the extra-amnionic cord. This explains why the extra-amnionic cord is a well-defined entity at foaling. 

In the following image, another facet of the extra-amnionic cord is illustrated: the fact that the yolk sac (or what remains of the yolk sac) forms a major part of the extra-amnionic cord. A pair of forceps has been placed under the extra-anionic cord, spreading it to show the highly vascularized yolk sac. Once again, the equine placenta affords good comparison; remnants of the yolk sac often being found in the extra-amnionic cord in the newborn foal. 

Figure 2. Image size: 1080 x 1436 px.

Other structures in the extra-amnionic cord are the umbilical  arteries and veins. The urachus on the other hand, leaves the umbilical cord immediately after it leaves the amnion, filling the allantois which lies between the amnion and chorion. 

*Mossman, Harland, W. Vertebrate Fetal Membranes. ISBN: 0-8135-1132-1. Copyright © 1987 by Rutgers, the State University. This inset image can only be used commercially with their permission.

Canine cryptorchid dissection

Keywords: cryptorchid, canine, dissection, anatomy

The dissected specimen; a young German Shepherd Dog cryptorchid on its left side.

Salient parts of the dissection specimen are keyed in color below. Of special interest is the clearly visible mesodeferens (MD) adjacent to the retained testicle (RT). It would be much longer (caudal-to-cranial) if the testicle had descended into the scrotum on that side. The epididymis (EP) of the retained testicle and the retained testicle itself are clearly visible without any dissection because they are not covered by a vaginal tunic, specifically a visceral layer of a vaginal tunic. Obviously, there is no vaginal tunic in the abdomen. The descended testicle (DT) is however, covered by the visceral layer of the vaginal tunic and for that reason, it cannot be seen without further dissection in this specimen. 

The descended testicle serves as reminder for normal anatomy. The parietal vaginal tunic (PVT) is shown in green below, cut away and folded back towards the top of the image, revealing the red vascular bundle (V) that contains the spermatic artery and vein and the blue ductus deferens (DD). Both of these structures and the testicle itself of course, are revealed here because they lie in the vaginal cavity. The reader is reminded however that although they are visible, they are in fact, covered with the visceral layer of the vaginal bursa (a small point for the anatomic purist!). On the other hand, a very practical point is the location of the ductus deferens on the medial side of the testicle. This means that the ductus can be reached most easily for vasectomy by entering the medial side of the vaginal cavity and even more easily from the cranial aspect of the scrotum than the caudal aspect. This is because the mesorchium can interfere with entry to the medial cavity if a caudal approach is adopted. Although dogs are seldom vasecomized, this anatomy holds true for any carnivore, wild or domestic. In fact, it holds true for all mammals.

The ductus deferens can be seen entering the abdomen through the inguinal canal (the yellow ring). The bladder (B) is colored yellow here, as are the ureters (U) .From the kidneys, each ureter travels caudally dorsal to the ductus deferens (DD) on each side then they enter the bladder.

This dissection is of course centered around the fact that this dog was a hemi-cryptorchid. The testicles will be retained, weighed and histopathology will be conducted on the retained testicle. As is usually the case, it is expected that the spermatogenesis will be absent in the retained testicle but present in the scrotal testicle. Even here, the retained testicle appears to be smaller than the descended testicle. Those images & data are pending.

Retained testicles in dogs become neoplastic at a rate that is 8 to 10 times higher than for descended testicles. Usually these are Sertoli cell tumors. For this reason, they are usually removed surgically. Diagnosis of cryptorchidism revolves around clinical signs and the use of ultrasonography, hCG stimulation paired with testosterone assay and more recently, antimullerian hormone (AMH) assay.

Canine fetus at 58 days

Keywords: Fetus, canine, anatomy, placenta

The image below shows a canine fetal-placental unit approximately 58 days into gestation.  The fetus is still within the placenta. Note the zonary placentation, a wide ring-like structure surrounding the chorion. Zonary placentation is typical of canids, felids, hyenas, seals, bears and elephants.

Image size: 1203 x 674 px

Dogs and cats have endotheliochorial placentation i.e. the endothelium of endometrial blood vessels is in direct contact with the chorion. Although this is the most intimate form of placentation in domestic animals, they are not able to absorb transferrin-bound iron directly from the maternal compartment like humans. Apart from horses which absorb iron from endometrial secretions, most domestic animals phagocytose red blood cells that have been extravasated by endometrial capillaries. This occurs across the areas of placental attachment. It is only in canids and felids that phagocytosis of red blood cells occur predominantly at the margins of their zonary placentas.

In dogs and cats, red blood cells are phagocytosed by specialized chorionic epithelium that does not interdigitate with the maternal epithelium occurs in the central, intimate area of the zonary placenta. The special villi in the marginal area have intricate surfaces that lie within the marginal hematomas on the endometrium forming the so-called hematophagous zones. The nature of the free standing fern-like villi in the hematophagous zone become obvious if the reader enlarges the image below.

Image size: 1203 x 794 px

Heme from maternal blood on the endometrium is immediately broke down by hemoxidase into biliverdin. Biliverdin is bright green in color, accounting for the appearance of the hematophagous zone (marginal hematoma). Heme is broken down in the same manner in felids, yet the hemotophagous zone is not green. In cats, biliverdin may be catabolized to bilirubin very rapidly in this area, so that its presence never becomes obvious but that is only supposition on the part of the author. Suffice to say, the postpartum discharge in a queen is brownish red and that in a bitch is green in color. Indeed, the image below shows the typical appearance of that discharge during second stage parturition in a bitch. The membrane at the vulvar lips is an amnion.

Image size: 720 x 1103 px

In the image below, the 58 day old fetus has been removed from the chorion but still lies within the amnion, attached to the inner surface of the chorion by the exocelom and extra-amnionic umbilical cord 

Image size: 2000 x 1122 px

References:

de Oliveira, C. M. et  al Iron transportation across the placenta. Anais da Academia Brasileira de Ciências Epub Aug 30, 2012 http://dx.doi.org/10.1590/S0001-37652012005000055

Enders, A.C. and Carter, A.M. 2012 The evolving placenta: Convergent evolution of variations in the endotheliochorial relationship. Placenta 33:319-326

The canine ovary

Keywords: Canine, ovary, bursa, infundibulum

A canine ovary viewed from its dorsal aspect. The tract is from a mature bull mastiff bitch. The ovarian bursa has been opened to show corpora lutea within the ovary. It also shows the infundibulum, barely distinguishable (green circle) as an irregularity against the smooth inside surface of the fat pad at the opening of the bursa.

The canine cervix and TCI

Keywords: canine, cervix, insemination, artificial, TCI,

This image shows the dorsal vaginal fold (dvf) and the cervical canal which has been opened. A metal rod lies within the uterus. The red arrows show the circuitous route that must be followed by the insemination instrument for transit cervical insemination. Because the external cervical os lies on the ventral surface of the dorsal vaginal fold it is sometimes extremely difficult or impossible to advance an insemination instrument through the external cervical os and into the cervical canal. That process is known as trans-cervical insemination or TCI.

The inset image shows the external cervical opening, located at the cranial- ventral portion of the dorsal vaginal fold. A metal probe has been passed through the cervical canal into the uterus.

Canine placental sites

Keywords: canine, anatomy, involution, placental, sites, uterus

A canine uterus viewed from its dorsal aspect. The tract is from a mature bull mastiff bitch. Placental sites from a previous pregnancy are shown here. Bitches experience the slowest uterine involution of all domestic species; about 90 days in duration. However even after involution is complete, evidence of previous pregnancies may be visible. Judging by the presence of corpora lutea in the ovaries of this animal, these placental sites must have been approximately 6 months old.