The umbilical vein and arteries in a bovine fetus

Keywords: bovine, umbilical, cord, artery, liver, vein, falciform

The equine umbilical circulation is discussed elsewhere in LORI and contributes to this entry.

Normally, the major blood vessels in the amnionic portion of umbilical cord of calves i.e. two veins and two arteries (three vessels in foals) snap and close by elastic recoil at the time of birth. Together with normal clotting mechanisms, this affords complete hemostatis.

Even after birth, two umbilical veins can be discerned close to the body wall of a calf using ultrasonography. These veins then fuse after entering the abdomen and drain towards the posterior vena cava through the liver. The single intra-abdominal umbilical vein is seen in figure 1. Unlike umbilical veins, umbilical arteries are not usually visible outside the body using ultrasonography intermediately after calving.

Figure 1: Perihepatic and perivesicular structures in a late gestation bovine fetus. These structures have been emphasized by post-processing coloration. The intra-abdominal umbilical arteries shown here carry de-oxygenated blood back to the placenta and are in that sense, akin to veins. Nevertheless, these arteries, like those in the umbilical cord, have histological features that are consistent with arteries. After birth, the intra-abdominal umbilical arteries are redundant and degenerate to form the round ligaments of the bladder.  The umbilical vein degenerates to form the round ligament of the liver. The membrane between the round ligament, body wall and liver becomes the falciform ligament (< Latin falc, meaning sickle ) in the calf. Image size: 1400 x 746

The urachus of course, degenerates completely in most animals. However, on rare occasions in cattle (but commonly in humans) the urachus may persist as a thin cord or tubule between the cranial aspect on the bladder and the abdominal wall. On rare occasions these remnants may cause intestinal strangulation.

Figure 2: An interesting comparison with figure 1 is seen in this image from Diseases of cattle, sheep and Swine by the French Veterinarian Gustave Moussu (1864-1945). Book copyright dated 1906. No known copyright restrictions. Image size: 1475 x 966

As mentioned, a single umbilical vein perfuses the liver. However, another major blood vessel diverges from the umbilical vein within the liver but does not perfuse the liver. Instead, it drains directly into the posterior vena cava. This vessel is the ductus venosus. Therefore, not all of the blood from the placenta perfuses the liver to exit that organ via the hepatic veins and enter the posterior vena cava. A small proportion, perhaps 30 percent, bypasses the liver through the ductus venosus and enters the posterior vena cava. As the fetal liver matures, progressively less blood bypasses the liver through this vessel. But even after birth, small amounts of umbilical blood may bypasses the liver and flow directly into the posterior vena cava.  In general, no umbilical blood should bypass the liver by 5 to 7 days postpartum When the ductus venosus persists after birth, some blood flows directly from the portal vessels into the posterior vena cava.  Because that portal blood bypasses the liver, it is not detoxified and neither does it carry beneficial nutrients (metabolized of the liver) into the systemic circulation. This is known as a portosystemic shunt. Portosystemic shunts occur in calves but are most common in dogs. They result in poor growth and hepatic encephalopathy.

Selected references:

Baxter, G.M. et al. 1987. Persistent urachal remnant causing intestinal strangulation in a cow. J Am Vet Med Assoc. 191: 555-558.

Reimer, J.M.  et al 1988 Diagnosis and surgical correction of patent ductus venosus in a calf. J Am Vet Med Assn 193: 1539-1541

Watson, E. et al 1994. Ultrasonography of the umbilical structures in clinically normal calves. Am J Vet Res. 1994 Jun;55(6):773-80.

The uterine arteries

Keywords: uterus, artery, middle, arteries, anatomy

During transrectal palpation of the pregnant bovine uterus, it is common to feel for the presence of fremitus in a uterine artery. A video of a windsock, simulating fremitus can be seen here. It shows non-linear, turbulent flow of air through a windsock; the sock is unable to constrain the airflow in a linear, orderly fashion. During pregnancy in ruminants, blood flow to the uterus increases rapidly, exceeding the ability to contain the blood flow in a linear flow. The effect is the same in both cases.

Since antiquity, this artery has been referred to by clinicians as the middle uterine artery, implying that there are several major arteries within the mesometrium. Indeed, this is clearly the case as shown below (A, B & C...perhaps more). However, the image also shows that there is only one major uterine artery (UA) from which the smaller arteries emanate. That artery should correctly be referred to as the uterine artery.

Image size: 1500 x 1000px

The question arises as to which of these arteries can develop fremitus during pregnancy. Clearly the major artery is capable of doing so. Therefore if there is any doubt as to which artery one is grasping during pregnancy diagnosis, it may be most correct to refer to "fremitus in the uterine artery" rather that "fremitus in the middle uterine artery". Finally, there is clearly potential for the development of an even number of large arteries in the mesometrium, in which case there can be no middle artery. Collectively therefore, the term "middle uterine artery" is probably incorrect in many instances of transrectal palpation. In the absence of clinical evidence to show otherwise, the term "uterine artery" should  be used.