The uterus, often called the womb, is the muscular organ responsible for housing developing fetuses in a female cat (queen). This dynamic reproductive structure is designed to support multiple pregnancies. Understanding its physical characteristics involves examining its unique shape, location, and the specialized tissues that form its wall.
Overall Structure and Location
The cat’s uterus is classified as bicornuate, shaped like the letter ‘Y’ lying on its side. This formation accommodates the simultaneous development of a litter of kittens. The structure is largely comprised of two long, muscular tubes called uterine horns, where multiple fetuses implant and grow.
These two horns converge at a short, central area known as the uterine body. The body is relatively small, measuring only a few centimeters in length in an unbred cat. From the body, the structure narrows down to the cervix, which separates the uterus from the vagina.
In a non-pregnant state, the uterus is pale, tubular, and small, often described as resembling two thin pieces of spaghetti. Its diameter is slight, generally less than half a centimeter. While the body is situated in the pelvic cavity, the longer uterine horns extend forward into the abdominal cavity.
This anatomical position allows for stretching and expansion as pregnancy progresses. Ligaments attach the structure to the abdominal wall and the pelvis, providing support while permitting movement for fetal development. The horns are significantly longer than the uterine body, dominating the organ’s overall appearance.
The horns are also more mobile than the body, which is anchored more firmly near the pelvis. The small, resting size of the non-pregnant uterus makes it difficult to detect without specialized imaging.
The Three Distinct Layers
The wall of the cat’s uterus is composed of three tissue layers, each contributing to the organ’s function. The innermost layer is the endometrium, which forms the lining of the uterine lumen (the central open space). This layer is highly glandular and changes thickness cyclically, preparing a surface for the fertilized egg to attach.
The endometrium is followed by the myometrium, the thickest part of the uterine wall. This middle layer is composed of dense, interlacing smooth muscle fibers. The myometrium’s muscularity provides strength and allows for the powerful contractions required during the birthing process.
Visually, the myometrium contributes to the firm, rubbery texture felt when palpating the organ in a non-pregnant state. The organized muscle fibers facilitate the expulsion of kittens once they are fully developed. This layer is pronounced in the horns, where the majority of the muscular work occurs.
Enveloping the exterior of the uterus is the perimetrium, the outermost protective layer. This thin, serous membrane is a continuation of the peritoneum, the lining of the abdominal cavity. The perimetrium appears smooth and translucent, providing a low-friction surface that allows the uterus to shift and expand without adhering to other organs.
The uterine wall in cross-section reveals the difference in thickness between these layers. The pinkish-white myometrium dominates the view, while the endometrium is softer and paler. The perimetrium is so thin it is almost invisible.
Appearance During Pregnancy
The appearance of the cat uterus changes once conception occurs, moving from a small, pale tube to a large, highly vascularized structure. The primary change is the increase in size, particularly within the uterine horns. The horns become distended and heavy as they accommodate the growing fetuses and surrounding fluids.
As pregnancy progresses, the uterus shifts noticeably, becoming darker and more reddish due to increased vascularization. A greater volume of blood is routed to the organ to support the developing kittens, resulting in a deeper coloration compared to the pale pink resting state. The tissue walls also become thinner and more stretched.
Around three to four weeks into gestation, specific swellings can be felt and sometimes identified along the uterine horns. These bulbous structures are the implantation sites, where individual placentas form to nourish each fetus. These sites give the horns a beaded or lumpy appearance, unlike the smooth tube of the non-pregnant organ.
The presence of these localized swellings is one of the first physical indications of pregnancy, altering the feel and look of the uterus. Later in gestation, the organ is so enlarged that it occupies a large portion of the abdominal cavity, contrasting with its initial position tucked into the pelvis.
The weight and volume of the pregnant uterus require the supporting ligaments to stretch considerably. The change from a resting diameter of a few millimeters to a structure several centimeters across is a profound transformation. The placentas appear as dark, circular bands within the uterus, facilitating the exchange of nutrients and waste between the queen and the fetus.