The uterine tube is divided into three divisions:
1. Infundibulum - The cranial opening of the uterine tube closest to the ovary, which is surrounded by a flat, fimbriae. These finger-like projections help to sweep the ova into the uterine tube. A small opening in the depth of the infundibulum leads to the interior of the uterine tube. 2. Ampulla – short, wide part of the tube where fertilization occurs 3. Isthmus – the thick walled, short isthmus is closest to the uterine horn. It acts as a holding reservoir for sperm until an ovum has been released. The uterine tube opens into the apex of the uterine horn of the uterus through a small orifice. This uterotubual junction is able in some way to distinguish between fertilized and infertile ova; the former are admitted to the uterus while the latter are denied entry.
The uterine tubes are lined with simple columnar ciliated epithelium and a smooth muscle layer to move the ova through the uterine tube.
Uterus – The uterus has a large body and 2 divergent horns which are approx. 20-25 cm long. The uterine horns lie entirely within the abdomen and are suspended from the roof of the abdomen by the mesometrium.
The broad ligaments (mesovarium, mesosalphinx & mesometrium) contain large amounts of smooth muscle and may play an active role in positioning the foal and uterus during parturition.
The body of the uterus, 18-20 cm long, is located in part in the abdominal cavity and partly in the pelvic cavity. Dorsally the uterus is associated with the colon & rectum and ventrally with the bladder and various parts of the intestine. The uterus terminates at the cervix.
The uterus is made up of 3 layers:
1. Perimetrium – the serosal layer, continuous with the broad ligament. 2. Myometrium – 2 layers of smooth muscle, a thick inner circular & thin outer longitudinal. Blood vessels & nerves are located between the 2 muscle layers. 3. Endometrium – contains a mucosa & submucosa (lamina propria). The inner epithelial lining is simple columnar cells with mucus glands that empty secretions into the uterus. It is NOT shed in mares. The appearance of the endometrium changes depending on the phase of estrous.
The uterus is considered a sterile environment. When the mare is not pregnant the uterus is small and collapsed.
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