Uterus - Anatomy & Physiology

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Introduction

The Uterus is the organ of pregnancy as this is where implantation and development of the feotus occurs. The Uterus is the reproductive organ with the most species variations. These variations occur in both the anatomical types of uterus aswell as the uterine horn appearance and endometrial linings. Duplex Uteri

• rabbits and marsupials

Bicornuate Uteri

• (previously Bipartite Uteri)
• A high degree of paramesonephric duct fusion leads to a uterine body and short poorly developed uterine horns as seen in the Mare.
• An intermediate degree of fusion leads to moderately developed uterine horns as in the Cow, Sheep and Goat.
• A low degree of fusion of the paramesonephric ducts leads to long uterine horns and a small uterine body as seen in the sow, bich and queen.
• This varying degree of paramesonephric duct fusion reflects the species differences in litter sizes. as either monotocous or polytocous animals

Simplex Uteri

• complete fusion of the paramesonephric ducts forming a single uterine body with no uterine horns. This is seen in primates and especially humans.

Structure

Perimetrium

Myometrium

Endometrium caruncles in ruminants are the sites of maternal tissue contribution to the placenta + feotal cotyledon = placentome uterine folds in sows and mare. Not shed in domestic species only in primates.

Function

• Provides a suitable environment for embryo development and attachment. The secretions produced by the endometrial glands are important for maintaining the preimplantion embryo.
• In response to increasing amounts of oxytocin production by the corpus luteum during the luteal phase the endometrium produces luteolytic PGF2a to cause degeneration of the corpus luteum if the female is not pregnant.
• The uterus contributes varying amounts of maternal tissues towards the placenta.
• The myometrium is involved with sperm transport through the uterus towards the oviduct.
• Contrations of the myometrium during parturition is important for feotus and placenta expulsion.

Anatomical Location & Boundaries

The Uterus body and Uterine horns are located within the abdominal cavity dorsal to the Intestinal mass. -broad ligament?

Histology

The appearance of the uterus varies with the stages of the oestrus cycle. Follicular phase

• Increasing numbers of uterine glands developing and elongating within the endometrium due to the influence of Oestrogens produced by the developing follicles.
• General increase in the thickness of the endometrium.
• The epithelium lining the glands is Simple Columna epithelium.

Luteal phase

• The endometrium is at its maximum thickness with a large number of highly developed glands.
• This is the secretory phase for the endometrium.

Anoestrus

• The endothelium is relatively thin and there is little proliferation or gland development.
• The glands are lined by Simple Cuboidal epithelium.

Innervation

The uterus is innervated by both Sypathetic and Parasympathetic fibres which play a part in the regulation of uterine activity. This is highlighted by Iatrogenic manipulation of parturition using β-Adrenoreceptor Agonists for delaying parturition and Antagonists for inducing parturition. However, uterine activity and normal parturition can be acheived when these nerves are severed.

Vasculature

• Uterine branch of the Ovarian artery supplies the cranial parts of the Uterine horns.
• Uterine artery supplies the rest of the uterine horns and the uterine body. This is a branch off the Internal Iliac artery in most domestic species, except the Mare where insted it is a branch off the External Iliac artery. The Uterine artery and the Ovarian artery anastomose within the Broad ligament.