Thecervix
The uterus and vagina are separated by the cervix, a structure with thick walls that resembles a sphincter. The cervix primarily consists of connective tissue, but its walls also contain some smooth muscles.
The cervix’s lumen is small and has annular rings. In cows and ewes, these annular rings are highly noticeable and form interlocking ridges. The corkscrew-shaped rings in the sow are broken by the spiral twisting in the boar’s penis tip. Even though the vaginal end forms a well-constricted os uteri, the cervical rings are less noticeable in mares. Tall columnar cells and goblet cells that secrete mucus line the cervix’s lumen.The cervical mucosa has a huge secretory surface because of its intricate folding. Glycoproteins make up cervical mucus, with 25% amino acids and 75% carbohydrates. Certain distinct biophysical characteristics of cervical mucus include ferning, elasticity, viscosity, and stickiness (tack), cervical mucus’s physical and chemical characteristics, as well as how much of it changes throughout the estrous cycle. For instance, the macromolecules in cervical mucous are oriented to increase intermolecular space to 2.5-5 μm when estrogens are present, but progesterone during the luteal phase causes it to decrease. The cervix performs a number of vital tasks, including: (i) sperm transport; (ii) sperm reservoir; (iii) sperm selection center; and (iv) shielding the upper reproductive tract from harmful substances. In most animals, the sperm are oriented towards the cervix as they are ejaculated into the vagina close to it. Enzymes that hydrolyze backbone proteins and cross-links in mucin increase the sperm penetrability of the cervical mucous as they beat and travel towards the upper reproductive tract. Sperm transit channels between the cervical mucous and semen soon form. Many sperm lodge in the cervical crypts during their journey through the cervix, and they may then be released phasically. As a result, the cervix may serve as a sperm reservoir, preventing a large number of sperm from entering the uterus at once. Additionally, sperm may become more or less continuously available at the site of fertilization with such periodic release (over a period of about 24 hours). Contrarily, sperm that enter cervical crypts may never be released, so the cervix restricts entry into the upper reproductive tract to only the strongest sperm. During the luteal phase, the cervical mucous that allows sperm to enter the uterus during estrus transforms into a thick, viscous secretion that seals the cervix. By doing this, the upper reproductive tract is shielded from toxins and other infections. This seal becomes liquefied at parturition and offers protection during the entire gestation period. When parturition approaches, the cervix’s connective tissue undergoes significant biochemical alterations that cause it to greatly expand in size, allowing the fetus to pass through.21.12
Source:
Rana Tanmoy (ed.). Principles of Veterinary Animal Physiology. CRC Press,2026. — 290 p.. 2026
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