Cervix
The cervix is a thick-walled marrow projection between the uterus and vagina. It acts as a physical barrier to protect the uterus from the invasion of foreign materials, particularly during pregnancy under the influence of progesterone.
It considers the point of orientation while examining the genital tract through the rectum in cows. The spindle-shaped flattened passage within the cervix is called the cervical canal (canalis cervicis) that opens into the anterior vagina through the external os (os externum) and into the uterus through the internal os (os uterinum). The finger-like projections at the internal and external os are termed plicae palmatae. The os is generally opened during the oestrus phase to allow sperm and during parturition to expel the foetus and remains tightly closed during other phases of the cycle. In cows, the penis touches the external os. The semen is deposited at the os, but in mares, the semen is directly deposited into the uterus due to a dilated cervix. During the opening, the cervix becomes flaccid. The cervix secretes mucus. The consistency of cervical mucus alters during different phases of the reproductive cycle. During oestrus, the cervical mucus is clear and watery, but it becomes thick and sticky during pregnancy and forms a plug to prevent the passage of spermatozoa and microorganisms. The portion of the cervix that projects into the vagina is called portio vaginalis.The junction of the cervix and vagina has a blind pouch called the fornix and is prominent in the mare and absent in sow. The spindle-shaped flattened passage within the cervix is called the cervical canal, characterised by transverse or spirally interlocking ridges called annular folds. The folds are prominent in cows and ewe and close the cervix securely. The number of annular folds is 5-6 in cows and 3-4 in buffalo. In sow, the fold is arranged as interdigitated pads and appears like a corkscrew adapted to the spiral twisting of the tip of the boar’s penis.
Several longitudinal folds of mucous membrane characterise the mare’s cervix that projects into the vagina.21.5.1 Histological Features
The cervix consists of mucosa, muscularis and serosa. The mucosal lining of the cervix is composed of tall columnar epithelium. There are goblet cells between the cervical epithelium responsible for cervical mucous secretion. The cervical wall is made of fibroelastic collagenous and muscular tissue responsible for the high tensile strength of the cervix. The cervix of the mare is more dilated due to less cartilaginous tissue.
21.5.2 Functions
The cervix acts as a physiological barrier against external pathogens. It facilitates sperm transport and acts as a sperm reservoir. The cervix is also responsible for selecting viable sperm and prevents the entry of non-viable and abnormal sperm. The dilation of the cervix at the time of parturition helps expel the foetus and foetal membrane. The cervical plug at the time of pregnancy protects the foetus from infections.
21.6