Cervix - Anatomy & Physiology

()Map REPRODUCTIVE SYSTEM (Map) FEMALE REPRODUCTIVE TRACT

Introduction

The cervix can be palpated transrectally and forms a sphincter controlling access to the uterus.The anatomy of the cervical canal is adapted to suit a particular pattern of reproduction and its composition will alter under the influence of reproductive hormones. Not only does it respond to the fluctuation in oestrodiol during the oestrous cycle, but is responsive to prostaglandins and oxytocin in order to 'soften' for parturition.

Structure

• The lumen of the cervix is the cervical canal.
• The canal is formed by, and often almost occluded by mucosal folds.
  • Single fold and smooth surface in the queen and bitch
  • Multiple folds protruding into the cervical canal in the cow, ewe, sow and mare.
• The cervical canal opens cranially into the body of the uterus at the internal uterine ostium.
• The cervical canal opens caudally into the vagina at the external uterine ostium.

Cow and Ewe

• High volume of mucous production
• Multiple folds
• Cervical rings form interlocking finger-like projections known as interdigitating prominences.
• Elaborate system of folds and crypts to provide a site of storage where sperm are protected from the spermicidal environment of the vagina and uterus in the ewe.
• Allows semen to be ejaculated directly into the uterus for rapid transport to the oviducts in the cow.

Sow

• Less mucous secretion
• Multiple folds
• Cervical folds form rings (cervical rings)
• Ensures a tight coupling of the penis with the cervix to ensure that the large volume of semen produced by the boar is deposited in the uterus.

Mare

• Simple cervix with the most caudal part bulging into the vagina to form a distinct recess (vaginal fornix).
• Low volume mucous secretion
• Multiple folds
• Many longitudinal folds of mucosa that protrude into the vagina (fornix vagina)
• Soft during oestrus

Bitch

• Simple cervix with the most caudal part bulging into the vagina to form a distinct recess (vaginal fornix).
• Single fold
• Relatively smooth surface
• A portion protrudes into the cranial vagina (fornix vagina).

Queen

• External uterine ostium opens on a small hillock projecting into the vagina.
• Small
• Thick walled compared to the uterus or vagina
• Single fold
• Smooth surface

Function

• Provides a physical barrier to the uterus therefore preventing abortion due to infection by isolating the foetus from the external environment. It does this by creasing a highly viscous mucous plug. Closure is via the mucosal folds.
• Barrier to sperm transport in the ewe, cow, bitch and queen, but not in the sow and mare.
• Assists with the storage and survival of sperm by admitting sperm to the genital tract at a time when fertilisation is possible (around ovulation).
• Mucus production for lubrication and to prevent microorganisms from entering the uterus.
• Remodels itself at the end of gestation to allow birth and to stimulate the development of maternal behaviour.

Anatomical Boundaries

• Located between the Uterus and the Vagina.

Histology

Histological Section of the Cervix of a Ewe- Courtesy of J.Bredl, Copyright RVC 2008

Histological Section of the Cervical Lumen of a Ewe- Courtesy of J.Bredl, Copyright RVC 2008

• The lumen of the cervix is lined by a simple columnar epithelium containing many mucus producing cells. Some cilia may be seen on these cells.
• Uterine cervix protrudes into the upper vagina and contains the endocervical canal that links the uterine cavity with the vagina.
• The endocervical canal is lined by a single layer of tall columnar mucus-secreting cells.
• Where the cervix is exposed to the vagina (the ectocervix), it is lined by thick stratified squamous epithelium.
  • Cells of the ectocervix often have clear cytoplasm due to their high glycogen content.
• The junction between the vaginal and endocervical epithelium is abrupt, normally located at the external os. This is the point where the endocervical canal opens into the vagina.
• The main bulk of the cervix is composed of tough, collagenous tissue with relatively little smooth muscle.
• Under the squamocolumnar junction, the cervical stroma is infiltrated with leukocytes which defend against microorganisms.
• It is the cervical stroma that is influence by the ovarian hormones.

Vascularisation

• Uterine artery off the Internal Iliac artery (External Iliac artery in the Mare).