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.

Structure

• Mare and carnivores have a simple cervix bulging into the vagina to form a distinc recess (vaginal fornix).
• Lumen is the cervical canal
• Folds surround the lumen
  • Single fold and smooth surface in the queen and bitch
  • Multiple folds protruding into the cervical canal in the cow, ewe, sow and mare

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

• Low volume mucous secretion
• Multiple folds
• Many longitudinal folds of mucosa that protrude into the vagina (fornix vagina)
• Soft during oestrus

Bitch

• Single fold
• Relatively smooth surface
• A portion protrudes into the cranial vagina (fornix vagina).

Queen

• 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 mucous 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).