Cervical alterations during pregnancy in Small Ruminants
 
P. Goswami and G. M. Wani
Directorate of Extension Education,
SKUAST-K, Shalimar Srinagar
 
 
The cervix uteri is a thick walled fibromascular tube connecting the body of the uterus and vagina. It a muscular organ composed of connective tissues predominantly elastic fibres. In the non pregnant ewes, the cervical canal is impassable except during oestrous. Five or six hard prominences within the canal assist the sphincter effect of the cervix (Nickel, Schummer & Seiferle, 1973). During the course of gestration, the length of cervix increases and in late pregnancy the wall becomes thicker, with an overall increase in the compliances of the tissues (Cloete, 1939; Abusineina, 1969). This may be related to disaggregation of densely packed collagen fibre in the cervix of pre-partum ewe. This paper will focus some of the important physical and microscopical changes occurred in the cervix of small ruminants during pregnancy
 
Anatomy of the cervix:
The cervix separates the uterus from the vagina. During pregnancy, it seals and protects the embryo and fetus from the external environment. The gross and microscopic anatomy of the cervix has been studied by various workers. The casts of the inside of the cervical lumen shows its convulated structure consisting five to six circular folds and the second fold being eccentric  to the other concentric folds and acting as physiological barrier. The cervical fold in small ruminants varies from five to six folds. In cow four large circular and 15-25 longitudinal primary folds each with many secondary and tertiary folds are present. Cervical mucosa is generally characterized by longitudinal primary fold and most of which maintained continuity throughout the cervix.   Superimposed on these secondary folds which is varied in length and depth. Abundant shallow uniformity and parallel longitudinal grooves covers all surface.
 
 
Morphological changes in the cervix:
Three major changes generally observe in cervix during pregnancy. These are described as growth (physical increase in length and breadth). Softening (changes in tensile properties) and dilation to allow passage of the foetus. The study carried out by different workers showed that ovine cervix shows an increase in width and length in the later stages of pregnancy. The analysis of the constituency of cervices shows increase softening from the mid pregnancy and there after firmness of cervix losses.
A small increase in the degree of hydration of the cervix or dry weight at different gestrational stages has been reported by Fosang et. al. (1994), ward 1968. This may be due to increased tissue mass rather than increase in size of water content. However some author reported no significant changes/differences in water content of the cervices from non pregnant to pregnant animals. The physical chemical and histological properties of cervix are constant throughout the length of cervix. However, Basset (1958) reported morphological changes in the fibroblast of the broad and sacro-iliac ligament by the 60th day of pregnancy but this information is not supported on ultrastructural studies.
 
Light Microscopical changes: 
Morphologically the most prominent feature of non pregnant cervix is heavy, densely packed collagen fibre interspersed with fibroblast (fig. 3 ). Small blood vessels are present throughout the depth of the tissue, but most numerous in deepest layer. Smooth muscle bundle are running both longitudinally and transversely in the middle and deeper layer. The figure represents a wall of non pregnant cervix. The lining epithelium is low columnar and secrets neutral  mucin. The sub epithelial connective tissue is vascular and contains variety of cells including eosinophil, macrophages, mast cells and plasma cells. The greater proportion of cervical wall is composed of dense fibrous connective tissue consisting of compactly arranged collagen fibre with some fibrocytes and occasional fibroblast embeds in sparse ground substance. The individually arranged smooth muscle fibre forms an incomplete muscularies of which the outer fibre is longer and more prominent than inner fibre. The electron microscopically the collagen fibre shows very compact in arrangement and the scarcity of the ground substance and the presence of fibrocytes. Fosang et. al . opined that there is no significant changes observe between proximal, middle and distal portion of cervix irrespective of stain used. The best stain normally use for differentiation between collagen fibre and the smooth muscle bundle are Massons’ Trichrome stain, where the alignment of the collagen fibre along with villi shows projecting towards lumen. In general collagen fibre are large and closely spaced and are organized either longitudinally or obliquely. Section stained with Toludine Blue stain revels metachromatic staining along the collagen fibrils with strong staining of epithelial cells associated mucus. The morphological changes donot become apparent until quite late in the gestration period. The description of non pregnant cervix applied equally to the connective tissues observed in the early stages of pregnancy even to 100 days.  
                                                             
Fig. Pregnant cervix showing
      
Fig: Dense Collagen fibre, inner circular & longitudinal muscular layer with epithelium H&E 4X
Fig. Central cervix Transverse section Loosening of epithelium and collagens layer H&E  (pregnant)
 
 
 
 
 
The histological section at 100 days of pregnancy revels no virtually distinguish alteration from that of non pregnant cervix (Calder et. al).   The tall columnar cervical epitheliums are the only changes represents in pregnancy and the secretions are a mixture of acid and neutral mucin. Acidity increases with the pregnancy age. Tissue breakdown and destruction of collagen networks is evident at 140 days of pregnancy. The cells are more widely spaced (empty area) and the collagen fibre losing their organization exposing smooth muscle cells. This can be best seen with Massons’ Trichrome. The infiltrating cell at this stage are lymphocytes and monocytes and few eosinophils. In late gestration increased fibroblast activity, smooth muscle hypertrophy, vascular edema and dissolution of collagen fibre bundle are reported by various worker. These findings contrasted with the rigid fibromuscular tissue observe in the non pregnant animals. The appearance of thinner fibre and empty areas between fibres in late pregnancy is lead to decrease concentrations of hydroxyproline in tissue. Collagen fibre dissolution in pregnant cervix has been extensively reported in several species and many authors have reported that active collagenolysis occurring during pregnancy may be the underlying mechanism of cervical softening. Ellowed et al (1981) have shown that ovine cervical explants produce both latent and active collagenase activity, with greater yields of activity in parturient tissue compared with the late pregnancy after 3-5 days in culture. Inflammatory cells invading cervix towards late gestration provide a potential source of collagenase and neutral protinease activity. Eosinophils also have been described as potential bearer of specific collagenase which may be responsible for collagen catabolism (Basset, 1972). At the term the disruption of collagen fibre are more even pronounced with virtually no large fibre remaining. In Haematoxyline & Eosin stain sectioned it sometimes appears very little or no collagen at all. But very little and small fibrils arranging random pattern are seen in Massons’ Trichrome stains. In this stage there is heavy infiltration of inflammatory cells among which eosinophils predominant. An area of haemorrhage is also a constant finding along with infiltrating cells. In late pregnancy there is complete network of subepithelial capillaries with a marked increase in the size of the vessels in the outer part of the cervical wall.
 
Ultrastructure feature:
Ultrastructuraly, non pregnant cervix reveals the typical dense connective tissue with collagen aggravated in closely packed fascicles and fibrocytes embedded in sparse ground substance. The ultrastructural characteristic in late pregnancy are presence of rough endoplasmic reticulum, mitochondria,plasmalemmal vesicle and extensive branching of individual fibres in contrast to the absence of these feature in muscle fibres of the non-pregnant cervix. This description is also similar to early pregnancy stage. The ultrastructural analyses of the cervical connective tissue reflects active changes in tissues, with a reorganization of the cervix prior to the functional changes at parturition.
 
 
 
Changes in collagen concentration:
The biochemical analysis of hydroxyproline in tissue can be used for collagen concentrations. Study carried out by Regassa et al. (1983) shows the total collagen content of cervix at all stages of pregnancy is significantly greater than that of caruncular mean and the intercaruncular areas. The concentration of hydroxyproline is not changed in cervix during Ist trimester of pregnancy. However the concentration of hydroxyproline progressively decreases at days 100, 140 days and in post partum tissues as compared to the non pregnant tissue(Fosang et. al 1984). The concentration is same between proximal, middle or distal region of the pregnant and non pregnant cervix.
In conclusion it is summarized that uterine cervix of small ruminants became softer during the pregnancy and that some associated changes first appear in early gestartion. There is no significant changes in water content through pregnancy although light increases is associated with cervical size and softening of the tissue. Physical and histological properties are identical in all section along the length of cervix. The changes associated with increasing length of gestration are absolute increase in width and length, relative increases in fibroblasts, smooth muscle and softening; relative decreases in collagen and fibrocytes. But increased vascularisation without any white cell infiltration of the tissue is specifically associated with late gestration.
 
 
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