Cervical mucus: present state of knowledge.
It is recommended that the term "crypts" be used to describe the pockets of columnar epithelium of the cervical mucosa. There are different types of secretory and ciliated cells. Nonciliated cells are covered with microvilli and contain many cytoplasmic granules. The intensity of periodic acid-Schiff (PAS) positive material in the cervical mucosa depends on the abundance of the cytoplasmic granules. Cells located deep in the cervical crypts contain more PAS material. The cilial action of the ciliated cells does not seem important in the transport of sperm but releases material into the cervical lumen and facilitates the flow of mucus into the upper vagina. Secretory hormones determine the rate of mucus secretion which varies from 600 mg during the midcycle to 20-60 mg during other periods. Cervical mucus contains 90% water. At midcycle the water increases to 95%. The secretion of different types of mucus and their biological qualities are determined by hormonal factors. However, inflammatory conditions may affect the secretory units. During the cycle, the components of the hydrogel change markedly. The 2 states are called Type E, estrogenic, and Type G, gestagenic. Type E is thin and watery mucus and Type G is thick, sticky mucus. Type E contains the macromolecular chains in a micellar structure with spaces large enough for sperm to penetrate. An estimation of the degree of crystallization, together with the index of consistency and determining spinnbarkeit provide useful clinical assessment of the bulk rheological properties of cervical mucus. The index of consistency is a measure of the bulk flow properties. Crystallization is related to sperm penetration and hormonal changes. Spinnbarkeit is a measure of the visco-elasticity property of midcycle mucus. The prinicpal constituent of cervical mucus is a glycoprotein, rich in carbohydrates, called mucin. Soluble components include inorganic salts and low molecular compounds such as glucose, amino acids, peptides, and lipids. Soluble proteins are 30% of nondialyzable material. Estrogens decrease and gestagens increase the concentration of soluble proteins. There is a complex interrelationship with various metallic ions. Zinc, manganese, and copper are important. The biophysical properties of the mucus are altered by an excess of copper ions. Sperm possesses metabolic and glycolytic enzymes. The mucus is a favorable medium for sperm survival. The storage of sperm in the cervical crypts and their gradual release ensures a constant supply into the upper tract and protects them from phagocytosis. This increases the chance of fertilization as the ovum has a short life span. The optimal pH of cervical mucus for sperm migration is between 7 and 8.5. Several recommendation for future studies are listed. Standardization of methodology and correlation of findings with hormonal changes are needed. Proteolytic enzymes present and their reactions require more study. Immune mechanisms in the cervix and the mucus may be important.