| total cleavage | Cleavage in which the blastomeres are completely separated; the entire egg participates in cell division. Synonym: complete cleavage, total cleavage. (05 Mar 2000) |
|---|---|
| enamel cleavage | The splitting of enamel in a plane parallel to the direction of the enamel rods. (05 Mar 2000) |
| equal cleavage | Cleavage producing blastomeres of like size. (05 Mar 2000) |
| equatorial cleavage | Cleavage in which the plane of cytoplasmic division is at right angles to the axis of the ovum. (05 Mar 2000) |
| yolk cleavage | Segmentation of the vitellus. (05 Mar 2000) |
| unequal cleavage | Cleavage producing blastomeres of different sizes at the two poles. (05 Mar 2000) |
| freeze cleavage | Method of specimen preparation for the electron microscope in which rapidly frozen tissue is cracked so as to produce a fracture plane through the specimen. The surface of the fracture plane is then shadowed by heavy metal vapour, strengthened by a carbon film and the underlying specimen is digested away, leaving a replica that can be picked up on a grid and examined in the transmission electron microscope. The great advantage of the method is that the fracture plane tends to pass along the centre of lipid bilayers and it is therefore possible to get en face views of membranes that reveal the pattern of Integral membrane proteins. The E face is the outer lamella of the plasma membrane viewed as if from within the cell, the P face the inner lamella viewed from outside the cell. Fracture planes also often pass along lines of weakness such as the interface between cytoplasm and membrane, so that outer and inner membrane surfaces can be viewed. Further information about the structure can be revealed by freeze etching. Extremely rapid freezing followed by deep etching has allowed the structure of the cytoplasm to be studied without the artefacts that might be introduced by fixation. (18 Nov 1997) |
| alveolonasal line | A line connecting the alveolar point and the nasion. (05 Mar 2000) |
| Amberg's lateral sinus line | A line dividing the angle formed by the anterior edge of the mastoid process and the temporal line. (05 Mar 2000) |
| anocutaneous line | The line between the simple columnar epithelium of the rectum and the stratified epithelium of the anal canal. Synonym: linea anocutanea, anocutaneous line, dentate line. (05 Mar 2000) |
| anterior axillary line | A vertical line extending inferiorly from the anterior axillary fold. Synonym: linea axillaris anterior, linea preaxillaris, preaxillary line. (05 Mar 2000) |
| anterior junction line | Radiographic projection of the mediastinal tissue septum between the upper lobes behind the sternum. (05 Mar 2000) |
| anterior median line | The line of intersection of the midsagittal plane with the anterior surface of the body. Synonym: linea mediana anterior. (05 Mar 2000) |
| arcuate line | An arching or bow-shaped line. See: arcuate line of ilium, arcuate line of rectus sheath. Synonym: linea arcuata. (05 Mar 2000) |
| arcuate line of ilium | The iliac portion of the linea terminalis of the bony pelvis. Synonym: linea arcuata ossis ilii. (05 Mar 2000) |