The need to develop a common terminology to describe the components of the ovary has been felt for some time (Gatz, 1955; Wischnitzer, 1966). A standard nomenclature would greatly facilitate the comparison of results relating to the development of the ovary and follicle growth under normal as well as experimental conditions. Various classifications have been used to describe stages of oocyte and follicle development. Some authors use the shape of the granulosa cells and the number of layers surrounding the oocyte as the main characteristic (Engle, 1927; Mandl & Zuckerman, 1950; Adams & Hertig, 1964; Hadek, 1965). Others take the largest diameter or the volume of the follicles as the distinguishing criterion (Boling, Blandau, Soderwall & Young, 1941; Paesi, 1949), while still others use a combination of the number of cell layers and follicle diameter to describe the stage
TORBEN PEDERSEN and HANNAH PETERS
HANNAH PETERS and EMILIA LEVY
The effect on the ovary of a single dose of 20 r X-ray given at different ages early in life varies according to the age of the animal at the time of radiation. This has been investigated by determining the number of oocytes surviving 24 hr after radiation, and at varying intervals after irradiation but at a constant age of the animal, i.e. 49 days. The sensitivity of the ovary depends on the response of the small oocytes as well as on the response of the growing and large oocytes. The sensitivity of these two groups differs. Further, a variation within the two groups is noted, which is age dependent. Fifty per cent of small oocytes survive 24 hr after radiation on the day of birth whereas radiation after this age leaves only between 1 and 9% of these cells intact. The number of oocytes in the ovary at the time the animal enters maturity is 85% of the normal number after irradiation at birth, but only 1% after irradiation at the age of 3 weeks. The changing radiation sensitivity is discussed in relation to certain morphological changes in the developing ovary.
HANNAH PETERS and EMILIA LEVY
During the ovarian cycle the mouse ovary undergoes changes which involve considerable movements of cells. Autoradiographs prepared at different time intervals after flash labelling with 3H-thymidine show that it is possible to mark cells in distinct cell groups in the ovary and to follow their growth, movement and disappearance from cycle to cycle for a considerable period of time. This method has been used to follow follicle development, the movements of corpora lutea and the development of the peripheral stroma through five cycles.
HANNAH PETERS, ANNE GRETE BYSKOV, RUTH HIMELSTEIN-BRAW and MOGENS FABER
Follicular growth is described as a continuum. It goes on at all times, at all ages, uninterrupted by pregnancy or other periods of non-ovulation. A distinction is made between the continuum at the beginning of follicular growth and events concerning the cyclicity at the end of follicular growth, i.e. ovulation. Follicles grow sequentially. Also large follicles continue to grow until they become atretic or ovulate. No evidence for a pool of large follicles held in reserve could be found. Examination of the effect of PMSG on the growth of large follicles showed that this hormone prevented the degeneration of large follicles, thus allowing more follicles to grow further.
As in the mouse, follicular growth occurs during human infancy and is the normal event during childhood. Ovaries without signs of follicular growth are uncommon in the child and are apparently connected with certain systemic diseases.
Ruth Himelstein-Braw, Anne Grete Byskov, Hannah Peters and Mogens Faber
The pattern of follicular atresia was studied in nine ovaries from children between the ages 3 months and 8 years. Atretic follicles were found among follicles at all stages of development. The percentage of follicles with signs of atresia became larger as the size of the follicles increased. Only 2% of small follicles (Type 3b) showed signs of atresia, while all follicles >1 mm in diameter (Type 8) were atretic. In follicles of Type 5 and larger, four stages of atresia, which represent consecutive stages of a single atretic process, were defined. The beginning of atresia was characterized by the presence of pyknotic granulosa cells. As atresia progressed, the granulosa layer disappeared, the oocyte became necrotic, the follicle collapsed and the theca cells became hypertrophied.
The oocyte can degenerate in several ways: it can be penetrated by cells, the nucleus can become pyknotic or it may complete meiotic prophase. It is suggested that the last event is only possible after the oocyte has reached its full size and has completed RNA synthesis.
SUE LINTERN-MOORE, HANNAH PETERS, G. P. M. MOORE and M. FABER
The morphology and growth pattern of human ovarian follicles has been studied between birth and 9 years of age. Follicles have been classified according to their morphology, diameter, the diameter of the oocyte and the number of granulosa cells in the widest cross-section. Nine major classes of follicle were recognized. The smallest, Class B follicles, contained a non-growing oocyte and were surrounded by a single layer of flattened granulosa cells. The largest, Class F follicles, which were up to 6 mm in diameter, contained an oocyte which had completed growth (80 μm) and a large fluid-filled antrum. The range of follicles and the pattern of oocyte growth in relation to follicle growth found in the ovary was independent of age during childhood.
Follicular growth and atresia are discussed in the light of current concepts of gonadal and pituitary function during infancy and childhood.