Ebook Atlas of histology of the juvenile rat: Part 2

Part 2 book "Atlas of histology of the juvenile rat" includes content: Female reproductive system, male reproductive system, the endocrine system, immune system, hematopoietic system, the eye and harderian gland, urinary system, cardiovascular system

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Ebook Atlas of histology of the juvenile rat: Part 2 Chapter 7 VetBooks.ir Female Reproductive System Catherine A. Picut and Amera K. Remick WIL Research, Hillsborough, NC, United States INTRODUCTION During the neonatal period (PND 0 to 7), the ovary is a solid parenchymal mass with no medulla, cortex, or hilus. It The female reproductive tract, composed of the ovaries, ovi- is comprised of ovigerous nests which are packets of oogo- ducts, uterus, cervix, and vagina, is immature at birth and nia enveloped by undifferentiated mesenchyme. Within the develops into a fully functional reproductive unit by PND 42. first few days, the ovigerous nests transform into primordial The ovary is considered mature once the rat has experienced follicles (ie, a primary oocyte surrounded by a single layer at least two ovulatory cycles, and this typically occurs by of flattened pre-granulosa cells). Follicular development PND 42. Follicle development is pituitary independent dur- starts in the core of the ovary, where these primordial fol- ing the first 10 days of life, and becomes dependent on, and licles become primary follicles (primary oocyte surrounded receptive to, gonadotropins thereafter. Early antral follicles by a single layer of cuboidal granulosa cells) and secondary are not typical, and develop from the medulla outward to follicles (primary oocyte surrounded by more than one layer the cortex. After PND 21, apoptosis of granulosa cells first of cuboidal granulosa cells). During this neonatal period becomes apparent. Then a wave of follicular atresia ensues of development, the ovary is independent of, and unre- at around PND 27 which has the result of clearing away old sponsive to, pituitary gonadotropins LH (luteinizing hor- follicles and leaving a defined cortex and medulla. From that mone) or FSH (follicle stimulating hormone) (Picut et al., point forward, ovulatory follicles develop in the cortex, and 2015). Follicular development is under the control of local first ovulation occurs at around PND 33. Significant biologi- paracrine and autocrine factors. cal variability occurs with ovulation and anything that dis- The infantile period (PND 8 to 20) is the time when the rupts the maturation or balance of the hypothalamic pituitary granulosa cells of the ovary start responding to FSH and ovarian (HPO) axis, such as stress, would affect this param- LH. Follicles develop an antrum (ie, fluid-filled cavity), eter. The aim of this chapter is to describe the postnatal histo- which is the hallmark feature of the effect of gonadotro- logical development of the female reproductive tract tissues pins. These early antral follicles are “atypical” because they and highlight important developmental landmarks in each have plump granulosa cells and thecal cells, with little dis- tissue at the various postnatal ages. cernment between these two layers. These atypical follicles have poor adhesion between the individual granulosa cells OVARY and no zona pellucida surrounding the oocyte (Hirshfield and DeSanti, 1995). As the infantile period proceeds into its The ovary undergoes considerable postnatal development second half (PND 14 to 20), the antral follicles lose these in the rat. It becomes morphologically mature by PND 42, atypical features: the thecal cells elongate, the plump granu- at which time there are corpora lutea representing at least losa cells become tightly packed, and a protective zona pel- two ovulations. Generally, the first ovulation will occur by lucida forms around the primary oocyte. Throughout the PND 35, but there is considerable individual animal varia- entire infantile period, follicle development proceeds from tion, and first ovulation has been reported to occur in rats the central core of the ovary toward the periphery, with the ...