Female Reproductive System - Lec 1 & 2 PDF

Female Reproductive System - HPHS222 Dr Meleshni Naicker Department of Human Physiology University of KwaZulu-Natal - Westville [email protected]  Learning Outcomes Development of Female Reproductive System Organization o...

Female Reproductive System - HPHS222 Dr Meleshni Naicker Department of Human Physiology University of KwaZulu-Natal - Westville [email protected]  Learning Outcomes Development of Female Reproductive System Organization of Female Reproductive System Oogenesis Follicular Development  Development of the Reproductive Systems In the absence of In the presence anti-mullerian of anti-mullerian hormone hormone Male and female reproductive systems develop from similar embryonic tissue. First few weeks of development, male and female embryos are indistinguishable. Adult reproductive systems share some functional similarities.  Female Reproductive System Lecture 1 Organization of Female Reproductive System  Female Reproductive System Principal functions: To produce the ova for sperm fertilization, To provide the appropriate conditions for embryo implantation, fetal growth & development & birth Regulation: Directed by the hypothalamic-pituitary-ovarian axis – ovarian cycle, which involves changing patterns of hormone production & secretion, regulates the hypothalamic-pituitary-gonadal axis in a classical negative feedback pattern. Female Reproductive Organs Female Reproductive System Female Reproductive System - The list above has superficial features of the female external genitalia. - Note the fallopian tubes: fimbriae, infundibulum, ampulla, isthmus, and uterine parts. Note the various parts of the uterus, cervix, and vagina as well.  Female Reproduction Unlike males, who are able to produce sperm cells throughout their reproductive lives, females produce a finite number of egg cells. During early fetal development germ cells migrate into the ovaries and differentiate into oogonia. Oogenesis: before birth During fetal development, oogonia (germ cells) divide by mitosis to make 1 to 2 million primary oocytes in the embryo. Primary oocytes begin meiosis and stop in prophase I until puberty. Primordial follicles: Support cells that surround the oocyte in the ovary. 2 million present at birth 400,000 remain at puberty Oogenesis: after puberty Each month, hormones cause several follicles to develop, which triggers the primary oocyte to resume meiosis I. Polar bodies: When the cell divides, all the cytoplasm and organelles stay with one of the new cells (secondary oocyte), the other cell is just DNA, (& is called a polar body which may or may not divide but its products degenerate & it is discarded). Secondary oocyte: The stage at which ovulation occurs. The secondary oocyte begins meiosis II, but stops in metaphase II. The secondary oocyte is ovulated. Meiosis II is completed only if it is fertilized. If fertilization does occur, a mature ovum and another polar body is produced.  Oogenesis: oogonia to oocytes Germ cells from yolk sac migrate to ovary and become potential egg cells called oogonia. In fetus, millions of oogonia produced by mitosis but most of them degenerate (atresia). Some develop into immature egg cells called primary oocytes during fetal development 200,000 to 2 million present at birth 400,000 remain at puberty but only 400 mature during a woman’s reproductive lifespan. Each month, hormones cause meiosis I to resume in several follicles so that meiosis II is reached by ovulation. Each month about 20 primary oocytes become secondary oocytes but usually only one survives to be ovulated from the Graafian follicle. Penetration by sperm causes the final stages of meiosis to occur.  Oogenesis Process by which female gametes (ova/egg) are generated. i.e. the process of the formation of a mature ovum from the oogonia in females. Oogenesis starts in the outermost layer of the ovary during early female fetal development. The steps in oogenesis up to the production of primary oocytes occur before birth. Primary oocytes do not divide further; instead they become either secondary oocytes or degenerate. In oogenesis, diploid (2n) oogonium (germ cells) undergoes mitosis until one develops into a primary oocyte, which will begin the first meiotic division, but will then arrest until later in life when it will complete this division as it develops in the follicle, giving rise to a haploid (n) secondary oocyte and a smaller polar body. The secondary oocyte begins the second  Ovary Female Gonads Paired Lie in the peritoneal cavity Suspended by suspensory ligament  Ovary: Follicle Development Each follicle consists of an immature egg called an oocyte. Cells around the oocyte are called: Follicle cells (one cell layer thick) Stimulated to mature by FSH from the pituitary gland Granulosa cells (when more than one layer is present) Thecal cells: Cells in the ovarian stroma Thecal & granulosa cells work together to produce estrogen. A protective layer of glycoprotein forms around the egg called the zona pellucida.  Ovary: Follicle Development The ovary contains the oocytes, enclosed in follicles consisting of endocrine theca & granulosa cells, which provide the ovarian hormones. Follicles start to develop further shortly after the first menstrual cycles. Each cycle a small number of follicles develop into Graafian follicles, with increased numbers of granulosa & theca cells, & a vascularized outer layer that supplies blood born substances such as LH and FSH. On day 5- 7 of the menstrual cycle, 1 follicle becomes dominant & grows very fast, until it ruptures & releases the oocyte. The rest of the follicle forms the corpus luteum, which provides hormones that are necessary for implantation & early development of a fertilized ovum. If there is no conception, the corpus luteum regresses over ~14 days to become the corpus albicans.  Ovary: Follicle Development Follicle Development: Primordial follicle: one layer of squamous-like follicle cells surrounds the oocyte. Primary follicle: two or more layers of cuboidal granulosa cells enclose the oocyte. Secondary follicle: has a fluid-filled space between granulosa cells that coalesces to form a central antrum. Graafian follicle: secondary follicle at its most mature stage that bulges from the surface of the ovary. Ovary: Follicle Development Female Reproductive System Lecture 2 Follicular Organisation & Development  Primordial Follicle: Undeveloped follicles known as primordial follicles are inactive structures, awaiting stimulation from FSH before reentering their developmental pathway. Most numerous of the follicles in the cortex. Primordial follicles are composed of a primary oocyte surrounded by a single layer of flattened/squamous follicular cells. The primary oocyte has a large nucleus with dispersed finely granular chromatin, a prominent nucleolus and little cytoplasm. The oocyte is called primary oocyte and is in prophase of first meiotic division. Further meiotic activity arrested.  Primary Follicle: Once stimulated, by FSH, 30-50 primordial follicles re-enter development, and become primary follicles. Follicular or granulosa cells, enlarge - a single layer of cuboidal cells. Follicle enlarges in size - primary follicle. A layer of glycoprotein (zona pellucida) develops around the oocyte.  Primary Multilaminar Follicle: The primary follicle oocyte (O) has greatly enlarged and the follicular cells (F) have multiplied by mitosis and become cuboidal in shape. They are now known as granulosa cells. A zona pellucida (ZP) layer develops between the oocyte and the granular cells – this is a thick homogeneous layer containing glycoprotein and acid proteoglycans. Wheater’s Functional Histology, 6th Edition  Secondary Follicle: The zona granulosa (ZG) continues to proliferate. In addition, small fluid-filled spaces begin to develop between the granulosa cells, and these fuse to form the follicular antrum (FA). This is now referred to as the secondary follicle. At this stage, the oocyte (O) has nearly reached full size and becomes situated eccentrically within a thickened area of the zona granulosa called the cumulus oophorus (CO). The zona pellucida (ZP) can also be seen in this image. Antrum contains a hormone-rich fluid  Secondary Follicle: Stroma around the developing follicle differentiates into thecal cells. At the periphery of the follicle, the theca folliculi has developed two layers: (i) the theca interna TI, comprising several layers of rounded cells, (ii) and the less well-defined theca externa TE, consisting of spindle-shaped cells that merge with the surrounding stroma.  Graafian Follicle: Continued maturation and enlargement of secondary follicle - Graafian follicle (mature follicle) - occurs just before ovulation. On approaching maturity, further growth of the oocyte ceases - At this stage, the oocyte (O) is known as the secondary oocyte. The follicular antrum (FA) is markedly enlarged. Zona granulosa (ZG) forms a layer of even thickness around the periphery of the follicle. At this stage, the maturing follicle has reached between 1.5 and 2.5 cm in diameter and appears as a bulge beneath the ovarian surface. Cumulus oophorus diminishes, and the oocyte O is instead surrounded by the corona radiata CR (i.e a thickened cell layer), which remains attached to the zona Wheater’s Functional Histology, 6th granulosa (ZG) by thin bridges of cells. Edition Graafian Follicle: mature follicle  Corpus Luteum Following ovulation, the ruptured follicle collapses and fills with a blood clot (B) to form the corpus luteum of menstruation. The blood clot B is surrounded by a wide zone of granulosa lutein cells G, penetrated by septa S containing large blood vessels. A thin zone of theca lutein cells T can be seen peripherally. Thus, rearrangement of granulosa cells and theca interna cells. Externally, the corpus luteum is bounded by condensed stromal tissue, that represents the theca externa of the Graafian follicle. The corpus luteum serves to provide hormones that are necessary for implantation and early Wheater’s Functional Histology, 6th development of a fertilized ovum.  Corpus Luteum Hormones - corpus luteum inhibit pituitary LH and FSH preventing ovulation of other follicles. Corpus Luteum secretes:- Progesterone – completes the preparation of uterine lining Estrogens – work with progesterone Relaxin – relaxes uterine muscles and pubic symphysis Inhibin – decreases secretion of FSH and LH.  If a pregnancy occurs, corpus Corpus Luteum luteum produces progesterone to maintain the wall of the uterus during the early period of development - 4-5 months – stimulated by placental human chorionic gonadotropin (HCG) - a hormone produced primarily by syncytiotrophoblastic cells of the placenta during pregnancy. If fertilization does not occur (i.e there is no pregnancy), the corpus luteum degenerates & regresses (over approx. 14 days) after ovulation to become the corpus albicans → i.e inactive fibrous tissue mass - a white scar tissue left after the corpus luteum dies. Secretory cells of the