Histology of the Female Reproductive System

The video of this lecture was only 15 minutes long therefore, the sheet will be fairly short. In previous histology lectures we discussed the histology of the renal system, male genital system, and in this lecture, we will discuss the histology of the female reproductive system. Please check the slides for pictures. Let’s start with a revision of the Female Reproductive System, it consists of: 1. 2. 3. 4. Vagina Uterus A pair of Fallopian Tubes (which connect the ovaries to the uterus) A pair of Ovaries Histology of the Uterus: The uterus consists of three parts: 1. Cervix 2. Fundus 3. Body Subsequently, histologically its wall is composed of three layers: 1. Endometrium: The innermost layer of the uterus which can be divided into two layers: a. Functional Layer: The layer that is sloughed off during menstruation. Consists of: i. Surface epithelium ii. Lamina Propria: Containing glands. b. Basal Layer: Deep layer responsible for the regeneration of the functional layer following menstruation. 2. Myometrium: Thickest layer of the uterus, from the prefix myo- we can conclude that it is a muscular layer. It is composed of three poorly defined areas which are separated by connective tissue: a. Stratum Submucosa: Thin inner layer composed of two layers arranged as Longitudinal and Circular muscle fibres b. Stratum Vasculare: Thick middle layer characterised by being highly vascular -hence the name- with irregularly arranged muscle fibres. Due to the fact that this is the most 2|Page contractable layer. The fibres run Longitudinally, Obliquely, Circularly, and Transversely. c. Stratum Subserosum: The outer layer of myometrium and the majority of fibres are oriented Longitudinally. The myometrium is oestrogen dependant/sensitive, meaning that in its presence stimulation of the smooth muscle cells occurs leading to their hypertrophy and hyperplasia. During pregnancy the ability of the uterus to contract is inhibited by the hormone Relaxin which is secreted by the Corpus Luteum. On the other hand, during labour the hormone Oxytocin which is secreted by the Posterior Pituitary Gland induces contraction of the uterus. 3. Adventitia: Also known as Perimetrium and is the outermost layer of the uterus. This layer is of two types: a. If it is covered by peritoneum then it is called Serosa, which is a single layer of simple squamous mesothelium b. If the aforementioned layer of perimetrium is not covered by peritoneum then it is called Adventitia, which is composed of Areolar Connective Tissue. Blood Supply of the Uterus: As we know the blood supply of the Uterus is by the Uterine artery, the uterine artery penetrates the myometrium giving off Arcuate arteries, which then give rise to Radial Arteries. These radial arteries penetrate the endometrium giving rise to Basal Arteries that supply the basal layer of the endometrium, and then the Radial Arteries terminate as Spiral Arteries (coiled in shape) which supply the functional layer. Basal Arteries Uterine Arteries Arcuate Arteries Radial Arteries Spiral Arteries 3|Page Menstrual Cycle: The menstrual cycle consists of four phases: 1. Menstrual Phase: Days 1-4 2. Proliferative/Follicular Phase: Days 5-14 of the cycle. This phase occurs due to the effects of Eostrogen that is secreted by the Theca cells of the ovarian follicles. This phase can be divided into two subphases: a. Early proliferative: Glands are small b. Late proliferative: Proliferation of the cells occurs leading to the formation of simple columnar epithelium, the glands also enlarge and become coiled in shape, and the spiral arteries begin to penetrate the functional layer. 3. Ovulation: Approximately occurs on the 14th day of the cycle 4. Secretory/Luteal Phase: Days 15-28 of the cycle. This phase occurs due to the effects of Progesterone secreted by the Corpus Luteum. In this stage the glands are coiled and filled with secretions, the spiral arteries are now coiled and penetrate the functional layer, and now the endometrium has reached its full thickness of approximately 5mm. After this phase we have two options: a. Fertilization occurs and the zygote is implanted into the uterine wall b. No fertilization occurs causing the breakdown of the Corpus Luteum, which leads to decreased levels of progesterone. This decrease in the levels of progesterone causes vasoconstriction of the spiral arteries supplying the functional area. This causes hypoxia and ischemia to the cells of the functional layer leading to their necrosis and they start to slough off and bleed in the phase of menstruation. Uterine Cervix: Histologically the cervix consists of a mucosa, musculosa, and adventitia. It is important to know that unlike the mucosa of the fundus and body of the uterus, the mucosa of the cervix does not slough off during menstruation. The glands located within the cervix are branched tubuloalveolar glands which secrete mucus. This mucus is thin in mid-cycle, however; following ovulation the mucus secretions become thick. If obstruction of the glands occurs for any reason it will give rise to 4|Page Nabothian Follicles. The lamina propria of the cervix contains connective tissue, elastic fibres, and muscle fibres. Finally, the musculosa consists of inner circular and outer longitudinal muscle cells. The cervix consists of two parts: 1. Endocervical Canal: Located inside the Uterus and is lined by simple columnar partially ciliated epithelium 2. Vaginal part: As the name suggests is located inside the vagina and therefore has the same lining has the vagina which is stratified squamous non-keratinized epithelium. Between the previous two layers there is a transitional zone of epithelium. Uterine Tube: Also known as the fallopian tube which as stated in the beginning of this sheet connect the ovaries to the uterus and it important to know that it pierces the peritoneum. This tube is composed of four parts: 1. 2. 3. 4. Intramural segment: related to the uterine wall Isthmus: adjacent to uterine wall Ampulla: Most dilated part Infundibulum: Funnel shaped segment near the ovary but not in direct relation (does not touch the ovary) contains fimbria, to “pick up” the oocyte after ovulation. The layers of the tube are as follows: 1. Mucosa: Lined by simple columnar epithelium which is partially ciliated in some areas. The non-ciliated cells contain microvilli on their surface and are called peg cells. The mucosa is characterized by having folds along the length of the uterine tubes. 2. Musculosa: consists of inner circular and outer longitudinal layer of cells. The peristaltic movement of this layer together with beating movement of the cilia causes the pushing of the oocyte throughout the tubes and into the uterus 3. Serosa: Due to the fact that is covered by peritoneum it is comprised of simple squamous mesothelium and contains the blood vessels and nerves to the fallopian tubes. 5|Page Vagina: is a muscular tube connecting the cervix with the external female genitalia. It is composed of three layers: 1. Mucosa: the surface epithelium is stratified squamous nonkeratinized epithelium. Lying under the surface epithelium is the lamina propria containing dense connective tissue and a vast network of elastic fibres. A characteristic of the mucosa of the vagina is that it does not contain glands. Therefore, the secretions that are found in the vagina are either from transudates of the blood vessels in the lamina propria or the secretions of the cervical glands. The thickness of the mucosa differs by age, in prepubertal and postmenopausal females the mucosa is thin, and in females in the reproductive age it is thick. This is due to either an increase in the mitotic activity of the basal cells or parabasal cells or hypertrophy of the superficial cells due to accumulation of lipids within the cells. 2. Musculosa: Inner circular and outer longitudinal cell layers 3. Adventitia: Rich in elastic fibres to allow its distention during labour and child birth. 6|Page