Female Reproductive System Flashcards
describe fluctuations in LH and FSH in pre-pubescent, pubescent, and adult females
Pre pubescent: more or less constant LH and FSH concentrations in their plasma despite low concentrations
Pubescent: gradual maturation of hypothalamus neutrons during the beginning of puberty causes an increase in synthesis and release of GnHR. as puberty approaches the very low concentration pulsatile nature of LH and FSH hormones becomes more pronounced
Adult: GnRH regulates release of LH and FSH- they are released in short bursts every 1-4 hours. LH and FSH promote ovulation and stimulate secretion of the sex hormones
describe follicle development
The human ovary consists of an inner medulla and outer cortex with indistinct boundaries. The medulla contains the blood vessels and nerves, while the cortex is occupied by developing follicles. A cross-section of an ovary will reveal follicles in various stages of development.
primordial follicle –> primary follicle –> secondary follcile –> graafian follicle –> corpus luteum –> Corpus Albicans
describe the Primordial Follicle
An ovarian follicle progresses through several distinct phases before it releases its ovum. During the first five months of development, a finite number of primordial follicles form in the fetal ovary. These follicles consist of oocytes surrounded by a single layer of squamous follicular cells. These primordial follicles remain in the process of the first meiotic division. At puberty, they begin to develop further and become primary follicles.
describe the primary follicle
Early Primary Follicle: At the start of each menstrual cycle a limited number of primordial follicles are triggered to develop. The first apparent histological stage is the early primary follicle that consists of a central oocyte surrounded by a single layer of follicular cells which have become cuboidal. The zona pellucida is a thin band of glycoproteins that separates the oocyte and follicular cells. Proteins on the surface of sperm will bind to specific glycoproteins in the zona pellucida.
Late Primary Follicle: The late primary follicle stage is reached when the follicular cells proliferate into a stratified epithelium known as the zona granulosa. The zona pellucida enlarges and can be seen even more clearly in this image.
describe the Secondary Follicle
The characteristic feature that distinguishes secondary from primary follicles is the appearance of a follicular antrum within the granulosa layer. The antrum contains fluid which is rich in hyaluronan and proteoglycans. Note the increase in cell layers of the zone granulosa, the thicker zone pellucida, and larger oocyte. At this stage, a layer of cells outside the follicle become evident. These cells compose the theca interna and contribute to the production of estrogens.
Recall that the production of estrogen requires both the cells of the theca interna and granulosa cells. Estrogens, like all steroid hormones, are produced from cholesterol through a multi-step process that requires several different enzymes. Neither the cells of the theca interna nor the granulosa cells contain all of the enzymes necessary to convert cholesterol into estrogens. Theca cells contain enzymes that catalyze the initial conversion of cholesterol into androgens but lack aromatase that carries out the final steps of converting androgens into estrogens. Consequently, androgens produced by theca cells diffuse into the granulosa cells which contain aromatase but lack the enzymes for the initial steps in estrogen synthesis. The theca cells are in a better position to catalyze the initial steps in estrogen synthesis because they are closer to blood vessels and can take up LDL to obtain cholesterol.
describe the graafian follicle
The Graafian follicle is the stage after the first meiotic division has completed but before ovulation. The oocyte is now a 2N haploid. The follicle is characterized by a large follicular antrum that makes up most of the follicle. The secondary oocyte, having undergone the first meiotic division, is located eccentrically. It is surrounded by the zona pellucida and a layer of several cells known as the corona radiata. When released from the Graafian follicle and into the oviduct, the ovum will consist of three structures: oocyte, zona pellucida and corona radiata.
describe the corpus luteum
After release of the ovum, the remaining cells of the granulosa and theca interna form the corpus luteum. The center contains the remains of the blood clot that formed after ovulation. Surrounding the clot are glanulosa lutein cells and on the outside theca lutein cells. These cells produce progesterone and to a lesser extent cholesterol.
The granulosa lutein cells have an appearance characteristic of steroid-producing cells, with pale cytoplasm indicating the presence of lipid droplets. Theca lutein cells are smaller and more deeply stained. Blood vessels penetrate into region of the granulosa lutein cells allowing them to take up cholesterol to be used to synthesize progesterone.
The activity of the cells of the corpus luteum is sustained by leutenizing hormone. If the ovum is fertilized and implants in the uterine wall, human chorionic gonadotropin replaces leutenizing hormone to sustain the activity of the cells in the corpus luteum.
describe the Corpus Albicans
If fertilization does not occur, the cells of the corpus luteum remain active for roughly 14 days until the levels of LH fall and the corpus luteum involutes to form the corpus albicans. The secretory cells of the corpus luteum degenerate, are phagocytosed by macrophages and replaced by fibrous material
describe the Atretic Follicle
Each menstrual cycle, several primordial follicles are stimulated to continue development but only one follicles completes development to release an ovum. The other follicles degenerate through a process called atresia which can occur at any stage of development. During atresia, granulosa cells undergo apoptosis and are replaced by fibrous material. The oocyte degenerates and the basement that separated the oocyte from granulosa cells thickens to become the glassy membrane.
describe the of LH and FSH during follicle development and the production of progesterone
initially as the primordial follicles develop, they produce oestrogens and in particular oestrodiol. this accounts for increase in oestrogens during follicular phase of the menstrual cycle. the rise in oestrogen causes FSH and LH concentrations to fall because oestrogen will cause negative feedback to the level of the pituitary and the hypothalamus causing gondotrophin levels to fall. as oestrogen concentrations rise there is a small increment in progesterone concentration, as oestrogen is converted to progesterone by the corpus luteum. during the ovulary stage FSH and LH surge- normally oestrogen inhibits FSH and LH production through negative feedback but at this time oestrogen causes positive feedback and promotes a surge in gondatropins. GnHR pulses and oestradiol both cause more LH to be released during the late follicular phase than the early follicular phase. after ovulation the corpus luteum is induced to produce progesterone and ostardiol which reduce proportion of FSH and LH. Inhibits are produced during the menstrual cycle in 2 forms
- inhibin B comes from dominant follicles to reduce FSH production during the late follicular phase
- inhibin A comes from the corpus luteum and it’s production mirrors that of progesterone and oestroidol. Inhibin A feeds back on the pituitary to suppress FSH and LH production during the luteal phase of the cycle
describe the hormonal changes that occur during the menstrual cycle
On Day 1 of the menstrual cycle, estrogen and progesterone levels are low. Low levels of estrogen and progesterone signal the pituitary gland to produce Follicle Stimulating Hormone (FSH). FSH begins the process of maturing a follicle (fluid-filled sac in the ovary containing an egg).
The follicle produces more estrogen to prepare the uterus for pregnancy. At ovulation, usually around Day 12 – 14, increased estrogen levels trigger a sharp rise in Luteinizing Hormone (LH) from the pituitary gland, causing release of the egg from the follicle.
The ruptured follicle (corpus luteum) now secretes progesterone and estrogen to continue to prepare the uterus for pregnancy. If the egg is not fertilized, estrogen and progesterone levels drop and, on Day 28, the menses begin.
The menstrual cycle occurs in three phases: follicular, ovulatory and luteal. The first half of the cycle is known as the follicular phase and the second half of the cycle is considered the luteal phase. Midway through the cycle between days 12 and 16 ovulation occurs, known as the ovulatory phase.
describe the effects of gondola steroids on cervical mucus, vaginal secretions and breast physiology
during the proliferation phase of the cycle the uterine wall proliferates to a depth where implantation is possible
cervical mucus shows a property called spinnbarkeit which means it offers less resistance to sperm
when left to dry on microscope slides the mucus shows the property of ferning which relies to ability of the mucus to form channels to direct sperm towards the uterine cavity.
vaginal secretions are increased
the luteal phase causes swelling of the breasts
during the late luteal phase the arteries constrict and cause a period i.e.e sloughing off of the developed secretions of the uterine mucosal wall
