Lecture 46 Flashcards
What are the steps in oogenesis?
Oogenesis starts as a fetus and involves cells undergoind mitosis to produce a large number of primary oocytes from oogonium (diploid). Before birth the prophase I of meiosis starts and is suspended. During puberty GnRH (gonadotrophin releasing hormone) influence leads to the primary oocyte completing meiosis I to form two daughter cells (both haploid 23), one is a secondary oocyte and one is a much smaller polar body. The secondary oocyte (many formed in one cycle but only one released) halts at metaphase II and is suspended until fertilisation. Meiosis II resumes when the sperm penetrates the plasma membrane of the ovum at fertilisation, leading to a zygote. If not fertilised it will die (atresia, three polar bodies are also formed overall which also die), and therefore never complete meiosis.
What is the difference between primary follicles and secondary follicles in structure?
Primary follicles are a single primary oocyte surrounded by granulosa cells, these divide into secondary oocytes/follicles (more layers of granulosa cells) and develop fluid (known as the antrum) around the oocyte , these then divide again to form the mature follicel which will then be released in ovulation.
What are the main female reproductive hormones?
The main female reproductive hormones are: gonadotrophin releasing hormone leads to rellease of follicle stimulating hormone (stimulates several primary follicles to begin growing and leads to initial estrogen secretion) and luteinising hormone (ovulation, completion of follicle and oocyte growth and luteinization (leads to formation of corpus luteam which will help with maintaining pregnancy)., from the anterior pituitary. The ovary follicles will release estradiol (an estrogen) and the corpus luteum will release inhibin (suppresses FSH release) and progesterone (inhibits GnRH, maintains pregnant state and stimulates endometrial proliferation).
What are the two female cycles?
The ovarian cycle produces ovum each month and helps regulate menstrual cycle, the menstrual/endometrial cycle is done to ensure the lining of the uterus is suitable for implantation.
What does the ovarian cycle consist of?
The ovarian consists of the follicular (preovulatory phase) roughly from day 1-14, it acts to recruit follicles (reduction of FSH due to inhibin) and ovulate them, it involves a LH spike (due to estradiol from follicles leading to GnRH) at the end and highest levels of FSH at the start, it ends with the rupturing of the follicle. It also consists of the luteal from roughly day 15-28. The ovulated follicle will collapse and form corpus luteum cells (leading to progesterone, estradiol and inhibin and hence decrease FSH and LH secretion.) The progesterone stimulates uterine development (if pregnancy occurs this will remqain for roughly 3 months), the luteinizing hormone levels fall towards the end.
What occurs in the menstrual cycle?
The menstrual cycle consist fo the proliferative (and menstrual) phase from day 1-14 roughly and the secretory (and pre-menstrual) from day 15-28 roughly. Estradiol levels rise towards the end of the proliferative and increases endometrium levels , the progesterone levels then rise rapidly (estradiol drops a bit) at the start of the secretory and plateau, leading to secretory endometrium and a readying blood supply. Towards the end of the secretory period the progesterone levels drop and the lining is shed.
What is amenorrhea? What is a common cause and what is also commonly gotten?
Amenorrhea is the absence of normal menstruation it can be primary (never occured) or secondary (menstruated previously, now don’t or very few). It tends to be caused by low levels of estradiol and hence low luteinizing hormone produced, therefore no endometrium thickening. at least 16% body fat is neccessary to effectively make estradiol (because its a steroid, hence needing cholesterol), this means weight loss can be a common cause. Osteoporosis is also often linked because lack of estradiol leads to bone break-down and deposition of new bone.
What is the function and structure of the breasts? What hormone changes help regulate this process?
The breasts lie on the pectoralis major muscles, they function to nourish infants and are prepared for this by estradiol and progesterone. The order of structures is lobes into lobules into alveoli into lactiferous ducts into lectiferous sinuses which then open at the nipple pores. The glands are supported by suspensory ligaments. After birth the estradiol levels lower but prolactin secretion increases (increases milk production), oxytocin secretion also increases and helps to let milk out of the nipple in response to suckling.
What is menarche and menopause? Why do they occur?
Menarche is the commencement of cyclic menstrual function (at puberty, roughly age 13), it is stimulated by estradiol. Menopause is the cessation of menstruation. It occurs at roughly age 45-50 due to absence off or non responsiveness of follicles and hence reduction of estradiol and progesterone. Due to no anterior feedback no longer occuring FSH and LH levels are high.
