How does oogenesis work

Correct answer: Oogonium, primary oocyte, secondary oocyte, and ovum. Explanation : Oogonia are the primordial oocytes formed inside females either during or shortly after birth. Example Question 6 : Understanding Oogenesis. Possible Answers: Ovary. Correct answer: Ovum. Explanation : The female gamete is called the ovum ova, plural. Example Question 7 : Understanding Oogenesis. Possible Answers: diploid. Correct answer: haploid. Explanation : After completing meiosis II, ova are haploid cells containing one chromosome.

Example Question 8 : Understanding Oogenesis. Possible Answers: oogenesis. Correct answer: ovulation. Explanation : The release of the secondary oocyte from the ovaries is ovulation. Example Question 9 : Understanding Oogenesis.

Possible Answers: Anaphase I. Correct answer: Prophase I. Explanation : Primary oocytes enter meiosis I and replicate their genomes, but they do not make their first meiotic division.

Example Question 10 : Understanding Oogenesis. Possible Answers: an embryo. Correct answer: a secondary oocyte. Explanation : A primary oocyte becomes a secondary oocyte when the follicle grows and matures and the primary oocyte completes its first meiotic division.

Copyright Notice. View Tutors. Erin Certified Tutor. Ethan Certified Tutor. Jordan Certified Tutor. University of Alabama at Birmingham, Bachelor of Sc Report an issue with this question If you've found an issue with this question, please let us know. Do not fill in this field. Louis, MO Or fill out the form below:. Company name. Copyright holder you represent if other than yourself. At adolescence, anterior pituitary hormones cause the development of a number of follicles in an ovary. This results in the primary oocyte finishing the first meiotic division.

The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell. This second cell is called a polar body and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct.

If the secondary oocyte is fertilized, the cell continues through the meiosis II, completing meiosis, producing a second polar body and a fertilized egg containing all 46 chromosomes of a human being, half of them coming from the sperm. Spermatogenesis occurs in the wall of the seminiferous tubules, with stem cells at the periphery of the tube and the spermatozoa at the lumen of the tube.

Immediately under the capsule of the tubule are diploid, undifferentiated cells. These stem cells, called spermatogonia singular: spermatagonium , go through mitosis with one offspring going on to differentiate into a sperm cell, while the other gives rise to the next generation of sperm. Meiosis begins with a cell called a primary spermatocyte. Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1.

Energy Flow 3. Carbon Cycling 4. Climate Change 5: Evolution 1. Evolution Evidence 2. Natural Selection 3. Classification 4. Cladistics 6: Human Physiology 1. Digestion 2. The average age of menopause in women is 52 years, but it can occur anytime between 45 and The Uterine Cycle : High estrogen and progesterone levels stimulate increased endometrial thickness, but following their decline from a lack of implantation, the endometrium is shed and menstruation occurs. Normal menstrual flow can occur although ovulation does not occur.

This is referred to as an anovulatory cycle. Follicular development may start but not be completed although estrogen will still stimulate the uterine lining. Anovulatory flow that results from a very thick endometrium caused by prolonged, continued high estrogen levels is called estrogen breakthrough bleeding. However, if it is triggered by a sudden drop in estrogen levels, it is called withdrawal bleeding. Anovulatory cycles commonly occur before menopause and in women with polycystic ovary syndrome.

The menstrual cycle is controlled by a series of changes in hormone levels, primarily estrogen and progesterone. The menstrual cycle is the physiological change that occurs under the control of the endocrine system in fertile women for the purposes of sexual reproduction and fertilization.

The Menstrual Cycle : The menstrual cycle is controlled by the endocrine system, with distinct phases correlated to changes in hormone concentrations. The menstrual cycle is divided into three stages: follicular phase, ovulation, and the luteal phase. During the follicular phase or proliferative phase , follicles in the ovary mature under the control of estradiol.

Follicle-stimulating hormone FSH is secreted by the anterior pituitary gland beginning in the last few days of the previous menstrual cycle. Levels of FSH peak during the first week of the follicular phase. The rise in FSH recruits tertiary-stage ovarian follicles antral follicles for entry into the menstrual cycle.

Follicle-stimulating hormone induces the proliferation of granulosa cells in the developing follicles and the expression of luteinizing hormone LH receptors on these cells. Under the influence of FSH, granulosa cells begin estrogen secretion.

This increased level of estrogen stimulates production of gonadotropin-releasing hormone GnRH , which increases production of LH. LH induces androgen synthesis by theca cells, stimulates proliferation and differentiation, and increases LH receptor expression on granulosa cells. Throughout the entire follicular phase, rising estrogen levels in the blood stimulate growth of the endometrium and myometrium of the uterus.

This also causes endometrial cells to produce receptors for progesterone, which helps prime the endometrium to the late proliferative phase and the luteal phase. Two or three days before LH levels begin to increase, one or occasionally two of the recruited follicles emerge as dominant.

Many endocrinologists believe that the estrogen secretion of the dominant follicle lowers the levels of LH and FSH, leading to the atresia death of most of the other recruited follicles.

Estrogen levels will continue to increase for several days. High estrogen levels initiate the formation of a new layer of endometrium in the uterus, the proliferative endometrium.

Crypts in the cervix are stimulated to produce fertile cervical mucus that reduces the acidity of the vagina, creating a more hospitable environment for sperm.

Estrogen levels are highest right before the LH surge begins. The short-term drop in steroid hormones between the beginning of the LH surge and ovulation may cause mid-cycle spotting or bleeding. Under the influence of the preovulatory LH surge, the first meiotic division of the oocytes is completed.

The surge also initiates luteinization of theca and granulosa cells. In the preovulatory phase of the menstrual cycle, the ovarian follicle undergoes cumulus expansion stimulated by FSH. The ovum then leaves the follicle through the formed stigma. The luteal phase begins with the formation of the corpus luteum stimulated by FSH and LH and ends in either pregnancy or luteolysis.

The main hormone associated with this stage is progesterone, which is produced by the growing corpus luteum and is significantly higher during the luteal phase than other phases of the cycle.

Several days after ovulation, the increasing amount of estrogen produced by the corpus luteum may cause one or two days of fertile cervical mucus, lower basal body temperatures, or both. This is known as a secondary estrogen surge. The hormones produced by the corpus luteum suppress production of the FSH and LH, which leads to its atrophy. The death of the corpus luteum results in falling levels of progesterone and estrogen, which triggers the end of the luteal phase.

Increased levels of FSH start recruiting follicles for the next cycle. Alternatively, the loss of the corpus luteum can be prevented by implantation of an embryo: after implantation, human embryos produce human chorionic gonadotropin hCG.

Human chorionic gonadotropin is structurally similar to LH and can preserve the corpus luteum. If implantation occurs, the corpus luteum will continue to produce progesterone and maintain high basal body temperatures for eight to 12 weeks, after which the placenta takes over this function. Estrogen and progesterone have several effects beyond their immediate roles in the menstrual cycle, pregnancy, and labor.

Both estrogens and progesterone serve functions in the body beyond their roles in menstruation, pregnancy, and childbirth. Estrogens are a group of compounds named for their importance in the estrous cycle of humans and other animals.

They are the primary female sex hormones, although they are found in males as well. The three major naturally occurring forms of estrogen in women are estrone E1 , estradiol E2 , and estriol E3. Estetrol E4 is produced only during pregnancy. Natural estrogens are steroid hormones, while some synthetic versions are non-steroidal.

Estrogens are synthesized in all vertebrates as well as some insects, and their presence in both suggests that they have an ancient evolutionary history. Like all steroid hormones, estrogen readily diffuses across the cell membrane.

Once inside the cell, it binds to and activates estrogen receptors which in turn modulate the expression of many genes. Estriol : Another one of the three main estrogens produced in humans. While estrogens are present in both men and women, they are usually at significantly higher levels in women of reproductive age.