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Exercise 43
Physiology of Reproduction; gametogenesis & female cycles
| Question | Answer |
|---|---|
| where do gametes produce? | only in the testis or ovary |
| what type of chromosomes do gametes have | they have only half the normal chromosome number (designated as n, or the haploid complement) |
| in humans, gametes have how many chromosomes? | 23 chromosomes instead of 46 of other tissue cells |
| theoretically every gamete has a ___ | full set of genetic instructions, a conclusion borne out by the observation that some animals can develop from an egg that is artificially stimulated rather than by sper entry |
| what is gametogenesis | the process of gamete formation |
| what does gametogenesis involve | it involves reduction of the chromosome number by half |
| why does it do this | it is important bc it maintains the characteristic chromosomal number of the species generation after generation; otherwise there would be a doubling of chromosome number w. each succeeding generation & the cells would become so chock-full of genetic mate |
| homologous chrommosomes | are egg & sperm chromosomes that carry genes for the same traits |
| zygote | fertilized egg that occurs after a sperm & egg fuse |
| how many chromosomes does a zygote have? | it is said to conatin 23 pairs of homologous chromosomes; or the diploid (2n) chromosome number of 46 |
| define mitosis | nuclear division process; it assures that al cells of the developing human body have a chromosome content exactly identical in quality & quantity to that of the fertilized egg |
| define meiosis | a specialized type of nuclear division that occurs in the ovaries & testes during gametogenesis; it occurs in order to produce gametes w. the reduced (haploid) chromosomal number |
| what happens just before meiosis begins | the chromosomes are replicated in the mother cell or stem cell just as they are before mitosis; as a result, the mother cell briefly has double the normal diploid genetic complement; the stem cell then undergoes 2 consecutive nuclear divisions termed meio |
| what is the purpose of cytokinesis | it produces 4 haplid daughter cells, rather than the 2 diploid daughter cells produced after mitotic division |
| list the phases in mitosis | prophase, metaphase, anaphase & telophase |
| what happens during the first maturation division (meiosis I) | an event not seen in mitosis occurs dring prophase; the homologous chromosomes, each now a duplicated structure, begin to pair so that they become closely aligned alon their entire length |
| what is this pairing called | synapsis |
| what is the result of this pairing | 23 tetrads (groupings of four chromatids) form, become attached to the spindle fibers, & begin to align themselves on the spindle equator |
| crossover (chiasmata) | occurs while in synapsis, the "arms" of adjacent homologous chromosomes coil around each other forming these many points; the (conjugal bed of the cell) |
| what happens wen anaphase of meiosis I begins | the homogues separate from one another, breaking & exchanging parts at points of crossover, & move apart toward opposite poles of the cell |
| what are dyads | the centromers holding the "sister" chromatids (threads of chromaatin) together (do not break at the point of crossing over) |
| what happens in the 2nd maturation division, & whats different? | the events are parallel to those in mitosis, except that the daughter cells do not replicate their chromosomes before this division, & each daughter cell has only half of the homologous chromosomes rather than a complete set |
| what is spermatogenesis | human sperm production; begins at puberty & continues wo interruption throughout life; the process of gametogenesis in males |
| where does spermatogenesis occur? | in the seminiferous tubules of the testes |
| what is spermatogonia | primitive stem cells |
| where are spermatognia found? | at the tubule periphery, they divide extensvel to build up the stem cell line |
| before puberty all divisions are ___ | mitotic divisions that produce more spermatogonia |
| what happens after puberty in a male | under the influence of FSH secreted by the anterior pituitary gland each mitotic division of a spermatogonium produces one spermatogonium & one primary spermatocyte which is destined to undergo meiosis |
| as meiosis occurs, the _____ | deividing cells approach the lumen of the tubule |
| the progression of meiotic events can be followed from the _____ to the ____ | tubule periphery to the lumen |
| spermatids are what type of cells | haploid cells that are the actual product of meiosis, are not functional gametes |
| describe spermatids | they are nonmotile cells & have too much excess baggage to function well in a reproductive capacity |
| spermiogenesis | follows meiosis, strips away the extaneous cytoplasm from the spermatid, converting it to a motile, streamlined sperm |
| what is a follicle | it is a saclike stucture within each ovary where each immature ovum develops in; it is encased by one or more layers of smaller cells called follicle cells (when one layer is present) or granulosa cells (when there is more than one layer) |
| oogenesis | female gamete formation |
| where does oogenesis occur? | in the ovary |
| what does oogenesis begin with | primitive stem cells calle oogonia, located in the ovarian cortices of the developing female fetus |
| during fetal development the oogonia undergo___ | mitosis thousands of times |
| what happens after the oogonia undego mitosis? | then tey become encapsulated by a single layer of squamouslike follicle cells & form the PRIMORDIAL FOLLICLES of the ovary |
| what are primary oocytes | they are in the prophase stag of meiosis I |
| what is a primary follicle | as the follicle grows, tis epithelium changes from squamous to cuboidal cells & this is what it turns into |
| what does the primary follicle begin to produce? | estrogens; & the primary oocyte completes its first maturation division, producing 2 haploid daughter cells that are ery dispoportionate in size |
| secondary oocyte | one of the two haploid daughter cells produced; it contains nearly all of the cytoplasm in the primary oocyte |
| what is the other haploid daughter produced? | first polar body |
| when the first polar body completes the second maturation division it produces | 2 or more polar bodies; these eventually disintegrate for lack of sustaining cytoplasm |
| as the follicle containing the 2ndary oocyte continues to enlarge, blood levels of estrogens __ | rise |
| estrogen exerts a ____ feedback influence on __ | negative; on the release of gonadotropins by the anterior pituitary |
| what triggers ovulation | a sudden burstlike release of LH (& to a lesser extend, FSH) by the anterior pituitary |
| as the follicle reaches the mature ___ or _____ stage, rising estrogen levels become highly stimulatory & ovulations is eventually triggered | vesicular or Graafian follicle |
| after this occurs the secondary oocyte is extruded & begins its journey down the uterine tube to the uterus; if penetrated en route by a sperm, the secondary oocyte will | undergo meiosisII, producing one large ovum & a tiny second polar ody |
| when second maturation division is complete, the chromosomes of the gg & sperm | combine to form teh diploid nucleus of the fertilized egg |
| if sperm penetrationdoes not occur, the secondary oocyte | disintegrates wo ever producing th efemale gamete in human females |
| in the female , meiosis produces how many gametes | only one functional gamete |
| how many gametes are produced in the male | four |
| describe the male sperm | they are tiny, & equipped w tails for locomotion; have few organelles & virtually no nutrient-containing cytoplasm; hence the nutrients contained in semen are essential to their survival |
| describe the female egg | is relatively large nonmotile cell, well stocked w. cytoplasmic reserves that nourish the developing embryo until implantation can be accomplished |
| essentially all the zygote's organelles are | "delivered" by the egg |
| once the secondary oocyte has been expelled from the ovary, LH transforms the ruptured follicle into the | corpus luteum |
| what does the corpus luteum produce | progesterone & estrogen |
| rising blood levels of the 2 ovarian hormones inhibit | FSH release by the anterior pituitary |
| as FSH declines its stimulatory effect on follicular production of estrogens | ends & estrogen blood levels begin to decline |
| rising estrogen levels trigger | LH release by the anterior pituitary |
| falling estrogen levels result in | declinign levels of LH in the blood |
| corpus luteum secretory function is maintained by | high blod levels of LH |
| as LH blood level begin to drop toward the end of the 28- day cycle progesterone production | ends |
| what happens to the corpus luteum | it begins to degenerate & is replaced by scar tissue (corpus albicans( |
| germinal epithelium | outermost layer of the ovary |
| primary follicle | one or a few layers of cuboidal follicle cells surrounding the larger central developing ovum |
| secondary (growing) follicles | follicles consisting of several layers of follicel (granulosa) cells surrounding the central developing ovum, & beginning to show evidence of fluid accumulation & antrum (central cavity) |
| vesicular (Graafian) follicle | when the follicle has a large antrum containing fluid produced by the granulosa cells. the developing 2ndary oocyte is pushed to one side of the follicle & is surounded bya capsule of several layers of granulosa cells called the CORONA RADIATA (radiating |
| theca | encloses the follicle |
| corpus luteum | a solid glandular structure or a structure containing a scalloped lumen that develops from the ruptured follicle |
| uterine cycle; menstual cycle | hormonally controlled by estrogens * progesterone secreted by the ovary |
| name the three stages | menstrual, proliferative & secretory |
| describe the menstual phase (menses) | approx 1-5 days; sloughing off of the thick functional layer of the endometrial lining of the uterus, accompanied by bleeding |
| proliferative phase | approx 6-14 day; under the influence of estrogens produced by the growing follicle of the ovary, the endometrium is repaired, glands & blood vessels proliferate, & the endometriumthickens. ovulation occurs at the end of this stage |
| secretory phase | approx 15-28 days; under the influence of progesterone produced by the corpus luteum, the vascular supply to the endomeetrium increases further. the glands increase in size & begin to secrete nutrient substances to sustain a developing embryo |
Created by:
Brina
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