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Exercise 43

Physiology of Reproduction; gametogenesis & female cycles

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