Lecture 11: Gametogenesis and Fertilization Flashcards Preview

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Flashcards in Lecture 11: Gametogenesis and Fertilization Deck (31):
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Gametogenesis

Formation of egg/sperm (gametes).
shape/structure altered, and meiosis leads to chromosome number divided by half

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Meiosis Division I

Reduction division, diploid --> haploid. When DNA replicates and recombinates

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Meiosis Division II

Sister chromatids divide, when random assortment happens. 2 haploid cells --> 4 haploid cells

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Spermatogenesis definition

process from which spermatogonia, which are dormant until puberty --> mature sperm.

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Spermatogenesis steps

Spermatogonia (46, XY) undergo many steps of mitosis during puberty --> called primary spermatocyte after DNA replication/mitosis step is complete (46 XY) --> first meiotic division --> secondary spermatocytes (23X, 23Y) --> second meiotic division --> spermatids (23x, 23x, 23y, 23y) --> spermiogenesis --> mature sperms

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Where does spermatogenesis happen?

In the seminiferous tubules, and then maturation (spermiogenesis) happens in the epididymis

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Spermiogenesis

Golgi region --> acrosomal head, contains enzymes that help penetrate corona radiata and zona pellucida; Centrioles --> coordinate microtubules that form the tail; cytoplasm --> decreases; mitochondria --> form sheath around tail, provide energy for motility

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regions of mature sperm

head --> haploid nucleus, acrosome
Tail --> middle has mitochondria, principle piece is thicker, end piece is thin

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oogenesis

oogonia turn into mature oocytes, begins in embryo process completed after puberty (final stage upon fertilization)

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Steps of oogenesis

oogonium undergoes mitosis during fetal period--> before/at birth undergoes meiosis, starts developing primordial follicle--> becomes primary oocyte--> after birth arrested in the middle of first meiotic division, still primary oocyte, has primary follicle (2n, 4c) --> after puberty 1st meiotic division completed, still primary oocyte but with secondary follicle --> starts second meiotic division, develops tertiary follicle, now called secondary oocyte (1n, 2c); Arrested at metaphase II--> ovulation --> at fertilization second meiotic division is completed (1n, 1c + sperm)

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Timelines of female and male gametogenesis compared

Female --> begins during embryogenesis, arrests until puberty, completed upon fertilization. 1 germ cell --> 1 ovum
Male --> begins after puberty, 1 germ cell --> 4 spermatozoa

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GRH

Gonadotropin releasing hormone, neurosecretory cells in hypothalamus

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FSH

follicle stimulating hormone, stimulate development of follicles, stimulate follicle into making estrogen

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LH

leutenizing hormone, triggers ovulation
stimulates follicular cells and corpus luteum into making progesterone, induces growth of follicles and endometrium

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primary follicle

has zona pellucida: translucent, non-cellular membrane between primary oocyte and follicular cells

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secondary follicle

has antrum: cavity filled with liquor folliculi (liquid)
follicular cells are proliferating

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tertiary follicle

presses on ovarian wall at this stage, follicle is mature

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corpus luteum

walls of ovarian follicle collapse, form folds. Develop glandular structures secreting progesterone and estrogen

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When is ovulation triggered

12-24 hours after LH surge

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What is expelled during ovulations

secondary oocyte surrounded by zona pellucida and corona radiata ( follicular cells), but the follicle remains in ovary

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Phases of female menstrual cycle

Menstrual phase, proliferative phase, luteal phase

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What happens during proliferative phase of menstrual cycle

growth of ovarian follicles, controlled by estrogen peaking, endometrium thickens

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luteal phase of menstrual cycle

triggered by LH surge and ovulations, formation, functioning and growth of corpus luteum, progesterone stimulates glandular epithelium

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In the event of no fertilization

CL degenerates, estrogen and progesterone levels fall, blood to secretory endometrium is constricted (called ischemia), leading to menstruation

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In the event of fertilization

zygote becomes blastocyst, implates in endometrium, hCG (human chorionic gonadotropin) produced by synctiotrophoblast, keeps CL producing estrogen and progesterone

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how does oocyte get to fallopian tube

during oculation end of fallopian tube touches ovary, suction/fluid currents sweep up oocytes, peristalsis carries oocyte up

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sperm transport

epididymus--> ductus deferens through peristalsis --> urethra. Accessory sex glands produce secretions of semen

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Where/when does fertilization happen

in ampullary beginning portion of tube, 12-24 hours after ovulation

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capacitation

reaction sperm undergoes in uterus before fertilization --> allows acrosomal rxn to occur
Glycoprotein coat digested from acrosome
membrane cholesterol/phospholipids ratio altered
increase in motility

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Acrosome reaction

acrosome binds to zp3 protein on zona pellucida, holes formed in acrosome membrane, hyaluronidase and acrosin released

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phases of fertilization

1. penetration corona radiata, followed by zona pellucida 2. fusion of plasma membranes 3. zona rxn, makes zona pellucida impermeable to other sperm 3. two pronucleii breakdown, chromosomes join--> zygote formed