Lecture 11: Gametogenesis and Fertilization

Question 1

Gametogenesis

Answer 1

Formation of egg/sperm (gametes).

shape/structure altered, and meiosis leads to chromosome number divided by half

Question 2

Meiosis Division I

Answer 2

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

Question 3

Meiosis Division II

Answer 3

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

Question 4

Spermatogenesis definition

Answer 4

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

Question 5

Spermatogenesis steps

Answer 5

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

Question 6

Where does spermatogenesis happen?

Answer 6

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

Question 7

Spermiogenesis

Answer 7

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

Question 8

regions of mature sperm

Answer 8

head –> haploid nucleus, acrosome

Tail –> middle has mitochondria, principle piece is thicker, end piece is thin

Question 9

oogenesis

Answer 9

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

Question 10

Steps of oogenesis

Answer 10

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)

Question 11

Timelines of female and male gametogenesis compared

Answer 11

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

Question 12

GRH

Answer 12

Gonadotropin releasing hormone, neurosecretory cells in hypothalamus

Question 13

FSH

Answer 13

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

Question 14

LH

Answer 14

leutenizing hormone, triggers ovulation

stimulates follicular cells and corpus luteum into making progesterone, induces growth of follicles and endometrium

Question 15

primary follicle

Answer 15

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

Question 16

secondary follicle

Answer 16

has antrum: cavity filled with liquor folliculi (liquid)

follicular cells are proliferating

Question 17

tertiary follicle

Answer 17

presses on ovarian wall at this stage, follicle is mature

Question 18

corpus luteum

Answer 18

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

Question 19

When is ovulation triggered

Answer 19

12-24 hours after LH surge

Question 20

What is expelled during ovulations

Answer 20

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

Question 21

Phases of female menstrual cycle

Answer 21

Menstrual phase, proliferative phase, luteal phase

Question 22

What happens during proliferative phase of menstrual cycle

Answer 22

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

Question 23

luteal phase of menstrual cycle

Answer 23

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

Question 24

In the event of no fertilization

Answer 24

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

Question 25

In the event of fertilization

Answer 25

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

Question 26

how does oocyte get to fallopian tube

Answer 26

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

Question 27

sperm transport

Answer 27

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

Question 28

Where/when does fertilization happen

Answer 28

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

Question 29

capacitation

Answer 29

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

Question 30

Acrosome reaction

Answer 30

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

Question 31

phases of fertilization

Answer 31

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