reproduction system - production of gametes / fertilization

gametogenesis

process of differentiation that produces cells specialized for reproduction

1. spermatogenesis

2. oogenesis

spermatogenesis

process of producing sperm with half the number of chromosomes (haploid) as somatic cells

• produces sperm

• spermatogonia (starting cell) differentiates / turns into spermatozoa (sperm cell)

spermatogonia

starting sperm cell

spermatozoa

mature sperm cell

spermatogenesis location

takes place in seminiferous tubules in testes

cells involved with spermatogenesis

1. sertoli cells

2. leydig cells

sertoli cells

• support for germ cell

• environment for germ cells to develop

• located inside seminiferous tubules

leydig cells

produce testosterone and are located in interstitial space

The overall results of spermatogenesis

1. cell proliferation

2. cell differentiation

3. spermatid maturation

4. genetic variability

spermatogenesis cell proliferation

spermatogonia can copy themselves to make more germ cells using mitotic division (starting cell)

spermatogenesis cell differentiation

spermatogonia (2N2n) synthesis primary daughter cell (4N2n) to primary spermatocyte 4N2n meiosis 1 2 secondary spermatocytes (2n1n) meiosis 2 4 spermatids (1N1n)

spermatid maturation

has to go through spermatogenesis process to gain flagellum and officially become mobile / motile sperm

genetic variability

• independent assortment during meiosis (genes are randomly divided and each sperm has different combination)

• crossing over during prophase 1 of meiosis

oogenesis

differentiation of female primordial germ cell into an unfertilized egg

1. produces eggs (ovum)

2. oogonia (starting cell) differentiates / turns into ovum (mature egg cell)

3. takes place in ovary

oogonia

starting egg cell

ovum

mature / fertilized egg cell

ovarian / ovulating cycle

the maturation of the follicle and egg

follicle

tiny sac that holds an immature egg, each follicle contains a single oogonia

• follicle grows / matures with the egg each month until one becomes dominant (most mature primary ooctye)

• releases egg during ovulation, then becomes graafian follicle / corpus lutenum

ovarian cycle process

1. hypothalamus releases GnRH once a month

2. ant. pit releases FSH and LH

3. FSH stimulates the growth / maturity of 1 follicle by stimulating follicle to secrete own estrogen

4. estrogen stimulating follicle then stimulates release of LH

5. LH triggers immature oocyte / oogonia in follicle to complete meiosis 1

6. then oocyte becomes mature and is released into fallopian tube with the help of enzymes and follicle (ovulation complete)

7. damaged follicle slows down estrogen production and becomes corpus luteum

8. corpus luteum releases progesterone to inhibit release of FSH and LH

9. if egg fuses with sperm it completes meiosis II to become ovum

10. if doesn’t egg breaks down and leaves body during menstrual cycle with endometrium ining shedding

fallopian tubes

where fertilization occurs

uterus

where fertilized / non fertilized egg goes

menstrual cycle

happens in uterus to prepare for a single fertilized egg

the overall results of oogenesis

1. cell proliferation

2. growth phase

3. cell differentiation

oogenesis cell proliferation

oogonia can copy themselves to make sure females have enough cells that can become eggs (occurs before puberty using mitotic division)

growth phase

primary oocyte grows

oogonia cell differentiation

oogonia in follicle (2N2n) to primary daughter cell (2N2n) grows primary oocyte synthesis primary ooccyte (4N2n) meiosis I secondary oocyte / mature follicle (2N2n) 1st polar body (2N2n) if it fertilizes with sperm meiosis II mature ovum (1N1n) 2nd polar body (1N1n)

polar body

non functional eggs and eventually die

meiosis II

mature secondary oocyte only completes meiosis II when sperm and oocyte connect and oocyte becomes ovum

fertilization

fusion of gametes (egg and sperm form zygote)

general overview of fertilization events

1. activation of sperm

2. finding the egg

3. sperm penetration

4. prevention of polyspermy

5. fusion of egg and sperm

6. initiation of development

activation of sperm mobility

• sperm maturing in epididymis increases motility

• motility is triggered by ejaculation of semen into the female reproductive tract; gradually increases when getting closer to egg

attraction of sperm to the egg

uses chemotaxis

chemotaxis

chemical signals released by ovum that attracts sperm to egg

sperm penetration of egg

1. capacitation

2. acrosome reaction

capacitation

period of time needed for sperm to mature in female reproductive tract before they’re capable of fertilized the egg

acrosome reaction

• acrosome leaks hydrolytic enzymes to help get through oocytes protective outer layers

• once sperm is flooded with calcium ions after binding to receptors, acrosomal reaction is trigger to get through zona pellcida

corona penetrating enzyme

enzymes released from sperm loosen the corona radiata cells so sperm can reach zona pellucida

FSH

increase # of spermatocyes production

LH

triggers testes to make testosterone which increases how quickly sperm are made

HCG

maintains corpus luteum temporarily

progesterone

• makes endometrium secrete

• inhibits FSH and LH after mature secondary oocyte is released from follicle into fallopian tube

estrogen

made from follicle

• regulates GnRH

• regulates LH

• regulates / effect endometrium (thickens it)

acrosome

cap on tip of sperm head

layers of oocyte

1. corona radiata (outer)

2. zona pellucida

3. vitelline membrane (inner)

corona radiata

made of granulosa (outer layer)

zona pellucida

layer of glycoproteins, covers plasma membrane (vitelline)

vitelline membrane

inner layer

fusion of sperm and egg

1. zonal reaction

2. vitelline envelope

3. fertilizaton cone

4. synkaryon

zonal reaction

after sperm penetration, zona pellucida / membrane lift away so other sperm receptors don’t toch egg (blocks other sperm)

vitelline envelope

has sperm receptors

fertilization cone

extension of egg cytoplasm, engulfs sperm

synkaryon

when egg takes sperm nucleus and sperm and egg nuclei combine to form diploid zygotic nucleus

reaction of egg to fertilization

2 responses

1. early reaction = prevention of polyspermy

2. late responses = lead to formation of embryo

polyspermy

more than one sperm fertilzes egg

prevention of polyspermy

1. only one sperm can fertilizes the egg

2. prevents polyploidy

3. ensures equal contribution from both parents

polyploidy

when there are more than 2 sets of chromosomes

strategies for preventing polyspermy

cortical receptors / reactions

corticol receptors / reactions

makes vitelline envelope / membrane hard and destroys all nonactivated sperm receptors

• contains protedytic enzymes and cortical granules

initiation of development

• second meiotic division is completed after sperm penetration

• second polar body disintegrates and egg is now ovum / zygote

• egg has two haploid sets of chromosomes (maternal and paternal)

development following fertilization

• fertilized ovum remains in fallopian tube for 72 hours

• cells of zygote divide mitotically to form morula

• morula enters uterus and turns into blastocyst

morula

solid ball of cells

blastocyst

fluid filled structure that attaches to the uterine wall