Fertilization

What is fertilization?

Fusion of nuclear material of 2 haploid cells

male - gamete

female - ovum

What is the result of fertilization

Diploid Cell - new organism

Location of fertilization

ampulla of uterine tubes

Ampulla of uterine tube

requires sperm capacitation

What is sperm capacitation

removal of coating over the acrosome

Sperm must penetrate ________ and ________ to get to oocyte

Corona radiata

zona pellucida

Fertilization is an _________ reaction

Acrosome

• hyaluronidase + acrosin enzymes released

Fertilization requires _______ activation

oocyte

What happens in oocyte activation?

exocytosis of enzymes that prevent additional sperm penetration

successful sperm transport requirements?

seminal fluids

female factors

capacitation

Successful sperm transport

movement through male reproductive/urinary tract

deposition in vagina

movement through female reproductive tract to oviduct

What makes up seminal fluids?

Water

Buffers

Nutrients

Zinc

Clotting and liquefaction factors

Prostaglandins

ATP

What is the purpose of buffers in seminal fluids?

neutralize acidity of male urethra

neutralize acidity of female vagina

What nutrients are present in seminal fluids?

sugar (fructose) + others

enzymes: actions contribute to availability of nutrients

what is the purpose of zinc?

antibacterial activity

what is the purpose of water in seminal fluids?

needed to flow through passages (male and female)

What is the purpose of clotting and liquefaction factors?

decreases loss from vagina (coagulation)

increases movement toward cervix into uterus (liquefaction)

What is the process of clotting and liquefaction

initial coagulation

• semenogelins from seminal vesicles

Followed by liquefaction

• PSA (prostate-specific antigen)

  • zinc binds to semenogelins to free up PSA

What is the purpose of prostaglandins in seminal fluid?

cause contraction of smooth muscle in walls of male passages

What female factors affecting sperm transport?

Female orgasm

Vaginal acidity

Cervical mucus

Vaginal fornices

Cervical folds/crypts

Uterine contractions

Ciliary and muscular action

Immunity

How does female orgasm affect sperm transport?

vaginal muscular contractions increase pressure to push sperm into uterus

How does vaginal acidity affect sperm transport?

neutralization required for viability

How does cervical mucus affect sperm transport?

variable viscosity

estrogen

• high at ovulation to increase chance of reaching oocyte

How does cervical folds/crypts affect sperm transport?

Sperm get trapped

• die

• delayed

How does uterine contractions affect sperm transport?

oxytocin-mediated

• penile mechanical stimulation of cervix

How does ciliary and muscular action affect sperm transport?

fimbriae and oviducts

estrogen increases # of cilia + progesterone increases ciliary movements

How does immunity affect sperm transport?

leukocytes (white blood cells) attack sperm (foreign cell) + get rid of dead ones

Sperm Statistics

200 million deposited

< 1 million enter cervix

few thousand reach oviducts

few hundred reach oviduct with ovulated oocyte

20-200 reach oocyte

lifespan ~ 6 days

What are the phases of fertilization?

Phase 1:

• sperm penetrates corona radiata

Phase 2:

• sperm undergoes acrosome rxn and penetrates zona pellucida

Phase 3:

• sperm and oocyte plasma membrane fuse

What is capacitation of sperm?

destabilization of sperm membrane

increase in motility

hyaluronidase enzyme availability

what is functions of hyaluronidase enzyme

• degrades hyaluronic acid

What happens in acrosome reaction?

sperm binds to glycoproteins of zona pellucida

exocytosis of enzymes from sperm used to break through

sperm moves through perivitelline space

sperm makes contact with vitelline membrane

“lies down” next to egg cell membrane

fusion of cell membranes

entry of sperm DNA into egg cytoplasm

What are the three steps to Egg Activation?

Cortical reaction

Complete 2nd meiotic division

• haploid cell + polar body

Mitosis preparation

What does cortical reaction prevent?

Multiple sperm entering the egg

can be lethal

what do cortical granules beneath oocyte cell membrane in cortical reaction do

release enzymes from the granules

• b/c high calcium levels at fusion

The enzymes released by cortical granules do?

change the structure of zona pellucida

Changing the structure of the zona pellucida in cortical reaction means what?

no more receptors for sperm to bind

no access to egg

What does blocking polyspermy do

Stops further sperm entry

ONLY 2 COPIES OF EACH CHROMOSOME IN FERTILIZED OVUM

what stimulates completion of meiosis

calcium

meiosis in fertilization

completion of 2nd meiotic division

ovum pronucleus

nuclear membrane that forms around DNA

how does sperm enter the egg cytoplasm?

Nuclear Membrane breaks down

sperm pronucleus forms

migration of pronuclei towards eachother

pronuclei fuse

mitotic division begins

what is considered the “highway” when pronuclei migrate towards each other?

microtubules

when pronuclei fuse it’s _________

diploid zygote

syngamy

merging of 2 haploid organism

if there are chromosomal aberrations what happens

spontaneous abortion

______ amount of embryos spontaneously abort within 1st trimester

90%

Faternal twins

2 ova are fertilized by different sperm

2 zygotes formes

identical twins

1 ovum is fertilized by one sperm

early embryo divides

IVF treatment types

high FSH

hCG (human chorionic gonadotropin) hormone similar to LH

In IVF eggs are removed when?

prior to ovulation

What happens post fertilization in IVF

embryo transplanted to uterus via catheter

3 days old - 8 cells

5 days old - blastocyst/70-100 cells