Gamete Transport And Fertilization

Question 1

How sperm change in the female system

Part 1: capacitation

Answer 1

Destabilization of sperm plasma membrane:

• required for fertilization
• occurs in uterus (in response to proteolytic enzymes and high ionic strength)
• removes the glycoprotein coat on the spermatids surface- exposing glycostransferases needed to interact with egg

Question 2

How sperm change in the female system

Part 2: activation/hyper activation

Answer 2

Flagellum beating

• on way to Fallopian tube, and in close proximity to the egg
• ca2+ in follicular fluid increases vigor of sperm tail beating, which is essential for sperm to get through the zona pellucida.
• involves further changes to spermatids plasma membrane: to fuse with egg
• activated sperm have a chemotactic response towards the egg
• activates sperm lose viability rapidly

Question 3

Importance of Ca2+ channels for fertilization

Answer 3

• nice genetically made without catsper are infertile but have a normal sperm count. Without catsper the sperm do not have hyper activation thus low motility
• Cabot penetrate oocytes with a zona pellucida
• however they can penetrate oocytes when the zona pellucida is removed artificially

Question 4

Vaginal sperm

Answer 4

• semen deposited in vagina near external cervical os
• within 1 minute: seminal coagulation due to fibrogenase enzyme
• seminal fluid increases pH of vagina to be more alkaline which increases sperm motility
• after seminal coagulation, sperm re-liquify in about 20 minutes due to fibrinolytic enzymes in seminal plasma
• movement largely controlled by female: pressure gradient due to orgasmic platform and contractions in lower end of vagina.

Question 5

When do sperm reach Fallopian tube

Answer 5

-Sperm can be found in Fallopian tube within 5 minutes (99% lost already)

Question 6

When can sperm enter the cervix

Answer 6

Only sperm present at the right time will have the possibility of entering the cervix due to blockage by thick mucus at other times
-near ovulation due to high estrogen and low progesterone the mucus is thinner and permits sperm transport, and even nourishes sperm

Question 7

Sperm may remain in _______ for many hours or even days

Answer 7

Cervical crypts

-fewer than 1M of about 200m even make it this far

Question 8

The cervix is about _____ long and contains several hundred ______ which are

Answer 8

20-30mm
Cervical crypts

Glands lined by cells that respond to hormone levels

Question 9

P mucus

Answer 9

The most superior crypts- liquefies L mucus so sperm stored in lower crypts can be released when the time is right

Question 10

S mucus

Answer 10

Secreted in crypts in superior cervix. Produced string like mucus and present just before and up to three days after ovulation- nourishment for high quality spermatids and channels for their transport

Question 11

L mucus

Answer 11

Attracts low quality spermatids for elimination or temporary storage

Question 12

G mucus

Answer 12

Produces thick mucus and closes cervix during most of the cycle

Question 13

Uterine sperm

Answer 13

• movement largely controlled by female (love and dead spent move at the same rate) for passed through uterus.
• 3mm/minute though spermatids tails are beating and may be involved in part of movements
• fluid currents are set up by uterine muscular contractions
• arrival of sperm in uterus sets up massive invasion of leukocytes to engulf dead/dying sperm (only few thousand make it)

Question 14

What percent of sperm go to the wrong oviduct

Answer 14

50%

Question 15

Oviduct sperm

Answer 15

• most sperm that read the Fallopian tube do so in 4-24 hours
• rarely more than 100 sperm at a time here which is controlled by: rate of movement out of cervical crypts, passage through utero-tubal junction, Soren linger in the vicinity of the isthmus

-more friendly environment for sperm: leukocyte attack reduced and sperm move more slowly as well as make connections with epithelial cells for nourishment from mucus

Question 16

Intermittent sphincter

Answer 16

Uterine-tubal junction

Ensures quality of sperm

Question 17

Sperm move up the oviduct by…

Answer 17

Swimming and by Cilia in dell recesses that beat towards ovary
-egg is moving down the tube on ciliary ridges beating towards uterus

Question 18

3 navigation methods of sperm

Answer 18

Rheoraxis- movement against the fluid flow (mucus secreted by follicle)

Thermotaxis- movement in a temperature gradient (warmer in fertilization site

Chemotaxis- movement of a cell in a gradient of chemistrractant (molecules released by oocyte/ follicular fluid)

Question 19

Where does fertilization occur?

Answer 19

Ampullary-isthmic junction

Question 20

What structures do spermatids have to move through to penetrate the oocyte from external to internal?

Answer 20

Cumulus oophorus, zona pellucida, perivitelline space, oocyte

Question 21

Binding to zona pellucida and acrosomal reaction part 1

Answer 21

• sperm passage through the cumulus oophorus by acrosomal hyrunonidase to dissolve hyaluronic acid
• Soren passage through the zona pellucida: sperm plasma membrane bind to receptors on the zona pellucida glycoproteins ZP3 and ZP4 which will increase intracellular Ca2+, cAMP and pH and causes exocytosis

Question 22

Binding to zona pellucida and acrosomal reaction part 2

Answer 22

Triggers acrosome reaction in which spermatids plasma membrane fuses with outer acrosomal membrane
-breakdown of outer acrosomal membrane and exocytosis of contents such as acrosin

Question 23

Binding to zona pellucida and acrosomal reaction part 3

Answer 23

Degrade zona pellucida near spermatids head to create a tunnel for sperm
-Soren inner acromsomal membrane now exposed, and binds to receptors on the zona pellucida glycoprotein ZP2.

Question 24

Throughout the whole process of acrosomal reaction the sperm are still

Answer 24

Swimming

Question 25

Binding to zona pellucida and acrosomal reaction part 4

Answer 25

Sperm fuse to egg - once through zona pellucida, Soren approaches egg sideways and the back part of the head attaches to microvili of the egg cell membrane - as soon as fusion occurs, Soren stops moving

Question 26

From start of movement through cumulous oophorus to membrane fusion it takes…

Answer 26

10-20 minutes

Question 27

Binding to zona pellucida and acrosomal reaction part 5 (after fusion)

Answer 27

The Soren nucleus, mid piece and most of the tail sink into the egg cytoplasm= egg activation

Question 28

Egg activation step 1

Answer 28

- first step of egg activistion is the cortical reaction: to prevent polyspermy - In Response to fusion with sperm, Ca+ released from endoplasmic reticulum in egg - cortical granules located beneath egg plasma membrane respond to the increased Ca2+ and release enzymes to perivitelline space - this alters ZP glycoproteins and inhibits acrosin so no more sperm could gain access - the cell membrane of the egg becomes non-fusible due to changes in ion flow across

Question 29

Egg activation step 2

Answer 29

- occurs about 2-3 hours after spermatids and egg members be fuse (egg finally resumes and completes meiosis 2) - also initiated in response to high calcium - results in release of second polar body - final formation of the haploid ovum - haploid nucleus of the newly formed ovum is the female pro nucleus

Question 30

Creation of male pro nucleus

Answer 30

- once inside the egg, the sperm nucleus undergoes a series of changes that result in the formation of the male pro nucleus - de-condensation of chromatin - breakdown of original nuclear membrane - swelling of the nucleus and formation of a new membrane around the pro nucleus - completed in 4-7 hours lost fusion

Question 31

What happens to the other parts of the sperm during pro nucleus

Answer 31

- tail and mitochondria are destroyed and recycled by the egg because they are labelled in spermatogenesis with ubiquitous to make them for destruction - we inherit all our mitochondrial DNA from our mother - centriole becomes part of the zygote

Question 32

Syngamy

Answer 32

The fusion of two haploid gametes to form a a zygote - 12hours from beginning of egg activation - haploid male and female pro nucleus move toward the Center of the cell and fuse - the new zygote is formed and the end of fertilization process and the beginning of the new diploid individual

Question 33

Zygote

Answer 33

Fertilized egg Divides by mitosis called cleave divisions= because nuclear replication and cytokinesis occur without any cellular growth

Question 34

All material required for the zygote to develop come form the

Answer 34

Egg (RNA, cytoplasm, new membrane materials, microtubules, energy etc -Sperm contribute their haploid chromosomes and centrosome

Question 35

First cleavage division complete=

Answer 35

A pre embryo consisting of 2 blastomeres Completed about 18-21 hours after initial fusion of egg and sperm

Question 36

After fertilization

Answer 36

- conceptus remains in Fallopian tube for 3-4 days - divides by mitosis a number of times and slowly moves towards the uterus - blastomeres becomes smaller as the entire structure remains the same size and is still surrounded by the zona pellucida - at 16 cell stage a compact sphere called a morula is formed - cells in morula increase metabolic activity - embryo continues to cleave, producing a hollow so where of about 64 cells by day 4= blastocyst - blastocyst reaches uterus and is ready for implantation