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Human Reproductive Biology > Gamete Transport And Fertilization > Flashcards

Gamete Transport And Fertilization Flashcards

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1
Q

How sperm change in the female system

Part 1: capacitation

A

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
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2
Q

How sperm change in the female system

Part 2: activation/hyper activation

A

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
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3
Q

Importance of Ca2+ channels for fertilization

A
  • 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
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4
Q

Vaginal sperm

A
  • 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.
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5
Q

When do sperm reach Fallopian tube

A

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

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6
Q

When can sperm enter the cervix

A

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

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7
Q

Sperm may remain in _______ for many hours or even days

A

Cervical crypts

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

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8
Q

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

A

20-30mm
Cervical crypts

Glands lined by cells that respond to hormone levels

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9
Q

P mucus

A

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

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10
Q

S mucus

A

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

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11
Q

L mucus

A

Attracts low quality spermatids for elimination or temporary storage

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12
Q

G mucus

A

Produces thick mucus and closes cervix during most of the cycle

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13
Q

Uterine sperm

A
  • 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)
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14
Q

What percent of sperm go to the wrong oviduct

A

50%

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15
Q

Oviduct sperm

A
  • 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

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16
Q

Intermittent sphincter

A

Uterine-tubal junction

Ensures quality of sperm

17
Q

Sperm move up the oviduct by…

A

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

18
Q

3 navigation methods of sperm

A

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)

19
Q

Where does fertilization occur?

A

Ampullary-isthmic junction

20
Q

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

A

Cumulus oophorus, zona pellucida, perivitelline space, oocyte

21
Q

Binding to zona pellucida and acrosomal reaction part 1

A
  • 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
22
Q

Binding to zona pellucida and acrosomal reaction part 2

A

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

23
Q

Binding to zona pellucida and acrosomal reaction part 3

A

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.

24
Q

Throughout the whole process of acrosomal reaction the sperm are still

A

Swimming

25
Q

Binding to zona pellucida and acrosomal reaction part 4

A

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
26
Q

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

A

10-20 minutes

27
Q

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

A

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

28
Q

Egg activation step 1

A
  • 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
29
Q

Egg activation step 2

A
  • 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
30
Q

Creation of male pro nucleus

A
  • 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
31
Q

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

A
  • 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
32
Q

Syngamy

A

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
33
Q

Zygote

A

Fertilized egg

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

34
Q

All material required for the zygote to develop come form the

A

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

35
Q

First cleavage division complete=

A

A pre embryo consisting of 2 blastomeres

Completed about 18-21 hours after initial fusion of egg and sperm

36
Q

After fertilization

A
  • 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

Human Reproductive Biology (5 decks)

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