Gametogenesis And Fertilization (wk 2) Flashcards Preview

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Flashcards in Gametogenesis And Fertilization (wk 2) Deck (107):

Sex cells are called



Spermatogenesis creates what



Oogenesis creates

Oocyte in females


Haploid is

The number of chromosomes (23)

22+either x or y

Usual number is 46


Meiosis is

Process of cell division that occurs in the production of gametes

2 cell divisions (meiosis 1 & 2)

Results in 4 gametes - each contain 1/2 chromosomes


Meiosis step 1

Reduction division
- reduced from 46 to 23 chromosomes
- 22 homologues and one sex (x or y) chromosome

Secondary gamatocytes are produced


Meiosis step 2

Each secondary gamatocyte divides

Skips nml interphase (no DNA replication)

Forms 2 haploid cells



Primordial sperm cells (stem cells)


How long are spermatogonium sperm cells dormant

Until puberty

Inb the seminiferous tubles


During spermatogenesis, what occurs

1 spermatogonium becomes 1 primary spermatocyte (46 diploid)


What occurs to the primary spermatocyte during the first meiotic division

It becomes 2 secondary spermatocytes

The cytoplasm division is equal ***


What occurs to the 2 secondary spermatocytes during the second meiotic division?

They form 4 spermatids (23 haploid)

No DNA replication in the second meiotic division


Spermiogenesis is the process that

Transforms spermatids into mature sperm


Where are the spermitids stored

In the epididymis until they become functionally mature

2 months


What are the charateristics of mature sperm

Majority of the sperm is the head - contains the nucleus w/ the 23 chromosomes
Free swimming and motile


Head of the sperm characteristics

Anerior 2/3 covered by the acrosome


What is an acrosome

A sac like organelle containing several enzymes that allow the sperm to penetrate the oocyte during fertilization

- corona radiata and ZONA PELLUCIDA


Tail of the sperm characteristics

3 segments

Middle piece
Principal piece
End piece


What does the middle piece of the sperm contain

Mitochondria - provides ATP required for motility


Oogenesis is the process where

Oogonia (primordial oocytes) become mature oocytes


When does oogenesis occur/stop

Begins prior to birth early in the fetal period

Stops at birth

Resumes at puberty

Complete cessation at menopause


During prenatal maturation of oocytes the oogonia become what

During what period

Primary oocytes

Prenatal period


Are oogonia present in the post natal period



What forms as the primary oocyte forms

A connective tissue surrounds the oocyte producing a single layer of follicular cells

This is called the primordial follicle


During puberty what occurs to the primordial follicle

It enlarges to become a primary ovarian follicle


What is the primary oocyte surrounded by

A glycoprotein material called the zona pellucida


When does the first meiotic division begin

When the primary oocyte is surrounded by a glycoprotein material called the zona pellucida

But it is not completed


When is prophase completed

Not until puberty


What occurs between the time of the first meiotic division and puberty

No further development


When does a primary oocyte complete the first meiotic division?

(Postnatal maturation of oocytes)

Shortly before ovulation


First meiotic division what occurs

(Postnatal maturation of oocytes)

Cytoplasm division is unequal

Secondary oocyte is formed w/ most of the cytoplasm

First polar body is formed with little cytoplasm-degenerates


What happens to the secondary oocyte at ovulation

(Postnatal maturation of oocytes)

The nucleus of the secondary oocyte begins the second meiotic division


When does the second meiotic division stop

At metaphase


If fertilization occurs at ovulation, what happens

The second meiotic division is completed

Second polar body is also formed


What happens if no fertilization occurs at ovulation?

No fertilization - the oocyte is discarded in menses


Polar bodies

The left over chromosomes from meiosis

23 total


Ovarian vs menstrual cycle

Both approx 28 days

Ovarian - development of the primary oocyte and supporting tissues in the ovary

Menstrual - preparation of the uterus for implantation of the fertilized oocyte


Hypothalamus produces what

Gonadotropin-releasing hormone

Transported to the anterior lobe of the pituitary gland of the pituitary gland


What does the anterior lobe of the pituitary gland release

Follicle stimulating hormone (FSH)

Luteinizing hormone (LH)



Follicle stimulating hormone

Stimulates the development of ovarian follicles and the production of estrogen by the follicular cells



Luteinizing hormone

Serves as the “trigger” for ovulation (release of the secondary oocyte) and stimulates the follicular cells and corpus luteum to produce progesterone


What does LH and FSH do during the ovarian cycle

They cause changes in the ovaries resulting in:
- development of follicles (FSH) that produce estrogen
- ovulation (LH)
- corpus luteum formation (LH) produces progesterone


FSH stimulates primary follicular growth causing what

Connective tissue surrounding the follicle forms a capsule called the theca folliculi *


Theca folliculi forms 2 layers

- theca externa-outer capsule
- theca interna-vascular layer


Follicle cells form a layer around the primary oocyte and what happens

It is pushed aside

The adjacent cavity is filled with a follicular fluid and is called there antrum*

Once the antrum is formed the ovarian follicle is called the secondary follicle*


Characteristics of the secondary follicle

Becomes oval shaped

The primary oocyte is at the concentric end

The follicular cells surrounding the primary oocytes are called the cumulus oophorus

Follicular cells produce estrogen


What occurs to the follicle mid ovarian cycle

It has a growth spurt


What occurs during the follicles growth spurt

It produces a bulge on the surface of the ovary called a stigma*

Caused by both FSH and LH


Prior to ovulation the primary oocyte completes what

Its first meiotic division

Primary oocyte and first polar body


A surge of LH production is triggered by what and causes what?

Triggered by high levels of estrogen in the blood

Forms the growth of follicular cells


High levels of LH cause the stigma to bulge out forming a vesicle and eventually ruptures, what is this called


12-24 hours after the LH surge


When does the second meiotic division start and stop

Starts just after ovulation

Stops at metaphase


Some follicular cells surround the primary oocyte and for what

The corona radiate

Covers the zona pelluicida - covers the oocyte


After ovulation, the ovarian follicle and the theca folliculi collapse and form grandular tissue called

Corpus luteum

Secretes progesterone and small amounts of estrogen


If fertilization occurs, the corpus luteum becomes

The corpus luteum of pregnancy and produces progesterone and estrogen until 20 weeks when it is replaced by the placenta


If fertilization does not occur, the corpus luteum becomes

The corpus luteum of menstruation and degenerates


Corpus albicans

White scar tissue on the ovary from the corpus luteum


What does the menstrual cycle mirror

The ovarian cycle


What are the 4 phases of the menstrual cycle

Menstrual : 1-5
Proliferative : 5-14
Luteal : 14-27 (secretory)
Ischemia : 27-28


What occurs during the menstrual phase

The functional layer of the uterine wall is sloughed off and discarded with menstrual flow or menses 4-5 days

Compact and spongy layers


What occurs during the proliferative phase

Lasts 9 days

Coincides with the growth of ovarian follicles and is controlled by estrogen secreted by the follicles

There is two- to three-fold increase in the thickness of the endometrium and in its water content during this phase of repair and proliferation


What occurs during the luteal phase

Aka secretory phase

Ovulation is at the beginning of this phase

Lasts 13 days

Growth of the corpus luteum (from follicular cells)

Spiral arteries grow into the compact layer

The venous network grows and large lacunae (venous spaces) form


Whats lacunae

Venous spaces


If fertilization does not occur what happens and what phase comes up

The corpora lutea degenerate, menstration occurs

Estrogen and progesterone levels fall and the secretory endometrium enters the ischemic phase


What occurs during the ischemic phase

Spiral arteries constrict

Corpora lutea degenerates dec progesterone levels

Uterine gland secretions stop

Endometrium shrinks

Necrosis occurs in functional tissues

Blood vessels rupture resulting in bleeding into the uterus

20-80 ml of blood is lost

Compact and most spongy layers are shed in menses


If fertilization does occur what happens?

Cleavage of the zygote and formation of a blastocyst begin
- beginning of the embryo

The blastocyst begins to implant in the endometrium on 6th day of luteal phase

HCG keeps the corpora lutea secreating estrogens and progesterone - produced in the outer layer of the blastocyst (synchytiotrophoblast)

The luteal phase continues and menstration does not occur



Fertilized ovum



Pre-implantation embryo consisting of a thin-walled hollow sphere of 16-40 cells



The outer wall cells of the blastocyst which attach the zygote to the uterus

Becomes the placenta



Outter layer of the trophoblast

Produces HCG


Second Oocyte is expelled when and from where

At ovulation from the ovarian follicle

Fimbriae move back and forth over the overy

They sweep the secondary oocyte into the infundibulum of the uterine tube

Oocyte passes into ampulla of the uterine tube and on into the uterine body of the peristaltic action of the uterine tube

Fertilization occurs ampulla


Ejaculation of semen - 2 phases

Emission - semen passes to the prostatic part of the urethra through the ejaculatory ducts by the peristaltic movements of the ductus deferens

Ejaculation - semen is expelled from the urethra through the external urethral orifice
- the prostates change shape, closing off the bladder and opening the ejaculatory duct into the urethra


Semen is composed of how many sperm

400-600 million

2-6 ml

About 200 sperm reach the fertilization site in the ampulla


Before fertilization can occur, sperm must undergo a maturation process called


Takes 7ish hours

Exposing the acrosome


Once the sperm has matured, what happens

They pass through the corona radiata
They penetrate the zona pellucida

Membranes fuse, the sperm enters


Once the sperm enters the zona pellucida what happens

It transforms into a zona reaction and becomes impermeable to other sperms


What happens when the second meiotic division completes

Forms a second polar body and a zygote is formed


Enzymes in the acrosome are called ____ and ___and do what?

Hyaluronidase to help the sperm transverse the coronat radiata

Acrosin to Help the sperm transverse the zona pellucida


Results of fertilization

Stimulates the secondary oocyte to complete the second meiotic division

Restores the nml diploid number of chromosomes (46) in the zygote

Results in variation!

Determines sex of embryo
X = female
Y = Male

Causes metabolic activation of the oocyte which initiates cleavage of the zygote


Cleavage of the zygote consists of

Begins when

Undergoes what

Consists of repeated mitotic divisions of the zygote resulting in a rapid increase in the number of cells - blastomeres

Begins 30 hrs after fertilization

Zygote still surrounded by the zona reaction

Undergoes compaction after the 8 cell stage - allowing greater cell to cell interaction



12-32 blastomeres

2 layers
- inner cells : embryoblast or inner cell mass
- outer layer : layer of flattened blastomeres that form the trophoblast


Trophoblast secrete what

An immunosuppressant protein called early pregnancy factor

- appers in the maternal serum w/in 24-48 hrs after implantation


Formation of the blastocyst

The morula enters the uterus
- 4 days after fertilization

Uterine fluid passes through the zona rxn to form a fluid filled space
- the blastocystic cavity aka blastocoele

As fluid increases in the cavity, the blastomeres are seperated into two parts
- trophoblast - thin outer cells that give rise to the embryonic part of the placenta
-embryoblast - primordium of the embryo


Implantation occurs when

Approx 6 days after fertilization of the blastocyst attaches to the epithelium of endometrium

Embryonic pole - area where the embryoblast attaches to the trophoblast and then to the endometrial epithelium


The trophoblast of the blastocyst being differentiating into 2 layers

Cytotrophoblast - inner layer of cells
Synchtiotrophoblast - outer layer

Begins at end of week 1



A layer of mononucleated cells

It forms new trophoblastic cells that migrateinto the increasing mass of the synchytiotrophoblast



A rapidly expanding multinucleated mass in which no cell boundaries are discernible


Fingerlike processes of synchytiotrophoblast extend through what to do what

Through the endometrial epithelium

To invade the endmetrial connective tissue

By the end of the first week the blastocyst is superficially implanted in the compact layer of the endometrium


Synchtiotrophoblasts produce what

Proteolytic enzymes that cause adjacent endometrial cells to ungergo apoptosis (programmed cell death) to allow for implantation


The degenerated cells (decidual cells) contain lipids and glycoproteins that do what

Provide an immunology privileged site for the conceptus

Provide nutrition for the embryo

Produce hCG


When the syncytiotrophoblast produces proteolytic enzymes that erode the endometrium the blastocyst does what

Burrows into the endometrium


What occurs during the hypoblast formation

A cuboidal layer of cells on the surface of the embryoblast, facing the blastocystic cavity

Appears at end of first week

This begins the formation of the embryonic disc


What does hCG do

Maintains the development of the spiral arteries

Continues the development of the synchtiotrophoblast
- self maintaining


How does the embryonic disc form

Embryoblast (inner cell mass) seperates into two layers forming the bilaminar embryonic disc

Epiblast - thicker layer, high columnar cells adjacent to the amniotic cabity

Hypoblast - thinner layer, small cuboidal cells adjacent to the exocoelomic cavity

Happens spontaneously w/ implantation


How does the formation of the amniotic cavity occur

Simultaneously with implantation

A small space developos in the embryoblast - amniotic cavity
- lined with aminoblasts which form a thin membrane called the amnion - lines the amniotic cavity

Epiblast is the floor


Exocoelomic cavity

When the amniotic cavity and embryonic disc from the exocoelomic membrane forms lining the blastocystic cavity
- lines the cytotrophoblast

Forms the exocoelomic cavity

Roof is the hypoblast

The exocoelomic membrane and cavity from the primary umbilical vesicle
- aka primary yolk sac


Primary umbilical vesicle is

Aka yolk sac

Seperated from the amnion and embryonic disc

The outer layer of cells from extraembryonic mesoderm
- connective tissue
- premordium of multiple structures


Lacunae formation

Takes place as the amnion, embryonic disc, and primary umbilical vesicle form

Isolated cavities filled with a mixture of maternal blood and cellular debris provide embryonic nutrition

Fluid in the lacunae called embryotroph


Lacunae formation is the beginning of

Uteroplacental circulation


What happens at the 10 day mark

Implantation is complete

The implantation site does not completely close until the 12th day

Covered by a closing plug - fibrous coagulum of blood

Day 12 the lacunae have fused to form large lacunar networks - spongelike


Extraembryonic mesoderm enlarges after implantation is complete to form what

Extraembryonic coelomic spaces

Spaces rapidly fuse to form a lg cavity called the extraembryonic coelom

Extraembryonic coelom surrounds the amnion and the umbilical vesicle, except for where they are attached to the chorion by the connecting stalk


As the extraembryonic coelom forms, the primary umbilical vesicle (yolk sac) does what

Decreases in size

Forms a larger secondary umbilical vesicle

Day 14

Part of the primary vesicle gets pinched off


The extraembryonic coelom splits the extraembryonic mesoderm into two layers

1) extraembryonic somatic mesoderm - lines the trophoblast and covers the amnion
2) extraembryonic splanchnic mesoderm - surrounds the umbilical vesicle


A new membrane surrounds the embryo called ____ that has what three layers

Called the Chorion

1) extraembryonic somatic mesoderm
2) cytotrophoblast
3) synchtiotrophoblast

The internal wall of the chorionic sac surrounds the chorionic cavity
- extraembryonic somatic mesoderm


What is the role of the connecting stalk

Suspends the embryo in the chorionic cavity

This is the future site of the placenta


When do primary chorionic villi appear

At the end of the second week

These are cellular extentions formed from cytotrophoblastic cells that grow into the overlying syncytiotrophoblast forming the primary chorionic villi

This is all caused by extraembryonic somatic mesoderm


Prechordial plate forms when

Day 14

Endodermal cells in a localized are from a thickened circular area

This is the site of the mouth and is an important organizer of the head rgn