1. Gametes, fertilization, cleavage and blastulation Flashcards
1
Q
What is fertilization?
A
Male and female gamets fuse giving rise to the formation of the zygote
2
Q
This is scale of prenatal development.
- Weeks that embryogenesis occur?
- Weeks that fetal development (fetus) occur?
A
- 3rd → 8th weeks: embryogenesis
- 9th → 40th weeks: fetal development (fetus)
3
Q
What is this?
A
Female gamete/ oocyte/ egg
4
Q
Identify
A
5
Q
What is Zona Pellucida (ZP_?
A
specialized extracellular matrix (ECM) which is produced by the oocyte and follicular granulosa cells
6
Q
What are main glycoproteins of Zona Pellucida (ZP)?
A
ZP1, ZP2, ZP3, ZP4
7
Q
6 general functions of Zona Pellucida (ZP)?
A
- protection
- transport
- sperm binding
- prevention of polyspermy
- support of blastocyst development
- prevention of early implantation
8
Q
Function of ZP
A
required for structural integrity of the matrix, minimize precocious hatching
9
Q
2 Functions of ZP1, ZP3 and ZP4
A
- bind to the capacitated human spermatozoa
- induce acrospmal reaction
10
Q
2 functions of ZP2
A
- sperm recognition receptor (It is cleaved by ovastacin released from cortical granules after fertilization and other sperm can not bind to the oocyte)
- plays an important role in defence against polyspermy.
11
Q
How can ZP2 participate in sperm recognition receptor?
A
specialized extracellular matrix (ECM) which is produced by the oocyte and follicular granulosa cells
12
Q
What is gametogenesis?
A
The conversion of germ cells into male and female gametes
→ It happens in order to reduce the number of chromosomes and to complete their maturation
13
Q
What are Prenatal events?
A
Primordial germ cells develop from epiblast during the second week and appear in the wall of the yolk sac at the end of the 3 rd week of development.
Germ cells migrate from the yolk sac toward the developing gonads (primitive sex glands). They arrive at the end of the 4 th or the beginning of the 5 th week.
14
Q
Gametogenesis → Prenatal events
- Primordial germ cells develop from (1)____ during the (2)____ week and appear in the wall of the yolk sac at the end of the (3)____ week of development.
- Germ cells migrate from the yolk sac toward the (4)____. They arrive at the end of the (5)___ week or the beginning of the (6)___ week.
A
- epiblast
- second
- third
- developing gonads (primitive sex glands)
- fourth
- fifth
15
Q
Gametogenesis → Prenatal events
- (1)____ develop from epiblast during the second week and appear in (2)___ at the end of the 3 rd week of development.
- Germ cells migrate from (3)____ toward the developing gonads (primitive sex glands). They arrive at the end of the 4 th or the beginning of the 5 th week.
A
- Primordial germ cells
- the wall of the yolk sac
- the yolk sac
16
Q
Identify
A
17
Q
Identify
A
18
Q
What is spermatogenesis?
A
the sequence of events by which spermatogonia are transformed into mature gametes: sperm (spermatozoa).
19
Q
3 events of spermatogenesis
A
- Spermatocytogenesis : asymmetric division of spermatogonia. Some of them remain „stem cell”, others start the differentiation process.
- Meiosis: meiotic division of spermatocytes (I and II)
- Spermio (histo)genesis: spermatids are transformed to sperm that can fertilize eggs
20
Q
Sequences of formation of spermatids
A
SPERMACYTOGENESIS AND MEIOSIS
Spermatogonia
→ mitosis, growth
→ primary spermatocytes
→ first meiotic division
→ second spermatocytes
→ second meiotic division
→ spermatids
21
Q
What is Spermio(histo)genesis?
A
Transformation of spermatids into spermatozoa
22
Q
4 events happening during Spermio(histo)genesis?
A
(a) Formation of acrosome cap (lysosome-hydrolytic enzymes for acrosomal reaction of fertilization)
(b) Condensation and elongation of the nucleus
(c) Development of flagellum (formation of neck, middle piece and tail)
(d) Shedding of most of the cytoplasm
23
Q
During spermatogenesis
→ The supporting cells are derived from the (1)___ and become (2)____
A
surface epithelium of the testis
Sustentacular/Sertoli Cells
24
Q
Just before puberty, the sex cords acquire lumen and become the ____
A
Seminiferous Tubules
25
Just before puberty, ___ acquire lumen and become the **Seminiferous Tubules**
the **sex cords**
26
Just before puberty, the **sex cords** acquire lumen and become the **Seminiferous Tubules**
**→** At the same time PGCs give rise to \_\_\_
**Spermatogonial cells**
27
What is **Type A Spermatogonia?**
**Type A spermatogonia, derived from the spermatogonial stem cell population, represent the first cells in the process of spermatogenesis.**
→ undergo a limited number of divisions to **clone** themselves
(with the last division producing Type B Spermatogonia)
28
**Type B Spermatogonia** divide to form ____ which stay in prophase for ~22 days
**Primary Spermatocytes**,
29
\_\_\_ divide to form **Primary Spermatocytes**, which stay in prophase for ~22 days
**Type B Spermatogonia**
30
**Type B Spermatogonia** divide to form **Primary Spermatocytes**, which stay in prophase for ~22 days
→ After completing **Meiosis 1**, these cells form (1)\_\_\_
→ During **Meiosis 2**, (2)\_\_\_ are formed
1. **Secondary Spermatocytes**
2. haploid **Spermatids**
31
Spermatogonia and Spermatids are embedded in deep recesses of ____ while they develop
Sertoli cells
32
Spermatogenesis is regulated by ___ by the Pituitary Gland
LH (Luteinizing hormone) production
33
Spermatogenesis is regulated by LH (Luteinizing hormone) production by \_\_\_
the Pituitary Gland
34
Spermatogenesis is regulated by LH production by the Pituitary Gland
o LH binds to (1)\_\_\_ -\> stimulates **testosterone** production -\> binds to Sertoli cells -\> promotes (2)\_\_\_
FSH binds to Sertoli cells -\> stimulates (3)\_\_\_
1. Leydig cells
2. spermatogenesis
3. testicular fluid & intracellular androgen receptor production
35
Spermatogenesis is regulated by LH (Luteinizing hormone) production by the Pituitary Gland
* (1)\_\_\_ binds to Leydig cells -\> stimulates **testosterone** production -\> binds to (2)\_\_\_ -\> promotes spermatogenesis
* (3)\_\_\_ binds to Sertoli cells -\> stimulates testicular fluid & intracellular androgen receptor production
1. LH (Luteinizing hormone)
2. Sertoli cells
3. The ***follicle stimulating hormone*** (***FSH***)
36
Fully formed **Spermatozoa** enter (1)\_\_\_
→ they are pushed toward the (2)\_\_\_
1. the lumen of the Seminiferous tubules
2. **Epididymis** (where they will gain full motility)
37
In the *first stage of meiosis,* (1)\_\_\_ are divided
In the *second stage of meiosis*, (2)\_\_\_ are divided.
1. the homologous chromosomes
2. the chromatids
38
Spermatocyte meiosis occurs in ____ in the testes and results in four gametes (spermatids) of equal size.
the convoluted seminiferous tubules
39
Spermatocyte meiosis occurs in the convoluted seminiferous tubules in the testes and results in \_\_
four gametes (spermatids) of equal size.
40
Ejaculate (semen, seminal fluid) is composed of __ (2 parts)
a cellular part and a fluid part.
41
Ejaculate (semen, seminal fluid) is composed of a cellular part and a fluid part.
→ What does the cellular part consist?
The cellular component consists mainly of spermatozoa, as well as sloughed-off epithelial cells from the genital tract.
42
Ejaculate (semen, seminal fluid) is composed of a cellular part and a fluid part.
→ What does the fluid part consist?
The fluid component of semen, known as seminal plasma, consists of fluid secreted in the epididymis and accessory sex glands (prostate, seminal vesicle)
43
After migration, sperm cells undergo (1)\_\_\_, a process that is also assisted by (2)\_\_\_ (which hormone?).
1. **capacitation**
2. estrogen
44
What is Capacitation?
A biochemical and physiological “maturation process” that allows the sperm cell to penetrate an egg cell.
→ The resulting changes to the plasma membrane of the spermatozoa are necessary for the subsequent acrosome reaction.
45
What is Oogenesis?
Oogenesis is the process whereby oogonia differentiate into mature oocytes.
46
OOGENESIS
Identify
47
**_Oogenesis_**
Identify
48
What are contraceptive pills?
**combination of estrogen and progesteron or progesteron only (mini pills)**
49
3 events that ***Contraceptive pills*** inhibit?
**(i) the release of FSH and LH from the pituitary gland →** **inhibition of ovulation** **(****but permit menstruation****)**
**(ii) preparation of the lining of the uterus for implantation and**
**(iii) changing the uterine mucus to avoid sperm penetration into the egg.**
50
4 events of oogenesis
1. Primary Oocyte Formation
2. Folliculogenesis
3. Follicular Growth & Development
4. Follicular Atresia
51
When will oogenesis begin?
Before BIRTH
52
How is primary oocyte formed?
In the female, PGCs form oogonia.
→ After repeated mitotic divisions, some of these arrest in prophase of meiosis I to form primary oocytes.
53
In the female, PGCs form oogonia.
→ After \_\_\_\_, some of these arrest in prophase of meiosis I to form primary oocytes.
repeated mitotic divisions
54
In the female, PGCs form oogonia.
→ After repeated mitotic divisions, some of these arrest in ___ to form primary oocytes.
prophase of meiosis I
55
OOGENESIS
By the seventh month, many oogonia have become (1)\_\_\_\_
→ only (2)\_\_\_ remain surrounded by a layer of follicular cells derived from the surface epithelium of the ovary
1. atretic
2. primary oocytes
56
**OOGENESIS**
By the (1)\_\_\_ month, many oogonia have become atretic
→ only primary oocytes remain surrounded by a layer of (2)\_\_\_\_ derived from the surface epithelium of the ovary
1. seventh
2. follicular cells
57
**_Oogenesis_**
By the seventh month, many oogonia have become atretic
→ only primary oocytes remain surrounded by a layer of follicular cells derived from \_\_\_
the surface epithelium of the ovary
58
Identify
A. Oogonia are grouped in clusters in the cortical part of the ovary. Some show mitosis; others have differentiated into primary oocytes and entered prophase of the first meiotic division
59
Identify
B. Almost all oogonia are transformed into primary oocytes in prophase of the first meiotic division.
60
Identify
C. There are no oogonia. Each primary oocyte is surrounded by a single layer of follicular cells, forming the primordial follicle. Oocytes have entered the diplotene stage of prophase, in which they remain until just before ovulation. Only then do they enter metaphase of the first meiotic division.
61
Oogenesis at puberty
→ describe
At puberty, a pool of growing follicles is recruited and maintained from the finite supply of primordial follicles.
62
3 stages that follicles must pass to mature
(1) primary or preantral
(2) vesicular or antral
(3) mature vesicular or graafian follicle.
63
The primary oocyte remains in prophase of the first meiotic division until \_\_\_
the secondary follicle is mature.
64
The primary oocyte remains in prophase of the first meiotic division until the secondary follicle is mature.
→ At this point, a surge in ___ stimulates preovulatory growth
luteinizing hormone (LH)
65
a surge in luteinizing hormone (LH) stimulates preovulatory growth: (1)\_\_\_\_ is completed, and (2)\_\_\_\_\_ (2 things) are formed.
1. Meiosis I
2. secondary oocyte and polar body
66
the secondary oocyte is arrested in (1)\_\_\_\_ approximately 3 hours before (2)\_\_\_ and will not complete this cell division until (3)\_\_\_.
1. metaphase of meiosis II
2. ovulation
3. fertilization
67
Describe follicular growth
A. Vesicular [antral] stage follicle. The oocyte, surrounded by the zona pellucida, is off center; the antrum has developed by fluid accumulation between interce||u|ar spaces.
B. Mature vesicular [graafian] follicle. The antrum has enlarged considerably, is filled with follicular fluid, and is surrounded by a stratified layer of granulosa cells. The oocyte is embedded in a mound of granulosa cells, the cumulus oophorus.
68
Describe follicular growth
## Footnote
A. Vesicular [antral] stage follicle. The oocyte, surrounded by (1)\_\_\_, is off center
→ (2)\_\_\_\_ has developed by fluid accumulation between interce||u|ar spaces.
1. the zona pellucida
2. the antrum
69
Describe follicular growth
## Footnote
B. Mature vesicular [graafian] follicle.
→ (1)\_\_\_\_ has enlarged considerably, is filled with follicular fluid, and is surrounded by (2)\_\_\_.
→ The oocyte is embedded in (3)\_\_\_\_
1. The antrum
2. a stratified layer of granulosa cells
3. a mound of granulosa cells, the cumulus oophorus.
70
Identify (spermatogenesis)
71
What is ovulation?
The process in which Ovum enlarges and follicle ruptures then shed from ovary
72
With each (1)\_\_\_\_, a number of primary follicles begin to grow, but usually only one reaches full maturity, and only one oocyte is dis- charged at (2)\_\_\_
1. ovarian cycle
2. ovulation
73
What happen during ovulation?
The oocyte, in metaphase of meiosis II, is discharged from the ovary together with a large number of cumulus oophorus cells.
→ Follicular cells remaining inside the collapsed follicle differentiate into lutein cells.
74
Ovulation
→ What is stigma?
*avascular area appears over most convex point of follicle*
75
What is the role of the corpus luteum?
* To produce hormones (progesterone, estrogen) essential for preparing the uterus for pregnancy and then for maintaining that pregnancy until the placenta becomes fully functional (approximatelythe beginning ofthe fourth month).
* The corpus luteum originates from the theca interna (derived from ovarian stromal cells) and from granulosa cells that remain in the ovary after ovulation.
76
What is the origin of the corpus luteum?
* The corpus luteum originates from the theca interna (derived from ovarian stromal cells) and from granulosa cells that remain in the ovary after ovulation.
77
corpus luteum produce progesterone and estrogen
→ The role of progesterone alone?
progesterone is the primary hormone produced
→ causes the uterus to enter the progestational (secre- tory) phase
78
corpus luteum produce progesterone and estrogen
→ The role of both estrogen and progesterone alone?
progesterone is the primary hormone produced
→ causes the uterus to enter the progestational (secre- tory) phase
79
**Spermatozoa are not capable of fertilizing oocyte!!! They must undergo**
The three phases of fertilization are (1) pene- tration of the corona radiata, (2) penetration of the zona pellucida, and (3) fusion of the oo- cyte and sperm cell membranes. Once fusion occurs, the egg undergoes the cortical and zona reactions to prevent polyspermy. Corti- cal granules next to the oocyte plasma mem- brane release lysosomal enzymes that alter the cell membrane and the zona pellucida, such that additional sperms cannot enter the egg.
80
**Spermatozoa are not capable of fertilizing oocyte!!! They must undergo**
The three phases of fertilization are (1) pene- tration of the corona radiata, (2) penetration of the zona pellucida, and (3) fusion of the oo- cyte and sperm cell membranes. Once fusion occurs, the egg undergoes the cortical and zona reactions to prevent polyspermy. Corti- cal granules next to the oocyte plasma mem- brane release lysosomal enzymes that alter the cell membrane and the zona pellucida, such that additional sperms cannot enter the egg.
81
What happen during capacitation
Capacitation, during which time a glycoprotein coat and seminal plasma proteins are removed from the spermatozoon head
82
What happen during acrosomal reaction?
**afer binding to zona pellucida, release of enzymes (acrosin, trypsin like substances) induced by zona pellucida proteins**
83
During fertilization, the spermatozoon must penetrate ___ (3 things)
1. The corona radiata
2. The zona pellucida
3. The oocyte cell membrane (Fig. 3.5)
84
What are the 3 phases of fertilization?
* **Phase 1*****: Penetration of the corona radiata**
* **Phase 2*****: Penetration of the zona pellucida**
* **Phase 3*****: Fusion of the oocyte and sperm cell membranes**
85
**_Fertilization_**
## Footnote
What happen during **Phase 1: Penetration of the corona radiata?**
**Capacitated sperm penetrates the barrier corona radiata by „the corona radiata penetrating enzyme”, hyaluronidase, phosphatase and acrosine .**
**→ The enzymes are released from the plasma membrane of the sperm, that break apart the cell junctions and ECM.**
86
**_Fertilization_**
## Footnote
**Phase 1: Penetration of the corona radiata**
Capacitated sperm penetrates the barrier corona radiata by „the corona radiata penetrating enzyme”, which are ___ (3 enzymes)
→ The enzymes are released from the plasma membrane of the sperm, that break apart the cell junctions and ECM.
hyaluronidase, phosphatase and acrosine .
87
**_Fertilization_**
## Footnote
**Phase 1: Penetration of the corona radiata**
Capacitated sperm penetrates the barrier corona radiata by „the corona radiata penetrating enzyme”, which are **hyaluronidase, phosphatase and acrosine .**
→ The enzymes are released from (1)\_\_\_, that break apart (2)\_\_\_
1. the plasma membrane of the sperm
2. the cell junctions and ECM.
88
**_Fertilization_**
## Footnote
What happen during **Phase 2: Penetration of the zona pellucida**
The outer membrane of the sperm binds to ZP proteins (ZP1, ZP3 and ZP4 of the ZP)
→ (acrosomal reaction begins) formation of composite membrane
→ release of enzymes (neuramidase and acrosine)
→ breaking down ZP
→ sperm reaches the vitelline membrane of the oocyte
89
**_Fertilization_**
## Footnote
**Phase 1: Penetration of the zona pellucida**
The outer membrane of the sperm binds to (1)\_\_\_\_
→ (acrosomal reaction begins) formation of composite membrane
→ release of enzymes which are (2)\_\_\_
→ breaking down ZP
→ sperm reaches the (3)\_\_\_\_
1. ZP proteins (ZP1, ZP3 and ZP4 of the ZP)
2. neuramidase and acrosine
3. vitelline membrane of the oocyte
90
**_Fertilization_**
## Footnote
What is cortical reaction?
When **fertilin** (on the head of the fastest sperm) connects to integrin of the oocyte vitellin membrane, Ca2+-influx (depolarization) increases and then exocytosis of **cortical granules (CG)** occurs**.**
**→** Enzymes released from the CG cleave ZP molecules and inhibit the docking of other sperm. Other peptides from CG facilitate the increase of osmotic pressure → the periveitelline space takes up water and expands. The structural composition of the membrane changes. These events prevent polyspermy.
91
**_Fertilization_**
## Footnote
CORTICAL REACTION
When (1)\_\_\_\_ connects to integrin of the oocyte vitellin membrane, (2)\_\_\_\_ increases and then exocytosis of (3)\_\_\_ occurs**.**
1. **fertilin** (on the head of the fastest sperm)
2. Ca2+-influx (depolarization)
3. **cortical granules (CG)**
92
**_Fertilization_**
## Footnote
CORTICAL RACTION
When **fertilin** (on the head of the fastest sperm) connects to integrin of the oocyte vitellin membrane, Ca2+-influx (depolarization) increases and then exocytosis of **cortical granules (CG)** occurs**.**
→ Enzymes released from the CG cleave (1)\_\_\_ and inhibit (2)\_\_\_\_.
→ Other peptides from CG facilitate the increase of (3)\_\_\_
→ the periveitelline space takes up water and expands.
→ The structural composition of the membrane changes.
→ These events prevent (4)\_\_\_.
1. ZP molecules
2. the docking of other sperm
3. osmotic pressure
4. polyspermy
93
**_Fertilization_**
## Footnote
What happen during **Phase 3: fusion of the oocyte and sperm cell membrane?**
**Membrane of the oocyte and the inner acrosomal membrane of the sperm fuse**
**→ head and tail of the sperm enter the cytoplasm of oocyte but the plasmamembrane is left behind. „***Only maternal mitochonria will be in the zygote.”*
***→*** **The oocyte finishes its second meiotic division (definitive oocyte and 2nd polar body).**
**→ Female pronucleus and sperm pronucleus are in close contact (DNA replicated) and loose their nuclear envelope**
**→ metabolic activation, initiation of cleavage**
94
**_Fertilization_**
## Footnote
What happen during **Phase 3: fusion of the oocyte and sperm cell membrane?**
**Membrane of the oocyte and the inner acrosomal membrane of the sperm fuse**
**→ head and tail of the sperm enter the cytoplasm of oocyte but the plasmamembrane is left behind. „***Only maternal mitochonria will be in the zygote.”*
***→*** **The oocyte finishes its second meiotic division (definitive oocyte and 2nd polar body).**
**→ Female pronucleus and sperm pronucleus are in close contact (DNA replicated) and loose their nuclear envelope**
**→ metabolic activation, initiation of cleavage**
95
**_Fertilization_**
## Footnote
**Phase 3: fusion of the oocyte and sperm cell membrane**
**Membranes of (1)\_\_\_\_ (2 things) fuse**
**→ head and tail of the sperm enter the (2)\_\_\_\_ but the plasmamembrane is left behind. „***Only maternal mitochonria will be in the zygote.”*
***→*** **The oocyte finishes its (3)\_\_\_**
**→ Female pronucleus and sperm pronucleus are in close contact (DNA replicated) and loose their nuclear envelope**
**→ metabolic activation, initiation of (4)\_\_\_**
1. the oocyte and the inner acrosomal membrane of the sperm
2. cytoplasm of oocyte
3. second meiotic division (definitive oocyte and 2nd polar body).
4. cleavage
96
**_Fertilization_**
## Footnote
**Phase 3: fusion of the oocyte and sperm cell membrane**
**Membrane of the oocyte and the inner acrosomal membrane of the sperm fuse**
**→ head and tail of the sperm enter the cytoplasm of oocyte but the (1)\_\_\_\_ is left behind. „***Only (2)\_\_\_\_ mitochonria will be in the zygote.”*
***→*** **The oocyte finishes its second meiotic division (definitive oocyte and 2nd polar body).**
**→ (3)\_\_\_\_ and (4)\_\_\_ are in close contact (DNA replicated) and loose their nuclear envelope**
**→ metabolic activation, initiation of cleavage**
1. plasmamembrane
2. *maternal*
3. Female pronucleus
4. sperm pronucleus
97
**_Fertilization_**
## Footnote
What are 3 results of the fertilization?
1. Restoration of the diploid number of chromosomes (new combination of chromosomes that differs from both parents)
2. Determination of sex (XX- female embryo; XY - male embryo)
3. Initiation of cleavage
98
**_Fertilization_**
3 results of the fertilization
1. Restoration of ____ (new combination of chromosomes that differs from both parents)
2. Determination of \_\_\_\_
3. Initiation of \_\_\_
1. the diploid number of chromosomes
2. sex (XX- female embryo; XY - male embryo)
3. cleavage
99
What happen during cleavage?
Zygote in 2-cell stage
→ series of mitotic division
→ increase in cell number – cells become smaller and arranged loosely (blastomeres)
→ following the 3rd cleavage blastomers form a compact ball (tight junctions are among the cells)
→ segregation of inner and outer cells (communication with gap junctions)
→ morula, mulberry (16-cell stage)
100
**_CLEAVAGE_**
Zygote in (1)\_\_\_
→ series of mitotic division
→ increase in (2)\_\_\_\_ – cells become smaller and arranged loosely (blastomeres)
→ following the (3)\_\_\_\_ form a compact ball (tight junctions are among the cells)
→ segregation of (4)\_\_\_\_ (communication with gap junctions)
→ morula, mulberry (16-cell stage)
1. 2-cell stage
2. cell number
3. 3rd cleavage blastomers
4. inner and outer cells
101
**_CLEAVAGE_**
Zygote in 2-cell stage
→ series of (1)\_\_\_
→ increase in cell number – cells become smaller and arranged loosely (blastomeres)
→ following the 3rd cleavage blastomers form a compact ball (tight junctions are among the cells)
→ segregation of inner and outer cells (communication with gap junctions)
→ (2)\_\_\_\_ (16-cell stage)
1. mitotic division
2. morula, mulberry
102
What is compaction?
This process, compaction, segregates inner cells, which communicate extensively by gap junctions, from outer cells
103
**_Cleavage_**
## Footnote
The inner cell mass gives rise to (1)\_\_\_, and the outer cell mass forms (2)\_\_\_, which later contributes to the (3)\_\_\_.
1. tissues of the embryo proper
2. the trophoblast
3. placenta
104
**_Cleavage_**
## Footnote
What are blastomere?
1. tissues of the embryo proper
2. the trophoblast
3. placenta
105
What happen during blastocyst formation?
Morula enters the uterine cavity, fluids began to penetrate through the zona pellucida into the intercellular spaces
→ single cavity the *blastocele* is formed
→ blastocyst stage : inner cell mass-embryoblast, outer cell mass-trophoblast (epithelial wall). Zona pellucida disappears
→ implantation begin
106
**_Blastocyst formation_**
## Footnote
(1)\_\_\_\_ enters the uterine cavity, fluids began to penetrate through the (2)\_\_\_ into the intercellular spaces
→ (3)\_\_\_ is formed
→ blastocyst stage : inner cell mass-embryoblast, outer cell mass-trophoblast (epithelial wall). (4)\_\_\_\_\_ disappears
→ (5)\_\_\_\_ begin
1. Morula
2. zona pellucida
3. single cavity the *blastocele*
4. Zona pellucida
5. implantation
107
**_Blastocyst formation_**
## Footnote
Morula enters the uterine cavity, fluids began to penetrate through the zona pellucida into the intercellular spaces
→ single cavity the *blastocele* is formed
→ At this time, the embryo is a (1)\_\_\_. Cells of the inner cell mass, now called the (2)\_\_\_, are at one pole, and those of the outer cell mass, or (3)\_\_\_,
→ implantation begin
1. blastocyst
2. embryoblast
3. trophoblast
108
Identify
