Fertilization and Embryo Development

Question 1

What species have sperm deposition in the uterus?

Answer 1

Rodents, dog, pig, horse

Question 2

What species have sperm deposition in the cervix?

Answer 2

Cat and pig

Question 3

What species have sperm deposition in the vagina?

Answer 3

Cat, rabbit, sheep, cattle, human

Question 4

What is the shift of pH in the upper vagina once sperm is deposited?

Answer 4

4.3-> 7.2 in 10 seconds

Question 5

What is deposited in the upper vagina during copulation?

Answer 5

Seminal fluid

Question 6

What is the purpose of seminal fluid?

Answer 6

Its composition and buffering capability protect spermatozoa from the acidity of the upper vagina

Question 7

How long does the buffering effect last in the reproductive tract, and what is its significance?

Answer 7

The buffering effect lasts only a few minutes, which is enough for sperm to approach the cervix in a pH range of 6 to 6.5, optimal for sperm motility.

Question 8

What role does the cervix play in spermatozoal transport?

Answer 8

The cervix is a major barrier to spermatozoal transport and serves as a spermatozoal reservoir.

Question 9

What happens to mucus production in the cervix during estrus?

Answer 9

Copious mucus is produced under the influence of estrogen, regulating the transport of spermatozoa.

Question 10

How does the composition and viscosity of cervical mucus change?

Answer 10

It varies throughout the menstrual cycle; during days 9-16, its water content increases, facilitating sperm passage at ovulation.

Question 11

3 functions of the cervix

Answer 11

a) it is receptive to sperm penetration and inhibits sperm migration during other phases of estrus cycle
b) It protects sperm from hostile environment in the vagina
c) it filters defective and immotile spermatozoa

Question 12

What are the two types of sperm transport?

Answer 12

Rapid transport

Slow release and transport

Question 13

What occurs immediately after insemination/ejaculation regarding sperm transport?

Answer 13

Spermatozoa penetrate the cervical mucus and some are quickly transported through the cervical canal to the uterine tubes within one hour of ejaculation

Question 14

What facilitates the rapid transport of spermatozoa?

Answer 14

Muscular movements of the female reproductive tract.

Question 15

Is it clear whether the first spermatozoa entering the oviduct participate in fertilization?

Answer 15

It is still unclear whether the first spermatozoa entering the oviduct participate in the fertilization of the ovum.

Question 16

What is the swimming speed of spermatozoa through cervical mucus?

Answer 16

Spermatozoa swim through cervical mucus at a rate of 2-3 mm/hr.

Question 17

How are spermatozoa stored and released in the cervix?

Answer 17

They are stored in cervical crypts and released sequentially for a prolonged period, allowing passage through the cervical canal for as long as 3-4 days after ejaculation.

Question 18

What is the significance of slow sperm release from the cervix?

Answer 18

It ensures the continued availability of spermatozoa for entry into the oviduct to effect fertilization.

Question 19

What is the role of anatomical and physiological barriers in the female reproductive tract?

Answer 19

They help prevent polyspermy

Question 20

Where does fertilization usually occur?

Answer 20

Ampullary part of the uterine tube

Question 21

What is fertilization?

Answer 21

Series of processes beginning with the spermatozoa penetrating the corona radiata and ending with the intermingling of maternal and paternal chromosomes after the spermatozoon entered the egg

Question 22

How many spermatozoa typically surround the corona radiata?

Answer 22

12

Question 23

What enzyme from the sperm head might assist in penetrating the corona radiata?

Answer 23

Hyaluronidase, emanating from the acrosome of the sperm head.

Question 24

What role does sperm motility play in relation to the corona radiata?

Answer 24

Major role in penetration of the corona radiata

Question 25

What is the primary function of the zona pellucida regarding sperm entry?

Answer 25

It allows only sperm of the same species to enter the egg.

Question 26

What happens to sperm entry after fertilization?

Answer 26

The zona pellucida prevents any other spermatozoon from entering the egg.

Question 27

What does the zona pellucida act as during the first cleavage divisions?

Answer 27

It acts as a filter, allowing substances from the uterine tubes to enter the egg.

Question 28

What part of the oocyte plays a role in preventing premature implantation?

Answer 28

zona pellucida

Question 29

What is the acrosomal reaction?

Answer 29

It is the orderly fusion of the spermatozoal plasma membrane and the outer acrosomal membrane

Question 30

What is released during the acrosomal reaction that aids in penetrating the zona pellucida?

Answer 30

Acrosomal enzymes (Hyaluronidase and acrosin) that allow the spermatozoon to digest its way through the zona pellucida.

Question 31

Where is the trigger for the acrosome reaction in several species?

Answer 31

zona pellucida

Question 32

What is the state of the membranes of the sperm head before the acrosomal reaction?

Answer 32

All membranes of the head are intact

Question 33

What occurs during the acrosomal reaction regarding the membranes?

Answer 33

The plasma membrane begins to fuse with the outer acrosomal membrane, creating pores

Question 34

What is the significance of the pores created during the acrosomal reaction?

Answer 34

They allow acrosomal enzymes to pass through, enabling sperm to penetrate the zona pellucida

Question 35

What remains intact after the acrosomal reaction?

Answer 35

The inner acrosomal membrane and nuclear cap remain intact, while vesicles are sloughed off

Question 36

What happens when sperm completely penetrates the zona pellucida?

Answer 36

The sperm reaches the perivitelline space, and cortical granules migrate to the periphery of the oocyte

Question 37

What occurs when the plasma membrane of the oocyte fuses with the sperm?

Answer 37

The plasma membrane fuses with the equatorial segment, and the fertilizing sperm is engulfed

Question 38

What happens to the cortical granules during fertilization?

Answer 38

Cortical granules are released into the perivitelline space

Question 39

What occurs after the fusion of the oocyte's plasma membrane with the sperm's equatorial segment?

Answer 39

The sperm nuclear membrane disappears, and the nucleus of the sperm decondenses

Question 40

What must happen once sperm-egg fusion occurs?

Answer 40

entry of other spermatozoa into the egg must be avoided to prevent abnormal development

Question 41

What happens during the fast block?

Answer 41

Rapid depolarization of the egg plasma membrane. *Occurs 2-3 seconds after fusion

Question 42

What happens during the slow block?

Answer 42

Its the cortical reaction Granules fuse with the PM of the oocyte, release content that eats all ZP protein on ZP so it kills the receptor which prevents any more sperm from entering

Question 43

What happens after sperm-egg fusion regarding calcium?

Answer 43

There is a propagation of a Ca²⁺ wave from the site of sperm-egg fusion

Question 44

What occurs when cortical granules fuse with the plasma membrane?

Answer 44

They release hydrolytic enzymes and polysaccharides into the perivitelline space

Question 45

What is the effect of the contents of cortical granules on sperm receptors?

Answer 45

The contents hydrolyze the sperm receptor molecules in the zona, creating the "zona block."

Question 46

What is the first event that occurs ~ 24 hours after fertilization?

Answer 46

Cleavage

Question 47

What is cleavage in embryonic development?

Answer 47

Rapid cell divisions that convert the unicellular zygote into a multicellular embryo.

Question 48

How does the timing of cell divisions in cleavage affect the embryo?

Answer 48

The divisions are not synchronous, leading to embryos with an odd number of cells.

Question 49

How long does it typically take between each cell division during cleavage?

Answer 49

Approximately 12-24 hours

Question 50

What is the total size of the embryo during cleavage?

Answer 50

The total embryo size remains approximately 0.1 mm in diameter.

Question 51

How does the number of cells in the embryo change during cleavage?

Answer 51

It increases exponentially

Question 52

What characterizes the initial divisions of the zygote?

Answer 52

Rapid mitotic divisions with no growth phases.

Question 53

What are the resulting daughter cells from the cleavage called?

Answer 53

Blastomeres

Question 54

How does the size of blastomeres change with each division?

Answer 54

Blastomeres become smaller with each division since there is no overall growth

Question 55

What stage is reached with blastomeres up to 8 cells? When is it important?

Answer 55

They are totipotent, which is important in twinning

Question 56

What occurs when a cavity appears within the morula?

Answer 56

It converts the morula into a cystic structure called the blastocyst.

Question 57

what happenes to the arrangement of cells in a blastocyst/what layers do they form?

Answer 57

- Inner mass (embryoblast) which will form all the tissues of the embryo - Outer layer called trophoblast which invade the uterine wall

Question 58

What is the inner cell mass of the blastocyst called?

Answer 58

Embryoblast

Question 59

What is the outer cell mass of the blastocyst called?

Answer 59

Trophoblast

Question 60

What does the trophoblast contribute to?

Answer 60

It becomes the fetal contribution to the placenta.

Question 61

What are the two poles of the blastocyst?

Answer 61

Embryonic pole and abembryonic pole.

Question 62

Where is the inner cell mass located in relation to the blastocyst?

Answer 62

The inner cell mass is located at the embryonic pole.

Question 63

When does blastocyst hatching occur?

Answer 63

Just before implantation

Question 64

What are some reasons for not hatching that can lead to infertility?

Answer 64

-Altered ZP -Absense of proteases -Embryos lacking ZP protein leading to premature hatching

Question 65

How does the embryo break through the zona pellucida (ZP)?

Answer 65

It breaks through due to proteases secreted by the blastocyst

Question 66

3 steps in preimplantation embryo development?

Answer 66

-Translation of maternal mRNA transcripts -Activation of embryonic transcription -Morphogenetic events

Question 67

What point should all embryos reach post fertilization?

Answer 67

At least reach the 8-cell stage