Fertilization and Development

Question 1

polyspermy

Answer 1

When an egg gets fertilized by more than one sperm. It usually results in unsuccessful fertilization

Question 2

What is the first step of fertilization

Answer 2

An exocytosis of digestive enzymes from the acrosome of the sperm

Question 3

What is the acrosomal reaction

Answer 3

Exocytosis of enzymes from the acrosome occurs. The enzymes digest the jelly of the outer membrane, while actin filaments grow from the acrosomal process. The sperm binds to the egg cell membrane receptors

Question 4

What is the fast block to polyspermy?

Answer 4

Contact and fusion of the egg and sperm occur. The egg’s membrane voltage changes (depolarization) as Na+ ion channels open and Na+ ions flood the cell membrane. This prevents any further sperm cells from fusing with the cell membrane.

Question 5

What is the slow block to polyspermy?

Answer 5

Cortical Reaction

Ca++ ions are released from the endoplasmic reticulum. The Ca++ ions help cortical granules (special egg organelle) fuse with the plasma membrane. Sperm binding receptors are removed from the plasma membrane and a fertilization envelope forms. The forming of the fertilization envelope is termed the slow block to polyspermy

Question 6

progesterone

Answer 6

A hormone release from the oocyte that helps with sperm motility among other functions.

Question 7

zona pelludica

Answer 7

Extracellular egg matrix. Includes the receptors for sperm.

Question 8

cleavage

Answer 8

Once fertilization occurs, a rapid period of mitosis, S, and M phases are carried out. The cytoplasm divides into smaller units called blastomeres.

Question 9

Blastomere

Answer 9

The smaller units that result from rapid cell division upon fertilization

Question 10

Morula

Answer 10

a solid ball of cells resulting from rapid cell division from fertilization.

Question 11

blastocoel

Answer 11

A fluid filled cavity within the morula that begins to hollow out the morula.

Question 12

Blastula

Answer 12

a hollow ball of cells (about 128 cells or 7 cleavages)

Two Poles:

• Vegetal Pole: High in Yolk
• Animal Pole: Low in Yolk

Yolk distribution is the most important driving factor that influences the cleavage pattern in many animals.

Question 13

How does yolk distribution affect cleavage?

Answer 13

The heavy yolk in birds and other animals sinks to the bottom of the cell and there is less of the cytoplasm available for cleavage. Those with high yolk content end up with smaller replications and those like humans with very little yolk end up with more equal cleavages.

Question 14

gastrula

Answer 14

We see a shape change

• Forms from a blastula.
• A new central cavity called the archenteron is formed that will become the primitive gut.
• The opening of the archenteron is called the blastopore. This forms the mouth in protosomes and the anus in deuterostomes.

-Three germ layers in a dome shape with a hole at the bottom (blastopore):
Ectoderm
Mesoderm
Endoderm

Question 15

Deuterostomes

Answer 15

chordates and echinoderms

Question 16

Protosomes

Answer 16

Mollusks, Arthropods, and annelids

Question 17

What is the order of fertilized cell division groups?

Answer 17

Zygote -> Morula - > Blastula -> Gastrula

Question 18

Ectoderm

Answer 18

• Outermost layer - Most sensitive to radiation
• Skin
• Nails
• Hair
• Sweat glands
• Tooth enamel
• Cornea and lens of eye
• Adrenal medulla

Question 19

Mesoderm

Answer 19

• Middle layer
• Bone
• Muscle
• Blood
• Connective Tissues
• Notochord
• Excretory, lymphatic systems
• dermis of skin
• adrenal cortex

Question 20

Endoderm

Answer 20

• Innermost layer
• Epithelial linings of respiratory, excretory, and digestive tracts, urinary bladder, and lining of reproductive systems and urethra
• Glands such as the thymus, thyroid, and parathyroid
• Liver and pancreas

Question 21

Organogenesis

Answer 21

We see a big shape change

• Condensing of the mesoderm gives rise to the notochord. This is a rod of stiffened tissue that gives structure to all chordates
• Neural plate forms from the ectoderm and rolls into the neural tube which becomes the CNS (brain and spinal chord)
• Somites are formed, they represent blocks of mesoderm that give rise to vertebrae and muscle. Somites are arranged along the notochord

Question 22

Amniotes

Answer 22

Bird, reptiles, and mammals

All contain a fluid like sac called the amnion

Question 23

Extraembryonic membranes

Answer 23

Think everything surrounding the embryo, amniotic fluid, part of the placenta, etc

• Located outside the embryo:
• Yolk Sac: Encloses the yolk, provides needed nutrients
• Amnion: Absorbs shocks, keeps embryo from drying out
• Chorion: Gas exchange, forms part of the placenta
• Allantois: Disposes of nitrogen waste and gas exchange. In humans it does not store wastes, but is involved in O2 and nutrient transport.
• Visibly found in most shelled eggs

Question 24

Yolk Sac

Answer 24

Encloses the yolk, provides needed nutrients

Question 25

Amnion

Answer 25

Absorbs shocks, keeps embryo from drying out

Question 26

Chorion

Answer 26

Gas exchange, forms part of the placenta

Question 27

Allantois

Answer 27

Disposes of nitrogen waste and gas exchange. In humans it does not store wastes, but is involved in O2 and nutrient transport.

Question 28

Totipotent

Answer 28

- Capable of developing into all different cell types | - A zygote is Totipotent plus the next three cell divisions to a Morula

Question 29

Pluripotent

Answer 29

- Capable of developing into many different cell types, but NOT extraembryonic tissues. - Stem Cells - Blastocyst inner mass cells are pluripotent

Question 30

Unipotent

Answer 30

Normal organ cells that create clones of themselves

Question 31

Implantation

Answer 31

- Occurs in the Endometrium and occurs before the end of the first week - It's the blastocyst that adheres to the endometrium. (blastocyst is the mammalian version of the blastula)

Question 32

blastocyst

Answer 32

Mammalian version of the blastula

Question 33

Human yolk sac

Answer 33

Plays a role in developing the digestive tract. Does not provide nourishment like egg laying animals

Question 34

Umbilical cord

Answer 34

- Connects the human embryo to parts of the yolk sac, allantois, and amnion - Well endowed with blood vessels.

Question 35

Chorion development

Answer 35

Develops around the embryo and secretes chorion gonadotropin hormone that helps maintain the corpus leutum

Question 36

Corpus Leutum

Answer 36

Secretes progesterone during the first three months of pregnancy (trimester I) After the first three months the placenta takes over to produce progesterone and estrogen (steroid hormones)

Question 37

Trimester 1

Answer 37

- Most growth and differentiation occurs here - Most sensitive to radiation and drug toxicity - Main period for organogenesis - After eight weeks the embryo is called a fetus - Outer layer of the blastocyst called the trophoblast grows within the endometrium to form the placenta

Question 38

Trimester 2

Answer 38

- All major organs formed - Pregnancy is obvious - Corpus luteum deteriorates as levels of hCG decrease. - The placenta takes over the role of making progesterone and estrogen

Question 39

Trimester 3

Answer 39

- Further development | - Fetus can generally survive at 8 months

Question 40

viviparous

Answer 40

young are born alive after nourishment in the uterus from the placenta

Question 41

oviparous

Answer 41

Young hatch from eggs laid outside the mother

Question 42

trophoblast

Answer 42

The outer layer of the blastocyst that attaches to the endometrium and helps form the placenta

Question 43

Fraternal vs identical twins

Answer 43

Fraternal: Two eggs drop and are fertilized Identical: The cell divides after fertilization

Question 44

Summary of human development

Answer 44

zygote -> Morula -> blastocyst -> embryo -> fetus - > baby

Question 45

Homeotic gene

Answer 45

A gene that regulates the placement and spatial organization of body parts in animals, plants, and even fungi These control the development and the fate of many cell groups A homeotic mutation in an insect could result in a leg being placed where an antenna should be.