Chapter 3.1

Question 1

What happens to the secondary oocyte following ovulation?

Answer 1

The secondary oocyte will leave the ovary and enter the abdominal cavity. It will then be pushed to the fallopian tube where it can potentially be fertilized.

Question 2

What is the cortical reaction and how does it affect the ovum?

Answer 2

When a sperm penetrates the cell membrane of an ovum, a flood of calcium ions occurs and the ovum’s cell membrane depolarizes. This serves 2 purposes.

1. The depolarized cell membrane is impenetrable to more sperm, preventing multiple sperm from fertilizing one egg.
2. The increased calcium concentration increases the metabolic rate of the newly formed zygote, helping it to grow and survive.

Question 3

What is the fertilization membrane?

Answer 3

The fertilization membrane is the depolarized and impenentrable membrane of a zygote following the cortical reaction.

Question 4

What are the two types of twins?

Answer 4

1. Dizgotic, or Fraternal
2. Monozygotic, or Identical

Question 5

How do dizygotic twins come to be?

Answer 5

Dizygotic twins form from the fertilization of two different eggs that were released in one ovulatory cycle by two different sperm. Both of these zygotes will implant in the uterine wall and be carried to full term.

Question 6

How do monozygotic twins come to be?

Answer 6

Monozygotic twins occur when a single fertilized ovum (zygote) splits into two without differentiating into other tissues. Because the genetic material in daughter cells is identical in mitosis, these two twins will carry the same genetic information and share appearance.

Question 7

What is cleavage? (in embryonic development)

Answer 7

Cleavage is the series of rapid mitotic divisions undergone by a newly fertilized zygote.

These cleavages are distinct because they do not result in an increase of the size of the organism, they just result in more cells.
This increases surface area to volume ratio which increases area for nutrition and gas exchange

Question 8

What are the two types of cleavage?

Answer 8

1. Intermediate
2. Determinate

Question 9

What is indeterminate cleavage?

Answer 9

Intermediate cleavage results in cells that can still develop into complete organisms. This is actually what happens in monozygotic twins. At some point, the embryo undergoes an indeterminate cleavage that results in another organism forming in addition to the original.

Question 10

What is Determinate cleavage?

Answer 10

Determinate cleavage results in cells with fates that are determined. That is to say, they are already committed to differentiating into a certain type of cell.

Question 11

By what factor does the number of cells increase after each cleavage?

Answer 11

2x

Question 12

What is a morula

Answer 12

Morula refers to the solid mass of cells that culminates from several divisions of the zygote. It’s name comes from the latin word for mulberry, which is what the morula looks like.

Question 13

What is blastulation?

Answer 13

Blastulation is the name for the transformation of the morula into the blastula.

Question 14

What is a blastula?

Answer 14

A blastula is a hollow ball of cells with a fluid filled inner cavity know as a blastocoel.

Question 15

How is a blastocsyt distinct from a blastula?

Answer 15

Blastocyst is just the name for a mammalian blastula.

Question 16

What are the two notweorthy cell groups in a blastocyst?

Answer 16

1. The trophoblast cells
2. The inner cell mass

Question 17

What is the function of the trophoblast cells?

Answer 17

The trophoblast cells surround the blastocoel and give rise to the chorion and later the placenta.

Question 18

What is the function of the inner cell mass?

Answer 18

The inner cell mass is the group of cells that will give rise to the organism being born.

Question 19

Describe the path of a fertilized egg, starting from the ovary and ending with implantation.

Answer 19

1. From the supply with which females are born, a primary oocyte will be allowed to develop into a secondary oocyte.
2. The secondary oocyte will burst forth from the follicle, leave the ovary, and enter the abdominal cavity.
3. The secondary oocyte is taken up by the Fallopian tube with the help of cilia.
4. The secondary oocyte is fertilized by sperm at some point in the fallopian tube.
5. After fertilization, the zygote continues its path through the fallopian tube.
6. As the zygote travels through the fallopian tube, it undergoes blastulation, eventually forming a blastocyst (blastula).
7. The blastocyst implants in the thickened endometrium and begins secreting hCG, a hormone that mimics LH.

Question 20

What is the chorion?

Answer 20

The chorion is an extraembryonic membrane that forms from the trophoblast cells and develops into the placenta.

Question 21

What is the umbilical cord?

Answer 21

The umbilical cord is a thick cord comprised of two arteries and one vein encased in a gelatinous substance. The umbilical vein carries oxygen and nutrient rich blood to the embryo from the placenta and the umbilic arteries carry deoxygenated blood from the embryo to the placenta.

NOTE: This is opposite of the normal situation, which is arteries carrying oxygenated blood and veins carrying deoxygenated blood.

Question 22

What is the yolk sac?

Answer 22

The yolk sac is a temporary structure from which the embryo draws nutrients and forms red blood cells. The yolk sac supports the embryo until the umbilical cord and the placenta are fully formed and can take over supplying the embryo.

Question 23

What is the amnion?

Answer 23

The amnion is a thin, tough membrane which produces amniotic fluid. It serves as a shock absorber to protect the developing fetus.

Question 24

What is gastrulation?

Answer 24

Gastrulation is the term used to refer to the
inward folding of the blastula to create a layered structure with a prominent invagination known as a gastrula.

Question 25

What 5 important structures are developed during gastrulation?

Answer 25

During gastrulation, the three primary germ layers are developed as well as the archenteron and the blastopore.

Question 26

What are the three germ layers and what is their collective function?

Answer 26

The three germ layers are the Ectoderm, the Mesoderm, and the Endoderm. These three layers provide the base for the development of all of the tissues in the human body. Each layer will develop into its own specific tissues.

Question 27

What is the archenteron?

Answer 27

The archenteron is the name of the invagination that forms during gastrulation.

Question 28

What is the blastopore?

Answer 28

The blastopore is the name for the mouth of the opening in the gastrula known as the archenteron.

Question 29

How deep is the Ectoderm in the Gastrula and what tissues are derived from it?

Answer 29

The Ectoderm is the outermost germ layer. It develops into skin (epidermis), hair, nails, the lens of the eye, the entire nervous system, the inner ear, the adrenal medulla, pituitary gland, and the epithelial linings of the mouth and anus. MNEMONIC: Ectoderm = "Attracto" derm. We are attracted to good skin, good brain, and pretty eyes.

Question 30

How deep is the Mesoderm in the Gastrula and what tissues are derived from it?

Answer 30

The Mesoderm is in between the outermost Ectoderm and the innermost Endoderm. The Mesoderm develops into the musculoskeletal system, the circulatory system, the heart, the spleen, the kidney, bone, connective tissue layers of the digestive and respiratory system, the gonads, and the adrenal cortex. MNEMONIC: Mesoderm = "means" oderm. These tissues provide us the means to move around (musculoskeletal), the means to move things within our body (circulatory system), the means to get rid of things (kidneys), and the means to have sex (the gonads).

Question 31

How deep is the Endoderm in the gastrula and what tissues are derived from it?

Answer 31

The Endoderm is the innermost of the three germ layers. It develops into the epitelial lining of the digestive tract (except for the mouth and the anus) and the lungs. It also develops into the pancreas, thyroid, bladder, distal urinary tracts, and part of the liver. MNEMONIC: Endoderm = linings of the "endernal" organs (digestive and respiratory tract) and the accessory organs attached to these systems (such as the pancreas, thyroid, bladder, and liver.)

Question 32

Every single cell in the human body contains the ____ DNA

Answer 32

same

Question 33

If every single cell in the human body contains the same DNA, and DNA is the blueprint for the development of the cell, how is it that cells can be so different from one another?

Answer 33

Certain cells will express different parts of the genome while not expressing others. For example, heart cells will express the heart related segments of our DNA, where as kidney cells will express the kidney related segments of our DNA.

Question 34

What is selective transcription?

Answer 34

Selective transcription is when a cell develops a specialized function by only transcribing certain parts of the genome.

Question 35

What is induction?

Answer 35

Induction is the ability of one group of cells to influence the development of other nearby cells through the use of inducers.

Question 36

What are inducers?

Answer 36

Inducers are the chemical signals that are used by cells to cause induction.

Question 37

What are the two main layers of the adrenal gland and from what germ layers are they derived?

Answer 37

1. The Adrenal Cortex, derived from the Mesoderm 2. The Adrenal Medulla, derived from the Ectoderm

Question 38

What is Neurulation?

Answer 38

Neurlation is the development of the internal nervous system from the external ectoderm.

Question 39

What is the notochord and what is its function in Neurulation?

Answer 39

The notochord is a long rod of mesodermal cells. During Neurlation, the notochord induces a segment of the ectoderm to slide inward. This establishes the neural folds and the neural groove.

Question 40

As the neural groove deepens, what happens to the neural folds?

Answer 40

As the neural groove deepens, the neural folds come closer to one another. They will continue to come closer to one another until they meet, forming the neural tube.

Question 41

What are the neural crest cells and into what will they develop?

Answer 41

The neural crest cells are cells at the tip of both of the neural folds. These cells will migrate from the neural folds and develop into the entirety of the peripheral nervous system (sensory ganglia, autonomic ganglia, adrenal medulla, schwann cells) as well as specific cell types in other tissues (calcitonin producing cells of the thyroid, melanocytes in the skin, etc.) Cells derived from ectoderm