Chapter 3 Embryogenesis and Development

Question 1

Fertilization is

Answer 1

Fertilization is the joining of a sperm and an ovum

• It usually occurs in the ampulla of the fallopian tube.
• The sperm uses acrosomal enzymes to penetrate the corona radiata and zona pellucida.
• Once it contacts the oocyte’s plasma membrane, the sperm establishes the acrosomal apparatus and injects its pronucleus.
• When the first sperm penetrates it causes a release of calcium ions, which prevents additional sperm from fertilizing the egg and increases the meta-bolic rate of the resulting diploid zygote. This is called the cortical reaction.

Question 2

Fraternal (dizygotic) twins result from the fertilization of

Answer 2

two eggs by two different sperm

Question 3

Identical (monozygotic) twins result from the

Answer 3

splitting of a zygote in two

Question 4

Monozygotic twins can be classified by the

Answer 4

placental structures they share (mono-vs. diamniotic, mono-vs. dichorionic).

Question 5

Cleavage

Answer 5

after fertilization in the fallopian tube, the zygote(unicellular) must travel to the uterus for implantation. as it moves to the uterus for implantation, the zygote undergoes rapid mitotic cell division in a process called: cleavage!

• Cleavage refers to the early divisions of cells in the embryo. These mitotic divisions result in a larger number of smaller cells, as the overall volume does not change.
• The zygote becomes an embryo after the first cleavage because it is no longer unicellular.
• There are two types of cleavage:

1. Indeterminate cleavage results in cells that are capable of becoming any cell in the organism. in fact monozygotic twins have identical genomes because they both originate from indeterminately cleaved cells of the same embryo.
2. Determinate cleavage results in cells that are committed to differentiating into a specific cell type. these cells are committed to differentiating inot a certain type of cell.

Question 6

The morula is a

Answer 6

the morula is a solid mass of cells seen in early development.

Question 7

Blastulation and Implantation

Answer 7

Blastilation:

• once the morula is formed it undergoes blastulation to form the blastula(blastocyst) which is a hollow ball of cells with fluid-filled inner cavity known as a blastocoel and has two different structures: the trophoblast (which gives rise to the chorion and later the placental structures) and the inner cell mass (which becomes the developing organism).

Implantation:

• The blastula implants in the endometrial lining and forms the placenta. The blastula moves from fallopian tube to the uterus when it implants in the endometium.
• The chorion contains chorionic villi, which penetrate the endometrium and create the interface between maternal and fetal blood.
• Before the placenta is established, the embryo is supported by the yolk sac.
• The allantois (the allantois is involved in early fluid exchange b/t the embryo and the yolk sac) is involved in early fluid exchange between the embryo and the yolk sac.
• The amnion lies just inside the chorion and produces amniotic fluid.
• The developing organism is connected to the placenta via the umbilical cord.

Question 8

During gastrulation, the archenteron is formed with a blastopore at the end. As the archenteron grows through the blastocoel it contacts the opposite side, establishing three primary germ layers.

Answer 8

• The ectoderm becomes epidermis, hair, nails, and the epithelia of the nose, mouth, and anal canal, as well as the nervous system (including adrenal medulla) and lens of the eye. ector attractor to physical things.
• The mesoderm becomes much of the musculoskeletal, circulatory, and excretory systems. Mesoderm also gives rise to the gonads and the muscular and connective tissue layers of the digestive and respiratory systems, as well as the adrenal cortex. means to how we get around
• The endoderm becomes much of the epithelial linings of the respiratory and digestive tracts and parts of the pancreas, thyroid, bladder, and distal urinary tracts. endo (internal)

Question 9

Neurulation, or development of the nervous system, begins after the formation of the

Answer 9

• The notochord induces a group of overlying ectodermal cells to form neural folds surrounding a neural groove.
• The neural folds fuse to form the neural tube, which becomes the central nervous system.
• The tip of each neural fold contains neural crest cells, which become the peripheral nervous system (sensory ganglia, autonomic ganglia, adrenal medulla, and Schwann cells), as well as specific cell types in other tissues (calcitonin-producing cells of the thyroid, melanocytes in the skin, and others).
• Remember: NS is dericed from the ectoderm.

Question 10

Teratogens are

Answer 10

Teratogens are substances that interfere with development, causing defects or even death of the developing embryo. Teratogens include alcohol, certain pre-scription drugs, viruses, bacteria, and environmental chemicals.

Question 11

Maternal conditions can affect what?

Answer 11

Maternal conditions can affect development, including diabetes (increased fetal size and hypoglycemia after birth) and folic acid deficiency (neural tube defects).

Question 12

Cell specialization occurs as a result of

Answer 12

determination and differentiation.

• Determination is the commitment to a specific cell lineage, which may be accomplished by uneven segregation of cellular material during mitosis or with morphogens(may cause neighboring cells to follow a particular development pathway), which promote development down a specific cell line. To respond to a specific morphogen, a cell must have competency.
• Differentiation refers to the changes a cell undergoes due to selective transcription to take on characteristics appropriate to its cell line.

*When a cell is derermined, it is committed to a particular cell lineage. when the cell differentiates, it assumes the structure, function, and biochemestry of that cell type.

Question 13

Stem cells are

Answer 13

Stem cells are cells that are capable of developing into various cell types. They can be classified by potency.

• Totipotent cells are able to differentiate into all cell types, including the three germ layers and placental structures.
• Pluripotent cells are able to differentiate into all three of the germ layers and their derivatives.
• Multipotent cells are able to differentiate only into a specific subset of cell types.

*stem cells are able to differentiate into different cell types. the totipotency of the stem cell determines how many different cell types a stem cell can become. As cells become more differentited, the potency of the cell decreases (from totipotent to pluripotent to multipotent)

Question 14

___ signals act on cells in the local area.

Answer 14

Cell-cell communication

Paracrine signal

Question 15

___act on the same cell that released the signal.

Answer 15

• Autocrine signals act on the same cell that released the signal.

Question 16

Cells communicate through a number of

Answer 16

Cells communicate through a number of different signaling methods. An inducer releases factors to promote the differentiation of a competent responder.

• Autocrine signals act on the same cell that released the signal.
• Paracrine signals act on local cells.
• Juxtacrine signals act through direct stimulation of adjacent cells.
• Endocrine signals act on distant tissues after traveling through the bloodstream.

Question 17

Cells may need to migrate to

Answer 17

arrive at their correct location.

Question 18

Inducers are often what?

Answer 18

growth factors, which are peptides that promote differentiation and mitosis in certaint tissues.

Interestingly, induction is not always a one way pathway. To the end, differentiation of the lens then triggers the optic vesicle to form the optic cup, which ultimately becomes the retina. This is known as reciprocal development. Most tissues will be exposed to multiple inducers during the course of develpment.

Question 19

Apoptosis is

Answer 19

Apoptosis is programmed cell death via the formation of apoptotic blebs that can subsequently be absorbed and digested by other cells. Apoptosis can be used for sculpting certain anatomical structures, such as removing the webbing between digits.

Question 20

necrosis

Answer 20

which is a process of cell death in which a cell dies as a result of injury. In necrosis, internal substances can be leaked, causing irritation of nearly tissues or even an immune response.

Question 21

Regenerative capacity is the

Answer 21

ability of an organism to regrow certain parts of the body. The liver has high regenerative capacity, while the heart has low regenerative capacity.

Question 22

Senescence is the result of

Answer 22

multiple molecular and metabolic processes, most notably, the shortening of telomeres during cell division.

* some cells, including germ cells, fetal cells, and tumor cells, express an enzyme known as telomerase. This enzyme is a reverse transcriptase that is able to synthesize the ends of chromosomes, preventing senescence. *

Question 23

Germ layer and organ: chart

Answer 23

Ectoderm (germ layer):
Organ: Integument (including the epidermis, hair, nails, and epithelia of the nose, mouth, and anal canal), lens of the eye, nervous system (including adrenal medulla), inner ear

Mesoderm(Germ layer):
Organ: Musculoskeletal system, circulatory system, excretory system, gonads, muscular and connective tissue layers of the digestive and respiratory systems, adrenal cortex

Endoderm (Germ layer):
Organ: Epithelial linings of digestive and respiratory tracts, and parts of the liver, pancreas, thyroid, bladder, and distal urinary and reproductive tracts

Question 24

ectopic pregnancy

Answer 24

somwetimes the blastula implants itself outside the uterus, a situation known as an ectopic pregnancy.

over 95 % of ectopic pregnancies occur in the fallopian tube. these pregancies are generally not viable because the narrow fallopian tube is not an environment in which an embryo can properly grow. if the embryo does not spontaneously abort, the tube may rupture and a considerable amount of hemorrhaging may result. in fact, a suspected actopic pregnancy is often a surgical emergency.

Question 25

Type of Potency/Cell Lineages

Answer 25

Totipotency: (Cell Lineages) Any cell type in the developing embryo (primary germ layers) or in extraembryonic tissues (amnion, chorion, placenta)

Pluripotency: (Cell Lineages) Any cell type in the developing embryo (primary germ layers)

Multipotency: (Cell Lineages) Any cell type within a particular lineage (for example, hematopoietic stem cells)

Question 26

Endoderm

Answer 26

germ layer

Interna layer

• pancreas
• liver
• thyroid
• lung
• bladder
• urethra

Question 27

Mesoderm

Answer 27

germ layer

Middle layer

• bone marrow
• skeletal, smooth and cardiac muscle
• heart and blood vessels
• kidney tubules

Question 28

Ectoderm

Answer 28

germ layer

External layer

• skin
• neurons
• pituitary gland
• eyes
• ears

Question 29

Cell- cell communication:

the cell secreting the signal is called?

the cell that is acting on it is called?

Answer 29

inducer: the cell secreting the signal

Responder: the cell that is induced (to be induced a responder ust be competent or able to respond to the inducing signal)

Question 30

_____ signals do not usually involve diffusion, but involve a cell directly stimulating receptors of an adjacent cell.

Answer 30

cell-cell communication

Juxtacrine signals

Question 31

___ signals involve secreted hormones that travel thu the bloodstream to a distant target tissue

Answer 31

cell-cell communication

Endocrine Signals

Question 32

Fetal Circulation

Answer 32

START

Question 33

the placenta is what kind of organ?and why?

Answer 33

endocrine organ because it produces progesterone, estrogen, and human chorionic gonadotropin (hCG), all which are essential for maintaining pregnancy.

Question 34

detoxificanion and metabolism are primarily controlled in fetus by?

Answer 34

by the mothers liver

* The lung and liver both do not serve significant functions prior ro birth. *

Question 35

What occurs in the placenta?

Answer 35

Nutrient

gas

waste exchange occurs at the placenta.

Question 36

Oxygen and carbon dioxide are

Answer 36

Oxygen and carbon dioxide are passively exchanged due to concentration gradients. PASSA PASSA

Question 37

Fetal hemoglobin (HbF) has a

Answer 37

higher affinity for oxygen than adult hemoglobin (primarily HbA); this affinity assists in the transfer (and retention) of oxygen into the fetal circulatory system.

*to further enhance the transfer of oxygen from maternal to fetal circulation, fetal blood cells contain fetal hemo (HbF), which has a greater affinity for O2 than maternal (adult) hemoglobin (primary HbA). this also assists with the transfer (and retention) of oxygen into the fetal circulatory system. waste material and carbon dioxide move in the opposite direction. *

Question 38

The placental barrier also serves as

Answer 38

• Immune protection against many pathogens, and antibodies are transferred from mother to child.
• Remember, gas exchange in the fetus occur across the placenta. Fetal lungs do not function until birth.

Question 39

The placenta serves

Answer 39

endocrine functions, secreting estrogen, progesterone, and human chorionic gonadotropin (hCG).

Question 40

The umbilical arteries carry?

The umbilical vein carry?

Where does the oxygenation occur?

Answer 40

deoxygenated blood from the fetus to the placenta.

oxygenated blood from the placenta back to the fetus.

The oxygenation occur: at the placenta, rather than in fetal lungs.

Question 41

The fetal circulatory system differs from its adult version by having three shunts:

Answer 41

• The _for_amen ovale connects the right atrium to the left atrium, bypassing the lungs.
• The ductus arteriosus connects the pulmonary artery to the aorta, bypassing the lungs.

• The ductus venosus connects the umbilical vein to the inferior vena cava, bypassing the liver.

Question 42

Gestation and Birth START!!

Answer 42

START

Question 43

In the first trimester

Answer 43

In the first trimester, organogenesis occurs (development of heart, eyes, gonads, limbs, liver, brain).

• Heart beats: 22 days, and soon after the eyes, gonads, limbs, and liver start to form.
• 5 weeks: embryo is 10mm in length
• 6 weeks: 15mm
• 7th week: cartilaginous skeleton beigins to harden into bone
• 8th week most ogans have formed, the brain is fairly developed and embryo becomes known as a fetus.
• 3rd MONTH: fetus is 9cm long

Question 44

In the second trimester

Answer 44

In the second trimester, tremendous growth occurs, movement begins, the face becomes distinctly human, and the digits elongate.

• End of 6 MONTHS: fetus measures 30 to 36 cm long.

Question 45

In the third trimester

Answer 45

In the third trimester, rapid growth and brain development continue, and there is transfer of antibodies to the fetus.

The growth rate slows and the fetus becomes less active, as it has less room to move about.

Question 46

During birth the cervix

Answer 46

During birth the cervix thins out and the amniotic sac ruptures. Then, uterine contractions, coordinated by prostaglandins and oxytocin, result in birth of the fetus. Finally, the placenta and umbilical cord are expelled.

Question 47

1st, 2nd, and 3rd trimester months ?

Answer 47

1st: 1, 2, 3 months(1-13 weeks)
2nd: 4, 5, 6 months (14-26 weeks)
3rd: 7, 8, 9 (27-40 weeks)