CH 3 – Embryogenesis and Development

Question 1

Fertilization usually occurs in the widest part of the fallopian tube, known as the ___. The first sperm that comes into contact with the secondary oocytes cell membrane form a tube-like structure known as the ___. Its pronucleus may freely enter the oocyte once meiosis II has been completed.

Answer 1

ampulla; acrosomal apparatus

Question 2

After penetration of the sperm though the membrane, the ___, a release of calcium ions occurs. Ca ions depolarize the ovum membrane, which prevents fertilization by multiple sperm and increase the metabolic rate of the new diploid zygote. The now depolarized and impenetrable membrane is called the __.

Answer 2

cortical reaction; fertilization membrane

Question 3

Dizygotic (fraternal) twins

Answer 3

form from fertilization of two different eggs released during one ovulatory cycle by two different sperm. Each develops its own placenta, amnion, and chorion.

Question 4

Monozygotic (identical) twins

Answer 4

form when a single zygote splits into two. Because the genetic material is identical, the genomes of the offspring will be too. If division is incomplete, conjoined twins may result.

Question 5

Monochorionic/monoamniotic twins Monochorionic/diamniotic twins Dichorionic/diamniotic twins

Answer 5

Share the same amnion and chorion.
Share the same chorion but have different amnions
Each have their own amnions and chorions.
Which type occurs is a result of when the separation occurred. As more gestational structures are shared, there are more risks as the fetuses grow and develop.

Question 6

After fertilization in the fallopian tubes, zygote travels to the uterus for implantation. As it moved towards the uterus, zygote undergoes rapid mitotic cell division in a process called ___

Answer 6

cleavage

Question 7

First cleavage officially creates an ___, as it becomes multicellular. During first few divisions, cells stay the same size but divide into smaller cells; thus increasing the SA:V and Nucleus:Cytoplasm ratio.

Answer 7

embryo

Question 8

2 types of cleavage:

Answer 8

Indeterminate and determinate. Indeterminate cleavage results in cells that can still develop into complete organisms. Monozygotic twins have identical genomes because they both originate from indeterminate cleaved cells of the same embryo.
Determinate cleavage results in cells which are committed to differentiating into a certain cell type.

Question 9

Several divisions later the embryo becomes a solid mass of cells known as ___. Once formed, it undergoes __ which forms the __, a hollow ball of cells with a fluid filled inner cavity known as a __.

Answer 9

morula; blastulation; blastula; blastocoel

Question 10

Mammalian blastula known as a __ and consists of the __ and __.

Answer 10

blastocyst; trophoblast; inner cell mass
Trophoblast cells surround the blastocoel and give rise to the chorion and later the placenta
Inner cell mass protrudes into the blastocoel and gives rise to the organism itself.

Question 11

Stages of Zygote division (after fertilization)

Answer 11

Zygote->embryo(cleavage)->morula(cleavage)->blastula(blastulation)->gastrula(gastrulation)

Question 12

The blastula moves through the fallopian tube to the uterus, where it burrows into the endometrium. __ give rise to the __, an extraembryonic membrane that develops into the placenta. The trophoblasts form the __, which are microscopic finger like projections that penetrate the endometrium. As these chorionic villi develop into the placenta, they support maternal-fetal gas exchange. Embryo is connected to the placenta by the __, which consists of two arteries and one vein encased in a gelatinous substance.

Answer 12

Trophoblastic cells; chorion; chorionic villi; umbilical cord

Question 13

Until the placenta is formed, the embryo is supported by the __, which is also the site of early blood development.

Answer 13

yolk sac

Question 14

the allantois and amnion.

Answer 14

Extraembryonic membranes
The allantois is involved in early fluid exchange between the embryo and yolk sac. The umbilical cord is formed from remnants of the yolk sac and the allantois.
The allantois is surrounded by the amnion, a thin tough membrane filled with amniotic fluid. This fluid serves as a shock absorber during pregnancy, lessening the impact of the maternal motion on the developing embryo.

Question 15

ectopic pregnancy

Answer 15

Sometimes the blastula implants itself outside the uterus, known as an ectopic pregnancy. Over 95% of ectopic pregnancies occur in the fallopian tube. Ectopic pregnancies are generally not viable; if the embryo does not spontaneously abort, the tube may rupture. Suspected ectopic pregnancy is often a surgical emergency.

Question 16

Once the cell mass implants it can begin further developmental processes such as __, the generation of 3 distinct cell layers. This begins with a small invagination in the blastula. Cells continue to move towards the invagination, resulting in elimination of the blastocoel. A tube through the middle is formed by merging of membranes and a __ is formed. The membrane invagination into the blastocoel is called the __, which later develops the gut.

Answer 16

gastrulation; gastrula; archenteron

Question 17

The opening of the archenteron is called the __.

Answer 17

blastopore
In deuterostomes, such as humans, the blastopore develops into the anus.
In protostomes it develops into the mouth.

Question 18

Eventually, some cells will also migrate into what remains of the blastocoel. This establishes 3 layers of cells called the __.

Answer 18

primary germ layers

Question 19

primary germ layers

Answer 19

The outermost layer called the ectoderm and gives rise to epidermis, hair, nails & epithelial of nose, mouth, anus. Lens of the eye. Nervous system, Adrenal medulla (contains nervous tissue)
Middle layer mesoderm which develops into the musculoskeletal system, circulatory, and most of the excretory systems. Mesoderm also gives rise to the gonads and muscular & connective tissue layers of the digestive and respiratory systems. Adrenal cortex & Notochord
Endoderm inner most layer and forms epithelial lining of digestive and respiratory tracts. Also, parts of liver, pancreas, thyroid, bladder, distal urinary tracts.

Question 20

__ of the genome transcribes only genes needed for a particular cell type, allowing for cells with the same genes to develop into different cells. Often related to the concept of __, which is the ability of one group of cells to influence the fate of nearby cells. This process is mediated by chemical substances called __ which diffuse from the organizing cells to the responsive cells

Answer 20

Selective transcription; induction; inducers

Question 21

Once the 3 germ layers form, __ or development of the nervous system can begin. Describe it

Answer 21

neurulation
Nervous system derived from the ectoderm. A rod of mesodermal cells known as the notochord form along the axis of the organism like a primitive spine. Notochord induces a group of overlying ectodermal cells to slide inward to from the neural folds, which surround a neural groove. The neural folds grow towards one another until they fuse into a neural tube, which gives rise to the central nervous system. At the tip of each neural fold are neural crest cells. These cells migrate outward to form the peripheral nervous system. Finally, ectodermal cells will migrate over the neural tube and crest to cover the rudimentary nervous system.

Question 22

Early development is a highly sensitive time. __ are substances that interfere with development, causing defects or death of the embryo.

Answer 22

Teratogens
It is believed that unique genetics of the embryo influences the effects of the teratogen, as well
as route and length of exposure, rate of placental transmission of the teratogen, and identity of the teratogen. Common teratogens include alcohol, prescription drugs, viruses, bacteria, and environmental chemicals.

Question 23

3 stages of cell specialization

Answer 23

specification, determination, and differentiation

Question 24

Specification, determination, and differentiation

Answer 24

is where the cells are reversibly designated as a specific cell type.
This is followed by determination, which is the commitment of a cell to a particular function in the future. Prior to determination cell can become any type, even if it has gone through specification. Multiple pathways by which determination occurs. During cleavage, the presence of a specific mRNA and protein molecules may result in determination; also occur due to secretion of specific molecules from nearby cells. These molecules called morphogens may cause neighboring cells to follow a particular developmental pathway.
After a cells fate has been determined, the cell must undergo changes that cause the cell to develop into the determined cell type. This includes changing the structure, function, and biochemistry of the cell to match the cell type, a process known as differentiation. When a cell is determined, it is committed to a particular cell linage. When the cell differentiates, it assumes the structure, function, and biochemistry of that cell type.

Question 25

Stem cells & Cell potency

Answer 25

Cells that have not yet differentiated or give rise to other cells that will differentiate are known as stem cells. Stem cells exist in embryonic and adult tissues. The tissues a particular cell can differentiate into are determined by its potency.
Cells with the greatest potency are called totipotent and include embryonic stem cells; totipotent cells can differentiate into any cell type either in the fetus or placental structures. After the 16-cell stage, cells of the morula differentiate into the inner cell mass and the trophoblast. After a few more division cycles these totipotent cells start to differentiate into the 3 germ layers.
At this stage the cells are said to be pluripotent; these cells can differentiate into any cell type except for those found in the placental structures. Finally, as the cells continue to become more specialized, they are said to be multipotent, which can differentiate into multiple cell types within a particular group.
Ex: hematopoietic stem cells can differentiate into all the cells found in blood, but not into skin or muscle cells or neurons. Potency is a spectrum. Stem cells are able to differentiate into different cell types. The potency of the stem cell determines how many different cell types can arise. As the cells become more differentiated, the potency of the cell decreases from totipotent to pluripotent to multipotent.

Question 26

Surrounding tissues induce a developing cell to become a particular cell type via __; the term inducer may also refer to the cell secreting the signal. The cell that is induced is called a __ ; to be induced a responder must be competent, or able to responds the inducing signal.

Answer 26

inducers; responder

Question 27

4 types of cell signaling

Answer 27

Autocrine signals act on the same cell that secreted the signal in the first place.
Paracrine signals act on cells in the local areas.
Juxtacrine signals do not usually involve diffusion but involve a cell directly stimulating receptors of an adjacent cell.
Endocrine signals involve secreted hormones that travel through the bloodstream to a distant target tissue.

Question 28

Inducers are often __, which are peptides that promote differentiation and mitosis in certain tissues. Most growth factors only function on specific cell types or in certain areas. Induction is not always a one-way pathway, known as __.
One of the main methods of signaling occurs via gradients

Answer 28

growth factors; reciprocal development
Ex: Lateral outpocketings from the brain (optic vesicles) grow out and touch overlying ectoderm. Optic vesicles induce ectoderm to form the lens placode. Lens placode then induces the optical vesicle to create the optic cup. Optic cup then induces the lens placode to form the cornea and lens.

Question 29

Cells must be able to disconnect from adjacent structures and migrate to their correct location

Answer 29

Ex: anterior pituitary gland originates from a segment of oral ectoderm and must migrate from the top of the mouth to its final location just below the hypothalamus. Neural crest cells undergo extensive migration. These cells begin at the edge of neural folds, and during neurulation they migrate throughout the body to form many different sensory ganglia and other specific cell types.

Question 30

Apoptosis occurs at various times in development. Ex: fingers are originally webbed during hand development. However, cells of the webbing undergo apoptosis resulting in finger separation. Apoptosis also occurs in the digestive track where the central lumen is formed, helping create a functional anus. Describe process of apoptosis

Answer 30

Apoptosis may occur via apoptotic signals or preprogramming. During apoptosis cell undergoes changes in morphology and divides into many self-containing protrusions called apoptotic blebs, which can be broken apart into apoptotic bodies and digested by other cells. Allows for material re-cycling and prevents leakage of harmful substances into extracellular environment.

Question 31

__ is the ability of an organisms to regrow certain parts of the body and varies from species to species. Species such as newts or salamanders have extensive clusters of stem cells allowing for enhanced capacity to regenerate. When regeneration is required, these stem cells can migrate to the appropriate part of the body to initiate growth. These species are said to undergo __, in that lost or damaged tissues are replaced with identical tissues. In contrast, __ implies that newly formed tissue is not identical in structure or function to the tissue that has been injured or lost.

Answer 31

Regenerative capacity; complete regeneration; incomplete regeneration
Humans typically inhibit incomplete regeneration. Liver tissue has high regeneration capacity. Heart has very little to no regenerative capacity. Kidneys have moderate regenerative capacity.

Question 32

As organisms age, changes occur in both molecular and cellular structure. __, or biological aging, can occur at the cellular or organismal level as these changes accumulate.

Answer 32

Senescence;
At the cellular level, senescence results in the failure of cells to divide. Research has demonstrated this may be due to shortened telomeres, which are the ends of chromosomes. Telomers reduce the loss of genetic information from the ends of chromosomes and help prevent DNA from unraveling. Telomers are difficult to replicate and shorten during each round of DNA synthesis. Eventually telomers become too short and cell is no longer able to replicate. Some cells such as germ, fetal, tumor express an enzyme telomerase. This enzyme is a reverse transcriptase that can synthesize the ends of chromosomes, preventing senescence.

Question 33

Placenta

Answer 33

is the organ where nutrient, gas, and waste exchange occur. Maternal and fetal blood do not mix as they may be different blood types. Simplest method to move substances is by diffusion. This is the preferred method for water, glucose, amino acids, and inorganic salts
depends on close proximity of the embryonic and maternal bloodstreams, facilitating diffusion between them. To further enhance transfer of O2 from maternal to fetal circulation, fetal blood cells contain fetal hemoglobin (HbF) which has a greater affinity for O2 then adult hemoglobin (primarily HbA).
Waste material and CO2 move in opposite directions
Placental barrier also serves as immunologic immunity. Crossing over of antibodies across the placental membrane serves a protective function. Placenta also qualifies as an endocrine organ because it produces progesterone, estrogen, and hCG, all of which are essential for maintaining pregnancy.

Question 34

Umbilical arteries and veins

Answer 34

Umbilical arteries carry blood away from the fetus towards the placenta. Similar to other arteries that carry blood away from the heart.
Umbilical vein carries blood towards the fetus and from the placenta. Similar to other veins that carry blood towards the heart.
Oxygenation occurs at the placenta. Umbilical arteries carry deoxygenated blood with waste products and umbilical vein carries oxygenated blood with nutrients.

Question 35

Lungs and liver don’t serve significant functions prior to birth. Gas exchange occurs at the placenta and not the lung. Detoxification and metabolism are primarily controlled by the mother’s liver, and nutrient and waste exchange occurs at the placenta. Fetus constructs 3 __ to actively direct blood away from the lungs and liver while they develop due to high blood pressure sensitivity of these organs postpartum.

Answer 35

shunts

Question 36

3 shunts

Answer 36

Two different shunts are used to reroute blood from the lungs. The first called the foramen ovale, is a one-way valve that connects the right atrium to the left atrium. This allows blood entering the right atrium from the inferior vena cava to flow into the left atrium instead of the right ventricle, and thereby be pumped through the aorta into systemic circulation directly. Unlike in adult circulation, the right side of the heart is at a higher pressure in the fetus than the left side, which pushes blood through the opening. After birth, this pressure differential reverses, shutting the foramen ovale.

Second, the ductus arteriosus shunts the leftover blood from the pulmonary artery to the aorta. Again, the pressure differential between the right and left sides of the heart pushes blood through the opening and into systemic circulation.

The liver is bypassed via the ductus venosus, which shunts blood returning from the placenta via the umbilical vein directly into the inferior vena cava. The liver still receives some blood supply form smaller hepatic arteries in the systemic circulation.

Question 37

Gestation

Answer 37

Human gestation lasts an estimated 280 days, which is divided into 3 trimesters. As a general rule, the larger the animal, the longer the gestational period and fewer offspring per pregnancy

Question 38

First Trimester:

Answer 38

Major organs begin to develop during the first few weeks. Organogenesis. Heartbeat begins at 22 days, and soon afterwards the eyes, gonads, limbs, and liver start to form. Cartilaginous skeletons begin to harden into the body by the 7th week. By the end of 8 weeks, most organs have formed, brain is fairly developed, and the embryo becomes known as the fetus. End of 3 months, fetus is ~ 9 cm long.

Question 39

Second Trimester:

Answer 39

Fetus undergoes tremendous amount of growth. Begins to move within amniotic fluid, face takes on human appearance, and toes & fingers elongate. End of 6 months fetus ~ 30-36 cm

Question 40

Third Trimester:

Answer 40

Continued rapid growth and further brain development. Lung last structure to become fully functional. Antibodies are transported by highly selective active transport from the pregnant individual to the fetus for protection against foreign agents in preparation for life outside the womb; this transfer begins earlier in pregnancy but is highest in the 9th month before birth. Growth rate slows and fetus has less room to move around.

Question 41

Vaginal childbirth, or __, is accomplished by rhythmic contractions of uterine smooth muscle, coordinated by __ and the peptide hormone __. Births consist of 3 basic phases.

Answer 41

parturition; prostaglandins; oxytocin
First, the cervix thins out and the amniotic sac ruptures, commonly called water breaking. Next, strong uterine contractions result in the birth of the fetus. Finally, placenta and umbilical cord are expelled, known as afterbirth.

Question 42

What stage of development does implantation occur

Answer 42

blastula