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Embryogenesis and Development Flashcards

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1
Q

What is Fertilization?

A

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 metabolic rate of the resulting diploid zygote. This is called the cortical reaction

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2
Q

Identical and Fraternal twins?

A

Fraternal (dizygotic) twins result from the fertilization of two eggs by two different sperm. Identical (monozygotic) twins result from the splitting of a zygote in two. Monozygotic twins can be classified by the placental structures they share (mono- vs. diamniotic, mono- vs. dichorionic).

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3
Q

What is cleavage?

A

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 aer the first cleavage because it is no
longer unicellular.

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4
Q

what is indeterminate vs determinate cleavage?

A

Indeterminate cleavage results in cells that are capable of becoming
any cell in the organism, while determinate cleavage results in cells
that are committed to differentiating into a specific cell type.

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5
Q

What is the morula?

A

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

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6
Q

Parts of the Blastula?

A

The blastula (blastocyst) has a fluid-filled center called a blastocoel and has two different structures: the trophoblast (which becomes
placental structures) and the inner cell mass (which becomes the developing organism).

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7
Q

Where does blastula implant?

A

The blastula implants in the endometrial lining and forms the
placenta.

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8
Q

What is the chorionic villi?

A

The chorion contains chorionic villi, which penetrate the
endometrium and create the interface between maternal and fetal
blood.

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9
Q

Before the placenta is established, the embryo is supported by the
____ ____

A

Before the placenta is established, the embryo is supported by the
yolk sac

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10
Q

The ______ is involved in early fluid exchange between the embryo
and the yolk sac

A

The allantois is involved in early fluid exchange between the embryo
and the yolk sac

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11
Q

The ______ lies just inside the chorion and produces amniotic fluid.

A

The amnion lies just inside the chorion and produces amniotic fluid.

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12
Q

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

A

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.

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13
Q

The developing organism is connected to the placenta via the ______ _______

A

The developing organism is connected to the placenta via the umbilical cord

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14
Q

What is the ectoderm?

A

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.

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15
Q

What is the mesoderm?

A

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

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16
Q

What is the endoderm?

A

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

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17
Q

What is Neurulation?

A

Neurulation, or development of the nervous system, begins aer the
formation of the three germ layers.

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18
Q

What is notochord?

A

The notochord induces a group of overlying ectodermal cells to form
neural folds surrounding a neural groove.

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19
Q

what is neural tube?

A

The neural folds fuse to form the neural tube, which becomes the central nervous system

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19
Q

What is the neural crest cells?

A

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)

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20
Q

What are teratogens?

A

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

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21
Q

Material conditions affecting development

A

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

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22
Q

What is Determination?

A

Determination is the commitment to a specific cell lineage, which
may be accomplished by uneven segregation of cellular material
during mitosis or with morphogens, which promote development
down a specific cell line. To respond to a specific morphogen, a cell
must have competency

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23
Q

What is Differentiation?

A

Differentiation refers to the changes a cell undergoes due to selective transcription to take on characteristics appropriate to its cell line

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24
Q

Stem cells are cells that are capable of developing into various cell types.

They can be classified by potency.

What are they?

A

Totipotent cells, Pluripotent cells, Multipotent cells

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25
Q

What is Totipotent cells?

A

They’re able to differentiate into all cell types, including
the three germ layers and placental structures.

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26
Q

What are Pluripotent cells?

A

Pluripotent cells are able to differentiate into all three of the germ layers and their derivatives.

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27
Q

What is Multipotent cells?

A

Multipotent cells are able to differentiate only into a specific subset
of cell types.

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27
Q

What is an inducer?

A

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

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28
Q

What is an autocrine?

A

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

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29
Q

What is Paracrine?

A

Paracrine signals act on local cells.

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30
Q

What is a Juxtacrine?

A

Juxtacrine signals act through direct stimulation of adjacent cells.

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31
Q

What is endocrine?

A

Endocrine signals act on distant tissues aer traveling through the
bloodstream.

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32
Q

What are growth factors

A

Growth factors, which are peptides that promote
differentiation and mitosis in certain tissues.

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33
Q

What is reciprocal induction

A

If two tissues both induce further differentiation in each other, this is
reciprocal induction.

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34
Q

Signaling occurs via _____

A

Signaling often occurs via gradients.

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35
Q

What is Apoptosis

A

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?

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36
Q

What is Regenerative Capacity?

A

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

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37
Q

What is Senescence?

A

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

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38
Q

Describe the nutrients and stuff that gets exchanged in fetal circulation

A

Nutrient, gas, and waste exchange occurs at the placenta.

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

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39
Q

What is fetal hemoglobin (HbF)?

A

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

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40
Q

Function of placenta barrier and placenta:

A

The placental barrier also serves as immune protection against many
pathogens, and antibodies are transferred from the pregnant individual to child.

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

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41
Q

What are the umbilical arteries?
The umbilical viens?

A

The umbilical arteries carry deoxygenated blood from the fetus to the placenta;

the umbilical vein carries oxygenated blood from the
placenta back to the fetus.

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42
Q

What makes the fetal circulatory system different?

A

The fetal circulatory system differs from its adult version by having
three shunts:
1. Foramen ovale
2. ductus arteriosus
3. ductus venosus

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43
Q

What is the forman ovale?

A

The foramen ovale connects the right atrium to the left atrium, bypassing the lungs

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44
Q

What is the ductus arteriosus?

A

The ductus arteriosus connects the pulmonary artery to the aorta,
bypassing the lungs

45
Q

What is the ductus venosus?

A

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

46
Q

What happens in 1st trimester?

A

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

47
Q

What happens in second trimester?

A

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

48
Q

Wat happens in the 3rd trimester?

A

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

48
Q

What happens during birth?

A

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.

49
Q

What is the difference between determinate and indeterminate cleavage?

A

Determinate cleavage refers to cell division that results in cells having definitive lineages; that is, at least one daughter cell is programmed to
differentiate into a particular cell type.

Indeterminate cleavage refers to cell division that results in cells that can differentiate into any cell type (or a whole organism).

50
Q

From zygote to gastrula, what are the various stages of development?

A

Zygote → 2-, 4-, 8-, and 16-cell embryo → morula → blastula (blastocyst)
→ gastrula

51
Q

During which stage of development does implantation occur?

A

Implantation occurs during the blastula (blastocyst) stage.

52
Q

Germ Layers and organs formed:

A

Ectoderm:
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:
Musculoskeletal system, circulatory system, excretory system,
gonads, muscular and connective tissue layers of the digestive and
respiratory systems, adrenal cortex

Endoderm:
Epithelial linings of digestive and respiratory tracts, and parts of the liver, pancreas, thyroid, bladder, and distal urinary and reproductive
tracts

53
Q

What is induction and how does it influence development?

A

Induction is the process by which nearby cells influence the differentiation of adjacent cells. This ensures proper spatial location
and orientation of cells that share a function or have complementary
functions.

54
Q

What tissues do neural crest cells develop into?

A

Neural crest cells become the peripheral nervous system (including the
sensory ganglia, autonomic ganglia, adrenal medulla, and Schwann
cells) as well as specific cell types in other tissues (such as calcitoninproducing cells of the thyroid, melanocytes in the skin, and others).

55
Q

What is the difference between determination and differentiation?

A

Determination is the commitment of a cell to a particular lineage.
Differentiation refers to the actual changes that occur in order for the
cell to assume the structure and function of the determined cell type.

56
Q

Type of
Potency
And Description of
Cell linage

A

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

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

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

57
Q

What are the four types of cell–cell communication?

A
  1. Autocrine (the signal acts on the same cell that secreted it)
  2. Paracrine (the signal acts on local cells),
  3. Juxtacrine (a cell triggers adjacent cells
    through direct receptor stimulation),
  4. endocrine (the signal travels via the bloodstream to act on cells at distant sites)
58
Q

What is the difference between apoptosis and necrosis?

A

Apoptosis is programmed cell death and results in contained blebs of
the dead cell that can be picked up and digested by other cells. Necrosis
is cell death due to injury and results in spilling of cytoplasmic
contents.

59
Q

What is the oxygenation status of the blood in the umbilical arteries? In
the umbilical vein?

A

The umbilical arteries carry deoxygenated blood.

The umbilical vein
carries oxygenated blood.

60
Q

What are the (1) three fetal shunts? (2) What vessels or heart chambers do they
connect? (3) What organ does each shunt bypass?

A
  1. Foramen ovale. 2. Right atrium to left atrium 3. Lungs
  2. Ductus arteriosus 2. Pulmonary artery to aorta 3. Lungs
  3. Ductus venosus 2. Umbilical vein to inferior vena cava 3. Liver
61
Q

What are some of the key developmental features of each trimester?

A

In the first trimester, organogenesis occurs (development of heart, eyes,
gonads, limbs, liver, brain). In the second trimester, tremendous
growth occurs, movement begins, the face becomes distinctly human,
and the digits elongate. In the third trimester, rapid growth and brain
development continue, and there is transfer of antibodies to the fetus.

62
Q

What occurs in each of the three phases of birth?

A

In the first phase of birth, the cervix thins out and the amniotic sac
ruptures. In the second phase, uterine contractions, coordinated by
prostaglandins and oxytocin, result in birth of the fetus. In the third
phase, the placenta and umbilical cord are expelled.

63
Q

[…] results in the formation of the neural tube, which gives rise to both the spinal cord and the brain

A

Neurulation results in the formation of the neural tube, which gives rise to both the spinal cord and the brain

64
Q

[…] is when a group of cells influence the fate of nearby cells

A

Induction is when a group of cells influence the fate of nearby cells

Mediated by inducers, which are commonly growth factors

65
Q

Identical twins are […]

A

Identical twins are monozygotic

66
Q

[…] is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a multilayered structure known as the gastrula

A

Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a multilayered structure known as the gastrula

67
Q

[…] is when a cell acquires the structures and functions of a specialized cell

A

Cell differentiation is when a cell acquires the structures and functions of a specialized cell

68
Q

Blood in the umbilical vein is [oxygenated or deoxygenated]

A

Blood in the umbilical vein is oxygenated

69
Q

[…] stem cells have the potential to develop into any cell found in the human body

A

Totipotent stem cells have the potential to develop into any cell found in the human body

70
Q

[Germ layer] develops into the nervous system, skin, hair, nails, mouth, and anus

A

Ectoderm develops into the nervous system, skin, hair, nails, mouth, and anus

“Atract-oderm”: Skin and hair are things people are attracted to

71
Q

Implantation begins with […] of the blastocyst at the uterine epithelium, generally about 2-4 days after the morula enters the uterine cavity

A

Implantation begins with apposition of the blastocyst at the uterine epithelium, generally about 2-4 days after the morula enters the uterine cavity

During apposition process, the blastocyst differentiates into an inner cell mass (embryo) and trophectoderm (placenta)

72
Q

[…] begins with puberty and is a two year long period of sexual maturation

A

Adolescence begins with puberty and is a two year long period of sexual maturation

73
Q

Fraternal twins are […]

A

Fraternal twins are dizygotic

74
Q

[…] signaling is when a cell signals another cell that is directly adjacent or attached

A

Juxtacrine signaling is when a cell signals another cell that is directly adjacent or attached

75
Q

A/an […] is a hollow sphere of cells, referred to as blastomeres that implants in the endometrial lining

A

A/an blastula is a hollow sphere of cells, referred to as blastomeres that implants in the endometrial lining

76
Q

The […] is a shunt that allows blood from the right ventricle to bypass the fetus’s non-functioning lungs

A

The Patent ductus arteriosus is a shunt that allows blood from the right ventricle to bypass the fetus’s non-functioning lungs

It connects the main pulmonary artery to the proximal descending aorta in a fetus

77
Q

[…] refers to the process by which extra neurons and synaptic connections are eliminated in order to increase the efficiency of neuronal transmissions

A

Synaptic pruning refers to the process by which extra neurons and synaptic connections are eliminated in order to increase the efficiency of neuronal transmissions

Synaptic pruning is thought to help the brain transition from childhood to adulthood

78
Q

[…] is a shunt that allows blood to bypass the fetal lungs

A

Patent Foramen Ovule is a shunt that allows blood to bypass the fetal lungs

In the wall between the left and right atria of a fetus

79
Q

[… motor] skill is the coordination of small muscles in movements; usually involving the synchronisation of hands and fingers with the eyes

A

Fine motor skill is the coordination of small muscles in movements; usually involving the synchronisation of hands and fingers with the eyes

80
Q

[…] signaling releases signals into the bloodstream, which carries them to target cells in distant parts of the body

A

Endocrine signaling releases signals into the bloodstream, which carries them to target cells in distant parts of the body

81
Q

pregnancy is divided into the following trimesters:

First trimester is from week […] to the end of week […]

Second trimester is from week […] to the end of week […]

Third trimester is from week […] to […]

A

A pregnancy is divided into the following trimesters:

First trimester is from week 1 to the end of week 12

Second trimester is from week 13 to the end of week 26

Third trimester is from week 27 to the end of the pregnancy

82
Q

A/an […] is a hole or a small passage which allows fluid to move from one part of the body to another

A

A/an shunt is a hole or a small passage which allows fluid to move from one part of the body to another

Example: Shunt vessels connect an artery directly to a vein so the blood skips the capillaries

83
Q

[…] signaling is when a cell produces a signal to induce changes in nearby cells

A

Paracrine signaling is when a cell produces a signal to induce changes in nearby cells

84
Q

[… motor] skills are large movements a baby makes with his or her arms, legs, feet, or entire body

A

Gross motor skills are large movements a baby makes with his or her arms, legs, feet, or entire body

Crawling, running, and jumping are gross motor skills

84
Q

[…] stem cells can develop into multiple specialized cell types

A

Multipotent stem cells can develop into multiple specialized cell types

Most adult stem cells are multipotent stem cells

85
Q

Fetal hemoglobin has a [greater or lesser] affinity for O2 than adult hemoglobin

A

Fetal hemoglobin has a greater affinity for O2 than adult hemoglobin

86
Q

[…] is when a cell commits to becoming a certain type of cell

A

Cell determination is when a cell commits to becoming a certain type of cell

87
Q

[…] is when the cell secretes a hormone or chemical messenger that binds to a receptor on itself

A

Autocrine signaling is when the cell secretes a hormone or chemical messenger that binds to a receptor on itself

88
Q

[…] stem cells can be any cell except those found in placental structures

A

Pluripotent stem cells can be any cell except those found in placental structures

89
Q

A/an […] is a solid ball of cells resulting from division of a fertilized ovum

A

A/an morula is a solid ball of cells resulting from division of a fertilized ovum

90
Q

Blood in the umbilical artery is [oxygenated or deoxygenated]

A

Blood in the umbilical artery is deoxygenated

91
Q

[…] is the process by which the embryo forms and develops

A

Embryogenesis is the process by which the embryo forms and develops

92
Q

[…] is the period of time between conception and birth

A

Gestation is the period of time between conception and birth

93
Q

[Germ layer] develops into the GI tract, respiratory tract, endocrine glands, bronchi, bladder, and stomach

A

Endoderm develops into the GI tract, respiratory tract, endocrine glands, bronchi, bladder, and stomach

“In-doderm”: Things that are inside

94
Q

The CNS and PNS derive from the [germ layer]

A

The CNS and PNS derive from the ectoderm

95
Q

[Germ layer] develops into muscoskeleton, circulatory system, gonads, and adrenal cortex

A

Mesoderm develops into muscoskeleton, circulatory system, gonads, and adrenal cortex

“Move-oderm”: Involved in moving things such as muscles, RBC, steroids

96
Q

Which of the following signaling molecules coordinate uterine contractions
during childbirth?
A. Oxytocin and prolactin
B. Progesterone and prostaglandins
C. Oxytocin and progesterone
D. Oxytocin and prostaglandins

A
  1. D
    Prostaglandins promote cervical dilation and the onset of contractions, and oxytocin
    promotes uterine contractions in a positive feedback loop. Oxytocin is also involved
    in milk letdown and helps the uterus to contract (shrink) following delivery. ese
    factors together lead to (D) as the right answer. By contrast, prolactin, which
    promotes milk production, is produced following childbirth, which eliminates (A),
    and progesterone maintains the pregnancy and actually inhibits uterine contractions,
    eliminating (B) and (C).
97
Q

Which of the following associations of a primary germ layer and an adult
organ is correct?
A. Endoderm—cardiac muscle
B. Endoderm—lens of the eye
C. Ectoderm—fingernails
D. Mesoderm—lining of digestive tract

A
  1. C
    To answer this question, it could be useful to review quickly the embryonic layers.
    e ectoderm gives rise to the integument (the epidermis, hair, nails, and the epithelia
    of the nose, mouth, and anal canal), the lens of the eye, and the nervous system
    (including the adrenal medulla). e endoderm gives rise to the epithelial linings of
    the digestive and respiratory tracts and parts of the liver, pancreas, thyroid, and
    bladder. Finally, the mesoderm gives rise to the musculoskeletal system, the
    circulatory system, the excretory system, the gonads, and the adrenal cortex.
    Therefore, the only correct association can be found in (C) because the fingernails are
    derived from ectoderm
98
Q

From which of the following layers does the notochord form?
A. Ectoderm
B. Mesoderm
C. Endoderm
D. Archentero

A

. B
A rod of mesodermal cells called the notochord develops along the longitudinal axis
just under the dorsal layer of ectoderm. rough inductive effects from the
notochord, the overlying ectoderm starts bending inward and forms a groove on the dorsal surface of the embryo. 
The dorsal ectoderm will eventually pinch off and
develop into the spinal cord and brain. While the neural tube forms from ectoderm,
the notochord itself is mesodermal.

99
Q

The influence of a specific group of cells on the differentiation of another
group of cells is called:
A. competence.
B. senescence.
C. determination.
D. induction.

A

D
The influence of a specific group of cells on the differentiation of another group of
cells is termed induction. For example, the eyes are formed through reciprocal
induction between the brain and the ectoderm. Competence refers to the ability of a
cell to respond to a given inducer, but not the influence of the group of organizing
cells, eliminating (A). Senescence is a term for biological aging, eliminating (B).
Determination may be the result of induction, but this term does not refer to the
general concept of the effect of one group of cells on the differentiation of another
group of cells, eliminating (C).

100
Q

Which of the following is likely to be found in the blood of a person who
is pregnant?
A. Immunoglobulins produced by the fetus
B. Fetal hemoglobin released from fetal red blood cells
C. Progesterone produced by placental cells
D. Carbon dioxide exhaled from fetal lungs

A

C
During pregnancy, the placenta produces estrogen and progesterone to maintain the
endometrium. ese hormones are necessary for proper gestation of the fetus and
should be measurable in maternal blood because they act on maternal organs. Prior
to birth, the fetus is immunologically naïve and does not yet produce
immunoglobulins, eliminating (A). It is worth noting, though, that maternal
immunoglobulins cross the placenta to enter fetal blood. Fetal hemoglobin is a large
protein and, thus, cannot easily cross the placenta. Further, red blood cells are much
too large to cross the barrier themselves, eliminating (B). Carbon dioxide from fetal
metabolism can be found in maternal blood, but the fetal lungs are nonfunctional
prior to birth as the fetus is suspended in amniotic fluid. Carbon dioxide is
transferred across the placenta directly from the fetal bloodstream, eliminating (D).

101
Q

A cell releases a substance that diffuses through the environment, resulting
in differentiation of a nearby cell. This is an example of what type of cell–cell
communication?
A. Autocrine
B. Juxtacrine
C. Paracrine
D. Endocrine

A

C
e question stem states that a cell releases a substance that diffuses through the
environment and causes differentiation of a nearby cell. Because the cell is acting on a
nearby cell and the molecule spreads by diffusion, this is an example of paracrine
signaling. Autocrine signaling, (A), occurs when a molecule secreted by a cell acts on
the same cell. Juxtacrine signaling, (B), occurs between adjacent cells, but the signal
does not spread by diffusion. In endocrine signaling, (D), a molecule is secreted that
travels via the bloodstream to a distant target.

102
Q

A cancer cell is removed from a patient and cultured. The cells in this culture
seem to be able to divide indefinitely with no cellular senescence. Which
protein is likely activated in these cells that accounts for this characteristic?
A. Epidermal growth factor
B. Sonic hedgehog
C. Transforming growth factor beta
D. Telomerase

A

D
Cells that are able to divide indefinitely with no senescence are not exhibiting normal
cell behavior. Normally, somatic cells divide a limited number of times until the
telomeres become too short to be effective protectors of genomic material. When this
occurs, the cells stop dividing. However, in this case, the cells have continued to
divide indefinitely. It is likely that the enzyme telomerase has been activated, which
allows for synthesis of telomeres to counteract shortening during DNA replication.

103
Q

Anencephaly is a rare physiological abnormality in which the cerebrum fails
to develop. During which trimester of pregnancy would this disorder
manifest?
A. First trimester
B. Second trimester
C. Third trimester
D. Any trimester

A

A
Organogenesis primarily occurs during the first trimester of pregnancy; aer 8 weeks
of gestation, the brain is fairly developed and most of the organs have formed. e
severity of anencephaly suggests a defect very early in fetal development, leading to
(A) as the correct answer. e second and third trimesters are marked by significant
growth and further development. Defects in these stages may cause structural
abnormalities, but the absence of an organ is unlikely

104
Q

Which of the following is FALSE with regard to adult stem cells?
A. They retain inherent pluripotency if harvested from selected organs.
B. They are less controversial than embryonic stem cells.
C. They require treatment with various transcription factors.
D. There is a reduced risk of rejection if the patient’s own stem cells are used.

A

A
Embryonic stem cells are controversial because they require termination of an
embryo to harvest, eliminating (B). Adult stem cells are significantly less
controversial, but require treatment with various transcription factors in order to
increase the level of potency, eliminating (C). Rejection is a concern when foreign
cells are introduced into an individual; using one’s own stem cells should remove this
risk, eliminating (D). Adult stem cells are not naturally pluripotent, unless
pluripotency has been induced by strategic use of transcription factors. erefore, (A)
is the correct answer.

105
Q

A child is born with an imperforate anus, in which the anal canal fails to form
correctly and the rectum is not connected to the outside world. This
pathology is most likely accounted for by a failure of:
A. cell differentiation.
B. cell determination.
C. apoptosis.
D. neurulation

A

C
During development, programmed cell death occurs in multiple locations in order to ensure development of the correct adult structures. One of the places in which this occurs is between fingers and toes; another is the digestive tract, where a central lumen is formed. If apoptosis does not occur correctly in the digestive tract, an
imperforate anus could result. Failure of determination or differentiation would likely
result in the absence of anorectal structures altogether, eliminating (A) and (B).

Failure of neurulation would lead to the absence of a nervous system and would not be compatible with life, eliminating (D).

106
Q

Following a myocardial infarction, the heart often heals by the creation of a
scar by fibroblasts. This is an example of:
A. complete regeneration.
B. incomplete regeneration.
C. competency.
D. multipotency.

A

B
Aer an injury, healing occurs by some sort of regenerative process. In humans, some
tissues, such as the liver, are capable of regenerating tissue with much the same
function and structure as the original tissue. However, the heart is not capable of this
sort of regeneration, oen forming a fibrous scar in an area of injury. is is an
example of incomplete regeneration, in which newly formed tissues are not identical
in structure or function to the tissues that have been injured or lost.

107
Q

Neurofibromatosis type I, or von Recklinghausen’s disease, is a disorder that
causes formation of tumors in multiple nervous system structures as well as
the skin. While all cells carry the same mutation on chromosome 17,
selective transcription of the genome appears to cause the most significant
tumorigenesis in which of the following primary germ tissue layers?
A. Ectoderm
B. Mesoderm
C. Endoderm
D. Notochord

A

A
Here, the mutation affects the skin and the nervous system, both of which are derived
from ectoderm. e other germ tissue layers do not lead to skin or nervous system
formation, eliminating (B) and (C). e notochord is not actually a primary germ
tissue layer, and thus cannot be an answer to the question, eliminating (D).

108
Q

Which of the following shows the correct order of early developmental
milestones during embryogenesis?
A. Blastula → gastrula → morula
B. Morula → gastrula → blastula
C. Morula → blastula → gastrula
D. Gastrula → blastula → morula

A

C
Aer the first cell divisions occur, the embryo consists of a solid ball of cells known as
a morula. en a hollow center forms, creating the blastula. Finally, as the cells begin
to differentiate into the three germ layers, the embryo is considered a gastrula. (C) is
therefore the correct answer.

109
Q

A woman who is pregnant is accidentally given a single dose of a teratogenic
drug late in the third trimester. The baby is born three days later. Which of the
following is the most likely outcome?

A. Complete failure of organ development and death of the fetus
B. Partial failure of organ development with survival of the fetus
C. Serious disfigurement of the fetus
D. Respiratory distress at birth, but no long-term effects

A

D
e question stem states that the woman was given the drug three days before the
baby was born. It is important to remember that organogenesis occurs during the first
trimester. e last structure to become fully functional is the lungs. Because the
organs were already largely formed prior to the administration of the teratogenic
drug, it is likely that there was no major effect on the development of most organs as a
result of exposure to the teratogen, eliminating (A), (B), and (C). However, because
lung tissues are so sensitive and because they mature so late, it is likely that the infant
may have some respiratory distress at birth.

110
Q

Which of the following statements regarding fetal circulation is FALSE?
A. In the umbilical cord, there are more arteries than veins.
B. The foramen ovale is the only shunt that connects two chambers of the
heart.
C. Blood flow in the ductus arteriosus is from the aorta to the pulmonary
artery.
D. The ductus venosus is the only shunt that bypasses the liver

A

C
Blood flow in the ductus arteriosus is from the pulmonary artery to the aorta. e
direction of flow is determined by the pressure differential between the right side of
the heart (and pulmonary circulation) and the le side of the heart (and systemic
circulation). Unlike in adults, the right side of the heart is at a higher pressure during
prenatal life than the le side, so blood will shunt from the pulmonary circulation to
the systemic circulation through both the foramen ovale and ductus arteriosus.

Ali MCAT Biology (5 decks)

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