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MCAT - Biology > Embryogenesis & Development > Flashcards

Embryogenesis & Development Flashcards

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1
Q

What is neurulation?

A

The formation of the neural tube

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2
Q

What will the neural tube become?

A

The nervous system

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3
Q

Up to how many time after ovulation can the oocyte be fertilized?

A

24 hours

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4
Q

Where does fertilization usually occurs?

A

In the widest part of the Fallopian tube, the ampulla

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5
Q

What is formed when the first sperm gets in contact with the oocyte

A

The sperm releases acrosomal enzymes that lets the head penetrate the corona radiate and the zona pellucida
The acrosomal apparatus, which extends to and penetrate the cell membrane

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6
Q

When the sperm pronucleus can enter the oocyte?

A

Once meiosis 2 has come to completion, after the acrosomal apparatus has been formed

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7
Q

What happens after the penetration of the sperm through the cell membrane?

A

The cortical reaction, a release of calcium ions

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8
Q

What is the process and the use of the cortical reaction?

A

The cortical reaction releases calcium ions, which depolarize the oocyte membrane. This prevents from fertilization of the ovum by multiple sperm cells AND calcium ion increase increases the metabolic rate of the newly form zygote

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9
Q

How do we call the depolarized membrane of the ovum?

A

Fertilization membrane

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10
Q

What are the 2 mechanisms of twins?

A

Dizygotic (fraternal) twins will be formed by the release of two ovum who will both be fertilized. They will both have their own placenta, chorion and amnion.
Monozygotic (identical) twins will be formed by the separation of the one zygote formed by the fertilization.

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11
Q

What happens if division is incomplete from the zygote (which would normally form 2 identical twins?

A

Conjoined twins

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12
Q

How are monozygotic twins classified as?

A

By the number of structures they share. Monochorionic/monoamniotic (share both), Monochorionic/Diamniotic (share the chorion, each have amnion) and Dichorion/Diamniotic (each have their own chorion and amnion)

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13
Q

What causes more risks as the fetuses grow and develop in monozygotic twins?

A

The most gestational structures they share

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14
Q

What is cleavage?

A

Cleavage is a process of rapid mitotic cell divisions as the zygote moves to the uterus for implantation

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15
Q

What is formed from the first official cleavage?

A

Embryo

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16
Q

What is the point of cleavage after several rounds of mitosis?

A

Increase both the ratio of nuclear to cytoplasmic (N:C) and the surface are to volume ratio

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17
Q

What does the increase of surface area to volume ratio from cleavage results in?

A

Increases area for gas and nutrients exchange

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18
Q

What are the 2 types of cleavage?

A

Determinate and indeterminate

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19
Q

What is a determinate cleavage?

A

Results in cells that their fate is already determined

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20
Q

What is indeterminate cleavage?

A

Creates cells that can still develop into complete organism

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21
Q

What type of cleavage is made to create monozygotic twins?

A

Indeterminate cleavage

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22
Q

What is a morula?

A

When the embryo becomes solid mass of cells after many divisions

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23
Q

What happens once the morula is formed?

A

Blastulation

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24
Q

What is blastulation?

A

Creates the blastula from the morula

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25
Q

What is the fluid-filled inner cavity of a blastula called?

A

Blastocoel

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26
Q

What is the blastocoel?

A

The fluid-filled inner cavity of the blastula

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27
Q

How do we call the mammalian blastula?

A

Blastocyst

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28
Q

What are the 2 cell groups that consist the blastocyst?

A

Trophoblast and inner cell mass

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29
Q

What are the functions of the 2 cells groups in a blastula?

A

The trophoblast surround the blastocoel and give rise to the chorion and eventually the placenta.
The inner cell mass protrudes into the blastocoel and give rise to the organism itself

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30
Q

What is created originally from the trophoblasts?

A

The chorion, the chorionic villi and the placenta

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31
Q

What is created from the inner cell mass?

A

The organism itself

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32
Q

What is the chorion?

A

An extramembryonic membrane that develops into the placenta

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33
Q

What is the role of the chorionic villi?

A

Penetrate the endometrium.
They will eventually develop into the placenta to support maternal-fetal gas exchange

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34
Q

How are the embryo and the placenta connected?

A

By the umbilical cord

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35
Q

What is in the umbilical cord?

A

2 arteries and 1 vein, all encased in a gelatinous substance

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36
Q

What is inside the umbilical arteries and vein?

A

Vein carries freshly oxygenated blood from the placenta to the embryo
The arteries carry deoxygenated blood and waste to the placenta for exchange

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37
Q

What is the role of the yolk sac?

A

To support the embryo until the placenta is functional
It is also the site of early blood cell development

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38
Q

What happens before the placenta is functional?

A

The embryo is supported by the yolk sac

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39
Q

What is the role of the allantois?

A

Is involve in early fluid exchange between the embryo and the yolk sac

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40
Q

What is the umbilical cord made of?

A

The remnants of the yolk sac and the allantois

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41
Q

What is the amnion?

A

Surround the allantois, is a thin layer filled with amniotic fluid.
Its role is to be a shock absorber during pregnancy

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42
Q

What is the role of the chorion in protection of the embryo?

A

Forms an outer membrane around the amnion to add more protection

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43
Q

What is the result of gastrulation?

A

Developmental processes that generates 3 distinct cell layers (ectoderm, mesoderm and endoderm)

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44
Q

What is the archenteron?

A

The membrane invagination into the blastocoel
Later develops into the gut

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45
Q

What is the blastopores?

A

The opening of the archenteron

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46
Q

What is the opening of the archenteron called?

A

Blastopores

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47
Q

What does the blastopores develop as in deuterostomes and in protostomes?

A

In deuterostomes, it develops into the anus
In protostomes, it develops into the mouth

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48
Q

What is the ectoderm? What does it gives rise to?

A

The outermost layer
Gives rise to the integument (epidermis, hair, nail, epithelia of the nose, mouth, lower ana canal).
Also give rise to :
Lens of the eyes,
Nervous system (including adrenal medulla)
Inner ear

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49
Q

What does the mesoderm develops into?

A

Several systems: Musculoskeletal, circulatory and most of the excretory systems
Gonads
Muscular and connective tissue layers of the digestive and respiratory systems
Adrenal Cortex

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50
Q

What forms the endoderm?

A

Epithelial lining of the digestive and respiratory tracts (including the lungs)
Pancreas
Thyroid
Bladder
Distal urinary tract
Parts of the liver

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51
Q

Why would we say the adrenal glands have a dual embryonic origin?

A

The adrenal cortex is derived from the mesoderm and the adrenal medulla is derived from the ectoderm

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52
Q

Why is the adrenal medulla derived from the ectoderm?

A

Because it contains some nervous tissue

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53
Q

Why does cells are able to develop into such distinctly different cell types with highly specialized functions?

A

Selective transcription of the genome

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54
Q

What is selective transcription of the genome?

A

Only the genes needed are transcribed

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55
Q

What is induction?

A

Ability of the surrounding cells to influence the fate of nearby cells
It also ensures proximity of different cell types that work together within an organ

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56
Q

How is selective transcription mediated?

A

By chemical substances called inducers that diffuse from organizing cells to the responsive cells

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57
Q

When can neurulation begin?

A

Once the three germ layers are formed (gastrulation)

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58
Q

What is neurulation?

A

The development of the nervous system

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59
Q

What is the process of neurulation?

A

A rod of mesodermal cells (notochord) form which induces a group of ectodermal cells to slide inward (creating the neural folds and the neural groove).
The neural folds will then meet and fuse to create the neural tube which gives rise to the central nervous system.
Neural crest cells forms at the tip of each neural folds. They will create the peripheral nervous system and specific cell types in other tissues.
Finally, ectodermal cells will migrate over the neural tube and crest to cover them.

60
Q

What are notochords?

A

Rod of mesodermal cells who induce the ectodermal cells to slide inward

61
Q

What is the neural groove?

A

The inward parabola (the inward bridge being created in neurulation)

62
Q

What are neural folds?

A

The 2 places where the ectoderm will fold to bring the neural groove inward in neurulation

63
Q

What are neural crest cells?

A

Cells that forms at the tip of each neural folds (neural crest cells will form the peripheral nervous system)

64
Q

What are teratogens?

A

Substance that interferes with development, causing defects or even death of the developing embryo or fetus

65
Q

What can influence the effects of teratogens?

A

The unique genetic of the embryo
The route of exposure, length of exposure, rate of placental transmission and the identity of the teratogens

66
Q

What are some common teratogens?

A

Alcohol, prescription drugs, viruses, bacteria, environmental chemicals (like polycyclic aromatic hydrocarbons)

67
Q

What are other things that can influence development other than teratogens?

A

Maternal health (ex. diabetes)

68
Q

How does diabetes affect the baby?

A

Overexposure to sugar in utero can lead to a fetus that is too large to be delivered and that suffers from hypoglycaemia soon after birth

69
Q

How does maternal folic acid deficiency may cause on the baby?

A

Failure to completely close the neural tube which would result in Spina Bifida
Anencephaly, in which the brain fails to develop

70
Q

What are the 3 stages of cell specialization?

A

Specification, determination and differentiation

71
Q

What is the specification stage?

A

The cell is reversibly designated as a specific cell type

72
Q

What is the determination stage?

A

When a cell irreversibly commits to a particular function in the future.

73
Q

At which point of the cell specialization process can a cell become any cell type?

A

Before determination (after specification)

74
Q

How can determination occur?

A

By the presence of specific mRNA and protein molecules from the parent cell.
Secretion of specific molecules from nearby cells (morphogens)

75
Q

What are morphogens?

A

Molecules that cause neighbouring cells to follow a particular development path

76
Q

What is the goal of differentiation?

A

The cell goes through changes to develop into the determined cell type
Change of the structure, function and biochemistry of the cell

77
Q

What are called cells that have not yet differentiated?

A

Stem cells

78
Q

What is potency?

A

Determine the tissue a particular stem cell can differentiate into

79
Q

What are cells with the greatest potency called?

A

Totipotent

80
Q

What are pluripotent cells?

A

Cells that can differentiate into any cell type except for those found in the placental structures

81
Q

What are multipotent cells?

A

Cells that can differentiate into a multitude of cell types within a certain group

82
Q

What type of cells (potency) are the cells that forms the 3 germ cell layers?

A

Pluripotent

83
Q

In who does stem cells exists?

A

Embryos, but also adults

84
Q

What could be the consequence of injecting stem cells from a different genetic makeup?

A

Can evoke an immune response, resulting in rejection.
Once injected, pluripotent cells may not differentiate into the desired tissue and may become cancerous

85
Q

Where can we find stem cells in an adult donor?

A

Blood, bone marrow and adipose tissue

86
Q

What could decrease the risk of rejection of stem cells?

A

Taking the stem cells from the patient, scientifically induce them to become the desired tissue type and then implant it into the same patient

87
Q

What does the term inducer refer to?

A

The cell secreting the signal to the responder in the cell-cell communication to induce development

88
Q

What does the term responder means?

A

The cell induced by the inducers

89
Q

What does it means to say a cell is competent?

A

Able to respond to the inducing signal

90
Q

What type of signals can occur in cell-cell communication?

A

Autocrine, paracrine, juxtacrine and endocrine

91
Q

What is an autocrine communication?

A

Act on the same cell that secreted the signal

92
Q

What is a paracrine communication?

A

Acts on the cell in the local area

93
Q

What is a juxtacrine communication?

A

A cell directly stimulating receptors of an adjacent cell (do not usually involve diffusion)

94
Q

What is an endocrine communication?

A

Hormones are secreted and travel through the bloodstream to a distant target tissue

95
Q

What are usually inducers?

A

Growth factors

96
Q

What are growth factors?

A

Peptides that promotes differentiation and mitosis in certain tissue

97
Q

What is a reciprocal development?

A

When the induction of a cell also results in other cells to be inducted (for example, the differentiation of the lens then triggers the optic vesicle to form the optic cup)

98
Q

Are tissues exposed to multiple inducers during their development?

A

Yes

99
Q

What is the main method of signalling in cell communication?

A

Via the use of gradients (morphogens will be diffuse throughout the body, locations closer will have higher concentration, while further locations will have less. Multiple morphogens are secreted simultaneously creating unique exposure of morphogens throughout the body)

100
Q

What are some common morphogens?

A

Transforming growth factor beta (TGF-beta), Sonic-hedgehog (Shh) and Epidermal growth factor (EGF)

101
Q

What is cell migration?

A

The capacity of a cell to disconnect from adjacent cells and migrate to their correct location

102
Q

Which type of cells usually undergo extensive migration?

A

Neural crest cells

103
Q

What is the process of apoptosis?

A

The cell undergo many changes in morphology and divides into many self-contained profusion (apoptotic blebs) which are then broken apart (into apoptotic bodies) and finally digested by other cells

104
Q

What are the advantages of apoptosis?

A

Allows recycling of material and because the blebs have membrane, it prevents the release of harmful substances into the extracellular environment

105
Q

What is the difference between necrosis and apoptosis?

A

Necrosis happens when a cell is injured and dies, resulting in the release of internal substances that can irritate nearby tissues or can create an immune response.
Apoptosis is programmed cell death in which the cell dies by itself and contains all its substances in different blebs with a membrane

106
Q

What is the name for the nucleus condensing in apoptosis?

A

Pyknosis

107
Q

What is the name for nucleus fragmenting in apoptosis?

A

Karyorrhexis

108
Q

Why does some species have a greater regenerative capacity?

A

They retain extensive clusters of stemm cells within their bodies

109
Q

What are the 2 types of generation of tissue? And what’s the difference?

A

Complete regeneration and incomplete regeneration
Complete regeneration= the new cells are identical to the cell lost
Incomplete regeneration = the new cells are not identical in structure or in function

110
Q

What type of regeneration humans usually exhibit?

A

Incomplete

111
Q

What is senescence?

A

Biological aging

112
Q

What happens to cell in senescence at the cellular level?

A

Cells cannot divide after approx 50 divisions in vitro

113
Q

Why do cell cannot divide more than 50 times?

A

Could be because of the shortening of the telomers, because they shorten at every division

114
Q

What is the role of telomers?

A

Reduce the loss of genetic information and keeps the DNA to unravel

115
Q

Why can’t the telomers knot off the end of chromosomes?

A

Because of their high concentration of guanine and cytosine

116
Q

What is telomerase?

A

An enzyme (reverse transcriptase) that is able to synthesize the ends of chromosomes preventing senescence, which allows the cells to divide indefinetely

117
Q

What cells express telomerase?

A

Germ cells, stem cells and tumour cells

118
Q

What other factors could influence in the aging other than senescence?

A

Accumulation of chemical and environmental insults over time

119
Q

What does senescence means at the organismal level?

A

Changes in the body’s ability to respond to a changing environment

120
Q

Why is it crucial for maternal and fetal blood to not mix?

A

They could be different blood types

121
Q

What is the simplest method to move nutrients and waste product from and to the fetus?

A

Diffusion

122
Q

What does diffusion requires for it to work?

A

A gradient (high partial pressure of oxygen in the maternal blood than in the fetal blood)

123
Q

What helps the transfer of oxygen from maternal to fetal circulation?

A

Fetal blood cells contains (fetal hemoglobin, HbF) that has a greater affinity for oxygen than the maternal hemoglobin

124
Q

What is the role of the placenta in immunology?

A

The crossing of antibodies across the placental membrane serve as a protective function of pathogens

125
Q

Is placenta an endocrine or exocrine organ?

A

Endocrine because it produces progesterone, estrogen and human chorionic gonadotropin (hCG)

126
Q

What type of blood is carried in the umbilical arteries and vein?

A

Arteries carry blood away from the heart (to the placenta), so it carries deoxygenated blood
Vein carries blood from the placenta to the fetal heart, so it carries oxygenated blood

127
Q

Where does gas exchange occur prior to birth?

A

At the placenta
The lungs don’t serve a significant function prior to birth

128
Q

Where does detoxification and metabolism controlled?

A

The mother’s liver

129
Q

Why are the liver and the lungs both underdeveloped at birth?

A

Because they are both not of use before birth. (gas exchange at the placenta, and detoxification and metabolism from the mother’s liver)

130
Q

What is the roles of the shunts created in the fetus?

A

Direct away blood from the organs not of use (liver and lungs)
2 are used to direct away from the lungs, 1 for the liver

131
Q

What are the shunts created by the fetus for blood circulation?

A

The foramen ovale: blood goes from the right atrium directly to the left atrium because it does need to go to the lungs for oxygenation
The ductus arteriosus: from the pulmonary artery to the aorta
The ductus venosus: blood from the umbilical vein goes directly into the inferior vena cava

132
Q

What helps the blood pass through the foramen ovale?

A

The right side of the heart is at higher pressure than the left side

133
Q

What shuts the foramen ovale?

A

The change in pressure (from the right side being higher to the left side being higher after birth)

134
Q

Does the liver receive blood supply before birth?

A

Yes, from the smaller hepatic arteries

135
Q

How many days lasts human gestation

A

280

136
Q

What happens in the first trimester?

A

Major organs begin to develop
Heart begins to beat at approx 22 days
After the eyes, gonads, limbs and liver starts to form
By week 7, the cartilaginous skeleton beings to harden into bone
By the 8th week, most organs have formed
At the end of the first semester (3 months), the fetus is about 9cm long

137
Q

When is the embryo switched to become a fetus?

A

By the end of week 8 (first trimester)

138
Q

What happens in the second trimester?

A

Tremendous amount of growth
Begins to move within the amniotic fluid
Its face takes on a human appearance
Toes and fingers elongate
By the end of the 6th month, the fetus is 30-36cm long

139
Q

What happens in the third trimester?

A

Months 7 and 8 = continued rapid growth and further brain development
Antibodies are transported from the mother to the fetus (by highly selective active transport) - highest at the 9th month
Growth rate slows and the fetus is less active

140
Q

How do we call scientifically child birth?

A

Parturition (vaginal childbirth)

141
Q

How does vaginal childbirth is accomplished?

A

By rhythmic contractions of the uterine smooth muscle

142
Q

By what are the rhythms contractions of the smooth uterine muscle coordinated?

A

Prostaglandins and oxytocin

143
Q

What are the phases of birth?

A

1- Cervix thins out and the amniotic sac ruptures (water breaking)
2- Strong uterine contractions results in the birth of the fetus
3-The placenta and the umbilical cord are expelled

144
Q

How do we call the expelling of placenta and umbilical cord?

A

Afterbirth

145
Q
A

MCAT - Biology (12 decks)

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