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biology > Chapter 3: Embryogenesis and Development > Flashcards

Chapter 3: Embryogenesis and Development Flashcards

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AP® Biology flashcards
1
Q

Define fertilization.

A

the formation of a diploid zygote from the joining of a sperm and an ovum (egg)

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2
Q

Where does fertilization usually occur?

A

in the ampulla (the widest part of the fallopian tube)

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3
Q

What is the acrosomal apparatus?

A

the tubelike structure formed once the sperm comes into direct contact with the secondary oocyte’s cell membrane

this structure extends to and penetrates the cell membrane

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4
Q

What is the cortical reaction, when does it occur, and what are its purposes?

A

The cortical reaction is the release of calcium ions following sperm penetration through the cell membrane.

Purpose: the calcium ions depolarize the ovum membrane to:

  • prevent fertilization of the ovum by multiple sperm cells
  • increase the metabolic rate of the newly formed diploid zygote
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5
Q

What is the fertilization membrane?

A

the depolarized and impenetrable membrane produced following the cortical reaction

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6
Q

Provide an overview of the process of fertilization. (6 steps)

A
  • a secondary oocyte is ovulated and travels into the fallopian tube
  • a sperm binds to the secondary oocyte in the ampulla
  • the bound sperm releases acrosomal enzymes which allow the sperm to penetrate the corona radiata and zona pellucida of the oocyte
  • the sperm forms the acrosomal apparatus to penetrate the oocyte’s cell membrane
  • the sperm’s pronuclear then enters the oocytes once meiosis II completes
  • the cortical reaction occurs, releasing calcium ions to depolarize the ovum membrane
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7
Q

What are the 2 mechanisms by which twins can occur?

A

dizygotic / fraternal twins

monozygotic / identical twins

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8
Q

Explain the formation of dizygotic / fraternal twins.

A

form from fertilization of 2 different eggs released during one ovulatory cycle by 2 different sperm

each zygote develops its own placenta, chorion, and amnion

have the same genetic diversity as regular siblings

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9
Q

Explain the formation of monozygotic / identical twins.

A

form when a single zygote splits into two

the genetic material is identical between the 2 offspring

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10
Q

What are conjoined twins and how do they result?

A

conjoined twins: two offspring which are physically attached at some point

result if the division of the zygote is not complete

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11
Q

Monozygotic twins can be classified by the number of structures they share. What structures do monochorionic/monoamniotic twins share?

A

they share the same amnion and chorion

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12
Q

Monozygotic twins can be classified by the number of structures they share. What structures do monochorionic/diamniotic twins share?

A

they share the same chorion, but each have their own amnion

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13
Q

Monozygotic twins can be classified by the number of structures they share. What structures do dichorionic/diamniotic twins share?

A

they each have their own amnion and chorion

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14
Q

What is the endometrium?

A

the lining of the uterus

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15
Q

What is the process of cleavage?

A

cleavage is the process by which the zygote rapidly undergoes mitotic cell divisions as it travels from the fallopian tube to the uterus for implantation

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16
Q

When is the embryo officially created?

A

following the first cleavage (mitotic cell division of the zygote)

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17
Q

The zygote remains the same size during the first few mitotic divisions. Which two ratios does this affect?

A

As the zygote divides into progressively smaller cells, the nuclear : cytoplasm ratio and surface area : volume ratio increase

provides increased surface area for gas and nutrient exchange relative to overall volume

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18
Q

State and describe the two types of cleavage.

A

indeterminate cleavage: results in cells that can become any cell in the organism
- monozygotic twins result from indeterminately cleaved cells of the same embryo

determinate cleavage: results in cells that are committed to differentiating into a certain cell type

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19
Q

What is the morula?

A

a solid mass of cells seen in early development

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20
Q

Define blastulation.

A

the stage in early embryonic development the produces the blastula

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21
Q

What happens to the morula following its formation?

A

the morula undergoes blastulation to form the blastula

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22
Q

What is the blastula?

A

a hollow ball of cells with a fluid-filled inner cavity (blastocoel)

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23
Q

What is the blastocoel?

A

the fluid filled inner cavity of the blastula

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24
Q

What is the mammalian blastula named and which 2 cell groups does it consist of?

A

blastocysts

trophoblast cells

  • surround the blastocoel
  • gives rise to the chorion and the placenta

inner cell mass

  • protrudes into the blastocoel
  • gives rise to the organism itself
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25
Q

Describe the process of implantation.

A
  • the blastula moves through the fallopian tube to the uterus and burrows into the endometrium
  • the trophoblast cells give rise to the chorion which contains chorionic villi
  • the chorionic villi penetrate the endometrium and create an interface between the maternal blood supply and the embryo

possibly fix this flashcard

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26
Q

What is the chorion?

A

an extra embryonic membrane that develops into the placenta

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27
Q

What does the yolk sac do?

A

supports the embryo prior to placenta establishment

the site of early blood cell development

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28
Q

What is the allantois?

A

an extra embryonic membrane involved in early fluid exchange between the embryo and the yolk sac

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29
Q

What is the amnion? (2)

A

surrounds the allantois; lies just inside the chorion

a thin, tough membrane which produces amniotic fluid

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30
Q

What is the function of the umbilical cord?

A

connects the embryo to the placenta

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31
Q

Define grastulation.

A

the process by which a grastula forms from a blastula with 3 distinct cell layers

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32
Q

How does gratulation begin?

A

with a small invagination of the blastula, eventually eliminating the blastocoel

once the membranes merge, a tube forms within

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33
Q

What is the archenteron and what does it develop into?

A

the membrane invagination

develops into the gut

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34
Q

What is the blastopore and what does it develop into (in humans)?

A

the opening of the archenteron

develops into the anus

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35
Q

What are the 3 primary germ layers?

A

the ectoderm

the mesoderm

the endoderm

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36
Q

Describe the ectoderm.

A

the outermost primary germ layer

gives rise to:

  • the integument (epidermis, hair, nails, epithelia of the nose, mouth, and lower anal canal)
  • the lens of the eye, the nervous system, the inner ear
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37
Q

Describe the mesoderm.

A

the middle primary germ layer

develops into:

  • the musculoskeletal, circulatory, and most excretory systems
  • the gonads
  • the muscular and connective tissue layers of the digestive and respiratory systems
  • the adrenal cortex
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38
Q

Describe the endoderm.

A

the innermost primary germ layer

develops into:

  • the epithelial findings of the digestive and respiratory tracts
  • the pancreas, thyroid, bladder, distal urinary tracts, and parts of the liver
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39
Q

What is selective transcription?

A

the process by which only the genes needed for a particular cell type are transcribed

40
Q

What is induction, what does it ensure, and how is it mediated?

A

the process by which one group of cells influence the differentiation of nearby cells

ensures proper spatial location and orientation of cells that share function or have complementary functions

mediated by inducers

41
Q

What are inducers?

A

chemical substances which mediate the process of induction

they diffuse from the organizing cells to the responsive cells

42
Q

What is neurulation and when does it occur?

A

the development of the nervous system

begins after the formation of the 3 germ layers

43
Q

Which primary germ layer does the nervous system arise from?

A

the ectoderm

44
Q

Describe the processor neurulation. (4 steps)

A
  • the notochord (a rod of mesodermal cells) induces a group of overlying ectodermal cells to slide inward to form neural folds which surround a neural groove
  • the neural tube is formed when the neural folds fuse together
  • the neural tube develops into the central nervous system
  • the neural crest cells develop into the peripheral nervous system
45
Q

Neural crest cells

A

exist at the tup of each neural fold

they migrate outward to form the peripheral nervous system and cells in some other tissues

46
Q

Ectodermal cells

A

migrate over the neural tube and crests to over the rudimentary nervous system

47
Q

What is organogenesis?

A

the production of organs

48
Q

What are teratogens?

A

substances that interfere with development and cause defects or even death of the developing embryo

49
Q

What influences the effect of teratogens?

A
  • genetics of individuals
  • route of exposure
  • length of exposure
  • rate of placental transmission of the teratogen
  • exact identity of teratogen
50
Q

What are common teratogens?

A
  • alcohol
  • prescription drugs
  • viruses
  • bacteria
  • environmental chemicals
51
Q

What are the 4 levels of human organization?

A

cells

tissues

organs

organ systems

52
Q

What are the 3 stages of cell specialization?

A

specification

determination

differentiation

53
Q

What is specification?

A

the initial stage of cell specialization where the cell is reversibly designated to a specific cell type

54
Q

What is determination?

A

the second stage of cell specialization

the cell irreversibly commits to a particular cell type

55
Q

Describe 2 pathways by which determination can occur.

A
  • if specific mRNAs and proteins in the parent cell are asymmetrically distributed between daughter cells during cleavage
  • due to secretion of specific molecules (morphogens) from nearby cells
56
Q

What are morphogens?

A

molecules secreted by cells and cause other nearby cells to follow a particular developmental pathway

57
Q

What is differentiation?

A

the final stage of cell specialization

the changes a cell undergoes due to selective transcription to take on characteristics appropriate to its determined cell type

includes changing the structure, function, and biochemistry of the cell

58
Q

What are stem cells? (3)

A
  • cells that are capable of developing into various cell types
  • have not yet differentiated
  • a stem cells potency determines the tissue a particular stem cell can differentiate into
59
Q

Totipotent cells

A

can differentiate into all cell types, including the 3 germ layers and placental structures

greatest potency

60
Q

Pluripotent cells

A

can differentiate into any cell type except for the placental structures (all 3 the germ layers and their derivatives)

61
Q

Multipotent cells

A

can differentiate only into a specific subset of cell types

ex. hematopoietic stem cells which can differentiate into any cell found within the blood (WBC, RBC, platelets, etc.)

62
Q

Autocrine signals

A

act on the same cell that secreted the signal

63
Q

Paracrine signals

A

act on cells in the local area

64
Q

Juxtacrine signals

A

signals act through direct stimulation of receptors on the adjacent cell

do not usually involve diffusion

65
Q

Endocrine signals

A

involve secreted hormones that travel through the bloodstream to a distant target tissue

66
Q

Inducers are often ________.

A

growth factors

67
Q

What are growth factors?

A

peptides that promote differentiation and mitosis in certain tissues

most growth factors only function on specific cell types or in certain areas, as determined by the competence of these cells

they can code for particular tissues

68
Q

What is reciprocal development?

A

two tissues which both induce further differentiation in one another

69
Q

What are 3 key components of development?

A

cell migration: cells might need to migrate to arrive at their correct location

cell death

regeneration

70
Q

What is apoptosis?

A

programmed cell death

may occur via apoptotic signals or preprogramming

71
Q

Describe apoptosis.

A

the cell divides into many self-contained protrusions (apoptotic blebs)

the apoptotic blebs are then broken into apoptotic bodies

the apoptotic bodies are digested by others cells

72
Q

What are 2 purposes of apoptosis?

A

allows for recycling of materials

prevents the release of potentially harmful substances into the extracellular environment (ex. enzymes)

73
Q

What is necrosis?

A

a process of cell death in which a cell dies as a result of injury

internal substances are leaked

causes irritation of nearby tissues or possibly an immune response

74
Q

What is regenerative capacity?

A

the ability of an organism to regrow certain parts of the body

75
Q

Complete vs incomplete regeneration

A

complete regeneration: the lost/damaged tissues are replaced with identical tissues

incomplete regeneration: the lost/damaged tissues are replaced with tissues which are not identical in structure or function to the original tissue

76
Q

Regenerative capacity in humans varies by tissue type. Provide a tissue examples with high, low, and moderate regeneration capacities.

A

high regeneration capacity = liver

low regeneration capacity = heart

moderate regeneration capacity = kidneys

77
Q

What is senescence?

A

biological aging

occurs as changes in molecular and cellular structures accumulate at both the cellular and organismal level

78
Q

How does senescence result at the cellular level, and what might cause this?

A

senescence results in the failure of cells to divide

may be due to the shortening of telomeres

79
Q

What is a key function of telomeres?

A

reduce the loss of genetic information from the ends of chromosomes

prevent DNA from unravelling

they shorten during each round of DNA synthesis

once they become too short, the cell can no longer replicate

80
Q

What is telomerase?

A

a reverse transcriptase (enzyme) expressed in some cells (germ cells, fetal cells, tumor cells) which can synthesize the ends of chromosomes, preventing senescence

allows cells to divide indefinitely and plays a role in the survival of cancer cells

81
Q

What processes occur at the placenta?

A

nutrient, gas, and waste exchange occurs via diffusion

82
Q

Explain the difference in partial pressure in maternal vs fetal blood and its importance.

A

maternal blood has a higher partial pressure than fetal blood, allowing oxygen to diffuse down their concentration gradient

note: it is crucial that maternal and fetal blood do not mix as they may have different blood types

83
Q

Explain how oxygen are transferred from maternal blood to fetal blood.

A
  • note: there is no actual mixing of maternal an dfetal blood (crucial as they may have different blood types)
  • the placenta allows close proximity of maternal and fetal blood, allowing diffusion between the two
    • maternal blood has a higher partial pressure than fetal blood, so oxygen diffuses into the fetal blood
    • fetal blood cells contains fetal hemoglobin (HbF) which has a higher affinity for oxygen than maternal hemoglobin
84
Q

Explain how the placental barrier serves as an immune protection.

A

antibodies cross the placental membrane to protect the fetus which has not been exposed to pathogens

85
Q

Explain the blood flow oxygen state and direction of the umbilical arteries and vein.

A

the umbilical arteries carry deoxygenated blood away from the fetus (think away from the heart in adults)

the umbilical vein carries oxygenated blood toward the fetus (think towards the heart in adults)

note: the oxygenation state of umbilical arteries and veins are opposite that of most

86
Q

Where does gas exchange occur for the growing fetus?

A

at the placenta (until birth the lungs do not exchange gas)

87
Q

What are 2 organs not significantly utilized by the fetus prior to birth and how are their functions performed instead?

A

the fetus does not depend on its lungs and liver prior to birth

gas exchange (lung function) occurs at the placenta

detoxification and metabolism (liver function) are controlled by the mothers liver

nutrient and waste exchange (liver function) occur at the placenta

88
Q

What purpose do the fetal shunts serve?

A

they actively direct blood away from the fetal lungs and liver while they develop

89
Q

What are the 3 fetal shunts and which structures do they connect and bypass?

A

the foramen 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

90
Q

What is gestation?

A

the period of time between conception and birth (pregnancy)

91
Q

What are some key developmental events during the first trimester?

A

organogenesis occurs (organ development)

  • the heart, eyes, gonads, limbs, liver, and brain form
  • cartilage begins to harden into bone
92
Q

What are some key developmental events during the second trimester?

A
  • tremendous growth occurs
  • movement begins
  • the face becomes distinctly human
  • the digits elongate
93
Q

What are some key developmental events during the third trimester?

A
  • rapid growth
  • further brain development
  • high amounts of antibodies are transferred to the fetus
94
Q

What is parturition?

A

vaginal childbirth

95
Q

What contributes to the rhythmic contraction of the uterine smooth muscle?

A

coordinated by prostaglandins and oxytocin (a peptide hormone)

96
Q

List and describe the 3 basic phases of birth.

A
  • the cervix thins out and the amniotic sac ruptures (water breaking)
  • strong uterine contractions result in the birth of the fetus
  • the placenta and umbilical cord are expelled (afterbirth)

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