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MCAT Biology > Embryogenesis And Development > Flashcards

Embryogenesis And Development Flashcards

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1
Q

On which day of the menstrual cycle is the secondary oocyte ovulated from the follicle

A

Day 14

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2
Q

Explain the process of the travel of the oocyte during ovulation

A

The secondary oocyte travels into the fallopian tube where it can be fertilized up to 24 hours after ovulation. Fertilization usually occurs in the widest part of the fallopian tube called the ampulla.

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3
Q

Explain what happens during fertilization and the formation of the zygote

A

The sperm meets the secondary oocyte in the fallopian tube and penetrates the corona radiata in the zona pellucida. After the acrosomal apparatus penetrates the cell membrane. The pro nucleus may freely enter the oocyte once meiosis two has come to completion. After penetration the cortical reaction, a release of calcium ions, occurs. These calcium ions depolarize the membrane of the ovum which prevents fertilization of the ovum by multiple sperm cells, and the increased calcium concentration increases the metabolic rate of the newly formed diploid zygote. The now depolarized and impenetrable membrane is called the fertilization membrane.

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4
Q

Explain how a pair of fraternal twins come about

A

Dizygotic twins form from fertilization of two different eggs release during one ovulatory cycle by two different sperm

Each zygote will implant in the uterine wall, and each develops its own placenta, chorion, and amnion

If the zygote implant close together the placentas might grow onto each other

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5
Q

Explain how a pair of identical twins come about

A

Monozygotic twins form, when a single zygote splits into two

The genomes of the offspring are identical

If division is in complete, the twins are conjoined

Twins can either be monochorionic and monoamniotic, or monochorionic and diamniotic

As more gestational structures are shared there are more risks for the fetuses

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6
Q

Where must the zygote go after fertilization in the fallopian tubes?

A

The zygote must travel to the uterus for implantation

If it arrives too late, there will no longer be an endometrium capable of supporting the embryo

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7
Q

Define cleavage

A

As the zygote moves toward the uterus, experiences rapid mitotic cell division to eliminate the zygotes defining characteristic: unicellularity

The total size of the embryo remains unchanged during the first few divisions

This is done to increase the ratios of nuclear to cytoplasm and surface area to volume

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8
Q

Define indeterminate cleavage

A

Indeterminate cleavage results in cells that can still develop into complete organisms

Monozygotic twins have identical genomes, because they both originate from indeterminately cleaved cells of the same embryo

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9
Q

Define determinate cleavage

A

Determinate cleavage resulting cells with fates that are already determined

These cells are committed to differentiating into a certain type of cell

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10
Q

By the time the embryo reaches the uterus and has undergone several divisions what does it become?

A

Morula

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11
Q

After several mitotic divisions, and the formation of the morula, what does the embryo undergo?

A

Blastulation

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12
Q

Explain the process of blastulation and blastula formation

A

A blastocyst with a fluid filled cavity known as a blastocoel consists of the trophoblast and the inner cell mass

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13
Q

Explain the trophoblast

A

Surround the blastocoel and give rise to the chorion and later the placenta

Act as an interface between the maternal blood supply and the embryo as they may not be the same blood type

Form chorionic villi that penetrate the endometrium to support maternal-fetal gas exchange

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14
Q

Explain the inner cell mass

A

Protrudes into the blastocoel and gives rise to the organism itself

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15
Q

Once the blastula is formed where does it travel to?

A

It buries itself into the endometrium

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16
Q

What connects the embryo to the placenta

A

The umbilical cord which consists of two arteries and a vein encased in gelatinous substance

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17
Q

What supports the embryo until the placenta is fully developed

A

Yolk sac

Site of early blood cell development

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18
Q

What is the function of the allantois

A

Involved in early fluid exchange between the embryo and the yolk sac

Ultimately the umbilical cord is the remnant of the allantois and the yolk sac

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19
Q

What surrounds the allantois

A

The amnion

Thin tough membrane filled with amniotic fluid

Serves as a shock absorber during pregnancy

Chorion forms an outer membrane surrounding the amnion

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20
Q

Once the cell mass implants into the endometrium what process follows

A

Gastrulation

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21
Q

Explain the beginning of gastrulation

A

Cells of the blastula move toward the archenteron, invagination, resulting in the elimination of the blastocoel

The archenteron later becomes the gut and it’s blastopore becomes the anus in deuterosomes whereas in protosomes it becomes the mouth

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22
Q

List and describe the three primary germ layers

A

ectoderm: gives rise to the integument (epidermis, hair nails, and the epithelia of the nose, mouth and lower anal canal) the lens of the eye, nervous system (including the adrenal medulla), and inner ear

mesoderm: gives rise to the musculoskeletal, circulatory and most of the excretory systems, gonads, as well as the muscular and connective tissue layers of the digestive and respiratory systems and the adrenal cortex

endoderm: forms the epithelial lining of the digestive and respiratory tracts, including lungs, pancreas, thyroid, bladder, and distal urinary tracts as well as parts of the liver

23
Q

What is the basis of differentiation?

A

Selective transcription of the genome

24
Q

Explain induction

A

Induction is often related to the concept of selective transcription, which is the ability of one group of cells to influence the fate of nearby cells

This process is mediated by chemical substances, called inducers, which diffuse from the organizing cells to the response of cells. These chemicals are responsible for processes, such as the guidance of neuronal axons.

Induction also ensures the proximity of different cell types that work together with an organ

25
Q

Explain neurulation

A

This is the process of the development of the nervous system by the ectoderm

The notochord forms along the long axis of the organism like a primitive spine

Some of it remains in the intervertebral discs later on

The notochord induces a group of overlying ectodermal cells to slide inwards, to form neural folds, which surround a neural groove

These neural folds grow toward one another until they fuse into a neural tube which gives rise to the central nervous system

The neural crest cells migrate outward to form the peripheral nervous system

Ectodermal cells will migrate over the neural tube and crest to cover the rudimentary nervous system

26
Q

teratogens

A

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

ex: alcohol, prescription drugs, viruses, bacteria, and environmental chem polycyclic aromatic hydrocarbons

27
Q

effects of diabetes and hyperglycemia on fetus

A

overexposure to sugar in utero can lead to too large of a fetus and that could be hypoglycemic soon after birth due to XS insulin synthesis to compensate

28
Q

maternal folic acid deficiency

A
  • prevent complete closure of neural tube, spina bifida

spina bifida: parts of NS exposed to the outside world or covered in a thin membrane

  • or anencephaly

anencephaly: brain fails to develop

29
Q

specification

A
  • initial stage of cell specialization
  • cell is reversible designated to specific type
30
Q

determination

A
  • second step of cell specialization
  • commitment of cell to particular function in future/lineage
  • prior to this cell can become any cell type, regardless of specification
  • multiple pathways
  • during cleavage, where existing mRNA and protein in the parent cell has been asymmetrically distributed between daughter cells the presence of specific mRNA and protein molecules may result in determination
  • determination may also occur due to secretion of morphogens from nearby cells
31
Q

morphogens

A

secreted by cells; may cause neighboring cells to follow a particular developmental pathway during determination

32
Q

differentiation

A
  • third step of cell specialization
  • stem cells
33
Q

stem cells

A

cells that have not yet differentiated or that give rise to other cells that will differentiate

34
Q

potency

A

determines the tissues a particular stem cell can differentiate into

35
Q

totipotent

A
  • greatest potency of all stem cell types
  • include embryonic stem cells
  • can differentiate into any cell type either in the fetus or placental structures
36
Q

pluripotent

A
  • after 16-cell stage, cells of morula begin to differentiate into two groups: inner cell mass and trophoblast
  • after several cycles of cell division totipotent cells start to differentiate into the three germ cell layers
  • these cells can differentiate into any cell type except for those found in placental structures
37
Q

multipotent

A
  • cells continue to become more specialized after germ layer stage
  • can differentiate into multiple cells from a particular category
  • ex: hematopoietic stem cells
38
Q

true or false: potency is on a spectrum

A

true

39
Q

what is a significant issues in pluripotent stem cell implantation?

A

may not necessarily differentiate into the desired tissue and may even become cancerous

40
Q

briefly describe the research done around stem cell harvesting in adults

A
  • adult stem cells multipotent at best
  • researchers may use various transcription factors to inc potency
  • offers reduced risk of rejection when own stem cells utilized
  • challenging to induce specific differentiation
  • limited success
41
Q

cell-cell communication outline

A
  • surrounding inducers secrete signals for competent developing responders to become a particular cell type
42
Q

autocrine

A

signals act in same cell doing the secretions

43
Q

paracrine

A

signal acts on cells in the local area

44
Q

juxtacrine

A

do not involved diffusion but involve a cell directly stimulating receptors of an adjacent cell

45
Q

endocrine

A

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

46
Q

inducer

A

often a growth factor, which are peptides that code for specific tissue differentiation

reciprocal development, chain events of development like in the eye

47
Q

apoptosis

A

programmed cell death

48
Q

apoptosis process

A

cell undergoes changes in morphology and divides into many self contained protrusions called apoptotic blebs which can then be broken down into apoptotic bodies and digested by other cells

49
Q

necrosis

A

cells death as a result of injury

50
Q

complete regeneration

A

ability of organisms to regrow body parts

some species retain excessive clusters of stem cells within their bodies which can travel and initiate regrowth

51
Q

incomplete regeneration

A

newly formed tissue is not identical in structure or function to the tissue that has been injured or lost

humans

liver can extensively regenerate

kidneys moderate

heart little to none

52
Q

senescence

A

biological aging are cellular and organismal changes that accumulate

after 50 divisions in vitro, failure of cells to divide

shortened telomeres, loss of cap means loss of genetic info and DNA unraveling

telomeres shorten during each round of DNA synthesis

53
Q

telomerase

A

enzyme that is a reverse transcriptase that is able to synthesize the ends of chromosomes preventing senescence

54
Q

oocyte stage and when

A

birth to menarche PI
ovulation MII

MCAT Biology (13 decks)

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