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Semester 2 > 1/2. Embryology > Flashcards

1/2. Embryology Flashcards

1
Q

What is embryology?

A

The study of embryos

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2
Q

What are the 3 stages of the development of a human?

A
  • Pre-embryonic phase 0-3 weeks
  • Embryonic phase 4-8 weeks
  • Foetal phase 9-40 weeks
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3
Q

What are the parent cells called that produce sperm and ova?

A
  • Spermatogonium

- Oogonium

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4
Q

What is the processes that produce sperm and ova called?

A
  • Spermatogenesis

- Oogenesis

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5
Q

What is the end product of meiosis?

A

-4 unique sperm
OR
-1 ovum and 3 polar bodies

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6
Q

What happens during fertilisation

A
  • Several sperm surround the ovum, only one penetrates.

- Pro nucleus of sperm enters and fuses with the pro nucleus of ovum to give a diploid cell called the zygote

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7
Q

What happens during week 1 of pre-embryonic phase.

A
  • Zygote is formed; divides to form a blastocyst

- Moves through uterine tube to reach uterine cavity

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8
Q

What is the zygote?

A
  • 1st cell in the body

- Diploid

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9
Q

Why are zygotes genetically unique?

A

It has 23 of the mothers and 23 of the fathers chromosomes

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10
Q

Where do the mitochondria cell organelles come from?

A

The mother

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11
Q

What happens to the zygote?

A

Cell divides by mitosis to form a solid ball of cells called the morula

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12
Q

What is an example of a mitochondrial inherited disease?

A

Lebers hereditary Optic Neuropathy which causes blindness

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13
Q

Why does a morula develop into a blastocyst?

A
  • As the number and size of cells increases, getting nutrition to the central core of cells starts to become difficult.
  • Therefore a cavity develops called the blastocystic cavity
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14
Q

What does a blastocyst look like?

A
  • Cavity- blastocystic cavity
  • Cells accumulate at one end to form an inner cell mass
  • The outer lining is called the trophoblast
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15
Q

Endometrium

A

Lining of the womb

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16
Q

What aids in the movement of the zygote to uterus?

A

Uterine tubes have ciliated epithelium to help the ovum move through the reproductive system

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17
Q

How long does the first cell division take?

A

36 hours

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18
Q

What happens to the time of cell divisions?

A

Take less time with each successive division

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19
Q

What happens around day 5/6 of the pre-embryonic stage?

A

The blastula has formed and has reached the uterine cavity ready to implant

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20
Q

When might an ectopic pregnancy occur?

A

If the cilia function is abnormal

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21
Q

What happens during week 2 of the pre-embryonic phase?

A
  • Implantation occurs in the uterine endometrial layer and placenta begins to develop
  • Cells that later form the embryo form a bilaminar disc
  • Sacs, membranes and cord to nourish the human conceptus start to form
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22
Q

What does the trophoblast ultimately form?

A

Chorion and develops finger like processes: chorionic villi

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23
Q

What does the chorion do?

A
  • Implantation process
  • Forms part of the placenta in due course
  • Secretes human Chorionic gonadotropin (HCG)
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24
Q

What does HCG do?

A

Sends signal to the ovary to keep producing oestrogen and progesterone to ensure the endometrium is not shed

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25
Q

What is used to detect pregnancy?

A

HCG

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26
Q

What happens at around 7 days?

A

The blastocyst begins to burrow into the uterin wall

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27
Q

What plays an important role in burrowing?

A

The chorion

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28
Q

Decidua basalis

A

Part of the endometrium deep to the implanted conceptus

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29
Q

What happens to maternal blood and urine levels of HCG?

A

They increase till around 12 weeks gestation

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30
Q

What happens to the inner cell mass?

A

The cells of the inner cell mass form a 2-layered flat disc called the bilaminar disc

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31
Q

What 2 cavities form?

A
  • Amniotic cavity

- Yolk sac

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32
Q

What are the main functions of the placenta?

A
  • Foetal nutrition
  • Transport of waste and gases
  • Immune
33
Q

Describe the foetal part and surface of the placenta.

A

Smooth with foetal blood vessels and end of umbilical cord

34
Q

Describe the maternal part of the placenta.

A

Decidua basalis of endometrium. Rough and has maternal blood vessels

35
Q

When does the placenta mature?

A

Matures by 18-20 weeks

36
Q

How much does the placenta weigh?

A

1/6 of the foetus

37
Q

How do fraternal/dizygotic twins occur?

A
  • 2 ova release, 2 sperms which leads to 2 separate zygotes
  • Different genetic makeups, 2 plancentae
  • Can run in families
38
Q

How do identical/monozygotic twins occur?

A
  • 1 ovum, 1 sperm, 1 zygote initially which divides into 2 and each cell develops into a different embryo
  • Same genetic make up share 1 placenta (might/might not share amniotic and chorionic sac)
39
Q

Summarise the progress of the conceptus up till the end of week 2.

A
  • Fertilisation
  • Zygote
  • Morula
  • Blastocyst with inner cell mass
  • Bilaminar disc with amniotic cavity above and yolk sac below
40
Q

Summarise where everything takes place up until week 2.

A
  • Morula reaches uterine cavity
  • Blastocyst implants
  • Outer cells form chorionic villi which help implantation
  • Decidua basalis forms
  • Placental formation begins
41
Q

What occurs during week 3 of the pre-embryonic stage?

A
  • Formation of germ layers
  • Formation of neural tube
  • Development of somites
  • Early development of CVS
42
Q

Gastrulation

A

Formation of germ layers

43
Q

Neurulation

A

Formation of neural tubes

44
Q

Primitive streak

A

Depression formed in the midline of the epiblast by the dipping in of cells

45
Q

What is formed alongside the primitive streak?

A

The axis of the embryo

46
Q

How are germ layers formed?

A
  • Epiblast cells migrate into space between epiblast and hypoblast layers
  • Cells then displace hypoblast
47
Q

What are the 3 germ layers formed?

A
  • Ectoderm
  • Mesoderm
  • Endoderm
48
Q

What do the 3 germ layers form?

A

Trilaminar disc

49
Q

When do cells become specialised?

A

When the germ layers are formed

50
Q

Notochord

A

Solid tube of cells

51
Q

How is the notochord formed?

A

Cells from the primitive streak sink down and the notochord is formed at the mesoderm

52
Q

What does the notochord do?

A

Induces ectodermal cells in the midline to form a neural tube

53
Q

How is the neural tube formed?

A

Neural plate sinks down

54
Q

What does the neural tube do?

A

Induces the mesoderm to thicken

55
Q

Once thickened what happens to the mesoderm?

A

It separates into 3 parts

56
Q

What 3 parts does the mesoderm separate into?

A
  • Paraxial mesoderm
  • Intermediate mesoderm
  • Lateral plate mesoderm
57
Q

What happens to the lateral plate mesoderm?

A

It splits to form a somatic and splanchnic mesoderm

58
Q

What is the space between the somatic and splanchnic mesoderm called?

A

Intraembryonic coelm

59
Q

What divides to form somites?

A

Paraxial mesoderm

60
Q

What becomes the urogenital system?

A

Intermediate plate mesoderm

61
Q

What becomes the body cavity and coverings?

A

Lateral plate mesoderm

62
Q

What occurs during weeks 4-8, embryonic stage?

A

-Folding into a tube completes
-Neural tube development
-Heart starts to beat on day 24
-Gut formation from endoderm
-Urogenital system formation from intermediate mesoderm
-Body cavities from lateral plate mesoderm
-43 pairs of somites form in the paraxial mesoderm and differentiate further
Limb buds form
-Neck development- pharyngeal arches

63
Q

What are the 3 sections that each somite divides into?

A
  • Dermatome
  • Myotome
  • Sclerotome
64
Q

What do the dermatomes develop into?

A

Dermis of skin

65
Q

What do the myotomes develop into?

A

Muscles

66
Q

What do the sclerotomes develop into?

A

Bones including vertebrae

67
Q

Teratology

A

Study of when things go wrong during development

68
Q

Teratogens

A

Environmental factors that cause abnormal development

69
Q

What are examples of things that can go wrong during pregnancy?

A
  • Congenital rubella syndrome casued by contraction of German measles when pregnant
  • Malformed limbs due to maternal use of Thalidomide
70
Q

What are the causes of abnormal development?

A
  • Unknown aetiology 60%
  • Multifactorial 20%
  • Environmental 10%
  • Genetic 10%
71
Q

What environmental factors are there?

A
  • Drugs- prescription/other
  • Alcohol
  • Tobacco
  • Infectious agents: ToRCH can transfer through placenta and affect developing embryo
  • Others, e.g radiation
72
Q

What does ToRCH stand for?

A
  • Toxoplasma
  • Rubella
  • Cytomegalovirus
  • Herpes
73
Q

What genetic factors are there?

A
  • Too many/too few chromosomes (Turner’s syndrome- 24 chromosomes single X ) (Down’s syndrome- 24 chromosomes- trisomy 21)
  • Structural changes- deletions of genes, segments of chromosomes
74
Q

What can cause problems related to genetic factors?

A
  • Increased maternal age

- Damage from environmental factors such as radiation

75
Q

How do the risks of teratogenesis differ with time?

A
  • Weeks 1-2: high risk of death, low risk from teratogens
  • Weeks 3-8: period of greatest sensitivity to teratogens
  • Weeks 9-38: decreasing sensitivity to teratogens
76
Q

What does the risk posed by a teratogen depend on?

A
  • Exposure during critical periods of development
  • Dosage of drug/chemical/ factor
  • Genetic constitution of embryo i.e some more susceptible than others at equivalent doses
77
Q

How can malformations be diagnosed prenatal?

A
  • Blood- AFP
  • Ultrasound scan- 12 week anomaly scan
  • Invasive tests- chorionic villus sampling and amniocentesis
78
Q

How can malformations be diagnosed postnatal?

A
  • Hip stability
  • Testes descent
  • Fingers and toes
  • Hearing

Semester 2 (150 decks)

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