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IMS > Topic 6 - Embryology > Flashcards

Topic 6 - Embryology Flashcards

Lectures 18,19,26 & 27

1
Q

What is Embryology?

A

The branch of biology that studies the prenatal development of gametes, fertilization, and development of embryos and fetuses.

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2
Q

Why is embryology important to us?

A
  • Logical framework for adult anatomy
  • Better understanding of pathology
  • Anatomical variations
  • Congenital malformations/anomalies and pathologies
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3
Q

Where do the gonads originate?

A

Posterior abdominal wall, they descend during development. In males -> scrotum. In females -> abdomen.

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4
Q

How do horseshoe kidneys occur?

A

The kidneys can fuse as they travel down during development.

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5
Q

What are the aspects of a human adult?

A

Anterior - front
Posterior - back
Superior - top
Interior - bottom

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6
Q

What are the aspects of a human embryo?

A

Ventral - front
Dorsal - back
Cranial - top
Caudal - bottom

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7
Q

What is a ‘lateral’ section?

A

Horizontal across the abdomen.

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8
Q

What is a ‘sagittal’ section?

A

Vertical down the middle from the front.

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9
Q

What is a ‘coronal’ section?

A

Vertical down the middle from the side.

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10
Q

What is a ‘menstrual age’?

A

Dates the pregnancy from the womans last menstrual period.
Full gestation 40 weeks.
Three equal trimesters.

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11
Q

Who is menstrual age used by?

A

Clinicians

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12
Q

What is a ‘fertilisation’ age?

A

Dated from exactly when the sperm fertilized the egg.

Full gestation 38 weeks.

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13
Q

Who uses fertilisation age?

A

Embryologists

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14
Q

What are the three periods of fertilisation age?

A
  • Early Development
  • Embryonic (organogenesis)
  • Foetal
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15
Q

What happens in the foetal period of fertilisation age?

A

Growth and maturation of all the organs fromed in the embryonic period.

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16
Q

How are birth defects caused?

A

Genetics (meiosis and mitosis)

Environment (teratogens)

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17
Q

What can be the genetic causes for birth defects?

A
  • Monogenic (defective gene on autosome)

- Chromosomal (numerical/structural)

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18
Q

What is Trisomy 21 and what does it cause?

A

Down’s Syndrome.

  • growth retardation
  • intellectual retardation
  • craniofacial abnormalities
  • congenital heart defects
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19
Q

What are the types of teratogens?

A
  • Infectious (taxoplasmosis, rubella, hep B, herpes, cytomegalovirus, syphylis)
  • Chemical (alcohol, thalidomide)
  • Physical (radiation)
  • Maternal disease (diabetes)
  • Deficiency (folic acid)
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20
Q

When is the fetus most sensitive to terotogens?

A

During the embryonic period - around 5 weeks of gestation, as it is developing its organs. First prenatal visit tends to fall around 8 weeks.

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21
Q

How do infectious teratogens get to the embryo?

A

The diseases cross the placenta.

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22
Q

What are the infectious teratogens?

A

TORCH

  • Toxoplosmosis
  • Other (syphilis, hepatitis B)
  • Rubella
  • Cytomegalovirus (CMV)
  • Herpes simplex virus (HSV)
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23
Q

What is toxoplasmosis?

A

A parasite usually contracted by the mother through raw meat/cat faeces during early pregnancy (organogenesis). Asymptomatic in adults.

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24
Q

What birth defects can toxoplasmosis cause in early pregnancy?

A
  • inflammation of the retina and eye (micropthalmia)
  • hearing loss
  • enlarger liver/spleen
  • hydrocephaly
  • microcephaly
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25
Q

What is hydrocephaly?

A

Accumulation of fluid at the top of the head.

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26
Q

What is microcephaly?

A

A condition where the head circumference is smaller than normal.

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27
Q

What symptoms does Rubella cause as a birth defect?

A

-Cloudy cornea
-Intellectual disability
-Microcephaly
-Heart defects
Infection passes through placenta in the first 3 months of pregnancy

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28
Q

What is Cytomegalovirus?

A

Crosses the placenta, infection vie body fluids, usually symptomatic.

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29
Q

What does cytomegalovirus cause as a birth defect?

A
  • Micropthalmia (inflammation of retina)
  • Enlarged spleen/liver
  • Mineral deposits on the brain
  • Microcephaly
  • Psychomotor retardation
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30
Q

What is the Varicella Zoster virus?

A

Chicken Pox

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31
Q

When is chickenpox most dangerous?

A

13-20 weeks of development or just before birth to 2 days postpartum.

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32
Q

What does chickenpox cause as a birth defect?

A
  • Segmental skinloss/scarring
  • Limb hypoplasia/paresis
  • Microcephaly
  • Visual defects
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33
Q

What is hypoplasia?

A

Underdevelopment or incomplete development of an organ

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34
Q

What is paresis?

A

A condition of muscular weakness caused by nerve damage or disease

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35
Q

What does the Zika virus cause as a birth defect?

A
  • Microcephaly

- Severe cognitive disabilities

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36
Q

What is thalidomide?

A

Drug prescribed for morning sickness in the 1950s. Caused birth defects such as shortened or absent limbs. In some places now used to treat Leprosy and HIV.

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37
Q

What is Foetal Alcohol Syndrome associated with?

A
  • Prenatal and postnatal growth retardation
  • Intellectual disability
  • Impaired motor ability and coordination
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38
Q

When is a fetus most sensitive to radiation?

A

First trimester

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39
Q

What can radiation cause as a birth defect?

A
  • Microcephaly
  • Mental and cognitive disabilities
  • Haemopoietic malignancies and laukemia
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40
Q

What can Diabetes Mellitus cause as a birth defect?

A
  • Macrosomia (big baby)
  • Ventricular Septal Defects
  • Spina bifida
  • Renal Agenesis
41
Q

What is spina bifida?

A

A birth defect where there is incomplete closing of the backbone and membranes around the spinal cord

42
Q

What can a lack of folic acid in mothers diet cause as a birth defect?

A
  • Spina bifida

- Anencephaly

43
Q

By how much do OTC supplements reduce risk of malformation during pregnancy?

A

60%

44
Q

What is anencephaly?

A

The absence of a major portion of the brain, skull, and scalp that occurs during embryonic development

45
Q

What percentage of pregnancies are unplanned?

A

Around 50%.

46
Q

What is fertilisation?

A

Fusion of male and female gametes to form a zygote

47
Q

What is capacitation?

A

Sperm undergoes capacitation in the female reproductive tract as it is chemically altered as only capacitated sperm can fertilise an egg.

48
Q

Where does fertilisation usually take place?

A

At the ampulla of the uterine tube

49
Q

How does the acrosome reaction occur?

A
  • capacitated sperm pass through corona radiata
  • acrosome releases enzymes that allow sperm to penetrate zona pellucida
  • sperm penetration initiates cortical reaction
  • zona pellucida becomes impenetrable
50
Q

How many cells is the morula?

A

16-32

51
Q

Which part of the morula goes on to form what?

A

Inner cell mass -> embryo proper (embryoblasts)

Outer cell mass -> placenta (trophoblasts)

52
Q

What is a cyst?

A

Fluid filled space

53
Q

What does the blastocyst have to do in order to implant on the uterine wall?

A

Sheds the original zona pellucida

54
Q

What is the blastocyst comprised of?

A

Embryoblast and Trophoblast

55
Q

How is the blastocyst formed?

A

Morula fills with fluid to make the blastocyst

56
Q

What does the Emryoblast differentiate into?

A

Hypoblast and Epiblast

57
Q

What does the Trophoblast differentiate into?

A

Cytotrophoblast

Syncytiotrophoblast

58
Q

How does the syncytiotrophoblast stop the immune system from recognizing the embryo as a foreign body?

A
  • By chemically hiding the embryo from the immune system
  • By losing cell surface membranes between cells, becoming multinucleated so the gaps between cells are too small for the WBC to get through.
59
Q

What do syncytiotrophoblasts do?

A
  • Aid implantation
  • Establish uteroplacental circulation
  • Protect embryo from mothers immune system
  • Release hCG
60
Q

What is the significance of the embryo becoming bilaminar?

A
  • first stage of organisation of the body plan
  • establishes dorsal/ventral axis of the embryo
  • epiblast forms the dorsal surface
  • hypoblast forms the ventral surface
61
Q

Which axis of the embryo does the hypoblast form?

A

Ventral

62
Q

Which axis of the embryo does the epiblast form?

A

Dorsal

63
Q

How does the amniotic cavity form?

A

As a small fluid filled cavity in the epiblast.

64
Q

When does the morula form?

A

Day 4

65
Q

When does the blastocyst form?

A

Day 5

66
Q

When does full implantation occur?

A

Day 9

67
Q

When do the trophoblast and embryoblast differentiate?

A

Day 7

68
Q

When does the amniotic cavity form?

A

Day 8

69
Q

What occurs simultaneously to full implantation?

A

Mitigation of hypoblast cells to encase the blastocyst cavity, forming the Heuser’s membrane

70
Q

How does the developing embryoblast receive nutrients without placental circulation?

A

Nutrients diffuse through the uterine gland into the trophoblastic lacuna

71
Q

When does uteroplacental circulation occur?

A

10-11 Days

72
Q

How is uteroplacental circulation established?

A

Syncytiotrophoblast erodes walls of maternal capillaries using digestive enzymes.
This may cause light spotting.

73
Q

When does the formation of the Extraembryonic mesoderm occur?

A

10-11 Days

74
Q

What is the extraembryonic mesoderm?

A

A layer of connective tissue derived from the yolk sac cells which forms between the primary yolk sac and cytotrophoblast. Eventually covers the amniotic cavity.

75
Q

Which cavity forms in the extraembryonic mesoderm?

A

Chorionic cavity

76
Q

When does the chorionic cavity form?

A

12-13 Days

77
Q

When does the definitive yolk sac form?

A

12-13 Days

78
Q

Which cells is the definitive yolk sac formed from?

A

Hypoblast

79
Q

Which are the 3 most important embryonic cavities?

A
  • Chorionic cavity
  • Definitive yolk sac
  • Amniotic cavity
80
Q

What is the connecting stalk?

A

Attaches embryo to the support structure and will become the umbilical cord.

81
Q

What occurs at the end of week 2 after fertilisation?

A

Amniotic cavity and secondary yolk are suspended in the chorionic cavity by a connecting stalk.

82
Q

Migration of which cells form the definitive yolk sac?

A

Hypoblast

83
Q

Which hormone does the syncytiotrophoblast produce?

A

hCG

84
Q

What does hCG stand for?

A

Human Chorionic Gonadotrophin

85
Q

What is the role of hCG?

A

Helps to maintain the endometrium and plays a role in maternal immunotolerance

86
Q

What was the Bufo test?

A

Early pregnancy test - inject toad with female urine and if high hCG levels are present, the toad would ovulate within 24 hours

87
Q

What is an ectopic pregnancy?

A

Implantation in an abnormal site - outside the uterine cavity

88
Q

What percentage of pregnancies are ectopic?

A

2%

89
Q

What percentage of pregnancy related deaths are due to an ectopic pregnancy?

A

9%

90
Q

Where does fertilisation usually occur?

A

The ampulla

91
Q

What is placenta previa?

A

A condition where the placenta is attached very low down on the uterine wall and perhaps right over the cervix.

92
Q

What are the risks associated with placenta previa?

A
  • Baby may lose blood supply

- Mother may haemorrhage

93
Q

What percentage of ectopic pregnancies occur in the ampulla?

A

80%

94
Q

What can an ectopic pregnancy in the right uterine tube be mistaken for?

A

Appendicitis - pain felt in a similar area

95
Q

How does abdominal implantation occur?

A

There is a gap between the ovary and the uterine tube - therefore the egg can enter the abdomen

96
Q

What is a lithopaedion?

A

When an abdominal pregnancy goes undiagnosed and the foetus dies, if it is too large to reabsorb the body will calcify it as a way of protecting the mother from necrotic tissue

97
Q

What condition can give a false positive on a pregnancy test?

A

Hydatidiform mole releases hCG

98
Q

How does a hydatidiform mole form?

A

Sperm fertilises an ‘empty’ egg lacking a nucleus - suggests paternal genes favour the formation of the trophoblast at the expense of the embryo (paternal imprinting)

99
Q

What is fully established by the end of week 2 of development?

A
  • bilaminar embryo in between amniotic cavity and secondary yolk sac
  • fully implanted and established uteroplacental circulation
  • dorsal/ventral axis established

IMS (13 decks)

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