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Embryology > Introduction to Embryology > Flashcards

Introduction to Embryology Flashcards

1
Q

What is embryology?

A

The study of how we develop from a single-celled organism, formed after fertilisation, into a multicellular organism

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2
Q

Why is embryology studied?

A
  1. as it gives a logical framework for adult anatomy
  2. it gives a better understanding of pathology
  3. identification of anatomical variations which may result from problems during development
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3
Q

What is pathology?

A

It is concerned with the diagnosis of disease by analysing body fluids and tissues

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4
Q

How is a horseshoe kidney formed?

A

The inferior parts of the kidney may fuse as they ascend upwards towards the posterior abdominal wall

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5
Q

What is a congenital malformation?

A

A birth defect caused when something along the developmental journey goes slightly wrong

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6
Q

Why does studying embryology help with identifying congenital malformations?

A

The developmental process is tightly regulated, so if something goes wrong, knowing the developmental journey allows you to see why this has happened

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7
Q

Why is different terminology used to describe the foetus?

A

It develops in a C-shape

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8
Q

What are the 4 words used to describe the regions of the foetus?

A

head end - cranial

tail end - caudal

front - ventral

back - dorsal

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9
Q

Why is pregnancy dated?

A

It allows you to work out the development stage of the embryo

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10
Q

How is menstrual age used to date pregnancy?

How long is the full gestation period?

A

It dates pregnancy from the woman’s last menstrual period

It is split into 3 equal trimesters and full gestation period is 40 weeks

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11
Q

How is fertilisation age used to date pregnancy?

How long is the full gestation period?

A

It dates pregnancy from the moment of fertilisation

Full gestation is 38 weeks

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12
Q

Why is the gestation period shorter when using fertilisation age?

A

The release of the oocyte occurs 2 weeks into the menstrual cycle

The oocyte cannot be fertilised until it is released

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13
Q

How is fertilisation age split into sections?

A

Early developmental stage occurs from 0 - 3 weeks

Embryonic stage occurs from 3 - 8 weeks

Foetal period occurs from 8 - 38 weeks

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14
Q

What happens during the early developmental stage?

A

Rapid cell division as the zygote divides

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15
Q

What happens during the embryonic stage?

A

It is also known as the organogenesis stage as the organs are being formed

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16
Q

What happens during the foetal period?

A

Growth and maturation of the organs and systems formed during the organogenesis period

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17
Q

How many births in the UK a year result in a congenital defect?

What is a congenital malformation?

A

It is a serious deleterious physical anomaly

It occurs in 1 in 44 births in the UK

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18
Q

What is a malformation syndrome?

A

This results from a typical combination of malformations affecting more than one body part

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19
Q

What factors can cause a congenital malformation?

A

18% of defects are caused by genetic problems

7% of defects are caused by environmental factors (teratogens)

25% of defects are a combination of both environmental and genetic factors

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20
Q

What is a teratogen?

A

An agent or factor that causes the malformation of an embryo

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21
Q

What does it mean if a congenital malformation is monogenic?

A

There is a single defective gene on an autosome

This can be inherited or can be spontaneous with no family history

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22
Q

What does it mean if a congenital malformation is chromosomal?

A

There could be a different number or structure of chromosomes

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23
Q

What are infectious agents that act as teratogens?

A

They are parasites or viruses that can cross the placenta

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24
Q

What does TORCH stand for in infectious agents that can cause congenital malformations?

A 
Toxoplasmosis
Other (e.g. hepatitis B, syphilis)
Rubella
Cytomegalovirus
Herpes
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25
Q

What is toxoplasmosis caused by?

Where is this found?

A

The parasite, Toxoplasma gondii

It is found in cat faeces, undercooked meat and contaminated water

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26
Q

What chemical factors act as teratogens?

A

Any medical or recreational drugs

e.g. thalidomide and alcohol

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27
Q

What physical factors act as teratogens?

What maternal diseases act as teratogens?

A

Physical factors - X - rays

Maternal disease - Diabetes

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28
Q

What deficiency can cause congenital malformations?

A

Folic acid

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29
Q

What determines whether an environmental factor does or doesn’t affect the developing embryo?

A

It depends how far along in the development process the embryo is

It is most susceptible during the organogenesis period and less susceptible during the foetal period

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30
Q

Under what conditions will toxoplasmosis affect a developing embryo?

A

It will only affect the embryo if the mother contracts it when she is newly pregnant

It will not cause problems if she contracted it prior to conception

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31
Q

What does toxoplasmosis cause?

A
  1. inflammation of the retina and micropthalmia (small eyes)
  2. hearing loss
  3. enlarged liver and spleen
  4. hydrocephaly (fluid on the brain)
  5. microcephaly (small head/brain)
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32
Q

When does rubella cross the placenta to affect the foetus?

A

Infection passes over the placenta in the first 3 months of pregnancy

It can be prevented by the MMR vaccine

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33
Q

What does rubella cause?

A
  1. cloudy cornea
  2. intellectual disability due to problems with development of the CNS
  3. microcephaly
  4. heart defects
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34
Q

What does cytomegalovirus cause?

A
  1. inflammation of the retina and micropthalmia
  2. enlarged liver and spleen
  3. mineral/calcium deposits on the brain
  4. microcephaly
  5. psychomotor retardation
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35
Q

What do herpes simplex 1 and herpes simplex 2 cause?

A

Herpes simplex 1 causes cold sores

Herpes simplex 2 causes genital warts

36
Q

What does Herpes Zoster cause?

When is this most dangerous to the foetus?

A

It causes chickenpox

This is the Varicella zoster virus and it is most dangerous between the 13th - 20th weeks of pregnancy

or just before birth, in the 2 days postpartum

37
Q

What is the most common route of transmission of herpes to the foetus?

A

It is rare for it to travel up the reproductive tract

It is more common for the mother to transfer the herpes virus during birth

It can also be passed on if the mother contracts chickenpox during pregnancy

38
Q

What does herpes virus cause in the developing foetus?

A
  1. segmental skin loss and scarring
  2. limb hypoplasia/paresis
  3. microcephaly
  4. visual defects
39
Q

What does the Zika virus cause?

A
  1. fever, rash, joint pain and red eyes
  2. microcephaly
  3. severe cognitive disabilities
40
Q

What was thalidomide given for in the 1950s?

What did it lead to?

A

It was given to treat morning sickness

It leads to shortened or absent limbs

41
Q

What is thalidomide given to treat nowadays?

A

It is used to treat symptoms associated with leprosy and HIV

42
Q

What are the symptoms of foetal alcohol syndrome?

A
  1. prenatal and postnatal growth retardation
  2. intellectual disability
  3. impaired motor ability and coordination
43
Q

Why is alcohol consumption such an issue when it comes to congenital abnormalities?

A

50% of pregnancies are unplanned so many people continue to drink alcohol as they are unaware they are pregnant

44
Q

What does radiation cause in the developing foetus?

A

Cell death or chromosome changes leading to…

  1. microcephaly
  2. mental and cognitive disabilities
  3. haemopoietic malignancies and leukaemia
45
Q

What part of the foetus is most sensitive to radiation?

A

The central nervous system

The foetus is most sensitive during the first trimester

46
Q

What does diabetes mellitus cause in the foetus?

A
  1. macrosomia - a larger than average baby
  2. ventricular septal defects
  3. spina bifida
  4. renal agenesis
47
Q

What does folic acid deficiency cause?

A

Malformations in central nervous system formation

48
Q

What is significant about folic acid deficiency?

A

Folic acid levels must be high for a number of weeks before fertilisation

If pregnancy is unplanned, folic acid levels may not be high enough

49
Q

What does folic acid deficiency cause in the developing foetus?

A
  1. spina bifida

2. anencephaly - the centre of the brain fails to form correctly

50
Q

What is gametogenesis?

A

The process in which cells undergo meiosis to form gametes

51
Q

What are gametes?

A

Haploid cells that contain only one set of chromosomes and are made through meiosis

52
Q

Where does sperm production take place?

A

Seminiferous tubules in the testes

These are kept separate from systemic circulation by the blood-testis barrier

53
Q

What is the role of the blood-testis barrier?

A

It prevents hormones and components of the systemic circulation from affecting the developing sperm

54
Q

Why must the blood-testis barrier prevent the immune system from recognising sperm as foreign?

A

Sperm are genetically different from male cells so will have different surface antigens

55
Q

What are spermatogonia?

A

The initial pool of diploid cells that will divide by mitosis to form 2 identical cells

56
Q

What is the difference between Type A1 spermatogonia and Type B spermatogonia?

A

A1 - replenish the pool of spermatogonia so the male remains fertile his whole life

B - these form mature sperm

57
Q

What happens to the type B spermatogonia?

A

They divide by mitosis several times to form identical diploid cells linked by cytoplasm bridges

These are primary spermatocytes

58
Q

What happens when the primary spermatocytes undergo meiosis?

A

Meiosis I produces 2 haploid cells - secondary spermatocytes

Meiosis II produces 4 haploid cells - spermatids

59
Q

What happens during spermiation?

A

The cytoplasm bridges break down and the spermatids are released into the lumen of the seminiferous tubule

60
Q

What happens to the spermatids once they are in the seminiferous tubule?

A

They travel along the tubule and differentiate into mature spermatozoa

61
Q

When does the process of oogenesis begin?

What cells are present at this point?

A

Oogenesis begins in the foetus prior to birth

The cells that begin meiosis I before birth are primary oocytes

62
Q

What are primary oocytes arranged to form?

A

They are arranged in the gonads in clusters

They are surrounded by flattened epithelial cells (follicular cells) to form a primordial follicle

63
Q

What stage of meiosis are primary oocytes arrested in?

A

prophase stage of meiosis I

64
Q

What happens during the pre-antral stage of oogenesis?

A
  1. primary oocyte grows dramatically whilst being arrested in meiosis I
  2. follicular cells grow and proliferate to form stratified cuboidal epithelium
  3. the cells have become granulosa cells
65
Q

What do granulosa cells do?

A

They secrete glycoproteins to form the zona pellucida around the primary oocyte

66
Q

What happens during the antral stage of oogenesis?

A

fluid-filled spaces form between granulosa cells

these will combine to form the antrum - a central fluid-filled space

The follicles are now secondary follicles

67
Q

What happens during the pre-ovulatory stage of oogenesis?

A

The LH surge induces this phase and meiosis I is completed

2 haploid cells form within the follicle, but they are unequally sized

68
Q

What cells are formed during the pre-ovulatory stage?

A

One daughter cell receives far less cytoplasm - first polar body

The other haploid cell is the secondary oocyte

69
Q

What happens after the cells produced in the pre-ovulatory stage undergo meiosis II?

A

The first polar body gives rise to 2 polar bodies

The secondary oocyte arrests in metaphase of meiosis II

70
Q

What do the conditions inside the female reproductive tract cause the sperm to undergo?

A

Capacitation

The cholesterol and glycoproteins are removed from the head, allowing the sperm to bind to the zona pellucida of the oocyte

71
Q

When does the secondary oocyte complete meiosis II?

What does it form?

A

It completes meiosis II on fertilisation

This results in a fertilised egg and a third polar body

72
Q

Where does fertilisation take place?

What must happen prior to this?

A

It occurs in the ampulla of the uterine tube

Fimbriae must sweep the oocyte into the uterine tube, as it is not connected to the ovary

73
Q

What happens prior to the acrosome reaction?

A

The capacitated sperm pass through the corona radiate

74
Q

what is the acrosome reaction?

A

The acrosome releases degradative enzymes that break down and allow the sperm to penetrate the zona pellucida

75
Q

What happens once one sperm has penetrated the zona pellucida?

A

The cortical granules in the oocyte start the cortical reaction to prevent polyspermy

76
Q

What is the result of the cortical reaction?

A

The zona pellucida becomes impenetrable

77
Q

What does cleavage refer to?

A

Cell divisions that are not associated with significant growth of the embryo

78
Q

What is a blastomere?

How is it formed?

A

It is a cell formed by cleavage of a fertilised ovum

After fertilisation, the zygote begins to divide

There is no change in size of the zygote as the blastomeres get smaller

79
Q

What is a morula?

A

A ball of cells containing 16 - 32 cells

The cells begin to become organised

80
Q

What is the inner cell mass of a morula made up from?

A

Embryoblast cells

These will go on to form the embryo itself

81
Q

What is the outer cell mass of a morula made up from?

A

Trophoblast cells

These will go on to form the support structures needed by the embryo to survive

82
Q

What is the blastocyst and when does it form?

A

It is a fluid-filled cavity which forms by day 5

83
Q

What do embryoblasts and trophoblasts form in the blastocyst?

A

Trophoblasts form the thin layer around the outside

Embryoblasts form a compact inner cell mass

84
Q

When does blastocyst formation begin?

A

When a fluid-filled cavity opens up in the morula

85
Q

What is the blastocoel and how is it formed?

A

It is the inner fluid-filled blastocyst cavity

The trophoblast cells pump Na+ ions into the blastocyst, which causes water to follow through osmosis

This forms the blastocoel

86
Q

On which day does the blastocyst implant into the uterine wall?

Why does this happen?

A

It implants into the uterine wall between days 5 and 6

It does this as it needs a blood supply as it cannot get enough oxygen and nutrients through osmosis

87
Q

What is blastocyst hatching and why is it needed?

A

This is where the blastocyst loses the zona pellucida

This allows it to implant into the uterine wall

Embryology (4 decks)

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