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Systems: Resp. WK > 19. Embryology 1 &2 > Flashcards

19. Embryology 1 &2 Flashcards

1
Q

What is the pre-embryonic phase? (in weeks)

A

0-3 weeks (clump of cells)

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2
Q

What is the embryonic phase? (in weeks)

A

4-8 weeks (embryo and cells start to develop systems)

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3
Q

What is the foetal phase? (in weeks)

A

9-40 weeks (system further development)

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4
Q

Are pregnancy trimesters the same as embryonic stages?

A

NO, they are completely different. Embryonic stages are much more unequal

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5
Q

What is the process for formation of sperm called?

A

spermatogenesis

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6
Q

What is the process for formation of eggs called?

A

oogenesis

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7
Q

What are the parent cells of sperm and egg called?

A
  • spermatogonium (46 chromosomes)

- oogonium (46 chromosomes)

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8
Q

In oogenesis, how many polar bodies are formed?

A

3 polar bodies ( 4 eggs are made at the end of meiosis and only 1 survives- the other 3 become polar bodies)

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9
Q

Where is spermatogonium found?

A

In seminiferous tubules in the testis

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10
Q

Where is oogonium found?

A

In tiny follicles in the ovaries

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11
Q

Millions of sperms are released on fertilisation yet only one penetrates. What is this process called?

A

facilitation

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12
Q

What happens to pro-nuclei of sperm and ovum?

A
  • (pro)nuclei fuse together to form a zygote

- sperm leaves behind its body and mitochondria which degrades and its genetic make up is used

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13
Q

What is a zygote?

A
  • firt cell in the human body
  • enters week 1 of pre-embryonic phase
  • diploid ( 46 chromosomes)
  • genetically unique (has 2 genetic sets)
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14
Q

What occurs once the zygote is formed? (what is formed after the zygote?)

A

Zygote divides further to form a morula

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15
Q

What does a blastocyst do?

A
  • moves through uterine tube to reach the uterine cavity where the blastocyst embeds itself into the uterus and “makes it its home”
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16
Q

What is a morula?

A
  • a solid ball of cells formed after zygote starts to divide
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17
Q

In the zygote, what cell features come from the mother?

A
  • mitochondria
  • cell organelles
  • cytoplasm
  • cell body etc
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18
Q

What is mitochondria’s special feature which makes it very unique?

A
  • It has its own genetic make up and can have genetic defects leading to several inherited diseases.
  • mitochondrial DNA
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19
Q

What does mitochondrial DNA code for? (2)

A
  • provide instructions for making enzymes involved in oxidative phosphorylation
  • provide instructions for making tRNA and rRNA which help assemble amino acids into functional proteins
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20
Q

How many genes can mitochondrial DNA encode for?

A

37 genes

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21
Q

What are common examples of mitochondrial diseases which are ALWAYS inherited from the mother?

A
  1. Leber’s hereditary Opic Neuropathy (blindness)

2. Leigh syndrome; neurological disorder causing brain abnormalities ( in 20% cases)

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22
Q

What is formed from the morula?

A

a blostocyst

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23
Q

Why is a blastocystic cavity formed?

A
  • As number of cells and size in a morula increases, getting nutrition to the central core of cells starts to become very difficult therefore a cavity develops (blastocystic cavity)
  • Morula changes shape to give central cells nutrients
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24
Q

In a blastocyst, cells accumulate at one end to form what mass?

A

inner cell mass

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25
Q

In a blastoust, what is the ouer lining of cells called?

A

a thromboblast

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26
Q

What are 3 parts of a blastocyst?

A
  1. blastocyst cavity
  2. inner cell mass
  3. thromboblast
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27
Q

On what day of the pre-embryonic stage is a blastocyst formed?

A

on day 5/6

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28
Q

What are the 3 stages a zygote goes through in week 1 of the pre-embryonic stage?

A

Zygote -> Morula-> Blastocyst

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29
Q

What is the myometrium?

A
  • middle layer of the uterine wall
  • consists of uterine smooth muscle
  • lies between the perimetrium (outer lining of uterine wall) and endometrium (inner layer of uterine wall)
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30
Q

Where does meiosis occur in females?

A

in ovaries

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31
Q

What occurs in the endometrium with hormone influences?

A
  • inner uterine lining contains many blood vessels that are going to grow under the influence of hormones like progesterone and oestrogen (produced by the ovary)
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32
Q

In which part of the fallopian tube will fertilisation usually occur in?

A

in the DISTAL part

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33
Q

After zygote is created, what is the time scale for the first cell division to occur?

A

36 hours

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34
Q

What happens to time taken for divisions to occur from zygote to morula cell divisions?

A
  • It takes less time with each division (36…24…12 hours…and so on)
  • It gets easier and easier for division to occur over time (successive divisions) as cells become more specialised (cells learn how to divide and develop)
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35
Q

How does the ovum travel down the fallopian tube? What allows this to happen?

A

Healthy ciliated epithelium which lines fallopian tubes (uterine tubes) and moves the ovum in fallopian tube,leading to the uterine cavity

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36
Q

By which day has the blastula formed and has reached the uterine cavity for implantation?

A

Day 5-6

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37
Q

What can occur if cilia function in the fallopian tubes is abnormal?

A

Ectopic pregnancy

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38
Q

Describe why ectopic pregnancy occurs.

A
  • women who suffer from infection will have inflammation in fallopian tubes
  • cilia do not work properly and blastocyst cannot therefore move into the uterine cavity
  • blastocyst implants itself into fallopian (uterine) tube and starts to develop leading to an ectopic pregnancy
  • this can result in loss of fallopian tube due to rupture
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39
Q

What major step occurs by day 6 of 1st week and into 2nd week of pre-mebryonic phase?

A

Implantation in the uterine endometrial layer and placenta begins to develop

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40
Q

What are the main 2 events in week 2 of pre-embryonic phase?

A
  1. bilaminar disc formed from cells that later develop into the embryo
  2. sacs, membranes and cord to nourish the human conceptus (baby) start to form
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41
Q

What mass of cells form the bilaminar disc?

A

inner cell mass

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42
Q

What are the cells that form the outer cell mass/ layer of blastocyst called?

A

the throphoblast

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43
Q

What happens to the throphoblast in week 2?

A

Divides to form 2 layers (outer cell mass and inner cell mass) forming the CHORION

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44
Q

What structures develop from the chorion? What do they do?

A
  • chorionic villi (finger like processes)

- these villi penetrate the endometrium to attach the embryo to it (invades the endometrium)

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45
Q

What are the 3 functions of the chorion?

A
  1. implantation process (chorionic villi)
  2. forms part of the placenta in due course
  3. secretes human chorionic gonadotropin (HCG); used to detect pregnancy
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46
Q

What does the HCG allow the ovaries to do?

A
  • allows for secretion of progesterone and oestrogen to maintain the endometrium full of nutrients for the developing embryo and to prevent uterus shedding
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47
Q

On approximately what day does the blastocyst undergo implantation into the uterine wall (endometrium)?

A

~ day 7

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48
Q

What is the term which describes the part of the endometrium deep to the implanted conceptus. (ie What is the endometrium called once the blastocyst implants itself into it)

A

Decidua basalis: The area of endometrium between the implanted chorionic vesicle and the myometrium, which becomes the maternal part of the placenta.

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49
Q

What is the primary role of HCG?

A

Maintains the endometrium and secreted by the chorion

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50
Q

Maternal blood and urine levels of HCG increase until which week of gestation?

A

12th week

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51
Q

Why do levels of HCG start to fall after 12th week?

A

Because placenta takes over and acts as an endocrine gland which maintains hormone levels

52
Q

Describe the 5 steps (main terms) of development from a zygote to a chorion.

A
  1. zygote
  2. morula
  3. blastocyst
  4. throphoblast
  5. chorion
53
Q

What do the cells of the inner cell mass form?

A

They form a 2-layered flat disc called the BILAMINAR DISC

54
Q

What two layers is the bilaminar disc made up of?

A
  • epiblast

- hypoblast

55
Q

What two cavities will form from the blastocystic cavity?

A
  1. amniotic cavity (top)

2. yolk sac (bottom)

56
Q

What happens in the allantoic cavity? What happens to it as pregnancy progresses?

A
  • Waste will collect there

- Gets bigger as waste increases over time

57
Q

What will the chorionic villi eventually develop into?

A

the placenta

58
Q

What occurs through the yolk sac?

A

Blood supply and nutrients are delivered

59
Q

Does the chorion separate the maternal and foetal blood?

A
  • yes; there is NO mixing of maternal and foetal blood

- mother will not reject the child

60
Q

What are the 4 main regions in a human embryo? (cavities and sacs)

A
  1. amniotic cavity
  2. chorionic cavity
  3. allantoic cavity
  4. yolk sac
61
Q

What are the 3 main functions of a placenta?

A
  1. foetal nutrition
  2. transport of waste and gases
  3. Immunity
    etc
62
Q

What is the foetal part of the placenta like? (facing the foetus)

A
  • smooth with foetal blood vessels and end of umbilical cord
  • lined by amniotic sac and membrane
63
Q

What is the maternal part of the placenta like? (facing the mother)

A
  • Decidua basalis end of endometrium

- Rough and has maternal blood vessels

64
Q

How are fraternal/ dizygotic twins created?

A
  • 2 ova released by mother and fertilised by 2 sperm forming 2 separate zygotes
  • Different genetic make up and 2 placentae
  • can run in families
65
Q

How are identical/ monozygotic twins created?

A
  • 1 ovum fertilised by 1 sperm forming 1 zygote
  • zygote divides into two and each cell develops into a different embryo
  • same genetic make up and share 1 placenta
  • might/might not share amniotic and chorionic sac
66
Q

Summarise what occurs in week 1 and 2 of life.

A

Fertilisation-> zygote-> morula-> blastocyst with inner and outer cell mass-> trophobloast-> chorion (from outer) and bilaminar disc formed (from inner) with amniotic cavity above and yolk sac below

67
Q

Summarise the implantation process in week 1 and 2 of life.

A

Morula reaches the uterine cavity-> blastocyst implants-> outer cells form chorionic villi which help implantation-> decidua basalis formed and placental formation begins

68
Q

What occurs in week 3 of gestation?

A
  1. formation of germ layers (gastrulation)
  2. Formation of neural tube (neurulation)
  3. development of somites
  4. early development of cardiovascular system
69
Q

What is the primitive streak?

A

Formed in the midline of the epiblast by the dipping in of cells (invagination/depression of cells)

70
Q

What arises once the primitive streak is formed?

A

the axis of the embryo (location of head and tail is not known until the primitive streak is formed)

71
Q

What is the process of formation of 3 germ layers?

A

Gastrulation

72
Q

Describe the process of gastrulation.

A
  • epiblast cells migrate into space between epiblast and hypoblast layers
  • cells displace hypoblast as cells migrate downwards, forming a TRIlaminar disc
  • cells are now specialised
73
Q

What are the 3 germ layers?

A
  1. ectoderm
  2. mesodern
  3. endoderm
74
Q

Once germ layers are formed, where are amniotic cavity and yolk sac?

A
  • amniotic cavity remains at the top of ectoderm

- yolk sac remains at the bottom of endoderm

75
Q

Describe the steps from inner cell mass of blastocyst to formation of germ layers.

A

inner cell mass of blastocyst-> bilaminar disc -> epiblast and hypoblast formed-> primitive streak formed on epiblast-> cells from primitive streak invaginate and displace hypoblast-> germ layers formed; ectoderm, mesoderm and endoderm

76
Q

Describe the notochord formation.

A

-cells from the primitive streak on ectoderm (previous epiderm) migrate downwards forming a solid tube just below mesoderm creating the notochord (solid tube of cells)

77
Q

What is the function of a notochord?

A
  • rigid structure for muscle attachment

- provides signals to surrounding tissues during developement

78
Q

What is the name for neural tube formation?

A

Neurulation

79
Q

Describe the process of neurulation (formation of neural tube)

A
  • notochord induces ectodermal cells in the midline to form a neural tube by sending signals to ectoderm
  • by responding to signals from notochord, the neural plate is formed in ectoderm
  • neuronal plate sinks down to form a neural tube (just above mesoderm)
80
Q

What does the neural tube help develop in the embryo?

A

Has head end for the brain and a tail end for the spinal cord

81
Q

What abnormalities would occur if there was a fault in the formation of the notochord?

A

Brain and spinal abnormalities in the embryo

82
Q

What is the function of the neural tube in terms of its influence on the mesoderm.

A

The neural tube induces the mesoderm to thicken and separate into 3 parts

83
Q

What are the names of the 3 parts that the mesoderm separates into at each end? (from neural tube/ embryo outwards)

A
  1. paraxial mesoderm
  2. intermediate plate mesoderm
  3. lateral plate mesoderm
84
Q

What 2 parts does lateral plate mesoderm split intoo?

A
  • somatic mesoderm

- splanchnic mesoderm

85
Q

What is the name of the cavity/ space between the somatic and splanchnic mesoderm?

A

Intraembryonic coelom

86
Q

What does paraxial mesoderm form?

A

Somites

87
Q

What is a somite (from the paraxial mesoderm)

A

segmented portions or paired blocks of the paraxial mesoderm (little blocks of mesoderm outside the neural tube)

88
Q

What does intermediate plate mesoderm form?

A

urogenital system (kidneys + reproductive)

89
Q

What does lateral plate mesoderm form?

A

body cavity and coverings

90
Q

Each somite (“block”) divides further into 3 sections. What are they?

A
  1. dermatome
  2. myotome
  3. sclerotome
91
Q

What is a dermatome?

A

Area of the skin supplied by a single spinal nerve root (develops into dermis of skin)

92
Q

What is a myotome?

A

Muscle that is supplied by a single spinal nerve root; motor equivalent of a dermatome (develop into muscles)

93
Q

What is a sclerotome?

A

Area of a bone supplied by/innervated by a single spinal nerve root/ segment (develop into vertebrae and ribs; bone)

94
Q

During ebryonic period in weeks 4-8, what is another name for this period?

A

Organogenetic period

95
Q

What developmental changes occur in the embryonic period (4-8) in the embryo?

A
  • folding into a tube (lateral folds) which started in 3rd week completes
  • neural tube develops
  • heart starts to beat
  • gut formation
  • urogenital system formation
  • body cavities formation
  • 43 pairs of somites formed in paraxial mesoderm differentiate further
  • limb buds form
  • neck development; pharyngeal arches
96
Q

What does the neural tube form? (4)

A
  • spinal cord
  • forebrain
  • midbrian
  • hindbrain
97
Q

On what day does the heart start to beat?

A

Day 24

98
Q

From which layer does gut formation happen?

A

Endoderm (and many other organs)

99
Q

How many pairs of somites are there in the paraxial mesoderm which differentiate further in weeks 4-8?

A

43 pairs

100
Q

During lateral folding of the embryo, what happens to the lateral plate mesoderm layers?

A

They will split (the somatic and splanchnic layers join in a circle from both sides of the mesoderm) and forms a round layer around the endoderm which surrounds the embryo.

101
Q

What happens in terms of the amniotic cavity once lateral folding occurs?

A

Amniotic cavity now surrounds the whole embryo

102
Q

What do the two somatic and splanchnic mesoderm form ultimately?

A

somatic layer; forms body wall

splanchnic layer; forms the circulatory system

103
Q

Ultimately what does ectoderm form? (2)

A
  1. epidermis of skin

2. neural tube

104
Q

Ultimately what does the mesoderm form? (3)

A
  1. paraxial mesoderm (somites; dermatome, myotome, sclerotome)
  2. intermediate plate mesoderm (urogenital system; kidneys+reproductive)
  3. lateral plate mesoderm (peritoneum, pleura, body cavities)
105
Q

Ultimately what does the endoderm form? (2)

A
  • gut

- respiratory

106
Q

What do somites give rise to ultimately?

A
  • vertebrae of vertebral column
  • rib cage
  • part of occipital bone
  • tendons
  • cartilage
  • skeletal muscle
107
Q

What is teratology?

A

Study of when things of wrong during development?

108
Q

What are teratogens?

A

environmental factors that cause abnormal development

109
Q

What is a famous example of teratology?

A

Thalidomide disaster; which prevented the growth of new blood vessels in embryos, has 2 isomers; one is safe and one isn’t

110
Q

What are the main causes of abnormal development? (from most common to least)

A
  1. unknown aetiology (60%)
  2. multifactoral (20%)
  3. genetic (10%)
  4. environmental (10%)
111
Q

What are some common environmental factors which can lead to abnormal developments?

A
  • drugs (prescription/other)
  • alcohol/ tobacco
  • infectious agents
  • others; e.g. radiaiton
112
Q

What are common infectious agents which can transfer across the placenta and affect the developing embryo? (5)

A
  • toxoplasma
  • rubella
  • cytomegalovirus
  • herpes
  • zika virus
113
Q

What are common genetic factors (conditions) affecting embryonic development?

A
  • Too many/ too few chromosomes:
    1. Turner’s syndrome (45 chromosomes, X)
    2. Down’s syndrome (47 chromosomes, trisomy 21)
  • structural changes (deletion of genes or segments of chromosomes)
114
Q

What are the common causes for genetic factors? (2)

A
  1. increased maternal age

2. damage from environmental factors such as radiation e.g. x rays

115
Q

What is the risk of teratogenesis in weeks 1-2?

A
  • low risk of teratogens

- high risk of death

116
Q

What is the risk of teratogenesis in weeks 3-8?

A

-period of greatest sensitivity to teratogens

117
Q

What is the risk of teratogenesis in weeks 9-38?

A

-decreasing sensitivity to teratogens

118
Q

The risk posed by teratogens depends on 3 factors, what are they?

A
  1. exposure during critical periods of development
  2. dosage of drug/chemical/factor
  3. genetic constitution of the embryo i.e. some more susceptible than others at equivalent doses due to genetic make up
119
Q

What are the common pre-natal diagnosis methods for malformations? (3)

A
  1. Blood (AFP; alpha fetoprotein test)
  2. ultrasound scan (12 week anomaly scan)
  3. invasive tests; chorionic villus sampling and amniocentesis
120
Q

What are the common postnatal diagnsosis methods for malformations?

A
  1. hip stability
  2. testes (descent)
  3. fingers and toes
  4. hearing
121
Q

Why is the chorion sometimes sampled?

A

has the same genetic make up as the baby but it’s a more invasive test

122
Q

What happens in week 1 gestation in summary? (2)

A
  1. blastocyst formation

2. moves to uterine cavity

123
Q

What happens in week 2 gestation in summary? (3)

A
  1. bilaminar embryo
  2. implantation
  3. placenta formation
124
Q

What happens in week 3 gestation in summary? (3)

A
  1. gastrulation
  2. neurulation
  3. somite formation
125
Q

What happens in week 4 gestation in summary? (2)

A
  1. folding of embryo

2. organogenesis

Systems: Resp. WK (40 decks)

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