19. Embryology 1 &2 Flashcards
1
Q
What is the pre-embryonic phase? (in weeks)
A
0-3 weeks (clump of cells)
2
Q
What is the embryonic phase? (in weeks)
A
4-8 weeks (embryo and cells start to develop systems)
3
Q
What is the foetal phase? (in weeks)
A
9-40 weeks (system further development)
4
Q
Are pregnancy trimesters the same as embryonic stages?
A
NO, they are completely different. Embryonic stages are much more unequal
5
Q
What is the process for formation of sperm called?
A
spermatogenesis
6
Q
What is the process for formation of eggs called?
A
oogenesis
7
Q
What are the parent cells of sperm and egg called?
A
- spermatogonium (46 chromosomes)
- oogonium (46 chromosomes)
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)
9
Q
Where is spermatogonium found?
A
In seminiferous tubules in the testis
10
Q
Where is oogonium found?
A
In tiny follicles in the ovaries
11
Q
Millions of sperms are released on fertilisation yet only one penetrates. What is this process called?
A
facilitation
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
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)
14
Q
What occurs once the zygote is formed? (what is formed after the zygote?)
A
Zygote divides further to form a morula
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”
16
Q
What is a morula?
A
- a solid ball of cells formed after zygote starts to divide
17
Q
In the zygote, what cell features come from the mother?
A
- mitochondria
- cell organelles
- cytoplasm
- cell body etc
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
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
20
Q
How many genes can mitochondrial DNA encode for?
A
37 genes
21
Q
What are common examples of mitochondrial diseases which are ALWAYS inherited from the mother?
A
- Leber’s hereditary Opic Neuropathy (blindness)
2. Leigh syndrome; neurological disorder causing brain abnormalities ( in 20% cases)
22
Q
What is formed from the morula?
A
a blostocyst
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
24
Q
In a blastocyst, cells accumulate at one end to form what mass?
A
inner cell mass
25
In a blastoust, what is the ouer lining of cells called?
a thromboblast
26
What are 3 parts of a blastocyst?
1. blastocyst cavity
2. inner cell mass
3. thromboblast
27
On what day of the pre-embryonic stage is a blastocyst formed?
on day 5/6
28
What are the 3 stages a zygote goes through in week 1 of the pre-embryonic stage?
Zygote -> Morula-> Blastocyst
29
What is the myometrium?
- 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)
30
Where does meiosis occur in females?
in ovaries
31
What occurs in the endometrium with hormone influences?
- 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)
32
In which part of the fallopian tube will fertilisation usually occur in?
in the DISTAL part
33
After zygote is created, what is the time scale for the first cell division to occur?
36 hours
34
What happens to time taken for divisions to occur from zygote to morula cell divisions?
- 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)
35
How does the ovum travel down the fallopian tube? What allows this to happen?
Healthy ciliated epithelium which lines fallopian tubes (uterine tubes) and moves the ovum in fallopian tube,leading to the uterine cavity
36
By which day has the blastula formed and has reached the uterine cavity for implantation?
Day 5-6
37
What can occur if cilia function in the fallopian tubes is abnormal?
Ectopic pregnancy
38
Describe why ectopic pregnancy occurs.
- 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
39
What major step occurs by day 6 of 1st week and into 2nd week of pre-mebryonic phase?
Implantation in the uterine endometrial layer and placenta begins to develop
40
What are the main 2 events in week 2 of pre-embryonic phase?
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
41
What mass of cells form the bilaminar disc?
inner cell mass
42
What are the cells that form the outer cell mass/ layer of blastocyst called?
the throphoblast
43
What happens to the throphoblast in week 2?
Divides to form 2 layers (outer cell mass and inner cell mass) forming the CHORION
44
What structures develop from the chorion? What do they do?
- chorionic villi (finger like processes)
| - these villi penetrate the endometrium to attach the embryo to it (invades the endometrium)
45
What are the 3 functions of the chorion?
1. implantation process (chorionic villi)
2. forms part of the placenta in due course
3. secretes human chorionic gonadotropin (HCG); used to detect pregnancy
46
What does the HCG allow the ovaries to do?
- allows for secretion of progesterone and oestrogen to maintain the endometrium full of nutrients for the developing embryo and to prevent uterus shedding
47
On approximately what day does the blastocyst undergo implantation into the uterine wall (endometrium)?
~ day 7
48
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)
Decidua basalis: The area of endometrium between the implanted chorionic vesicle and the myometrium, which becomes the maternal part of the placenta.
49
What is the primary role of HCG?
Maintains the endometrium and secreted by the chorion
50
Maternal blood and urine levels of HCG increase until which week of gestation?
12th week
51
Why do levels of HCG start to fall after 12th week?
Because placenta takes over and acts as an endocrine gland which maintains hormone levels
52
Describe the 5 steps (main terms) of development from a zygote to a chorion.
1. zygote
2. morula
3. blastocyst
4. throphoblast
5. chorion
53
What do the cells of the inner cell mass form?
They form a 2-layered flat disc called the BILAMINAR DISC
54
What two layers is the bilaminar disc made up of?
- epiblast
| - hypoblast
55
What two cavities will form from the blastocystic cavity?
1. amniotic cavity (top)
| 2. yolk sac (bottom)
56
What happens in the allantoic cavity? What happens to it as pregnancy progresses?
- Waste will collect there
| - Gets bigger as waste increases over time
57
What will the chorionic villi eventually develop into?
the placenta
58
What occurs through the yolk sac?
Blood supply and nutrients are delivered
59
Does the chorion separate the maternal and foetal blood?
- yes; there is NO mixing of maternal and foetal blood
| - mother will not reject the child
60
What are the 4 main regions in a human embryo? (cavities and sacs)
1. amniotic cavity
2. chorionic cavity
3. allantoic cavity
4. yolk sac
61
What are the 3 main functions of a placenta?
1. foetal nutrition
2. transport of waste and gases
3. Immunity
etc
62
What is the foetal part of the placenta like? (facing the foetus)
- smooth with foetal blood vessels and end of umbilical cord
- lined by amniotic sac and membrane
63
What is the maternal part of the placenta like? (facing the mother)
- Decidua basalis end of endometrium
| - Rough and has maternal blood vessels
64
How are fraternal/ dizygotic twins created?
- 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
How are identical/ monozygotic twins created?
- 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
Summarise what occurs in week 1 and 2 of life.
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
Summarise the implantation process in week 1 and 2 of life.
Morula reaches the uterine cavity-> blastocyst implants-> outer cells form chorionic villi which help implantation-> decidua basalis formed and placental formation begins
68
What occurs in week 3 of gestation?
1. formation of germ layers (gastrulation)
2. Formation of neural tube (neurulation)
3. development of somites
4. early development of cardiovascular system
69
What is the primitive streak?
Formed in the midline of the epiblast by the dipping in of cells (invagination/depression of cells)
70
What arises once the primitive streak is formed?
the axis of the embryo (location of head and tail is not known until the primitive streak is formed)
71
What is the process of formation of 3 germ layers?
Gastrulation
72
Describe the process of gastrulation.
- 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
What are the 3 germ layers?
1. ectoderm
2. mesodern
3. endoderm
74
Once germ layers are formed, where are amniotic cavity and yolk sac?
- amniotic cavity remains at the top of ectoderm
| - yolk sac remains at the bottom of endoderm
75
Describe the steps from inner cell mass of blastocyst to formation of germ layers.
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
Describe the notochord formation.
-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
What is the function of a notochord?
- rigid structure for muscle attachment
| - provides signals to surrounding tissues during developement
78
What is the name for neural tube formation?
Neurulation
79
Describe the process of neurulation (formation of neural tube)
- 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
What does the neural tube help develop in the embryo?
Has head end for the brain and a tail end for the spinal cord
81
What abnormalities would occur if there was a fault in the formation of the notochord?
Brain and spinal abnormalities in the embryo
82
What is the function of the neural tube in terms of its influence on the mesoderm.
The neural tube induces the mesoderm to thicken and separate into 3 parts
83
What are the names of the 3 parts that the mesoderm separates into at each end? (from neural tube/ embryo outwards)
1. paraxial mesoderm
2. intermediate plate mesoderm
3. lateral plate mesoderm
84
What 2 parts does lateral plate mesoderm split intoo?
- somatic mesoderm
| - splanchnic mesoderm
85
What is the name of the cavity/ space between the somatic and splanchnic mesoderm?
Intraembryonic coelom
86
What does paraxial mesoderm form?
Somites
87
What is a somite (from the paraxial mesoderm)
segmented portions or paired blocks of the paraxial mesoderm (little blocks of mesoderm outside the neural tube)
88
What does intermediate plate mesoderm form?
urogenital system (kidneys + reproductive)
89
What does lateral plate mesoderm form?
body cavity and coverings
90
Each somite ("block") divides further into 3 sections. What are they?
1. dermatome
2. myotome
3. sclerotome
91
What is a dermatome?
Area of the skin supplied by a single spinal nerve root (develops into dermis of skin)
92
What is a myotome?
Muscle that is supplied by a single spinal nerve root; motor equivalent of a dermatome (develop into muscles)
93
What is a sclerotome?
Area of a bone supplied by/innervated by a single spinal nerve root/ segment (develop into vertebrae and ribs; bone)
94
During ebryonic period in weeks 4-8, what is another name for this period?
Organogenetic period
95
What developmental changes occur in the embryonic period (4-8) in the embryo?
- 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
What does the neural tube form? (4)
- spinal cord
- forebrain
- midbrian
- hindbrain
97
On what day does the heart start to beat?
Day 24
98
From which layer does gut formation happen?
Endoderm (and many other organs)
99
How many pairs of somites are there in the paraxial mesoderm which differentiate further in weeks 4-8?
43 pairs
100
During lateral folding of the embryo, what happens to the lateral plate mesoderm layers?
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
What happens in terms of the amniotic cavity once lateral folding occurs?
Amniotic cavity now surrounds the whole embryo
102
What do the two somatic and splanchnic mesoderm form ultimately?
somatic layer; forms body wall
| splanchnic layer; forms the circulatory system
103
Ultimately what does ectoderm form? (2)
1. epidermis of skin
| 2. neural tube
104
Ultimately what does the mesoderm form? (3)
1. paraxial mesoderm (somites; dermatome, myotome, sclerotome)
2. intermediate plate mesoderm (urogenital system; kidneys+reproductive)
3. lateral plate mesoderm (peritoneum, pleura, body cavities)
105
Ultimately what does the endoderm form? (2)
- gut
| - respiratory
106
What do somites give rise to ultimately?
- vertebrae of vertebral column
- rib cage
- part of occipital bone
- tendons
- cartilage
- skeletal muscle
107
What is teratology?
Study of when things of wrong during development?
108
What are teratogens?
environmental factors that cause abnormal development
109
What is a famous example of teratology?
Thalidomide disaster; which prevented the growth of new blood vessels in embryos, has 2 isomers; one is safe and one isn't
110
What are the main causes of abnormal development? (from most common to least)
1. unknown aetiology (60%)
2. multifactoral (20%)
3. genetic (10%)
4. environmental (10%)
111
What are some common environmental factors which can lead to abnormal developments?
- drugs (prescription/other)
- alcohol/ tobacco
- infectious agents
- others; e.g. radiaiton
112
What are common infectious agents which can transfer across the placenta and affect the developing embryo? (5)
- toxoplasma
- rubella
- cytomegalovirus
- herpes
- zika virus
113
What are common genetic factors (conditions) affecting embryonic development?
- 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
What are the common causes for genetic factors? (2)
1. increased maternal age
| 2. damage from environmental factors such as radiation e.g. x rays
115
What is the risk of teratogenesis in weeks 1-2?
- low risk of teratogens
| - high risk of death
116
What is the risk of teratogenesis in weeks 3-8?
-period of greatest sensitivity to teratogens
117
What is the risk of teratogenesis in weeks 9-38?
-decreasing sensitivity to teratogens
118
The risk posed by teratogens depends on 3 factors, what are they?
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
What are the common pre-natal diagnosis methods for malformations? (3)
1. Blood (AFP; alpha fetoprotein test)
2. ultrasound scan (12 week anomaly scan)
3. invasive tests; chorionic villus sampling and amniocentesis
120
What are the common postnatal diagnsosis methods for malformations?
1. hip stability
2. testes (descent)
3. fingers and toes
4. hearing
121
Why is the chorion sometimes sampled?
has the same genetic make up as the baby but it's a more invasive test
122
What happens in week 1 gestation in summary? (2)
1. blastocyst formation
| 2. moves to uterine cavity
123
What happens in week 2 gestation in summary? (3)
1. bilaminar embryo
2. implantation
3. placenta formation
124
What happens in week 3 gestation in summary? (3)
1. gastrulation
2. neurulation
3. somite formation
125
What happens in week 4 gestation in summary? (2)
1. folding of embryo
| 2. organogenesis
