Embryology Flashcards
(98 cards)
1
Q
What is embryology?
A
Drama of life before birth
2
Q
List the stages of development of the human?
A
- Pre-embryonic phase 0-3 weeks
- Embryonic phase 4-8 weeks
- Foetal phase 9-40 weeks
- Postnatal, childhood, adolescence…
3
Q
What are spermatagonia and oogonia?
A
Parent cells containing 46 chromosomes
4
Q
When do spermatogonium undergo meiosis?
A
After adolescence
5
Q
In females, when does meiosis 1 occur? What happens subsequently?
A
Occurs prior to birth and is arrested. Each month a matured ovum is formed and released.
6
Q
What is a characteristic of every sperm and ovum released?
A
Each are genetically unique
7
Q
How much sperm surrounds and penetrates the ovum?
A
Several surround, one penetrates
8
Q
What components of the sperm penetrates the egg?
A
Pro nucleus i.e. just the chromosomes enter and fuse with the pronucleus of the ovum (thus forming the first cell of the human body)
9
Q
What is the term for the first cell of the human body and how many chromosomes are present?
A
Zygote (46 chromosomes)
10
Q
How much sperm is formed during meiosis?
A
4
11
Q
What is formed during meiosis 1 in oogenesis?
A
1 ovum and 3 polar bodies
12
Q
What happens during week 1 of the pre embryonic phase?
A
Zygote is formed and divides to form a blastocyst. This moves through the uterine tube, to reach the uterine cavity?
13
Q
What does the zygote divide to form?
A
Blastocyst
14
Q
46 chromosomes indicates what kind of cell?
A
Diploid cell
15
Q
Which parent does the mitochondria come from?
A
Mother
16
Q
By which process does the zygote divide?
A
Mitosis
17
Q
The continuous division of cells eventually results in the formation of what?
A
Morula
18
Q
What is Leber’s hereditary optic neuropathy?
A
blindness caused due to mitochondrial DNA being abnormal
19
Q
By definition what is a solid mass of cells?
A
Morula
20
Q
What happens when the number and size of cells begin to increase?
A
Nutrition to the central core of cells starts becoming difficult
21
Q
What is formed to assist the nutrition delivery as the number and size of cells increase?
A
Blastocystic cavity?
22
Q
What is a blastocystic cavity?
A
reorientation of cells
23
Q
What does a blastocyst consist of?
A
outer and inner cell mass
24
Q
What does the outer lining of the cell mass called?
A
trophoblast
25
How does the endometrium grow?
due to hormone release
26
What processes are at the end of the fallopian tubes?
fimbrae
27
Where does fertilisation occur?
End of the fallopian tube
28
What happens to mitosis as the cell passes through the fallopian tube?
Mitosis speeds up
29
How does the ovum and eventually zygote move up the tube?
Simple cilialted epithelium which beats the zygote up the tube
30
What happens when the uterine gains infection?
repaired, fibrosis scar tissue forms and cilia is lost
31
How long does the first, second and 3 cell division take respectively?
36 hrs
24 hrs
12 hrs
(successive cell divisions take lesser time)
32
What happens by day 5 or 6?
the blastula has formed and has reached the uterine cavity ready to implant in it.
33
What could occur if cilia function is abnormal?
Ectopic pregnancy
34
What happens in week 2 of the pre-embryonic phase?
- Implantation
- Cells that later form the embryo form a bilaminar disc
- Sacs, membranes and cord to nourish the human conceptus
(baby) start to form
35
Where does implantation occur and what happens?
At ~ 7 days the blastocyst begins to burrow into the uterine wall (endometrium)
36
What plays an important role in the burrowing of the blastocyst?
Chorion
37
How is the chorion developed?
further development of the trophoblast (divided into 2 layers)
38
What is a chorion?
mushy plate like disc (without cell membrane)
39
What does the chorion do/what is it part of?
1. Implantation process (chorionic villi)
2. Forms part of the placenta in due course
3. Secretes human Chorionic gonadotropin (HCG)
40
What is HCG used for?
To detect pregnancy
41
What doe hCG do?
help maintain the endometrium
| by circulating through maternal blood (and urine)
42
when do levels of hCG increase?
Levels of hCG increase till around 12 weeks -18 weeks gestation
43
What happens to the cells of the inner cell mass?
The cells of the inner cell mass form a 2-layered flat disc called the BILAMINAR DISC which are epiblast and hypoblast.
2 cavities begin to form which are the
Amniotic cavity and
Yolk sac
44
What is the purpose of the Yolk Sac?
embryo feeds off as well as the blood vessels and transfer of nutrients through placenta
45
What is the placenta formed from?
Chorionic villi
46
What are the main functions of the placenta?
1. Foetal nutrition
2. Transport of waste and gases
3. Immunity
47
The feotal part of the placenta contains what and is what texture?
foetal blood vessels and is smooth
48
The maternal part of the placenta contains what and is what texture?
Rough and has maternal blood vessels
49
The blood from maternal side does not mix with blood from uterus. So how do exchanges occur?
Via diffusion
50
In what weeks does the placenta mature?
18-20wks
51
Fraternal twins originate from how many zygotes? What does this say about their genetic makeup? How many placanta?
2 - dizygotic
| Different genetic makeup, 2 placantae
52
Identical twins originate from how many zygotes? How many placanta?
One - monozygotic (zygote divides into two by mitosis)
| Same genetic makeup, share placenta
53
What processes occur in week 3?
1. Gastrulation
2. Neurulation
3. Development of Somites
4. Early development of CVS
5. Primitive streak
54
What is GASTRULATION
| Discuss what happens during this process.
FORMATION OF 3 GERM LAYERS (specialisation of cells)
1. Epiblast cells migrate into space between epiblast and hypoblast layers
2. Primitive streak is formed
3. Cells of primitive streak invaginate and displace Hypoblast
Forms 3 germ layers:
- Ectoderm
- Mesoderm
- Endoderm
55
What does it mean by trilaminar disc?
Ectoderm
Mesoderm
Endoderm
56
What does each germ layer of the trilaminar disc give rise to?
1. Ectoderm - forms skin and nervous system (including neural tube)
2. Mesoderm - forms vertebrae, muscles, cavities etc
3. Endoderm - gut, respiratory system e.g.lungs
57
What is the notochord and how is it formed?
- A solid of cells
- First back bone.
- Formed from primitive streak and trimlaminar disc
58
what eventually happens to the notochord?
Most of the notochord degenerates. The remnant of the notochord persists as the nucleolus pulposus
59
What is the function of the notochord?
Notochord sends out signals (SHH pathway) thus induces ectodermal cells in the midline to form the neural tube.
60
What does the neural tube form?
forebrain, midbrain, hindbrain and spinal cord development
61
How is the neural tube formed?
Notochord sends signals which thicken cells and form a neural plate.
As a result, cells thicken, forming a nueral plate.
This plate sinks to form the neural tube
62
What is the function of the neural tube?
Induces the medoserm to thicken
63
The thickened mesoderm separates into 3 parts, what are these parts called?
1. Paraxial mesoderm - either side of axis
2. Intermediate plate mesoderm
3. Lateral plate mesoderm
64
What does the lateral plate mesoderm split to form?
Somatic and splanchnic mesoderm
65
What is the space that is formed between the somatic and splanchnic mesoderm?
Intraembryonic coelom
66
The paraxial mesoderm further segments itself into bricks known as what?
Somites
67
What innervates each pair of somites?
spinal nerves
68
How many somites are there?
43 pairs
69
What is derived from somites?
Dermatome
Myotomes
Sclerotome
70
What do dermatomes form?
Dermis of the skin
71
What do myotomes form?
skeletal muscle
72
What does the sclerotome form?
bones including the vertebrae
73
How is the embryo able to fold on it's lateral ends?
due to the weight of the mesoderm
74
What covers the baby upon lateral folding?
Amniotic sac
75
What forms part of the gut upon lateral folding
Yolk sac (endoderm)
76
What does the intermediate plate mesoderm form?
Urogenital system (kidneys and reproductive system)
77
What does the lateral plate mesoderm form?
Peritoneum, pleura and body cavities
78
What day does the heart start to beat
day 24
79
During what weeks does the pharyngeal arches develop?
Between 4th and 8th week
80
What is teratology
Study of when things go wrong during development
81
What are teratogens
environmental factors that cause abnormal development.
82
What causes Congenital rubella syndrome (catarax)
contraction of german measles when pregnant
83
What caused malformed limbs?
maternal use of thalidomide
84
What are the breakdown causes of abnormal development?
60 unknown aetiology
20 multifactorial
10 environmental
10 genetic
85
Name some environmental factors that can cause abnormal development
- Drugs e.g. prescriptions
- Alcohol/ tobacco
- Infectious agents e.g. Rubella
- Others - eg: radiation
86
Name some genetic factors that can cause abnormal development
- Too many/too few chromosomes e.g. Down's syndrome and Turner's syndrome
- Structural changes - deletions of genes, segments of chromosomes from increased maternal age for example
87
What are the risks of teratogenesis during week 1-2?
High risk of death, low risk from teratogens
| Spontaneous abortion is most likely to occur
88
What period of development has greatest sensitivity to teratogens?
week 3-8
89
Why is week 3-8 known as a danger period to the risks of teratogenesis?
Danger period as when things/systems begin to develop there is a high risk of major defects
Mum may still not know they are pregnant so could be taking supplements to aid themselves but harmful to the babies development.
90
What weeks have a decreasing sensitivity to teratogens?
week 9-38
91
The risk posed by a teratogen depends on what 3 factors?
- 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
92
How would you diagnose malformations prenatally?
o Blood - (to check for alpha fetoprotein)
o Ultrasound scan - 12-week anomaly scan
o Invasive tests: chorionic villus sampling and amniocentesis
93
How would you diagnose malformations postnatal?
```
Looking at;
o Hip stability
o Testes (descent)
o Fingers and toes
o Hearing
```
94
Between what weeks does the respiratory system develop?
4-8
95
When and where do the lungs and trachea develop from?
4 weeks of gestation
| Ventral wall of the foregut
96
What is the adult relationship between the oesophagus and the trachea?
Trachea anterior to oesophagus
97
The folding of the embryo gives rise to what?
Primitive gut tube formed from the embryo
98
The gut tube forms from the endoderm. What are the different parts of the gut?
foregut
midgut
hindgut
