early embryogenesis Flashcards
1
Q
what is the germinal period
A
- first 2 weeks
- begins with fertilisation
- where the sperm fertilises the egg to form a zygote
2
Q
what is the embryonic period
A
- weeks 3-8
- where the major organs and structures of the organism develop eg. neural tubes, heart, limbs
3
Q
what is the fetal period
A
- weeks 9 - birth
- characterised by the growth and maturation of existing structures
4
Q
what is LMP
A
- last menstrual period
5
Q
how much longer is clinical gestational timings than embryologist timing
A
2 weeks longer
6
Q
what is gametogenesis
A
germ cell development
7
Q
where does gametogenesis take place
A
in the gonads - testes and ovaries
8
Q
what is spermiogenesis
A
development of male germ cells
9
Q
what is oogenesis
A
development of female get, cells
10
Q
what is PGC’s
A
- primordial germ cells
- develop into germ cells of both sexes
11
Q
when do you find PGC’s
A
- 3rd week of embryonic development
- in the wall of the yolk sac
12
Q
where do PGC’s migrate too
A
- primodrium of the gonads
- enter gametogenesis as spermatogonia or oogonia forming sperms or oocytes
13
Q
describe the timeline from 1-33 weeks for the development of undifferentiated gonads
A
week 1-6 - no sexual differentiation
week 6-7 - differentiation of the mesonephric and paramesonephric ducts begins
week 12- development of external genitalia complete
week 20 - phenotypic differentiation is complete
week 33 - descent of gonads is complete
14
Q
what gene codes for the testis determining factor
A
- SRY gene found on the Y chromosome
15
Q
what does testis determine factor do
A
stimulates the differentiation of the primitive sex cords into testes
16
Q
what does ductal differentiation do
A
- wolffian in males and mullerian in females
- development of embryonic ducts into internal sex organs
17
Q
what does external genitalia differentiation depend on
A
relies on estradiol and dihydrotestosterone (DHT)
18
Q
what are PGC’s converted to by 3rd month
A
oogonium
19
Q
how to oogonia proliferate
A
- mitosis
- fetal life in ovary
20
Q
what forms when oogonium enlarges
A
primary oocyte
21
Q
what are primary oocytes
A
within the primordial follicle begins the first meiotic division in embryo
22
Q
how long do primary oocytes remain arrest
A
12-50 years
23
Q
where does spermatogenesis take place
A
seminiferous convoluted tubules of the testes
24
Q
how long does a cycle of spermatogenesis last
A
60-74 days
25
what are the 3 phases of spermatogenesis
- spermatogonial phase
- spermatocyte phase
- spermatid phase
26
what occurs in spermatogonial phase
spermatogonia divide by mitosis to replace themselves and provide a population of spermatogonia which then goes onto primary spermatocytes
27
what happens in the spermatocyte phase
primary spermatocytes undergo two meiotic divisions to reduce chromosome number to produce haploid cells called spermatids
28
what occurs in the spermatid phase
spermatids differentiate into mature sperm cells
29
what happens when spermatogenesis is complete
sperm enter the lumen of the seminiferous tubules and move to the epididymis where they are stored and become functionally mature
30
what are the [arts of the sperm
- head
- neck
- tail or flagellum
31
what is found in the head of the sperm
- nucleus with haploid set of chromosomes
- acrosome which contains enzymes for penetrating female egg
32
what is the acrosome a deviation of
golgi complex
33
what does the neck of a sperm contain
proximal centriole
34
what the 3 parts of a sperms tail
- middle piece
- principal piece
- end piece
35
what does the middle piece of a sperms tail contain
- distal centriole
- central axoneme
- mitochondria
36
what does the principal price of the sperms tail contain
- axoneme surrounded by a sheath of fibres
37
what does the end piece of the sperm tail contain
- duplication of plasma membrane and some fibres only
38
what are the parts of the oocyte
- nucleus
- cytoplasm
- york inclusions
- cortical granules
39
what does yolk inclusions do
nutrition to the embryo for the first time
40
what do cortical granules do
contain conical reaction with prevent polispermia
41
what does the protective covering contain in oocytes
- cytolemma - cell membrane
- zona pellucida - contain proteoglycans (receptors for sperm)
- corona radiata - layers of follicular cells
42
what are the main stages of embryogenesis
1) fertilisation
2) cleavage
3) implantation
4) gastrulation
5) histogenesis
6) organogenesis
7) development of organ systems
43
where does fertilisation occur
ampulla of the uterine tube
44
what does the layer of zona pellucida prevent
ectopic pregnancy
45
what is the distant phase of fertilisation
- taxis - active movement of sperm
- chemotaxis - follow concentration gradient of female reproductive tract
- rheotaxis - ability to move against fluid
- capacitation - glycoprotein coat removed from surface of sperm so acrosone secretes substances in uterus
46
what occurs if there is successful capacitation
hyperactivation by influx of Ca2+ into tail of sperm
47
what occurs in the contact stage of fertilisation
- acrosome reaction releasing enzymes to destroy zona pellucida
- cortical reaction - release enzymes, oocyte membrane becomes impenetrable to prevent polyspermia
48
what is the type of cleavage determined by
the amount of yolk in the egg fertilised
49
what are the types of cleavage
holoblastic - total
unequal - uneven distribution of cytoplasm between daughter cells
asynchronous - different speed of division in different cells
50
what occurs in cleavage
repeated mitotic division of zygote
51
where does cleavage take place
uterine tube
52
what are the results of cleavage
- around 16 cells form morula which is without cavity inside
- later small cavity occurs which is a blastocyst
53
what is the structure of blastocyst
- inner mass that forms embryoblast
- outer cell mass - forms trophoblast - connects mother and embryo
- cavity - blastocoele
54
what occurs at inplantation (5-6) days
- adhesion - uterus enters secretory/ lurer phase (implantation window)
- invasion
55
when does luteal phase occur
6 days after luteinzing hormone peak
56
what is blastocyst hatching
breakdown or thinning of zona pellucida
57
describe adhesion in implantation
- trophoblast subdivide into inner layer ( cystotrophoblast) and outer layer (syncytiotrophoblast)
58
what do L selection on trophoblast cells do
initial attachment of blastocyst to uterus
59
what is the invasion stage of implantation
- syncytiotrophoblast produce enzymes with destroy endometrium of uterus
- trophoblast enters direct contact to blood of mothers vessels
60
what is an ectopic pregnancy
implantation of embryo outside the uterus
61
what are the risk factors for ectopic pregnancy
- endometriosis
- pelvic inflammatory disease
- tubular pelvic surgery
- exposure to diethylstilbestrol.
62
what are the symptoms of ectopic pregnancy
- abnormal or uterine bleeding
- sudden abdominal pain
- missed period
- positive chorionic gonadotropin test
- positive sonogram
63
what type of nutrition does the embryo get before invasion
histiotrophic - uptake of oviductal and uterine secretions by trophoblast
64
what type of nutrition do embryo receive after invasion
haemotrophic - exchange between maternal and fetal circulations within the placenta
65
what is hCG
a glycoprotein produced by syncytiotrophoblast
stimulates progesterone promotion by corpus luteum
66
what is corpus luteum
temporary endocrine gland that appears in second part of cycle and prepares organism for pregnancy by producing progesterone
67
how can hCG be assayed
blood or urine in early pregnancy
68
what does low hCG predict
spontaneous abortion or ectopic pregnancy
69
what does Hugh hCG predict
multiple pregnancy, hydatiform mole or gestational trophoblastic disease
70
what is the decidual reaction
changes in endometrium induced by implanted baslocyst
71
when does decidual reaction begin
3rd day after fertilisation and continues throughout whole endometrium
72
what occurs in decidual reaction
- local proliferation of vessels near blastocyst transforming the to sinusoids
- differentiation of stroll fibroblasts of lamina propria into secretory decidual cells
73
what is gastrulation
formation of three germ layers of the embryo
74
what are the three germ layers of the embryo
- ectoderm
- mesoderm
- endoderm
75
what are the two stages of human gastrulation
early - delamination
late - migration and invagination
76
what occurs in delamination
- embryo blast splits into epiblast and hypoblast
- 2 fluid sacs - amniotic and yolk
- floor of the amnion and roof of the yolk sac from a two layered plate or embryonic disc
77
what are stem cells
undifferentiated cells with unique ability to develop into various specialised cell types
78
what is found in the wall of the yolk sac
- first primitive vessel and blood elements
- primordial germ cells which migrate to the bases of the gonads
79
what is the stages in the formation of the amniotic cavity and primary yolk sac
1) small cavity between ectoderm and trophoblast forming amniotic cavity
2) trophoblasts split and from roof of amniotic cavity
3) cells of endoderm proliferate and line cavity of blastocyst
4) cavity is now primary yolk sac
5) flattened cells lining primary yolk sac form heusers membrane
80
what are the cells derived from trophoblasts called and what do they do
amniogenic cells
secrete amniotic fluid within amniotic cavity
