Embryology Flashcards
(113 cards)
1
Q
- Definition of Embryology
A
Embryology is the branch of medicine that studies human development
2
Q
- What are the parts of the development period?
A
Embryonic period - beginning of embryo development, first eight weeks
Fetal period - begins on the ninth week of development
3
Q
- When do you start counting the weeks of development?
A
In embryology, from the fertilisation
For pregnancy, from day one of last menstrual cycle (about two weeks earlier)
4
Q
- Parts of uterine wall
A
Perimetrium - most external, vascularised
Myometrium - farthest away from the uterine cavity
Endometrium - composed by basal and functional layer
5
Q
- Classification of functional layer of the endometrium
A
Compact layer - outermost layer, dense connective tissue that surrounds the neck of uterine gland
Spongy layer - highly vascularised, connective tissue, contains branched uterine glands
6
Q
- Origin and storage of primordial germs cells.
A
Derive from epiblast during blastula development and remain dormant until puberty.
During the embryonic period the PGCs are kept aside in the yolk sac to be preserved from mutations
6th week of embryonic development - males PGCs will arrest divisions and enter premeiotic stage
5th month of embryonic development - same happens to females
7
Q
- Effects of testosterone production.
A
All secondary sex characteristics, induces testis growth and seminiferous tubules maturation and commencement of spermatogenesis.
8
Q
- Immune privilege of the testicles.
A
Sertoli cells + seminiferous tubules basement
Blood testis barrier
Needed because sperm cells are highly immune reactive
9
Q
- Function of the epididymis.
A
Allows storage and full maturation of sperm cells
Adds fluids to help the travel.
10
Q
- Capacitation of the sperm cells
A
Functional maturation that takes place as soon as it enters the female organs due the pH change
The acrosome prepares for the release of proteolytic enzymes to enter the zona pellucida
11
Q
- Reasons for infertility.
A
Males
- Problems with the enzyme in the acrosome (IVF can solve)
Females
12
Q
- Oogenesis
A
Fetal period - proliferation of immature oocyte to form primary oocyte.
Puberty - primary oocyte completes first meiotic division, forms secondary oocyte and one polar body that will degenerate
Ovulation - beginning of secondary division, which is completed in case of fertilisation
13
Q
- Male meiosis inhibitor.
A
Microenviroment factor produced by Sertoli cells to help the differentiation of male PGCs
If the PGCs fail to reach the gonads they will mature as oocytes, even with the presence of the Y chromosome
14
Q
- Menstrual cycle
A
Menstrual phase - shedding of functional layer of the endometrium
Proliferative phase - follicular cells will produce estrogen, estrogen will stimulate thickening of the uterine wall, once it’s thick enough, ovulation occurs and the mature follicle is released
Luteal phase - leftovers of the follicle degenerate and form the corpus luteum and produce progesterone inducing the differentiation of uterine wall cells in order to allow implantation
With no fertilisation, the cycle restarts
15
Q
- What is the ovarian cycle?
A
The process that leads to the development of a mature follicle, followed by follicle rupture and oocyte expulsion for fertilisation
16
Q
- How do primordial follicles mature into primary follicles?
A
Through the change of feeding cells from squamous epithelium to cuboidal epithelium (becomes thicker)
It’s yet unknown the specific process and hormones
17
Q
- Which hormone will be responsible for the maturation of the follicles?
A
FSH will help proliferation and differentiation of the primary into mature follicles
18
Q
- What are the four staged of the follicle maturation
A
- Unilaminar primary follicle (up to 150 µm, enlarged nucleus, cuboidal cells and beginning of basal lamina)
- Multifamiliar primary follicle (proliferation and stratification around oocyte, follicular cells are now granulosa or stromal cells and zona pellucida is formed)
- Secondary (antra) follicle (increased number of follicular cells and accumulation of liquor folliculi)
- Graafian (mature) follicle (formation of the antrum and corona radiata)
19
Q
- What is the function of the theca interna and esterna?
A
Interna - originated by the granulosa cells, it will produce androstenedione (male sex hormone) which will be converted into estrogen
Esterna - made of fibrous connective tissue
20
Q
- How and when the release of the oocyte happens?
A
On the day 14, a sudden surge of LH production by hypophysis will complete maturation and induce the release into the Fallopian tubes
21
Q
- What is the cumulus oophorus?
A
They are the cells that attach the oocyte to the follicle wall
22
Q
- What are the possible ends for the corpus luteum?
A
If fertilisation occurs, it increases in size and will keep producing progesterone and will begin producing hCG (human chorionic gonadotropin) that will help it’s survival
If it doesn’t, it will degenerates to corpus albicans and progesterone levels will drop causing menstruation
23
Q
- What does IVF stand for?
A
In vitro fertilization
24
Q
- What is IVF used for?
A
Induce pregnancy when fertilization isn’t possible: for example if there’s scarring in uterile tubes.
25
3003. How can the egg be retrieved to perform IVF?
FSH + clomiphene citrate (drug that prevents hypothalamic cells from detecting estrogen in blood)
26
3004. How would you check if the FSH is working using a blood test in IVF?
Estrogen level. If the FSH will actually help the follicle to grow, the estrogen level in the blood is supposed to go up.
27
3005.Once we have enough follicles ready, what do we need in order to reach complete maturation in IVF?
High Dose of LH
28
3006. At what stage is the oocyte implanted in IVF?
As late blastocyst
29
3007. What happens when blastocyst reaches uterus?
Gets rid of the zona pellucida and adheres to the uterine lining.
30
3008. What is the decidual reaction?
In endometrial stroma, adjacent cells respond to the presence of the blastocyst and of progesterone by differentiating into metabolically active cells, called decidual cells
31
3009. What do the endometrial glands right before implantation?
They enlarge, allowing vascularization of uterine wall, helping with the implantation
32
3010. What are the elements needed for implantation?
The secretion of both endometrial glands and decidual cells. They contain growth factors and metabolites that will contribute to the growth of the embryo
33
3011. What produces human chorionic gonadotropin (hCG) and what does it do?
If an embryo implants, cells of the trophoblast produce hCG, which supports the corpus luteum and thus maintains the supply of progesterone (maternal recognition of pregnancy
34
3012. What's an ectopic pregnancy?
It's when the blastocyst implants at the wrong location. Can be fatal to mother, because embryo keeps growing.
Has to be surgically stopped.
35
3013. How can ovulation be controlled?
Through the pill, contains estrogen + progestin
| Blocks release of FSH and LH
36
3014. What drugs can be used to stop a pregnancy?
1. RU-486, mifepristone, which is an antagonist of progesterone. Can be used up until 8 weeks after the last menstrual cycle.
2. Plan B (the morning-after or day-after pill) is an abortifacient. Contains progestin levonorgestrel.
Must be taken soon after intercourse. It also works by inhibiting/delaying ovulation
37
3015. What do the cells of the blastocyst differentiate in?
1. Embryoblasts (the inner cell mass), will lead to the formation of the body of the baby
2. Trophoblasts (surrounding cells) feed growing embryo
38
3016. When does implantation start?
6 days after fertilization
39
3017. What happens during initiation of implantation?
Trophoblast starts to proliferate and then differentiates into 2 cell types called:
1. Syncytiotrophoblast: outer layer that is composed of a multinucleated protoplasmic mass (formed by the fusion of cells)
2. Cytotrophoblast: inner layer of the trophoblast
40
3018. What happens at the end of first week?
Syncytiotrophoblast develops finger-like projections which increase the area between itself and the uterine wall where the blastocyst will get implanted.
41
3019. How does implantation happen?
The implantation happens with syncytiotrophoblast invading the maternal endometrium
42
3020. What's the embryonic pole?
It's an area where the syncytiotrophoblast, the cytotrophoblast and the inner cell mass are connected
43
3021. Where does implantation happen?
In the endometrium and usually in the superior part of the uterus (fundus)
44
3022. First stage of implantation (1/4)
The actively erosive syncytiotrophoblast invades the endometrial connective tissue that supports the uterine capillaries and glands.
The blastocyst slowly embeds itself into the endometrium.
45
3023. Second stage of implantation (2/4)
Syncytiotrophoblast cells produce proteolytic enzymes that degrade all the collagen in CT . Trigger apoptosis in endometrial cells, which facilitates the implantation.
Decidual cells provide a rich source of nutrients, also control the depth of penetration of the syncytiotrophoblast.
46
3024. Third stage of Implantation (3/4)
Syncytiotrophoblast continues to grow and differentiate until all of the blastocyst is surrounded.
47
3025. Fourth stage of Implantation (4/4)
Cytotrophoblast cells proliferate quickly and lose their membrane to fuse with growing syncytiotrophoblast
48
3026. How can we obtain a positive result from pregnancy test?
By checking the level of hCG in the blood at the end of the second week.
49
3027. When does the embryo becomes fully implanted in the endometrium.
Between days six and nine
50
3028. What's coagulation plug?
It's the sealing point that tells us where the implantation has occurred. This point is found on the fundus of the uterine.
51
3029. What does progesterone induce?
Uterus shift from non-receptive stage to a receptive stage.
52
3030. What happens during receptive stage?
The number of apical microvilli decreases and large pinopodes form in order to help the implantation.
53
3031. What does estrogen do?
Estrogen stimulates the endothelium of the endometrium so that it can produce insulin-like growth factor 1 and prevent the shedding of the uterine.
54
3032. What's perlecan?
Perlecan helps in the attachment is perlecan (heparan sulfate proteoglycan).
Heparan sulfate proteoglycans bind to specific extracellular matrix proteins and growth factors/cytokines that serve as attachment factors.
55
3033. What's Hb-Egf?
This factor binds to the blastocyst only if the blastocyst is capable of expressing both the Egf receptor and the heparan sulfate proteoglycan.
56
3034. Why isn’t the Conceptus Rejected by the Mother?
3 theories:
1. Fetal and maternal cells are physically separated from one another (false)
2. The conceptus is antigenically immature (true in early phases)
3. The maternal immune system is suppressed or becomes tolerant to the conceptus during pregnancy (best answer)
57
3035. When do bilaminar embryonic disc form?
When implantation is complete, end of second week.
58
3036. What are the 2 layers of bilaminar embryonic disc?
Epiblast and hypoblast
59
3037. What does bilaminar embryonic disc do?
1. The epiblast gives rise to primordial germ cells that will lead to the development and the differentiation of germ cells.
2. Gives rise to germ layers (endoderm, ectoderm, mesoderm) that form all the tissues and organs of the embryo.
60
3038. Structure formed from bilaminar embryonic disc?
- amniotic cavity
- amnion
- umbilical vesicle (yolk sac)
- connecting stalk and chorionic sac.
61
4001. When is defined the primitive dorsal-ventral axis?
As soon as the bilaminar embryonic disc is formed, epiblast refering to dorsal and hypoblast to ventral
62
4002. How and when is formed the amnion?
Cell migration from the epiblast throughout the embryonic pole around the 8th day
63
4003. What is the function of the amniotic fluid?
Protection and shock absorber
64
4004. What is the heuser’s membrane?
Is the layer of the cells lining originated by the first wave of migration of the hypoblast, also known as primary yolk sac or exocoelomic membrane
65
4005. What is the extraembrionic mesoderm?
Loosely arranged fibroblasts that will give be responsible for the future formation of the placenta. Its not yet known where it is originated from.
66
4006. What is the chorion ?
Trophoblast tissue together with blood vessels. Futurely will form the placenta together with the uterine wall.
67
4007. How and when is the chorionic cavity formed?
The mesoderm will proliferate until it covers the whole embryo and then it will split giving rise to the chorionic cavity (also known as extraembryonic coelom) by the 11th day
68
4008. What does the extraembryonic mesoderm divides into?
Extraembryonic somatic mesoderm - attached to cytotrophoblast and amnion
Extraembryonic splanchnic mesoderm - lining with the yolk sac
69
4009. How and when the definitive yolk sac is formed?
On the 12th day, a secondary wave of migrating cells from the hypoblast will give rise to the secondary yolk sac (also known as umbelical vesicle), that will squeeze and degrade the primary one, becoming the definitive.
70
4010. What is Meckel’s diverticulum?
Anomaly on the digestive tract caused by the permanence of the yolk sac after birth
There’s no need to be removed
71
4011. What is the connective stalk?
Part of the extraembryonic mesoderm that will keep the developing embryo connected to the cytotrophoblast
72
4012. How does the embryo get nutrients in early development?
During the first week, by simple diffusion since it is still small and with few cells
73
4013. When does the uteroplacental circulatory system starts to develop?
During the second week
74
4014. How does the exchange of metabolites and gases between mother and fetus occur?
Through diffusion, blood is never mixed
75
4015. What are the trophoblast lacunae?
Vacuoles that open within the syncytiotrophoblast from the 9th day, they will fuse to form lacunar networks
76
4016. What are maternal sinusoids?
Maternal capillaries that expanded towards the syncytiotrophoblast
77
4017. Primary chorionic stem villi
Formation of lacunar networks and maternal sinusoids
formation of a network of maternal blood vessels in the lacunar network
Proliferation and extension of the cytotrophoblast overlaying the syncytiotrophoblast
78
4018. Secondary chorionic stem villi
Formed around the 16th day with the penetration of the extraembryonic mesoderm on the core of the primary chorionic stem villi
79
4019. Tertiary chorionic stem villi
Formed by the end of third week, we have the formation of blood vessels in the extraembryonic mesoderm
Blood mixing still not possible thanks to the syncytiotrophoblast.
80
4020. When does the heart starts to be developed?
Around the 22nd day we already have a primitive heart and a heartbeat can already be heard
81
4021. How does the exchange between mother and fetus occur?
Maternal oxygenated blood flows into the trophoblastic lacunae from the spiral endometrial arteries while deoxygenated blood flows from the lacunae to the endometrial veins
Nutrients gases and waste cross the placental barrier
82
4022. What the placental barrier consists of?
Endothelium of the villus capillaries
Extraembryonic mesoderm (loose connective tissue)
Cytotrophoblast
Syncytiotrophoblast
83
4023. What is the rule of two?
```
Week 2
Embryoblast splits in 2 layers
Trophoblast gives rise to 2 tissues
Formation of 2 yolk sacs
Formation of 2 cavities
Extraembryonic mesoderm splits in 2 layers
All become 2 layered membranes
```
84
5001. What processes are responsible for the formation of the cardiovascular system?
Vasculogenesis - gives rise to heart and first primitive vascular plexus
Angiogenesis - remodelling and expansion of the vascular network
85
5002. How does the vasculogenesis takes place?
1. MSC differentiate into endothelial cell precursors and angioblasts (vessel-forming cells) will aggregate and form blood islands
2. Appearance of cavities within blood islands
3. Appearance of hemangioblasts (blood cells progenitor) from blood vessels’ mesoderm and organization around the cavities to give rise to primordial endothelium.
4. Endothelium-lined cavities fuse into a primordial vascular network of endothelial channels
86
5003. How does the angiogenesis takes place?
Vessels sprout into non vascularised areas and fuse with other vessels
There’s is the development of erythroblasts from the hemangioblasts in the yolk sac
Mesenchymal cells surround the primordial blood vessels differentiate into muscle and connective tissue
Formation of a primordial heart tube from endothelium-line channels or endocardial tubes and joining with blood vessels
Formation of primordial cardiovascular system
87
5004. What are stem chorionic villi?
Villi that attach to the maternal tissues through cytotrophoblastic shell
Also called anchoring villi
88
5005. How does the exchange between mother and fetus takes place?
By diffusion, on the terminal villi
The molecules have to cross four different layers
- endothelium of the villus capillaries
- loose connective tissue in villus core
- cytotrophoblast
- syncytiotrophoblast
89
5006. When does gastrulation takes place?
On the third week, bilaminar embryonic disc becomes trilaminar
90
5007. What are the three main events of gastrulation?
- appearance of primitive streak
- development of the notochord
- differentiation of the three germ layers
91
5008. What is the gastrulation?
The beginning of morphogenesis, development of the body form
| Formation of the trilaminar embryonic disc
92
5009. How does the primitive streak is formed?
15th - thickening of the mainline on both caudal and dorsal side as a consequence of proliferation and migration of epiblast cells
Elongation of primitive streak until reach same length of the embryonic disc
The primitive streak always start at the caudal side of the embryonic disc
93
5010. What is the primitive node?
Nodular area
Contains a depression called primitive pit
Is connected to the primitive groove
94
5011. How does the trilaminar layer is formed?
The epiblast cells enter trough the primitive groove
Firstly they displace the hypoblast cells forming a new proximal cell layer, the endoderm, that will in the future give rise to the lining of the gut and derivatives
By the 16th day the remaining cells of the epiblast will now be called the ectoderm, the most distal layer
Some invaginated epiblast cells remains between the two previous layers forming the mesoderm on the beginning of the 3rd week
95
5012. Hormonal stimulation of endothelial to mesenchymal transition
TGFß and Wnt families from extraembryonic region stimulates epiblast to express nodal
Nodal and Fgf8 stimulate transcription factors which allows the formation of the primitive streak
One of these transcription factors is the Snail, that activates or represses important genes for cell adhesion
96
5013. How does the process of vasculogenesis takes place?
Extraembryonic mesoderm start to form blood islands (cluster of angioblasts)
Formation of cavities inside the blood islands and appearance do hemangioblasts from mesodermal endothelial cells
Angioblasts start to become flattened and surrounding the cavities (primordial endothelium)
Fusion of these cavities form a primordial vascular network
97
5014. What are the subdivisions of the mesoderm?
Cardiogenic mesoderm
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
98
5015. What are the four morphogenic movements involved in the gastrulation?
Epiboly - spreading of an epithelial sheet (most important)
Emboly - movement inside an epithelial sheet
Convergence - toward the midline
Extension - lengthening in the cranial-caudal plane
99
5016. How is the notochord formed?
17th day - mesenchymal cells migrate from primitive node to the underlying layer forming a tube-like structure, the notochordal canal
It elongates cranially until the prechordal plate
21st day - notochordal canal reaches maximum elongation
Notochordal canal fuses with the endoderm forming the oropharygeal membrane (future mouth) and the notochordal plate
Notochordal plate will deatach from the endoderm and form a solid cord
100
8001. What is the placenta and when is it formed?
It’s the primary site of exchange of nutrients and gas between mother and baby and its completed by week 9-10
101
8002. What composes the placenta?
There is two components
The fetal part that develops from the chorionic sac and the maternal part that comes from the decidua
102
8003. What is the decidua?
It’s the functional layer of the endometrium that separates from uterus after childbirth. It has three regions, basalis, capsular is and parietalis.
103
8004. Describe the different parts of the decidua
Basalis — it’s the part deep in the embryo forming the maternal face of the placenta and it’s connected to the embryo, it’s where the connective stalk (future umbilical cord) is found
Capsularis — superficialities part overlaying the concept us, covers the fetus on the opposite to the basalis
Parietalis - all the leftover endometrium
Parietalis and capsularis together fuse into the decidua Vera
104
8005. What is the decidua reaction?
Due to the increased progesterone levels, the connective tissue of the decidua enlarge as glycogen and lipid accumulate into the decidual cells cytoplasm in order to feed the baby in this first phase
105
8006. Where can the chorionic villi be found?
A part of them will invade the decidua basalis (anchoring villi) and the other will be floating in the uterine cavity (floating villi)
By the 8th week they should be covering the entire chorionic sac
106
8007. What is the smooth chorion
An area in the placenta formed in the 8th week from the degeneration of the villi associated with the decidua capsularis
107
8008. What is the chorion frondosum?
The area formed through the enlargement of the villi associated with the decidua basalis in the 8th week to compensate the smooth chorion
108
8009. How are the umbilical vessels formed?
On the 8th week the extraembryonic mesoderm enters the yolk sac where there’s going to be the formation of two arteries and one vein
109
8010. When does the uterine cavity disappears?
By the 3rd month, due to the baby growth and the fusion of the decidua capsularis and parietalis
110
8011. What’s the process of mother-child exchange?
1. Maternal blood enter the intervillous space through the spiral arteries found in the decidua basalis, through gaps in the cytotrophoblastic shell.
2. The intervillous space is drained by endometrial veins that also penetrate the cytotrophoblastic shell
The syncytiotrophoblast covers the fetal villi not allowing the blood to mix
111
8012. What defines the shape of the placenta?
The shape of the chorion frondosum, so it will be a discoid shape
112
8013. What are the cotyledons and how are they formed?
It’s the spaces in the intervillous space divided by septa, each one has at least two stem villi and several branched villi
They are formed during placental formation, as chorionic villi invade the decidua basalis and the decidual tissue is eroded, producing the septa projecting towards the chorionic plate
113
8014. How is the amniochorionic membrane formed?
Due to the embryonic folding, the amniotic sac eventually covers the entire embryo and fuse with the smooth chorion forming the amniochorionic membrane
The amniochorionic membrane fuses with the decidua capsularis that eventually will disappear and fuse with the decidua parietalis.
