Embryology Flashcards
At what phase of fetilisation is the male pronucleus formed?
The third phase of fertilization includes the process of degeneration of the sperm mitochondria and tail to become the male pronucleus.
Describe the sequence of oogenesis.
- oogonium,
- prophase of 1st meiotic division: primary oocyte,
- completion of 1st meiotic division: secondary oocyte and first polar body
- completion of the second meiotic division: second polar body and definitive oocyte,
- third and fourth polar bodies.
List some of the functions of the Zona pellucida
- Provides nutritional and mechanical support to the oocyte
- Helps in binding of sperm
- Protmotes acrosomal reaction
- Prevents polyspermy
List the four outcomes of fertilisation:
- Restores normal diploid number of chromosomes (46)
- Secondary oocyte completes meiosis
- The sex of the embryo is established
- Initiation of cell division (cleavage)
The rapid mitotic division of cells in a zygote is known as
Cleavage
What is the outcome of “cleavage?”
- Zygote undergoes rapid cell divisions with no overall growth, producing a cluster of cells.
- Different cells derived as a result of cleavage are called blastomeres
- Result is a compact mass/ball of cells called a morula
What are the normal sites of implantation of the embryo?
The fundus of the uterus, posterior wall of the uterus, sometimes the side walls
What is the outcome of implantation of the embryo in the fallopian tubes?
Ectopic pregnancy
What are the names of the three major germ layers in an embryo?
Endoderm, mesoderm, ectoderm
What is meant by the “ovarian cycle”?
Development of follicles, ovulation, formation and subsequent regression of corpus luteum.
Define the approximate date of ovulation and describe the hormonal background!
• Around midcycle (14 days) under the influence of FSH and LH, triggered by a surge of LH production.
Describe the processes that make the spermatozoa capable of fertilising the oocyte
- Epididymal maturation: changes in metabolism, acquiring the capability for movement.
- Capacitation: a glycoprotein coat and seminal plasma proteins are removed from the plasma membrane that overlies the acrosomal region of the spermatozoa.
- Acrosomal reaction: Release of enzymes from the acrosome: a) hyaluronidase; b) proteolitic enzymes.
Name the phases of fertilisation and describe the reactions of the fertilised oocyte.
- Penetration of the corona radiata
- Penetration of zona pellucida
- Fusion of oocyte - sperm cell membranes
- The spermatozoon (except for the cell membrane) enters the cytoplasm of the oocyte.
• Reactions of the egg: cortical and zonal reaction; resumption of the second meiotic division; metabolic activation of the egg.
What is meant by cleavage and blastocyst formation?
- Cleavage: Formation of morula and then the blastocyst by mitotic divisions of fertilized ovum.
- Blastocyst formation: fluid begins to penetrate into the intercellular spaces of the inner cell mass. The spaces become confluent and a single cavity, the blastocoel is formed: the blastocyst.
What are the components of the early blastocyst?
- Blastocyst cavity
- Outer cell mass or trophoblast
- Inner cell mass or embryoblast
How does the endometrium change during the menstrual cycle?
• Stages of the menstrual cycle:
- Menstrual phase: rupture of blood vessels and detachment of the functional layer of the endometrium.
- Regeneration phase: regeneration of the functional layer
- Proliferative phase (follicular or estrogenic stage): gradual growth of the endometrium.
- Secretory (luteal ) phase: development of the compact and spongy layers in the functional layer. Secretory activity of glands, decidual reaction of stroma cells, formation of coiled arteries within the endometrium, edema in the stroma.
- Regression: temporary contraction of coiled arteries resulting in ischaemia of the endometrium. Consecutive dilatation of vessels followed by hyperemia of the endometrium.
Where is the preferred site of implantation? List few abnormal implantation sites!
- Normal: Along the posterior. and anterior. wall of the body of the uterus, between the openings of the glands.
- Abnormal: close to the internal os of the uterus; outside the uterus (extrauterine or ectopic pregnancy): any place of the abdominal cavity, ovary, uterine tube.
What is the difference between syncytiotro-phoblast and cytotrophoblast?
Cytotrophoblast: mononucleated cells that form the inner layer of trophoblast (Langhans cell layer).
• Syncytiotrophoblast: outer multinucleated zone of trophoblast without distinct cell boundaries.
What is the role of syncytiotrophoblast during implantation?
• Secretion of proteolytic enzymes which erode the endometrial epithelium and the stroma of the endometrium, so that the blastula can penetrate, and get implanted in the endometrium.
What is the connecting stalk and how does it develop further?
- Part of the extraembryonic mesoderm containing the allantois, vitelline duct, as well as the umbilical and vitelline vessels.
- Later the amnion envelops the connecting stalk and the yolk sac stalk with their vessels, forming the primitive umbilical cord.
From which germ disk does the blood, lens of eye, epithelium of kidney tubules, and thymus develops?
a) Blood - mesoderm
b) Lens of eye - ectoderm
c) Kidney tubules - mesoderm
d) Thymus - endoderm
From which germ disk does the bone, hypophysis, chief cells of the parathyroid glands and the thyroid glands develop?
a) bone - mesoderm
b) hypophysis - ectoderm
c) chief cells of the parathyroid gland – placod plate
d) thyroid gland - endoderm
What is the notochord and the primitive pit?
- At the cephalic end of the primitive streak the primitive node develops.
- The primitive pit develops from the primitive node by cell-invagination.
- These cells migrate straightforward towards the cephalic end, and form a tube - like process: the notochordal or head process.
- The canal of the head process is the cranial extension of the primitive pit.
- The dorsal wall of the notochordal process proliferates and forms the definitive notochord.
What is the neural plate? What is meant by neural induction?
• Thickening of the ectoderm, primordium of the nervous system. The notochord has an inductive influence on the ectoderm, resulting in the formation of the neural plate.
List and characterize the different developmental stages of the placental villi!
a) Primary villi : cyto- and syncytiotrophoblast cells
b) Secondary villi: cyto- and syncytiotrophoblast cells + extraembryonic mesoderm in the centre of villi
c) Early tertiary villi: blood vessels in the mesoderm layer + the layers of the secondary villi.
d) Late tertiary villi: the cytotrophoblast partially disappears, and the syncytium and the endothelial wall of the blood vessels may be in direct contact. Villi form richly arborizing tree-like structure.
List the separating layers between fetal and maternal blood in the early and the matured placenta!
- Early: syncytiotrophoblast, cytotrophoblast, trophoblast basement membrane, connective tissue, capillary basement membrane, endothelium
- Late: syncytiotrophoblast, trophoblast basement membrane, capillary basement membrane, and endothelium. Some connective tissue may be present between the two basement membranes.
Define the term of decidua! Name its parts in relation to the implanted embryo!
Decidua: Functional layer of the gravid endometrium.
- Decidua basalis: between the chorion frondosum and myometrium. Primordium of placenta materna.
- Decidua capsularis: over the abembryonic pole.
- Decidua parietalis: rest of the decidua, except the basalis and capsularis.
Describe the parts of the full term placenta!
- Fetal portion: chorionic plate, chorion villi.
2. Maternal portion: decidua basalis.
Name the layers of the chorionic plate!
- amnionic epithelium
- central mesoderm
- chorionic mesoderm
- trophoblasts (syncytio-, and cyto-)
Define the term of cotyledon!
• The compartments of the placenta, partially separated by the decidual septa, each cotyledon consists of one or more stem villi surrounded by maternal blood.
List the functions of placenta !
- Transport and exchange of gases, nutrients, waste products,
- Transport of antibodies to fetus,
- Endocrine function,
- Mechanical protection,
- Barrier for some germs and drugs.
List the hormones that are produced by the placenta!
• Progesteron, estrogenic hormones, human chorionic gonadotropins (hCG),human chorionic somatotropin (hCS), human chorionic thyreotropin (hCT), relaxin, human chorionic adreno-corticotropin (hCACTH).
List the most common types of twin formation and characterize the relationship of placentas and the fetal membranes of the twins!
a) Monozygotic or identical twins:
i) with separate placenta, amnion and chorion.
ii) common placenta and chorion, separate amnionic cavities.
iii) common placenta, chorion and amnionic cavity.
b) Dizygotic or fraternal twins:
i) separate placenta, separate chorion, separate amnion.
ii) separate placenta and amnion, fused chorion.
Blastula
Less than 32 cells beginning on day 2.
Morula
16 cells on day 4
Where does fertilization occur?
Ampulla of fallopian tube
Blastocyst
When fluid secreted within the morula forms the blastocyst cavity on day 5. Inner cells is embryoblast (embryo), outer cells are trophoblast/placenta
Implantation
Occurs on day 6 on the posterior wall of the uterus which is in progestational phase.
Bilaminar embryonic disk
Epiblast and hypoblast form during second week from differentiation of embryoblast.
Changes during second week
Bilaminar embryonic disk forms; amniotic cavity and yolk sac form. Syncytiotrophoblast grows into endometrium reaching blood vessels.
hCG
Produced by syncytiotrophoblast stimulates progesterone production by corpus luteum. Important until week 8 when placenta produces progesterone.
Extraembryonic mesoderm
Derived from epiblast during 2nd week. Extrambryonic somatic mesoderm lines cytotrophoblast and forms connecting stalk. Extraembryonic visceral mesoderm covers the yolk sac.
Gastrulation
Week 3. Primitive streak forms within epiblast; Epiblast becomes ectoderm and gives rise to neuroectoderm and neural crest; Hypoblast becomes mesoderm and gives rise to paraxial mesoderm (35 pairs of somites), intermediate and lateral mesoderm; Epiblastic cells migrate through primitive streak to form endoderm between ecto and mesoderm
Acrosomal reaction
Spermal enzymes are released to allow penetration of zona radiata and zona pellucida.
Dorsal layer of the bilaminar disc, forms entire embryo
Epiblast
Ventral layer of the bilaminar disc forms the lining of the yolk sac, but it does not form any parts of the embryo.
Hypoblast
