Embryology Flashcards
Q: When does gamete formation occur in males and females?
Males: Starts at puberty and continues throughout life.
Females: Begins during fetal life, pauses, and resumes at puberty until menopause.
Q: What are the parts of a mature sperm?
Head: Contains the nucleus and acrosomal cap.
Neck: Connects the head and middle piece.
Middle piece: Contains mitochondria for energy.
Tail: Helps the sperm move toward the ovum.
Q: What is the function of the acrosomal cap in sperm?
A: It contains enzymes that help the sperm penetrate the ovum’s coverings.
Q: What are the coverings of the mature ovum?
Zona Pellucida: Glycoprotein coat with sperm receptors.
Corona Radiata: Outer layer of follicular cells.
Q: Where does fertilization occur?
A: In the ampulla of the uterine tube.
Q: What are the phases of fertilization?
Penetration of the corona radiata (hyaluronidase enzyme).
Penetration of the zona pellucida (acrosomal enzymes).
Fusion of sperm and oocyte plasma membranes.
Q: What are cortical and zona reactions?
Reactions that prevent polyspermy by:
Changing sperm-binding sites on the zona pellucida.
Making the oocyte membrane impenetrable to other sperm.
Q: What are the results of fertilization?
Formation of the zygote.
Restoration of the diploid chromosome number (46 chromosomes).
Determination of the zygote’s sex (XX or XY).
Initiation of cleavage and migration.
Q: What are the stages of early cleavage?
Day 1: 2-cell stage.
Day 2: 4-cell stage.
Day 3: 16-cell stage (morula).
Q: What is a blastocyst, and what are its components?
Outer cell mass (Trophoblast): Forms the placenta.
Inner cell mass (Embryoblast): Forms the embryo.
Blastocele: Fluid-filled cavity.
Embryonic pole: Near the embryoblast.
Abembryonic pole: Opposite side of the embryonic pole.
Q: What is in-vitro fertilization (IVF)?
A: Fertilization outside the body, with the embryo implanted into the uterus at the 8-cell stage.
Q: What is intracytoplasmic sperm injection (ICSI)?
A: Direct injection of a single sperm into the oocyte cytoplasm, used for low sperm count or penetration issues.
Q: What is gamete intrafallopian transfer (GIFT)?
A: Gametes are placed into the ampulla of the fallopian tube for natural fertilization.
Q: What is the size of a mature sperm?
A: A mature sperm is 55 microns long.
Q: What is the size of a mature ovum?
A: The diameter of a mature ovum is approximately 120 microns.
Q: What is the role of the zona pellucida?
A: The zona pellucida has sperm receptors that attract and bind sperms, facilitating fertilization.
Q: What enzyme helps the sperm penetrate the corona radiata?
A: The enzyme hyaluronidase dissolves hyaluronic acid between the corona radiata cells.
Q: What is the cortical reaction?
A: The cortical reaction prevents polyspermy by releasing lysosomal enzymes that alter sperm-binding sites on the zona pellucida.
Q: What are the pronuclei, and how are they formed?
A: The male and female pronuclei are formed when the sperm nucleus enlarges and fuses with the oocyte nucleus.
Q: How does the zygote migrate to the uterine cavity?
Peristalsis of the uterine tube muscles.
Motion of cilia lining the tube.
Mucus secretion providing nutrition and facilitating migration.
Q: When does the zona pellucida begin to degenerate?
A: At the end of the 5th day of development, allowing blastocyst formation.
Q: What are the key events of the first week of development?
Fertilization in the ampulla of the uterine tube.
Cleavage of the zygote.
Formation of the morula.
Migration to the uterine cavity.
Formation of the blastocyst.
Q: When does implantation occur?
A: It starts on the 7th day and is completed by the 11th day.
Q: Where does implantation usually occur?
A: In the endometrium of the upper part of the posterior wall of the uterus (near the fundus).
Note: It can also occur in the upper part of the anterior wall.
Q: What phase is the endometrium in during implantation?
A: The secretory phase of the menstrual cycle.
Q: What are the characteristics of the endometrium during the secretory phase?
Increased thickness of the endometrium.
Increased number and size of endometrial cells.
Glands are spiral and rich with secretion.
Arteries are spiral with arterio-venous anastomoses.
Q: What is the syncytiotrophoblast, and how does it form?
A: It is a new layer of trophoblastic cells formed at the embryonic pole. It lacks cell membranes and secretes proteolytic enzymes.
Q: What happens at the 9th day of implantation?
A: The site of penetration by the blastocyst is blocked by a fibrin clot.
Q: What role does the trophoblast play during implantation?
A: The trophoblast proliferates to form the syncytiotrophoblast, which facilitates implantation by eroding the endometrium.
Q: What are the two layers formed by the trophoblast during implantation?
Syncytiotrophoblast (outer layer).
Cytotrophoblast (inner layer).
Q: What are the two cavities formed during implantation?
Amniotic cavity.
Yolk sac cavity.
What is the double-layered embryonic disc?
Epiblast: Upper layer of cells.
Hypoblast: Lower layer of cells.
What is placenta previa?
: It is an abnormal implantation of the blastocyst in the lower segment of the uterus, near or over the internal os.
Q: What are the three types of placenta previa?
placenta previa parietalis: Placenta margin near the internal os.
Placenta previa marginalis: Placenta margin covers the internal os.
Placenta previa centralis: Placenta center completely covers the internal os.
Q: Why is placenta previa life-threatening?
It causes antepartum hemorrhage (maternal bleeding before birth).
It may lead to fetal death.
Q: What is the internal os?
A: It is the inner opening of the cervical canal of the uterus.
Q: What is an ectopic pregnancy?
A: It is the abnormal implantation of the blastocyst outside the uterus.
Q: What are the common sites of ectopic pregnancy?
Tubal: Uterine tube (ampulla, isthmus, or intramural parts).
Ovarian: On the surface of the ovary.
Omental: In the peritoneum (abdominal or pelvic cavity).
Q: What happens in a tubal ectopic pregnancy?
A: The uterine tube may rupture at the 8th week of pregnancy, leading to severe internal hemorrhage.
Q: Why does ectopic pregnancy in the uterine tube commonly occur in the ampulla?
A: The ampulla is the widest part of the uterine tube, making it a frequent site for abnormal implantation.
Q: What are the potential outcomes of ectopic pregnancies if untreated?
Rupture of the implantation site.
Severe internal hemorrhage.
Maternal shock or death if untreated promptly.
Q: How is placenta previa different from a normal implantation?
A: In placenta previa, implantation occurs in the lower segment of the uterus, whereas normal implantation occurs in the upper part of the posterior uterine wall.
Q: What is the decidua?
A: The decidua is the endometrium of the uterus after implantation of the blastocyst.
Q: What phase does the decidua represent in the endometrium?
exaggerated secretory phase
Q: What are the main features of the decidua?
Increased thickness of the endometrium.
Increased number and size of endometrial cells.
Glands become spiral and full of secretions.
Arteries become spiral and show arterio-venous anastomoses.
Q: What are the three parts of the decidua?
Decidua basalis: Lies between the implanted embryo and the myometrium.
Decidua capsularis: Covers the embryo, separating it from the uterine cavity.
Decidua parietalis: Lines the rest of the uterine cavity.
Q: Where is the decidua basalis located?
A: It is the part of the decidua that lies between the implanted embryo and the myometrium.
Q: What is the location of the decidua capsularis?
A: It covers the embryo and separates it from the uterine cavity.
Q: Where is the decidua parietalis found?
A: It lines the rest of the uterine cavity, excluding the areas of basalis and capsularis.
Q: What happens to the decidua basalis?
A: It persists as the maternal part of the placenta and is called the decidual plate.
Q: What happens to the decidua capsularis and parietalis?
A: They fuse together, obliterating the uterine cavity, and eventually degenerate.
Q: What happens to the blastocyst on the 8th day of development?
The blastocyst is partially implanted.
The trophoblast differentiates into:
Inner cytotrophoblast.
Outer syncytiotrophoblast.
Hypoblast forms as cuboidal cells facing the blastocele.
The amniotic cavity appears within the embryoblast.
Amnioblast cells secrete amniotic fluid, forming the cavity between amnioblast and epiblast.
The bilaminar embryonic disc (epiblast + hypoblast) is formed.
Q: What is the hypoblast, and when does it form?
A: The hypoblast forms on the 8th day as cuboidal cells of the inner cell mass facing the blastocele.
Q: How is the amniotic cavity formed on the 8th day?
A: It appears within the embryoblast when amnioblast cells adjacent to the cytotrophoblast secrete amniotic fluid.
Q: What structure forms between the amnioblast and epiblast?
amniotic cavity
Q: What happens on the 9th and 10th days of development?
The blastocyst becomes completely embedded in the endometrium.
The site of penetration is closed by a fibrin clot.
Heuser’s membrane (flat cells from the hypoblast) lines the blastocele, transforming it into the primary yolk sac.
The syncytiotrophoblast extends to surround the entire blastocyst.
Lacunae (empty spaces) appear in the syncytiotrophoblast (Lacunar stage).
Q: What is Heuser’s membrane, and when does it form?
A: It is a layer of flat cells derived from the hypoblast that lines the blastocele on the 9th and 10th days.
Q: What structure does the blastocele transform into on the 9th day?
A: The blastocele becomes the primary yolk sac, lined by Heuser’s membrane.
Q: What happens on the 11th and 12th days of development?
The endometrial epithelium grows over the fibrin clot (implantation completed).
Lacunae fill with maternal blood, forming utero-placental circulation.
Extraembryonic mesoderm forms from the wall of the yolk sac, appearing between:
The cytotrophoblast (external layer).
The embryonic disc with amniotic and yolk sac cavities (internal layers).
Spaces appear in the extraembryonic mesoderm.
Q: What is the role of lacunae during the 11th and 12th days?
A: Lacunae fill with maternal blood, establishing the early utero-placental circulation.
Q: What is the extraembryonic mesoderm, and when does it form?
A: It forms on the 11th and 12th days from the wall of the yolk sac and appears between the cytotrophoblast and the embryonic disc.
Q: What separates the extraembryonic mesoderm into spaces?
A: Multiple spaces appear within the extraembryonic mesoderm during the 11th and 12th days.
Q: When is implantation completed?
by the 11th and 12th days
Q: What structures are formed during the second week of development?
Bilaminar embryonic disc (epiblast and hypoblast).
Amniotic cavity.
Primary yolk sac.
Extraembryonic mesoderm.
Utero-placental circulation (via lacunae).
Q: What are the key events on the 9th and 10th days?
Complete embedding of the blastocyst.
Formation of Heuser’s membrane.
Transformation of the blastocele into the primary yolk sac.
Appearance of lacunae in the syncytiotrophoblast.
Q: What happens to the syncytiotrophoblast during the 9th day?
A: The syncytiotrophoblast expands to surround the entire cytotrophoblast and the blastocyst.
Q: What induces the formation of the central nervous system (neurulation)?
A: Growth factors secreted from the developing notochord.
Q: What is the neural plate?
A thickened median region of ectoderm between the primitive node and prochordal membrane, induced by notochord factors.
List the derivatives of Ectoderm:
Epidermis
Hair, Nails
Sweat glands
Enamel of teeth
Lens of the eye
Mammary gland
Epithelium of oral and nasal cavities
Pituitary gland
Otic placode (outer ear canal) (inner ear structure)
Brain & Spinal cord
Retina
Peripheral nervous system (sensory ganglion, Schwann cell, autonomic ganglia)
Melanocyte
Adrenal medulla
Connective tissue of the head
Bones and cartilage of the face
Aortic pulmonary septum
Lens placode
Sensory epithelium
Peripheral nerves
Site of intraembryonic mesoderm
It is present between ectoderm and endoderm except in the
following sites:
a) Buccopharyngeal membrane.
b) Cloacal membrane.
c) Median region which is occupied by developing
notochord and neural tube.
At the 17
th day, the intraembryonic mesoderm is divided
into 3 parts
. Paraxial mesoderm:
Intermediate mesoderm:
Lateral plate mesoderm
It is the part of intraembryonic
mesoderm that is present on both sides of notochord and
neural tube.
Paraxial mesoderm
It is present between paraxial and
lateral plate mesoderm
intermediate mesoderm
It is the most lateral part of intra-embryonic mesoderm
Lateral plate mesoderm:
What do cells from the cranial part of the primitive streak form
Paraxial mesoderm
What do cells from the middle part of the primitive streak form
Intermediate mesoderm
What do cells from the caudal part of the primitive streak form
Lateral plate mesoderm
What are somites?
Somites are segmented masses of the paraxial mesoderm.
Segmentation starts at the occipital region and extends caudally.
When does the first pair of somites appear?
On the 20th day of development
How many somites are formed?
42–44 pairs of somites.
What does each somite differentiate into?
Each somite divides into:
Sclerotome: Forms the vertebral column and intervertebral discs.
Dermomyotome: Forms the skeletal muscles of the body and limbs.
What does the intermediate mesoderm form?
It forms the urogenital system.
How is the lateral plate mesoderm connected cranially?
It is continuous on both sides cranial to the buccopharyngeal membrane.
Into what does the lateral plate mesoderm divide?
Pericardial cavity:
Peritoneal canals
Pleural cavities:
What is the shape of the placenta?
Disc-shaped
What is the weight of a full-term placenta?
500–600 grams.
What is the diameter of the placenta?
15–25 cm.
Where is the placenta located most commonly?
In the upper segment of the posterior wall of the uterine cavity near the fundus.
What are the two surfaces of the placenta?
The fetal surface and the maternal surface.
What are the characteristics of the fetal surface?
It is smooth.
It is covered with a transparent amnion.
The umbilical cord is attached near its center.
What are the characteristics of the maternal surface?
It is in contact with the uterine wall.
It has 15–20 elevations called cotyledons separated by grooves.
It is covered by decidua basalis.
What are the two main parts forming the placenta?
Maternal part: Decidual plate (decidua basalis).
Fetal part: Chorionic plate (chorion frondosum)
Structure of the Placenta
Q11: What are the components of the chorionic plate?
(From external to internal):
Amnion.
Somatic extraembryonic mesoderm.
Cytotrophoblast.
Syncytiotrophoblast.
What are the components of the decidual plate?
(From internal to external):
Syncytiotrophoblast.
Cytotrophoblastic shell.
Decidua basalis.
What are chorionic villi?
they are tertiary villi of the chorion frondosum.
What are the layers of chorionic villi?
Syncytiotrophoblast (outer layer).
Cytotrophoblast.
Somatic extraembryonic mesoderm.
Endothelium of fetal blood vessels.
What are the types of chorionic villi?
Stem (anchoring) villi: Extend between chorionic and decidual plates.
Floating villi: Branches that float in maternal blood for exchange of materials.
What are placental septa?
Incomplete extensions of decidua basalis into intervillous spaces.
What is the structure of placental septa?
A core of decidua basalis covered by cytotrophoblast and syncytiotrophoblast.
What are the layers of the early placental barrier?
Endothelium of fetal blood vessels.
Somatic extraembryonic mesoderm.
Cytotrophoblast.
Syncytiotrophoblast.
What are the layers of the late placental barrier?
Endothelium of fetal blood vessels.
Syncytiotrophoblast.
What hormones are produced by the placenta?
Progesterone.
Estrogen.
Human chorionic gonadotropin (hCG).
Somatomammotropin.
Why does the placental barrier become thinner in the 2nd half of pregnancy?
To allow rapid exchange of gases and nutrients for the growing fetus.
