Embryology Minimals

Describe the sequence of oogenesis

1. Oogonium2. Prophase of 1st meiotic: primary oocyte.3. Completion of 1st meiotic division: secondary

oocyte and first polar body.4. Completion of the 2nd meiotic division:

second polar body and definitive oocyte.5. 3rd and 4th polar bodies.

Name the stages of development of the ovarian follicle in sequence. Make a drawing of the Grafian follicle &

label the major parts• Primordial, primary, secondary (growing), tertiary or vesicular

follicle. • 1. Theca externa• 2. Theca interna• 3. Follicular antrum with fluid• 4. Cumulus oophorus• 5. Corona radiata• 6. Membrana granulosa • 7. Oocyte• 8. Zona pellucida

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Define the term “ spermiogenesis”. Describe the spermatogenesis in sequence. Draw a mature spermium and label parts.

• Spermiogenesis = formation of spermatozoa from spermatid.

• Sequence of spermatogenesis: spermatogonium, primary spermatocyte, secondary spermatocyte, spermatid.

• 1. Head• 2. Neck• 3. Middle piece • 4. Principal piece• 5. End piece

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Which cells of spermatogenesis are isolated from the blood-born antigens by the blood-testis barrier?

• Late primary spermatocytes• Secondary spermatocytes • Spermatids• Sperm cells (spermatozoa)

What is meant by the “ovarian cycle?”

• Development of follicles, ovulation, formation and subsequent regression of corpus luteum.

Acronym: FOF

Define the approx. date of ovulation and describe hormonal background!

• Around midcycle (14 days) under the influence of FSH and LH triggered by a surge of LH production

What is the fate of matured ovarian follicle?

1. Release of the oocyte by rupture of the follicle: ovulation2. The collapsed wall of the follicle surrounds a central clot of retained

blood and follicular fluid (corpus hemorrhagicum). From the granulosa cells the granulosa luteal, and from the theca interna cells, the theca luteal cells develop respectively.

3. In case of pregnancy, corpus luteum further develops and forms the persisting corpus luteum, otherwise it degenerates and becomes corpus albicans.

4. Matured, but discharged follicles undergo degeneration resulting in atretic follicles.

From which structure does corpus luteum develop, and what does it secrete?

• From corpus hemorrhagicum, by proliferation of theca interna, & granulosa cells.

• Progesteron and oestrogen

Describe the processes that make the spermatozoa capable of fertilizing the oocyte!

• Epididymal maturation: changes in metabolism, acquiring the capability for movement.

• Capacitation: a glycoprotein coat & 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: hyaluronidase & proteolitic enzymes

Names the phases of fertilization and describe the reactions of the fertilized oocyte!

1. Penetration of the corona radiata2. Penetration of zona pellucida3. Fusion of oocyte – sperm cell membranes4. Spermatozoon (except cell membrane) enters

cytoplams 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 blastocele is formed (the blastocyst)

Make a schematic drawing of the early blastocyst and label major parts!

1. Blastocyst cavity2. Outer cell mass or trophoblast3. Inner cell mass or embryoblast

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How does the endometrium change during the menstrual cycle?

Stages of menstrual cycle: 1) rupture of blood vessels and detachment of the functional layer of the endometrium2) Regeneration phase: regeneration of functional layer3) Proliferative phase (follicular or estrogenic stage): gradual growth of the endometrium4) 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.5) 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 implantations!

• Normal: Along the posterior and anterior body wall 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 or uterine tube.

Names those parts by the arrow!

1. Syncytiotrophoblast with lacunae2. Cytotrophoblast3. Amnionic cavity4. Epiblast (Ectoderm)5. Hypoblast (Endoderm)6. Exocoelomic cavity (primitive yolk sasc)7. Exocoelomic (Heuser’s) membrane

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What is the difference between syncytiotrophoblast and cytotrophoblast?

• Cytotrophoblast: mononucleated cells that form the inner layer of trophoblast (Langhans cell layer)

• Syncytiotrophoblast: outer multinucleated zone of trophoblast without distinct cell boundries

What is the role of syncytiotrophoblast during implantation?

• Secretion of proteolytic enzymes which erode the eendometrial epithelium and the stroma of the endometrium, so that the blastula can penetrate, and get implanted in the endometrium

What is the difference between the extraembryonic and intraembryonic mesoderm?

Where do they originate from?• Extraembryonic mesoderm: derives from the

trophoblast and form a fline, loose connective tissue, which is located outside the embryo.

• Intraembryonic mesoderm: the third germ layer between the epiblast and hypoblast layers.

• Origin: Epiblast

List the components of the extraembryonic mesoderm

1. Somatopleuric mesoderm2. Splanchnopleuric mesoderm3. Connecting stalk4. Chorionic mesoderm

What is the connecting stalk and how does it develop further?

• Part of the extraembryonic mesoderm containing the allantois, viteline duct, as well as the umbilical and vitellin 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, eye lens, epithelium of kidney tubules and thymus

develop?• Blood – mesoderm• Lens of eye – ectoderm• Kidney tubules – mesoderm• Thymus - endoderm

From which germ disk does bone, hypophysis, chief cells of parathyroid glands and the thyroid

glands develop?• Bone – mesoderm• Hypophysis – ectoderm• Chief cells of the parathyroid gland – placod

plate• Thyroid gland - endoderm

Make a drawing showing the dorsal view of a 16-day old embryo, & Label!

1. Prochordal plate2. Notochordal process3. Primitive streak4. Primitive node5. Future cloacal membrane6. Ectoderm

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Make a drawing showing transverse section of the trilaminar germ disc at the cephalic part of an 18-

day old embryo, label!1. Mesoderm2. Notochord3. Ectoderm4. Entoderm5. Yolk sac

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What is the notochord and the primitive pit? Indicate place in 16-day old embryo.

• 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.

1. Amnionic cavity2. Ectoderm (epiblast)3. Primitive pit4. Prochordal plate5. Notochordal process6. Primitive streak7. Allantois8. Yolk sac

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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.

What is the “placode” and what are its derivatives

• Placode: thickenings of the surface ectoderm at the head region of the embryo.

• a) Hypophyseal placode (1): Rathke’s pouch. (adenohypophysis).• b) Nasal placode (2): olfactory epithelium. • c) Lens placode (2): lens of eye.• d) Trigeminal placode (2): semilunar ggl. • e) Acoustic placode (2): sensory epithelium of vestibular and

cochlear receptors, ganglions.• f) Epibranchial placode (2): sensory epithelium of taste buds.• g) Branchial placode (2): sensory ganglia of VIIIth, IXth, Xth

cranial nerves.

What are the derivative of the paraxial, intermediate & lateral plate of mesoderm?

• Paraxial mesoderm: breaks up into blocks of somites, and somitomers at the cephalic region. The somites differentiate into sclerotom, dermatome, myotome.

• Intermediate: in the cervical and upper thoracic region it gives rise to the nephrotomes. Caudally the nephrogenic cord develops from it.

• Lateral plate: somatic or parietal mesoderm layer, splanchnic or visceral mesoderm layer, intraembryonic celomic cavity.

What is meant by a) cephalo-caudal and b) lateral foldings of the embryo?

• Folding of a flat trilaminar embryonic didsc into a somewhat cylindrical embryo.

• A) Cephalo-caudal fold: Cranially, the developing forebrains grows beyond the buccopharyngeal membrane and overhangs the developing hear. Caudaly the tail region projects over the cloacal membrane.

• B) Lateral/transverse folds: Each lateral body wall folds towards the median plane in a ventral direction.

Make a simple drawing to demonstrate the primitive gut in a 4-week old embryo, label!

1. Pharyngeal gut2. Tracheobronchial

diverticulum3. Esophagus4. Stomach5. Pancreas6. Liver7. Gallbladder8. Vitelline duct9. Allantois10. Cloaca

11. Primitive intestinal loop

12. Hindgut13. Cloacal14. Buccopharyneal

membrane

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What are the fetal membranes?

• Amnion, chorion, decidua parietalis and capsularis

List and characterized the different development stages of the placental villi!

a) Primary villi: cyto- and syncytiotrophoblast cellsb) Secondary villi: cyto- and syncytiotrophoblast cells +

extraembryonic mesoderm in the centre of villic) 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 endometrium1. Decidua basalis: between the chorion frondosum &

myometrium. Primordium of placenta materna2. Decidua capsularis: over the abembryonic pole.3. 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• Maternal portion: decidua basalis

Name the layers of the chorionic plate

1. Amnionic epithelium2. Central mesoderm3. Chorionic mesoderm4. Trophoblasts (syncytio-, and cyto-)

ACCT

Define the term 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!

1. Transport and exchange of gases, nutrients, waste products

2. Transport of antibodies to fetus3. Endocrine function4. Mechanical protection5. Barrier for some germs and drugs

T.TEMB

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 adrenocorticotropin (hCACTH)

What is the difference in the composition of the primitive and matured umbilical cord?

• Contents of primitive cord: the connecting stalk that contains allantois, umbilical vessels consisting of 2 arteries and 2 veins, yolk sac stalk accompanied by the vitelline vessels.

• Contents of the matured cord: 2 umbilical arteries, 1 umbilical vein, Wharton’s jelly.

What are the names of the blood vessels of mature umbilical cord? Which of them transport

oxigenated blood?• 2 umbilical arteries• One umbilical vein. The vein transports

oxygenated blood.

List signs of maturity of a newborn!

• Weight: above 2.5 kg• Nipples protruding out from the skin• Nails extend beyond finger tips• Testes are in scrotum• Labia majora covers labia minora• Forehead-hair border evident

List most common features of twin formation and characterize the relationship of placentas & fetal

membranes of twins!a) Monozygotic or identical twins1. With separate placenta, amnion and chorion.2. Common placenta and chorion, separate amnionic cavities3. Common placenta, chorion and amnionic cavityb) Dizygotic or fraternal twins1. Separate placenta, separate chorion, separate amnion.2. Separate placenta and amnion, fused chorion.

Define the fontanels of the newborn skull! Describe their positions related to the bones of

the skull!• Anterior, posterior, anterolateral or sphenoid, posterolateral

or mastoid fontanels.1. Anterior: where the 2 parietal and frontal bones meet2. Posterior: where the occipital and 2 parietal bones meet3. Anterolateral: where the parietal, frontal, temporal and

sphenoid bones meet4. Posterolateral: where the occipital, parietal and temporal

bones meet (mastoid)

Draw superior aspect of the calvaria of newborn and label the fontanels, sutures and bones!

1. Frontal bone2. Occipital bone3. Parietal bone4. Anterior (or frontal) fontanel5. Posterior (or occipital) fontanel6. Coronal suture7. Sagittal suture8. Lambdoid suture

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Which bones develop from the chondrocranium?

• Occipital bone (except the upper portion of squamous part), petrous and mastoid parts of temporal bone, sphenoid bone (except the medial plate of the pterygoid process), ethmoid bone.

What bones develop from the viscerocranium?

• Maxilla• Mandible• Zygomatic bone • squamous and tympanic parts of the temporal bone• Styloid process of temporal bone• Nasal bone• Lacrimal bone• Vomer• Hyoid bone• Inferior concha• Medial plate of the pterygoid process of the sphenoid bone• Palatine bone

What is meant by the rearrangement of the sclerotomes in development of the vertebral

column?• The caudal half of each cranial sclerotom proliferates,

proceeds into the subjacent tissue and joins the cephalic part of the subjacent sclerotom. The fused halves of the adjacent sclerotomes with the incorporated intervertebral tissue from the cartilaginous vertebral body that becomes intersegmental in origin.

Describe the malformation called “spina bifida”!

• Imperfect fusion or nonunion of the vertebral arches.

Into which parts can the intraembryonic celomic cavity be divided in the 4th embryonic week?

• Pericardial cavity, pleuroperitoneal canal, peritoneal cavity.

Which structures separate the pericardial and pleural cavities from each other?

• Left and right pleuropericardial folds

From which structures does the diaphragm develop?

• Septum transversum• Pleuroperitoneal membranes• Dorsal mesentery of esophagus• Muscular component of the lateral and dorsal

body wall

Name and characterize the most common malformation of the thoracic diaphragm! Describe

mechanism of malformations

• Diaphragmatic hernia: caused by failure of the pleuroperitoneal membrane(s) to close the pleuroperitoneal canal(s). The peritoneal and pleural cavities are continous with each other along the posterior body wall.

• Parasternal hernia: a small muscular part of the anterior portion of the diaphragm fails to develop

• Esophpageal hernia: is due to a congenital shortness of the esophagus.

What are the derivatives of the ventral mesentery?

• Lesser omentum, falciform ligament

Good Luck with the Exam!!!

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