1st Lecture on Revision of General Embrology for 1st Year Mbbs Students by Dr. Roomi

8/2/2019 1st Lecture on Revision of General Embrology for 1st Year Mbbs Students by Dr. Roomi

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BY

DR. MUDASSAR ALI ROOMI

REVISION OF EMBRYOLOGY


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SPERMATOGENESIS


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Definition?

Steps?

Role of acrosome??

SPERMIOGENESIS


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OOGENESIS

Germ cell derivedfrom????

First meiotic division

stops at..?? 2nd meiotic division is

not completeduntil.????

Why with increasing agemore chances ofnon-disjunction???


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OVOGENESIS


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Role of theca interna

and theca externa?????


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SHORT NOTES

Biological importance of mitosis and

meiosis??

Importance of crossing over during meiosis??

Cause of variations in human beings???


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DIFFERENCES BETWEEN

Spermatogenesis Begins at puberty.

Occurs in testis for formation ofsperms.

One spermatogonium forms four

spermatids. Thousands of cells are dividing at a time

to form sperms.

Parent cell divides into equal cells.

Completes irrespective of thefertilization.

Mature Sperms are not surrounded byprotective cells.

Time required for a spermatogonium tobecome a mature sperm is usually 64days.

Oogenesis Begins before birth.

Occurs in ovaries for formation of ova.

One oogonium forms one mature eggonly.

5-15 primordial follicles enter in onecycle.

Parent cell divides into unequal cells.

2nd meiotic division completes afterfertilization.

Ovum is surrounded by follicular cells.

Total Time for oogenesis may be as longas 45 years.


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STRUCTURE OF A SPERM

What is capacitation???

What is acrosomal

reaction???


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STRUCTURE OF GRAAFIAN FOLLICLE

WHAT IS THE ROLE OF THECA INTENA

AND THECA EXTERNA??

ROLE OF ZONA PELLUCIDA??


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QUESTIONS

Spontaneous abortions andbirth defects??

Numerical or structuraldefects of chromosoms;gene mutations ??

Non-disjunction and itsrelation with maternalage???

Euploidy and aneuploidy??

Monosomy and trisomy?? Mosaicism??

Tranlocation (balance andunbalanced)??


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DOWN SYNDROME (MONGOLISM)

CAUSE??

RELATION TO MATERNAL AGE??


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CLINICAL FEATURES OF DOWN SYNDROME

Smiling but expressionless face.

Hypotonia.

Mental retardation.

Small and low set ears.

cardiac defects.

High incidence of leukemia,

infections and alzeimers disease.


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Feature found in males

and detected usually at

puberty.

Testicular atrophy. Sterility.

Gynacomastia.

KLINEFELTER SYNDROME


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TURNER SYNDROME


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TRANSLOCATION 14-21 CHROMOSOMAL MOSAICISM


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MENSTRUAL CYCLE


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OVULATION

Mechanism of ovulation (LHsurge)??

Fate of ovulation????

What is corpus luteum, corpusluteum gravidarum, corpus

albicans and corpus atreticum??? How corpus luteum is formed???

Fate of corpus luteum???

What to do in women who fail toovulate???

What is the role of progesteron inmaintenace of pregnancy andfrom where is it secreted???


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Where does fertilization occurs??

What is capacitation andacrosomal reaction???

What is cortical reaction and zonareaction???

1. Passage of the sperm throughcorona radiata.

2. Penetration of the zonapellucida.

3. Fusion of the plasma membraneof the oocyte and sperm.

4. Completion of the secondmeiotic division of oocyte andformation of female pronucleus.

5. Formation of the malepronucleus.

6. As the pronuclei fuse into asingle diploid aggregate ofchromosomes, the ootidbecomes a zygote.

PHASES OF FERTILIZATION


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CLINICAL CORRELATIONS

Contraceptive methods

Barrier methods ( condoms,

diaphragm).

OCPs.

IUCDs.

Permanent methods

(vasectomy and tubal

ligation).

infertility

Causes of male infertility?

Causes of female infertility?

IVF ???

GIFT ????

ZIFT ???

ICSI???


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MORULA AND BLASTULA


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FIRST WEEK OF DEVELOPMENT


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UTERUS AT THE TIME OF IMPLANTATION


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Second week of Development is the Week of twos:

The Trophoblast differentiates into 2 layers: The syncytiotrophoblast and the

cytotrophoblast.

The embryoblast (Inner Cell Mass) splits into 2 layers: The epiblast (forms the embryo) and

the hypoblast.

The extraembryonic mesoderm splits into 2 layers: the extraembryonic somatopleure and

the extraembryonic splanchnopleure

2 cavities form: The aminoic cavity and the yolk sac.


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QUESTIONS

What is decidua reaction???

Role of beta hCG?

Zygote is not rejected although it is a foreignbody to the mother. reason behind??

SLE and rejection of conceptus???


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SUMMARY OF IMPLANTATION

1. Zona pellucida degenerates (day 5).

2. Blastocyst adheres to the endometrial epithelium.

3. Trophoblast differentiate into two layers.

4. Syncytiotrophoblast erodes the endometrial tissue.

5. Blood filled lacunae appear In thesyncytiotrophoblast.

6. Blastocyst sinks beneath the endometrial epitheliumand the defect is filled by a fibrin plug.

7. Maternal blood flows in the lacunae.8. Defect in the endometrial epithelium is repaired.

9. Primary chorionic villi develop (day 13 and 14).


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Definition??

Incidence???

Causes (PID)???

Role of zona pellucida??? Common sites???

Placenta previa??

Clinical features???

Risk to mother???

Diagnosis???

ECTOPIC PREGNANCY


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HYDATIDIFORM MOLE

Definition?

Cause?

Clinical features?


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SUMMARY OF THE SECOND WEEK

1. Decidua reaction of the endometrium occurs.

2. Implantation completes.

3. Primary yolk sac develops.

4. extra-embryonic mesoderm develops and it splits to form

extra-embyonic coelom.

5. Amniotic cavity appears.

6. Embryblast differentiates into bilaminar germ disc.

7. Secondary yolk sac forms parallel to the formation of the

extra-emryonic coelom.8. Prechordal plate develops as a localized thickening of

hypoblast.


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SACCROCOCCYGEAL

TERATOMA

CAUDAL DYSGENESIS

(SIRENOMELIA)


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DEVELOPMENT OF NOTOCHORD


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FATE OF NOTOCHORD?????

Nucleus pulposes of the intervertebral

discs of the vertebral column.

What are chordomas????


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NEURULATION

NTDs AND ROLE OF FOLIC

ACID????


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TROPHOBLAST

AT THE END OF2ND WEEK


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TROPHOBLAST

AT THE END OF

3RD WEEK


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SUMMARY OF THIRD WEEK

1. Primitive streak appears at the caudal end of the embryonic disc.2. Gastrultion i.e. the formation of three germ layers is the result of

migration of cells from primitive streak.

3. Oropharyngeal and cloacal membranes also appear.

4. Notochord also develops from the primitive streak.

5. Neural tube and neural crest also formed.

6. Paraxial mesoderm starts forming somites.

7. Coelom arises in the lateral plate mesoderm

8. Blood vessels develop by angiogenesis and vasculogenesis.

9. Heart tube also starts developing.

10. Primary villi change to secondary and then to tertiary villi.

11. Cytotrophblastic shell also develops.


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DERIVATIVES OF ECTODERM

SURFACE ECTODERM

Epidermis, hair, nails, sweat

and mammary glands.

Ant. Part of the pituitarygland.

Enamel of the teeth.

Internal ear.

Lens of the eye.

NEUROECTODERM

CNS.

Retina.

pineal body.

Post. Part of the pituitarygland.

Carnial and sensory ganlia andnerves.

Medulla of adrenal glands. Pigment cells (melanocytes).

Pharyngeal arch cartilages.

Head mesenchyme.


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DERIVATIVESOF NEURAL CREST???


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DERIVATIVES OF ENDODERM

1. Epithelial parts of:Trachea, bronchi and lungs.

2. Epithelial parts of:

GIT, liver, pancreas and urinarybladder.

3. Epithelial parts of:

pharynx, thyroid gland, tympanic

cavity or middle ear, eostachian tube orpharyngotympanic tube, tonsils and parathyroidglands.


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DERIVATIVES OF MESODERM

1. Paraxial mesoderm:(muscles of the head,skeletal muscle of limbs and trunk, skeletonexcept cranium, dermis of skin and connectivetissue).

2. Intermediate mesoderm: (urogenital systemincluding gonads, ducts and accessory glands).

3. Lateral plate mesoderm: (connective tissue andmuscle of viscera; primordial heart; serous

membranes of pleura, pericardium andperitonium; blood and lymphatic cells; spleen;adrenal cortex).


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FOLDING OF THE EMBRYO

Head and tail folding or foldingin the median plane

1. Occurs due rapid growth of

CNS.

2. Responsible for formationof foregut and hindgut

mainly.

3. It Converts the embryo

into a curved structure.

Lateral folding or folding in thehorizontal plane

1. Occurs due to rapid growth

of somites.

2. Responsible for formationof midgut mainly.

3. It converts the embryo into

a cylinder like structure.


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HEAD AND TAIL FOLDING

LATERAL FOLDING

RESULTS OF THE FOLDING OF


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RESULTS OF THE FOLDING OF

EMBRYO

1. Formation of Foregut, midgut and hindgut.

2. Formation of omphaloenteric or

vitellointestinal duct (vitelline duct).

3. Disc like embryo becomes cylinder like.

4. Incorporatin of allantois in the embryo.

5. Brain goes cranially and heart comescaudally. Oropharyngeal membrane is in

between.


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SOMITES


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Gestational age (LNMP).

Crown rump length (CRL).

Number of somites. Biparietal diameter (BPD).

Femur length.

Abdominal diameter.

ESTIMATION OF THE EMBRYONIC AGE

TH TH


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SUMMARY OF THE EVENTS FROM 4TH TO 8TH WEEK

At the beginning of 4th week folding of the embryo occurs in the

median and horizontal planes. As the head folds ventrally, part of the endoderm incorporated in

the head region forms foregut.

As the caudal eminance folds ventrally, part of the endodermalgerm layer incorporated in the caudal end of the embryo forms thehind gut.

Folding in horizontal plane forms midgut.

Three germ layers differentiates into various tissues and organs.

External appearance of the embryo becomes human like by the endof 8th week.

The embryogenesis period is the most critical as for as theteratogenesis is concerned.

Reasonable estimate of the age of the embryo can be made bysome parameters of the embryo.

KEY EVENTS DURING 4TH WEEK


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1st Lecture on Revision of General Embrology for 1st Year Mbbs Students by Dr. Roomi

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