Embryology

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Questions and Answers

What is the correct sequence of development stages after fertilization?

Morula, Zygote, Blastocyst

Morula, Blastocyst, Zygote

Blastocyst, Morula, Zygote

Zygote, Morula, Blastocyst (correct)

What defines the morula stage in embryonic development?

An early stage where the inner cell mass is formed

A hollow structure with a cavity

A 16-32 cell structure within the zona pellucida (correct)

A single-layered cell structure

What is the role of the trophoblast in early embryonic development?

It provides nutrients to the developing zygote

It forms the inner cell mass of the embryo

It creates the primitive streak for body axis formation

It contributes to the formation of the placenta (correct)

Which germ layer is formed during gastrulation that develops into skin and nervous system?

Ectoderm Signup and view all the answers

What occurs during the cleavage stage of zygote development?

The zygote undergoes mitotic divisions without growth in size Signup and view all the answers

Which statement best describes the blastocyst stage?

It includes a cavity called blastocoele surrounded by the inner cell mass Signup and view all the answers

Which layers are established from the inner cell mass during development?

Epiblast and hypoblast Signup and view all the answers

What is the primary function of the primitive streak established during embryogenesis?

It indicates the position for gastrulation and axis formation Signup and view all the answers

Which term refers to the disruption of normal embryonic development due to harmful substances?

Teratogen Signup and view all the answers

What is a teratogen?

An agent causing congenital anomalies Signup and view all the answers

What happens to the embryo during the pre-differentiation stage due to teratogen influences?

The embryo dies Signup and view all the answers

Which type of ducts develop in males during gonad development?

Mesonephric ducts Signup and view all the answers

What is the default sex for every embryo during development?

Female Signup and view all the answers

How many haploid cells are produced at the end of meiosis?

4 haploid cells Signup and view all the answers

What is the primary outcome of mitosis during gametogenesis?

Production of identical diploid daughter cells Signup and view all the answers

What hormone do Sertoli cells produce that affects sex determination?

Anti-Mullerian hormone Signup and view all the answers

During which stage of development do structural defects primarily occur due to teratogen exposure?

Organogenesis stage Signup and view all the answers

Which process involves the division of spermatogonia to produce primary spermatocytes?

Mitosis Signup and view all the answers

What is the relationship between primary spermatocytes and secondary spermatocytes?

Primary spermatocytes divide into secondary spermatocytes Signup and view all the answers

What are the primary components of the trilaminar disc formed during gastrulation?

Ectoderm, mesoderm, and endoderm Signup and view all the answers

Which of the following structures is derived from the ectoderm?

Nervous tissue Signup and view all the answers

Which layer is responsible for forming the urogenital system during development?

Intermediate mesoderm Signup and view all the answers

What type of cell potency can only form one specific cell type?

Unipotent Signup and view all the answers

Which of the following is a critical function of teratogens during embryonic development?

Causing congenital anomalies Signup and view all the answers

Which component does not belong to the mesoderm layer?

Neuroectoderm Signup and view all the answers

What does pluripotent refer to in terms of cell differentiation?

Ability to develop into any cell of the embryo Signup and view all the answers

What is the primary role of the notochord formed from the axial part of the mesoderm?

To provide a support structure during development Signup and view all the answers

Which of the following structures is NOT derived from the endoderm?

Muscle tissue Signup and view all the answers

Which of the following statements about mesoderm is accurate?

It differentiates into various tissue types including muscle and connective tissues Signup and view all the answers

What initiates the process of meiosis I in primary oocytes?

Puberty hormone release Signup and view all the answers

What occurs during the acrosome reaction?

Enzymes digest the zona pellucida Signup and view all the answers

Which of the following correctly describes the completion of meiosis II?

Requires fertilization with sperm Signup and view all the answers

What is the role of cortical reactions during fertilization?

To prevent polyspermy Signup and view all the answers

What is true regarding the timing of meiosis in female gametogenesis?

Meiosis II completes post-fertilization only Signup and view all the answers

How do spermatogenesis and oogenesis begin?

Both begin with mitosis of specific cells Signup and view all the answers

What is a significant difference between spermatogenesis and oogenesis?

Oogenesis results in one viable gamete versus many in spermatogenesis Signup and view all the answers

What occurs to primordial oocytes during the female gametogenesis process?

They remain inactive until puberty Signup and view all the answers

What factor can cause spermatozoon hyperactivity during fertilization?

Uterine secretions during capacitation Signup and view all the answers

How does meiosis contribute to genetic variability in gametes?

Via crossing over and independent assortment Signup and view all the answers

Study Notes

Development from Zygote through Gastrulation

Fusion of two haploid gametes forms a diploid zygote.
Zygote undergoes cleavage via mitosis into blastomeres without size increase.
Morula stage is reached with 16-32 blastomeres.
Blastocoele develops within the morula, giving rise to the blastocyst.
Inner cell mass forms a bilaminar disc of epiblast and hypoblast, establishing the dorsoventral axis.
Epiblast cells migrate to create a primitive streak, establishing the craniocaudal axis.
Formation of three germ layers during gastrulation: ectoderm, mesoderm, and endoderm.

Definitions

Male Pronuclei: Male gamete post-meiosis (1n).
Female Pronuclei: Ovum nucleus post-fertilization, before fusing with sperm.
Cleavage: Zygote division via mitosis into blastomeres; no increase in cell size.
Morula: Solid ball of 16-32 blastomeres.
Blastocyst: Cavity within the morula, called blastocoele.
Inner Cell Mass (Embryoblast): Cells that develop into the embryo.
Trophoblast: Outer blastocyst cells that develop into placenta.
Epiblast: Dorsal part of the bilaminar disc.
Hypoblast: Ventral part of the bilaminar disc.
Gastrulation: Formation of a trilaminar disc from the epiblast.
Ectoderm: Forms skin, oral/nasal cavity linings, and nervous system.
Mesoderm: Develops into connective tissue, muscle, mesothelium, and cardiovascular system.
Endoderm: Forms linings and glands of digestive and respiratory systems.
Teratogen: Any factor causing congenital anomalies during embryonic development.

Totipotent: Ability to form any embryonic or placental cell.
Pluripotent: Can differentiate into any embryonic cell type.
Multipotent: Can develop into various organ and tissue cells.
Unipotential: Ability to differentiate into only one cell type.
Differentiation: Gene interaction and cell signaling guiding cell specialization.

Derivatives of Germ Layers

Ectoderm: Gives rise to epithelium and nervous tissue.
Mesoderm: Forms connective tissue, muscle, and parts of the urogenital tract.
Endoderm: Develops into endothelium and digestive/respiratory glands.

Mesoderm Divisions and Somite Derivatives

Axial Part: Forms the notochord.
Paraxial Part: Forms somites, which further differentiate.
Intermediate Part: Develops the urogenital system.
Lateral Plate: Forms somatic and splanchnic mesoderm.
Somite Derivatives:
- Dermatome: Contributes to the dermis.
- Myotome: Develops into muscles.
- Sclerotome: Forms vertebrae and ribs.

Common Developmental Anomalies and Teratogens

Teratogens: Cause congenital anomalies; include genetic, radiation, chemical, and infectious agents.
Influences of Teratogens:
- Pre-differentiation Stage: May lead to embryo death.
- During Organogenesis: Causes structural defects.
- During Fetal Growth: Impacts functional maturation and minor structural defects.

Embryology of the Gonads

Primordial germ cells migrate from yolk sac and allantois to the genital ridge -> become bipotential gonad.
Bipotential gonad has the potential to develop into either sperm or ova.
Default sex is female unless influenced by male-specific mechanisms.
Sertoli cells produce Anti-Mullerian hormone, inhibiting Müllerian duct development in males.
Male (XY): Develops from mesonephric ducts into epididymis and ductus deferens.
Female (XX): Develops from paramesonephric ducts into uterus, uterine tubes, and cervix.

Gametogenesis

Gametogenesis: Production of haploid gametes (sperm and ovum).
Mitosis: Results in two identical diploid daughter cells.
Meiosis: Produces four genetically diverse haploid cells.
Male Gametogenesis:
- Spermatogonia -> primary spermatocytes (mitosis).
- Primary spermatocytes -> secondary spermatocytes (meiosis).
- Further division leads to mature spermatozoa.
Female Gametogenesis:
- Fixed number of primordial oocytes at birth.
- Primordial -> primary oocytes (mitosis), then meiosis (stops at prophase I).
- Meiosis I completes at puberty; secondary oocyte formed.
- Meiosis II resumes and completes post-fertilization.

Differences in Spermatogenesis and Oogenesis

Similarities:
- Occur in specialized organs (testes/ovaries).
- Both involve multiplication of germ cells by mitosis and formation of gametes via meiosis.
- Importance of genetic variability through crossing over and independent assortment.
- Limited survival if fertilization does not occur.

Fertilization Steps

Capacitation: Sperm undergo hyperactivation in the uterine environment.
Acrosome Reaction: Enzymes are released to digest the zona pellucida of the oocyte.
Cortical Reactions: Cortical granules release upon sperm contact, creating a barrier to polyspermy through zona pellucida modification.

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Describe the development of a fetus, list terms associated with embryology, define the germ layers etc.