Embryology Lec 1: Embryogenesis Overview

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Questions and Answers

What term is used to describe the developmental stage beginning from the ninth week of gestation?

Blastocyst

Embryo

Zygote

Fetus (correct)

Which hormone is NOT involved in regulating the female monthly cycle?

Follicle-stimulating hormone (FSH)

Luteinizing hormone (LH)

Estrogen (correct)

Gonadotropin-releasing hormone

During which process does the fertilized egg transition through multiple stages before implantation?

Mitosis (correct)

Developmental cleavage

Embryonic folding

Gamete approximation

Which stage comes immediately after fertilization in early human development?

Morula formation Signup and view all the answers

Which of the following is NOT considered a major event in the first week of embryonic development?

Neural tube formation Signup and view all the answers

What is the multi-layered structure that develops after morula formation?

Blastocyst Signup and view all the answers

What is the term used to describe a solid sphere of cells within the zona pellucida when there are around sixteen cells?

Morula Signup and view all the answers

What biological process describes the division of a fertilized egg into smaller cells post-fertilization?

Cleavage Signup and view all the answers

What is the primary factor that ensures the successful fertilization and implantation of the embryo?

All of the above Signup and view all the answers

What forms the inner cell mass (ICM) of the blastocyst?

Embryoblasts Signup and view all the answers

During which process does the blastocyst begin to burrow into the endometrium?

Invasion Signup and view all the answers

What is the first cavity formed during embryonic development?

Blastocoel Signup and view all the answers

What process follows the initial formation of the morula in terms of the embryonic developmental stages?

Blastulation Signup and view all the answers

Which of the following describes the period of apposition during implantation?

Weak interactions between the blastocyst and the uterine wall Signup and view all the answers

The outer layer of the blastocyst is known as what?

Trophoblast Signup and view all the answers

What initiates the process of implantation in the embryonic development timeline?

Hatching of the blastocyst Signup and view all the answers

What triggers the ovaries to produce follicles each month?

Hormones released by the pituitary gland Signup and view all the answers

Which type of follicle matures right before ovulation?

Graafian follicle Signup and view all the answers

What occurs to the follicle after ovulation?

It turns into a corpus luteum Signup and view all the answers

What is the role of the corpus luteum?

To release progesterone and estrogen Signup and view all the answers

What is the cumulus oophorus?

A group of cells surrounding the oocyte Signup and view all the answers

Which layer surrounds the zona pellucida?

Corona radiata Signup and view all the answers

What happens to the corpus luteum if fertilization does not occur?

It shrinks and forms corpus albicans Signup and view all the answers

What composition primarily makes up the corona radiata?

Proteins, carbohydrates, and hyaluronic acid Signup and view all the answers

What is the primary outcome of fertilization regarding chromosome number?

Restoration of the diploid number of chromosomes with genetic variation. Signup and view all the answers

What initiates the acrosome reaction in sperm during fertilization?

Binding to the zona pellucida. Signup and view all the answers

What is the significance of capacitation for sperm before fertilization?

Only capacitated sperm can penetrate the corona cells. Signup and view all the answers

What is produced during the cleavage process after fertilization?

Blastomeres are produced as cell division occurs. Signup and view all the answers

Which sperm chromosome combination leads to a male embryo?

XY combination from the male parent. Signup and view all the answers

What describes the zygote's size during the cleavage process?

It remains similar in size and form despite increased cell number. Signup and view all the answers

What role do zona proteins play in fertilization?

They induce the acrosome reaction. Signup and view all the answers

What is true about the conceptus after fertilization and during the cleavage phase?

It includes both embryonic and extraembryonic structures. Signup and view all the answers

Study Notes

Embryogenesis Overview

Human embryogenesis transforms a fertilized egg into an embryo over the first eight weeks of development.
The embryo progresses from a zygote to a multi-layered, multi-dimensional structure with primitive organs.
By the ninth week, the embryo is referred to as a fetus, characterized by recognizable features and developing organs.

First Week of Development

The early developmental events crucial for fertilization and implantation occur, including:
- Gamete approximation
- Contact and fusion of gametes
- Fertilization
- Mitotic cleavage of the blastomere
- Morula and blastocyst formation
- Implantation of the blastocyst

Ovulation

Begins at puberty, regulated by gonadotropins from the hypothalamus; includes follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
The pituitary gland controls ovarian cycles, leading to the release of an egg (ovulation).
Follicles grow, with typically only one reaching maturity while others degenerate.
After ovulation, the Graafian follicle ruptures, releasing the oocyte and forming the corpus luteum, which produces progesterone and estrogen.

Key Structures

Cumulus Oophorus: A cluster of cells surrounding the oocyte, with the innermost layer known as the Corona Radiata.
Zona Pellucida: Glycoprotein layer that protects the oocyte's plasma membrane.

Fertilization Process

Fusion of mature male and female gametes creates a zygote.
Sperm undergo capacitation in the female reproductive tract, allowing them to penetrate the oocyte.
Acrosome Reaction: Release of enzymes necessary to penetrate the zona pellucida after sperm binds with it.

Results of Fertilization

Restoration of the diploid chromosome number, combining genetic material from both parents.
Determination of genetic sex based on the sperm type (XX for female, XY for male).
Initiates cell cleavage.

Morula Formation

Following fertilization, rapid mitotic cleavage transforms the zygote into a morula, which is a solid sphere of cells.
Morula remains the same size as cell count increases due to compaction, within the zona pellucida.

Blastulation and Blastocyst Formation

The blastocyst forms a few days post-fertilization and comprises:
- An Inner Cell Mass (ICM), later developing into the embryo.
- An outer Trophoblast layer surrounding the ICM and the blastocoel (first cavity).
The blastocyst hatches through the zona pellucida as it enlarges.

Implantation Process

Implantation is a critical biochemical and mechanical process occurring in the first week, extending into the second.
Subdivided into:
- Apposition Phase: Weak interactions between blastocyst and uterine wall.
- Attachment Phase: Stronger binding to the uterine epithelium.
- Invasion Phase: Blastocyst burrows into the endometrium.

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Description

This quiz focuses on the first week of embryogenesis, covering key processes such as ovulation, fertilization, and implantation. Understand the intricate development from a zygote to a complex embryo with functioning organs during the critical first eight weeks. Test your knowledge on this fundamental phase of human development.