Embryology

The result of fertilisation of the ovum and sperm is the zygote which multiplies through mitotic division for growth and development. It develops into an embryo which undergoes numerous morphological changes and generation of different types of tissues, organs and systems. The branch of biology that deals with this embryo development type is called embryology. It is inclusive of the journey from a single cell to a well-developed baby.

Embryology

Image: Embryology

Table of Contents

Processes Involved in Embryo Development
Organ Systems in Embryogenesis
Significance of Embryology
Stages of Embryogenesis
Practice Problems
Frequently Asked Questions

Processes Involved in Embryo Development

The embryo development undergoes different types of processes, such as

Cell Division: It is important for cell growth and proliferation. The zygote undergoes division through cleavage, which results in the formation of a blastocyst. Cell division is a never-ending process regardless of the embryogenesis stage.
Cell Migration: It helps in tissue and organ formation by the migration of cells at specific locations. For instance, neural crest cells migrate to birth different neural cells such as neurons, pigment and glial cells.
Growth: It refers to an increase in cell number and overall size of developing embryos as they contribute to growth and expansion. The growth is regulated through growth factors and signalling molecules.
Cell Differentiation: Differentiation is the process of becoming a specialised cell and acquiring a specific function. The conversion into a specific type imparts such ability. The commonly differentiated cells include muscle, epithelial, goblet, and others.
Apoptosis: Also referred to as programmed cell death, it is required for sculpting and refining tissues. For instance, apoptosis is responsible for the separation of fingers.
Cell Rearrangement: It is the movement and cellular reorganisation of cells in the embryo. It helps to shape the tissues and organs. The rearrangement is seen to convert from blastula to gastrula.

Organ Systems in Embryogenesis

There are multiple organ systems developing simultaneously in the embryo.

Nervous System: It includes the formation of the neural tube through neurulation from the ectoderm. Further, the neural crest development, brain and spinal cord development.
Cardiovascular System: It involves heart formation from the mesoderm, which begins with a linear heart tube. It also includes vasculogenesis and angiogenesis.
Digestive System: Occurring from endoderm, the gut tube forms first, further differentiating into foregut, midgut and hindgut. Further develops the organs and then mesentery formation.
Respiratory System: The foregut region of the developing digesting system buds off to form the respiratory system. Subsequently, the trachea and bronchial tree formation begins along with vascularisation.
Urinary System: Kidney development begins from the intermediate mesoderm. It includes the formation of metanephros, which further develop into nephrons. Further other parts like the ureter, bladder and urethra begin developing.
Musculoskeletal System: Somites form from the mesoderm, which results in the development of the musculoskeletal system. The differentiation takes place, forming the bone and muscles, and limbs.
Reproductive System: The gonad development begins from gonadal ridges where the sex determination occurs by the presence of sex chromosome Y. Based on its presence or absence, the external genitalia develops, and gamete production begins.

Significance of Embryology

The study of the development of the embryo is of significance because it helps in

Understanding the human development of tissues, organs and organ systems that helps in recognising birth anomalies and defects.
Medical applications for better insights and development of reproductive medicine, paediatrics, cardiac health and others. It also aids in analysing prenatal development.
Understanding evolutionary relationships.
Developing regenerative medicine for tissue regeneration for conditions concerning neurons.
Gaining insights into stem cell research, beginning of life and Assisted Reproductive Technologies (ART).
Understanding the developmental biology from the core at cellular and microbial levels to identify the role of genes, signalling pathways and environmental factors for better clinical applications.

Stages of Embryogenesis

The different involved stages in embryogenesis are:

Fertilisation involves the union of male and female gametes, which are sperm and ovum, respectively.
Blastocyst formation through constant division of the fertilised zygote.
Blastocyst implantation into the endometrium, where external blastocyst cells and uterine inner lining form the placenta.
Blastocyst develops into an embryo, which includes the beginning of the development of internal organs and external structures.
Foetal development is the twelfth week of fertilisation, where they can respond to sound, change positions and have developed organs.

Practice Problems

Q1. Who is the father of embryology?

a. Robert Leeuvenhoek
b. Kary Mullis
c. Socrates
d. Karl Ernst von Baer

Ans. d. Karl earner von Baer

Karl earner von Baer was a Baltic German scientist who was studying embryonic development discovering the blastula stage of development and the notochord.

Q2. What is the time span of human gestation?

a. 38 weeks
b. 9 months
c. 266 days
d. All of the above

Ans. d. All of the above

The gestation period is mentioned in just different forms of days, months and weeks which all equals the same.

The human gestation period lasts about 9 months, equivalent to 266 days and 38 weeks.

Q3. What is an antimullerian hormone?

a. Degradation of male gonads in female embryos
b. Degradation of female gonads in male embryo
c. To control excess secretion of pituitary gland
d. To control testosterone levels

Ans. b. Degradation of female gonads in the male embryo

Inhibin controls excess pituitary gland secretion and Androgen binding protein controls testosterone levels.

Frequently Asked Questions

Q1. What is gametogenesis and its involved stages?
Ans. Gametogenesis is the process of the formation of gametes capable of developing into a child. It involves three stages, multiplication, growth and maturation.

Q2. What are vasculogenesis and angiogenesis?
Ans. Vasculogenesis is the new or de novo formation of blood vessels, while angiogenesis is the formation of blood vessels from pre-existing blood vessels.

Q3. How is an embryo studied in real life?
Ans. The study of embryos utilises tools and experimental techniques like a microscope, cell culture, genetic analysis, ultrasound and confocal microscopy and animal models.