Introduction To Embryology

Embryology is the branch of biology that studies the prenatal development of gametes, fertilization, and development of embryos and foetuses. Additionally, embryology encompasses the study of congenital disorders that occur before birth, known as teratology.

Embryology can be mainly studied under two main divisions. They are EMBRYOGENESIS and ORGANOGENESIS.

Embryogenesis is the process of initiation and development of an embryo from a zygote (zygotic embryogenesis) or a somatic cell (somatic embryogenesis). Embryo development occurs through an exceptionally organized sequence of cell division, enlargement and differentiation.

Studying embryogenesis can be easier if we go through the topics below.

01 GAMETOGENESIS

• Origin and migration of the germ cells
• Male gonadal primordium
• Female gonadal primordium
• Spermatogenesis
• Oogenesis

02 FERTILIZATION

• Explaining the ovulation process
• Knowing the necessary steps which lead to spermatozoa being ready
• Describing how the enabling of the spermatozoa takes place
• Describing how the spermatozoon penetrates into the oocyte
• Knowing the process whereby a zygote is formed

03 IMPLANTATION

• Describe the histological structures of the endometrium
• Explain the phases of endometrial changes during the menstruation cycle
• Know the effects of the hypophysial hormones in the regulation of the menstruation cycle
• Explain the various stages of implantation
• Know the fundamental mechanisms of the implantation at the molecular level
• List the normal types of implantation and the anomalies of the extra-uterine pregnancies
• List the various possibilities for hindering an implantation and thus a pregnancy

04 EMBRYONIC DISC

• The differentiation of the embryonic germ layers, emanating from the trilaminar embryo
• The mechanism of gastrulation and especially the morphogenetic role of the primitive streak
• The arrangement of the intraembryonic mesoblast, its segmentation and the formation of the intraembryonic coelomic cavity
• The formation of the notochord and its role in the differentiations of nerve tissue
• The stages of neurulation and the first steps in the genesis of the central and peripheral nervous system

05 EMBRYONIC PHASE

• The differentiations of the germinal layers during the fourth week of development that lead to an individualization of the embryo.
• The key concepts of the embryonic period that describe the first stages of organogenesis.
• The various types of congenital abnormalities and be able to cite a few characteristic examples.

06 FOETAL PHASE

• The duration of the pregnancy and its various developmental stages.
• Various techniques of prenatal diagnostics.
• The differences among premature, full-term and post-term births.
• The intrauterine development of the child.
• Positions of the child during birth.
• Swiss legal aspects of pregnancy termination (abortion).
• Various causes of embryo-/ fetopathies and possibilities for therapy.
• Sensitivity of the embryo or foetus to teratogenic substances.

07 FETAL MEMBRANES AND PLACENTA

• name the foetal membranes and cavities together with their components and functions
• distinguish between the maternal and foetal parts of the placenta
• describe the macroscopic morphology of the placenta
• explain the development of the placental structures during pregnancy and their influence on the physiologic functions of the placenta
• name the structural and functional characteristics of the foetal blood circulation and the properties of the hemato-placental barrier
• list the endocrine functions of the placenta
• describe the peculiarities of twin pregnancies
• name the pathologies of embryonic development (ectopic pregnancy, hydatid mole, foetal erythroblastosis) in connection with the foetal membranes

08 CHROMOSOMAL AND GENE ABERRATION

• The difference between various kinds of chromosomal aberrations and gene mutations
• Possible causes of such disorders
• Interactions between genotype and the environment
• Polygeny and abnormalities
• General clinical symptoms of chromosomal aberrations

ORGANOGENESIS, in embryology, the series of organized integrated processes that transforms an amorphous mass of cells into a complete organ in the developing embryo. The cells of an organ-forming region undergo differential development and movement to form an organ primordium, or anlage. Organogenesis continues until the definitive characteristics of the organ are achieved.

01 MUSCULAR SYSTEM

• The origin of the three muscle types
• The development of the hypaxial and epaxial parts of the muscles based on the development of the somites and their differing innervation
• The histological development of muscle fiber to maturity
• The approximate segment level of the innervation of large muscle groups as well as the partial displacement
• Congenital muscle ailments and their causes which can be understood by knowing muscle development

02 CARDIOVASCULAR SYSTEM

• The first signs of heart development as well as the location of the cardiogenic tissues
• How the serial blood circulation system is converted to a parallel one during the course of embryonic development and which factors promote this development
• The processes that occur in the partitioning of the atria and ventricles.
• An enumeration of the arterial and venous systems with their various components that are near the heart
• The relationships of the pericardial cavity in adults, taking into account pericardial development
• The various nerves that are responsible for cardiac innervation

03 BLOOD AND LYMPHATIC TISSUES

• know the development from stem cells to differentiated blood cells
• know the location where erythropoiesis occurs
• have a concept of the functions of the various blood cells both before and after birth.
• know the organs of the lymphatic system
• know how they arise
• know the difference between cell-derived and humoral immunity
• have a concept of how immunological competence arises

04 RESPIRATION TRACT

• know the various prenatal stages of lung development.
• be able to list and localize the various cells that are typical for lung tissue.
• know the components of the blood-air barrier.
• be able to describe the development of the various somatic cavities.
• know where the pericardio-peritoneal duct lies.
• know the difference between the vasa publica and privata in the lungs.
• be able to explain the occurrence of fistulas between the esophagus and trachea based on your knowledge of the development of the two structures.
• know the various mechanisms in charge of the switch of the circulation systems at birth.

05 DIGESTION TRACT

• describe the various parts that are involved in forming the face.
• trace the development of the teeth.
• explain the innervation of the tongue from an embryologic point of view.
• list the derivatives of the individual pharyngeal arches.
• construct the relationship between the aortic and pharyngeal arches.
• describe the individual portions of the intestine and know their definitive location in the abdomen.
• describe the mesenteric relationships with the associated intestinal sections and blood vessels.
• determine which blood vessel is responsible for which intestinal portion.
• map out the course
• of the portal vein and explain it from an embryologic point of view.
• know the individual parts of the pancreas and explain their derivation.
• draw the relationships of the duodenal loops in a fetus.
• discuss the development of the urogenital sinus with respect to the formation of the hind gut and anus.

06 URINARY SYSTEM

• Describe the sequence of transitory and definitive anlagen of the upper urinary tract as well as their functions over the course of their development.
• Describe how the lower urinary tract forms from the cloaca.
• Explain some of the basic mechanisms that can lead to pathological development of the urinary system.

07 GENITAL SYSTEM

• list the genetic and hormonal factors that lead to sexual differentiation
• describe the steps that occur in the differentiation of the testicles and ovaries
• explain the formation of the internal and external genitals of both sexes
• name the abnormalities that indicated disorders in the most important mechanisms of genital development

08 NERVOUS SYSTEM

• describe typical features of the central and peripheral nervous systems
• distinguish between primary and secondary neurulation
• summarize the molecular mechanisms that underlie the development of the nervous system
• correlate the formation of the brain vesicle with the structures of the completely developed brain
• name the main functional divisions of the brain and the peripheral nervous system
• explain the histological and functional differentiation of nerve tissue cells (neurons and glial cells)
• describe and interpret the importance of the basic phenomena that occur during brain development (apoptosis, cell migration, splicing)
• explain the structural equivalents between embryonic development of the spinal cord and supraspinal centers
• sketch out blood circulation in the brain