EMBRYOLOGY.pdf

Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology MODULE 1 INTRODUCTION TO EMBRYOLOGY OVERVIEW The teaching of embryology has long been an establish...

Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology MODULE 1 INTRODUCTION TO EMBRYOLOGY OVERVIEW The teaching of embryology has long been an established feature of universities throughout the world, both for students in biology and students in medical sciences. Life cannot be fully accounted for without understanding of its dynamic nature, which expresses itself in the incessant production of new organisms in the process of ontogenetic development. This module is the introduction to embryology subject which teach the meaning and significance of embryology, different branches of embryology and history of embryology. INDICATIVE CONTENT · Definition and Significance of Embryology · Branches of Embryology · History of Embryology LEARNING OUTCOMES · Understand the meaning and significance of embryology and its importance in the field of veterinary medicine. · Describe what the different branches of embryology are. · Know the history of embryology. DISCUSSION DEFINITION AND SIGNIFICANCE OF EMBRYOLOGY EMBRYOLOGY – study of changes which organism undergo during their development from fertilization to birth - study of the growth and differentiation undergone by an organism in the course of its development from a single fertilized egg cell into a highly complex and independent living being like its parents - the study of ontogenetic development of organism - ontogenetic development: refers to gradual historical transformation of the forms of life, starting with simple forms which might have been the first to appear Stages of Ontogenetic Development 1. Gametogenesis – formation of gametes a. Spermatozoon in males b. Ovum in females 2. Fertilization – union of male and female gametes to produce zygote - essentially all higher animals start their lives from a single cell, the fertilized ovum (zygote) - represents the starting point in the life history, or ontogeny, of the individual 3. Cleavage – phase of mitotic cell division - gives rise to a compact heap of cells, but the cells are arranged in a hollow spherical body, a blastula, with a layer of cells, the blastoderm, surrounding a cavity, the 1 Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology  blastocoele 4. Gastrulation – the blastoderm (a single layer of cells) gives rise to two or more layers of cells known as the germinal layer a. Ectoderm (outermost) – gives rise to skin and nervous system b. Mesoderm (middle) – gives rise to muscle, blood vessels, vascular system, lining of secondary body cavity, sex organs, excretory system, internal skeleton c. Endoderm (innermost) – alimentary canal.digestive glands 5. Organogenesis – organ formation 6. Growth and histological differentiation – an increase in the size or number of cells in the whole or any part of the organism Embryogenesis - formation of body structures and organs Sequence of Early Embryogenesis Gametogenesis Fertilization Cleavage Gastrulation Neurulation Teratology - Deals with causes and results of abnormal development or congenital malformations. Congenital malformation/defect - abnormality that arises during prenatal development due to hereditary or environmental factors. Anomaly - developmental disturbance in an organ or portion of an organ. Montrosity - involves several organs and causes great distortion of the individual. Significance of Embryology Understand the formation of tissues and organs and their subsequent development into adult forms. Identify the relationships between tissues and organs, particularly those that drastically change their relative positions during development. Identify the embryologic parts and principles involved in their development w/c are necessary to understand congenital malformations. Help appreciate more complex anatomy of adult animal. BRANCHES OF EMBRYOLOGY 1. DEVELOPMENTAL ANATOMY – the study of the organism’s development from fertilization to its resemblance to its adult form. 2. DEVELOPMENTAL BIOLOGY – this field includes not only embryonic development but also postnatal processes such as normal and neoplastic growth, metamorphosis, regeneration and tissue repair at levels of complexity ranging from the molecular to the organismal. The focus is on processes and concepts rather than specific morphologic structures. 3. DESCRIPTIVE EMBRYOLOGY - the study concerned with the direct observation and description of embryological development. 4. COMPARATIVE EMBRYOLOGY - defined as the embryological development of 2 Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology  different species is studied, analysed and compared. 5. EXPERIMENTAL EMBRYOLOGY - defined as the embryos are experimented for studying the various developmental stages. Hence, it helps to understand the fundamental mechanisms of the organisms. In this field the embryos are dissected and the various parts of the embryo are removed, transplanted and even the environmental conditions are altered. It is also called as Casual Embryology or Analytical Embryology. 6. CHEMICAL EMBRYOLOGY - The chemical embryology deals with the biophysical, biochemical and physiological techniques. 7. TETRALOGY - branch of embryology which deals with the malfunctions of the embryo. HISTORY OF EMBRYOLOGY Aristotle (384 – 322 B.C.) – wrote the first treatise on embryology - formulated the alternative that an embryo must be ether preformed and only merely enlarging during its development, or it must be actually differentiating froma formless beginning Graaf (1672) – described the ovarian follicle Hamm and Leeuwenhoek (1677) – first seen the human sperm Bonnet (1745) – discovered that the eggs of some insects can develop parthenogenetically - parthenogenesis – the process wherein the unfertilized eggs may become activated and develop into viable individuals as part of the normal life cycle Spallanzani (1729-1799) – demonstrated that both the female and the male sex products are necessary for the initiation of development Wolff (1733-1794) wrote a brilliant thesis setting forth his conception of epigenesist; embryological development occurs through progressive growth and differentiation - epigenesis – method of progressive development from the simpler to the more complex, through the utilization of building units known as cells Harvey (1651) and Malphigi (1672) – contributed fundamental descriptions of the stages of the developing chick, as seen with simple lenses Pander (1817) – demonstrated the three primary germ layers from which the chick embryo and its constituent parts develop Karl Ernst von Baer (1829 – 1837) – “Father of Modern Embryology” – generalized the existence of germ layers in all animals; identified the mammalian egg Van Beneden (1883) – proved that male and female sex cells contribute the same number of chromosomes to the fertilized egg Boveri (1888;1909) – supported that the chromosomes perpetuate themselves by mitosis, maintain a persistent individuality and possess different hereditary qualities Methods Used in the Study of Embryonic Development 1. Direct Observation of Living Embryos with naked eye or with simple lenses - provides one with a good overall view of the embryo and impresses the observer with the dynamic and often sweeping changes that constitute embryonic development 2. Examination of Fixed Material – the embryo is treated with various chemicals, such as formalin, to arrest a process at a critical phase, that will preserve the structures as faithfully as possible without causing undue distortion or other artifacts in the tissue 3. Histochemical Methods - used to localize specific chemical substances or sites of chemical activity on morphological structures that are disturbed as little as possible 3 Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology 4. Autoradiography – a methods that allows the localization of a radioactive isotope within cells  or tissues by employing methods similar to those used in photography 5. Tracing Methods - uses markers/vital dyes to trace cell movements in the growing embryo - changes of position of cells treated with dyes can be followed through an extensive period of growth before the dye becomes so diffused that identification is no longer possible 6. Immunological Methods – used to localize specific molecules in tissues by means of antibodies 7. Microsurgical Techniques – necessitated the development of special tools due to smallness of embryo a. ablation – removal of part of an embryo to determine what effect the absence of that structure will have on the remainder of the embryo b. transplantation/explantation – consists of excising a small sample of embryonic tissue and growing it in an artificial environment i. autografting – same embryo ii. heterografting – hosts of different species iii. xenografting – different order 8. Culture techniques – grows components of embryos or even whole embryos in an artificial environment - cell, tissue, organ, whole embryo culture - the embryonic material is placed into dishes or tubes of glass or plastic and surrounded by an artificial culture medium designed to resemble as closely as possible the environment surrounding the material in its normal site in the embryo 9. Biochemical and Molecular Techniques – used to determine the presence or absence of specific compounds and their amounts - e.g. analysis of enzyme activity is frequently used in studies on the metabolic properties of embryos 10. Irradiation Techniques – used mainly to inflict some form of damage on parts of the embryo Key Events in Animal Development Gamete  Formation   Sperm  and  eggs  form,  mature     Fertilization  Egg  and  sperm  fuse     Cleavage   Egg  subdivides,  determinates  partitioned  in       blastomeres     Gastrulation   Germ  layers  form     Neurolation  Neural  tube  form     Organogenesis   Body  organs  form,  cell  interact,  differentiate     Growth     Organs  increase  in  size,  adult  body  formed  attained   4 Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology  EXERCISES/ DRILLS Activity No. 1 Directions: In a separate sheet, answer the following questions below. 1. As a future veterinarian, what is the importance/ significance of veterinary embryology subject in your profession? 2. Enumerate the key events in animal development and explain each development. 3. Enumerate the 7 branches of embryology and explain each. 4. Describe the differences between anomaly and monstrosity and cite at least one example. 5. Name at least 5 scientists and give its contribution in the world of embryology. Activity No. 2 Directions: In a separate sheet, draw pictures of embryo of the following species. 1. Dog 2. Pig 3. Cattle 4. Goat 5. Chicken EVALUATION MULTIPLE CHOICES Directions: Read the questions carefully. Choose the letter of the correct answer and encircle your answer. 1. Which of the following is the third phase in ontogenic development of embryo? a. Gastrulation b. Fertilization c. Cleavage d. Gametogenesis 2. Which method is used in the Study of Embryonic Development that allows the localization of a radioactive isotope within cells or tissues by employing methods similar to those used in photography? a. Histochemical Methods b. Autoradiography c. Microsurgical Techniques d. Immunological Methods 3. Which of the following refers to the removal of part of an embryo to determine what effect the absence of that structure will have on the remainder of the embryo? a. Transplantation b. Explantation 5 Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology c. Autografting d. Ablation 4. Who is known as the “Father of Modern Embryology”? a. Karl Ernst von Baer b. Van Beneden c. Harvey d. Wolff 5. What is the fourth stage in the sequence of early embryogenesis? a. Neurulation b. Gastrulation c. Cleavage  d. Fertilization 6. What germinal layers that forms the sex organs of animals? a. Ectoderm b. Mesoderm c. Endoderm 7. Which of the scientist below demonstrated the three primary germ layers from which the chick embryo and its constituent parts develop? a. Harvey b. Spallanzani c. Pander d. Aristotle 8. During gastrulation period, what parts of embryo was formed? a. Sperm b. Eggs c. Germinal layers d. Morula 9. What germ layer gives rise to skin? a. Ectoderm b. Mesoderm c. Endoderm 10. What germ layer gives rise to muscle? a. Ectoderm b. Mesoderm c. Endoderm 11. Which of the following involves several organs and causes great distortion of the individual? a. Anomaly b. Congenital malformation/defect c. Monstrosity 12. Who wrote a brilliant thesis that sets forth his conception of epigenist? a. Pander b. Wolff c. Bonnet 13. Which of the following uses markers/vital dyes to trace cell movements in the growing embryo? a. Tracing Techniques b. Microsurgical Techniques c. Examination of Fixed Material 14. When the embryos are dissected and various parts are removed, transplanted and even the environmental conditions are altered. It is called? a. Chemical Embryology 6 Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology b. Experimental Embryology c. Casual Embryology 15. Which of the following refers to an increase in the size or number of cells in the whole or any part of the organism? a. Growth and histological differentiation b. Gametogenesis c. Gastrulation 16. Which of the following is the first stage of the early embryogenesis? a. Fertilization b. Gametogenesis c. Cleavage  17. It deals with the causes and results of abnormal development or congenital malformations. a. Teratology b. Montrosity c. Anomaly 18. Which of the following explains to the union of male and female gametes to produce zygote? a. Fertilization b. Embryogenesis c. Ontogenesis 19. Who demonstrated that both the female and the male sex products are necessary for the initiation of development? a. Aristotle b. Spallanzani c. Boveri 20. Which of the following refers to the study of the organism’s development from fertilization to its resemblance to its adult form? a. Development Anatomy b. Developmental Biology c. Development Physiology 21. It refers to the gradual historical transformation of the forms of life, starting with the simple forms which might have been the first to appear. a. Embryology b. Teratology c. Anatomy 22. Which of the following stages is an increase in the size or number of cells in the whole or any part of the organism? a. Growth and Histological Differentiation b. Gastrulation c. Organogenesis 23. What do you call to the study concerned with the direct observation and description of embryological development? a. Comparative Biology b. Descriptive Biology c. Experimental Embryology 24. He proved that male and female sex cells contribute the same number of chromosomes to the fertilized egg. a. Karl Ernst von Baer b. Van Beneden c. Graff 25. Which of the following used mainly to inflict some form of damage on parts of the embryo? 7 Veterinary Developmental Anatomy (Embryology) Module 1: Introduction to Embryology a. Irradiation Techniques b. Culture Techniques c. Microsurgical Techniques 26. It refers to the removal of part of an embryo to determine what effect the absence of that structure will have on the remainder of the embryo. a. Transplantation b. Ablation c. Explanation 27. What method allows the localization of a radioactive isotope within cells or tissues by employing methods similar to those used in photography? a. Histochemical Methods  b. Autography c. Tracing Methods 28. He was known for writing the first treatise on embryology. a. Harvey b. Pander c. Aristotle d. Boveri 29. Which of the following methods is used to localize specific molecules in tissues by means of antibodies? a. Immunological Methods b. Tracing Methods c. Histochemical Methods 30. He demonstrated the three primary germ layers from which the chick embryo and its constituent parts develop. a. Bonnet b. Pander c. Harvey d. Spallanzi ADDITIONAL READINGS ISU, 2005. Lecture Notes on Veterinary Embryology. Balinsky BI. 1981. An Introduction to Embryology. 5th ed. Philadelphia: W.B. Saunders Co. REFERENCES Mc Geady, TA., Quinn, P.J., FitzPatrick, E. S. and Ryan, M.T. 2006. Veterinary Embryology. Black well Publishing Ltd. ISU, 2005. Lecture Notes on Veterinary Embryology. 8