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Nature and Scope of Embryology

Embryology is the science that treats of the origin and development of the individual organism.
It is a gradual bringing to completion both in structure and in function. Its chief characteristic is cumulative change in a progressive direction.

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Nature and Scope of Embryology

  1. 1. Embryology is the science that treats of the origin and development of the individual organism. It is a gradual bringing to completion both in structure and in function. Its chief characteristic is cumulative change in a progressive direction.
  2. 2. PRE-NATAL AND POST-NATAL In many animals like fishes and amphibians, they are capable of an independent existence at relatively immature stages - free-living forms called larvae In man, the human newborn, is fairly complete anatomically, yet dependent on its elders for food and care
  3. 3. Infancy, childhood and adolescence – completion of some organs and a gradual remodeling of body shape Only at about the age of 25 are the last of these progressive changes finished and the body stabilized in the adult condition
  4. 4. OVUM – Fertilization to end of first week EMBRYO – Second to eighth week, inclusive FETUS – Third to tenth lunar month, inclusive BIRTH
  5. 5. NEWBORN – Neonatal period, birth to end of second week INFANCY – Third week, until assumption of erect posture at end of first year CHILDHOOD – Early – Milk tooth period, second to sixth year, inclusive Middle – Permanent tooth period, 7 – 10 years, inclusive Later – Prepubertal period, from 9 or 10 years to 12-15 years in females, and to 13-16 years in males
  6. 6. ADOLESCENCE – the six years following puberty ADULT – Prime and transition – between 20 and 60 years Old age and senescence – From 60 years on DEATH
  7. 7. Morphological and functional categories DEVELOPMENTAL ANATOMY Morphological – deals with form, structure and relations - purely descriptive and comparative in treatment - it traces the formative history of animals from a germ cell of each parent to the resulting , adult offspring
  8. 8. DEVELOPMENTAL PHYSIOLOGY Functional – attempts to explain on the basis of experiment and analysis, the ways in which development works EXPERIMENTAL EMBROLOGY – experimental attack CHEMICAL EMBRYOLOGY – chemistry of developmental processes
  9. 9. COMPARATIVE EMBRYOLOGY – deals with different closely related groups EVOLUTIONARY EMBRYOLOGY MEDICAL EMBRYOLOGY AND TERATOLOGY VALUE AND IMPORTANCE OF EMBRYOLOGY - logically, it is a key that helps unlock the secrets of heredity, the determination of sex, and organic evolution
  10. 10. - Medically, it is important because it supplies a comprehensive and rational explanation of the intricate arrangements of human anatomy. The body does not just happen to be arranged as it is; each end-result is preceded by a definite course of developmental events. Because of this, malformations of various kinds can be explained on the basis of departures from the usual pattern.
  11. 11. It is also able to interpret vestigial structures, to explain growth, differentiation and repair, and to shed light on some pathological conditions. - It is essential to sound training in anatomy, pathology and surgery. Furthermore, obstetrics is largely applied embryology. Subspecialties like pediatrics and OB find it an indispensable tool
  12. 12. ANCIENT VIEWS OF HUMAN EMBRYOLOGY Egyptians of the Old Kingdom, about 3,000 B.C. knew of methods for incubating birds’ eggs but they left no records. Akhnaton (Amenophis IV) praised the sun- god, Aton, as the creator of the germ in woman, maker of the seed in man, and giver of life to the son in the body of his mother. The ancient Egyptians believed that the soul entered the child at birth through the placenta
  13. 13. Aristotle – first to formulate the alternative that an embryo must either be preformed and only merely enlarging during its development, or it must be actually differentiating from a formless beginning - favored epigenesis Francesco Redi
  14. 14. Louis Pasteur William Harvey Kaspar Friedrich Wolff – revived Epigenesis -observed the development of a chick embryo, he demonstrated that the embryonic parts develop from tissues have no counterpart in adult organism
  15. 15. Marcello Malphighi – all organs of the adult were prefigured in miniature within the sperm or the egg Albrecht von Haller and Charles Bonnet Immanuel Kant and Johann Friedrich Blumenbach
  16. 16. Christian Pander – discovered the 3 germ layers Ectoderm, Mesoderm, Endoderm Triploblastic vs diploblastic - The germ layers did not form their organs independently enough to indicate what it truly is, it still needs the help and interaction
  17. 17. Karl Ernst von Baer – discovered the notochord - also discovered the mammalian egg Heinrich Rathke – described the formation of the vertebrate skull
  18. 18. - studied the development of inverts, especially the crayfish. - discovered the Rathke’s pouch, the embryonic rudiment of the pituitary.
  19. 19. Heredity operates through internal factors -genes as hereditary determiners -direct the development of a host of enzymic reaction-systems Environment supplies the external factors -can condition the appearance of genetic characters -can modify the developmental expression of inherited characters
  20. 20. -can alter the genetic constitution of chromosomes (mutations and teratology) METHODS OF STUDY - In proper age-sequence - Serial, related series that permits changing appearances - Depth, breadth and length - Time
  21. 21. EPIGENESIS -embryo organs de novo (from scratch) PREFORMATION -all adult organs are preformed and prefigured in miniature within the sperm or the egg -aligned with Descartes
  22. 22. 1. The general features of a large group of animals appear earlier in development than do the specialized features of a smaller group 2. Less general characters develop from the more general, until finally the most specialized appear
  23. 23. 3. The embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them 4. Therefore, the early embryo of a higher animal is never like a lower animal, but only like its early embryo
  24. 24.  Cell Proliferation - carried out by mitosis -DNA synthesis at interphase -prophase -metaphase -anaphase -telophase – daughter cell formation
  25. 25. - Developmental increase in mass - Fundamental property of life - Important factor in development
  26. 26. 1. Protoplasmic synthesis – building up of new protoplasmic material from available food stuff -takes place when anabolism exceeds catabolism 2. Water uptake – colloids within cells imbibe water and swell ionic concetrations – can hold or release water
  27. 27. 3. Intercellular deposition – results from the manufacture and the deposit of non-living substances like jelly, fibers and ground substance of cartilage and bone 4. Intracellular storage – fat deposition underneath the skin or in between organs
  28. 28. A. Absolute rate – amount of increase during any period divided by the length of that period B. Relative rate – relative increase per unit of time - computed by dividing each absolute rate by the initial value (in weight/volume/or length)
  29. 29. Absolute gain in weight of a 10 lb baby and a 100 lb youth may be 1 lb each but expressed in relative terms would be 10% and 1% Generally, organisms grow at the same relative rate Differential growth – progressive alteration of form and proportions both external and internal
  30. 30.  Constitutional factor – control the speed of growth to be approximately the same in all individuals of a species; there is little difference in the final size attained - inherited qualities predispose toward a definite basic rate of cell division and growth
  31. 31.  Temperature – each species has its critical maximum and minimum range at which development ceases - optimum temperature – most favorable temperature for growth  Nutritional factor – creation of new protoplasm -amino acids – building blocks 9 a.a. are indispensable for growth
  32. 32.  Growth promoting factors – embryonic factors increase mitosis and shorten division time - hormones – secretions of ductless glands which regulate growth thyroid hormone – increases rate of cell metabolism and oxidative processes hypophysis – stimulates growth of various tissues
  33. 33. - vitamins – accessory food substances which animals obtain from plants vit A – for weight gain/growth of skeleton vit B12 (riboflavin) – exerts specific influence on growth; no growth without it vit C and vit D – essential for normal growth
  34. 34.  Growth arresting factors – check and balance in growth to prevent gigantism - Differentiation – implies increasing structural complexity - Morphogenesis – change in shape and organization of the body and its parts - Histogenesis – progressive change in the substance and structure of the cells themselves whereby tissues are created
  35. 35. – molding of the body and its organs into form and pattern Cell multiplication and growth 1. Cell migration 2. Cell aggregation – masses, cords sheets 3. localized growth – enlargements of various kinds and constrictions 4. fusion and splitting
  36. 36. 5. Folding – evaginations - invaginations 6. Bending – due to unequal growth 7. Degeneration – to remove temporary or excess parts Vestigial organs: teeth appendix
  37. 37. - Cell specialization controlled by the genes in the chromosomes (DNA) to transmit coded information to RNA - during histodifferentiation, germ layers that are at first alike in visible structure and lack of specific shape are designated by the suffix blast neuroblast – nerve cell myoblast – muscle cell
  38. 38.  Change form and character as they produce hairs, nails, lens of eye, enamel of teeth  Glandular derivatives – sweat glands, mammary glands, salivary glands, anterior lobe of hypophysis  Local specializations – sensory epithelium of organs of smell, hearing and vision
  39. 39.  Cell proliferation  Morphogenesis  Histogenesis - decentralizing processes -need to be re-investigated into a cooperative working mechanism -control is supplied by endocrine glands and nervous system