Basic Embryology for 1st BDS students.pptx

Basic Embryology for 1st BDS students

1. embryology Introduction Development of face Development of tongue Development of palate Development of maxilla & mandible - Dr.Smitha Rao

2. A human being develops from a single cell structure to an organ having billions of cells during a period of 9mths The time of retention of the embryo or fetus in the uterus – dev – called Gestation Period – 266 days

3. Phases of development

4. Three fundamental processes: 1. Morphogenesis (morph- = shape, + genesis = origin) Origin of shape, form 2. Differentiation Process of cells becoming different, and specializing for different functions 3. Growth Increase in size, requires input of matter, food

5. Embryology Sequence of Events: Fertilization Cleavage Gastrulation Organogenesis

6. 1. Fertilization Gametes join in fertilization gametes are produced (gametogenesis) through meiosis What process produces every other cell in the human body? MITOSIS

7. Let the Division Begin!

8. 2. Cleavage Cleavage is a series of rapid mitotic divisions (without cell growth) The two-celled zygote divides repeatedly until a ball of 32 cells is formed This is the morula - 32 cells 

9. Continued divisions make the hollow blastula These few cells are pluripotent (have the potential to become ANY of the 220 types of cells in the human body). These are embryonic stem cells

10. 3. Gastrulation Gastrulation = formation of a gut; Major MORPHOGENIC event !!! At the end of the cleavage stage, cells making up the blastula move about and surface proteins help cells recognize each other Location of cells after GASTRULATION determines further development The gastrula is formed, which can consists of 3 “germ layers” 1. Endoderm “inside skin” 2. Mesoderm “middle skin” 3. Ectoderm “outside skin”

11. Gastrulation

12. Human Development The gestation period lasts 266 days from fertilization to birth Organogenesis (development of the organs and organ systems) begins with the nervous system

13. Development in Classification Tissues -collections of specialized cells working together and isolated from other tissues by membranous layers. (germ layers) Diploblastic Animals Have two germ layers, ectoderm and endoderm. (Jellyfish) Triploblastic Animals Have three germ layers, ecto -, meso -, and endoderm. (All "higher" and "intermediate" animals, from flatworms to  humans , are  triploblastic )

14. Zygote Cleavage Eight-cell stage Cleavage Blastula Cross section of blastula Blastocoel Blastocoel Gastrula Gastrulation Endoderm Ectoderm Blastopore Early embryonic development in animals In most animals, cleavage results in the formation of a multicellular stage called a blastula. The blastula of many animals is a hollow ball of cells. 3 The endoderm of the archenteron de- velops into the tissue lining the animal’s digestive tract. 6 The blind pouch formed by gastru- lation, called the archenteron, opens to the outside via the blastopore. 5 Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer). 4 Only one cleavage stage–the eight-cell embryo–is shown here. 2 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage. 1

15. Gestation Period composed of: Germinal period – 1-3 rd week after fertilization- zygote dev & trilaminar germ disc formation Embryonic period – 3- 8 th week – differentiation & formation – most of the tissues & organs Fetal period – 3- 9 th mth – rapid growth of the fetus & complete dev of placenta

16. A HIGHLY SPECIALIZED TOTIPOTENT CELL- ZYGOTE . Prenatal development is divided into 1.Pre implantation period - 1 st week 2.Embryonic period – 2 nd to 8 th week 3.Fetal period – 9 th to 38 th week.

17. 1.Pre implantation period Period of cell proliferation from the zygote to morula , blastocyst and formation of bilaminar embryonic disc. Birth defects do not originate during this period because body systems and structures have not yet developed.

18. General embryology 3 successive phases Prenatal development Fetal stage Embryonic stage

19. Fertilized egg initially undergoes a series of rapid divisions that lead to the formation of a ball of cells called the morula Fluid seeps into the morula , & its cells realign themselves to form a fluid-filled hollow ball ,the blastocyst 2 cell populations can be distinguished within the blastocyst: Trophoblast Embryoblast Formation of germ layers

20. At day 8 of gestation Embryoblast Bilaminar germ disc differentiates Ectodermal layer Endodermal layer Amniotic cavity Secondary yolk sac

21. Bilaminar embryo

22. Germ layer derivatives 3 germ layers 3 germ layers Ectoderm Mesoderm Endoderm

23. During 3 rd week of development bilaminar embryonic disc is converted into a trilaminar disc. Mesoderm is situated between the ectoderm and endoderm paraxial Mesoderm intermediate lateral plate During next 3 to 4weeks of development major tissues and organs differentiate from the triphoblastic embryo-head and face and the tissues contributing to the development of teeth Key events – differentiation of nervous system and neural crest tissues from the ectoderm, differentiation of mesoderm Folding of embryo in 2 planes ( rostrocaudal &lateral axis)

24. NEURAL CREST D erived from the ectoderm, the neural crest has sometimes been called the fourth germ layer because of its importance . The neural crest cells originate at the dorsal most region of the neural tube

25. The neural crest cells migrate extensively to generate a prodigious number of differentiated cell types . These cell types include (1) the neurons and glial cells of the sensory, sympathetic, and parasympathetic nervous systems, ( 2) the epinephrine-producing (medulla) cells of the adrenal gland , (3) the pigment-containing cells of the epidermis, and (4) many of the skeletal and connective tissue components of the head. 

26. Schwann’s sheath cell, Sensory ganglia, Autonomic ganglia, Glial cells Neural Crest Derivatives Neurogenic cells Pigment cells Mesenchymal cells Melanocyte in all tissue Melanophores of iris Pharyngeal arches, Bones and cartilages of face Dental papilla, PDL, cementum

27. Neural crest derivatives Cranial and sensory ganglia and nerves Adrenal medulla Ectomesenchyme bones and skull Dentin Periodontal ligament Alveolar bone

28. Embryonic stage Begins with gastrulation in the bilaminar disc and ends with an embryo that looks very human. The embryonic disc folds into a cylinder to establish the basic characteristics of the vertebrate body plan, and the primordia of all the organ systems develop. Pharyngeal arches appear. It is very dynamic period of differentiation, development and morphological change.

29. Head fold primitive stomatodeum or oral cavity Lateral folding ; Paraxial mesoderm remains adjacent to neural tube Intermediate mesoderm forms urogenital tissue Lateral plate mesoderm cavitates to form coelom & the mesoderm bounding the cavity lines the body wall & gut Folding of the embryo

30. Fetal stage   The embryo changes to a recognizable human being and develops all the basic outlines of its organs and is then called a fetus. Morphogenesis Involves many intricate embryologic processes Congenital defects develop

31. Derivatives of the branchial(pharyngeal)arch system Arch Nerve Muscles Skeletal stuctures ligaments First (mandibular) trigeminal Muscles of mastication Mylohyoid & anterior belly of digastric Tensor tympani Tensor veli palatani Malleus Incus Anterior ligament of malleus Sphenomandibular ligament Second (hyoid) facial Muscles of facial expression Stapedius Stylohyoid Posterior belly of digastric Stapes Styloid process Lesser cornu of hyoid bone Upper part of body of hyoid bone Stylohyoid ligament

32. f Arch Nerve Muscles Skeletal structures Third glossopharyngeal Stylopharyngeas Greater cornu of hyoid bone Lower part of body of hyoid bone Fourth & sixth Superior laryngeal branch of vagus Recurrent laryngeal branch of vagus Cricothyroid Levator veli palatini Constrictors of pharynx Intrinsic muscles of larynx Striated muscles of esophagus Thyroid cartilage Cricoid cartilage Arytenoid cartilage Corniculate cartilage Cuneiform cartilage Derivatives of the branchial(pharyngeal)arch system

33. Development of face

34. 5 facial primordia : The single frontonasal prominence The paired maxillary prominences The paired mandibular prominences

35. FNP (FRONTONASAL PROMINENCE) surrounding the ventrolateral part of forebrain Frontal part Nasal part optic vesicles that form eyes Fore head Nose

36. Paired maxillary prominence lateral boundary of stomodeum Paired mandibular prominence caudal boundary of the stomodeum Facial development -4-8weeks Lower jaw & lower lip are the first parts of the face to form

37. By the end of 4 th week nasal placodes develop on the inferolateral parts of the FNP

38. Formation of medial & lateral nasal prominences Nasal pits- primordia of the anterior nares(nostrils) & nasal cavities

39. By the end of 5thweek ,the primordia of the auricles have begun to develop 6 auricular hillocks form around the first pharyngeal groove, the primordia of the auricle & the external acoustic meatus respectively

40. By the end of 6 th week maxillary prominence merge with the lateral nasal prominence along the line of nasolacrimal groove This establishes continuity between the side of nose & the cheek region

41. Between 7 th &10 th weeks the medial nasal prominence merge with each other &with the maxillary & lateral nasal prominences Intermingling of underlying mesenchymal cell s

42. Merging of the medial nasal &maxillary prominence: continuity of the upper jaw & lip & separation of nasal pits from the stomodeum Merging of medial nasal prominences form an intermaxillary segment

43. Intermaxillary segment Middle part of the upper lip Premaxillary part of the maxilla & its associated gingiva The primary palate

44. summary Fronto nasal prominence forehead &dorsum &apex of the nose Lateral nasal prominences alae of the nose Medial nasal prominences nasal septum, ethmoid & cribriform plate Maxillary prominences upper cheek regions & the upper lip Mandibular prominences chin, lower lip& lower cheek regions

45. By the end of 4 th week nasal placodes develop on the inferolateral parts of the FNP

46. Formation of medial & lateral nasal prominences Nasal pits- primordia of the anterior nares(nostrils) & nasal cavities

47. Development of nasal cavities Nasal sacs are separated from the oral cavity by the oronasal membrane By the end of the 6 th week , oronasal membrane ruptures Nasal & oral cavities communicate with each other

48. Development of nasal cavities

49. Primordial choanae-region of continuity between the nasal & oral cavities After secondary palate develops ,chonae are located at the junction of the nasal cavity & pharynx Superior ,middle & inferior nasal conchae develop as elevations of the lateral walls of the nasal cavities

50. Specialized ectodermal epithelium in the roof of the nasal cavity form the olfactory epithelium Some epithelial cells differentiate into olfactory receptor cells(neurons) The axons of these cells constitute olfactory nerves

51. Most of the upper lip, maxilla & secondary palate form from the maxillary prominences Mesenchyme from the second pair of pharyngeal arches invade the primordial lips & cheeks which differentiate into facial muscles Muscles of facial expression are supplied by the facial nerve Mesenchyme in the first pair of arches differentiates into the muscles of mastication & few others-innervated by trigeminal nerves

52. Development of palate 2 stages: Primary palate Secondary palate

53. Primary palate Palatogenesis begins in 6 th week Early in the 6 th week, the primary palate –median palatal process(inter maxillary segment)-begins to develop Primary palate forms the premaxillary part of the maxilla Represents only a small part of the adult hard palate

54. Secondary palate Primordium of the hard and soft parts of the palate Develop from 2 mesenchymal projections in the 6 th week During 7 th & 8 th weeks the lateral palatal processes assume a horizontal position above the tongue Bone develops in primary palate, forms the premaxillary part of the maxilla which lodges the incisor teeth Bone extends from the maxilla & palatine bones into palatal processes to form hard palate

55. Secondary palate Palatal processes extend posteriorly beyond the nasal septum & fuse to form soft palate including the uvula Nasopalatine canal persists in the median plane Nasal septum develops as a downward growth from internal parts of the merged medial nasal prominences

56. Development of palatal processes

57. Fused palatal processes

58. Development of tongue Develop at 4 weeks Local proliferation of mesenchyme-number of swelling in the floor of the mouth First a swelling, tuberculum impar arises in the midline in the mandibular process 2 lingual swellings arise Lateral lingual swellings enlarge &merge with each other &the tuberculum impar to form a large mass From this mass mucous membrane of the anterior two thirds of the tongue is formed

59. Root of the tongue arises from a large midline swelling developed from the mesenchyme of the second, third & fourth arches This swelling consists of a copula & a large hypobranchial eminence Posterior part of the fourth arch marks the development of the epiglottis The tongue separates' from the floor of the mouth by a downward growth of ectoderm around its periphery, which degenerates to form the lingual sulcus & gives the tongue mobility

60. Nerve supply of tongue Anterior two thirds of the tongue-5 th cranial nerve Posterior third of the tongue-ninth cranial nerve Muscles of the tongue-twelfth cranial nerve

61. Development of the mandible

62. Development of mandible At 6 weeks- meckels cartilage extends as a solid hyaline cartilaginous rod, surrounded by a fibro cellular capsule Mandibular branch of trigeminal nerve begins two thirds of the way along the length of the cartilage At this point mandibular nerve divides into lingual & inferior alveolar branches Inferior alveolar nerve further divides into incisor & mental branches

63. Development of mandible On the lateral aspects of meckel’s cartilage, condensation of mesenchyme occurs in the angle formed by the division of the inferior alveolar nerve & its incisor & mental branches At 7 weeks , intramembraneous ossification begins in this condensation, forming the first bone of the mandible From this centre of ossification bone formation spreads rapidly anteriorly to the midline,& posteriorly to the point where mandibular nerve divides

64. Development of mandible The two separate centre of ossification remain separated at the mandibular symphysis shortly after birth Backward extension of ossification along the lateral aspect of meckel’s cartilage forms a canal From this bony canal, medial & lateral alveolar plates of bone develop in relation to the forming tooth germs In this way body of mandible is formed

65. Development of mandible Ramus of the mandible develops by a rapid spread of ossification posteriorly into the mesenchyme of the first arch, turning away from meckel’s cartilage By 10 weeks the rudimentary mandible is formed almost entirely by membranous ossification

66. Fate of the meckel’s cartilage Most posterior extremity forms the incus & malleus of the inner ear & the sphenomalleolar ligament From the sphenoid to the division of the mandibular nerve ,the cartilage is totally lost ,but its fibro cellular capsule persists as the sphenomandibular ligament From the Lingula forward to the division of the alveolar nerve, meckel’s cartilage degenerates

67. Development of mandible Further growth of the mandible until birth is influenced by the appearance of 3 secondary cartilages: The condylar cartilage The coronoid cartilage & The symphyseal cartilage

68. Development of maxilla Formed by maxilla proper & premaxilla Maxilla proper is developed as an extension of mandibular arch Forms by intramembraneous ossification Ossification starts at about 6 weeks of intrauterine life https://www.youtube.com/watch?v=SBkGnzgVoFI https://youtu.be/SBkGnzgVoFI?si=H0P4KXehE1Ura-ee

69. Development of maxilla Ossification centre appears near the part which forms enamel organ of the canine tooth germ Ossification spreads backwards towards zygomatic bone & forwards towards premaxilla Premaxilla forms primary palate

70. Clefts Congenital defects CLEFTS Oblique facial cleft Median cleft lip Bilateral cleft lip microstomia macrostomia Mandibular cleft

71. Lip & anterior maxilla-defective development of the embryonic primary palate Facial clefts-deficiency of mesenchyme in the facial region due to the failure of the neural crest to migrate or failure of the facial mesenchyme to proliferate Causes of Clefts

72. Failure of the shelves & septum to contact each other Failure of the shelves & septum to fuse Rupture after fusion of the shelves Defective merging & consolidation of the mesenchyme of the shelves Causes of palatal Clefts

73. Infectious agents X-ray radiation Drugs Hormones Nutritional deficiencies Environmental factors affecting the embryo