Week 1 Oral Histology: Prenatal Development (PDF)

Week 1 Monday, 8 July 2024 12:27 pm Lecture Oral Histology: General Embryology Prenatal development, face/neck Embryology Embryology is the branch of biology that studies the prenatal development of gametes, fertilization, and development of embryos and foetuses Embryology encompasses t...

Week 1 Monday, 8 July 2024 12:27 pm Lecture Oral Histology: General Embryology Prenatal development, face/neck Embryology Embryology is the branch of biology that studies the prenatal development of gametes, fertilization, and development of embryos and foetuses Embryology encompasses the study of congenital disorders that occur before birth, known as teratology. For the Dental Practitioner, it is important to have an foundational understanding of typical embryonic development and developmental anomalies. Common terms Induction: To start an embryonic phenomenon (formation of something). Inducer: The molecular or cellular element that starts the induction. Primitive streak is the inducer of notochord Differentiation: The process by which cells, tissues, and organs acquire specialized featu during development. Gamete: a mature male or female germ cell; a sperm or ovum Haploid: the single chromosome set carried by the sperm and egg cells which are recom after fertilisation to create the diploid chromosome set present in every cell of the body except sperm and eggs Diploid: a cell such as a somatic cell having two chromosome sets, as opposed to the ha situation of eggs and sperm which have only one chromosome set Oocyte: the mature female germ cell; the egg Stem cell: an undifferentiated cell which is a precursor to a number of differentiated (specialised) cell types. - Stem cells may be totipotent, pluripotent, or committed to a particular cell lineage (eg.  Tutorial Embryology order 1. Fertilisation Fusion of haploid gametes (sex cells) Forms a diploid zygote Nuclear membrane breaks down, DNA replication commences (Mitosi 2. Zygote Formation Occurs at the distal end of the fallopian tube (Ovi duct). The newly formed Zygote then travels via motions generated by micro contractions towards the uterus 3. Cleavage rapid cell division without cell growth Total cytoplasm remains constant Cell size rapidly decreases as number of cells increased 4. Morula is formed Now a ball of 16-20 cells flattened against the zona pellucida 5. Blastocyst ures A cavity forms within the morula, and the ball of cells is now termed th 6. Implantation occurs mbined Motility slows, Adhesion to uterine epithelium, as the cells of the blast y endometrium, permitting deeper penetration and attachment 7. Bilaminar embryonic disk is formed aploid Epiblast: gives rise to future germ cell layers Hypoblast: transient - gives rise to some umbilical tissues 8. Trilaminar embryo Gastrulation Begins with Emergence of the Primitive streak (caudal) & neural induction and migration of cells into 3 layers to become the trilaminar is) oscopic cilia and he blastocyt tocyst digest the uterine & node formation r (3 layered) embryonic  Diploid: a cell such as a somatic cell having two chromosome sets, as opposed to the ha situation of eggs and sperm which have only one chromosome set Oocyte: the mature female germ cell; the egg Stem cell: an undifferentiated cell which is a precursor to a number of differentiated (specialised) cell types. - Stem cells may be totipotent, pluripotent, or committed to a particular cell lineage (eg. stem cell) Overview of Human Development The total human gestation is approx 40-weeks There are 3 key periods Critical periods exist where development and differentiation are primarily taking place Disruption to this critical period (e.g teratogen) can result in abnormality. Before anything In the Male: Spermatogenesis has taken place (Meiotic process). In the Female: Oogenesis has taken place (Meiotic process) Ovulation has occurred: release of an egg (ovum) from the ovaries aploid Epiblast: gives rise to future germ cell layers Hypoblast: transient - gives rise to some umbilical tissues 8. Trilaminar embryo Gastrulation Begins with Emergence of the Primitive streak (caudal) & neural induction and migration of cells into 3 layers to become the trilaminar disc LAYER LATER GIVES RISE TO… Ectoderm CNS, PNS, parts of sensory system, epithelium of mucosa of nasal and sinus cavities, teeth enamel. Mesoderm Blood, bone, muscles, some organs, remainder of Endoderm Epithelial lining of pharynx, stomach, intestines, lu organs of the urogenital tract. 9. Embryonic folding begins On the establishment of the trialaminar embryonic disc, the embryo th Embryonic Folding to establish the bodies axis. This allows for the formation of body cavities as a series of tubes. This is a very complex and dynamic process. 10. Stomadeum is formed e. Formed by an invagination ectoderm tissues (noticeable by the end o 11. 5 pharyngeal arches appear Pouches of endoderm extend into the surface ectoderm, which divid arches and clefts Establishes 5 pharyngeal arches (aka Branchial arches). Each contains an artery, cartilage, cranial nerve and mesodermal tiss Arches I-IV are involved in the development of structures in the face & node formation r (3 layered) embryonic skin, oral mucosa,. f tooth structures. ungs, bladder and hen undergoes of the third week). des mesoderm into sue and oral cavity. In the Male: Spermatogenesis has taken place (Meiotic process). In the Female: Oogenesis has taken place (Meiotic process) Ovulation has occurred: release of an egg (ovum) from the ovaries Didn’t watch this ^ Fertilisation 1. Fusion of haploid gametes (sex cells) 2. Forms a diploid zygote 3. Nuclear membrane breaks down, DNA replication commences (Mitosis) Sperm head enters zone pellucide enters the periphery Sperm head enters zone pellucide enters the periphery Occurs at the distal end of the fallopian tube (Ovi duct). The newly formed Zygote then tr via motions generated by micros cilia and contractions towards th uterus Germinal Period Day Name Events Day 0 Fertilisation Zygote Formation Day 0-3 Cleavage Cleavage: rapid cell division without cell growth Total cytoplasm remains constant Cell size rapidly decreases as number of cells increased Day 4 Morula Now a ball of 16-20 cells flattened against the zona pellucida The Morula is now located at the proximal end of the oviduct - 32 cells (tutorial)  ravels scopic he Day Name Events Day 5 Blastocyst A cavity forms within the morula, and the ball of cells is now terme blastocyst Day 7 Implantation Motility slows, Adhesion to uterine epithelium, as the cells of the blastocyst digest the uterine endometrium, permitting deeper penetration and attachment ed the Formation of a Bilaminar Embryo Day 8-9 Epiblast Gives rise to future germ cell layers Hypoblast Transient – gives rise to some umbilical tissues FOUR embryonic membranes develop 1. Amniotic sac/Amnion 2. Yolk sac Nourishment for disc 3. Chorion (Not displayed) this will eventually become the chorionic sac, which will, along with the uterine wall, will become the placenta 4. Allantois (Connecting stalk) contributes blood vessels from the embryo to the placenta; eventually becoming the umbilical cord Weeks 2-3 Gastrulation Gastrulation Begins: Emergence of the Primitive streak (caudal) & node formation induction and migration of cells into 3 layers to become the trilaminar (3 layered) embryonic disc - Trilaminar embryonic disk  - Trilaminar embryonic disk Trilaminar embryonic disk LAYER LATER GIVES RISE TO… Ectoderm CNS, PNS, parts of sensory system, epithelium of skin, oral mucosa, m of nasal and sinus cavities, teeth enamel. Mesoderm Blood, bone, cartilage, muscles, some organs, remainder of tooth structures (pulp and dentine) Endoderm Epithelial lining of pharynx, stomach, intestines, lungs, bladder and or of the urogenital tract. Though the level of detail is not required for this subject. It is important to know that also taking place is: Neuralation: The formation of the primitive nervous system. Somitogenesis – Mesoderm differentiates into specific sections that will later give rise t particular body tissues (e.g. splanchnic mesoderm – Heart & GI tract tissues). Early organogenesis has also commenced. mucosa rgans to Embryonic Folding On the establishment of the trilaminar embryonic disc, the embryo then undergoes Embryonic Folding to establish the bodies axis. This allows for the formation of body cavities as a series of tubes. This is a very complex and dynamic process.