Chapter 8 Embryology / Histology

Embryology Study of prenatal growth and development. Study of embryos immature organism contained within the coverings of an egg or within the body of the mother

Conception Ovum Sperm This begins gestation Female cell Fertilized by the Sperm Male cell This begins gestation The time from conception to birth 38 – 40 weeks average

Prenatal Phases Zygote (1st phase) Conception – 2 weeks Cells are blank ‘Stem cells’ Proliferation occurs Cells rapidly increasing in numbers Causes cell growth Multiply by dividing

Prenatal Phases Embryo (2nd phase) 5 weeks (ectopic pregnancy) 3 week – 8 week Differentiation occurs Development of individual characteristics Cells Tissues Forms and shapes 5 weeks (ectopic pregnancy) 18-19 days→

Stages of differentiation Cytodifferentiaton Development of different cells Histodifferentiation Development of different tissues Morphodifferentiation Development of different forms / shapes

Primary embryonic layers Ectoderm Outside layer of the embryo Forms Skin Hair Nails Brain Enamel of the teeth

Primary embryonic layers Mesoderm Middle layer of the embryo Forms Lining of stomach Bones Muscles Several body systems Dentin, cementum, pulp of the teeth

Primary embryonic layers Endoderm Inside layer of the embryo Forms Glandular organs Lining of respiratory system Digestive tract

Prenatal Phases Fetus (3rd phase) 9th week – birth Proliferation and differentiation continue Growth and development continue

Stomodeum (primitive mouth) 1st sign of a developing mouth on an embryo 30-32 days → 28-29 days ↓

Developmental disturbances Cause abnormal growth or development of the fetus. Genetics Medications Trauma Alcohol Drugs

Developmental disturbances Cleft Improper fusion or joining of body structure. Cleft lip Improper fusion of the max. process w/ the nasal process. Unilateral Bilateral Partial Complete

Developmental disturbances Cleft palate Improper fusion of the palatal process w/ the max. process. Unilateral Bilateral Partial Complete

Developmental disturbances FAS Fetal alcohol syndrome Consumption of alcohol during gestation. Stunts growth / weight Affects neurons / brain development Causes Craniofacial deformities

Transition / conclusion Understanding growth and development will lead you to understanding how different cells form different tissues. This leads us to the next part of this chapter….. Histology

Histology The study of tissue in thin slices. Aka microscopic anatomy Essential part of understanding biology

Tissue types 4 basic types of tissue Epithelial Nervous Muscle Connective

Tooth tissues Enamel Dentin Hardest tissue Ameloblasts Cells that form enamel Covers the top of the tooth. Anatomical crown Translucent Light passes through No nerves/blood supply No pain Dentin Harder than bone, harder than cementum. Odontoblasts Cells that form dentin Bulk of the tooth Comprised of dentinal tubules Filled w/ dentinal fluid Sends sensory info to the pulp. Gives a tooth it’s ‘hue’ Underlying color

Tooth tissues Cementum Pulp Covers dentin on the roots Cementoblasts Cells that form cementum. Softer than enamel or dentin. Can be brushed away. Pulp Provides Nourishment to the dentin. Detects Temperature and Chemical changes Transmits Stimuli to the brain

Tooth pulp Pulp chamber Pulp horns Pulp canals Bulk of the pulp located here! Pulp horns Upward projections at the top of the chamber Pulp canals Aka root canals Small hollow tubes from apical foramen to the chamber.

Tooth tissue junctions CEJ Cementoenamel junction DEJ Dentinoenamel junction

Periodontal tissues Gingiva Bone Covers bone Alveolar bone Sulcus Epithelial attachment Bone Alveolar bone Lamina Dura Compact bone that lines socket.

Periodontal tissues PDL Periodontal ligament Sharpey’s fibers Attaches tooth to bone “shock absorber” Nourishment to cementum Sharpey’s fibers Attach PDL to tooth and bone.

Conclusion You are NOW the expert! You should know the 4 different types of tooth tissues… Their purpose/function Where they are located on the tooth. Please review this info for the quiz. Any questions???????