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1st Trimester: Pre-Implantation Period (1st Week after conception)
Fertilization-union of ovum and sperm that forms a zygote (fertilized egg). Meiosis-during fertilization. The result is the joining of the ovum's chromosomes with those of the sperm. After fertilization-zygote undergoes mitosis that splits into more cells due to cleavage. Initial cleavage results in a morula (solid ball of cells). -
1st Trimester: Pre-Implantation Period (1st Week after conception)
Blastocyst-forms (5th day) due to ongoing process of mitosis within morula. Implantation (6th day)-blastocyst travels until it's embedded in the endometrium (innermost lining of uterus). Blastocyst forms two layers: outer trophoblast layer (forms prenatal support tissue) and the inner embryoblast layer (forms embryo). -
1st trimester: Embryonic period (2nd-8th week)
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1st trimester (Embryonic 2nd Week)
Implanted blastocyst grows from proliferation of embryonic cells, which form embryonic layers. Eventually develops the bilaminar embryonic disc (develops into the embryo later). The disc consists of the superior epiblast layer and inferior hypoblast layer, along with the amniotic cavities and yolk sac (nourishment). Placenta develops from trophoblast layer. -
1st Trimester (Embryonic 3rd Week)
Primitive steak forms within (middle) of bilaminar disc. Cells from the epiblast layer will migrate toward the hypoblast layer to the primitive steak to form the mesoderm. The epiblast layer is now considered the ectoderm. The hypoblast is now considered the endoderm. All three layers form the trilaminar embryonic disk. -
1st Trimester (Embryonic 3rd Week)
Trilaminar embryonic disk has a cephalic end and caudal end. The oropharyngeal membrane forms at the cephalic end and it will eventually house the stomodeum. The cloacal membrane forms at the caudal end, and will eventually house the future digestive tract. -
1st Trimester (Embryonic 3rd Week)
CNS begins to develop to make the spinal cord and brain. Neuroectoderm develop and are located in the neural plate. Neural plate forms the neural grooves and folds that eventually grows into the neural tube (4th week). NCCs from the neuroectoderm migrate to the mesoderm to form mesenchyme. -
1st Trimester (Embryonic 3rd Week)
Mesenchyme is involved in developing the face, neck, pharyngeal arches. Ectomesenchyme form tooth structures. Mesoderm forms the somites (gives risk to skeletal structures of the head, neck, trunk, muscles, dermis). -
1st Trimester (Embryonic 4th Week)
Formed neural tube that will give rise to the future spinal cord. Trilaminar embryonic disk begins embryonic folding and makes the embryo tubular with cephalic and caudal ends. The cephalic end will hold the future brain. The caudal end will hold the future digestive tract. -
1st Trimester (Embryonic 4th Week)
There are 3 major regions that make up future digestive tract. The anterior part (foregut) which will form the primitive pharynx. The posterior parts (midgut and hindgut) will form the rest of the pharynx and digestive tract. Four pairs of pharyngeal pouches will also form lateral to the larynx. -
1st Trimester (Embryonic 4th Week)
The face and neck structures will also begin to develop (the primitive eyes, ears, nose, oral cavity and jaw area). The developing face, brain, and heart are noted. -
Orofacial Development (4th Week)
The oropharyngeal membrane disappears to reveal and enlarge the stomodeum, allowing access to the primitive pharynx. The stomodeum will be the future oral cavity. -
Orofacial Development (4th Week)
Maxillary processes fuse with each medial nasal process to form upper lip (finishes at 7th week), and with each mandibular arch to form the labial commissures. Maxillary process will also form the midface (cheeks, secondary palate, posterior maxilla, canines, zygomatic and temporal bone). -
Orofacial Development (4th Week)
Cervical Development-develop from the primitive pharynx and branchial apparatus (arches, grooves, membrane, pouches). The branchial arches will give rise to important structures of the face and neck.
1st arch-mandibular arch.
2nd arch-hyoid.
3rd arch-part of hyoid.
4-6-pharynx and larynx.
1st groove-external acoustic meatus.
Pharyngeal membrane-tympanic membrane.
1st pouch-tympanic membrane and auditory canals
2nd pouch-palatine tonsil and pharyngeal walls
3-4th pouch-parathyroid and thymus -
Orofacial Development (4th week)
Frontonasal process forms the forehead, nasal placodes, nasal pit (nasal cavity), medial (middle and root of nose, upper tubercle of lip, philtrum), and lateral (alae) nasal processes, and intermaxillary segment to form the nose (nasal septum) and primary palate. -
Oral Facial Development (4th Week)
Mandibular processes fuse to form the mandibular arch, mandible, and lower lip (lower face). Also form the maxillary processes. Mandibular arch also involved in the formation of the tongue and the muscles of mastication. 5-6th week-primitive muscle cells from mesoderm, begin to differentiate. 7th week-mandibular muscle mass has grown larger and cells start to differentiate into the four muscles of mastication. 10th week-muscles of mastication formed -
Palatal Development (5th week-12 week)
5-6th week-primary palate (intermaxillary segment); Incisors 6-12th week-secondary palate (fused palatal shelves from maxillary processes). Gives rise to soft palate, uvula, canines, posterior teeth. Medial palatine raphe indicates the line of fusion. 12th week (fetal)-final palate (fusion of all three processes). Posterior part of the primary palate meet the secondary palate to form the final palate (hard and soft palate). Mature oral cavity is completely separated from the nasal cavity. -
Nasal Cavity and Septum Development (5th-12th Week)
Forms at the same time as palate. Later serve as part of the respiratory system. The septum is a growth from the fused medial nasal processes, which fuses with final palate after it forms (9th-12th week). Also separates nasal cavity from oral cavity. -
Tongue Development (4th-8 Week)
Develops from swelling on the primitive pharynx floor from the branchial arches. Body develops from 1st branchial arch.
Body-tuberculum (midline) impar and lateral lingual swellings appear. Swellings merge to encompass temporary tuberculum. The median lingual sulcus is the line of fusion of the swellings and frees the body from the floor of the mouth (except lingual frenum) -
Tongue Development (4-8th Week)
Base develops from the 2-4 arches. Base-Copula (posterior to swelling) overgrowing second branchial arches. Formed by mesenchyme of the 3-4th arches. Farther to the copular is the epiglottic swelling (mesenchyme of 4th arch); most posterior region of the tongue and site of future epiglottis. Sulcus terminalis is the fusion; points backward toward foramen cecum (origin of thyroid gland) Completed tongue-(8th week); merging on anterior swelling of body and copula of base -
Fetal Period (2nd and 3rd Trimester; 3rd to 8th month)
Maturation of existing structures that form the fetus from the embryo. Involves the physiologic processes from Embryonic period (maturation, proliferation, differentiation, morphogenesis).