CH 3: Overview of Prenatal Development

Embryology

-Study of prenatal development

Neural Folds

-Raised ridges in the neural plate that surround deepening neural groove

Morula

-Solid ball of cells that takes place after cleavage

Embryo

-Structure derived from implanted blastocyst

Epiblast Layer

-Superior layer of bilaminar disk composed of high columnar cells

Caudal End

-Tail end of structure

Zygote

-Fertilized egg formed by the union of the ovum and sperm

Amniotic Cavity

-Fluid-filled cavity that faces the epiblast layer

Induction

-1st physiological process involved during prenatal development -Action of 1 group of cells on another, which leads to the establishment of the developmental pathway in the responding tissue and which is now considered to be compartmentalized -Can also occur in later stages of development

Which trimester do most congenital malformations occur?

-1st trimester of pregnancy

Embryonic Period

-2nd period of prenatal development -From beginning of 2nd week to end of 8th week

Neural plate of the Embryo

-A central band of cells that extends the length of the embryo, from the cephalic end to the caudal end -Undergoes further growth and thickening, which causes it to deepen and invaginate inward, forming the neural groove

Trophoblast layer

-A layer of peripheral cells -Later gives rise to important prenatal support tissue during next prenatal period (embryonic period)

Placenta

-A prenatal organ that joins the pregnant female and developing embryo -Develops from interactions of trophoblast layer and endometrial tissue -Permits selective exchange of soluble blood borne substances between then (oxygen, carbon dioxide, nutritional and hormonal substances)

Embryoblast

-A small inner mass of embryonic cells -Later gives rise to embryo during next prenatal period, the embryonic period

Congenital Malformations

-Also called birth defects -Evident at birth

Oropharyngeal Membrane

-Also called buccopharyngeal membrane -Forms at cephalic end and consists of only ectoderm externally and endoderm internally, without any intermediate mesoderm -Is the location of future primitive mouth or stomodeum of embryo

Yolk Sac

-Fluid-filled sac which faces the hypoblast layer and serves as initial nourishment for the embryonic disc

Blastocyst

-Structure formed during prenatal development consisting of trophoblast cells and inner mass of cells (embryoblast) that develop into embryo

Down Syndrome

-Also called trisomy 21 -Extra chromosome number 21 is present after meiotic division -Flat, broad face -Widely spaced eyes -Flat-bridged nose -Epicanthic folds -Oblique eyelid fissures -Furrowed lower lip -Tongue fissures -Lingual papillae hypertrophy -Intellectual disability -Arched palate, weak tongue muscles --> open mouth position and protrusion of normal-sized tongue with speech difficulty -Increased level of periodontal disease, fewer teeth with microdontia

Foregut

-Anterior part of tube (future digestive tract) -Forms primitive pharynx (primitive throat) and includes part of primitive yolk sac as it becomes enclosed with folding

Cloacal Membrane

-At the caudal end and is the location of the future anus, or terminal end of the digestive tract

Syphillis

-Bacterial spirochete -Treponema pallidum -Produces defects in incisors (Hutchinson's incisor) and molars (Mulberry molar), blindess, deafness, paralysis

Maturation

-Begins during embryological period and continues later during the fetal period -Maturation of individual tissue types and organs also involves proliferation, differentiation, and morphogenesis -Not just attainment of correct adult size, but also correct adult form and function of tissue types and organs!

Radiation Injuries

-Can injure embryonic cells, resulting in cell death, chromosome injury, delay of mental and physical growth -Severity associated with absorbed dose, dose rate, state of embryonic or fetal development at time of exposure

Sperm

-Cell containing male contribution of chromosomal information that fertilizes female ovum

Patterning

-Certain physiological processes or spatial and temporal events that occur during embryonic period, which are considered key to further development -Includes: 1. Induction 2. Proliferation 3. Differentiation 4. Morphogenesis 5. Maturation

Differentiation

-Change occurs in embryonic cells, which are identical genetically but later become quite distinct structurally and functionally -Cells that perform specialized functions are formed by differentiation during embryonic period (major tissue types, organs, organ systems) -Occurs at various rates in embryo

What takes place at the beginning of the 1st week?

-Conception takes place

Cytodifferentiation

-Development of different cell types

Histodifferentiation

-Development of different tissue types within a structure

Morphodifferentiation

-Development of the differing structure or shape, or morphology, for each organ or system

What is the proper number of chromosomes that result from the sperm and ovum being joined?

-Diploid number of 46

Embryonic Folding

-Disc undergoes embryonic folding during 4th week -Establishes the axis for the 1st time --> places forming tissue types into their proper positions for further embryonic development and somewhat tubular embryo -Results from extensive proliferation of ectoderm and differentiation of basic tissue -Occurs mainly at cephalic end where brain will form -Grows beyond oropharyngeal membrane to overhang developing heart -Also occurs at caudal end and sides of embryo simultaneously -Causes positions of embryonic cell layers to take on more recognizable placement for further development of the embryo

When do the final stages of meiosis occur in the ovum?

-During fertilization

Amniocentesis

-During fetal period -Amniotic fluid sampled during 14th to 16th weeks after last missed menstrual period -Usually in older females when 1 or both parents have chromosomal abnormality or neural tube defect, when previous child was affected, or when parents are carriers of inborn errors of metabolism or X-linked disorders such as hemophilia

When does the preimplantation period take place?

-During the 1st week after conception

Bilateral Symmetry

-Each half of embryo mirrors the other half -Caused by primitive streak -Top View: Embryo resembles sole of a shoe with head end wider than tail end, and slightly narrowed middle

Implantation

-Embedding of blastocyst in endometrium

Trilaminar Embryonic Disc

-Embryonic disc with 3 layers: ectoderm, mesoderm, endoderm -Bilaminar disc becomes thickened into trilaminar embryonic disc

Mesoderm

-Embryonic layer located between ectoderm and endoderm -Formed by connective tissue -Epiblast cells migrate between epiblast layer and hypoblast layer and starts to form mesoderm

Teratogens

-Environmental agents or factors such as infections, drugs, radiation causing malformations

Fetal alcohol Syndrome

-Ethanol ingested by pregnant female crosses placenta -Prenatal and postnatal growth deficiency, intellectual deficiency, other anomalies (small head circumference, low nasal bridge, short nose, small mid face, widely spaced eyes with epicanthic folds and eyelid fissures, indistinct philtrum, thin upper lip); oral changes (crowding of dentition, mouth breathing, anterior open bite, gingivitis, increased finger sucking habit)

Bilaminar Embryonic Disc

-Eventually developed from blastocyst and appears as a flattened, essentially circular plate of bilayered cells -Has superior and inferior layer: 1. Epiblast Layer 2. Hypoblast Layer -After creation, it is suspended in uterus's endometrium between 2 fluid-filled cavities: 1. Amniotic Cavity 2. Yolk Sac

Rubella

-Examples of infective teratogen for the embryo is the virus causing rubella -Results in cataracts, cardiac defects, deafness

Treacher Collins Syndrome

-Failure of migration of neural crest cells to facial region -Also called mandibulofacial dysostosis -Develops in embryo -Failure of full facial development presenting with downward slanting eyes, micrognathia (small lower jaw), conductive hearing loss, underdeveloped zygomatic bone, drooping in part of lateral lower eyelids, and malformed or absent ears

Ovum

-Female reproductive cell or egg which can be fertilized

Proliferation

-Follows after induction -Controlled levels of cellular growth and accumulation of byproducts present during most of prenatal development -Later, migration of proliferated cells occurs -Growth also occurs as a result of accumulation of cellular byproducts by: 1. Interstitial growth (occurs from deep within a tissue type or organ) or 2. Appositional growth (A tissue enlarges by addition of layers on outside of a structure)

Describe the fetal period of prenatal development.

-Follows embryonic period -Encompasses the beginning of the 9th week (3rd month), to the 9th month -**Maturation of existing structures occurring as embryo enlarges to become fetus -Involves physiological process or maturation and further proliferation, differentiation, morphogenesis -Changes with fetus not as dramatic -Allow newly formed tissue types and organs to function -Heartbeat and fetal movements can be noted at END of 4TH WEEK

Primitive Streak

-Forms during beginning of the 3rd week of prenatal development within embryonic period -Forms within the bilaminar disk -Furrowed, rod-shaped thickening in the middle of the disc results from increased proliferation of cells in the midline area -Causes disc to have bilateral symmetry

Embryonic Cell Layer

-Germ layers derived from increased number of embryonic cells

Neural Groove

-Groove from further growth and thickening of neural plate

Cephalic End

-Head end of structure

Ectopic Pregnancy

-Implantation occurs outside the uterus (usually in fallopian tube) -Caused by various things that delay transport of dividing zygote to uterus like scarred uterine tubes due to pelvic inflammatory disease -Successfully treated with medications -Used to cause rupture and loss of embryo and threatened life of pregnant female

Hypoblast Layer

-Inferior bilaminar disk composed of small cuboidal cells

Ectodermal Dysplasia

-Involves abnormal development of 1 or more structures from ectoderm -Abnormalities of teeth, skin, hair, nails, eyes, facial structure, glands (these are derived from ectoderm) -Partial or complete anodontia (absence of teeth) -Frequent disturbances for teeth that are present -Use partial or full dentures -Implants considered after growth halts if enough bone

Fusion

-Joining of embryonic tissue of 2 separate surfaces or elimination of a furrow between 2 adjacent swellings or developmental disturbance in which adjacent tooth germs unite to form large tooth

Ectoderm

-Layer in trilaminar embryonic disc derived from epiblast layer and lining stomodeum in 3rd week

Endoderm

-Layer in trilaminar embryonic disc derived from hypoblast layer in 3rd week

Spina Bifida

-Neural tube defect -Defects in vertebral arches and various degrees of disability -Failure of fusion of neural tube

Describe origin, morphology, and future systemic tissues of endoderm.

-Origin: Hypoblast layer -Morphology: Cuboidal -Future systemic tissues: Respiratory and digestive system linings, liver and pancreatic cells -Green Sheet: -Epithelium of gastrointestinal tract (except oral cavity and anal canal) and epithelium of its glands, urinary bladder, gallbladder, and liver

Describe origin, morphology, and future systemic tissues of mesoderm.

-Origin: Migrating cells from epiblast layer -Morphology: Varies -Future systemic tissues: Dermis, muscle, bone, lymphatics, blood cells and bone marrow, cartilage, reproductive and excretory organs, PULP, DENTIN, CEMENTUM -Green Sheet: -Most smooth, and all cardiac muscle, bone, other connective tissue, dermis of skin, dentin, pulp, cementum, most connective tissue

Describe origin, morphology, and future systemic tissues of ectoderm.

-Origin: epiblast layer -Morphology: Columnar -Future systemic tissues: epidermis, sensory epithelium of eyes, ears, nose, nervous system, and neural crest cells, mammary and cutaneous glands, ENAMEL -Green Sheet: -Nervous tissue, epidermis of skin, epithelium of oral cavity, salivary glands, enamel

Enamel Dysplasia

-Overuse of amoxicillin in children with ear, nose, throat infections -Visible changes of surface smoothness and tooth color in permanent tooth enamel

Karyotype

-Photographic analysis of chromosomes by an orderly arrangement -Sex is known by presence of having XX chromosomes for females or XY for males

Hindgut

-Posterior part of tube (future digestive tract) -Forms rest of mature pharynx and remainder of digestive tract

Midgut

-Posterior part of tube (future digestive tract) -Forms rest of mature pharynx and remainder of digestive tract

What is the first period of prenatal development?

-Preimplantation period

What is the importance of meiosis?

-Prevents excess chromosomes from forming -During development in gonads, meiosis enables ovum and sperm to reduce by 1/2 the normal number of chromosomes (haploid 23) -So, zygote receives half of its chromosomes from female and half from male; so genetic material reflects both biological parents

Stomodeum

-Primitive mouth -Beginning of the digestive tract

Fertilization

-Process by which female's ovum is penetrated by and united with a male's sperm during the preimplantation period

Cleavage

-Process during prenatal development when mitosis converts a zygote to a blastocyst

Morphogenesis

-Process of development of specific tissue structure or shape -Occurs due to migration of embryonic cells, which is followed by inductive interactions of those cells, which continues to occur throughout embryonic period

Meiosis

-Process of reproductive cell production that ensures correct number of chromosomes (haploid number of 23 chromosomes) - 22 autosomes and 1 sex cell -Results of this process is joining of ovum's chromosomes with those of the sperm

Prenatal Development

-Process that occur from start of pregnancy and continues until birth of child -9 months of gestation: usually divided into 3-month time spans or trimesters

Primordium

-The earliest indication of a tissue types or an organ during prenatal development

Endometrium

-The innermost lining of the uterus on its back wall

"Shuffled" Chromosomes

-The joining of chromosomes from both biological parents that forms a new individual with "shuffled" chromosomes

Describe mitosis.

-The process that takes place during growth and repair -Mitosis that occurs during cell division is the self-duplication of chromosomes of the parent cell and their equal distribution to daughter cells -Result: daughter cells have same chromosome number and hereditary potential as the parent cells

Why are the 5 developmental processes in the embryo important?

-These processes cause implanted blastocysts to become, with further development, an embryo -Also allows teeth and associated orofacial structures, and other organ structures develop in the embryo

Neural Tube

-Tube formed when neural folds meet and fuse superior to neural groove -Forms future spinal cord as well as other neural tissue

Anatomical Variants

-Variation in lesser details of a bone's shape -These are common

Tetracycline Stain

-Within child's primary teeth that are developing -During fetal period -Intrinsic yellow to yellow-brown discoloration of teeth -Slight, moderate, or severe degrees -Antibiotic is chemically bound to dentin for life of tooth -Treatment: -Full-coverage crowns/veneers -Vital tooth whitening might work

What does the zygote become after the morula?

-Zygote becomes a vesicle known as a blastocyst (or blastula)

What happens to the zygote after fertilization?

-Zygote will undergo mitosis, or individual cell division with cleavage

Major congenital malformations result from chromosomal abnormality in about 1.___% of cases.

1. 10%

Describe what happens during the 2nd week of prenatal development.

1. 2nd week is within the embryonic period 2. Implanted blastocyst grow by increased proliferation of embryonic cells 3. Differentiation also occurs; results in changes in cellular morphogenesis 4. Increased number of embryonic cells creates embryonic cell layer (germ layers) within blastocyst 5. Bilaminar embryonic disc: -Developed from blastocyst -Suspended in uterus's endometrium between amniotic cavity and yolk sac -Develops into embryo later as prenatal development continues 6. Placenta develops from interactions of trophoblast layer and endometrial tissue -Placenta and developing umbilical circulation allows selective exchange of soluble blood borne substances between them (oxygen, carbon dioxide, nutritional and hormonal substances) 7. Prochordal plate on dorsal aspect of embryo where the head and mouth will be

Congenital malformations occur in 1.___ out of 2.___ cases, and are one of the 3._______ _______ of infant death.

1. 3 2. 100 3. leading causes

What are the 2 genetic factors that can cause congenital malformations?

1. Chromosome abnormalities 2. Environmental agents and factors

Describe the 4th week of prenatal development.

1. Disc undergoes embryonic folding: -Establishes axis --> places forming tissue types into their proper positions for further embryonic development and produces somewhat tubular embryo -Results from extensive proliferation of ectoderm and differentiation of basic tissue -Occurs mainly at cephalic end where brain will form -Tissue grows beyond oropharyngeal membrane to overhang developing heart -Also occurs at caudal end and sides of embryo simultaneously -Causes positions of embryonic cell layers to take on more recognizable placement for further development of the embryo -Endoderm is inside ectoderm and mesoderm fills in areas between the two -Movement of embryonic cell layers forms 1 long, hollow tube lined by endoderm from cephalic to caudal end of embryo (oropharyngeal membrane to the cloacal membrane) -Tube is future digestive tract (3 major regions) -4 pairs of pharyngeal pouches will form from evaginations on lateral walls lining the pharynx 2. Face and neck begin to develop with primitive eyes, ears, nose, oral cavity, jaw areas Green Paper: -Heart begins to beat -Neural folds fusing -Primordia of eye and ear present -2 pairs of branchial arches (day 24), then 3 pairs of branchial arches (day 25), then 4 pairs of branchial arches, arm & leg buds present (Day 27) -About 4-5mm in length

Environmental agents and factors of congenital malformations can include what 4 things?

1. Drugs 2. Chemicals 3. Infections 4. Radiation

Which prenatal development period(s) makes up the last 2 trimesters?

1. Fetal period

What are the 3 major regions of the future digestive tract?

1. Foregut 2. Midgut 3. Hindgut

1._____ takes place during growth or repair and is different from 2._______, which takes place during reproduction.

1. Mitosis 2. Meiosis

Folic acid supplements are being recommended during pregnancy to help with 1. ____ ____ defects, 2.___ ____ and 3.____ ____

1. Neural tube 2. cleft lip 3. cleft palate

What are the 3 distinct successive periods of prenatal development?

1. Preimplantation period 2. Embryonic period 3. Fetal period

Which prenatal development period(s) make up the 1st trimester of pregnancy?

1. Preimplantation period and 2. Embryonic period

Describe the 3rd week of prenatal development.

1. Primitive streak forms within bilaminar disc --> causes bilateral symmetry 2. Some cells from epiblast layer move/migrate toward hypoblast layer only in area of primitive streak 3. Mesenchymal cells between epiblast & hypoblast layers proliferate & differentiate into various connective tissues & creates mesoderm 4. Bilaminar disc thickened into trilaminar embryonic disc -Embryonic cell layers give rise to specific tissue -Ectoderm: becomes skin epidermis, central nervous system -Mesoderm: gives rise to skin dermis, cartilage, bone, blood, muscle -Endoderm: gives rise to respiratory epithelium & gland cells 5. Cephalic end with oropharyngeal membrane forms (location of stomodeum) 6. Caudal end forms with cloacal membrane (location of future anus) 7. CNS begins to develop -Specialized group of cells differentiates from ectoderm, localized to neural plate -Neural plate forms neural groove -End of 3rd week, neural groove is surrounded by neural folds 8. Neural tube is formed in 4th week by neural folds undergoing fusion 9. Notochord (skeletal spine), thyroid begins to develop; heart tubes about to fuse -About 2-3mm in length

Describe the preimplantation period.

1. WEEK 1 2. Conception: Male SPERM penetrates females OVUM during fertilization -Union of sperm and ovum is now called a ZYGOTE 3. During fertilization: final stages of meiosis occur in ovum 4. After fertilization: zygote undergoes MITOSIS (individual cell division with cleavage) -CLEAVAGE: -2 cells, 4, cells, 8, cells -Then 12-16 cells: solid ball of cells is known as MORULA 5. Ongoing process of mitosis and secretion of fluid by cells within morula -->zygote becomes vesicle known as BLASTOCYST 6. Rest of week: Further mitotic cleavage --> blastocyst splits into smaller and more numerous cells as it undergoes successive cell divisions by mitosis 7. End of 1st week: -Blastocyst stops traveling and undergoes IMPLANTATION/ embedded in prepared ENDOMETRIUM 8. Blastocyst consists of TROPHOBLAST LAYER and EMBRYOBLAST LAYER

Hard tissue growth, such as with mature bone or dental tissue, is usually 1. ______growth, whereas soft tissue such as skin or gingival tissue increases by 2. ______ growth. Some tissue types, such as 3._____ and 4.______, use both types of growth to attain their final size.

1. appositional growth 2. interstitial growth 3. cartilage 4. immature bone tissue

An 1. ____ is easily recognizable at the end of the embryonic period by the 2.____ week of prenatal development.

1. embryo 2. 8th

Females of 1.______ age should 2._____ teratogens to protect the developing infant from possible 3. ________

1. reproductive 2. avoid 3. malformations