Prenatal Development Flashcards
Embryology
the study of prenatal development
Prenatal development begins with ___ and ends with___
pregnancy; the birth of the child
The 9 months of gestation is usually divided into
3-month time spans or trimesters
Prenatal development consists of three distinct successive periods:
- Preimplantation period
- Embryonic period
- Fetal period
_____period make up the first trimester of pregnancy and___ period constitutes the last two trimesters
Preimplantation period and embryonic; Fetal
Each of the structures of the face, neck, and oral cavity has a primordium. What is a Primordium?
the earliest indication of a tissue type or an organ during prenatal development.
Developmental disturbances that involve the orofacial structures as well as other parts of the body can include congenital malformations or birth defects, which are evident at birth. Most of these occur during ____period.
both the preimplantation period and the embryonic aka the first trimester.
Developmental disturbances that occur during the first trimester occurrence
Occurs in 3 out of 100 cases and are one of the leading causes of infant death
What is Amniocentesis (or amniotic fluid test [AFT])?
a prenatal diagnostic procedure to detect chromosomal abnormalities
How is an AFT performed?
Amniotic fluid is removed and its fetal cells are grown for microscopic study of the chromosomes as well as sampled for determination of other fetal complications
AFT is Usually considered in the following situations:
- Older females
- If one or both parents have a chromosomal abnormality or neural tube defect
- When a previous child was affected
- When the parents are carriers of inborn errors of metabolism or X-linked disorders such as hemophilia
As an alternative to AFT, Pregnant women now have the option of getting a new type of prenatal genetic test called
non-invasive prenatal testing (NIPT)
What is NIPT?
a cell-free fetal DNA testing that involves a simple blood draw from the pregnant woman. It Does not pose any risk and Can be performed very early in the pregnancy
Malformations that occur during the first trimester can be due to
genetic factors, such as chromosome abnormalities
environmental agents and factors, called teratogens
Teratogens include
infections, drugs, and radiation
Women of reproductive age should avoid teratogens to
protect the developing infant from possible congenital malformations
Malformations in the face, neck, and oral cavity range
from a serious cleft in the face or palatal region to small deficiencies of the soft palate or developing cysts underneath an otherwise intact old mucosa
Orofacial congenital malformations are usually understandable and traceable to
a specific time in the embryologic development of the individual
The Preimplantation Period Takes place ___
during the first week after conception
What are the Key Events of preimplantation period?
- Fertilization
- Cleavage
- Blastocyst formation
- Implantation
What happens during fertilization of the PIP?
Sperm cell fuses with egg cell (ovum), creating a zygote
What happens during cleavage stage of the PIP?
Zygote undergoes rapid mitotic divisions, creating smaller cells called blastomeres
What happens during blastocyst formation stage of the PIP?
A fluid filled cavity (blastocoel) develops within the cell mass differentiating the cells into two distinct lineages:
* Inner cell mass (ICM): The group of cells inside the blastocyst that will eventually develop into the embryo
* Trophoblast: The outer layer of cells that will form the placenta and help with implantation
What happens during implantation stage of the PIP?
The blastocyst adheres to the uterine lining, establishing a connection with the maternal blood supply
Each cell normally contains how many chromosomes?
23 pairs of chromosomes, for a total of 46
What is a karyotype?
a visual representation of an individual’s complete set of chromosomes arranged in pairs according to their size and shape
What is the purpose of a karyotype?
Allows scientists to identify potential genetic abnormalities like missing or extra chromosomes, or structural changes within them
These chromosomes look the same in both men and women
Twenty-two of the 23 pairs of chromosomes called autosomes
These chromosomes differ between men and women
The twenty-third pair, the sex chromosomes
This picture of human chromosomes lined up in pairs, is called a
karyotype
Often used in genetic testing to diagnose conditions like Down syndrome or other chromosomal disorders
Karyotype
A karyotype displays
the number and structure of all chromosomes in a cell, including the sex chromosomes (X and Y)
XX chromosome is a
female
XY chromosome is a
male
If any disturbances occur during____, major congenital malformations result from the chromosomal abnormality in around 10% of cases
fertilization
One example of disturbance occur during fertilization is
Down syndrome, or trisomy 21
Down syndrome, or trisomy 21
An extra copy of chromosome number 21 is present after cell divisions
A syndrome is
a group of specific signs and symptoms. Syndromes have no cure or prevention measures because it is not a disease
Down syndrome presents with certain orofacial features that include:
- Flat, broad face with widely spaced eyes
- Flat-bridged nose
- Epicanthic folds and oblique eyelid fissures
- Furrowed lower lip
- Tongue fissures and lingual papillae hypertrophy
- Various levels of intellectual disability
An arched palate and weak tongue muscles
An arched palate and weak tongue muscles of those with DS lead to
an open mouth position with protrusion of the tongue of usual size and articulated speech is often difficult
Clinical considerations of people with DS (teeth)
The eruption of teeth in persons with Down syndrome is usually delayed as long as 2 to 3 years and may occur in an unusual order
There is an extremely high rate of missing teeth in both the primary and permanent dentitions
Other irregularities, such as microdontia and malformed teeth, may be seen
The oral cavity may have undersized bone structure, microdontia and missing teeth, and you may also see severe crowding of teeth
It may also involve increased levels of periodontal disease
The roots of the teeth in patients with Down syndrome tend to be small and conical. This is an important factor when considering orthodontic tooth movement and also contributes to early tooth loss in periodontal disease
Implantation may occur outside the uterus. This is referred to as an
ectopic pregnancy
Most ectopic pregnancies occur in the
fallopian tube
ectopic pregnancies has several causes, but is usually associated with
factors that delay or prevent transport of the dividing zygote to the uterus
* Example: scarred uterine tubes due to pelvic inflammatory disease
Embryonic Period Extends from
the beginning of the second week to the end of the eighth week
Certain physiologic processes called patterning occur during this period
Embryonic Period
Patterning
physiologic processes that occur during the Embryonic Period that is key to further development.
The physiologic processes or patterning that occurs during the Embryonic Period include
induction, proliferation, differentiation, morphogenesis, and maturation
Patterning causes
the structure of the implanted blastocyst to become, with further development, an embryo. Also allow the teeth and associated orofacial structures as well as other organ structures to develop in the embryo
Induction
A process where one part of an embryo influences the development of another part
During induction, one tissue, called the___, interacts with another tissue, called the___
inducing tissue; responding tissue
The interaction of the inducing tissue with the responding tissue causes the responding tissue to
change how it differentiates
Induction is a key mechanism in
vertebrate development
helping to organize cells into tissues and organs
* Example: the development of the eye lens from epidermis under influence of the eye cup
Proliferation
The process of cell division and migration that occurs during the development of an embryo and fetus
* Growth that occurs can be interstitial growth or appositional growth
Differentiation
The process where a fertilized egg’s cells progressively specialize and develop into different types of cells. Differentiation transforms a single cell into a complex organism with distinct functions across the body
Cytodifferentiation
development of different cell types
Histodifferentiation
development of different tissue types within a structure
Morphodifferentiation
development of differing morphology, which makes up the structure or shape, for each organ or system
Morphogenesis
The process by which the individual cells within the developing embryo move around and organize themselves to form the structures, organs and systems that make up the adult organism
Maturation is the process by which the embryo
attains full function and size due to proliferation, differentiation, and morphogenesis
Maturation Begins
during the embryologic period and continues later during the fetal period
An embryo is recognizable by the
eighth week of prenatal development, which is the end of the embryonic period
During the ____week of prenatal development, within the embryonic period, the implanted blastocyst grows by
second; increased proliferation and differentiation of the embryonic cells growth and changes in cellular morphogenesis.
During the____ week the bilaminar embryonic disc develops, what is that?
second; A circular plate of bilayered cells developed from the blastocyst
The superior layer of the bilaminar embryonic disc is the
epiblast layer
The epiblast later is composed of
columnar cells
The inferior layer of the bilaminar embryonic disc is the
hypoblast layer
The hypoblast layer is composed of
cuboidal cells
The bilaminar embryonic disc is suspended in
the endometrium lining the uterus between two fluid-filled cavities, the amniotic cavity, which faces the epiblast layer, and the yolk sac, which faces the hypoblast layer and serves as initial nourishment for the disc
Purpose of yolk sac
initial nourishment for the disc
During the___ week the placenta and umbilical cord develop, what is The placenta?
second; a prenatal organ that joins the pregnant female and developing embryo, develops from the interactions of the trophoblast layer* and endometrial tissue
The formation of the placenta and the developing umbilical circulation permit
selective exchange of soluble bloodborne substances between them. This includes oxygen and carbon dioxide as well as nutritional and hormonal substances
The trophoblast layer is the
outer layer of cells surrounding a developing embryo within a blastocyst
The trophoblast layer is Responsible for
attaching the embryo to the uterine wall
Providing nourishment to the growing fetus
Ultimately forming a large part of the placenta during pregnancy
Essentially, it acts as the “feeder” layer for the embryo by facilitating nutrient exchange between the mother and fetus
During the____ week of prenatal development within the embryonic period, the primitive streak forms within the bilaminar embryonic disc. What is that?
beginning of the third; A Furrowed, rod-shaped thickening in the middle of the disc that is a vital structure in early embryo development that helps establish the body plan, form germ layers, and guide cell migration. The PS Causes the disc to have bilateral symmetry, with a right half and left half
The primitive streak Results from
an increased proliferation of cells in the midline area
During the____ week, some cells from the epiblast layer move or migrate toward the hypoblast layer only in the area of the primitive streak. These cells become
third; mesoderm, an embryonic connective tissue, as well as embryonic endoderm
During the___ week, some cells from the epiblast layer move or migrate toward the hypoblast layer only in the area of the primitive streak. These cells become mesoderm, an embryonic connective tissue, as well as embryonic endoderm. Now with three layers present, the bilaminar disc has thickened into a
third; trilaminar embryonic disc
During the__ week, some cells from the epiblast layer move or migrate toward the hypoblast layer only in the area of the primitive streak. These cells become mesoderm, an embryonic connective tissue, as well as embryonic endoderm. Now with three layers present, the bilaminar disc has thickened into a trilaminar embryonic disc. With the creation of the new embryonic cell layers of mesoderm and embryonic endoderm, the epiblast layer is now considered
third; ectoderm
Within the trilaminar embryonic disc, each embryonic cell layer is distinct from the others and thus gives rise to specific tissue: The ectoderm gives rise to the
skin epidermis, the central nervous system (CNS), and other structures
Within the trilaminar embryonic disc, each embryonic cell layer is distinct from the others and thus gives rise to specific tissue: The mesoderm gives rise to
connective tissue, such as skin dermis, cartilage, bone, blood, muscle, and other associated tissue
Within the trilaminar embryonic disc, each embryonic cell layer is distinct from the others and thus gives rise to specific tissue: The endoderm gives rise to the
respiratory epithelium and cells of glands.
Mesoderm and associated tissue are found
in all areas of the future embryo except at certain embryonic membranes at both ends of the embryo and the pharyngeal pouches
In the areas without mesoderm present in the developing embryo, both the ectoderm and endoderm____
fuse together, thereby preventing the migration of mesoderm between them
In the___ week after the development of the embryonic tissue layers, The disc now has two ends called___
third; The cephalic end and the caudal end
At the cephalic end, the _____ membrane forms.
Oropharyngeal
The oropharyngeal membrane Consists of
only ectoderm externally and endoderm internally, without any intermediate mesoderm
The oropharyngeal membrane is the location of
the future primitive mouth or stomodeum of the embryo and thus the beginning of the digestive tract
At the caudal end, the___ membrane forms
cloacal
The cloacal membrane is the location of
the future anus, or terminal end of the digestive tract
During the____, the central nervous system (CNS) begins to develop in the embryo. Many steps occur during this week to form the beginnings of the spinal cord and brain
later part of the third week
During the______, the central nervous system (CNS) begins to develop in the embryo. Many steps occur during this week to form the beginnings of the spinal cord and brain. First,
later part of the third week; a specialized group of cells differentiates from the ectoderm and is now considered neuroectoderm
The cells of the neuroectoderm are localized to
The neural plate of the embryo
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
The neural plate undergoes further growth and thickening, which cause it to deepen and invaginate inward forming the
neural groove
Near the___ week, the neural groove deepens further and is surrounded by the
end of the third; neural folds
As further growth of the neuroectoderm occurs, the____ is formed during the ___week by the neural folds undergoing fusion at the most superior part
neural tube; fourth
In addition, during the___ week, another specialized group of cells (in addition to the differentiated ectoderm cells localized at the neural plate) ________develop from neuroectoderm
third; the neural crest cells (NCCs)
the neural crest cells (NCCs) migrate from the
____
crests of the neural folds and then disperse within the mesenchyme
What is mesenchyme?
a loosely organized, mainly mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph.
Mesenchyme is involved in the development of
___
many face and neck structures, such as the pharyngeal or branchial arches, because they differentiate to form most of the connective tissue of the head
The NCCs are essential in formation of
most oral and dental tissue except for the enamel and certain types of cementum
the development of the face and neck
NCCs undergo differentiation into
diverse cell types that are, in part, specified by local environmental influences
In future development, NCC become involved in the formation of components of the
nervous system, melanocyte pigment cells, connective tissue proper, cartilage, bone, and certain dental tissue by becoming a specialized type of mesenchyme, ectomesenchyme, such as with the formation of the pulp, dentin, cementum, alveolar process, and periodontal ligament
By the end of the___ week, the mesoderm
third; additionally differentiates and begins to divide on each side of the tube into 38-paired cuboidal segments of mesoderm, forming the somites
Somites later appear as
distinct elevations on the surface of the sides of the embryo
Somites Continue to develop in after week____ of prenatal development and Give rise to most of the
Three; skeletal structures of the head, neck, and trunk, as well as the associated muscles and dermis of the skin
During the___ week of prenatal development within the embryonic period, the disc undergoes
fourth; embryonic folding
embryonic folding
A process that occurs in the embryo as it changes shape from a flat disc to a cylinder
This process takes place in two planes, the horizontal plane and the median plane. Results in the development of the embryo’s axes
Anterior-posterior axis of embryo:
The line that runs from the head to the tail
Dorsal-ventral axis of embryo:
The line that runs from the back to the belly
Right-left axis of embryo:
The line that runs between the two sides of the body
Development of the axes occurs at the same time as
determination of right or left handedness
The axes purpose
places forming tissue types into their proper positions for further embryonic development as well producing a somewhat tubular embryo
anterior part of the tubular embryo is the
foregut
The foregut Forms the
primitive pharynx or primitive throat and Includes a part of the primitive yolk sac as it becomes enclosed with folding
The two more posterior parts of the tubular embryo
the midgut and hindgut, respectively
the midgut and hindgut form the
rest of the mature pharynx as well as the remainder of the digestive tract
During the___ week, _____begin to develop
fourth; the face and neck with the primitive eyes, ears, nose, oral cavity, and jaw areas.
Because the beginnings of all essential external and internal structures are formed during the embryonic period, this is considered
the most critical period of prenatal development
Developmental disturbances occurring during this period may give rise to major congenital malformations of the embryo
embryonic period
Ectodermal dysplasia
Abnormal development of one or more structures from ectoderm. Ectodermal dysplasia has a hereditary etiology
Ectodermal dysplasia Presents with:
- abnormalities of the teeth, skin, hair, nails. eyes, facial structure, and glands because these are derived from ectoderm or associated tissue
- There may be partial or complete anodontia, the absence of some or all teeth in each dentition
- The teeth that are present for either dentition frequently have developmental disturbances
Treacher Collins syndrome
Failure of migration of the neural crest cells to the facial region, TCS or mandibulofacial dysotosis develops in the embryo. Results in failure of specific areas of orofacial development
Treacher Collins syndrome Presents with:
- downward slanting eyes
- underdeveloped zygomatic bone
- drooping lateral lower eyelids
- conductive hearing loss, with malformed or absent ears
- dental developmental disturbances
- anodontia
- enamel dysplasia
- micrognathia (small lower jaw)
The rubella virus is a prime example of an___ because it is A virus that can cause birth defects when contracted by a pregnant woman
infective teratogen
Rubella Leads to potential complications like ____ in the developing fetus, collectively known as Congenital Rubella Syndrome (CRS)
cataracts, heart defects, and deafness
The bacterial spirochete Treponema pallidum (causes syphilis) is a prime example of an___
Infective teratogen
Orally, Syphilis Produces defects in the
incisors (Hutchinson incisor) and molars (mulberry molar)
Syphilis Can cause ___ if not treated
blindness, deafness, and possible paralysis
Fetal Alcohol Syndrome
A lifelong condition that caused by a pregnant woman drinking alcohol (especially excessively), during pregnancy (during the embryonic period particularly). Alcohol passes through the placenta and harms the developing fetus
Fetal alcohol syndrome presents with
noted orofacial features and various levels intellectual disability
* Abnormal facial features such as a smooth ridge between the nose and upper lip
* Small head size
* Delayed language and hearing
* Poor impulse control
* Low body weight
* Poor coordination
* Vision or hearing problems
Direct exposure to high levels of radiation can act as an____ during the embryonic period
environmental teratogen
Radiation may injure embryonic cells, resulting in
cell death, chromosome injury, and delay of intellectual and physical growth
The severity of embryonic damage from radiation is associated with
the absorbed dose, the dose rate, and the state of embryonic or fetal development at the time of exposure
Congenital abnormalities caused by radiation have not been directly linked to a diagnostic level of radiation, such as
that used in the dental setting
Scattered radiation from a radiographic examination of the oral cavity administers
a dose of only a few millirads to a pregnant woman, which is not known to be teratogenic to an embryo
The ADA recommends the use of _____ for pregnant dental staff who work with radiographic equipment
dosimeters and work practice controls
Studies of pregnant patients receiving dental care have affirmed the safety of dental treatment including the administration of radiographs when using the protective controls
However, Radiation exposure should be avoided during pregnancy unless
an emergency situation requires it
the correct dosage and timing of radiographs as well as protective precautions should be used with
all patients at all times as well as with the administering dental professionals
Spina Bifida
The neural tube, which develops into the brain and spinal cord, doesn’t close properly during pregnancy. Failure of fusion of the neural tube results in neural tube defects of the tissue overlying the spinal cord, such as the meninges, vertebral arches, muscles, and skin
One type of neural tube defect is spina bifida, characterized by defects in the vertebral arches and various degrees of disability
____can also have an important role as teratogens in causing neural tube defects
Nutritional and environmental factors
____supplements are recommended during pregnancy to help prevent spina bifida as well as cleft lip and cleft palate
Folic acid
The fetal period of prenatal development follows the
embryonic period
The fetal period encompasses
the beginning of the ninth week or third month continuing to the ninth month
During the fetal period,___ of existing structures occurs as the embryo is enlarging to become a fetus
The maturation
The fetal period involves
not only the physiologic process of maturation of the individual tissue types and organs but also further proliferation, differentiation, and morphogenesis, as discussed before with the development of the embryo. Developmental changes with the fetus are not as dramatic as those that occur during the embryonic period
Changes in this period of development are important because they allow the newly formed tissue types and organs to function
Fetal period
Systemic tetracycline antibiotic therapy of the pregnant woman can act as a____ during the fetal period
teratogenic drug
Systemic tetracycline antibiotic therapy of the pregnant woman can result in
tetracycline stain with the child’s primary teeth that are developing at that time
tetracycline stain Presents as
Intrinsic yellow to yellow-brown discoloration within the teeth. Can occur in slight, moderate, or severe degrees as the antibiotic becomes chemically bound to the dentin for the life of the tooth. This stain is easily visible because of the transparency of overlying enamel. Permanent teeth may also be affected, similarly to the primary teeth, if the drug is given to a child during their development
