Embryology- exam 1
Terms
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- Whats a parental imprint
- Maternal genes are more important for development of the embryo, paternal genes more important for placenta.
- Discuss Hydatidiform moles
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Complete mole is a cystic swelling that arises from an embryo that fails to develop (essentially placenta without an embryo),
-results from fertilization of empty oocyte (has no genetic material)
Typically secretes high levels of hCG
Partial mole is a poorly developed embryo, always triploid (XXX)
Approximately 5% of moles will develop into choriocarcinoma - What is a persistent trophoblastic disease
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When mole is not completely removed
invasive mole of choriocarcinoma - Why is second week of development called a week of 2's
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There are 2 tissues - embryoblast and trophoblast.
Embryoblast has two levels- hypoblast and epiblast.
Trophoblast has two levels - syncitiotrophoblast and cytotrophoblast
There are 2 embryonic cavities - amnionic and yolk sac
There are two parts of extraembryonic mesoderm - somatic and splanchnic - What are two events that start formation of trilaminar embryo
- Elongation of embryonic disc and formation of primitive streak
- Define gastrulation
- Process that defines three layers - ectoderm, mesoderm, endoderm
- Describe primitive streak
- Primitive streak develops on the surface of epiblast, and has two sides - cephalic and caudal which will develop in head and anus respectively. Primitive streak forms at the narrow - hea part.
- What are the functions of notochord
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1. It signals development of vertebral column
a. It dictates development of the CNS (inducers signal cells in ectoderm)
2. Designates the midline
3. Notochord is left over as nucleus pulposus of the IV disc - What are the two types of embryonic folding
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Longitudinal (Head-Tail)
Transverse (lateral) - What plays essential role in determining body axis
- Migration of the cells from primitive streak and node
- Describe situs inversus
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Complete - all organs are a mirror image of normal
Incomplete- dextrocardia (only heart is in the wrong place), malrotation - Sirenomelia
- Also called caudal dysgenesis, insufficient mesoderm at caudal portion of the embryo - can exhibit fusion and hypoplasia of limbs and other defects
- Saccrococcygeal teratoma
- Persistence of primitive sreak, contain tissues from all three germ layers
- What is the time frame of embryonic period
- week 3-8
- Buccopharyngeal membrane
- Another name - precordal plate, forms mouth
- Allantois
- bulge off yolk sac, involved in formation of urinary bladder
- Neural plate
- Thickening of ectoderm above notochord
- Neuropore
- Opening through which neural tube communicates with amniotic cavity, cranial closes at DAY 25, caudal closes at DAY 27
- Ectodermal placodes
- neural crest cells that instead of migrating get stuck
- Neural crest cells give rise to...
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1. Parasympathetic GANGLIA of CN III, VII, IX, X
2. Sensory ganglia of V, VII, VIII, IX, X
3.autonomic and dorsal ROOT GANGLIA - What will surface ectoderm give rise to?
- Epidermis, hair, nails, cutaneous and mammary glands
- What are mesoderm derivatives
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LATERAL PLATE- somatic layer, near ectoderm
splanchnic - near endoderm
INTERMEDIATE MESODERM - urinary and reproductive systems
PARAXIAL - somites, spinal cord
Also vasculo and angiogenesis - Endodermal derivatives
- Lining of respiratory, GI, glands
- Describe generally fetal period
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From WEEK 9-BIRTH
Indicated by external form of developing human and by presense of all major organ systems, time of rapid growth and development of organs, fetus becomes VIABLE during this period. Less susceptible to teratogens, but brain and eyes still remain in danger. - What are two important points about weeks 9-12
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-week 9 - LIVER is important site for erythropoiesis (RBC formation), after week 12 at SPLEEN
-after week 9 can disstinguish external genitals as male and female - What are two important points about weeks 13-16
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-sites of OSSIFICATION are evident
-EYE MOVEMENTS and EYES are facing forward - What are two importatn points about weeks 17-20
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-Primary ovarian FOLLICLES are formed
-TESTES are descending - What is an important thing about weeks 21-25
- Surfactant begins secretion at lungs
- What is important about weeks 26-29
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-Lungs are now capable of breathing
-CNS is now capable of controlling breathing and body temp
-spleen is still making blood cells, by 28 weeks blood formation shifts to bone marrow - What is important about weeks 35-38
- FINISHING PERIOD- final preparations of tissues important in transition to outside world (cardiovascular and respiratory)
- Describe amniocentesis
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Sampling of amniotic fluid, done for the following reasons
-mother of advanced age
-mother of previous Downs child
-Parents carry chromosomal abnormality
-parents are x linked carriers
-history of neural tube defects
-parents have inborn errirs of metabolisms - Polyhydraminos
- too much amniotic fluid, can indicate congenital abnormality
- Oligohydraminos
- not enough amniotic fluid, can indicate urinary defect
- Describe alpha fetoprotein test
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Alpha fetoprotein is a glycoprotein made in fetal LIVER, small amounts normally leak into amniotic fluid
High concentration of this protein indicates neural tube defect or ventral wall defect - Chorionic Villus Sampling
- biopsy of chorionic villi, done when there is a chance of abnormality, risk of fetal loss is relatively high - 1%
- Other fetal diagnostic techniques
- chromatin patterns, cell cultures, ultrasound, ct, mri...
- Malformation
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Occur during formation of structures, like organogenesis
Can result in complete or partial absense of structure, or alteration of normal configuration.
Caused by environmental/genetic factors acting independently or together
Most form 3-8 WEEKS of gestation - Disruption
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Morphological alteration of already formed structures due to destructive processes
-example vascular accident leading to gastric atresia or defects produced by amniotic bands - Deformation
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-mechanical force destruction acting on fetus over prolonged time
-example- clubbed feet caused by compression in amniotic cavity
-often involve musculoskeletal system - Syndrome
- group of anomalies occuring together that have specific common cause
- Association
- non random appearance of two or more anomalies that occur together but the common cause has not been found
- Principles of teratology
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1.Susceptibility to teratogens depends on genotype of fetus and how it interacts with environment, maternal genome is also important for drug metabolism, immune system, etc
2. Susceptibility varies with developmental stage at time of exposure. Most sensitive period 3-8 WEEKS, but could occur before or after
3. Depends on dose and duration of exposure
4. Teratogens have mechanisms for inducing pathogenesis - inhibition of biochemical or molecular process, pathogenesis - cell death, decreased proliferation, etc
5. Manifestation of teratogenesis are DEATH, MALFORMATION, GROWTH RETARDATION, FUNCTIONAL DISORDERS - Effect of hyperthermia
- Elevated body temperatures can lead to anencephaly, spina bifida, mental retardation, microphtalmia, cleft lip and palate, limb defficiencies, omphalocele(protrusion of intestines through umbilical cord) and cardiac abnormalities
- Effect of Toxoplasmosis
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causes birth defects, Toxoplasmosis protozoan comes from poorly cooked meat, animals, feces in contaminated soil
characteristic manifestation- cerebral calcification - Effect of radiation
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Very potent teratogen, kills rapidly prolifeating cells, can cause any type of birth defect depending on stage of development.
Can also be mutagenic - Effect of thalidomide
- Anti nausea and sleeping pill during 60's, was associated with AMELIA and MEROMELIA (total or partial absense of extremities), rare hereditary abnormality
- Effect of amphetamines
- CNS deffects
- Effect of alcohol
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Fetal alcohol syndrome- part of fetal alcohol spectrum disorder, structural defects, growth defficiency, mental retardation
Alcohol related neurodevelopmental disorder- less severe then FAS
Incidence is 1/100
Alcohol- LEADING CAUSE OF MENTAL RETARDATION - Effect of isoretinol
- analogue of vitamin A, causes VITAMIN A EMBRYOPATHY. Drug prescribed for treatment of cystic acne, highly teratogenic, cna produce any type of malformation.
- Effect of hormones
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ANDROGENIC - synthetic progestins used to prevent abortion, cause masculinization of female genitalia
ENDOCRINE DISRUPTORS - interfere with normal actions of hormones in development. Synthetic estrogens cause dysfunction of CNS and reproductive system
Cortisone- cleft palate
Should not take BCP - Effect of diabetes
- High incidence of stillbirths, neonatal deaths, abnormally large infants, congenital malformations. Long standing diabetes - 80% chance of birth deffect.Different deffects including serenomelia.
- Effect of phenylketonuria
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Disease of mother where she is defficient of enzyme called phenylalanine hydroxylase, increases serum concentration of phenylalanine
Infants are born with mental retardation, microcephaly and cardiac defects. - Effect of obesity
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Pre pregnancy obesity if BMI >30 kg.m sq., 2-3 times more risk of neural tube defect.
Also increased risk for heart defects, omphalocele and multiple anomalies - Effect of mercury
- Multiple neurological symptoms resembling cerebral palsy. Contains in fish, or mercury containing pesticides.
- Describe techniques used for fetal therapy
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FETAL TRANSFUSION- in case of fetal anemia, needle is inserted into umbilical cord vein and blood is transfused directly to fetus
MEDICAL TREATMENT- can be done through mother and crosses placenta or by intramuscular injection
FETAL SURGERY - placing shunts in utero, or can operate ex utero to repare life threatening problems