Embryology Exam 2

Front 1

birth defect (congenital malformation, congenital anomaly)

Back 1

synonymous terms used to describe structural, behavioral, functional, and metabolic disorders present at birth or soon after

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teratology and dysmorphology

Back 2

terms used to describe the study of birth defects

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percent of infants with physical anomalies

Back 3

4 to 6% total, with 2-3 at birth and 2-3 before 5

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mortality rate

Back 4

~21% of infant death, same among different races

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causes of birth defects

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unknown-50%
obvious genetic factors (chromosome abnormalities, mutant genes)-15%
environmental factors-10%
genetic+environmental factors-20-25%
twinning-0.5-1%

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minor anomalies

Back 6

occur in approx. 15% of newborns, are structural abnormalities, such as microtia (small ears), pigmented spots and short palpebral fissures, not detrimental to health but may be associated with larger defects
1 minor anomaly-3% chance of a major malformation
2 minor anomalies-10% chance
3 minor anomalies-20% chance

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malformations

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during organogenesis (3rd-8th week), normally caused by environmental and/or genetic factors acting independently or in concert, complete or partial absence of a structure or in alterations of its normal configuration

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disruptions

Back 8

result in morphological alterations of already formed structures and are due to destructive processes (ex: vascular accidents -> bowel atresias)

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deformations

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due to mechanical forces that mold a part of the fetus over a prolonged period, may be reversible postnatally, affects mostly musculoskeletal system, clubfeet (due to compression in the amniotic cavity)

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syndrome

Back 10

a group of anomalies occurring together that have a specific common cause, means a diagnosis is made

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association

Back 11

nonrandom appearance of two or more anomalies that occur together more frequently than by chance alone but whose cause has not been determined, ex: VACTERL association (vertebral, anal, cardiac, trachoesophageal, renal and limb anomalies), do not constitute diagnosis

Front 12

genetic factors of birth defects and spontaneous abortions

Back 12

numerical chromosomal abnormalities
structural chromosomal abnormalities
gene mutations

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nondisjunction

Back 13

occurs when chromosomes do not separate from each other and a cell gets either and extra copy or short a copy
meiotic: 22 or 24 gametes -> trisomy 47 or monosomy 45
mitotic: mosaicism (some have nondisjunction and some not)

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translocations

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balanced (non-phenotypical because no critical genetic material is lost) or unbalanced (phenotypcial, loss of critical genetic material causing a change in phenotype), common in chromosome 13, 14, 15, 21, 22 because they cluster during meiosis, when pieces of chromosome break and attach to another

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examples of numerical chromosomal abnormalities

Back 15

trisomy 21 (downs), 18 or 13
klinefelter Syndrome
Turner Syndrome

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Trisomy 21

Back 16

features: growth and mental retardation, craniofocal abnormalities, upward slanting eyes, epicanthal folds, flat facies and small ears, cardiac defects, hypotonia
cause: 95% is because of meiotic nondisjunction, 4% unbalanced translocation between chromosome 21 and 13, 14, or 15, 1% mosaicism
incidence: 1/2000 (<25 years old), 1/300 (35 years old), 1/100 (40 years old)

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trisomy 18

Back 17

features: mental retardation, congenital heart defects, low-set ears, flexation of finger and hands, micrognathia (small jaw), renal anomalies, syndactylyl (webbing of fingers), malformation of skeletal system
incidence: 1/5000 newborns
mortality: 85% lost between 10 weeks and term, those born live die < 2 months

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trisomy 13

Back 18

features: mental retardation, holoprosencephaly (single forebrain hemisphere), congenital heart defects, deafness, cleft lip, palate and eye defects (small eyes, absence of the globe, or optic fissure fails to close)
incidence: 1/20 000 newborns
mortality: 90% infants die < 1 month

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Klinefelter Syndrome

Back 19

features: males, sterility, testicular atrophy, hyalinization of seminiferous tubules, and gynecomastia (enlarged breasts)
karyotype: 47: XXY or 48: XXXY
cause: nondisjunction of XX homologues

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Turner Syndrome

Back 20

features: female-looking, gonadal desgenesis (absence of ovaries), short stature, webbed neck, lymphedema of the extremities, skeletal deformities, broad chest with widely spaced nipples
karyotype: 45: X, only viable monosomy
causes: meiotic nondisjunction of X in male or female gametes, or mitotic nondisjunction leading to mosaicism

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chromosomal structural abnormalities

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caused by chromosome breakage, caused by environmental factors (viruses), radiation or drugs

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Angelman syndrome

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a maternal microdeletion on the long arm of chromosome 15, mentally retarded, cannot speak, poor motor development, unprovoked and prolonged laughter

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Prader-willi Syndrome

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a paternal microdeltion on the long arm of chromosome 15, hypotonia, obesity, mental retardation, hypogonadism, cryptochidism

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genomic imprinting

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occurs when there is a difference in gene expression between the maternal and paternal alleles

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gene mutations and malformation

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8% of all human malformation from single gene mutations, can be dominant or recessive

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what determines the susceptibility of environmental factors on a fetus (aka principles of teratology)

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1. genotype of the conceptus + interaction between genes and environment + maternal genome (drug metabolism, resistance to infection)
2. exposure time: most sensitive during the 3rd-8th stage, but there is no safe time
3. dose and duration
4. mechanisms of teratogens to initiate pathogenesis (abnormal embryogenesis)
5. manifestations of abnormal development are death, malformation, growth retardation and functional disorders

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teratogens

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factors that cause birth defects

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infectious agents

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viruses: either directly or by fever (pyrogenic)
ex: toxoplasmosis and syphilis, leading to cerebral calcifications
other ex: rubella (~85% of women now immune), cytomegalovirus (deadly), herpes, HIV

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viruses are pyrogenic

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leads to elevated body temperature (which is teratogenic), defects that can result are anencephaly, spina bifida, mental retardation, microphtalmia, cleft lip, limb deficiencies, omphalocele, and cardiac abnormalities

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radiation

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killing of rapidly proliferating cells producing virtually any type of birth defect depending upon the dose and stage of exposure, mutagenic leading to genetic alterations of germ cells

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chemical agents

Back 31

difficult to assess because the studies are retrospective (based on the mother’s memory) and pregnant women take a large number of pharmaceutical drugs

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examples of chemical agents

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thalidomide, alcohol, smoking, anticonvulsants, antipsychotic drugs, antianxiety drugs, anticoagulant drugs, antihypertensive agents, aspirin, streptomycin, tetracycline, social drugs, isotretinoin)

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thalidomide

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an antinauseant and sleeping pill, its use led to Amelia and meromelia (total or partial absencec of the extremities), phocomelia (loss of long bones for short limbs)

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alcohol

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can lead to fetal alcohol syndrome and alcohol related neurodevelopmental disorder, leading cause of mental retardation

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fetal alcohol spectrum disorder (FASD)

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any alcohol related defects

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fetal alcohol syndrome (FAS)

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represents the severe end of the spectrum and includes structural defects, growth deficiency, and mental reatardation

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alcohol related neurodevelopment disorder (ARND)

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represents a less severe example of alcohol-related abnormalities

Front 38

smoking and birth defects

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not linked to major birth defects, but intrauterine growth retardation and premature delivery, may cause behavioral disturbances

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anticonvulsants

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ex: diphenylhydantion (phenytoin), valptoic acid, trimethadione
normally used by epileptic women, led to trimethadione and fetal hydantoin syndromes (facial clefts)

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antipsychotic drugs

Back 40

ex: phenothiazine and lithium
produces various congenital malformations

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antianxiety drugs

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ex: meprobamate, chlrodiazepoxide, diazepam (valium)
produces various congenital malformations, cleft lip

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anticoagulant

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ex: warfarin

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antihypertensive agents

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ex: angiotensin-converting enzymes (ACE inhibitors)
produce growth retardation, renal dysfunction, fetal death and oligohydramnios

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aspirin

Back 44

usually need to take it in large doses

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streptomycin

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can cause deafness

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tetracycline

Back 46

can cause bone and tooth anomoalies

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social drugs

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ex: LSD, PCP, cocaine
can cause limb abnormalities and malformation of the CNS in large doses of LSD, need large doses to make any noticeable affect, otherwise not considered a teratogen

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isotretinoin

Back 48

used to treat acne, an analogue of vitamin A that causes isotretinoin embryopathy, can cause any type of abnormality, must only take a moderate amount of vitamins (25,000 IU)

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Hormones

Back 49

androgenic agents: masculinization of the genitalia in female embryos (bigger clit)
oral contraceptives: contain estrogen and progesterone, low teratogenic potential
cortisone: cleft palate
environmental hormones: endocrine disruptors, interfere with estrogen to cause abnormalities of the CNS (masculinization and feminization of female and male) and reproductive tract

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maternal diabetes

Back 50

cause a high incidence of stillbirth, neonatal deaths, abnormally large infants and congenital malformations (3-4X higher in diabetic mothers), if control blood sugar levels can decrease the occurrence of malformations

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insulin and birth defects

Back 51

non-teratogenic

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hypoglycemic episodes and birth defects

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even brief episodes of hypoglycemia are teratogenic, must be cautious of the diabetes control in mothers

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maternal phenylketonuria (PKU)

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mothers with PKU, phenylalanine hydroxylase is deficient resulting in high [Phe], leads to an increase risk of mental retardation, microcephaly, and cardiac defects in infants

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how to prevent diabetes and PKU affecting fetuses

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strict metabolic control prior to conception

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iodine deficiency (nutritional deficiency)

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can lead to endemic cretinism which causes mental retardation and bone deformities, prevent through supplementation iodine in salt and water

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obesity

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pregnancy obesity determined through BMI >30 kg/m^2, obesity causes a 2-3 fold increase risk for neural tube defects and heart defects

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omphalocele

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congenital herniation of viscera into the base of the umbilical cord with a covering membranous sac of peritoneum-amnion

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hypoxia

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low birth-weight

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mercury

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organic mercury in sea foods can lead to neurological defects similar to cerebral palsy

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lead

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increase abortions, growth retardation and neurological disorders

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male-mediated teratogenesis

Back 61

anything that can damage the sperm, can lead to spontaneous abortion, low birth weight and various birth defects, advanced paternal age or younger paternal age (<20) is due to INC risk of limb and neural tube defects

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ultrasound

Back 62

used to determine age, birth defects, sex

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maternal serum screening

Back 63

detect alpha-fetoprotein (AFP) levels
INC-can mean omphalocele, gastroschisis, bladder exstrophy, amniotic vand syndrome, sacrococcygeal teratoma, intestinal atresia
DEC-down syndrome, trisomy 18, sex chromosome abnormalities

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indication of intrusive tests

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1. advanced maternal age (>= 35)
2. previous family history (downs, neural tube defects
3. presence of maternal diseases (diabetes, PKU)
4. abnormal ultrasound or serum test

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amniocentesis

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a biochemical assay used for detecting chromosomal banding and genetic analysis, after 14 weeks bec. it requires removal of about 20-30 mL of amniotic fluid, has a 1% risk of loss of fetus

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chorionic villus sampling

Back 66

involves inserting a needle transabdominally or transvaginally into the placental mass and aspirating approx. 5 to 30 mg of villus tissue, must be analyzed immediately, survive only 2 to 3 days, risk of fetal loss is 2X greater than in amniocentesis and INC risk for limb reduction defects

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fetal transfusion

Back 67

used in fetal anemia, use ultrasound to guide needle

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fetal medical treatment

Back 68

in some cases, agents may be administered to the fetus directly, instead of the through the mother, by intramuscular injection into the gluteal region of via the umbilicial vein

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fetal surgery

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possible to operate of fetus, only performed when there are no other reasonable options

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stem cell transplantation and gene therapy

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fetus does not have any immunocompetecne before week 18, can transplant tissues or cells before this time without any rejection

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three layers of mesoderm

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paraxial, intermediate and lateral plate

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paraxial mesoderm

Back 72

forms a segmented series of tissue blocks on each side of the neural tube known as somitomeres in the head (cephalic) region and somites from the occipital region caudally (dorsally)

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where does skeletal material come from

Back 73

1. somites-vertebrae and ribs, skull behind the prochordal plate (rostral (cephalic, head) end)
2. neural crest cells-skull in front of prochordal plate and face bones
3. lateral plate mesoderm (somatic and splanchnic)-long bones, pelvic and shoulder girdles

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what happens to somites as they differentiate

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they cavitate and then differentiate under the influence of several proteins elaborated by gene expression into a dermatomyotome and a sclerotome

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somite differentiation

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into a ventromedial sclerotome and a dorsolateral dermomyotome

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dermomyotome

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found dorsolaterally, consists of a dorsolateral and dorsomedial myotome regions and a dermatome in between the two

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mesenchyme

Back 77

formed in the fourth week from sclerotome cells, embryonic connective tissue, they can migrate and differentiate in many ways (osteoblasts, chondroblasts, fibroblasts), dermal mesenchyme can differentiate into bone (intramembranous ossification)

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intramembranous vs. endochondral ossification

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intramembranous, the mesenchyme turn directly into osteoblasts (in flat bones of the skull), endochondral, uses a hyaline cartilage model first then lays down bone (long bones)

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skull development division

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neurocranium-forms a protective case around the brain
viscerocranium-forms the skeleton of the face

Front 80

bones of the skull come from three different origins

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1. neural crest cells: ectoderm, form face and frontal, sphenoid, hyoids and temporal bones
2. paraxial mesoderm (somites): form the back of the head bones, parietal, occipital, temporal
3. lateral plate mesoderm: form the laryngeals

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what determines the division between neural crest derived and lateral plate derived skull bones

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occurs at the rostal end of the notochord at the prechordal plate, there is no paraxial mesoderm in front of prechordal plate so we need neural crest cells

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divisions of the neurocranium

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1. the membranous part consisting of flat bones, which surround the brain as a vault, comes from type of ossification
2. the cartilaginous part, or chondrocranium, which forms bones of the base of the skull, inclused most of the sphenoid bone, ethmoid bone, part of the temporal bone and occipital bone

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derivation of the membranous neurocranium

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derived from neural crest cells and paraxial mesoderm, mesenchyme invests the brain and undergoes membranous ossification creating bone characterized by needle-like bone spicules (which radiate from a primary ossification center), grows from bone growth on outside and osteoclast activity on the inside

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sutures of the skull

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connective tissue that separates the flat bones of the skull at birth, derived from neural crest cells (sagital) and paraxial mesoderm (coronal), can remain for a considerable time after birth, some even up until adulthood to compensate for growth

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fontanelles

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where more than two bones meet, wide sutures, can remain for a considerable time after birth

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anterior fontanelle

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most prominent of the fontanelles, found where the two parietal and two frontal bones meet, can give information as to whether ossification of the skull is proceeding normally and if pressure is normal with palpation

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derivation of the cartilaginous neurocranium/chondrocarnium

Back 87

initially consists of a number of separate cartilages, neural crest cells form the prechordal chondrocranium (rostral half, rostral to the sella turcica), paraxial mesoderm form the chordal chondrocranium (posterior half, posterior to the sella turcica), base of the skull is formed when these cartilages fuse and ossify by endochondral ossification

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viscerocranium

Back 88

formed from the first two pharyngeal arches

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first pharyngeal arch and viscerocranium formation

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gives rise to a dorsal portion (maxillary process) which extends forward beneath the region of the eye and gives rise to the maxilla, the zygomatic bone and part of the temporal bone

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second pharyngeal arch and viscerocranium formation

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gives rise to a ventral portion (mandibular process), contains the Meckel cartilage

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Meckel cartilage

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mesenchyme around here condenses and ossifies by membranous ossification to give rise to the mandible, disappears except in the sphenomandibular ligament

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dorsal tip of the mandible

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gives rise to the incus, malleus and stapes, ossification of the three ossicles begins in the 4th month, making these the first bones to be ossified

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where does the mesenchyme for the bones of the face come from?

Back 93

derived from neural crest cells, including the nasal and lacrimal bones

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why is the face so small compared to the neurocranium?

Back 94

1. virtual absence of the paranasal air sinuses
2. small size of the bones, particularly the jaw
appearance of teeth and development of the air sinuses causes the face to lose its babyish characteristics

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bones of cartilaginous neurocranium

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lesser and greater wins and body of sphenoid, occipital

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bones of membranous neurocranium

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frontal and parietal bone

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bones of cartilaginous viscerocranium

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thyroid cartilage, hyoid, malleus, stapes, incus

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bones of membranous viscerocranium

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mandible, maxilla, nasal bone, squama temporalis

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limb growth

Back 99

occurs at the end of the 4th week when limb buds become visible as outpocketings from the ventrolateral body wall, lower limb development lags behind upper limb development, occurs proximodistally as cells furthest from the AER differentiate into cartilage and muscle, minus the clavicle, form by endochondral ossification from the somatic part of lateral plate mesoderm

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characteristics of the outpocketings for limb growth

Back 100

consist of a mesenchymal core derived from the somatic layer of lateral plate mesoderm that will form the bones and connective tissues of the limb, covered by a layer of cuboidal ectoderm

Front 101

apical ectodermal ridge (AER)

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occurs during the 5th week, thickening of the ectoderm at the distal border of the limb, exerts an inductive influence on adjacent mesenchyme causing it to remain as a population of undifferentiated, rapidly proliferating cells, the progress zone

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hand and footplates

Back 102

occurs during the 6th week, the terminal portion of the limb buds that flatten, separated from the proximal segment by a circular constriction, second constriction occurs dividing the proximal portion into two segments

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cell death at the AER

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responsible for forming toes and fingers, separates the ridge into five parts, further growth is dependent on further outgrowth, condensation of the mesenchyme to form cartilaginous digital rays and the death of intervening tissue between the rays

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rotation found in the upper and lower limbs

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upper limb rotates 90 degrees laterally, so extensor muscles lie on the lateral and posterior surface and the thumbs lie laterally, whereas the lower limb rotates approx. 90 degrees medially, placing the extensor muscles on the anterior surface and the big toe medially

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hyaline cartilage models

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first ones laid down by the sixth week of development, formed by chondrocytes which are derived from the mesenchyme

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joint interzone

Back 106

form joints, formed in the cartilaginous condensations when chondrogenesis is arrested, cells in this region increase in number and density and then a joint cavity is formed by cell death, surrounding cells differentiate into a joint capsule, thought that WNT14 is the inductive signal

Front 107

endochondral ossification

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begins by the end of the embryonic period, needs a hyaline cartilage model, at birth the diaphysis is normally completely ossified but the epiphyses are still cartilaginous

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primary ossification centers

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present in all long bones of the limbs by the 12th week

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epiphyseal plates

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plays an important role in growth in the length of the bones, endochondral ossification occurs on both sides of the plate, when reaches full length the plate disappears

Front 110

molecular regulation of limb development

Back 110

1. lateral plate mesoderm induces limb bud formation
2. the AER forms under the influence of BMP
3. the ridge maintains the progress zone by causing proliferation of mesenchymal cells in the vicinity
4. there is an ant (cephalic) and posterior (caudal) organization induced by the ZPA
5. there is also a dorsal-ventral organization important for nerve and muscle distribution
6. homeobox genes determine the shape and size of the bones

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HOX genes

Back 111

are homeobox genes that regulate the position of the limbs along the craniocaudal axis, expressed in overlapping patterns from head to tail, also responsible for determing the types and shapes of the bones of the limb, also responsible for the patterning and shapes of different vertebrae

Front 112

TBX5 and FGF 10

Back 112

initiate limb outgrowth, secreted by the lateral plate mesoderm cells

Front 113

BMPs

Back 113

expressed in ventral ectoderm, induce formation of the AER by signaling thorugh the homeobox gene MSX2

Front 114

radical fringe

Back 114

expressed in the dorsal half of the limb ectoderm, restricts the location of the AER to the distal tip of the limbs

Front 115

SER2

Back 115

induced by radical fringe, found at the border between cells that are expressing radical fringe and those that are not

Front 116

Engrailed-1

Back 116

represses expression of radical fringe

Front 117

FGF4 and FGF8

Back 117

expressed after the ridge is established, maintain the progress zone, influence distal growth

Front 118

zone of polarizing activity

Back 118

regulate the anteroposterior axis of the limb, produce retinoic acid which initiates expression of sonic hedgehog that is responsible for regulating the anteroposterior axis, defects in ZPA causes mirror images of digits, SHH is the molecule secreted by ZPA resonponsible for this regulation

Front 119

signals that influence scerlotome

Back 119

sclerotome cells divide and expand under the influence of Noggin and SHH, migrate to form the vertebral column and the ribs

Front 120

migration of sclerotome cells to form vertebrae

Back 120

migrate ventrally to the notochord from the somite to form the vertebral body, they then migrate dorsally to form the spinous and transverse processes

Front 121

vertebrae formation

Back 121

form from the sclerotome portions of the somites, which are derived from paraxial mesoderm, occurs during the 4th week, notochord regresses into the vertebral bodies

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sclerotome cells and vertebrae

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sclerotome cells migrate around the spinal cord and notochord to merge with cells from the opposing somite on the other side of the neural tube

Front 123

resegmentation

Back 123

occurs at the sclerotome portion of each somite, occurs when the caudal half of each sclerotome grows into and fuses with the cephalic half of each subjacent sclerotome, forms each vertebrae from the cephalic and caudal halves of different sclerotomes fusing

Front 124

HOX genes and vertebra

Back 124

determine the patterning of the shapes of the different vertebrae

Front 125

development of the vertebral column

Back 125

each vertebra is formed by the lower and upper half of adjacent sclerotome condensations, moves the myotome into adjacent intervertebral regions and moves the artery into the middle of a vertebra, also gives ability to move the vertebral column

Front 126

mesenchyme between the cephalic and cranial parts of the vertebrae

Back 126

do not proliferate but fill the space between the two precartilaginous vertebral bodies, contribute to IV discs

Front 127

formation of the nucleus pulposus

Back 127

in the intervertebral regions the notochord hydrates and swells forming the nucleus pulposus, mesenchymal cells fill the space between the two precartilaginous vertebral bodies

Front 128

rib formation

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form from costal processes of thoracic vertebrae and thus are derived from the sclerotome portion of paraxial mesoderm, grow out the same sclerotome from their attachment point to the vertebra

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sternum formation

Back 129

develops independently in somatic mesoderm in the ventral body wall, two sternal bands are formed on either side of the midline and thse fuse to form cartilaginous models of the manubrium, sternebrae and xiphoid process

Front 130

neural crest cells and disease

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a target for teratogens as they leave the neuroectoderm

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craniosynostosis

Back 131

premature suture closure, found in 1/2500 births in >100 genetic syndromes

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scaphocephaly

Back 132

57% of the craniosynostosis, early closure of the sagittal suture, results in frontal and occipital expansion and skull becomes long and narrow

Front 133

brachycephaly

Back 133

early closure of the coronal and lambdoid sutures, results in a short, high skull

Front 134

what regulates suture closure

Back 134

release of transforming growth factor (TGF-beta) and the role of FGF, mutations in FGF receptors causes various types of craniosynostosis and even dwarfism
FGFR1-promotes osteogenic differentiation
FGFR2-increase proliferation
FGFR3-unclear

Front 135

achondroplasia

Back 135

most common form of dwarfism, affects long bones, inherited as an autosomal dominant trait

Front 136

hypochondroplasia

Back 136

milder form of achondroplasia

Front 137

thanatophoric dysplasia

Back 137

most common form of lethal dwarfism, autosomal dominant, type I has short femurs, type II has severe cloverleaf skull

Front 138

cranioschisis

Back 138

failure of the neurocranium to close due to a failure of the neural tube to close, brain tissue exposed to amniotic fluid degenerates and results in some type of anencephaly and the fetus is usually not viable

Front 139

meningoencephalocele

Back 139

variant of cranioschisis, occurs when meninges herniates the skull

Front 140

cranial meningocele

Back 140

variant of cranioschisis, occurs when brain tissue herniates the skull

Front 141

acromegaly

Back 141

caused by congenital hyperpituitarism and excessive production of growth hormone, enlarged face, hands and feet, gigantism

Front 142

microcephaly

Back 142

usually an abnormality in which the brain fails to grow and the skull fails to expand, severe retardation

Front 143

when is limb development most susceptible to teratogens

Back 143

during the 4th-5th week

Front 144

occurrence of limb defects

Back 144

relatively rare except in cases of teratogenic defects, often associated with other more sever congenital defects involving the cardiovascular, genitourinary or cranial-facial systems, more common in the upper limb than the lower limb,

Front 145

non-developmental defects of limbs

Back 145

amputations caused by amniotic bands, possible adhesions or tears of the amnion that get wrapped around portions of the extremities

Front 146

amniotic bands

Back 146

may cause ring constrictions and amputations of the limbs or digits, believed to originate from tears in the amnion that detach and surround part of the fetus

Front 147

bone age

Back 147

can use ossification centers in hands and wrists to determine if a child has reached a proper maturation age

Front 148

meromelia

Back 148

partial absence of one or more of the extremities

Front 149

Amelia

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complete absence of one or more of the extremities

Front 150

phocomelia

Back 150

when long bones are absent and rudimentary hands and feet are attached to the trunk by small, irregularly shaped bones

Front 151

micromelia

Back 151

all segments of the extremities are present but abnormally short

Front 152

brachydactyly

Back 152

shortened digits

Front 153

syndactyly

Back 153

two or more fingers or toes fused, occurs when cell death that forms fingers is stopped

Front 154

polydactyly

Back 154

presence of extra fingers or toes, lack proper muscle connections, usually bilarteral

Front 155

ectrodacyly

Back 155

absence of a digit, occurs unilaterally

Front 156

cleft hand and foot (lobster claw deformity)

Back 156

consists of an abnormal cleft between the 2nd and 4th metacarpal bones and soft tissues

Front 157

scoliosis

Back 157

can be caused by having two successive vertebrae fuse asymmetrically or have half a vertebra missing

Front 158

Klippel-Feil sequence

Back 158

have fewer than normal cervical vertebrae, with some fused or abnormally shaped

Front 159

spina bifida

Back 159

result of imperfect fusion or nonunion of the vertebral arches, may involve only the bony vertebral arches leaving the spinal cord intact

Front 160

spina bifida occulata

Back 160

when the bony defect is covered by skin and no neurological defects occur, occurs in lumbar sacral region, marked by a patch of hair overlying the region

Front 161

spina bifida cystica

Back 161

neural tube fails to close, vertebral arches fail to form and neural tissue and/or meninges is exposed

Front 162

meningocele

Back 162

a spina bifida where only fluid-filled meninges protrude through the defect

Front 163

meningomyelocele

Back 163

a spina bifida where neural tissue protrudes through the defect

Front 164

rachischisis

Back 164

a spina bifida where the neural folds do not elevate and remain as a flattened mass of neural tissue, tissue may become necrotic

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development of the muscular system

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develops from the mesodermal germ layer and consists of skeletal, smooth, and cardiac muscle

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skeletal muscle development

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paraxial, which forms somites from the occipital to the sacral regions and somitomeres in the head, differentiates into dermatomyotome and sclerotome

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smooth muscle development

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from splanchnic mesoderm surrounding the gut and its derivatives and from ectoderm, pupillary, mammary gland and sweat gland muscles

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cardiac muscle development

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splanchnic mesoderm surrounding the heart tub

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somites and muscle development

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from the occipital region caudally, form and differentiate into the sclerotome, dermatome, and two muscle-forming regions, the two muscle forming regions extend beneath the dorsal epithelium to form the myotome (more so DML), myotome is ventrally extended and the dermatome cells lose their epithelial configuration and migrate to the overlying ectoderm to form dermis

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dermatomyotome

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differentiates into three components a DML, a dermatome (intermediate) and a VLL

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ventrolateral lip (VLL)

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one of the muscle forming regions from the somites, found on the prospective dermomyotome, cells from the VLL contribute to formation of the myotome and also provide progenitor cells for limb and body wall musculature, become hypomere

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dorsomedial lip (DML)

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the other muscle forming region from the somites, these cells migrate ventral to the prospective dermatome and also contribute to the formation of the myotome, will form the muscles of the back (epimeric, epaxial musculature), becomes epimere

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myoblasts

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muscle precursor cells, fuse and form long, multinucleated muscle fibers, soon appear in the cytoplasm and by the end of the third month, cross striations appear

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somitomerese and muscle development

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similar process to the somites, but somitomeres remain loosely organized structures, never segregate into sclerotome and dermomyotome segments

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tendons

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for the attachment of muscles to bones are derived from sclerotome cells lying adjacent to myotomes at the anterior and posterior borders of somites

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scleraxis

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regulates the development of these cells

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BMP4, FGF and WNT

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BMP4 and FGF from lateral plate mesoderm and WNT from adjacent ectoderm signal VLL cells of the dermomytome to express the muscle-specific MYF4 and MYO-D, BMP4 from ectoderm cells induces WNT by the sdorsal neural tube and cause sonic hedgehog proteins to reach the DML cells of the dermomyotome, induce MYF5 and MYO-D and activate muscle development

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SHH and noggin

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secreted by the notochord and floor plate of the neural tube, cause the ventral part of the somite to form sclerotome and to express PAX1, which in turn controls chondrogenesis and vertebral formation, low SHH activates PAX3 which demarcates the dermomyotome, only plays a role in DML

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control of muscle formation patterns

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controlled by connective tissue into which myoblasts migrate, in head derived from neural crest cells, in the cervical and occipital regions, they differentiate from somitic mesoderm and in the body wall and limbs they originate from somatic mesoderm

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epimere

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found at the end of the fifth week, a small dorsal portion of muscle cells, formed from the dorsomedial cells of the somite that reorganized as myotomes, give rise to epaxial musculature (back muscles)

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hypomere

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found a the end of the fifth week, a large ventral part fromed by migration of dorsolateral cells of the somite, gives rise to hypaxial muscles (limbs and anterior and lateral body wall)

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dorsal primary ramus

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innervate the epimere, remain with their original muscle attachment throughout migration

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ventral primary ramus

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innervate the hypomere, remain with their original muscle attachment throughout migration

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signal for muscle migration

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comes from the adjacent connective tissue, these migration patterns and dedicated nerve supplies are responsible for the dermatomal maps and the myotomal maps

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extensor muscles of the vertebral column

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formed from myoblasts of the epimeres

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muscles of the limbs and body wall

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formed from myoblasts of the hypomeres

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scalene, geniohyoid and prevertebral muscles

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formed from myoblasts from cervical hypomeres

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external intercostal, internal intercostal and innermost intercostal

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formed from myoblasts from thoracic segments, ribs cause these muscles to maintain segmentation

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external oblique, internal oblique and transversus abdominis

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formed from myoblasts of the abdominal wall, walls of the abdominal wall fuse to form large sheets of muscle tissues

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quadratus lumborum

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formed from myoblasts from the hypoblast of lumbar segments

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pelvic diaphragm and striated muscles of the anus

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formed from myoblasts from the sacral and coccygeal regions

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rectus abdominus muscle and the infrahyoid musculature

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formed from a ventral longitudinal column that arises at the ventral tip of the hypomeres, rectus ab (abdominal region) and infrahyoid (cervical region)

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sternalis muscle

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formed from the longitudinal muscle in the thorax

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voluntary head muscles

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derived from paraxial mesoderm (somitomeres and somites) including musculature of the tongue, eye, and the pharyngeal arches (mastication, facial expression, larynx, pharynx and palate, and middle ear muscles) and ectoderm (muscles of the iris)

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preotic somites

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form muscle of the eye

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postotic somites

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form muscle of the tongue

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first indication of limb musculature occurs when?

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7th week as a condensation of mesenchyme (derived from the dorsolateral cells of the somites that migrate into the limb bud to form the muscles) near the base of the limb buds, once the buds form primary rami penetrate into the mesenchyme

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what occurs to muscle when the limb bud elongates

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the muscle tissue splits into flexor and extensor components, muscles of limbs are initially segmental, then fuse and are composed of muscle from different segments

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upper limb bud

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lie opposite the lower five cervical and upper two thoracic segments (C4-8, T1-2)

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lower limb bud

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lies opposite the lower four lumbar and upper two sacral segments (L1-5, S1-2)

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radial nerve

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supplies the extensor musculature, formed by a combination of the dorsal segmental branches

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ulnar and median nerves

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supply the flexor musculature, formed by a combination of the ventral branches

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prerequisite of complete functional differentiation of muscle

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need an early contact between the nerve and muscle cells

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spinal nerves

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play an important role in differentiation and motor innervation of the limb musculature, also provide sensory innervation for the dermatomes

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intercalated discs

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attachment point for cardiac myoblasts

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myofibrils

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develop as in skeletal muscle, but myoblasts do not fuse

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Purkinje fibers

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form the conducting system of the heart, occurs when a few special bundles of muscle cells with irregularly distributed myofibrils become visible, modified cardiac muscle fibers

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smooth muscle for the dorsal aorta and large arteries

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derived from lateral plate mesoderm and neural crest cells

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smooth muscle in the coronary arteries

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derive from proepicardial cells and neural crest cells

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smooth muscle in the gut

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derived from splanchnic layer of lateral plate mesoderm that surrounds these structures

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smooth muscle of the sphincter and dilator of the pupil and mammary and sweat gland muscle

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derived from the ectoderm

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serum response factor (SRF)

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a transcription factor responsible for smooth muscle cell differentiation, upregulated by growth factors through kinase phosphorylation pathways

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myocardin and myocardin-related transcription factors (MRTFs)

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act as coactivators to enhance the activity of SRF, thereby initiating the genetic cascade responsible for smooth muscle development

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Prune-belly syndrome

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total or partial absence of abdominal musculature, a defect in the migrating myotomal cells, causes a distended abdomen from atrophy of abdominal wall musculature

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Poland anomaly

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total or partial absence of the pectoralis major