Human Development 1 (pt 2)

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bbeckers88
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84669
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Human Development 1 (pt 2)
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2011-05-09 21:57:12
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Embryology
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continuation of 84404
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  1. Abdominal pregnancy
    • implants in rectouterine pouch, mesentary, or parietal peritoneum
    • intraperitoneal bleeding
    • risk of maternal death
    • some full term deliveries
    • stone fetus
    • possible simutaneous intra and extrauterine pregnancies
  2. inhibition of implantation
    • 30-50% of zygotes dont implant because:
    • - endometrium not receptive
    • -chromosomal abnormalities
    • -morning after pill
    • - upsets progesterone and estrogen balance
    • -speeds transport of zygote
    • -reduces receptivity of endometrium
    • -IUD
    • -reduces receptivity of endometrium by causing an imflammatory response
    • A- Amniotic cavity
    • B- Amnion (amnioblasts)
    • C- Epiblast
    • D- Hypoblast
    • A- syncytiotrophoblast
    • B- Exocoelomic cavity/ Chorionic cavity
    • C- Primary Umbilical Vesicle
    • D- Amnionic cavity
    • E- Extraembryonic somatic mesoderm
    • F- Extraembryonic splanchnic mesoderm
  3. Early uteroplacental circulation
    • -lacunaeform in syncytiotrophoblast and will fill with maternal blood. this will diffuse to embryonic disc
    • -lacunae fuse to form lacunar networks
    • -endometrial capillaries form sinusoids
    • -syncytiotrophoblasts invades endometrium
    • -diffusion thru cytotrophoblast supports embryonic development
  4. Chorion
    • consists of extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblasts
    • -embeds conceptus in endometrium
    • -allows for nutrient exchange
    • -secretes hCG and progesterone
    • Connecting stalk suspends amnion, umbilical vesicle and embryonic disc inside the chorionic cavity
  5. Chorionic villi
    • end of week 2, cytotrophoblast extensions form
    • primary villi - initial branch
    • secondary villi- branch filled with somatic mesoderm
    • tertiary villi- branches contain vasculature
  6. Cytotrophoblastic shell
    • surrounds chorionic sac and tertiary villi
    • stem chorionic villi and branch chorionic villi (tertiary villi)
    • -branch villi for materna exchange
  7. Placenta Components
    • Chorion- fetal contribution
    • Decidua- maternal contribution
    • -controls invasion by fetal cells
    • -glycogen and lipids
  8. Fetal-placental circulation
    • 2 umbilical arteries- d capillaries in deoxygenated blood from fetus to placenta from branch chorionic villi
    • capillaries in villi- material exchange
    • umbillical vein- oxygenated blood from placenta to fetus
  9. Maternal - placental circulation
    • Spiral arteries
    • -endometrial into intervillous spaces, lots of exchange
  10. Placenta functions
    • -Synthesize cholesterol, glycogen, FA for energy
    • -hCG, progesterone, and estrogen
    • -Gas exchange
    • -Nutrient exchange
    • -waste exchange
    • -maternal antibodies for protection
    • -Drugs can also cross over
  11. Week 3 of development
    • first week after missed period, pregnancy detectable by ultrasound
    • Bilaminar disc- epiblasts of amniotic cavity and hypoblasts of umbilical vesicle
    • prechordal plate- hypoblast cells. development of head region, site of mouth, thickened area of cells on embryonic disc
  12. Primitive Streak
    • Morphogenesis begins (development of body)
    • Gastrulation- establishes axial orientation

    • Thickened medial band on dorsal and caudal surfaces of epiblast
    • Formed as epiblasts proliferate and migrate to median
  13. Parts of primitive streak
    • primitive node- epiblast cells at cranial end
    • primitive pit- depression in primitive node
    • primitive groove- depression lengthwise in streak
    • pit and groove form as epiblast cells migrate inward
  14. Results of epiblasts migrating into primitive streak
    • Displacement of hypoblasts which become embryonic endoderm
    • Epiblast cells get located between epiblasts and hypoblasts
    • - form embryonic mesoderm (mesenchyme)
    • -fuse laterally with extraembyonic mesoderm
    • -migrate cranially to prechordal plate into cardiogenic area
    • remaining epiblasts form embryonic ectoderm
  15. Notochord formation
    • notochordal process
    • -median cord of mesenchymal cells in mesoderm from the primitive streak to prechordal plate
    • -no mesoderm
    • -becomes oropharyngeal membrane (mouth)
    • Cloacal membrane- caudal to primitive streak (anus)
    • -no mesoderm
  16. Notochord Functions
    • -Defines longitudinal axis
    • -provides regidity
    • -provides signals for development of CNS and axial muskuloskeletal structures
    • -Development of IVD
  17. Neural Tube Formation (Neurulation)
    • Neural plate- thickened midline ecoderm cells forms neuroectoderm because of notochord induction. extends cranially past notochord to form brain and spinal cord
    • Neural groove and fold- neural plate, day 18
    • Neural tube- closure of folds. begins in cervicals, extends both ways. separates and covered by ectoderm
    • cranial neuropore and caudal neuropore remain open
  18. Neural Crest Cells
    • migratory cells from "crests" (form tear-drops around neural tube)
    • migrate to dorsal-lateral region around tube
    • -form sensory ganglia for nerves
    • -autonomic ganglia, Schwanns cells, melanocytes, suprearenal medulla cells, CT in head
  19. Neural Tube defects
    • Disturbances to development in week 3
    • Failure of neural folds to fuse and close into neural tube
    • maroencephaly- partial absence of brain
    • Anencephaly- complete absence of brain
  20. Paraxial, intermediate, and lateral mesoderm
    • paraxial mesoderm- adacent to notochord, from mosoderm cells thru lateral primitive node and cranial primitive streak
    • Intermediate mesoderm- thru mid region of primitive streak, forms urogenital structures
    • lateral plate mesoderm- caudal primitive streak, continuous with extraembryonic mesoderm, forms body wall structures
  21. Somite formation
    • paired cuboidal structures from paraxial mesoderm, form in cranial-> caudal sequence
    • -future occipital region first
    • -42-44 by end of week 5
    • -used as segmental clock
    • -patterns depend on gene expression
    • -form muscles, skeleton, and dermis
    • -4 occipital, 8 cranial, 12 thoracic, 5 lumbar, 5 sacral, 8-10 coccygeal
  22. Intraembryonic coelom
    • embryonic body cavity
    • form from spaces inside the lateral plate mesoderm that become continuous with chorionic cavity
    • Somatic/parietal layer - adjacent to ectoderm
    • Splanchnic/visceral layer- adjacent to endoderm
  23. Early Cardiovasculature
    • week 2 = diffusion
    • week 3 = blood vessel formation

    • vasculogenesis= formation of new blood vessels
    • angiogenesis= branching of blood vessels
  24. vasculogenesis week 3
    • extraembyonic mesoderm- mesenchym cells form into angioblasts
    • cluster to form blood islands adjacent to umbilical vesicle
    • Cavities form in islands
    • angioblasts around cavities flatten forming endothelial cells
    • cavities fuse forming endothelial channels which form blood cells
  25. Heart development week 3
    • -in cardiogenic area- cranial to the oropharyngeal membrane
    • -paired endocardial tubes fuse forming heart tube which joins with blood vessels, connecting stalk, chorion, and umbilical vesicle
    • -Heart starts beating at week 3
  26. Head Fold week 4
    • -Neural folds thicken into primordial brain- oriented dorsally
    • -Forebrain enlarges, brain grows beyond oropharengeal membrane and hangs over primordial heart
    • -pushes structures ventrally
    • -part of umbilical vessicle endoderm becomes pinched into cranial embry forming the foregut (between brain and heart)
  27. Septum Transversum
    forms central tendon of diaphragm after folding between heart and liver
  28. Tail fold week 4
    • -rapid caudal growth of neural tube
    • -caudal eminence-over cloacal membrane
    • -caudal umbilical vesicle becomes hindgut
  29. Allantosis
    • evagination of umbilical vesicle into connecting stalk which persists as urachus in adults
    • -from urinary bladder to umbilicus
  30. lateral folds week 4
    • due to rapid spinal cord growth
    • -lateral edges roll ventrally forming a cylindrical embryo
    • -intraembryonic coelom sealed off
    • -midgut- enclosed central umbilical vesicle
    • -omphaloenteric duct- connection to umbilical vesicle
    • Amnion surrounds the embryo
  31. Subdivisions of intraembryonic coelom
    • Paricardial cavity = heart
    • Pericardioperitoneal cavity = pleural cavities
    • peritoneal cavities = abdominal and pelvic cavity

    • all lined by parietal mesothelium (somatic mesoderm)
    • organs surrounded by visceral (splanchnic mesoderm)
  32. Mesenteries
    • Double layered extensions of peritoneum between parietal and visceral peritoneum from organ to body wall for vasculature
    • dorsal mesentary- gut tube to dorsal wall
    • ventral mesentary- gut tube to ventral wall, falciform and lesser omentum
  33. Embryonic period
    • weeks 1-8
    • human appearance
    • risk of congenital abnormalities is high
    • susceptable to teratogens
  34. fetal period
    • weeks 9-birth
    • differentiation/growth of tissues
    • body growth increases
  35. fetal viability
    • weeks 0-22 = no
    • weeks 26-28 = with complications
    • weeks 35+ = yes
  36. 3 phases of development
    • growth- cell division and production of extracellular products
    • morphogenesis- develop structures of organs, requires specific events
    • differentiation- complete formation of tissues and organs
  37. Development of heart
    • angioblastic cords: in cardiogenic mesenchyme on both sides of embryo canalize forming small endocardial tubes
    • -lateral folding fuses tubes forming a heart tube made of endocardium, primordial myocardium, and cardiac jelly
  38. heart elongates forming:
    • bulbis cordis- cranial end, fixed by pharyngeal arches, contains truncus arteriosus
    • primordial ventricle
    • primordial atrium
    • sinus venosus- caudal end, fixed by septum transversum, venous return
  39. Veins into sinus venosus
    • common cardinal V- from embryo
    • vitelline V - from umbilical vesicle
    • umbilical V- from placenta
  40. Bulboventricular loop
    • bulbis cordis and ventricle grows faster
    • ends up lying caudally and ventrally, atrium and sinus venosus lie cranially and dorsally
  41. formation of pericardial sinuses
    • heart is bulging into pericardial cavity, epicardium adhears to the heart
    • dorsal mesocardium suspends the heart
    • transverse sinus: develops in degenerating dorsal mesocardium at base of the heart
    • oblique sinus- posterior to heart/ inferior to pulmonary Vs
  42. Atrioventricular canal partitioning
    • Endocardial cushions- form on dorsal and ventral walls from mesenchyme infiltrating cardiac jelly
    • -cushions fuse forming left and right AV canals
    • -will function as AV valves and help form membranous interventricular septum
  43. Atrium partitioning
    • septum primum- roof of atrium to endocardial cushions, partially divides atrium
    • foramen primum- between septum primum and cushions, is a shunt between atria
    • foramen secondum- central of septum primum
    • septum secondum- ventral wall of right atrium adjacent to atrial septum, covers the foramen secondum
    • foramen ovale- in septum secondum. septum primum breaks down leaving only the caudal portion as a valve for foramen ovale
  44. Sinus venous changes
    • sinuatrial orifice moves to the right
    • -L horn regresses leaving only coronary sinus
    • -R horn enlarges forming IVC from R vitelline V and SVC from R andterior and common cardinal Vs
  45. Right sinus horn incorporates into the right atrium
    • -Sinus venarum- from sinus venosus
    • -pectinate muscles- primordial atrium only
    • -crista terminalis- between sinus venarum and atria
    • -sulcus terminalis- external crista terminalis
  46. Primordial pulmonary V
    • -Dorsal outgrowth from atrial wall left of the artial septum
    • -4 primary branches get incorporated into the L atrium
    • -pectinate muscles only in the primordial atrium
  47. Ventricle partitioning
    • -interventricular septum- median ridge along the floor
    • - muscular septum- myoblasts toward cushion
    • -membranous septum- mesenchyme cushoins to muscular septum
    • -Interventricular foramen- between muscuar septum and cushions, closes in week 7
    • -Trabeculae carnae- cavitations in walls
    • -papillary muscles and chordae tendinae- function with AV valves
    • -valve membranes- form from cushions
  48. Bulbis cordis partitioning
    • bulbar and truncal ridges form from neural crest infiltration doing a 180 degree spiral forming aorticopulmonary septum
    • -truncus arteriosis- ascending aorta and pulmonary trunk
    • -bulbis cordis- conus arteriosis in R and Aortic vestibule in L
    • -semilunar valve- swellings from subendocardial tissue thin into lunule and sinus
  49. Conducting system of the heart
    • SA node- week 5 in wall of sinus venosus, right wall near SVC opening
    • AV node- base of interatrial septum superior to cushions and anterior to cornonary sinus opening
    • AV bundle- interatrial septum to interventricular septum, fibrous CT forms cardiac skeleton separtating the charges
  50. Dextrocardia
    • Heart tube bends to the left, heart displace to the right instead of left= transposition
    • Functions normally with sinus inversus
  51. Ectopic Cordis
    • -rare
    • -heart is exposed anteriorly
    • -sternum is split in 2 and paricardial sac is open
    • -lateral body folds dont fuse, usually fatal
  52. Atrial septal defects
    • -more connon in women
    • -patent foramen ovale- no problem if small
    • -causes:
    • -abnormal septal growth
    • -abnormal forameina perforations
    • -patent foramen primum
    • - failure of septum primum to fuse, associated with AV valve or AV septal defects
  53. Ventricular septal defects
    • -most common in males
    • -membranous interventricular septal defects
    • - failure to grow from cushions, incomplete closure of IV foramen, large foramen = pulmonary hypertension
    • -muscular interventricular septal defects
    • - from excessive cavitation of myocardium
  54. Persistant truncus arteriosis
    • failure of truncal ridges to from articopulmonary septum
    • -associated with ventricular septal defects
    • -single atrial trunk straddles both ventricles
  55. Transposistion of the Great Arteries
    • -failure of articopulmonary septum to spiral
    • -aorta from R ventricle, pulmonary trunk from L
    • -associated with atrial septal and ventricular septal defects
    • -fatal if not corrected
  56. Tetralogy of fallot
    • -pulmonary trunk stenosis
    • -dextroposition of aorta
    • -ventricular septal defect
    • -right ventricle hypertrophy
  57. Dorsal Artery development
    • -paired, run the length of the embryo
    • -upper L becomes descending thoracic aorts
    • -upper right regresses
    • -R and L fuse caudally to form lower thoracic and abdominal aorta
    • -terminates caudally as the median sacral artery
    • -cranial portion become pharyngeal arch arteries
  58. Intersegmental arteries
    • -from caudal dorsal aortas
    • -between somites, supply their derivatives
    • -merge cervical region to form vertebral arteries, lose their connection to the aorta
    • -thoracic region becomes posterior intercostal arteries
    • -lumbar region becomes lumbar arteries
    • -5th lumbar artery becomes common iliac arteries
    • -sacral region fuses to form lateral sacral arteries
  59. Vitelline Arteries
    • -from dorsal aorta to umbilical vesicle
    • -become celiac trunk, superior mesenteric, inferior mesenteric
  60. Umbilical arteries
    • -thru connecting stalk to chorion
    • -carry deoxygenated blood to placenta
    • -proximal segments become internal iliac arteries and superior vesical arteries
    • -dorsal segments become medial umbilical ligaments
  61. viteliline Vs
    • -poorly oxygenated blood from umbilical vesicle
    • -drain into sinus venosus
    • -L regresses
    • -R become hepatic portal V and IVC
  62. Umbilical V
    • -highly oxygenated blood from chorion
    • -drains to sinus venosus, will eventually drain to liver
    • -R and cranial L degenerate
    • -L becomes the umbilical V carrying blood from placenta to embry
  63. Ductus venosus
    • -in liver
    • -shunts blood from umbilical vein to IVC
    • -blood bypasses the liver and goes to the heart
  64. Common Cardinal V
    • -poorly oxygenated blood from the embryo
    • -recieve anterior and posterior cardinal Vs
    • anterior cardinal Vs- drain cranial parts, L brachiocephalic vein forms anastamosis of 2 veins, SVC from R anterior and R common cardinal
    • posterior cardinal vs- drain caudal parts form arch of the azygos V and common iliac V
  65. IVC and SVC abnormalities
    • IVC discontinuous- venous return thru azygos V, hepatic vs to R atrium
    • Double SVC- persistant L anterior and common cardinal, drains thru coronary sinus
    • Left SVC- persistant L anterior cardinal V, drains thru coronary sinus
  66. patent ductus arteriosus
    • more common in females
    • maternal rubella infectionduring pregnancy
    • hypoxia and low birth weight (fails to stimulate smooth muscle contracton to close duct)
    • aortic blood shunts
    • surgery needed
  67. aortic coarctation
    • -constriction of the aorta distal to the origin of the left subclsvian artery
    • -more common in males
    • postductal coarctation
    • -distal to ductus arteriosus allows development of collateral circulation
    • -involves anastomosis b/t internal thoracic and inferior epigastric As
    • preductsl coarctation
    • -proximal to ductus arteriosus, fetal circulation dependent onductus arteriosus
  68. development of the spinal cord
    • caudal to somite pair 4
    • neural tube walls thicken, narrowing the neural canal into the minute central canal
    • lined by pseudostratified columnar neuroepithelium
  69. ventricular zone of spinal cord
    • original neuroepithelium
    • gives rise to spinal cord neurons and astrocytes, oligodendrocytes, and ependymal cells
  70. intermediate zone of spinal cord
    • proliferation in original ventricular zone
    • forms neuroblasts
    • - spinal cord neurons
  71. Marginal zone
    • peripheral to the original ventricular zone
    • becomes white matter
  72. Glioblasts
    • from ventricular zone neuroepithelium after neuroblast formation ceases
    • found in all 3 zones
    • become astroblasts (astrocytes), oligodendroblasts (oligodendrocytes)
  73. Ependymal cell formation
    • from remaining ventricular zone neuroepithelium
    • persists as the ependyma lining in the central canal
  74. microglial cells
    • from mesenchyme
    • originate in bone marrow
    • invade CNS after it has been vascularized
  75. what happens as neuroepithelial cells proliferate and differentiate?
    spinal cord walls become thick, roof and floor become thin
  76. Sulcus limitans
    longitudinal groove on either side of central canal lumen
  77. alar plate
    • dorsal longitudinal bulge in the intermediate zone, will become dorsal columns in the gray matter
    • afferent neurons located here
    • dorsal median septum from alar plates enlarging bilaterally
  78. Basal plate
    • ventral longitudinal bulge in the intermediate zone, will become ventral and lateral columns in the gray matter
    • Efferent neurons located here
    • Ventral median fissure- from basal plates enlarging bilaterally
  79. Development of spinal ganglia (DRG)
    • pseudounipolar neurons, initially bipolar neurons
    • from neural crest cells
    • peripheral process thru sensory nerves, central process thru dorsal root to enter spinal cord
  80. Development of spinal meninges
    • primordial meninx- membrane from mesenchyme
    • Dura mater- thickened external layer
    • Leptomeninges- internal layer from neural crest
    • Subarachnoid space - fluid spaces in leptomeninges, separate as CSF is produced. forms arachnoid and pia mater
  81. Postition of spinal cord in embryo
    • extends entire lenght of vertebral canal
    • spinal nerves exit intervertebral foramina directly opposite their level
  82. spinal cord position in 6 month fetus
    conus medullaris extends to S1 level
  83. spinal cord level in newborn infant
    conus medullaris extends to L2(3)
  84. spinal cord level in adult
    • conus medularris extends to inferior border of L1
    • cauda equina- bundle of nerve roots inferior to conus medullaris
    • dura mater and arachnoid end at S2, filum terminale externum extends to coccyx
    • pia mater extends as filum terminale internum to first coccygeal vertebra
  85. Myelination of neuronal processes
    • forms in fetal period and continues thru first 1
    • coincides with tracts becoming functional
    • motor fibers first
    • produced by oligodendrocytes
  86. spinal dermal sinus
    posterior median skin dimple in sacral region indicating site of closure of caudal neuropore
  87. spina bifida occulta
    • failure of embryonic halves of vertebral arch to grow and fuse
    • 10% of people have it at L5-S1
    • small dimple with a tuft of hair is indicator
  88. Spina bifida cystica
    • protrusion of spinal cord and/or meningies thrugh vertebral arch defect
    • causes neurologic deficit
  89. Spina bifida with meningocele
    • sac contains meninges and CSF only
    • no neurological deficit
  90. spina bifida with meningomyelocele
    • sac contains spinal cord and/or spinal roots
    • significant functional deficits
  91. Myeloschisis
    • most severe form of spina bifida
    • caudal neuropore failed to close, spinal cord is flattened mass of nervous tissue
  92. Development of brain
    cranial to somite pair 4
  93. primary brain ventricles
    • Prosencephalon- forebrain
    • mesencephalon- midbrain
    • rhombencephalon- hindbrain
  94. prosencephalon partially subdivides into:
    • telencephalon
    • diencephalon
  95. rhombencephalon partially subdivides into:
    • metencephalon
    • myelencephalon
  96. Flexures of embryonic brain
    • midbrain flexure- ventral fold in the midbrain
    • cervical flexure- ventral fold at the junction of the hindbrain and spinal cord, future level of the superior rootlet of C1 spinal nerve
    • pontine flexure- dorsal fold b/t midbrain and cervical flexures, dibids hindbrain into 2 parts, becomes 4th ventricle
    • -metencephalon into pons and cerebellum
    • -myelencephalon into medulla oblongata
  97. Development of caudal myelencephalon
    • resembles spinal cord- is the closed part of medulla
    • small central canal closed by part of 4th ventricle
    • alar plates present, in dorsal position
    • -neuroblast migrate medially to form gracile nuclei
    • -neuroblasts migrate laterally to form cuneate nuclei
    • Pyramids- fiber bundles of pyramidal axons, descending corticospinal fibers
  98. Development of raustral myelencephalon
    • wide, thin roof
    • pontine flexure causes lateral walls to move laterally
    • -cavity become floor of 4th ventricle
    • -alar plates lie lateral to basal plates forming inferior olivary nucleus
    • -alar plate neuroblasts develop into afferent neurons
    • -basal plate neuroblast develop into efferent neurons
  99. Development of metencephalon
    • walls form cerebellum and pons
    • cavity forms superior 4th ventricle
    • pontine flexure spreads the lateral walls
  100. Cerebellar swellings
    • dorsal parts of alar plates into 4th ventricle
    • swell and fuse in the midline
    • bulge out and overlap pons and medulla oblongata
    • alar plae neuroblasts migrate into swellings, form neurons of cerebellar cortex
  101. Cerebellum structure
    • Archicerebellum- vestibular apparatus
    • Paleocerebellum- sensory input from limbs
    • Neocerebellum- selective control of limb movements
  102. Pons development
    connecting cerebral cortex and cerebellar cortex
  103. Choroid plexuses
    • in roof of 4th ventricle
    • pia mater invaginates thru roof of 4th ventricle
    • blood vessels in pia mater become vessels of choroid plexuses
    • occurs in roof of 3rd and medial walls of lateral ventricles
    • fluid produced called CSF
    • outpouchings from 4th ventricle become median and lateral aperatures
  104. Development of mesencephalon
    • comparatively little change
    • neural canal narrows to cerebral aqueduct
    • alar plate neuroblasts migrate into roof to form superior and inferior colliculi
    • basal plate neuroblasts give rise to groups of nuclei
    • cerebral peduncles become prominent
  105. Develpment of epithalamus
    • proliferation of neuroblasts in the roof and upper lateral walls of diencephalon, become relatively small
    • pineal gland
    • - median growth of caudal part of diencephalon roof
    • -photosensetive organ secretes melatonin
    • -regulates circadian rhythm
  106. Development of thalamus
    • grows rapidly and bulges into 3rd ventricle
    • -3rd ventricle reduces
    • -two sides fuse (70%)
    • relay station for afferent information heading to cerebral cortex
    • -some motor control
  107. Development of hypothalamus
    • ventral to the thalamus
    • coordinates many endocrine activities in the body
    • controlling center for the autonomic nervous system regulating blood pressure, body temp, fluid ion balance, body weight, appetite
  108. Development of pituitary gland
    • major controller of the endocrine system
    • ectodermal growths from:
    • -neurohypophysial diverticulum- downgroth from diencephalon, fomrs posterior lobe (neurohypophysis)
    • -hypophysial diverticulum- upgrowth from roof of stomodeum, forms anterior lobe (adenohypophysis)
  109. Development of verebral vesicles
    • lateral primordial cerebral hemispheres
    • cavities become lateral ventricle
  110. Development of cerebral hemispheres
    • cover diencephalon, midbrain and hindbrain
    • hemispheres meet and flatten in the midline, mesenchyme becomes falx cerebri
    • caudal end turns ventrally and rostrally forming temporal lobes
  111. Development of commissures
    • Anterior commissure- first, between olfactory bulbs and related cerebral cortical areas
    • Corpus callosum- connects neocortical areas
  112. Development of cortical layers
    • neuroblast migration
    • cortical surface is smooth initially
    • sulci and gyri develop as cortex grows and infolds, incraeses surface area
    • insula is buried in lateral sulcus
  113. Development of medullary center
    large volume of myelinated processes extending centrally
  114. Cranium bifidum
    • anomalies of brain/meningies
    • in median plane
    • squamous occipital bone or posterior foramen magnum
  115. cranial meningocele
    only meninges herniated
  116. cranial meningoencephalocele
    brain and meninges herniated
  117. cranial meningohydroencephalocele
    brain, ventricular components and meninges herniated
  118. Meroencephaly
    • failure of rostral neuropore to close
    • brian and calvarium do not develop normally
    • more frequent in females
    • -exencephaly- brain is exposed , nervous tissue degenerates
  119. Mirocephaly
    • brain and calvarium are small, face is normal
    • due to genetic or environmental factors
  120. Hydrocephalus
    • enlargment of the head
    • imbalance of CSF production and absorption
    • congenital aqueductal stenosis
    • cerebral hemispheres are squeezed
  121. Arnold-Chiari malformation
    • inferior displacement of vermis of cerebellum thru foramen magnum
    • interferes with CSF circulation
    • impacts cerebellum function
  122. Development of sensory neruons
    • formed from neural crest cells
    • initially bipolar neurons
    • later become unipolar
    • one process toward ventral root joining to form spinal nerve- peripheral process terminates at sensory ending
    • one process toward spinal cord to form dorsal root- central process
    • Satellite cells- ganglion support cells derived from neural crest cells, modified Schwann cells
  123. Development of motor neurons
    • from basal plate neuroblasts in week 4
    • emerge from ventrolateral aspect of spinal cord as ventral root
    • merge with spinal nerve, spiltis into:
    • -dorsal primary ramus- skin, musculature, of back
    • -ventral primary ramus- skin, musculature of ventrolateral body wall
    • nerves lengthen as body grows
  124. Development of Schwann cells
    neural crest cells that migrate into position to myelinate sensory and motor neurons
  125. Epidermis
    derived from surface ectoderm
  126. dermis
    derived from mesenchyme
  127. development of epidermis
    • surface ectoderm proliferates into keratinoblasts
    • forms a basal layer and squamous periderm
  128. vernix caseosa
    • white greasy substance of dead cells
    • protective covering on fetal skin
    • facilitates birth
  129. Development of epidermal strata
    • basal keratinoblasts continue proliferating to form an intermediate layer
    • -rete pegs are starting to protrude
    • -week 17, fingerprints start forming
    • periderm disappears and is replaced by stratum corneum
  130. Melanoblasts
    • week 7-8 ceural crest cells migrate into dermal mesenchyme
    • cross dermo-epidermal junction to become melanocytes
    • -melanin production begins prior to birth
  131. ichthyosis
    • exvessive keratinization
    • dry, scaling skin
    • epidermis cracks and begins to fall off with initial respiratory movements
    • curtail hair growth and development of sweat glands
    • inability to sweat
  132. generalized albinism
    • lack of pigmentation in skin, hair and retina
    • melanocytes unable to synthesize melanin
  133. piebaldism
    localized albinism causing lack of melanin in patches of skin or hair
  134. Development of dermis
    • from mesenchyme of somatic layer of lateral plate mesoderm
    • -dermatomes of somites
    • fibroblasts form and produce collagen and elstic fibers integrating dermal papilla and rete pegs
    • peripheral processes of sensory neurons grow into dermis
  135. dermal vascularization
    • simple endothelial lined tubes forming in mesenchyme
    • new vessels protruding from preexisting vessels
    • -develop various muscular coats
    • major vascular organization in skin by end of first trimester
  136. Hemangioma
    • vascular tumor
    • anterior or lateral face
    • solid cords of endothelial cells or hollow cords with blood
    • usually benign
  137. Development of nails
    • begin at tips of digits, fingernails before toenails
    • nail fields- in epidermis on dorsal tips of each digit
    • nail folds- epidermal cells proliferate laterally and proximally to nail fields, cellular proliferation and keratinization, formation of nail plate
    • nail plates- keratinized epithelial cells that had proliferated in the proximal nail fold
    • eponychium- epidermis covering the proximal base of the nail plate
    • hyponychium- skin under the nail plate
  138. Anonychia
    • absence of nails at birth
    • permanent condition
    • associated with abnormal hair or teeth development
  139. Development of hair
    • first recognizable on eyebrows, upper lip, and chin
    • hair follicle- proliferation of stratum basale into underlying dermis
    • -epithelial root sheath- epithelial cells of the invaginating hair follicle
    • -dermal root sheath- dermal mesenchymal cells surrounding the epithelial root sheath
    • hair bulb- club shaped deep end- germinal center
    • -hair shaft- cells in the germinal center proliferate and cbecome keratinized
    • -melanoblasts- migrate into bulb and differentiate itno melanocytes = hair color
  140. Hair papilla and arrector pili muscles
    • hair papilla
    • -dermal invagination into hair bulb providing vascular support
    • Arrector pili muscles
    • - from mesenchyme in dermis
    • -span from dermal root sheath to papillary dermis
    • -contraction causes goose bumps
  141. Lanugo
    • First hairs to appear, very fine and soft, lightly pigmented
    • hold vernix caseosa on the skin
    • replaced during the perinatal period
  142. Alopecia
    • absence or loss of scalp hair
    • congenital failure of hair follicles to form
  143. Hypertrichosis
    • excessive hairiness
    • extra hair follicles or persistence of lanugo hairs
  144. development of sebaceous glands
    • acinar buds from the epithelial root sheaths into the surrounding dermal CY
    • cells at the periphery of the bud ar mitotically active
    • central cells die and break down to produce sebum
    • - oily material thru hair follicle to surface to mix with vernix caseosa
  145. Development of eccrine sweat glands
    • in skin thru the body
    • tubular buds from the epidermis int othe underlying dermis
    • secretory component
    • -deep portion, coils on itself
    • -cells differentiate into secretory cells and myoepithelial cells
    • -produce aqueous secretory product
    • sweat duct
    • -canalized segment of tubular bud connected to surface
  146. Development of apocrine sweat gland
    • axilla, areolae of nipples, pubic region, and perianal regions
    • tubular buds from epidermis adjacent to hair follicles
    • ducts open into hair follicles superficial to sebaceous glands
    • secretory activity begins at puberty
  147. Mammary glands
    • mammary crests
    • -thickend strips of ectoderm from axillary to inguinal regions, persists only in pectoral region (breasts)
    • mammary buds
    • -pectoral epidermal invaginations of mammary crest into underlying mesenchyme, each primary buds forms several secondary mammary buds developing into lactiferous ducts.
    • - canalization of ducts from sex hormones in fetal circulation
  148. male and female rudimentary mammary glands
    • identical at birth
    • contain lactiferous ducts but no secretory acini
    • female breasts enlarge rapidly at puberty
  149. Gynecomastia
    • development of male mammary tissue
    • 2/3 of boys have breast hyperplasi (usually only for a few months)
  150. Athelia/Amastia
    • absence of nipple/breast development
    • bilaterally or unilaterally
    • absence of mammary crest formation or mammary bud development
  151. polythelia/polymastia
    • extra nipple/breast
    • usually just inferior to the normal breast, mistaken for moles

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