-
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
-
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
-
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
-
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
-
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
-
Cytotrophoblastic shell
- surrounds chorionic sac and tertiary villi
- stem chorionic villi and branch chorionic villi (tertiary villi)
- -branch villi for materna exchange
-
Placenta Components
- Chorion- fetal contribution
- Decidua- maternal contribution
- -controls invasion by fetal cells
- -glycogen and lipids
-
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
-
Maternal - placental circulation
- Spiral arteries
- -endometrial into intervillous spaces, lots of exchange
-
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
-
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
-
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
-
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
-
Results of epiblasts migrating into primitive streak
- Displacement of hypoblasts which become embryonic endodermEpiblast 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
-
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
-
Notochord Functions
- -Defines longitudinal axis
- -provides regidity
- -provides signals for development of CNS and axial muskuloskeletal structures
- -Development of IVD
-
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
-
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
-
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
-
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
-
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
-
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
-
Early Cardiovasculature
- week 2 = diffusion
- week 3 = blood vessel formation
- vasculogenesis= formation of new blood vessels
- angiogenesis= branching of blood vessels
-
vasculogenesis week 3
- extraembyonic mesoderm- mesenchym cells form into angioblastscluster 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
-
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
-
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)
-
Septum Transversum
forms central tendon of diaphragm after folding between heart and liver
-
Tail fold week 4
- -rapid caudal growth of neural tube
- -caudal eminence-over cloacal membrane
- -caudal umbilical vesicle becomes hindgut
-
Allantosis
- evagination of umbilical vesicle into connecting stalk which persists as urachus in adults
- -from urinary bladder to umbilicus
-
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
-
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)
-
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
-
Embryonic period
- weeks 1-8
- human appearance
- risk of congenital abnormalities is high
- susceptable to teratogens
-
fetal period
- weeks 9-birth
- differentiation/growth of tissues
- body growth increases
-
fetal viability
- weeks 0-22 = no
- weeks 26-28 = with complications
- weeks 35+ = yes
-
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
-
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
-
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
-
Veins into sinus venosus
- common cardinal V- from embryo
- vitelline V - from umbilical vesicle
- umbilical V- from placenta
-
Bulboventricular loop
- bulbis cordis and ventricle grows faster
- ends up lying caudally and ventrally, atrium and sinus venosus lie cranially and dorsally
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
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
-
Dextrocardia
- Heart tube bends to the left, heart displace to the right instead of left= transposition
- Functions normally with sinus inversus
-
Ectopic Cordis
- -rare
- -heart is exposed anteriorly
- -sternum is split in 2 and paricardial sac is open
- -lateral body folds dont fuse, usually fatal
-
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
-
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
-
Persistant truncus arteriosis
- failure of truncal ridges to from articopulmonary septum
- -associated with ventricular septal defects
- -single atrial trunk straddles both ventricles
-
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
-
Tetralogy of fallot
- -pulmonary trunk stenosis
- -dextroposition of aorta
- -ventricular septal defect
- -right ventricle hypertrophy
-
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
-
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
-
Vitelline Arteries
- -from dorsal aorta to umbilical vesicle
- -become celiac trunk, superior mesenteric, inferior mesenteric
-
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
-
viteliline Vs
- -poorly oxygenated blood from umbilical vesicle
- -drain into sinus venosus
- -L regresses
- -R become hepatic portal V and IVC
-
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
-
Ductus venosus
- -in liver
- -shunts blood from umbilical vein to IVC
- -blood bypasses the liver and goes to the heart
-
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
-
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
-
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
-
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
-
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
-
ventricular zone of spinal cord
- original neuroepithelium
- gives rise to spinal cord neurons and astrocytes, oligodendrocytes, and ependymal cells
-
intermediate zone of spinal cord
- proliferation in original ventricular zone
- forms neuroblasts- spinal cord neurons
-
Marginal zone
- peripheral to the original ventricular zone
- becomes white matter
-
Glioblasts
- from ventricular zone neuroepithelium after neuroblast formation ceases
- found in all 3 zones
- become astroblasts (astrocytes), oligodendroblasts (oligodendrocytes)
-
Ependymal cell formation
- from remaining ventricular zone neuroepithelium
- persists as the ependyma lining in the central canal
-
microglial cells
- from mesenchyme
- originate in bone marrow
- invade CNS after it has been vascularized
-
what happens as neuroepithelial cells proliferate and differentiate?
spinal cord walls become thick, roof and floor become thin
-
Sulcus limitans
longitudinal groove on either side of central canal lumen
-
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
-
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
-
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
-
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
-
Postition of spinal cord in embryo
- extends entire lenght of vertebral canal
- spinal nerves exit intervertebral foramina directly opposite their level
-
spinal cord position in 6 month fetus
conus medullaris extends to S1 level
-
spinal cord level in newborn infant
conus medullaris extends to L2(3)
-
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
-
Myelination of neuronal processes
- forms in fetal period and continues thru first 1
- coincides with tracts becoming functional
- motor fibers first
- produced by oligodendrocytes
-
spinal dermal sinus
posterior median skin dimple in sacral region indicating site of closure of caudal neuropore
-
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
-
Spina bifida cystica
- protrusion of spinal cord and/or meningies thrugh vertebral arch defect
- causes neurologic deficit
-
Spina bifida with meningocele
- sac contains meninges and CSF only
- no neurological deficit
-
spina bifida with meningomyelocele
- sac contains spinal cord and/or spinal roots
- significant functional deficits
-
Myeloschisis
- most severe form of spina bifida
- caudal neuropore failed to close, spinal cord is flattened mass of nervous tissue
-
Development of brain
cranial to somite pair 4
-
primary brain ventricles
- Prosencephalon- forebrain
- mesencephalon- midbrain
- rhombencephalon- hindbrain
-
prosencephalon partially subdivides into:
- telencephalon
- diencephalon
-
rhombencephalon partially subdivides into:
- metencephalon
- myelencephalon
-
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
-
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
-
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
-
Development of metencephalon
- walls form cerebellum and pons
- cavity forms superior 4th ventricle
- pontine flexure spreads the lateral walls
-
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
-
Cerebellum structure
- Archicerebellum- vestibular apparatus
- Paleocerebellum- sensory input from limbs
- Neocerebellum- selective control of limb movements
-
Pons development
connecting cerebral cortex and cerebellar cortex
-
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
-
Development of mesencephalon
- comparatively little change
- neural canal narrows to cerebral aqueductalar plate neuroblasts migrate into roof to form superior and inferior colliculibasal plate neuroblasts give rise to groups of nuclei
- cerebral peduncles become prominent
-
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
-
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
-
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
-
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)
-
Development of verebral vesicles
- lateral primordial cerebral hemispheres
- cavities become lateral ventricle
-
Development of cerebral hemispheres
- cover diencephalon, midbrain and hindbrain
- hemispheres meet and flatten in the midline, mesenchyme becomes falx cerebricaudal end turns ventrally and rostrally forming temporal lobes
-
Development of commissures
- Anterior commissure- first, between olfactory bulbs and related cerebral cortical areas
- Corpus callosum- connects neocortical areas
-
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
-
Development of medullary center
large volume of myelinated processes extending centrally
-
Cranium bifidum
- anomalies of brain/meningies
- in median plane
- squamous occipital bone or posterior foramen magnum
-
cranial meningocele
only meninges herniated
-
cranial meningoencephalocele
brain and meninges herniated
-
cranial meningohydroencephalocele
brain, ventricular components and meninges herniated
-
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
-
Mirocephaly
- brain and calvarium are small, face is normal
- due to genetic or environmental factors
-
Hydrocephalus
- enlargment of the head
- imbalance of CSF production and absorption
- congenital aqueductal stenosis
- cerebral hemispheres are squeezed
-
Arnold-Chiari malformation
- inferior displacement of vermis of cerebellum thru foramen magnum
- interferes with CSF circulation
- impacts cerebellum function
-
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
-
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
-
Development of Schwann cells
neural crest cells that migrate into position to myelinate sensory and motor neurons
-
Epidermis
derived from surface ectoderm
-
dermis
derived from mesenchyme
-
development of epidermis
- surface ectoderm proliferates into keratinoblasts
- forms a basal layer and squamous periderm
-
vernix caseosa
- white greasy substance of dead cells
- protective covering on fetal skin
- facilitates birth
-
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
-
Melanoblasts
- week 7-8 ceural crest cells migrate into dermal mesenchyme
- cross dermo-epidermal junction to become melanocytes
- -melanin production begins prior to birth
-
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
-
generalized albinism
- lack of pigmentation in skin, hair and retina
- melanocytes unable to synthesize melanin
-
piebaldism
localized albinism causing lack of melanin in patches of skin or hair
-
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
-
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
-
Hemangioma
- vascular tumor
- anterior or lateral face
- solid cords of endothelial cells or hollow cords with blood
- usually benign
-
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
-
Anonychia
- absence of nails at birth
- permanent condition
- associated with abnormal hair or teeth development
-
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
-
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
-
Lanugo
- First hairs to appear, very fine and soft, lightly pigmented
- hold vernix caseosa on the skin
- replaced during the perinatal period
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Alopecia
- absence or loss of scalp hair
- congenital failure of hair follicles to form
-
Hypertrichosis
- excessive hairiness
- extra hair follicles or persistence of lanugo hairs
-
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
-
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
-
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
-
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
-
male and female rudimentary mammary glands
- identical at birth
- contain lactiferous ducts but no secretory acini
- female breasts enlarge rapidly at puberty
-
Gynecomastia
- development of male mammary tissue
- 2/3 of boys have breast hyperplasi (usually only for a few months)
-
Athelia/Amastia
- absence of nipple/breast development
- bilaterally or unilaterally
- absence of mammary crest formation or mammary bud development
-
polythelia/polymastia
- extra nipple/breast
- usually just inferior to the normal breast, mistaken for moles
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