Embriology for Medical Students

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EMBYRO

• IMEC. INC
• Quick Learning
• Technique

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Important Concept

• Premordial Germs Cells (sperm and oocyte) go
  through division via meiosis and is influenced by
  Endocrine Hormones
• Cell growth happens via mitosis and is mediated
  and influenced by various growth factors, and
  local Paracrine and Juxtacrine Hormonal Influence
• As we can see with MIF in the following
  slide

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Starting with SEX

• Obviously we know that XY is male and XX is
  female coming from the 23rd chromosone
• In the male (TDF) Testicular Determining Factor,
  and (MIF) Mullarian Inhibitory Factor, close the
  Mullarian Duct around the seventh week, and
  either the medulla develops as in the male, or it
  degenerates as in the female
• Note in the female the cortical chords develop

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Gametogenisis

• During gametogenisis, the chromosome number is
  reduced by 50 and the shape of the cells is
  altered

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Starting with SEX

• Obviously we know that XY is male and XX is
  female coming from the 23rd chromosone
• In the male (TDF) Testicular Determining Factor,
  and (MIF) Mullarian Inhibitory Factor, close the
  Mullarian Duct around the seventh week, and
  either the medulla develops as in the male, or it
  degenerates as in the female
• Note in the female the cortical chords develop

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Male Spermatozoal Development
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Sex determination

• Obviously we know that XY is male and XX is
  female coming from the 23rd chromosone
• In the male (TDF) Testicular Determining Factor,
  and (MIF) Mullarian Inhibitory Factor, close the
  Mullarian Duct around the seventh week, and
  either the medulla develops as in the male, or it
  degenerates as in the female
• Note in the female the cortical chords develop

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Spermatogenesis

• Spermatogenesis in males starts at puberty
• Both Testosterone from the Leydig cells and FSH
  are very important in the development
• Also in the testis themselves are the Sertoli
  (follicular cells) that actually mature
  spermatids
• Note that during spermatogenesis we go through
  Mitosis, and the first and second Meotic
  divisions

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64 Days Total
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Sperm

• The sperm themselves rely heavily on glucose
• They have an Acrosomal head, for penetration
• Mitochondrial function in the body
• And a tail

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Enzymes

• Note we add these enzymes here because you will
  be introduces to various sexual disorders in
  pathology and you might as well as see
  intragration of subjects

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Enzymes(Notice 17-a 5-a)
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Oogenesis

• Oogenesis is a little different.
• Girls are born with all there ovum. They oogonium
  are arranged in cluster within the ovary and
  probably developed from one cell dividing via
  Mitosis.
• Note that each oogonium to oocyte and the
  eventually follicular cell is guided by estrogen
  and progesterone

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Note

• Primary Oocytes remain in prophase and do not
  finish their first meiotic division until puberty

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Ovarian Follicle
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Ovarian Follicle Formation
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Puberty in the Female

• During this time pooling of 15-20 Follicles begin
  to grow producing a granulosa cells (primary
  epitethelium), the theca interna (fibrous
  capsule) and zona pellucida

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Theca Interna, Granulosa Cells, Apipose
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Female Reproductive
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Control

• It is important to note the the reproductive
  control in this cycle actually comes from the
  hypothalmus and pituitary

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Fertilization
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Cleavage

• Once fertilized and the cell is actually now
  zygote, it actually starts at a two cell stage,
  and through mitotic division eventually and
  eventually ends up after 40 hours in a morula
  phase

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Morula

• As we can see the mitotic division from 2 cells
  to approximatelly 16 cells

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Blastocyst

• At about the time the morula enters the uterine
  cavity, fluid begins to penetrate through the
  zona pellucida.
• The blastocyst forms
• These trophoblastic cells begin to penetrate the
  uterine linings

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Corpus Luteum-Lipid Remnant
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Graffian Follicle-Embryo
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Meiosis

• Takes place on in germ cell
• The first is Reduction Division, because the
  chromosome number is reduced from diploid to
  haploidHomologous chromosomes separate
• These cells are primary oocytes, and
  spermatocytes
• The second meiotic division the sister chromotids
  separate
• These cells are secondary oocytes, and
  spermatocytes

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Allantois

• -A membranous sac that develops from the
  posterior part of the alimentary canal in the
  embryos of mammals, birds, and reptiles. It is
  important in the formation of the umbilical cord
  and placenta in mammals. Also called allantois.

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Amnion-

• The outer membrane enclosing the embryo in
  reptiles, birds, and mammals.

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GERM LAYERS
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FETAL LANDMARKS

• 1 week----------------Implantation
• 2 weeks---------------Bilaminar disk
• 3 weeks---------------Gastrulation
• 3 weeks-----Primitive streak/Neural Plate
• Weeks 3-8-----Organogenesis
• Week 4----------Heart begins to pump
• Week 10----------Genitalia Form

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Rule of 2s for 2nd week

• 2 Germ Layers (epiblast, hypoblast)
• 2 Cavities (amniotic and yolk sac)
• 2 Placental Components
• Cytotrophoblast, Syncytiotrophoblast
• NOTE---(epilast invaginates to form primitive
  streak? this forms to
• intra-embryonic mesoderm and endoderm

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Rule of 3s for 3rd week

• 3 germ layers
• PRIMITIVE STREAK FORMS
• GASTRULATION
• ECTODERM
• MESODERM
• ENDODERM

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Primitive Streak
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Notachord and Neural Tube

• At about 14-16 days the primitive streak has been
  established and the Notochord begins to develope
• The Neural Tube begins to form
• Mitotic division of cell layers begins to be
  established
• Knowing these is basic memorization

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ECTODERM

• SURFACE ECTODERM
• NEUROECTODERM
• NEURAL CREST

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Surface Ectoderm

• Adeno-hypophysis
• Lens of eye
• Epithelial lining
• Epidermis

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Neuroectoderm

• Neurohypophysis
• CNS Neurons
• Oligodendrocytes
• Astocytes
• Pineal Gland

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Neural Crest

• ANS
• Dorsal Root Ganglia
• Melanocytes
• Chromaffin cell of Adrenal Medulla
• Enterochromaffin cells
• Pia
• Celiac Ganglion
• Schwann Cells
• Odontoblasts
• Para-follicular Cells of Thyroid

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MESODERM

• Dura connective tissue
• Muscle
• Bone
• Cardio Structures
• Lymph
• Blood
• Uro structures
• Serous Linings of body cavities
• Spleen
• Adrenal Cortex

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Bone

• Developmental origin
• Intramembranous bone forms directly from
  mesenchyme
• Endochondrial (intracartilagenous) bone replaces
  cartilage model

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Bone (normal fetal growth plate)
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Intramembranous ossification

• Flat Bones
• Mechanism
• Clusters of mesanchymal cell differentiate into
  osteoblasts
• Osteoblast secrete matrix
• Spicules of bone form spongy bone
• Centers of ossicification grow together
• Bone is deposited in inner and outer surfaces
  forming layers of compact bone

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Endochondrial ossification

• Bone replaces a cartilage model
• Long and short bones
• Mechanism
• Hyaline cartlage model of bone is formed in fetus
• Chondrocytes of model hypertrophy and then
  regenerate-this hypertrophy causes matrix to
  reduce plates
• Matrix is cacified by hydroxapatite
• Osteoclast digest channels, so progenitor
  Osteoblasts can continue to synthesize matrix

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Ossification

• Resting zone
• an area of normal hyaline cartilage yet to be
  ossified
• Proliferative zone
• Chondrocytes divide forming isogenic groups
• Longitudal growth of entire bone
• Hypertrophic zone
• Chondrocyte enlarge and then die
• Matrix reduced to thin plates
• Calcified cartilage zone
• Hydroxapatite crystals are deposited in matrix
• Ossification zone
• Capillary invade, primary bone is deposited,
  spicules formed

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Fat Formation

• Primary Fat Formation (Brown Fat)
• Occurs early in embryogenesis
• Epitheloid precursor cells are laid down in
  specific areas
• Precursors differentiate into multi-occular
  adipocytes and accumulate lipid droplets
• Secondary Fat Formation (White Fat)
• Occurs later in embryogenesis
• Fusiform cells in many connective tissues
  differentiate into uniocular adipocytes and
  accumulate lipid

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ENDODERM

• Gut tubular epithelium
• LUNG, LIVER, PANCREAS, THYROID, PARATHYROID

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NOTOCHORD

• Induces ectoderm to form neuro-ectoderm
• NEURAL PLATE
• Its postnatal derivative of is nucleus pulposus
  of the inter-vertebral disk

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FETAL ERYTHROPOESIS
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Fetal Erythropoiesis

• (3-8 Week)------- ?Yolk Sac
• (6-30 Week)------?Liver
• (9-28 Week)------?Spleen
• (28 Week on)---- ?Bone Marrow

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Yolk sac

• A membranous sac attached to an embryo, providing
  early nourishment in the form of yolk in bony
  fishes, sharks, reptiles, birds, and primitive
  mammals and functioning as the circulatory system
  of the human embryo before internal circulation
  begins.

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HEART EMBYOLOGY

• MESODERM

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Cardiac Progenation

• Cardiac Cells lie in the Epiblast cell outside
  the neural plate
• They actually migrate the cranial cells and
  position themselves rostal to the oropharyngeal
  membrane and neural folds
• Initially this region is anterior to neural
  tube, embracing it for a short period before
  final to a primitive thorax region

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Heart Tube

• The heart tube bulges more and more into a cavity
• With further development we can see a dorsal
  region disappear creation a transverse
  pericardial sinus.
• This is formed by a cellular matrix rich in
  hyaluronic acid
• The epicardium is derived from mesothelial cell,
  thickening so called outflow tract/spectum

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Bulbus Cordus

• The atrial portion of the heart is actually the
  bulbus cordus, a narrow area except in proximal
  third where substantial interaction occurs at
  what we now refer to the interventricular foramen

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Formation of a Cardiac Loop

• There is a twisting/folding in the region as
  shown in the following slides that show this
  process

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EARLY HEART

• Early Heart and Primitive Heart Tube Folding
• (NEXT SLIDE) Picture of the fusion of two
  endocardial tubes into a single primitive heart
  tube. Details the descriptions of the movement of
  the bulbis cordis, primitive ventricle, primitive
  atrium, and sinus venosus

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Endocadardial Cushions
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Primitive Heart
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Inferior Vena Cava

• Derived from
• Common Cardinal Vein

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Most Common Defects

• Ventricular Septal Defect (VSD)
• Patent Ductus Arteriosis
• Patent Foramen
• Jxtaposition of Vessels
• Dextrocardia
• Tetrology of Fallot

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ARTERIAL

• TRUNCUS ARTERIOISIS
• BULBUS CORDIS
• PRIMITIVE VENTRICLE

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TRUNCUS ARTERIOSUS

• Gives rise to ascending aorta and pulmonary trunk

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Bulbus Cordis

• Smooth Part of Ventricles

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Primitive Ventricle

• Trabeculated Part of Ventricles

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VENOUS

• Left horn of sinus venosus
• Right Horn of Sinus venosus
• R- Common Cardinal Vein and Right anterior
  cardinal vein

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Primitive Atrium

• Trabelulated atrium

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Left Horn

• Coronary Sinus

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Right Horn

• Smooth Right atrial area

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Right Common Cardinal Vein

• Superior Vena Cava

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Umbilical Vein

• Ligamentum teres hepatis

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Urachal Cyst

• Remnant of allantois (urine drainage from bladder)

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Umbilical Arteries

• Medial Umbilical ligaments

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Ductus Arteriosis

• Ligamentum Arteriosum

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Ductus Venosus

• Ligamentum venosum

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Foramen Ovale

• Fossa ovale

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Aortic Arch Derivatives

• 1st Part ---------? Maxillary
• 2nd Part---------? Stapedial
• 3rd Part---------? Common Carotid
• 4th Part---------? Aortic Arch/Systemic
• 6th Part---------? Pulmonary

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Branchial Apparatus

• Branchial Clefts derived from ectoderm
• Branchial Arches derived from mesoderm
• Branchial Pouches derived form endoderm

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BRANCHIAL ARCH Mostly Ms

• Meckels Cartilage
• Mandible
• Malleus
• Muscles of Mastication (Masseter and medial
  pterygoids)
• Mylohyhoid
• Anterior digastric, tensor tympani, tensor veli
  palatini
• NERVE----CN V3

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BRANCHIAL ARCH IIMostly Ss (Smile)

• Reicherts Cartilage
• Stapes
• Styloid Process
• Lesser Hyoid
• Stylohyoid ligament
• Stapedius
• Muscle of facial expression
• Stapedius, Stylohyoid, posterior digastric
• NERVE-------CN VII

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BRANCHIAL ARCHIII Pharnyx

• Greater Hyoid
• Stylopharyngeus--? intervated by CN IX
• CN IX

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BRANCHIAL ARCH 4-6

• Cartilages-Thyroid, crycoid, arytenoid,
  corniculate , cuniform
• Muscles (4th) Pharnygeal constrictor
• Cricothyroid, Levator veli palatini
• Muscles (6th) all intrinsic except cricothyroid
• NERVE (4th) is CN X (VAGUS)
• NERVE (6th) is CN X (VAGUS)

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BRANCHIAL ARCH INNERVENTION

• Arch I------? CN V2 V3
• Arch II-----? CN VII
• Arch III----? CN IX
• Arch IV IV? CN X

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BRANCHIAL CLEFT

• 1st Cleft develops into external auditory meatus
• 2nd-4th Cleft for temporary cervical sinuses
  which are obliterated by the 2nd Arch Mesenchyme
• Note- Persistent cervical sinus can lead to a
  branchial cyst in the neck

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EAR DEVELOPEMENT

• Bones-----
• 1st Arch-----INCUS/MALLOUS
• 2nd Arch-----STAPES
• Muscles
• 1st Arch---TENSOR TYMPANI (CN V3)
• 2nd Arch---STAPEDIUS (CN VII)
• Miscellaneous
• External auditory meatus1st Cleft
• Ear drum, eustachian tube-1st pharnygeal membrane

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Prechordial Plate

• This is an area of hypoblast cell that are
  localized in one area
• The PLATE INDICATES FUTURE SITE OF MOUTH

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Branchial Pouch Derivatives

• 1st Pouch----Middle ear cavity, eustachian tube,
  mastoid air cell
• 2nd Pouch---lining of palentine tonsil
• 3rd Pouch (dorsal) ---inferior parathyroid
• 3rd Pouch (ventral)---thymus
• 4th Pouch----superior parathyroid
• Note abberent development of 3rd 4th
  pouches-?Digeorges syndrome?T-cell deficiency
  (thymic hypoplasia) and hypocalcemia (parthyroid
  gland)

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THYMUS DEVELOPMENT

• Site for T-Cell Maturation
• Encapsulated
• From epithelium of 3rd Branchial Pouch
• Cortex is dense with immature T-Cells
• Medulla is pale with mature T-Cells, epithelial
  reticular tissue and Hassalls corpuscles
• Positive and negative selection occurs at the
  cortico-medullary junction

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Thyroid Development

• Thyroid diverticulum arises from the floor of the
  primitive pharynx, and it DESCENDS into the neck.
• Connected to the tongue by the thryoglossal duct
  which normally disappear. Foramen Cecum is normal
  remnant of thyroglossal duct
• MOST COMMON ECTOPIC SITE FOR THYROID IS TONGUE

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Tongue Development

• 1st Branchial Arch forms anterior 2/3 of Tongue
• Pain Via CN V3, Taste via CN VII (facial)
• 3rd and 4th arches form posterior 1/3 of tongue
• Pain and taste mainly CN IX, some CN X
• Motor innervation CN XII

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CLEFT LIP/ CLEFT PALATE

• Cleft lip - Failure of fusion of Maxillary and
  Medial Nasal Processes
• Cleft Palate -Failure of fusion of palentine
  processes, the nasal septum, and/or median
  palentine processes

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Diaphragm Embryology

• SEVERAL PARTS BUILD DIAPHRAGM
• Diaphragm is derived from
• SEPTUM TRANSVERSUM
• PLEUROPERITONEAL FOLDS
• BODY WALL
• DORSAL MESENTARY OF ESOPHAGUS

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Bone Formation

• Intramembranous
• Spontaneous
• Endochondrial
• Ossicification

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Pancreas and Spleen

• Pancreas is derived from FOREGUT
• Ventral pancreas becomes head (uncinate)
• Dorsal becomes everything else (body, tail,
  isthmus, and accessory pancreatic duct)
• Spleen arises from DORSAL MESENTARY

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POTTERs Syndrome

• Bilateral Renal Agenesis-?Oligohydramnios-?facial
  deformities-?Pulmonary Hypoplasia
• Babies CANT PEE in UTERO

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GENITAL DUCT

• Mesonephric (Wolffian Duct) SEED
• Seminal Vesicles, Epididymis, Ejactulatory duct,
  Ductus Deferens
• Paramesonephric (Mullarian Duct)
• Fallopian Tubes, Uterus, Part of Vagina
• MULLARIAN INHIBITORY SUBSTANCE SECRETED BY TESTES
  SUPPRESSES DEVELOPMENT OF PARAMESONEPHRIC DUCT

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SPERM DEVELOPMENT

• Spermatogenesis begins with spermatagonia (Type A
  and Type B)
• Deriving from Sertoli cells of the seminephrous
  tubules (the Blood-Testis Barrier).
  Spermatagonium first become
• Primary Speramatocytes
• Secondary Spermatocytes
• Spermatids

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SPERM DEVELOPMENT

• Diploid---- ? spermatogonium
• (2N)
• Diploid---- ? 1 spermatocyte
• (4N)
• Haploid----? 2 spermatocyte
• (2N)
• Haploid----? spermatid
• (N)

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Derivation of sperm parts

• Acrosome is derived from golgi
• Flagellum from one or more centrioles
• Middle (neck) has Mitochondria

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Meiosis and Ovulation

• AN EGG (METaphase) a SPERM
• 1 oocytes begin Meiosis I during fetal life and
  complete Meiosis I just prior to ovulation.
• Meoisis I is arrested in PROPHASE until ovulation
• Meoisis II is arrested in METAPHASE until
  fertilization
• AN EGG (METaphase) a SPERM

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WEEK 1

• Conception
• Conceptus the embryo and its membranes

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Week 2

• The Primary Chorionic villi develop and begin to
  get a blood flow from mother
• Lacuna appear in synctiotrophoblast

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Synctiotrophobast

• Continues to grow into endometrium and at about
  day 10 start producing (hCG)

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Fetal Landmarks

• Week 1 ------------?Implantation of Blastocyst
• Week 2 ------------?Bilaminar Disk
• Week 3 ------------?Gastrulation
• Week 3-------------?Primitive streak/neural plate
• Week 4-------------?Heart begins to beat
• Week 10------------?Genitalia male/female
• NOTE----WEEKS 3-8 most susceptable to teratogens

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Early Developement
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Early Development
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Early Developement
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Prenatal period 3-8 weeks

• Embyonic period
• Mitotic divisions of cells called Blastomere
• Morula when 12 blastomeres have formed
• Blastocyst enters the uterus
• Gastrula- 3 layers
• Ectoderm
• Mesoderm
• Endoderm
• Neurula- (neural plate closes to form Neural tube
  at week 3)
• Embryo-(3-8th week)

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STAGES

• Fetal-After the embyonic period (week 9-birth)
• Neonatal-first month of life
• Infancy-1 month-1 yr
• Childhood-13 months-12 years
• Puberty- 12-15
• Adolescence 12-17

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Amniotic Fluid Abnormalities

• Polyhydraminios
• (gt1.5-2.0 L)
• Associated with esophageal/duodenal atresia and
  anacephaly
• Oligihydraminios
• (lt 0.5 L) of Amniotic Fluid Associated with
  bilateral renal agenisis or posterior urethral
  valves (in males)

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Horseshoe Kidney

• Inferior Poles of Both Kidneys are Fused
• AS THEY ASCENDThey get trapped under the
  inferior mesenteric artery and remain lower in
  the abdomen

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REMEMBER EMBRYO
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Teratogens

• ACE Inhibitors---------Renal Damage
• Cocaine------------------Fetal addiction
• DES----------------------Clear Cell CA
• Iodide--------------------Goiter
• 13-cis-retinoic acid-----Many other defects
• Thalidomide-------------Limb defects
• Warfarin-----------------Multiple anomalies

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UMBILICAL CHORD

• Contains 2 Umbilical Arteries
• DEOXYGENATED BLOOD FROM FETUS
• Contains 1 Umbilical Vein
• OXYGENATED BLOOD TO FETUS FROM PLACENTA
• Note- single umbilical artery is associated with
  chromosomal defect and/or congenital anomaly

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ECTODERM

• SURFACE ECTODERM
• NEUROECTODERM
• NEURAL CREST

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Surface Ectoderm

• Adeno-hypophysis
• Lens of eye
• Epithelial lining
• Epidermis

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Neuroectoderm

• Neurohypophysis
• CNS Neurons
• Oligodendrocytes
• Astocytes
• Pineal Gland

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Neural Crest

• ANS
• Dorsal Root Ganglia
• Melanocytes
• Chromaffin cell of Adrenal Medulla
• Enterochromaffin cells
• Pia
• Celiac Ganglion
• Schwann Cells
• Odontoblasts
• Para-follicular Cells of Thyroid

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MESODERM

• Dura connective tissue
• Muscle
• Bone
• Cardio Structures
• Lymph
• Blood
• Uro structures
• Serous Linings of body cavities
• Spleen
• Adrenal Cortex

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ENDODERM

• Gut tubular epithelium
• LUNG, LIVER, PANCREAS, THYROID, PARATHYROID

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NOTOCHORD

• Induces ectoderm to form neuro-ectoderm
• NEURAL PLATE
• Its postnatal derivitive of is nucleus pulposus
  of the inter-vertebral disk

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Early Development
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Rule of 2s for 2nd week

• 2 Germ Layers (epiblast, hypoblast)
• 2 Cavities (amniotic and yolk sac)
• 2 Placental Components
• Cytotrophoblast, Syncytiotrophoblast
• NOTE---(epilast invaginates to form primitive
  streak? this forms to
• intra-embryonic mesoderm and endoderm

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Rule of 3s for 3rd week

• 3 germ layers
• GASTRULA
• ECTODERM
• MESODERM
• ENDODERM

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FETAL ERYTHROPOESIS
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Fetal Erythropoiesis

• (3-8 Week)------- ?Yolk Sac
• (6-30 Week)------?Liver
• (9-28 Week)------?Spleen
• (28 Week on)---- ?Bone Marrow

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HEART EMBYOLOGY
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ARTERIAL

• TRUNCUS ARTERIOISIS
• BULBUS CORDIS
• PRIMITIVE VENTRICLE

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TRUNCUS ARTERIOSUS

• Gives rise to ascending aorta and pulmonary trunk

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Bulbus Cordis

• Smooth Part of Ventricles

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Primitive Ventricle

• Trabeculated Part of Ventricles

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VENOUS

• Left horn of sinous venosus
• Right Horn of Sinus venosus
• R- Common Cardinal Vein and Right anterior
  cardinal vein

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Primitive Atrium

• Trabelulated atrium

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Left Horn

• Coronary Sinus

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Right Horn

• Smooth Right atrial area

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Right Common Cardinal Vein

• Superior Vena Cava

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Umbilical Vein

• Ligamentum teres hepatis

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Urachal Cyst

• Remnant of allantois (urine drainage from bladder)

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Umbilical Arteries

• Medial Umbilical ligaments

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Ductus Arteriosis

• Ligamentum Arteriosum

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Ductus Venosus

• Ligamentum venosum

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Foramen Ovale

• Fossa ovale

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Aortic Arch Derivatives

• 1st Part ---------? Maxillary
• 2nd Part---------? Stapedial
• 3rd Part---------? Common Carotid
• 4th Part---------? Aortic Arch/Systemic
• 6th Part---------? Pulmonary

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Branchial Apparatus

• Branchial Clefts derived from ectoderm
• Branchial Arches derived from mesoderm
• Branchial Pouches derived form endoderm

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BRANCHIAL ARCH I Mostly Ms

• Meckels Cartilage
• Mandible
• Malleus
• Muscles of Mastication (Masseter and medial
  pterygoids)
• Mylohyhoid
• Anterior digastric, tensor tympani, tensor veli
  palatini
• NERVE----CN V3

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BRANCHIAL ARCH II Mostly Ss (Smile)

• Reicherts Cartilage
• Stapes
• Styloid Process
• Lesser Hyoid
• Stylohyoid ligament
• Stapedius
• Muscle of facial expression
• Stapedius, Stylohyoid, posterior digastric
• NERVE-------CN VII

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BRANCHIAL ARCH III Pharnyx

• Greater Hyoid
• Stylopharyngeus--? intervated by CN IX
• CN IX

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BRANCHIAL ARCH 4-6

• Cartilages-Thyroid, crycoid, arytenoid,
  corniculate , cuniform
• Muscles (4th) Pharnygeal constrictor
• Cricothyroid, Levator veli palatini
• Muscles (6th) all intrinsic except cricothyroid
• NERVE (4th) is CN X
• NERVE (6th) is CN X

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BRANCHIAL ARCH INNERVENTION

• Arch I------? CN V2 V3
• Arch II-----? CN VII
• Arch III----? CN IX
• Arch IV IV? CN X

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BRANCHIAL CLEFT

• 1st Cleft develops into external auditory meatus
• 2nd-4th Cleft for temporary cervical sinuses
  which are obliterated by the 2nd Arch Mesenchyme
• Note- Persistent cervical sinus can lead to a
  branchial cyst in the neck

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EAR DEVELOPEMENT

• Bones-----
• 1st Arch-----INCUS/MALLOUS
• 2nd Arch-----STAPES
• Muscles
• 1st Arch---TENSOR TYMPANI (CN V3)
• 2nd Arch---STAPEDIUS (CN VII)
• Miscellaneous
• External auditory meatus1st Cleft
• Ear drum, eustachian tube-1st pharnygeal membrane

171
Branchial Pouch Derivatives

• 1st Pouch----Middle ear cavity, eustachian tube,
  mastoid air cell
• 2nd Pouch---lining of palentine tonsil
• 3rd Pouch (dorsal) ---inferior parathyroid
• 3rd Pouch (ventral)---thymus
• 4th Pouch----superior parathyroid
• Note abberent development of 3rd 4th
  pouches-?Digeorges syndrome?T-cell deficiency
  (thymic hypoplasia) and hypocalcemia (parthyroid
  gland)

172
THYMUS DEVELOPMENT

• Site for T-Cell Maturation
• Encapsulated
• From epithelium of 3rd Branchial Pouch
• Cortex is dense with immature T-Cells
• Medulla is pale with mature T-Cells, epithelial
  reticular tissue and Hassalls corpuscles
• Positive and negative selection occurs at the
  cortico-medullary junction

173
Thyroid Development

• Thyroid diverticulum arises from the floor of the
  primitive pharynx, and it DESCENDS into the neck.
• Connected to the tongue by the thryoglossal duct
  which normally disappear. Foramen Cecum is normal
  remnant of thyroglossal duct
• MOST COMMON ECTOPIC SITE FOR THYROID IS TONGUE

174
Tongue Development

• 1st Branchial Arch forms anterior 2/3 of Tongue
• Pain Via CN V3, Taste via CN VII (facial)
• 3rd and 4th arches form posterior 1/3 of tongue
• Pain and taste mainly CN IX, some CN X
• Motor innervation CN XII

175
CLEFT LIP/ CLEFT PALATE

• Cleft lip - Failure of fusion of Maxillary and
  Medial Nasal Processes
• Cleft Palate -Failure of fusion of palentine
  processes, the nasal septum, and/or median
  palentine processes

176
Diaphragm Embryology

• SEVERAL PARTS BUILD DIAPHRAGM
• Diaphragm is derived from
• SEPTUM TRANSVERSUM
• PLEUROPERITONEAL FOLDS
• BODY WALL
• DORSAL MESENTARY OF ESOPHAGUS

177
Bone Formation

• Intramembranous
• Spontaneous
• Endochondrial
• Ossicification

178
Pancreas and Spleen

• Pancreas is derived from FOREGUT
• Ventral pancreas becomes head (uncinate)
• Dorsal becomes everything else (body, tail,
  isthmus, and accessory pancreatic duct)
• Spleen arises from DORSAL MESENTARY

179
GENITAL DUCT

• Mesonephric (Wolffian Duct) SEED
• Seminal Vesicles, Epididymis, Ejactulatory duct,
  Ductus Deferens
• Paramesonephric (Mullarian Duct)
• Fallopian Tubes, Uterus, Part of Vagina
• MULLARIAN INHIBITORY SUBSTANCE SECRETED BY TESTES
  SUPPRESSES DEVELOPMENT OF PARAMESONEPHRIC DUCT

180
SPERM DEVELOPMENT

• Spermatogenisis begins with spermatagonia (Type A
  and Type B)
• Deriving from Sertoli cells of the seminephrous
  tubules (the Blood-Testis Barrier).
  Spermatagonium first become
• Primary Speramatocytes
• Secondary Spermatocytes
• Spermatids

181
SPERM DEVELOPMENT

• Diploid---- ? spermatogonium
• (2N)
• Diploid---- ? 1 spermatocyte
• (4N)
• Haploid----? 2 spermatocyte
• (2N)
• Haploid----? spermatid
• (N)

182
Derivation of sperm parts

• Acrosome is derived from golgi
• Flagellum from on or more centrioles
• Middle (neck) has Mitochondria

183
Meiosis and Ovulation

• AN EGG (METaphase) a SPERM
• 1 oocytes begin Meiosis I during fetal life and
  complete Meiosis I just prior to ovulation.
• Meoisis I is arrested in PHOPHASE until ovulation
• Meoisis II is arrested in METAPHASE until
  fertilization
• AN EGG (METaphase) a SPERM

184
Amniotic Fluid Abnormalities

• Polyhydraminios
• (gt1.5-2.0 L)
• Associated with esophageal/duodenal atresia and
  anacephaly
• Oligihydraminios
• (lt 0.5 L) of Amniotic Fluid Associated with
  bilateral renal agenisis or posterior urethral
  valves (in males)

185
POTTERs Syndrome

• Bilateral Renal Agenisis-?Oligohydramnios-?facial
  deformities-?Pulmonary Hypoplasia
• Babies CANT PEE in UTERO

186
Horshoe Kidney

• Inferior Poles of Both Kidneys are Fused
• AS THEY ASCENDThey get trapped under the
  inferior mesenteric artery and remain lower in
  the abdomen

187
Bifid Uterus
188
Bifid Uterus

• A uterus that is more or less completely divided
  into two lateral horns as a result of imperfect
  union of the paramesonephric ducts it differs
  from septate uterus, in which there is no
  external mark of separation in bicornate uterus,
  the cervix may be single (uterus bicornis
  unicollis)
• The usually involves the paramesonephic duct not
  releasing