embryonic period Flashcards
Anterior visceral endoderm
Hypoblast cells migrate to the future cranial end of the embryo
Cranial end establishment: occurs before gastrulation
Important for head formation: transcription factors, OTX2, LIM1, HESX1, secreted factor Cerberus. All are inhibitors of nodal (pro caudal factors) activity in the cranial end of the embryo
Primitive streak initiated by…
Nodal (TGFB family)
Caudal end establishment
The node in the dorsal region is the organizer. Maintain by…
Nodal & HNF-3B
Once the streak is formed…
BMP-four is secreted throughout the bilaminar disc
BMP4 and FGF
Ventralize the mesoderm to contribute to kidneys, blood, and boy wall mesoderm.
Goosecoid activates chord, nagging and follistatin which…
Inhibit BMP expression of the dorsal mesoderm in the cranial region.
Ventralization is inhibited in the dorsal mesoderm of the cranial end of the embryo.
Regulate head formation
Brachyury T
Gene regulates the dorsal mesoderm in the middle and caudal regions. It encodes a transcription factor that binds to a T box in the DNA. It is expressed in the node, notochordal precursor cells and notochord.
Ventralization is inhibited in the dorsal mesoderm of the middle and caudal regions of the embryo.
Hox-C
Important in craniocaudal axis
Derivatives of the three germ layers
Endoderm, mesoderm, ectoderm
Paraxial mesoderm
Muscles of the head
Striated skeletal muscle
Skeleton except cranium
Dermis of skin
Connective tissue
Intermediate Mesoderm
Urogenital system including gonads, ducts, and accessory glands
Lateral mesoderm
Connective tissue and muscle viscera
Serous membranes of pleura, pericardium, and peritoneum
Primordial heart
Blood and lymphatic cells
Spleen
Suprarenal (adrenal) cortex
Mesoderm (Head)
Cranium
Connective tissue of head
Ectoderm
Neuroecotoderm
Surface ectoderm
Surface ectoderm
Epidermis, hair, nails, cutaneous glands, and mammary glands
Anterior part of pituitary gland
Enamel of teeth
Internal Ear
Lens of the eye
Neuroectoderm
Neural Crest
Neural Tube
Neural Crest
Cranial and sensory ganglia and nerves
Medulla of suprarenal gland (adrenal medulla)
Pigment cells
Pharyngeal arch cartilages
Head mesenchyme and connective tissue (visceral skeleton of head, and neck)
Bulbar and coral ridges in heart
Parafollicular cells of thyroid gland
Meninges except dura mater
Endoderm
Epithelial parts of Trachea, Bronchi, Lungs, of gastrointestinal tract, liver, pancreas, urinary bladder, urachus, pharynx, thyroid gland, tympanic cavity, pharyngotympanic tube, tonsils, parathyroid glands
By the beginning of the 3rd week, the paraxial mesoderm begins to organize into segments called somitomeres
the paraxial mesoderm begins to organize into segments called somitomeres
First appears in the 20th day in the…
cephalic region, then cephalocaudally
In the head region, somitomeres contribute to…
mesenchyme of the head
Paraxial mesoderm to segmented somites
Dermatome
Myotome
Dermatome
Lateral plate mesoderm
Somatopleure
Splachnopleure
Somatopleure
Parietal (somatic) mesoderm and ectoderm
Splanchnopleure
Visceral (splanchnic) mesoderm and endoderm
Parietal layer of the mesoderm contributes to
Serous membranes of pleura, pericardium, and peritoneum
dermis of the skin except in the neck, back, sides
Visceral layer of the mesoderm contributes to
the serous membrane lining the organs of the abdominal cavity
Endodermal Layer
Gastrointestinal tract
Bucopharyngeal membrane
ruptures during the 4th week (open connection between the amniotic cavity and the primitive gut)
Cloacal membrane
ruptures during the 7th week for the anus
The midgut temporarily communicates with the yolk sac by means of the vitelline duct
Later the vitelline duct is obliterated and the midgut obtains its free position in the abdominal cavity
By two months the yolk sac becomes redundant and shrivels away
Blood vessels form by
Vasculogenesis
Angiogenesis
Vasculogenesis
Vessels arise from blood islands (mesoderm of yolk sac and lateral plate mesoderm)
Celulas del mesodermos de las islas de sangre se rearreglan por factores de crecimiento (VEGF) formando hemangioblastos. Los hemangioblastos van a ser tanto prepulsores de las células de la sangre como la de los vasos sanguíneos. Luego ocurre un rearreglo para la formación de lumen del vaso sanguíneo
Angiogenesis
New vessels sprout from existing ones
Hemangioblast cells give rise to
Angioblasts
Hematopoietic stem cells
Blood island of the yolk sac are
transitory
Definitive hematopoietic stem cells arise from mesoderm surrounding the aorta. Eventually, these cells will colonize the…
liver (9 weeks)
At 12 weeks blood production arises from
Spleen and thymus (becomes the major hematopoietic organs of the fetus)
At 28 weeks stem cells form the liver colonize…
Bone marrow
By the end of the 3rd week, the heart tubes have fused to form a tubular heart
Dorsal aortas se fusionan en el centro
Endocardial heart tube se fusionan en el centro y de ahi se forman las cámaras del corazón
Fourth week (day 22)
Formation of somites, neurulation occurring, neuropores formation
Fourth week (day 23)
Optic groove (primordial of eye)
Neural folds fusing to form primary brain vesicles
Caudal neuropore
Fourth week (day 24)
Rostral neuropore closing
First arch (mandibular)
Second (hyoid) arch
Heart prominence
Caudal (posterior) neuropore open
Fourth week (day 26)
Forebrain prominence
Third pharyngeal arch
Caudal eminence
Fourth week (day 28)
Fourth pharyngeal arch
Lens placed (primordial of lens)
Upper limb bud
Lower limb bud
Fifth Week
Minor body changes
Growth of head (toward heart prominence)
Cervical Sinus is visible
Mesonephric ridges- future site of mesonephric kidneys
Sixth week
Larger hand plates
Digital rays
Spontaneous movements
Reflex responses to touch
Eyes are obvious
Head larger than trunk
Auricular hillocks- external auditory canal and ear
Seventh week
Notches between digital rays appear
Umbilical herniationn
Eighth week
Tail like caudal eminence is present at the beginning, but then disappears
Band around the head, scalp vascular plexus
Digits completely separated
Purposeful limb movement- ossification occurs in the femur
Distinct human characteristics, but still disproportion between head and trunk
