Embryology Flashcards
What is Embryology?
The study of prenatal development. Defines normal development and identifies the time at which an anomaly/defect may occur
Week one of prenatal development
Preimplantation: zygote to blastocyst
Weeks two through eight of prenatal development
Embryonic stage: germ disk to embryo
What is induction?
Development pathway by cell action
What is proliferation?
Controls cellular growth and byproduct production
What is differentiation? What are the two types?
Cellular change into distinctly different structures with different functions
Cytodifferentiation: different cells
Histodifferentiation: different tissues
What is Morphodifferentiation?
Development of specific tissue structure or shape due to induction and proliferation
What is maturation?
Attainment of function in size due to proliferation, differentiation and morphogenesis
What is embryogenesis? When does it occur?
Fertilization/fusion of oocyte and spermatozoon forming a zygote
Starts at time of fertilization in the fallopian tubes
What is a morula?
Ball of cells formed when a zygote divides
How is a blastocyst formed?
The morula forms a central cavity via fluid secretion.
This hollow ball of cells forms a blastocyst
What are the two parts of the blastocyst?
Trophoblast: peripheral cells that form the placenta
Embryoblast: Cells trapped inside the morula forms the embryo
When does implantation occur?
Days 6 to 11 the blaster cyst will attach to the uterus via trophoblast cells
What is the bilaminar germ disk formed from and when does it occur?
Embryoblast cells form two germ layers at days 7 to 8
What are the two germ layers of the billaminar germ disc called?
Epiblast (top layer) and hypoblast (bottom layer)
What is the amniotic cavity?
Space that forms between the epi-blast and amniotic sac
At which end of the bilaminar germ disc is the prechordal plate?
Cephalic end
Forms membrane which will separate future primitive mouth from the primitive gut
At which end of the bilaminar germ disk is the cloacal plate?
Caudal end
Forms membrane which establishes external openings for alimentary and genitourinary tract
What is the primitive groove and what does it do?
Longitudinal furrow/opening in the epi-blast at the caudal end.
Establishes bilateral symmetry
What is the primitive streak? What does it do
Elevation of the Epiblast on the posterior border of the privative groove.
Guides proliferating epiblast in forming the trilaminar germ disc
What is the primitive pit?
Depression/opening at the anterior end of the primitive groove/ streak
What is the primitive node/Hensens node
Elevation of Epiblast cells on the primitive pit guides more proliferating epiblast responsible for forming the future notochord
What are the three layers of the trilaminar germ disc?
Ectoderm
Mesoderm
Endoderm
When is the trilaminar germ disc formed and how?
Day 21
Epiblast undergo proliferation/mitosis, migrate to the primitive streak, enter the primitive groove and passing between the Epiblast and hypoblast to form an intermediate layer called the mesoderm 
What is the endoderm layer formed from?
Forms from the mesoderm when the HyperBlast is pushed laterally into the yolk sac
How is the ectoderm layer created?
Epiblast becomes the ectoderm
What is the notochord?
Pencil shaped column of cells that forms the axial skeleton (spine, ribs, sternum)
Cells induce the formation of the neural plate and synchronized development of the neural tube
 What is the neural plate formed from?
Neuroectoderm (fourth germ layer)
What is neurulation?  Which cells are involved?
Process by which the neural plate becomes the neural tube
Neural crest cells form the neural tube
 Structures formed by the neural tube
Brain, spinal cord, retinas, optic nerves, pineal body and posterior pituitary gland
What are the neural crest cells of the head?
Cranial ganglia
Autonomic ganglia
Adrenal medulla
Connective tissue of the lower face and neck
What is the ectomesenchyme?
Cells that have not yet been told what they are going to be; give rise to future Dentin, cementum, alveolar bone, pulp etc.
What are the neural crest cells of the trunk/body
Melanocytes (large amount, pigment cells)
Nerve cells
Spinal ganglia (dorsal root ganglion)
What is needed for the third germ layer/mesoderm to form?
Need the epiblast to migrate to the primitive streak and enter the primitive groove. Well then passed between the epiblast and the hyper blast to form the intermediate layer
What is embryonic folding and when does it occur?
Cephalic and lateral surfaces fold into a tube on day 28
Rearranges the forming tissues with the ectoderm now on the outside, endoderm on the inside and the mesoderm between the ectoderm and the endoderm
What does the inner tube form during embryonic folding?
Forms the primitive gut
Which structures are developing during week four?
Frontonasal process Stomodium (primitive mouth) Oropharyngeal membrane Rathke’s pouch Primitive pharynx and foregut First brachial arch/pharyngeal arch/mandibular arch Second and third brachial arches Primitive heart Somites
What does the ectoderm give rise to?
Skin, nails, hair, enamel
Sensory epithelium and Neuroectoderm
Salivary, mammary, cutaneous glands
What does the mesoderm give rise to?
Dermis/connective tissue Muscles Skeletal system Lymphatics, blood cells and bone marrow Reproductive and excretory organs
What does the endoderm give rise to?
Digestive tract lining: pharynx, esophagus, stomach, intestines
Respiratory tract lining: larynx, trachea, bronchi, lungs
Lining of circulatory system
Liver and pancreatic cells
What does the Neuroectoderm give rise to?
Neural crest cells of the head: pigment cells, connective tissue proper, cartilage, bone, dental connective tissue (dentin, pulp, cementum, PDL and alveolar bone)
What does the first brachial groove form?
External auditory canal
What do the remaining brachial grooves form? What happens if this fails?
Fuse to form the neck
Failure to fuse will form remnants/cervical sinus and may form a cervical cyst
What are the derivatives of the first brachial pouch?
Eustachian tube/internal auditory canal
Tympanic cavity/eardrum
Lining of the eardrum
Derivatives of the second brachial pouch
Palatine tonsils
Derivatives of the third brachial pouch
Thymus gland and inferior parathyroid gland
Derivatives of the fourth brachial pouch
Superior parathyroid gland
Derivatives of the 5th brachial pouch/ultimobrachial body
Fuses with thyroid gland and disseminates within it, gives rise to parafollicular cells
