Embryology Flashcards
On what day does the primary heart field form?
16-18
When does the secondary heart field develop?
Days 20-21
What forms the primary heart field?
Migration of progenitor heart cells
What does the primary heart field go on to form?
Atria, left ventricle and most of right ventricle
What does the secondary heart field become?
Remainder of right ventricle and the outflow tract
Where are the heart fields from?
Mesoderm
What does the inner cell mass of the morula become?
Embryo proper
What does the outer cell mass of morula become?
Trophoblast then placenta
What does the inner cell mass of the blastocyst become?
Embryoblast
What does the outer cell mass of the blastocyst become?
Trophoblast
What are the 2 layers the trophoblast differentiates into on day 8?
Cytotrophoblast (mononucleate)
Syncytiotrophoblast
What forms when the oocyte and spermatozoa fuse?
Zygote
Where does fertilization take place?
Ampullary region of fallopian tube
What are the two processes that must take place for fertilization?
Capacitation and Acrosome reaction
What happens in capacitation?
In the female reproductive tract
Period of conditioning sperm
Glycoprotein coat and seminal plasma over the acrosome removed for easier enzyme release
Sperm must undergo this to be able to continue
What happens in the acrosome reaction?
After binding to ZP, capacitated sperm can pass through corona radiata
Penetration of the ZP through enzyme release (e.g. acrosin)
What are the phases of fertilization?
Penetration of corona radiata by capacitated sperm
Sperm release acrosin to penetrate ZP
Sperm contact oocyte
Enzymes released from oocyte cortical granules
Zona reaction initated by enzymes prevent more sperm entering by inactivating receptors
Sperm and egg plasma membranes fuse
What is cleavage?
Series of fast mitotic divisions of zygote
Starts on Day 2 to reach 2 cell stage
When does the 16-cell morula form?
Day 3
What does the embryoblast differentiate into?
Hypoblast and epiblast
What happens on day 9?
Lacunar stage of trophoblast development
When is uteroplacental circulation established?
Day 12
What does the epiblast give rise to?
The 3 germ layers
What is gastrulation?
A process in week 3 that establishes the 3 germ layers
What forms during gastrulation on day 15-16?
The primitive streak on the embryo
What makes up the primitive streak?
Primitive node (containing pit) and groove
Groove separates body into left and right
What do the different cells of the trilaminar disc become?
Some epiblast displace ventral hypoblast and form endoderm
Some other epiblast in groove from mesoderm
Epiblast cells not in groove form ectoderm
What happens on day 15?
Cranial and caudal ectoderm fuse with endoderm to form two bilaminar regions
What does the cranial bilaminar region of ectoderm form?
Oropharyngeal membrane which disintegrates in week 4 to form mouth
What does the caudal bilaminar region of the ectoderm form?
Cloacal membrane which disintegrates in week 7 to form anal opening and GU tracts
What happens on day 17?
Mesoderm forms notochord which secretes SHH protein
What happens on day 20?
Neurulation
What happens in neurulation?
Ectoderm cells thicken and form neural plate
Mesoderm differentiates
What does the mesoderm differentiate into?
Paraxial, intermediate and lateral plate mesoderm
What does the paraxial mesoderm form?
Develops into pairs of somites, 3 pairs a day. Somites can be split into sclerotome, myotome and dermatome
What do the different regions of somites form? (paraxial mesoderm)
Sclerotome: bones and cartilage
Myotome: muscle
Dermatome: dermis
What does the intermediate mesoderm form?
Adrenal cortex, kidneys, testes, ovaries
(UG structures)
What does the lateral plate mesoderm give rise to?
Serous membranes
CVS system and thoracic and abdominal cavities
Pleura
Soft tissues of arms and legs
Muscular gut wall
What does the ectoderm form?
Otic placode (cranial): cochlear and inner ear
Lens placode: lens and cornea
Sensory epithelium
Glands (sweat, pituitary, mammary)
What does the endoderm form?
Epithelial lining of gut tube
Tonsils
Thyroid and parathyroid glands
Parts of liver
Pancreas and gallbladder
Urinary bladder and epithelial lining of urethra
What is the gut tube divided into?
Foregut
Midgut
Hindgut
What happens in 3rd week of development?
notochord appears in the mesoderm
What does the notochord do?
secretes growth factors which stimulate the differentiation of the overlying ectoderm into neuroectoderm – forming a thickened structure known as the neural plate
What do the lateral edges of the neural plate form?
Neural folds
What forms the neural tube?
The 2 neural folds meeting in the midline
What does the neural crest give rise to?
melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia
What is neuralation?
formation of neural tube
achieved by end of week 4
When does pronephros appear?
4th week of development
What are pronephros, the mesonephros, and the metanephros derived from?
Urogenital ridge
What forms the definitive kidney?
Metanephros
What is the collecting system of the kidney derived from?
Uteric bud
What is the excretory system of the kidney derived from?
metanephric blastema
What does the collecting system form?
ureter, renal pelvis, major and minor calyces and collecting tubules
What does the excretory system form?
nephron
In weeks 4-7, what does the urorectal septum divide the cloaca into?
Urogenital sinus
Anal canal
What does the urogenital sinus form?
Bladder
Urethra
Reproductive tract
What is the respiratory system derived from?
primitive gut tube
What forms the R and L bronchi?
Buds from the respiratory diverticulum
What does the ductus arteriosus do?
shunts blood from the pulmonary artery directly to the aortic arch
What are type 1 pneumocytes?
basic simple squamous epithelial cells
comprise 90% of the alveolus.
What are type 2 pneumocytes?
simple cuboidal cells which comprise the remaining 10% and are responsible for the production of surfactant
What does surfactant allow?
expand our lungs with minimal effort
When do the alveoli start to develop?
Week 26
What are the 6 regions of the primitive heart tube
Aortic roots (Arterial poles)
Truncus arteriosus
Bulbus cordis
Ventricle
Atrium
Sinus venosus (Venous poles)
What 2 things are responsible for the r to l shunt in developing atria?
ostium secundum and foramen ovale
What does the septum primum do?
Splits atria into 2
What is the adult remnant of the foramen ovale?
Fossa ovalis
What is the adult remnant of the ductus arteriosus?
Ligamentum arteriosum
What is the adult remnant of the ductus venosus?
Ligamentum venosum
What is the adult remnant of the umbilical vein?
Ligamentum teres
