Embryology Flashcards
What is the specific glycoprotein that the sperm binds to during fertilisation?
Zona pellucida
What happens to the head of the sperm once it has bound to the zona pellucida?
Acrosomal enzymes released from sperm head; the sperm digests its way into egg
What does sperm entry into the egg trigger?
Triggers cortical granule release in egg cortex triggering formation of fertilisation membrane, which is impenetrable to sperm
When is a fertilised egg described as a zygote?
When fusion of the male and female pronuclei restores the diploid number of chromosomes - day 0
What is the name given to the daughter cells that are formed by the multiple divisions of the zygote?
Blastomeres
Up until which point are blastomeres thought to be totipotent?
Until the 8 cell stage
What is blastocyst hatching?
When the blastocyst leaves the zona pellucida
What group of cells from the blastocyst give rise to the embryo?
Inner cell mast
What cells give rise to the trophoblast and what is its function?
The remaining cells that do not give rise to the embryo
Instead, they form the placenta
What is the syncytiotrophoblast?
The implanted embryo - has extended into endometrium by erosion and has contacted maternal blood supply
This occurs at 9-12 days
Where are the amniotic cavity and the yolk sac in relation to each other?
The amniotic cavity lies above the bilayered embryonic disc with the yolk sac below
What is the chorionic cavity?
A cavity which fully surrounds the embryo
What is gastrulation?
Formation of the germ layers - 2 layers (epiblast and hypoblast) becomes 3
What are the three germ layers?
Ectoderm
Mesoderm
Endoderm
Through which structure do cells migrate through during gastrulation?
Primitive streak
What does the ectoderm become?
Epidermis of skin
Nervous system
What does the endoderm become?
Lining of respiratory tract
Lining of GI tract
How many parts does the mesoderm divide into and around what structure?
3 sections around the notochord
What is the name given to each of the three parts of the mesoderm?
Paraxial
Intermediate
Lateral plate
What does the paraxial mesoderm become?
The axial skeleton
Parts of dermis and voluntary muscle
What does the intermediate mesoderm become?
Urogenital systems
What does the lateral plate mesoderm become?
Somatic part: Lining of body wall, most of dermis, parts of limbs
Visceral part: Mesothelial covering of organs, Cardiovascular system
What does lateral folding of the embryo do?
Creates a closed cavity, forming thoracic and abdominal cavities and closing fore and hind gut
Mid gut is the last to close
What does cranial folding of the embryo do?
Forms the foregut and defines the thoracic cavity; developing heart tube displaced into thoracic cavity
What does caudal folding of the embryo do?
Cloacal membrane and connecting stalk are displaced ventrally alongside the neck of the yolk sac, forming the hindgut, anus and the umbilical cord
What development has occurred by the third month of pregnancy?
Face more human looking (position of eyes&ears)
Limbs lengthen
1° ossification centres in long bones and skull
Sex can be determined by external genitalia
What development occurs in the 4th and 5th months of pregnancy?
Rapid growth in length
What development occurs from 6 months to birth?
Rapid increase in weight
When does the heart begin to develop?
4th week
What two structures must grow to provide normal atrial septation in babies?
Septum primum (flexible) Septum secundum (more rigid)
What structure allows communication between atria until birth?
Foramen ovale
In which direction does blood flow between atria occur before birth?
Right to left, through foramen ovale
What structure serves as a valve for the foramen ovale and how does this help its seal after birth?
Septum primum
After birth, direction of blood flow changes from left to right - this pins the septum primum to the septum secundum over the patent foramen ovale
How does the muscular portion of the ventricular wall develop?
Grows upwards from wall of expanding ventricle
How does the membranous portion of the ventricular wall develop?
Growth of tissue from Endocardial cushions
Which germ layer gives rise to the heart?
Visceral mesoderm
Where is the visceral mesoderm?
Cranial to the developing Neural Tube
What are the regions of the heart tube called (cranial-caudal)?
Truncus arteriosus Bulbus cordis Atrium Ventricle Sinus venosus
What does the truncus arteriosus become?
Pulmonary trunk and aorta
What does the bulbus cordis become?
Trabeculated part of right ventricle
Outflow part of both ventricles
What does the sinus venosus become?
Smooth part R. atrium
Coronary sinus
What day of development does the heart tube begin to fold?
Day 23
Initially, how many aortic arches are there?
6
Which 3 embryonic aortic arches are important?
3 → common carotid aa; first part of ICA
4 → right subclavian a.; part of aortic arch
6 → sprout branches that form pulmonary aa; ductus arteriosus on left
What are the vitelline veins and their function?
Drain the yolk sac
What do the vitelline veins become?
Portal venous system draining gut
Hepatic sinusoids and veins
Hepatic portion of IVC
What do the cardinal veins come to be?
Systemic venous system
From which structure does the epithelial lining of the respiratory tract come from?
Endoderm
From which structure does the lung tissue come from i.e. cartilidge, muscle etc?
Visceral mesoderm
What are the five stages of maturation of the lungs?
Embryonic Pseudoglandular; Canalicular Saccular Alveolar
What develops during the embryonic stage of lung maturation?
Respiratory diverticulum forms
Initial branching to give lungs, lobes and segments
What develops during the pseudoglandular stage of lung maturation?
More branching occurs and terminal bronchioles are formed
What develops during the canalicular stage of lung maturation?
Terminal Bronchioles
≥2 Respiratory bronchioles
3 – 6 alveolar ducts
What develops during the saccular stage of lung development?
Terminal sacs form
Capillaries establish close contact
What develops during the alveolar stage of lung maturation?
Alveoli mature
