Embryology Flashcards
What structure comes before blastocyst
Morula- a ball of undifferentiated cells within zona pellucida
Development from morula to blastocyst
Morula differentiates so inner cells differ from outer ones
Structure of blastocyst
Outer layer of trophectoderm with an inner cell mass and fluid filled cavity
When does blastocyst hatch from zona pellucida
6 days post fertilisation
What happens between day 6 to 10
Inner cells mass of blastocyst becomes bilayer disk made of hypoblast and epiblast cells
What is first change to bilayer disk of blastocyst
Gastrulation
What happens in gastrulation
Conversion of hypoblast and epiblast cells to 3 layers of germ cells
What are 3 layers of germ cells
Ectoderm
Mesoderm
Endoderm
Summarise gastrulation
Proliferation of epiblast cells into space between epiblast and hypoblasts cells which becomes endoderm cells. Then get apoptosis of hypoblast cells
What does ectoderm give rise to
Skin and nervous tissue
What does mesoderm give rise to
Muscles, blood, skeleton, heart and kidney
What does endoderm give rise to
Gut and lungs
What happens before end of gastrulation
Neurulation begins- differentiation of ectoderm to generate CNS
What controls neurulation
Notochord in mesoderm
What happens in junction with neurulation
Precursors of other tissues develop within embryo as it is converted from flattened tissue to 3D
What has happened by week 4
Precursors of all internal tissues have been laid and some external structures have begun to develop
Name given to extra digit
Polydactyly
What has happened to limbs by week 8
Limbs roate to definitive orientation resulting in helical pattern of lower extremity dermatomes
Link between thalidomide and limb deformties
Thalidomide was given to treat morning sickness. Morning sickness normally starts around 6 weeks which matches the main stages of limb development
How did thalidomide affect developing limbs
It damaged the developing blood vessels which were supplying them with the nutrients required for proper growth and development.
3 stages to kidney development
Pronephros-most immature form
Mesonephros- intermediate phase
Metanephros- most developed and persists as adult kidney
Where do gonads arise from
Intermediate mesoderm within urogenital ridges of embryo
Where do male genital ducts arise from
Mesonpehric ducts
Where do female genital ducts aruse from
Paramesonephric ducts
What determines differential development of male reproductive system
SRY on Y chromosome
Describe movement of kidney during its development
Ascends from near to bladder- ureters extend at same time as kidney ascends to maintain connections
Describe changes in vascular supply of kidney during development
Forms new connection with developing arterial system as it moves upwards- renal arteries are broken and reformed
Common kidney development abnormalities
One kidney may be retained in the pelvis
Retention of an artery may obstruct the ureter
Kidneys form seperately but then fuse to form horsehoe kidney
What covers gonad precursor
Colemic epithelial cells
What gives rise to gametes within gonads
Primordial germ cells
What regulates male development of urogenital tract
Testosterone from Leydig cells
What stimulates testosterone from leydig cells during development
hCG from maternal circulation- hCG levels peak around 7-8 weeks when this development starts
What do sertoli cells produce to regress Mullerian ducts
AMH- anti mullerian hormone
Differentiation of tracts to either male or female
Around 9 weeks the indifferent genitalia are converted to either male or female. This is regulated by DHT produced from testosterone originating in Leydig cells of testis
What are most mal-developments as a result of in males
Inability to produce AMH or testosterone
Inability of target organs to respond to these hormones
What causes Androgen insensitivity syndrome
Mutant androgen receptor in males
Effects of androgen insensitivity syndrome
Limited virilisation of external genitalia
Testis sructure is viable but do not descend
Mesonephric ducts are lacking
Why do paramesonephric ducts regress and no female structures are present
Can still produce AMH
What causes congenital adrenal hyperplasia
Mutant 21a hydroxylase enzyme
Effect of CAH
Lack of cortisol means no negative feedback on ACTH which remains high. This leads to overstimulation of adrenals causing an increase in weaker androgens. This results in partial virilisation of female genitalia
Why are internal systems normal in females with CAH
no SRY
Why are there no male ducts in females with CAH
No testosterone
Why do female ducts develop normally in CAH
No AMH as no sertoli cells
Describe cardiac embryology until the 21st day
Cardiogenic cells develop in a U pattern outside the proper embryo to form a pair of heart tubes. These fuse by day 21 and are able to pump blood unidirectionally
What gives rise to the 4 chambered structure
Looping and septation
What happens during looping and septation of the heart
Vascular connections are made eg veins to atria and valves develop
2 differences in structure of heart pre-delivery and after
Presence of foramen ovale which is gap between 2 atria
Presence of ductus arteriosus between right ventricle and left ventricle
Reason for foramen ovale
Allows blood passing from right atria to left atria to limit blood flow out of the right ventricle to lungs
Reason for ductus arteriosus
Blood flowing to lungs instead flows to rest of body through left ventricle
4 abnormalities assocaited with tetraology of fallot
- Pulnomary stenosis
- Thickened right ventricle wall
- Ventricular septal defect
- Overriding aorta
What is pulnomary stenosis
Narrowing of pulnomary valve
What is the ventricular septal defect in tetralogy of fallot
Hole in the wall of right ventricle
What is overriding left ventricle
Aorta is shifted to right and recieves blood from both ventricles
What causes blue baby syndrome
Babies become cyanotic as there is transposition of aorta and pulnomary artery meaning right ventricle pumps out deoxygenated blood to rest of body
What happens in spina bifida
Fusion of the neural tube should have happened by 3 weeks but in spina bifida there is a failure of fusion in an area and it leads to exposure of spinal chord above skin
Result of spina bifida
Inability to walk
Damage to tissues associated with supply from that area
Varies a lot between patients
Cause of spina bifida
low maternal folate diet
Where do facial structures develop at what period
After 5 weeks the primary structures are on the side of the face and move centrally over the next 5 weeks
What happens to facial features as they migrate medially
Clefts are formed and these are then filled by fusion of the tissue from either side
How do you get cleft palates and lips
Incomplete fusion of tissues from either side of the face
Is cleft palate normally asymmetric or not
symmetric
Is cleft lip normally asymmetric or symmetric
asymmetric
5 steps to lung development
Embryonic Psedoglandular Canalicular Saccular Alveolar
Describe lung development
Starts at bronchi and ends at alveoli
Effective moves all the way along
When does surfactant production begin
Start of third trimester
Why is surfactant production so important
Necessary for lung function when exposed to air
What lung condition do some preterm babies suffer from
Respiratory distress syndrome
What causes RDS
lack of surfactant
What can be given to increase surfactant production in babies who are going to be preterm
Glucorticoid injection to mother as accelerates production
Artificial surfactant has been developed that can be injected into babies
