Embryology Flashcards
What week doe the primordial heart start forming?
4th week
Describe the stages of vasculogenesis
- Angioblasts are formed from mesenchymal cells (stem cells)
- Angioblasts go on to form the lining of the endothelium of the vessels
- Blood islands form which form the lumen of the vessels
- These blood islands join together to form bigger islands so larger lumen can be formed
In what sites do the first blood vessels appear?
- yolk sac
- gallantois
- connecting stalk
- chorion (membrane under which the embryo is buried
What are the five chambers of the heart tube?
- trunchus arteriosus
- bulbus cordis
- primitive ventricle
- primitve atrium
- sinous venosus
What are the angioblastic cords?
the two tubes which join together to form the heart tube
cord like masses of splanchnic mesenchymal cells ventral to the primordial pericardial celom (a cavity in the mesoderm of an embryo that gives rise in humans to the pericardial cavity) that arrange themselves side-by-side to form the primordia of the endocardial heart tubes.
What chambers are responsible for the formation of the cardiac loop?
bulbus cordis
primitive ventricle
these both form the bulboventricular loop
What is dextrocardia ?
When the heart tube folds the wrong way so the heart is rotated the opposite way round.
What are the two types of heart muscle in the atria and ventricles and where are each found?
- trabeculae carnae: found in ventricles
- pectinate muscles: found in atria and atrial appendages (can remember pect muscles being up high in the chest so therefore at the top of the heart)
Form what type of mesoderm is the visceral pericardium derived?
splanchnopleuric mesoderm (splanchnic = at the organ)
so the visceral pericardium lies on top of the organ so is splanchnic
Form what type of mesoderm is the serous and fibrous pericardium derived?
somatopleuric mesoderm.
Between what days of development do the heart chambers form?
around 27th and 37th days
During the formation of heart chambers what two things have to form for this to happen?
septal formation
endocardial cushion formation
What occurs during the division of the atria?
- what four septa form?
- why is this done?
Septal Primum forms first which grows from the top of the atria down towards the endocardial cushion in the atrioventricular canal, which creates the foramen primum (ostium foremen) as cells grow up form the endocardial cushion towards the bottom of the septum primum.
Apoptosis (programmed cell death) results in cell death towards the top of the septum primum.
At the same time cells divide and grow up from the endocardial cushion and close over the foramen primum
The septal secondum forms in the left atrium beside the septal primum. As it grows it begins to overlap the foramen primum - this is done to form a valve for the oval foramen to prevent blood from flowing form the right to left atria.
This allows oxygenated blood from the placenta to flow from the left atria to the right atria (by passing the lungs) to be pumped around the embyro.
State the four main types of atrial septal defects.
A) Ostium secundum defect
B) Endocardial cushion defect with ostium primum defect
C) Sinus venosus defect
D) Common atrium
Are males or females more affected by ASD (atrial septal defects)?
females
Are males or females more affected by heart defects?
males
What maternal infection acquired during pregnancy can be associated with congenital heart defects?
rubella
What are some causes of heart defects?
- maternal alcohol abuse
- drug abuse
- radiation
- genetic (8%)
- chromosomes (2%)
Describe the 4 stages of the partitioning of the primitive ventricles.
- Muscular part develops from the proliferation of medial wall
- During the process the IV foramen (interventricular foramen) is formed between the free edge of muscular septum and the fused endocardial cushion
- IV foramen permits communication between left and right ventricles
- IV foramen is closed by the fusion of the right and left bulbar ridges with the endocardial cushion forming membranous part of IV septum.
What is the most common form of VSD and who is most affected?
congenital heart disease
males
In VSD, is the membraneous or muscular part more usually affected?
membraneous
At what stage of development does the bulbus cordis and truncus arteriosus divide?
during the 5th week
Why does the bulbus cordis and truncus arteriosus divide?
To form the aorta and the pulmonary trunk.
Describe the process of aorta and pulmonary trunk formation.
- there is active proliferation of the walls of the bulbus cordis and the truncus arteriosus.
- this forms trunchus and bulbar ridges on the walls
- They undergo 180 – degree spiralling result in the formation of aorticopulmonary (conotruncal) septum (beginning at the bottom with aorta at the posterior and the pulmonary trunk at the anterior, then in the middle the aorta is on the left as the ridges spiral in a clockwise motion, then the aorta ends up at the anterior of the heart)
- the cause of spiralling has not been found but it is though to be the turbulent blood flow.
- the aorticopulmonary septum divides the two ventricles so the aorta is coming out of one ventricle and the pulmonary trunk is coming out of the other ventricle.
What two causes can result in abnormal division of BC and TA?
- failure of the ridges to take a spiral course
- defective migration of neural crest cells
What is tetralogy of Fallot ?
congenital heart disorder with four abnormalities:
- Pulmonary stenosis (obstruction of right ventricular outflow)
- Ventricular septal defect (VSD)
- Dextroposition of aorta (overriding aorta)
- Right ventricular hypertrophy
what causes tetralogy of Fallot?
Unequal division of the conus (the upper front part of the right ventricle of the heart) due to anterior displacement of conotruncal (aorticopulmonary) septum
From what cells do the semilunar valves proliferate from?
subendocardial tissue
From what cells do the tricuspid and bicuspid valves proliferate from?
local tissue around the AV canal
During what week does the sinus atrial node develop?
5th week
From what heart chamber does the bundle of His develop from?
sinus venosus
Aortic Arches what forms the: - 3rd arch - 4th arch - 6th arch
3rd = the internal carotid arteries 4th = the aorta on the left side and the right subclavian artery on the right 6th = the pulmonary arteries and the ductus arteriosus
Where does the laryngeal nerve originate from?
a branch off the vagus nerve (10th cranial nerve)
Where does the laryngeal nerve go once leaving the vagus nerve?
LEFT - the vagus nerve loops around the left subclavian artery and forms the left recurrent laryngeal nerve
RIGHT - the vagus nerve loops under the aortic arch and forms the right recurrent laryngeal nerve
what is another name for ductus arteriosus?
ligamentum arteriosum
what are the purpose of vitteline arteries and veins?
arteries - supply the yolk sac
veins - drains blood from the yolk sac to the sinus venosus
What are the purpose of umbilical arteries and veins?
arteries -
Before birth:
Paired ventral branches of the dorsal aorta to placenta to allow the blood to be oxygenated.
After birth:
Proximal portion persists as internal iliac and superior vesical arteries
Distal portion degenerates & forms medial umbilical ligaments
veins -
drain blood from placenta to sinus venosus after being oxygenated
What is the purpose of the cardinal veins?
arteries - provides blood from the truncus arteriosus to the body of the embryo
veins - drain blood form the body of the embryo to the sinus venosus
what are the two sources from which coronary arteries are derived?
- Migration of proepicardial (angioblasts) cells
2. Cells of epicardium – epithelial to mesenchymal transition
What are some venous system abnormalities which can occur?
SVC is on the wrong side
IVC is absent
Double IVC
Double SVC
When do the cardinal veins develop?
5th to 7th week
When does the lymphatic system develop?
end of the 6th week
how many primary lymph sac develop?
6
Name the six primary lymph sacs?
Two jugular lymph sacs,
two iliac lymph sacs,
one retroperitoneal lymph sac,
one chyle cistern
Name two abnormalities which can occur with lymphatic system?
- Congenital lymphedema – Dilation of lymphatic vessels
- Cystic hygroma – lump in neck (downs syndrome)
what three changes to foetal circulation occurs after birth?
- Ductus venosus becomes the ligamentum venosum of the liver
- Oval foramen closes after birth by tissue proliferation and adhesion of septal structures
- Ductus arteriosus obliterates to form ligamentum arteriosum
- Ductus venosus - Bypass blood from the umbilical vein to IVC. Regulated by a sphincter (physiological sphincter)
- Oval foramen - Diverts blood from the right atrium to the left atrium
- Ductus arteriosus - Diverts blood from the pulmonary trunk into the descending aorta
What does PDA stand for?
patent ductus arteriosus (atrial septal defect)
What causes PDA?
Cause –
when there is a fistula between the aorta and the pulmonary trunk from failure of muscular wall to contract
respiratory distress syndrome (Low O2) and lack of surfactant in the lungs
Is PDA more common is females or males?
females
what infection is PDA sometimes associated with?
Rubella
What is coarctation of the aorta?
when the aorta becomes narrowed near or opposite the ductus arteriosus
90% of cases the narrowing is opposite the ductus arteriosus
What can be a clinical sign of coarctation?
peripheral pulses; popliteal, dorsal pedis and posterior tibial will be weaker or absent.
