Internal Features of the Heart and the Conducting System Flashcards
development of heart at 18 days
cardiogenic area near the head which distributes primitive blood vessels
heart development at 20 days
there is a caudal migration of the cardiogenic area from the head, which splits into two endocardial tubes
development of heart at 21 days
fusion of endocardial tubes into one large tube with two tubes on either end
development of heart at 22 days
top to bottom - truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium
development of heart at 23 days
central tube starts to twist into an s shape, ventricle and atrium develop, sinus venosus develops
development of heart at 35 days
aortic arch arteries have developed, right and left atria have developed separately with a septum primus between them, interventricular septum has begun to develop (ventricles are not yet separate)
heart development at 8 weeks
right atrium, tricuspid valve, right ventricle, foramen ovale, left atrium, mitral valve, left ventricle all present
describe liver bypass circuit in foetal hearts
nutrients are exchanged in placenta instead of the liver, a single umbilical vein with oxygenated blood and nutrient comes into liver and instead of being distributed around liver for further metabolism (not required) this blood is shunted by ductus stenosis, into inferior vena cava to return to the heart
describe lung bypass in foetal hearts
blood doesn’t need to travel to lungs to get oxygen, rather it needs to pass directly from the right to the left atrium - the foramen ovalis is a small hole in the interatrial septum and it shunts blood from the right to the left atrium to be sent around the around the body
describe pulmonary trunk bypass in foetal hearts
blood from left ventricle is shunted by the ductus arteriosis directly into aorta - passing by the pulmonary trunk because the lungs are not yet in use
four congenital heart defects
- patent foramen ovale
- coarctation of the aorta
- patent ductus arteriosis
- tetralogy of fallot
describe patent foramen ovale
- Failure of fusion of interatrial septum shortly after birth - foramen ovale remains
- More common congenital heart defect
- common in Downs Syndrome
- Causes problems - an air bubble or thrombus in right atrium will usually travel to the lungs where it can pop but in this heart disease it may pass into system circuit where it could travel as a clot to the brain and cause a stroke
describe coarctation of the aorta
- When the normal fibrotic process of closing the ductus arteriosis spreads to aorta
- The arch of aorta closes and blood cannot pass through it
describe coarctation of the aorta
- When the normal fibrotic process of closing the ductus arteriosis spreads to aorta
- The arch of aorta closes and blood cannot pass through it
describe patent ductus arteriosus
- Ductus arteriosus remains open
- Blood meant for the lungs can pass to the body through the aorta or vice versa
describe tetralogy of fallot
- Aorta emerges from both ventricles (deoxygenated blood can get into the systemic circuit)
- There is an intraventricular septal defect (meaning oxygenated and deoxygenated blood can mix in the heart)
- Enlarged right ventricle
- Stenosed pulmonary semilunar valve (cannot open or close properly)
- Thankfully quite rare
mitral valve function
The anterior cusp of mitral valve forms both inflow tracts of blood into the left ventricle, and outflow tracts of blood out of the left ventricle up to the aorta
mitral valve pathology
- Hypertrophic cardiomyopathy - training causes maldevelopment of ventricles such as over development of ventricular septa and the left ventricular wall
- This can cause asymmetric swellings of septa - valve is rigid and unyielding
- This leads to subaortic stenosis - the narrowing of outflow tracts of the left ventricle and is associated with sudden deaths of young athletes
aortic valve stenosis
- Wear and tear as we age can cause valves to degenerate and can lead to aortic stenosis
- Cusps don’t fit together properly - rigid and unyeilding, meaning they cannot open or close fully -
- This is detected as a heart murmur
parasynpathetuc innervation of the heart
The vagus nerve (CN X) originates from the dorsal motor nucleus of the vagus in the medulla → comes out from base of skull through jugular foramen → down carotid sheath → into neck → distributed to cardiac plexus → postganglionic fibres distributed to heart itself → only innervates atria
sympathetic innervation of the heart
Sympathetic chain begins at the cardioeacceleratory centre → through spinal cord → emerges from upper spinal cord (T1-T6) → forms sympathetic chain → into neck via cervical and sympathetic cardiac nerves → down to heart → innervates artia and ventricles
cardiac plexus location
- Anterior part lies near the ligamentum arteriosum
- Posterior part lies in front of the trachea in the area of the carina
conduction system
SA node fires action potential → signal travels to atria → atria depolarise and contract → signal travels to AV node → delay occurs to allow ventricles to fill → signals travel through bundle of his and purkinje fibres → ventricles depolarise and contract → blood is expelled through aorta and pulmonary artery
identify the congentital heart defect
patent foramen ovale
identify congenital heart defect
coarctation of the aorta
identify the congential heart defect
patent ductus arteriosis
identify the conginetal heart defect
Tetralogy of Fallot
1
superior vena cava
2
interatrial septum
3
limbus fossa ovalis
4
fossa ovalis
5
inferior vena cava
7
valve of inferior vena cava
8
valve on coronary sinus
9
coronary sinus
10
pectoralis muscles
11
crista terminalis
1
pulmonary valves
2
left coronary artery
3
circumflex artery
4
bicuspid valve
5
great cardiac vein
coronary sinus
7
tricuspid valve
8
right marginal artery
9
right coronary artery
10
aortic valves
