Anatomy of Bloodflow Through Fetal Heart

Question 1

what are the black arrows

Answer 1

valve flaps of the atrio-ventricular or tricuspid valve

Question 2

what are the red and pink arrows

Answer 2

red: chordea tendineae of tricuspid valve
pink: papillary muscles

Question 3

what is the structure of the right AV (tricuspid) valve

Answer 3

3 cusps: chordae tendineae and papillary muscles/fibrous annular ring support

Question 4

what is the action of the AV valve

Answer 4

passive/prevents backflow of blood into atrium at systole

1st heart sound lub = closure of right and left AV valves

Question 5

what are the structures of the right ventricle

Answer 5

Question 6

list 5 anatomical features of the right ventricle

Answer 6

1. wall: endocardium, myocardium and epicardium
2. trabecular septomarginalis: distinct feature of right atrium –> carries the short circuiting impulse to the walls –> related to the papillary muscles which will contract before the walls of the heart contract to prepare to hold the valves
3. trabecular carneae: elevation of wall –> act like pectinate muscle –> dampen out the turbulence of blood
4. pulmonary trunk exits RV on the left lateral side of the heart
5. walls are smooth and shiny

Question 7

what are the structures (transverse section through R&L ventricles)

Answer 7

1. most cranial point
2. right ventricle
3. interventricular septum
4. left ventricle

Question 8

identify the labels and describe how blood flows through the right side

Answer 8

right ventricle forms the cranial margin of heart

blood exits RV through pulmonary trunk (on left lateral side) through pulmonary semi-lunar valve

pulmonary trunk bifurcates into L&R pulmonary arteries which enter root of L&R lung

Question 9

list the anatomical features of the pulmonary semilunar valve

Answer 9

1. at junction of RV and pulmonary trunk
2. second heart sound ‘dub’ = closure of pulmonary and aortic semi lunar valves

Question 10

what is the ligamentum arteriosum

Answer 10

ligament linking the pulmonary trunk and aorta

fetal remnant of the ductus arteriosus

Question 11

what are these structures

Answer 11

Question 12

describe the blood flow through the left side of the heart

Answer 12

1. oxygenated blood enters left atrium (& auricle) from the lungs via pulmonary veins –> mitral valve (bicuspid) or left AV valve –> left ventricle –> aortic semi-lunar valve guards entrance to aorta –> aorta exits middle of base of heart

Question 13

what ventricle forms the base of the heart

Answer 13

left –> very thick wall

Question 14

what are the anatomical features of the mitral valve

Answer 14

2 cusps

Question 15

what are the structures of left atrium and ventricle

Answer 15

Question 16

what are the structures (dorsal view of heart after removal of atria)

Answer 16

1. right atrioventricular valve
2. left atrioventricular valve
3. aortic valve
4. pulmonary valve
5. left coronary artery
6. righ coronary artery
   cr: cranial

Question 17

what are the structures

Answer 17

A: mitral valve

B: semi-lunar valve

C: coronary circulation

Question 18

what is the puncta maxima

Answer 18

points on the chest wall where heart sounds are heard best

left thorax: between 3,4,5th intercostal space

right thorax: tricuspid 4th intercostal space

Question 19

what are the structures of the thorax

Answer 19

1. cranial extent of heart
2. caudal extend of heart
3. basal border of lung
4. line of pleural reflection
5. caudal border of lung percussion area shown on right side

Question 20

what are the structures shown here

Answer 20

1. right auricle
2. left atrium
3. left atrioventricular valve
4. interventricular septum
5. aorta

Question 21

what are the structures of the early fetal heart

Answer 21

placenta –> maternal and fetal blood flow coming close to each other

the umbilical vein has nutritious and highly oxygenated blood

returns deoxygenated blood to the placenta

Question 22

what is the 1st step in the formation of the 4 chambered heart

Answer 22

subdivision of the channel between the primitive atrium and ventricle

2 chambered heart recieving and distributing areas that is segmented in the middle –> partitions coming from above and below

Question 23

what is the second step in the formation of the 4 chambered heart

Answer 23

subdivision of the primitive ventricle continues –> interventricular septum

the atrioventricular channel splits into two-av canal cushions

the interatrial septum starts to form but is never complete

Question 24

what is the third step in the formation of the 4 chambered heart

Answer 24

ventricles are now separate

AV valves form

the atria continue to intercommunicate (RA to LA) via foramen ovale

Question 25

what is the distribution of blood in the fetus before birth

Answer 25

lungs not functional --\> high resistance pulmonary circulation blood flows mainly to the low resistance systemic circulation and the placenta 2 shunts make this possible --\> foramen ovale, ductus arteriosus

Question 26

what other shunt maximizes the PO2 of blood entering the heart from the placenta

Answer 26

ductus venosus in the liver

Question 27

what is the function of the ductus venosus

Answer 27

blood moves from the umbilicus towards the liver via umbilical vein (green) --\> shunt in liver (ductus venosus) prevents mixing of oxygenated blood from placenta (red) with fetal hepatic venous return from gut (blue) --\> blood enters right atrium via caudal vena cava (orange)

Question 28

what is the function of the foramen ovale

Answer 28

oxygenated blood entering right atrium (RA) passes through one way valve --\> foramen ovale --\> diverted into LA-LV-aorta (orange) --\> into aorta --\> preferential delivery of blood with high PO2 leaving left ventricle to heart and brain --\> blood entering RA from cranial vena cava flows into RV (as in adult) (dark blue) \*\*a passageway between right and left atrium don't want the blood to go into the right ventricle --\> goes through the hole and into the left side where it will go through the aorta to head the caudal vena cava --\> carries highly oxygenated blood cranial vena cava brings deoxygenated blood into the right atrium --\> there is a mixing of blood in the right atrium the cranial vena cava deoxygenated blood is forced into the right ventricle --\> bypassing the mixing --\> goes to the pulmonary trunk

Question 29

what is the function of the ductus arteriosus

Answer 29

2nd shunt links pulmonary trunk to aorta --\> allows blood entering right ventricle to bypass the lungs and pass into the aorta and eventually bakc to the placenta --\> exercises right ventricle in prep for delivering entire output to lungs after birth \*\*mixes with deoxygenated blood here from the aorta --\> nourishes other areas of the body before returning to the placenta

Question 30

how does the ductus venosus close and what are defects associated with it

Answer 30

often persists until birth in carnivores, ruminants and humans defect: persistent patent ductus venosus portacaval shunt: portal blood bypasses liver

Question 31

how does the foramen ovale close and what are defects associated with it

Answer 31

lung inflation causes increased pressure in left atrium --\> functional closure before anatomical closure --\> scar right atrium --\> forms scar tissue in interatrial wall (fossa ovalis) defect: patent foramen ovale not problematic

Question 32

how does the ductus arteriosus close and what are defects associated with it

Answer 32

inflation lungs causes turbulence --\> smooth muscle constriction --\> anatomical closure --\> forms ligamentum arteriosum defect: patent ductus arteriosus --\> serious characteristic machinery murmur

Question 33

what are the 3 main categories of congenital heart defects

Answer 33

1. failure of closure of fetal structures (foramen ovale, ductus arteriosus --\> PDA, ductus venosus --\> liver) 2. septal defects (interventricular septum) 3. great vessel defects --\> defects of outflow tracts --\> aortic or pulmonary valves - dysplasia - malformed or disorderly - stenosis - decreased lumen size - malposition/fusion of great vessels