cardiac embryology

Question 1

when do cardiac contractions and circulations first occur in the dog fetus

Answer 1

18-19 days

Question 2

when does cardiac partitioning first occur in the dog fetus

Answer 2

28 days –> one month is a sensible amount of time to see heart on US

Question 3

describe the beginning of cardiovascular development in embryo

Answer 3

• first organ to undergo functional differentiation
• cardiogenic plate of mesodermal tissue at head end of embryonic disk forms heart
• rapid development and flexion of head cause cardiac disc to lie below head and mouth but cranial to the foregut

Question 4

list the 5 zones of the primitive tube

Answer 4

Question 5

how does the primitive tube grow

Answer 5

• tube grows quicker than rest of embryo and is fixed at 2 ends
• becuase fixed, FOLDS
• falls to right (D-looping)
• can abnormally fall to left (L looping)

Question 6

what is the fate of the sinus venosus

Answer 6

• right horn of sinus becomes incorporated into the atrial wall (things can go wrong here)
• left horn is not incorporated and becomes coronary sinus

Question 7

describe the formation of the AV cushion and what it forms

Answer 7

• what cushion grows from outside towards centre to split atria from ventricles
• within the atrio-ventircular canal, cushion forms
• L and R AV cushions are developmental areas where can firther develop into chambers and then valves
• form chordae tendinae and AV valves
• if goes wrong, can get mitral/tricuspid dysplasia and/or ventricle septal defect

Question 8

describe the formation of the interatrial septa

Answer 8

• left and right atria are separated by the septum primum (gros down towards AV cushions)
• O1 (opening 1) - foramen primum - R to L blood flow (shunts blood between atria as blood doesnt need to go to lungs)
• to maintain R to L flow, second septum develops (septum secundum)
• forms a second foramen which occurs before closure of foramen primum to make a series to fenestrations

Question 9

describe the purpose of the foramen ovale

Answer 9

• shunts oxygenated blood straight through RA to LA
• pressure differences across formaen ovale keeps it open in fetus
• patency (kept open) maintained by high blood flow

when the pressure inside the heart changes at birth, holes should close

Question 10

describe the blood flow into the atria in utero

Answer 10

• lots of blood enters the atria from caudal vena cava at this stage
• aimed at septum primum, pushing to left to keep the formaen ovale open, flow from right atria to left atria
• blood then goes from left atria to left ventricle then to body
• small amount of blood from right atria to right ventricle to pulmonary artery to ductus arteriosis and to aorta (ductus arteriosis is the connection between the pulmonary artery to aorta and should close after birth)

Question 11

describe how the interatrial septa changes at birth

Answer 11

• septa secundum and septum primum appose to decrease pressure in right atrium and increased pressure in the left atrium leads to blood inflow from the lungs
• occurs within minutes of birth
• now called interatrial septum
• apposition but not fusion common especially in cattle

if doesnt close properly = persistent foramen ovale (common in cattle) and other types of atrial septal defect

Question 12

describe the truncus arteriosus and bulbus cordis

Answer 12

• true septation
• bulbar cushion (gradullay grow together and fuse to form compartments) in bulbis cordis and truncal cushions in truncus which then forms aorticopul onary septum as move up truncus arteriosus
• grow towards each other in a spiral
• contributes to interventicular spetum

Question 13

what happens wheh the truncus arteriosus and bulbus cordis fail to close

Answer 13

• persistent truncus arteriosus
• ventricle septal defect
• teralogy of fallot (right ventricle gets fatter, pulmonary stenosis)

Question 14

describe formation of the interventricular septum

Answer 14

• once atrioventricular and truncobulbar cushions form and fuse, last step is formation of 2 ventricles from a common chamber
• interventricular septum from caudal expansion and hypertrophy of the bulbus cordis and primitive ventricle rather than growth of a septum
• bulbus cordis and ventricle grow in caudoventral direction (trabeculation)

Question 15

what is trabeculation

Answer 15

• mesenchymal and myocardial cells dividing
• endocardial cells undergo apoptosis
• • gives rise to uneven surface of the ventricles to allow papillary muscles to form and support AV valves

Question 16

explain the closure of the intrerventricular septum

Answer 16

• growth of atrioventricular cushions plugs hole
• occurs at day 32 in dog

Question 17

how do the atrioventricular valves form

Answer 17

• form from reshaping and tissue loss within the ventricular walls
• ventricle dilates, walls hypertrophy, trabeculation uccurs and endodermal cell death leads to strands of cardiac wall and mesenchyme from atrio-ventricular cushions remaining in ventricular wall and form cusps of atrioventricular valves and chordae tendinae

Question 18

how do the aortic and pumonic valves form

Answer 18

• following formation/fusion of truncal ridges get three swellings in wall of aortic and pulmonary artery trunks
• expand into the lumen of each vessel
• very borad and then thin with cellular degradation

if dont thin = aortic/pulmonic stenosis leading to blockages

Question 19

describe the fibrous cardiac skeleton

Answer 19

• separates atria and ventricles
• insulates the AV bundle
• can include ossa cordis (bone)

Question 20

describe the pathway of bloodflow in the unborn baby

Answer 20

1. oxygen and nutrients from the mothers blood are transferred across the placenta and flows through the umbilical vein toward the baby’s liver
2. there it moves through a shunt called the ductus venosus
3. this allows some of the blood to go into the liver
4. most of the oxygenated blood flows to the caudal vena cava and then into the RA
5. most of the blood flows across to the LA through the foramen ovale
6. from the left atrium blood moves to LV and then aorta to the body
7. blood returning to the heart from the body contains CO2 and waste products as it enters the RA
8. it then flos down into the RV and into PA
9. then flows through the dusctus arteriosus into the descending aorta which connects to the umbilical arteries into the placenta
10. there the carbon dioxide and waste products are released into the mothers circulatory system

Question 21

what is persistent right aortic arch

Answer 21

supposed to only have left aortic arch but (because of evolution and fish have both right and left) sometimes it persists and forms a ring around esophagus which prevents food from passing through (vessle restricts esophagus)
- patients present at young age for being skinny and having repeated regurgitation after eating

Question 22

what is important about birds and their cardiac system upon stress

Answer 22

birds hearts are highly specialised and are constantly “on the edge” functioning at max capacity. too much stress can put them over the edge
- dont have a diaphragm so squeezing while handling can kill them

Question 22

what happens in tetralogy of fallot

Answer 22

• overriding aorta
• pulmonary stenosis
• VSD
• right ventricular hypertrophy