Development of the Heart & Blood Vessels Flashcards
Briefly outline the 5 steps involved in heart development
1) Formation of 4 chambered heart tube
2) Cardiac looping
3) Atriaventricular canal divide into left & right channels
4) Formation of atrial septa
5) Formation of tronocuncal cushions and division of outflow tract
What is dextrocardia
Heart loops/points to the wrong side
Points to right side instead of left
Blastocyst
- forms 5 days after fertilization during embryo development
- has 100 cells
-contains inner cell mass which creates all tissues in body
- outer layer of blastocyst consists of cells that are collectively known as trophoblast
- trophoblasts differentiate to form the placenta
Stages of embryo development
Day 1- 2 pronuclei
Day 3- 8 cells, identical and totipotent
Day 4- Morula, 16 cells
Day 6 to 10- Blastocyst, 100 cells
Day 16- Gastrula
Name the 3 germ layers made up of embryonic cells/tissue
Ectoderm- develops into skin or nerves
Mesoderm- develops into muscles or connective tissue
Endoderm- develops into GI tract, lungs, pancreas, liver
What is the function of the “notochord” and “primitive streak” in an embryonic disc
Notochord- backbone of embryonic disc, provides stability
Primitive streak- determines symmetry
Outline step 1 in heart development-
“Formation of heart tube”
1) blood islands found in mesoderm develop into heart
2) blood islands form 2 single tubes called Cardiogenic cords which merge together to form 1 tube (heart tube)
3) asymmetric openings result in an arterial end and a venous end
Name 2 diseases that may arise in step 1 of heart development (formation of heart tube)
1) Truncus arteriosus: congenital heart disease, where only 1 single blood vessel comes out of right and left ventricle instead of 2 separate vessels, pulmonary artery and aorta
2) Situs inversus: heart, lungs, liver, spleen etc are reversed, arises when primitive streak incorrectly determines symmetry
Outline step 2 in heart development-
“Cardiac looping”
1) cells at each end of heart proliferate making the tube longer
2) but due to limited space, heart folds to form cristae-like structure. Also bulges. Where the folds are is where the future left and right ventricles will be
3) initially primitive atrium will be below ventricles but will eventually loop up and reach correct location
4) primitive ventricles drop down and atria are now above. 4 interior chambers have formed but are not yet divided.
5) no pulmonary circulation as lungs not yet developed
Outline step 3 in heart development-
“Atriaventricular canal divides into left and right channel”
1) Septum primum is a wall of muscle that grows in the middle of the heart (midsaggital plane). This separates the atria.
Septum is the wall that separates the 4 chambers
2) Foramen primum is a hole in the septum primum
3) as lungs begin to develop, left atrium grows a pulmonary vein
4) vena cava also begin to develop in atrial walls
5) endocardial cushions fuse (av cushions) which divide atria from the ventricles horizontally
6) septum primum and ventricular septum attach to endocardial cushions
Name a disease that may arise in step 3 of heart development (Atriaventricular canal divide into left and right channel)
Ventricular septal defect
Arises due to endocardial cushions not being able to provide an anchor point for ventricular septum
- Septum is the wall that separates the 4 chambers
- AV septum is found in the middle, divides heart into left & right side
- hole in ventricular septum
- oxygenated blood from L ventricle mixes with deoxygenated blood from R ventricle
- contaminated blood is pumped to the lungs via RV then re enters LV via P vein and L atrium
Systemic circulation doesn’t receive all the blood from left ventricle as it has leaked to right ventricle, so body receives less O2
What is “pulmonary hypertension”
Hole in the ventricular septum causes blood to leak into the right ventricle
This increases the volume and pressure inside the right ventricle
This leads to pulmonary hypertension
What is “pulmonary oedema”
Too much fluid in right ventricle may cause it to be squeezed into lungs
Lungs end up with excess fluid, especially in air sacs
This causes difficulty breathing
Outline step 4 in heart development-
“Formation of atrial septa”
1) septum primum (wall of muscle) grows to form atrial septa. Atrial separates right and left atria.
2) foramen primum is a temporary hole in septum primum which allows foetal blood to flow from left atrium to right atrium. This doesn’t matter as there is no pulmonary circulation as of yet since lungs not developed in foetus.
3) foramen primum closes
4) foramen secundum, a second hole opens
5) this allows the “septum secundum” a more robust and muscular septum to grow over the initial hole, foramen primum
6) foramen secundum becomes foramen ovale, which is another hole
7) foramen ovale is a hole in atrial septum, permits blood flow
8) at birth, lungs become functional which reduces pulmonary blood pressure, so pressure in left atria is now greater than right atria, this moves septum primum over foramen ovale causing it to close
Outline the final step in heart development-
“Division of outflow tract”
Outflow tract is the part of the ventricle that blood passes in order to enter the pulmonary artery or aorta
1) At the moment the blood exiting the heart is leaving through one vessel. It needs to be separated into two vessels
2) ventricles are separated into left and right side by conotruncal septum》endocardial cushions》ventricular septum
If conotruncal septum is misaligned, you get a differently sized aorta and pulmonary artery
Or
It will not meet endocardial cushions resulting in a septal defect
