CVS

Question 1

Describe the structure of the primitive heart tube how is it formed?

Answer 1

• modified blood vessels with no chambers and valves (linear)
• contractile tube forces blood from bottom to top
• 2 endocardial tubes fuse to create the primitive heart tube.
• Eventually the primitive heart tube has to be divided to create 4 chambers and the inflow and outflow vessels must be remodelled


Question 2

How does the primitive heart tube fold?

Answer 2

• Cardiac looping
  
  • Tube elongates
  • Runs out of room
  • Twists and folds up (regular and predictable )
  • atria and ventricle expand

(Maximizes space and places the inflow and outflow in the correct orientation with respect to each other )

Question 3

Where does the both atria (left and right) develop from?

Answer 3

RIGHT ATRIA DEVELOPMENT
– most of the primitive atrium 
 – sinus venosus 

– receives venous drainage from the body (venae cava) and the heart (coronary sinus)

LEFT ATRIA DEVELOPMENT
– a small portion of the primitive atrium
– absorbs proximal parts of pulmonary veins
– receives oxygenated blood from the lungs

Question 4

What are the shunts in the circulatory system of the embryo?

Answer 4

• foramen ovale
  (between RA AND LA, shunts highly oxygenated blood from right atrium to left atrium)
• ductus venosus
  (between vessels around liver and vena cava, fetal blood vessel connecting the umbilical vein to the inferior vena cava)
• ductus arteriosus
  (between PT and aorta)

Question 5

How do the shunts close?

Answer 5

• at birth, respiration begins, LA pressure increases
• causing the foramen ovale to close, the Ductus arteriosus to contract and close
• placental support is removed and the ductus venous closes.

Question 6

What is septation of the atria?

Answer 6

• formation of the foramen ovale
  1. Septum primum (first wall):
• Endocardial cushion shelf formed between RA and LA. Wedge is formed on the endocardial cushion shelf. Ostium primum is the first hole in the Septum primum. Ostium Secundum appearing and complete.
  2. Septum Secundum being build and complete (second wall with another hole, but don’t line up)
• blood flow (right to left) will push the walls apart and into the other hole and shunt is maintained during fetal life
• after birth, septum pushed together, holes not aligned, not blood flow from left to right

Question 7

What is septation of the ventricles?

Answer 7

• 2 components: muscular and membranous
• Muscular portion forms most of the septum and grows upwards towards the fused endocardial cushions
• Membranous portion of the interventricuar septum is formed by connective tissue derived from the endocardial cushions to fill the gap

Question 8

What is septation of the great vessels?

Answer 8

• Endocardial cushions also appear in the Trucus arteriosis (single vessel)
• twist around and form a spiral septum, seperating into pulmonary trunk and aorta

Question 9

What is tetralogy of fallot?

Answer 9

• congenital heart defect which is classically understood to involve four anatomical abnormalities of the heart
  1. Large ventricular septal defect (hole b/w two ventricles)
  2. Overriding aorta (blood from both ventricles enter the aorta
  3. RV outflow tract obstruction (pulmonary stenosis)
  4. RV hypertrophy (enlargement of right ventricle)

Question 10

What does transposition of great vessels mean and what can it cause?

Answer 10

• Aorta arises from right ventricle, Pulmonary trunk arises from left ventricle instead
• Deoxygenated blood enters arterial system
• causes cyanosis (bluish hue to the skin, gums, fingernails, or mucous membranes caused by a lack of oxygen in the blood)