Working Mechanism of the Heart

Question 1

Diastole and Systole

Answer 1

• The heart serves to pump blood to all parts of the body
• contraction of a chamber reduces its volume and forces blood out which is called systolic phase
• relaxation brings it back to the original size to receive more blood which is called diastolic phase

Question 2

Auricles and Ventricles

Answer 2

• Auricles and ventricles do not contract in the same time
• Auricular systole occurs first followed by ventricular systole.
• Diastole of each chamber follows immediately upon completion of its systole.

Question 3

Old View

Answer 3

• The right side of the ventricle receives deoxygenated blood, which is guided into the truncus arteriosus by the spiral valve.
• Oxygenated blood enters from the left side of the ventricle.
• The ventricle contraction forces blood into the truncus arteriosus.
• Blood is directed into different arteries:
  i) Deoxygenated blood goes to the pulmocutaneous arch (to lungs and skin).
  ii) Mixed blood from the middle of the ventricle goes to the systemic arch (to body and viscera).
  iii) Oxygenated blood goes to the carotid arch (to head and brain).
• The old view suggests that blood is partially separated based on timing and anatomical structures, but acknowledges some mixing in the ventricle.

Question 3

Sinus venosus

Answer 3

• when sinus venosus contracts the mixed blood contained in it is pumped to the right auricle.
• at the same times, left auricle receives oxygenated blood from lungs through pulmonary vein.
• When auricles are full of blood, they contract simultaneously driving their blood into the ventricle through auriculo ventricular aperture.
• There are 2 views regarding functioning of the ventricle

Question 3

Modern View

Answer 3

• The modern view of blood circulation, as proposed by Vandervael (1933) and Foxon (1955), suggests:
• Complete mixing of oxygenated and deoxygenated blood occurs in the ventricle.
• Radioactive substances were used in experiments and found evenly distributed, supporting the idea of total mixing.
• The ventricle pumps mixed blood simultaneously into all three arterial arches, distributing it to various parts of the body.
• In frogs, the sinus venosus receives both deoxygenated blood (from the viscera) and oxygenated blood (from the buccal cavity and skin), which enters the right auricle.
• Blood from both auricles mixes in the ventricle, and the mixed blood is then pumped to all parts of the body, where purification occurs at different locations due to varying modes of respiration (pulmonary, buccal, cutaneous).