Cardiac cycle in CVS, Lecture notes of Animal Anatomy and Physiology

Download Cardiac cycle in CVS and more Lecture notes Animal Anatomy and Physiology in PDF only on Docsity!

CARDIOVASCULAR SYSTEM:

CARDIAC CYCLE

For:

Semester II

CC2TH/ GEN 2TH

Prepared and compiled by:

OLIVIA CHOWDHURY

DEPARTMENT OF PHYSIOLOGY

SURENDRANATH COLLEGE

May 2, 2020 OLIVIA CHOWDHURY

CARDIAC CYCLE The sequence of events that occur from the beginning of one heart beat to the beginning of the next beat is known as the cardiac cycle. The period of contraction that the heart undergoes while it pumps blood into circulation is called systole. The period of relaxation that occurs as the chambers fill with blood is called diastole. Both the atria and ventricles undergo systole and diastole, and their performance is carefully synchronised to ensure blood is pumped efficiently to the body.

PHASES OF THE CARDIAC CYCLE  Atrial cycle (0.8 sec):

 Atrial systole (0.1)

 Atrial diastole (0.7)

 Ventricular cycle (0.8 sec):

 Ventricular systole (0.3)

 Ventricular diastole. (0.5)

During atrial systole, the ventricles are relaxed During ventricular systole, the atria are relaxed

 Blood normally flows continually from great veins into atria  Narrowing of origin of great veins-decreasing venous return  75 % flows directly from atria into ventricles through the open AV valve before the atria contracts.  25 % of filling of ventricles – during atrial contraction  Intraatrial pressure rises  Intraventricular pressure rises ATRIAL CYCLE Atrial Systole

 Ventricular systole (0.3 sec)

• Phase of Isovolumetric (Isometric) Contraction
• Phase of ventricular ejection.

1. Rapid phase
2. Slow phase. VENTRICULAR CYCLE

 The AV valves close and the atrial pressure shows slight, but sharp increase  Due to sudden closure of AV valve the intraventricular pressure increases.  With all the valves being closed, the ventricles become closed chambers. So, the ventricles contract isometrically, i.e., without change in the length of its muscle fibers. Ventricular Systole Isovolumic Contraction Phase:

VENTRICULAR CYCLE  Ventricular Diastole (0.5 sec)

 Protodiastole

 Isovolumic or Isometric Relaxation phase.

 Rapid passive filling phase.

 Reduced filling & Diastasis

 Lasts for 0.04 sec

 Ventricular systole ends- ventricles relax

 Intraventricular pressure drops rapidly – blood tends to

flow from vessels to ventricles semilunar valves

Protodiastole

Lasts 0.1 sec Once the AV valves open, blood that has accumulated in the atria flows rapidly into the ventricles Ventricular volume increases Lasts 0.2 sec Rest of blood that has accumulated in the atria flows slowly into the ventricles. Ventricular volume increases more slowly now. The ventricles continue to fill with blood until they are nearly full. This slow filling of ventricles is called diastasis. Rapid Filling Phase: Reduced Filling Phase: May 2, 2020 OLIVIA CHOWDHURY

SUMMARY