The Cardiovascular (Cardiac and Blood Vessel) System

The cardiovascular system regulate distribution of blood through the body. The system involves the cardiac / heart and the blood vessels.


The Cardiac System

The heart is about the size of a fist. Despite its small size, the heart is capable of pumping blood through the whole body. This is made possible by heart’s special anatomy.

The heart contains four chambers: right atrium, right ventricle, left atrium, and left ventricle. The atrium receives oxygenated or deoxygenated blood and send it into the ventricles. The ventricles then pumps blood out of the heart either to the lung (right ventricle) or to the whole body (left ventricle). The walls of the left ventricle are thicker than the rest of the heart so that it could generate enough force to pump blood to the whole body. In addition, semilunar valves, tricuspid, and bicuspid valves are strategically placed inside the heart to prevent blood backflow when the heart is pumping (or when your doing head stand).




The heart muscle (cardiomyocytes) also contains features different from the skeletal muscles to ensure effective pumping function. These features are:

  1. Shorter and branched cells
  2. Intercalated discs connecting neighboring muscle fibres
  3. Smaller sarcoplasmic reticulum to ensure smaller Ca2+ reservoir
  4. Bigger and higher number of mitochondria for higher ATP generation
  5. Autoryhtmic for regular and constant muscle contraction. In this case, special patch of cardiomyocytes (sinoatrium – SA node) generate electrical impulse at constant rate to keep the heart pumping (contracting). SA node is body’s natural pacemaker.

The electrical impulse then travelled through the heart via special cardiomyocyte fibres that could conduct electrical impulses efficiently. These fibres are atrioventricular (AV) node, bundle of His, bundle branches, and Purkinje fibre.





The Blood Vessels

The blood vessels also play important role helping the heart distribute pumped blood through the body. The special features for this purpos are:

  1. Presence of smooth muscle innervated with sympathetic nerve fibres to regulate blood pressure.
  2. Presence of thick smooth muscle to withstand pressure from pumped blood.
  3. Presence of elastic fibres to propel blood forward.
  4. Presence of sphincter to regulate blood flow into the much thinner and fragile cappilaries.
  5. Presence of valve to prevent blood backflow.
  6. Located between skeletal muscles to help pump blood forward.





1- Write the sequence of cardiac cycle. What happens during ventricular systole and ventricular diastole?

2- Explain how special features of cardiomyocytes ensure a proper and efficient function of the heart?

3- A man suffers from gunshot wound. He is bleeding profusely and exhibits systolic blood pressure of 40 mmHg; weak pulse of 200 beats/minute; cool, pale, and clammy skin, and he is consistently asking for water despite not producing any urine. Explain what caused his symptoms.








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