THE CARDIOVASCULA
SYSTEM
THE HEART AND CIRCULAT
,INTRODUCTION
• The heart is actually two separate pumps: a right heart that pumps blood through
lungs, and a left heart that pumps blood through the peripheral organs. (Fig. 1)
• In turn, each of these hearts is a pulsatile two-chamber pump composed of an atri
ventricle. Each atrium is a weak primer pump for the ventricle, helping to move blo
the ventricle.
• The ventricles then supply the main pumping force that propels the blood either:
1. Through the pulmonary circulation by the right ventricle or
2. Through the peripheral circulation by the left ventricle.
• Special mechanisms in the heart cause a continuing succession of heart contraction
cardiac rhythmicity, transmitting action potentials throughout the heart muscle to
heart’s rhythmical beat.
,FIGURE 1: NORMAL HUMAN HEART
This image shows the components
that comprise the human heart as
well as the direction of blood flow
from the heart to the lungs, back to
the heart and to the rest of the bod
, • The heart is composed of three major types of cardiac muscle: atrial muscle, ventr
muscle, and specialized excitatory and conductive muscle fibres.
• The atrial and ventricular types of muscle contract in much the same way as skeleta
except that the duration of contraction is much longer.
• Conversely, the specialized excitatory and conductive fibres contract only feebly be
they contain few contractile fibrils; instead, they exhibit either automatic rhythmic
electrical discharge in the form of action potentials or conduction of the action po
through the heart, providing an excitatory system that controls the rhythmical beat
heart.
• Cardiac muscle fibres are arranged in a latticework, with the fibres dividing, recomb
and then spreading again (fig. 2).
• One also notes immediately that cardiac muscle is striated in the same manner as i
skeletal muscle (fig. 3).
• Further, cardiac muscle has typical myofibrils that contain actin and myosin filamen
almost identical to those found in skeletal muscle; these filaments lie side by side a
along one another during contraction in the same manner as occurs in skeletal mus
SYSTEM
THE HEART AND CIRCULAT
,INTRODUCTION
• The heart is actually two separate pumps: a right heart that pumps blood through
lungs, and a left heart that pumps blood through the peripheral organs. (Fig. 1)
• In turn, each of these hearts is a pulsatile two-chamber pump composed of an atri
ventricle. Each atrium is a weak primer pump for the ventricle, helping to move blo
the ventricle.
• The ventricles then supply the main pumping force that propels the blood either:
1. Through the pulmonary circulation by the right ventricle or
2. Through the peripheral circulation by the left ventricle.
• Special mechanisms in the heart cause a continuing succession of heart contraction
cardiac rhythmicity, transmitting action potentials throughout the heart muscle to
heart’s rhythmical beat.
,FIGURE 1: NORMAL HUMAN HEART
This image shows the components
that comprise the human heart as
well as the direction of blood flow
from the heart to the lungs, back to
the heart and to the rest of the bod
, • The heart is composed of three major types of cardiac muscle: atrial muscle, ventr
muscle, and specialized excitatory and conductive muscle fibres.
• The atrial and ventricular types of muscle contract in much the same way as skeleta
except that the duration of contraction is much longer.
• Conversely, the specialized excitatory and conductive fibres contract only feebly be
they contain few contractile fibrils; instead, they exhibit either automatic rhythmic
electrical discharge in the form of action potentials or conduction of the action po
through the heart, providing an excitatory system that controls the rhythmical beat
heart.
• Cardiac muscle fibres are arranged in a latticework, with the fibres dividing, recomb
and then spreading again (fig. 2).
• One also notes immediately that cardiac muscle is striated in the same manner as i
skeletal muscle (fig. 3).
• Further, cardiac muscle has typical myofibrils that contain actin and myosin filamen
almost identical to those found in skeletal muscle; these filaments lie side by side a
along one another during contraction in the same manner as occurs in skeletal mus
