← Cardiac Function
← The ability of cells to exchange materials with their immediate
environment is an absolute requirement in life. Diffusion works well for
short distance transport but for humans, diffusion cannot provide cells
with all that they need as quickly as they need it since diffusion is
efficient but is a slow process. Our body needs a much faster
mechanism of transport.
← The cardiovascular system can deliver materials throughout the
body faster than diffusion could because molecules in the blood move
by bulk flow. The most important function of the cardiovascular system
is to efficiently transport materials to and from places.
← 1. Overview of the cardiovascular system
← The cardiovascular system has three components: the heart,
blood and blood vessels. The heart is a muscular pump that drives the
blood through the blood vessels. The blood is the fluid that circulates
around the body carrying materials to and from the cells. The blood
vessels are the conduits through which blood flows.
Transport of substances
← The heart performs sensory and endocrine functions that help
regulate the cardiovascular variables such as blood volume and
pressure. The blood not only carries nutrients and wastes but also
transports hormones from one part of the body to another. Therefore,
they serve as a communication link acting in conjunction with the
nervous system. The blood vessels are not simply conduits but are
also important sensory and effector organs that can regulate blood
pressure and distribute blood to various parts of the body.
Additionally, regulation of the cardiovascular system requires
coopreration with other organ systems including the nervous system,
endocrine system and the renal system.
← The main function of the cardiovascular system is the
transportation of substances.
• Blood vessels
Arteries: Relatively large, branching vessels that conduct blood away
from the heart. Arteries carry oxygenated blood. The aorta is the
biggest artery that supplies flesh blood to our body.
← Veins: Relatively large converging vessels that conduct blood to
the heart Arterioles: Small, branching vessels with high resistance. Veins carry
deoxygenated blood. The biggest vein is called the vena cava
Capillaries: Site of exchange between blood and tissue
Venules: Small, converging vessels.
As blood flows away from the blood, a cycle follows.
• The Heart
The heart is located in the chest cavity where the diaphragm separates
the abdominal cavity from the thoracic cavity. The heart sits just
above the diaphragm. It is a muscular organ that is closed within a
sac called the pericardium. The function of the pericardium is to
lubricate the heart and to decrease its friction but also prevents the
heart from overstretching.
← ← Although the heart is full of oxygenated blood, the heart itself
does not draw or use the blood in the chambers to feed itself. Rather,
it has a coronary artery that arrives from the aorta.
← The heart is divided into the left and the right. The left and the
right heart is further divided into the upper chambers of the heart
called the atria and the lower chambers of the heart called the
ventricles. So, there is four chambers: the right atrium, the left
atrium, the right ventricle and the left ventricle. The ventricles are
significantly larger than atria and make the bulk of the heart. This is
because the ventricles need to generate great pressure to push the
blood away from the heart to the arteries. The atria receives blood and
transfers it only to the ventricles so the distance traveled is rather
limited. The blood goes in one direction, atria to ventricle to the
← The atria and the ventricles of the heart are separated by a wall
called the interventricular septum that prevents the blood in the left
heart from mixing with the blood in the right heart. The septum
separating the left and the right atrium is called the interatrial septum.
The ventricular muscle is thicker than the atrial muscle. ←
← The left ventricular muscle is much thicker than the right
ventricular muscle. This enables the left ventricle to create more
pressure and supply more blood to our body. The left heart supplies
blood to our body through the aorta while the right heart supplies
blood to our lungs only through the pulmonary artery. ←
← 2. The path and blood flow though the heart and vasculature
← The cardiovascular system is often referred to as the circulatory
system because the blood flows in an essentially circular path as it
travels through the body. The circulatory system consists of two
separate divisions: the pulmonary circuit and the systemic circuit. The
pulmonary circuit consists of blood vessels within the lungs and those
connecting the lungs with the heart. The systemic circuit encompasses
the rest of the blood vessels. Both pulmonary and systemic circuits
possess a dense network of capillaries where the exchange of nutrients
and materials take place. The right heart supplies blood to the
pulmonary circuit while the left heart supplies blood to the systematic
circuit. ← There is a series flow through the pulmonary and systemic
circuits which means that in order to get to one, you must go through
the other one. Within the pulmonary or the systemic circuit, there is
• Oxygenation of blood
The exchange between blood and tissue takes place in the capi