FACT
Clench your fist -
the size of your fist
is more or less the
size of your heart.
FACT
In humans, the left
lung is smaller than
the right lung to
make room in the
chest cavity for the
heart.
See video: SHORTCODEat http://www.everythingscience.co.zaSee video: SHORTCODEat http://www.everythingscience.co.zaThe heart and associated blood vessels DUMMY
External structure of the heartThe heart is a large muscle, about the size of your clenched fist, that pumps blood through
repeated rhythmic contractions. The heart is situated in your thorax, just behind your breast-
bone, in a space called thepericardial cavity. The heart is enclosed by a double protective
membrane, called thepericardium. The region between the two pericardium layers is filled
withpericardial fluidwhich protects the heart from shock and enables the heart to contract
without friction.The heart is a muscle (myocardium) and consists of four chambers. The upper two chambers
of the heart are calledatria(singular= atrium). The two atria are separated by the inter-atrial
septum. The lower two chambers of the heart are known asventriclesand are separated
from each other by the interventricular septum. The ventricles have more muscular walls
than the atria, and the walls of the right ventricle, which supplies blood to the lungs is less
muscular than the walls of the left ventricle, which must pump blood to the whole body.In addition, there are a number of large blood vessels that carry blood towards and away
from the heart. The terms ‘artery’ and ‘vein’ are not determined by what the vessel transports
(oxygenated blood or deoxygenated) but by whether the vessel flows to or from the heart.
Arteriestake blood away from the heart and generally carry oxygenated blood, with the
exception of the pulmonary artery. Veinstransport blood towards the heart and generally
carry deoxygenated blood, except the pulmonary vein. On the right side of the heart, the
superior vena cavatransports deoxygenated blood from the head and arms and the inferior
vena cava transports deoxygenated blood from the lower part of the body back to the heart,
where it enters the right atrium. Thepulmonary arterycarries deoxygenated blood away
from the right ventricle of the heart towards the lungs to be oxygenated. On the left side
of the heart, thepulmonary veinbrings oxygenated blood from the lungs towards the left
atrium of the heart and the oxygenated blood exits the left ventricle via theaortaand is
transported to all parts of the body.Since the heart is a muscle, and therefore requires oxygen and nutrients itself to keep beat-
ing, it receives blood from thecoronary arteries, and returns deoxygenated blood via the
coronary veins.226 8.2. Circulatory systems in animals