The heart is a muscular organ located
between the lungs in the centre of the chest (thorax), and is about the size of
a fist.
It pumps blood continuously
around the body. An organism can lose consciousness within just a few seconds
if the brain is deprived of blood.The heart is made from cardiac muscle and is a dual pump. This means that blood flows around the body in 2 routes simultaneously - both to and back from the lungs (the pulmonary circuit) and at the same time to and back from the body (systemic circuit).
Caption: : A light microscope image of cardiac muscle
The heart mainly consists of cardiac
muscle tissue, which like smooth muscle
(but not skeletal muscle), contracts involuntarily.
Cardiac muscle is made up of
cells that are connected by cytoplasmic bridges. This enables electrical
impulses to pass through the tissue.
It
contains large numbers of mitochondria (to supply high energy demands) and myoglobin molecules (a protein that stores oxygen to keep up with the high demand for oxygen due to continual contraction).
