The Heart

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The Heart

• BY
• Jamie, Alaine and Kit

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What the heart does?
From the moment it begins beating until the
moment it stops, the human heart works
tirelessly. In an average lifetime, the heart
beats more than two and a half billion times,
without ever pausing to rest. Like a pumping
machine, the heart provides the power needed for
life.
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Tissue Layers within the heart

• The heart wall is composed of three tissue
  layers
• epicedium,
• 2. myocardium.
• 3. endocardium

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Epicedium
Epicedium describes the outer layer of heart
tissue. When considered as a part of the
pericardium, it is the inner layer, or visceral
pericardium.
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Myocardium
The myocardium is made up of layers of cardiac
myocytes, attached to each other by connective
tissue fibres, and arranged in spiral bundles.
The connective tissue fibres are composed of
collagen and elastin, and together they form a
dense network called the fibrous skeleton of the
heart, which functions to reinforce the
myocardium, and provides an attachment surface
for the cardiac muscles. The myocardium is the
contractile layer of the heart.
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  Endocardium
Or The endocadium lines the lumen of the heart
and is composed of simple squamous epithelium and
a thin layer of loose connective tissue.
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Cells in the heart
It is the complex interaction of numerous cell
types that give the heart its ability to pump
blood. Some cells form heart connective tissue,
other cells grow into heart valves. And muscle
cells give the heart its ability to beat and pump
blood throughout the body.  
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The Conduction System

• Cells in the ventricular myocardium are excitable
  and contractile allowing the spread of action
  potential over the cell membrane. This triggers
  an internal cascade of events and so causing the
  cell to contract.
• The action potential is able to jump from one
  cell to the next via gap junction channels
  located in the intercalated disks.
• The spread of excitation, leads to muscle
  contraction.

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Stem cells
The heart uses stem cells to regenerate and
repair other dead cells. Researchers have
isolated cardiac stem cells from rats and showed
that when these cells were injected into rat
hearts that had been damaged, they reconstituted
the injured tissue. The same group has also
detected similar cells in human hearts.
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Cardiac Muscle Cells
Cardiac muscle cells are small with only one or
two nuclei. The regular arrangement of sarcomeres
within the myofibrils gives the tissue a striated
pattern (like voluntary muscle) but the cardiac
cells are not separately innervated. They lack
motor end plates and so instead rely on
communicating gap junctions to transmit
electrical signals directly from one cell to the
next. This means that in a normal healthy heart,
every cell depolarises every beat.