The heart is a muscular organ that pumps blood through the circulatory system using repeated contractions. It has three layers - the outer epicardium, middle myocardium made of cardiac muscle that contracts, and inner endocardium. The human heart is divided into four chambers - left and right atria which receive blood, and left and right ventricles which pump blood. It uses two circuits - pulmonary circulation to lungs and systemic circulation to body. The sinoatrial node sets the heart's rhythm, contracting without nervous input.

1. By: Rhea Chong CN 04
Denise Yang CN 26

2. The heart is a myogenic muscular organ found in all animals
with a circulatory system (including all vertebrate) that is
responsible for pumping blood throughout the blood
vessel by repeated, rhythmic contractions.
 Myogenic contractionrefers to a muscle
contraction initiated by the myocyte cell
itself instead of an outside occurrence or
stimulus such as nerve innervation.
 A myocyte (also known as a muscle cell) is the
type of cell found in muscles.
 Cardiac myocytes are responsible for
generating the electrical impulses that control
the heart rate, among other things.

3. Before each beat, your heart fills with blood. Then its
muscle contracts to squirt the blood along. When the
heart contracts (becomes smaller), it squeezes — try
squeezing your hand into a fist. That's sort of like what
your heart does so it can squirt out the blood. Your
heart does this all day and all night, all the time.

4. The vertebrate heart is composed of cardiac
muscle, which is an involuntary striated muscle tissue
(a form of fibers that are combined into parallel fibers)
found only in this organ, and connective tissue.

5. It is enclosed in a double-
walled sac called the
pericardium. This sac
protects the
heart, anchors its
surrounding
structures, and prevents
overfilling of the heart with
blood.

6. In the human body, the heart is usually situated in the
middle of the thorax with the largest part of the heart
slightly offset to the left, although sometimes it is on the
right, underneath the human sternum. The heart is
usually felt to be on the left side because the left heart
(left ventricle) is stronger (it pumps to all body parts).
The left lung is smaller than the right lung because the
heart occupies more of the left hemithorax.

8.  The outer wall of the human heart is composed of
three layers. The outer layer is called the
epicardium, or visceral pericardium since it is also the
inner wall of the pericardium.
 Its largest constituent is connective tissue and
functions as a protective layer. The visceral
pericardium apparently produces thepericardial
fluid, which lubricates motion between the inner and
outer layers of the pericardium.

9.  The middle layer is called the myocardium(cardiac
muscle) and is composed of muscle which contracts.
 It is composed of spontaneously contracting cardiac
muscle fibers which allows the heart to contract.
 It stimulates the heart contractions to pump blood from
the ventricles and relaxes the heart to allow the atria to
receive blood.
 These contractions produce what is known as a heart
beat.

10.  The inner layer is called the endocardium and is in contact
with the blood that the heart pumps.
 The endocardium, which is primarily made up of
endothelial cells, controls myocardial function.
 The cardiac endothelium controls the development of the
heart in the embryo as well as in the adult.
 Endothelium- thin layer of cells that lines the interior surface
of blood vessels, forming an interface between the
circulating blood in the lumen and the rest of the vessel
wall, it reduces the turbulence of the flow of blood, allowing
cells to be pumped further
 Lumen- inside space of the artery

11.  Additionally, the contractility and electrophysiological
environment of the cardiomyocyte are regulated by the cardiac
endothelium.
 Electrophysiolgy- involves measurements of voltage change or
electrical current.
 The endocardial endothelium may also act as a kind of blood-
heart barrier, thus controlling the ionic composition of the
extracellular fluid in which the cardiomyocytes bathe.
 Ion- atom or a group of atoms with a net electric charge
 Extracellular- outside the cell
 Also, it merges with the inner lining (endothelium) of blood
vessels and covers heart valves.

13.  The human heart is divided into four main
chambers: the the upper chambers are
called the left and right atria and two lower
chambers are called the right and left
ventricles. The atria are the receiving
chambers and the ventricles are the
discharging chambers. There is a thick wall
separating the right and left side of the heart
called tyhe septum. Normally with each beat
the right ventricle pumps the same ampunt
of blood into the lungs that the left ventricle
pumps out into the body.

14.  The pathway of blood through the human heart consists of
a pulmonary circuit and a systemic circuit.
 These pathways include the tricuspid valve the mitral
valve, the aortic valve, and the pulmonary valve. The mitral
and tricuspid valve are classified as the atrioventricular
valves.this is because they are found in between the atria
and ventricles. The aortic and pulmonary semilunar valves
separate the left and right ventricle from the pulmonary
artery and the aorta respectively.
 Semilunar valves- permit blood to be forced into the
arteries, but prevent backflow of blood from the arteries into
the ventricles.

15.  The right side collects de-oxygenated blood, in the right
atrium, from the body(via superior and interior vena
cava) and pump it(via the right ventricle) into the lungs
so that carbon dioxide can be dropped off and oxygen
picked up (gas exchange). This happens through the
passive process of diffusion.
 This process is called the pulmonary circulation.

16. • The left side of the heart collects oxygenated blood
from the lung into the left atrium. From the left atrium
the blood moves to the left ventricle, which pumps it
out to the body (via the aorta). On both sides, the
lower ventricles are thicker and stronger than the
upper atria. The muscle wall surrounding the left
ventricle is thicker than the wall surrounding the right
ventricle due to the higher force needed to pump the
blood through the systematic circulation.
• Systematic circulation- carries oxygenated blood
away from the heart to the body and returns
deoxygenated blood back to the heart

17.  Starting in the right atrium, the blood flows
through the tricuspid valve to the right
ventricle. Here it is pumped out of the
pulmonary semilunar valve and travels
through the pulmonary artery to the lungs.
From there, blood flows back through the
aortic semilunar valve to the aorta and to the
rest of the body. The deoxygenated blood
finally retutns to the heart through the inferior
vena cava and superior vena cava, and enters
the right atrium where the process begins.

20. Some cardiac cells are self-excitable, contracting without
any signal from the nervous system, even if removed
from the heart and placed in culture. Each of these cells
have their own intrinsic contraction rhythm. A region of
the human heart called the sinoatrial node, or
pacemaker, sets the rate and timing at which all cardiac
muscle cells contract. It is located in the right atrium of
the heart.

21. 1) The term cardiac (as in cardiology) means "related to
the heart" and comes from the Greek language
καρδιά, kardia, for "heart".
2) A kitchen faucet would need to be turned on all the
way for at least 45 years to equal the amount of blood
pumped by the heart in an average lifetime.
3) The volume of blood pumped by the heart can vary
over a wide range, from five to 30 liters per minute.
4) Grab a tennis ball and squeeze it tightly: that’s how
hard the beating heart works to pump blood.

22. 5) Laughing can be a great workout for your heart.
Whenever you laugh, the blood flow in your heart is
increased for up to 45 minutes, which in turn
improves your heart health.
6) The human heart can create enough pressure that it
could squirt blood at a distance of thirty feet.
7) For men, there is a strange link between the ring
finger and the heart. According to scientific
studies, the longer a man’s ring finger is, the lower
his chance of having a heart attack.
8) Most heart attacks occur between the hours of 8 and
9 AM.

23. 