BHHM.com BHHM: Best Heart Health Monitor
The heart is a muscular organ responsible for pumping blood through the blood
vessels by repeated, rhythmic contractions, or a similar structure in the
annelids, mollusks, and arthropods. The term cardiac (as in cardiology) means
"related to the heart" and comes from the Greek καρδία, kardia, for "heart." The
heart is composed of cardiac muscle, an involuntary muscle tissue which is found
only within this organ. The average human heart beating at 72 BPM, will beat
approximately 2.5 billion times during a lifetime of 66 years.
Early development
Heart development
At 21 days after conception, the human heart begins beating at 70 to 80 beats
per minute and accelerates linearly for the first month of beating.The human
embryonic heart begins beating approximately 21 days after conception, or five
weeks after the last normal menstrual period (LMP), which is the date normally
used to date pregnancy. The human heart begins beating at a rate near the
mother’s, about 75-80 beats per minute (BPM). The embryonic heart rate (EHR)
then accelerates linearly for the first month of beating, peaking at 165-185 BPM
during the early 7th week, (early 9th week after the LMP). This acceleration is
approximately 3.3 BPM per day, or about 10 BPM every three days, an increase of
100 BPM in the first month.
After peaking at about 9.2 weeks after the LMP, it decelerates to about 152 BPM
(+/-25 BPM) during the 15th week after the LMP. After the 15th week the
deceleration slows reaching an average rate of about 145 (+/-25 BPM) BPM at
term. The regression formula which describes this acceleration before the embryo
reaches 25 mm in crown-rump length or 9.2 LMP weeks is:
Age in days = EHR(0.3)+6
There is no difference in male and female heart rates before birth.
Structure
Anterior (frontal) view of the opened heart. Arrows indicate normal blood flow.
Image provided courtesy of www.3dscience.com.In the human body, the heart is
usually situated in the middle of the thorax with the largest part of the heart
slightly to the left (although sometimes it is on the right, see dextrocardia),
underneath the breastbone (see diagrams). 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. The heart is enclosed by a sac known as
the pericardium and is surrounded by the lungs. The pericardium is a double
membrane structure containing a serous fluid to reduce friction during heart
contractions. The mediastinum, a subdivision of the thoracic cavity, is the name
of the heart cavity.
The apex is the blunt point situated in an inferior (pointing down and left)
direction. A stethoscope can be placed directly over the apex so that the beats
can be counted. It is located posterior to the 5th intercostal space in the left
mid-clavicular line. In normal adults, the mass of the heart is 250-350 g (9-12
oz), or about three quarters the size of a clenched fist, but extremely diseased
hearts can be up to 1000 g (2 lb) in mass due to hypertrophy. It consists of
four chambers, the two upper atria (singular: atrium ) and the two lower
ventricles. On the left is a picture of a fresh human heart which was removed
from a 64-year-old British male.
Human heart
Functioning
The function of the right side of the heart (see right heart) is to collect
de-oxygenated blood, in the right atrium, from the body and pump it, via the
right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide
can be dropped off and oxygen picked up (gas exchange). This happens through a
passive process called diffusion. The left side (see left heart) collects
oxygenated blood from the lungs into the left atrium. From the left atrium the
blood moves to the left ventricle which pumps it out to the body. 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
systemic circulation.
Starting in the right atrium, the blood flows through the tricuspid valve to the
right ventricle. Here it is pumped out the pulmonary semilunar valve and travels
through the pulmonary artery to the lungs. From there, blood flows back through
the pulmonary vein to the left atrium. It then travels through the bicuspid
valve to the left ventricle and on to through the aortic semilunar valve to the
aorta. The aorta forks, and the blood is divided between major arteries which
supply the upper and lower body. The blood travels the arteries to the smaller
arterioles, then finally to the tiny capillaries which feed each cell. The
(relatively) deoxygenated blood then travels to the venules, which coalesce into
veins, then to the inferior and superior vena cavae and finally back to the
right atrium where the process began.
The heart is effectively a syncytium, a meshwork of cardiac muscle cells
interconnected by contiguous cytoplasmic bridges. This relates to electrical
stimulation of one cell spreading to neighboring cells.
First aid
See cardiac arrest for emergencies involving the heart
If a person is encountered in cardiac arrest (no heartbeat), cardiopulmonary
resuscitation (CPR) should be started and help called. If an automated external
defibrillator is available, this device may automatically administer
defibrillation if this is indicated. Usually, if there is enough time, the
victim can be rushed to the hospital where he or she will be cared for by a
cardiologist, a doctor who specializes in the heart and lungs.
Food use
The hearts of cattle, sheep, pigs, chickens and certain fowl are consumed in
many countries. They are counted among offal, but being a muscle, the taste of
heart is like regular meat. It resembles venison in structure and taste.
As a symbol
For more details on this topic, see Heart (symbol).
and Heart (Anthropology)
The heart was historically seen by some as the seat of the soul and the organ
responsible for human thought. The Romans for example noticed that changing
heart rates often corresponded with emotions such as fear, love and excitement.
While it is now known that the heart has nothing to do with thoughts or emotions
as such, people still carry on using the term "heart" metaphorically when
talking about love. When used in this metaphorical sense, the heart is often
illustrated as an icon (♥).
The term "heart" can also refer to the core or center of anything e.g. "The
heart of the matter". The center of the world, the magma, is the "heart of the
world."
The Aztec civilization used the heart as a sacrificial token during the
sacrifice of a human being. The priest used a stone knife to cut into the
thoracic cavity and remove the heart, upon which it would be placed on a stone
altar as an offering to the gods. The greatest sacrifice under the reign of
Montezuma involved the removal of the hearts of over 12,000 enemy soldiers.
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