Day 5_heart

Circulatory System
The Mammalian Heart
A hollow muscular organ that contracts
repeatedly without fatigue
It is located between the lungs in the
thoracic cavity
the heart is protected by a protective layer
of thin tissue called the pericardium
It is divided into 4 chambers: the right and left
atria (singular atrium) and right and left
• The right side pumps blood to the lungs
(pulmonary) and the left side pumps blood to
the body (systemic)
atria are collecting chambers that receive
blood from the lungs and body, and then
pump blood to ventricles.
ventricles have a thick muscular wall and
are the pumping chambers that push blood
out through blood vessels and into capillary
beds (in lungs and body).
The valves: In order to prevent backflow of
blood and make sure blood flows in the correct
direction through the heart, there are valves at
a few points:
Semilunar valves
Atrioventriclar valves
The left atrioventricular (AV) valve (bicuspid valve
or mitral valve) is located between the left atrium and
left ventricle. It has two parts (or cusps).
The right atrioventricular valve (tricuspid valve) is
located between the right atrium and right ventricle. It
contains three parts (or cusps).
The aortic semilunar valve is located between the left
atrium and ventricle – allows blood to flow to the rest
of the body.
The pulmonary semilunar valve allows blood to
travel from right ventricle to the lungs.
The “lub dub” sound the heart makes is
actually the sound of first the AV valves
closing and then the SL valves.
NOTE: the septum is the wall that
separates the right and left ventricles.
Systole and Diastole: “lubb-dubb, lubb-dubb”
-Contraction of the ventricles (blood is pushed out of the heart)
-AV valves shut to prevent blood from going back up into the
-Shutting of these valves produces a “lubb” sound
-Relaxation of the heart (heart fills with blood)
- SL valves shut to prevent blood from going back into the
ventricles from the arteries
-Shutting of these valves creates a “dubb” sound
Deoxygenated blood from the body
collects in a vein called the vena cava:
The superior vena cava returns
deoxygenated blood from the upper
portion of the body
the inferior vena cava returns
deoxygenated blood from the lower
portion of the body and legs.
Pathway of blood through
the heart:
Vena cava  right atrium  atrioventricular
valve  right ventricle  semi-lunar valve 
pulmonary arteries  lungs  pulmonary veins
 left atrium  atrioventricular valve  left
ventricle  semi-lunar valve  aorta
Flow of Blood Through the Heart:
Blood from the vena cava collects in the right atrium of the
When the atria contracts, blood flows from the right atrium,
through the left atrioventricular valve into the right
When the right ventricle contracts, it pumps blood out
through the pulmonary semilunar valve into the pulmonary
artery which carries the deoxygenated blood towards the
Oxygenated blood returns to the left atrium of the heart,
through the pulmonary veins.
When the left atrium contracts, blood flows through the
right atrioventricular valve into the left ventricle.
When the left ventricle contracts, blood flows through the
aortic semilunar valve into the systemic circulatory system