THE CIRCULATORY SYSTEM
Anatomy of the Circulatory System
The circulatory system is composed of the __heart_, blood vessels, and blood.
Function of the circulatory system - transport essential materials (__oxygen__, fuel
molecules, __hormones__, etc.) throughout the body to cells where they are needed and
to collect waste materials (_carbon diaoxide___, _lactic acid__, urea, etc.) generated by
the body's metabolic activity.
Circulatory system is divided into two sections:
(a) Pulmonary circuit - blood vessels going to and from the __lungs__
(b) __Systemic__ circuit - blood vessels going to and from the rest of the tissues of the
The heart is a four chamber, __muscular___ __pump__ which propels blood through
the blood vessels.
Atria - the two _upper__ chambers of the heart
Ventricles - the two lower chambers
A __septum__ divides the left and right sides of the heart two pumps. The right
ventricle pumps blood through the ___pulmonary__ circuit while left ventricle pumps
blood through the __systemic__ circuit.
The wall of the left ventricle is _thicker__ than the wall of the right ventricle because
the systemic circulation is a much higher pressure system than the pulmonary
The direction of blood flow through the heart is controlled by unidirectional
Heart murmur - valve is damaged or does not close properly ---> blood regurgitates,
causing a noise.
The heart muscle (myocardium) is a specialized type of muscle - __cardiac_ muscle.
Unlike skeletal muscle, all of the fibers or cells in cardiac muscle are anatomically
__interconnected___ - functional syncytium. When one fiber contracts, all fibers
The fibers of the atria are separate from the fibers of the ventricles.
B. Conduction System of the Heart
The heart's inherent contractile rhythm originates in an area of specialized tissue
located in the posterior wall of the right atrium - the ___S-A node__, the normal
pacemaker of the heart.
Pathway of conduction of the wave of depolarization (cardiac impulse) across the heart:
Atrial muscle fibers contraction
A-V node A-V bundle left and right bundle branches _Purkinhie
fibers__ which travel throughout the ventricular myocardium
simultaneous contraction of the left and right __ventricles__.
The wave of depolarization is delayed in the A-V node for approximately 0.10 seconds
in order to give the atria time to contract and empty their contents into the ventricles.
Electrocardiography (ECG) - record the wave of depolarization as it passes across the
heart using _electrodes__ on the surface of the body.
Components of a normal ECG waveform:
P wave - represents __atrial__ depolarization
QRS wave - represents _ventricular___ depolarization
T wave - represents ventricular __repolarization____
Arrhythmia - an irregularity in the ___rhythm____ of the heartbeat
Diagnosing arrhythmias - look at heart rate, amplitude and shapes of the components of
the ECG waveform, and time intervals.
[Don’t need to know.]
Examples of arrhythmias:
a) atrial - tachycardia
b) nodal - second and third degree heart blocks
c) ventricular - premature ventricular contraction (PVC), ventricular tachycardia,
C. Blood Supply to the Heart
The heart muscle is supplied by two major arteries which originate from the aorta just
above the aortic valve - left _coronary__ artery and right __coronary_ artery. The large
veins of the heart converge and empty into the right atrium.
Since cardiac muscle is highly dependent on aerobic metabolism, it has a rich _blood__
supply. At rest, normal blood flow to the myocardium is about _5%_ of the total 3
cardiac output. Approximately ___70-80%__ of the oxygen is extracted from blood
flowing in the coronary vessels compared to an average of _30%__ in other tissues.
D. Blood Vessels
Arteries - blood vessels that carry blood __away__ from the heart. They range in size
from the aorta which is about 25 mm in diameter in man to those about 0.5 mm.
Going from large arteries medium-sized arteries small arteries _arterioles__,
there is less elastic tissue in the wall of the artery and more __smooth__ muscle.
Arterioles - arteries under 0.5 mm in diameter
By constricting or relaxing the thick layer of _smooth_ muscle in the walls of arterioles,
blood flow can be increased or decreased to various capillaries.
Arteries and arterioles constitute the __high__ pressure part of the circulatory system.
Capillaries - very tiny (10 microns diameter), thin-walled vessels. This is the site of
exchange of __nutrients/wastes_____ and _gasesH__ between the blood and tissues.
All other organs of the circulatory system exist only to serve the capillary beds.
Capillaries in the human body:
- surface area = 6000 sq. meters
- 60,000 miles long
- mass - twice the size of the liver
Venules - small vessels which conduct venous blood from capillaries to __veins_
Veins - vessels that convey blood __toward__ the heart.
In general, veins are of greater ___diameter__, but thinner-walled than the arteries with
which they travel. There are both superficial and deep veins
Veins also have _smooth__ muscle in their walls which allow them to change their
[List of arteries and veins that we need to memorize are in the lab manual, unit 16]
The venules and the veins constitute the _low_ pressure part of the circulatory system.
Valves - found in those _veins__ which carry blood against the force of __gravity__,
especially in the veins of the legs
Mechanisms involved in return of blood to the heart:
a) __Pressure___ difference between left ventricle and right atrium
- 120 mm Hg - 3 mm Hg = 117 mm Hg driving pressure
b) Skeletal muscle pump - active muscles squeeze the _veins_ and push the blood
towards the heart 4
c) Respiratory pump - decreased pressure in thoracic cavity during _inspiration__
easier for blood to return from lower portions of body via inferior vena cava
thoracic cavity right atrium of heart
Blood is composed of specialized cells (red blood cells, white blood cells, and platelets)
suspended in a liquid, _plasma__ which makes up 50 to 60% of blood by volume.
The blood volum