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CLASS NOTES
CIRCULATORY SYSTEM
Function
 method by which oxygen, nutrients and waste products are exchanged
Types
 open circulatory system – circulating fluid is not contained in vessels
present in simple animals
use diffusion to move oxygen, nutrients and waste products
 closed circulatory system – circulating fluid (blood) is contained in a
system of vessels
Components of the Circulatory System
 blood
 blood vessels
 heart
Blood
 blood volume of an average adult is 4-5 liters (6-8% of body weight)
 composed of 55% plasma and 45% cells
 plasma (yellowish color fluid)
a. water – 90%
b. plasma proteins
--albumin – the main plasma protein, it functions as a carrier and to
maintain osmotic pressure
--globulin – used in the immune system (defense)
--fibrinogen – used for blood clotting
c. ions, sugars, lipids, amino acids, hormones, vitamins and gases
 cells in blood
a. red blood cells (RBC or erythrocytes) – function in oxygen and carbon
dioxide transport
b. white blood cells (WBC or leukocytes) – function in the immune system
(defense against foreign substances)
c. platelets – function in clot formation
Lymphatic System
 network of vessels that collects fluid (called lymph) lost by blood and
returns it to the circulatory system
 lymph nodes – organs located in the throat, armpits, groin that act as filters
and make WBC to prevent harmful material from invading body cells
Blood Vessels
 artery – large muscular vessel that carries blood away from the heart
--aorta is the largest artery in the body
 arteriole – a smaller vessel that branches off the artery to capillary
 capillary – single cell layer thick, it forms a network that is the site of gas
exchange (oxygen and carbon dioxide)
 venule – thicker vessel that branches off the capillaries
 vein – a large blood vessel that carries blood to the heart
--inferior vena cava – large vein carrying blood from the lower part of the
body to the right atria
--superior vena cava – large vein carrying blood from the upper part of the
body to the right atria
Heart
 composed primarily of muscle – myocardium
 also composed of nervous tissue and connective tissue lining the inside of
the heart
 pericardium – sac covering for protection and decrease friction
 septum – muscular wall that divides the heart into a right side (pathway to
lungs) and a left side (pathway to the body)
 4 chambers – 2 atria (upper chambers) and 2 ventricles (lower chambers)
 valves prevent the backward flow of blood
a. tricuspid valve – between right atria and right ventricle
b. bicuspid valve – between left ventricle and left atria
c. semilunar valves- between the ventricles and the large vessels that flow
away from the heart (pulmonary artery and aorta)
Blood Pathway
 Right or left vena cava right atrium  tricuspid valve  right ventricle 
pulmonary valve  pulmonary artery lungs pulmonary vein left
atrium bicuspid (mitral)valve left ventricle aortic valve aorta
 coronary arteries supply the heart with blood
Control of Heartbeat
 heartbeat can be detected 4 weeks after fertilization
 “lubb-dubb” sound due to valves closing “lubb” tricuspid and bicuspid
valves close “dubb” the pulmonary valves and aortic valves close
 sino-atrial(SA) node in the right atria, also called the “pacemaker” is
stimulated and causes the atria to contract
 the impulse is then picked up by the atrioventricular(AV) node and carried
to the ventricles
 the heart beats 72 times/minute 70 ml/contraction
5.5 liter/minute
 exercise increases the heart rate up to 200/minute
 hormones such as epinephrine (adrenalin) increase heart rate
 ECG-electrocardiogram diagram showing the functioning of the heart
 cardiac defibrillator – strong electrical current is applied to get the heart to
start beating
Blood Pressure
 the force of the blood on the wall of the arteries
 systole – the force felt in the artery when the ventricles contract
 diastole- the force felt in the artery when the ventricles relax
 typical blood pressure is 120/80
 140/90 is considered high (risk for cardiovascular disease)
 regulation of blood pressure
a. medulla oblongata – releases neurotransmitters (chemical messengers)
that cause the arteries to constrict or dilate
b. kidneys remove more water from blood to decrease blood
volume(resulting in a decrease in blood pressure)
Two Circuits of Blood Flow
1. pulmonary circulation
 carries oxygen depleted blood from the heart to the lungs and oxygen
rich blood back to the heart
 pulmonary artery is the only artery that carries oxygen depleted
blood
2. systemic circulation
 carries oxygen rich blood from the heart to the rest of the body and
oxygen-depleted blood back to the heart from the rest of the body
 pulmonary vein is the only vein that carries oxygen rich blood
Disorders of the Circulatory System
1. cardiovascular disease
 disorder involving the heart and blood vessels
2. atherosclerosis
 Condition in which fatty deposits called plaque accumulate on the
inner walls of arteries
3. hypertension
 high blood pressure
 caused by hardening of arteries, stress, heredity, poor diet, cigarette
smoking, aging
 forces heart to work harder and can result in damage to heart and
vessels
4. coronary thrombosis
 type of heart attack caused by a blockage of the coronary arteries
depriving the heart of oxygen
5. stroke
 caused by insufficient blood flow to the brain
 80% due to blood clot 20% due to bleeding in the brain
 may result in paralysis, lack of speech or death depending upon the
area of the brain that is affected
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9.
 symptoms- numbness in face, arm, leg; confusion, trouble speaking,
loss of balance
angina pectoris
 type of heart attack caused by narrowing of the coronary arteries
depriving the heart of oxygen
anemia
 inability of blood to carry adequate amounts of oxygen due to
defective or decreased number of RBC
leukemia
 disease of the bone marrow in which there is uncontrolled
production of WBC
edema
 blockages or damage to lymphatic vessels
 results in the swelling of tissue due to the build up of fluid (lymph)
10.varicose veins
 valves in veins in the legs weaken so that blood tends to accumulate
in that area