Circulatory System--BIO 0061 The Circulatory System rev 6-10 The circulatory system consists of the heart, blood vessels and the blood itself. The circulatory

Circulatory System--BIO 006 1

The Circulatory System rev 6-10

•The circulatory system consists of the heart, blood vessels and the blood itself.

•The circulatory system is essential •to supply all cells with what they need and •remove substances they no longer need.

•This system maintains homeostasis.


Types of Blood VesselsTypes of Blood Vessels

Arteries—carry blood away from the heart Veins—carry blood toward the heart Capillaries—carry blood from the arterioles

to the venules. Exchange of nutrients, wastes and respiratory gases takes place here because capillaries have only one layer.

Bigggest Artery, Biggest Vein• Aorta: carries blood out of the left ventricle of

the heart• Inferior and Superior Vena Cava return

blood to the right atrium of the heart after the blood has circulated throughout the body.


Structure--Arteries inner layer of endothelial cells middle: smooth muscle tissue

This layer is thicker in arteries than in veins outermost layer of connective tissue

Structure—Veins Inner: layer of endothelial cells

Valves prevent backward movement of blood Middle: smooth muscle tissue

thinner layer in veins than in arteries outermost layer of connective tissue

can be thicker than in arteries


Functions Arteries—take blood away from the heart to the body

distribute nutrients and gases; movement of blood is under higher pressure than in

veins; assist in maintaining blood pressure

Veins---return blood to the heart; lower pressure than in arteries; can act as a blood volume reservoir for blood

because they can expand veins have larger diameters (lumen) than arteries

blood-cardiovascular 5

• the larger diameter of veins allows them to stretch to accommodate large volumes of blood at low pressures– because veins can stretch, it is more difficult for

them to return blood to the heart against the force of gravity

– people who spend a lot of time on their feet may get varicose veins because of this

Factors which help veins to return blood to heart

• Contraction of skeletal muscles—skeletal muscle pump– as we move, muscles contract and relax and they

press against veins and help push blood to the heart


– One-way valves—blood can only flow in one direction

• Open passively to allow blood to move toward the heart and close whenever blood begins to flow backward


Pressure changes associated with breathing– movements associated with breathing also help

pump blood. This is called a respiratory pump and helps to push blood from the abdomen to the chest and to the heart.

• when we breathe, there are pressure changes in the thoracic and abdominal cavities

• during inhalation, abdominal pressure increases and squeezes abdominal veins

• simultaneously, pressure within the thoracic cavity decreases which dilates the thoracic veins and thus propels the blood.


Venous return of blood to the heart depends on five mechanisms:• a strongly beating heart, • adequate arterial blood pressure, • valves in the veins, • pumping action of skeletal muscles as

they contract (skeletal muscle pump), and • changing pressures in the chest cavity

caused by breathing (respiratory pump)


The HeartStructure: composed of cardiac muscle enclosed

by pericardium, a fibrous sac• located in mediastinum

– is approximately the size of a closed fist

Pericardium protects the heart, anchors it to surrounding structures, prevents it from overfilling with blood– Pericardial cavity separates it from heart muscle itself

and contains a tiny amount of fluid to allow heart and pericardium to glide smoothly every time the heart contracts

– Rate of pumping usually controlled by brain


Anatomy

Heart chambers The two upper chambers are called the right

and left atria and are the chambers which receive blood

The two lower chambers are the right and left ventricles; these are the chambers which eject blood

The wall of each heart chamber is composed of cardiac muscle tissue called myocardium


In order to keep the blood moving in a forward direction, there are valves in between each area the blood must go.

Valves of the heart Atrioventricular or AV valves are located

between the atria and the ventriclesLeft side: bicuspid or mitral valveRight side: tricuspid valve

Chordae tendineae are located inferiorly to the AV valves and

attach the valves to the heart wall


• Semilunar Valves are located between the 2 ventricles and the arteries that carry blood away from the heart when a contraction begins.– Pulmonary semilunar valve is located at the

beginning of the pulmonary artery– Aortic semilunar valve is located at the beginning of

the aorta


Blood flow through the heart venous blood enters the right atrium through the

superior and inferior venae cavae (biggest vein) passes from the right atrium through the tricuspid

valve to the right ventricle; from the right ventricle it passes through the

pulmonary semilunar valve to the pulmonary artery to the lungs

from the lungs blood flows to the left atrium through the pulmonary vein

passes through the bicuspid (mitral) valve to the left ventricle;

blood in the left ventricle is pumped through the aortic semilunar valve into the aorta (biggest artery) and is distributed to the entire body


• There are actually 2 circulations through the heart:

• The pulmonary circulation involves movement of blood from the right ventricle to the pulmonary arteries to the lungs and then through the pulmonary veins back to the left atria.

• The systemic circulation involves movement of the blood from the left ventricle throughout the body.


• Part of the systemic circulation includes the coronary circulation: blood supply to the heart muscle itself Blood, which supplies oxygen and nutrients

to the myocardium of the heart, flows from the first branch off the aorta through the right and left coronary arteries

Blockage of blood flow through the coronary arteries can cause a myocardial infarction (heart attack)


Types of CirculationTypes of Circulation

Systemic circulation Carries blood throughout the body Path goes from left ventricle through aorta, smaller

arteries, arterioles, capillaries, venules, inferior and superior venae cavae, to right atrium

Pulmonary circulation Carries blood to and from the lungs; arteries deliver

deoxygenated blood to the lungs for gas exchange

Path goes from right ventricle through pulmonary arteries, lungs, pulmonary veins, to left atrium


Hepatic portal circulation (blood route through the liver) • Veins from the spleen, stomach, pancreas,

gallbladder and intestines detour their blood to the liver via the hepatic portal vein

• Blood then goes through the capillaries of the liver where excess glucose from our meals is removed and stored as glycogen

– Blood is also detoxified---poisonous substances, alcohol, drugs are removed

• Then the blood enters into the systemic circulation via the inferior vena cava


Heart pumping– The contraction of the heart is called systole;

relaxation is diastole– When the heart beats, the atria contract first

and force blood into the ventricles– Once filled, the ventricles contract and force

blood out of the heart


Electrical Conduction System of the Heart Intercalated disks are electrical connectors that

join all the cardiac muscle fibers in a region together so that they receive their impulse and then contract at about the same time

4 structures are located in the wall of the heart. These are specialized to initiate strong impulses and rapidly conduct them to certain regions in the wall of the heart. This ensures that first the atria contract and then the ventricles contract in an efficient pattern


Cardiac Anatomy Quiz


Blood PressureBlood Pressure

• Blood pressure measures the force of blood in the blood vessels

• Highest in arteries, lowest in veins• Blood pressure causes blood to circulate—liquids

can flow only from the area where pressure is higher to where it is lower

• Top number= systolic reading—force the heart uses to pump the blood

• Bottom number= diastolic reading—heart at rest or relaxing

• Normal is approximately 120/70-80


• Blood volume, heartbeat, and viscosity (thickness) are the main factors that produce blood pressure

• Blood pressure varies within normal range from time to time

Pulse• Definition—alternate expansion and recoil

of the blood vessel wall• Places where the pulse is typically taken:

carotid artery, brachial artery, radial artery


Cardiovascular Disorders Angina pectoris: chest pain caused by

inadequate oxygen to the heart Pericarditis: layer of the coverings of the

heart becomes inflamed. This causes pain each time the heart beats

Heart murmur is created by obstructions the blood must flow over or if the valves don’t function properly

Coronary bypass surgery: veins from other parts of the body are used to bypass blockages in coronary arteries

Aneurysm: the arterial wall has a weakness and blood pushes it out into a balloon shape


• Hypertension: high blood pressure– Signs: headache, blurred vision– Causes: kidney disorders, smoking, overweight,

stress• Hypotension: blood pressure too low so blood can’t be

pushed throughout the body and back to the heart; generally thought of as reducing blood flow to the brain– Signs: dizziness, fainting– Causes: orthostatic, severe burns, blood loss


• Myocardial infarction/heart attack: permanent cardiac damage

• Congestive heart failure: decrease in pumping efficiency

• Embolism: blockage of blood vessels– Thrombus=clot that doesn’t move– Embolus=clot that travels through the circulatory system

• Stroke or Cerebrovascular Accident or brain attack: impaired blood flow with subsequent damage to the brain

Disorders of Blood Clotting• Thrombus: clot forms in the blood vessel• Embolus: clot which breaks off and circulates through

the blood– Medications to dissolve clots:

• Streptokinase and recombinant tissue plasminogen activator

• Hemophilia: Inherited condition caused by a deficiency of one or more clotting factors (known as clotting factor VIII)– When a blood vessel is damaged, blood either clots

very slowly or not at all



Reducing the Risks of Heart Disease

• Smoking: don’t • Weight: maintain a normal weight (weighing too much

will increase the risk of a heart attack or stroke)• Monitor cholesterol levels, HDL, LDL, triglycerides• Regular exercise• Blood pressure: treat hypertension• Control of diabetes mellitus• Stress: avoid chronic stress

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Circulatory System--BIO 0061 The Circulatory System rev 6-10 The circulatory system consists of the heart, blood vessels and the blood itself. The circulatory