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The Circulatory System

The function of a circulatory system is to carryblood or hemolymph into close contact with everycell in the body.The most sophisticated circulatory systems

consist of:one or more pumps called heartsarteries (tough, thick-walled tubes) that carryblood away from the heart under high pressure;small vessels called capillaries whose walls arejust one cell thick, allows the exchange of gasesand other molecules with tissues in networkscalled capillary beds; andvessels called veins that return blood to the

heart under low pressure


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Functions of the Circulatory System

Transport oxygen to cells Transport nutrients from

the digestive system to bodycells

Transport hormones to bodycells

Transport waste from bodycells to excretory organs

Distribute body heat


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How Are Oxygen and Carbon

Dioxide Transported in Blood?

Blood : connective tissue that consists ofcells in a watery extracellular matrixcalled plasmaRemainder of the blood is made up offormed elements: platelets, red blood cells,and several types of white blood cells:Platelets : Cell fragments thatminimize blood loss from ruptured blood

vessels by releasing material that assistsin the formation of clotsWhite blood cells: which are part of theimmune system fight infections


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RBCs

Red blood cells (RBCs):transport oxygen from the lungsto tissues throughout the bodycritical role in transporting

carbon dioxide from tissues tolungsIn humans, red blood cellsmake up 99.9% of the formedelements.

contain an oxygen-carryingmolecule called hemoglobin


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Circulation


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How Does the Heart Work?

In animals with closed circulatorysystems, the heart contains at least twochambers.

the atrium receives blood returning from

circulationthe ventricle generates force to propel theblood through the system.

Atria are separated from ventricles byatrioventricular valves.

The number of distinct heart chambershas increased as vertebrates diversified.


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How Does the Heart Work?

Vertebrates evolved two separate pumpingcircuits:

The pulmonary circulation is a lower-pressure circuit to the lungs.The systemic circulation is a higher-pressure circuit to the rest of the body.


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Components of the Human

Circulatory System

TheHeart

Blood Vessels

BloodLymphatic Vessels

Lymph


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Types of Blood Vessels

Capillaries:smallest vesselsthe site where gases, nutrients,and wastes are exchanged betweenthe blood and other tissues

The smallest veins are venules;carry blood back to the heart afterit passes through the capillariesveins have much thinner wallsand much larger interiordiameters than arteries


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Location ofHeart


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Pericardial Cavity


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Layers of Cardiac Tissue


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Visceral pericardium Outer protective layer composed of a serousmembrane

Includes blood capillaries, lymph capillaries,and nerve fibers.

Myocardium Relatively thick. Consists largely of cardiac muscle tissue

responsible for forcing blood out of the heartchambers.

Muscle fibers are arranged in planes,separated by connective tissues that arerichly supplied with blood capillaries, andnerve fibers.


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Heart Anatomy


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TheHumanHeart

The human circulatory system returns oxygen-depleted blood from the body to the right atriumof the heart through two large veins

the inferior and superior venae cavae.When the right atrium contracts:

deoxygenated blood is sent to the rightventricleit contracts and sends blood out to the lungsvia the pulmonary artery

One-way valves ensure that blood follows only

this path. After blood has circulated through thecapillary beds in the lungs alveoli:it becomes oxygenated

returns to the heart through the pulmonaryveins


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The Human Heart

TheHumanHeart

The oxygenated blood enters the leftatrium:

it contracts and pushes the bloodinto the left ventricle

The contraction of the left ventriclesends oxygenated blood at highpressure out the aorta and into:

the arteriescapillariesveins

forms the systemic circulation


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Heart Anatomy


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Heart Anatomy


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Valves


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bicuspid valve

aortic semi lunar

valve

tricuspid valve

pulmonary semi

lunar valve

Heart ValvesHeart Valves


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The Cardiac Cycle

The contraction phase of the atriaand the ventricles:

called systoleis coordinated with their

relaxation phasecalled diastole

A cardiac cycle:consists of one complete

systole and one completediastole


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Contraction cycle of the heart


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Contraction Cycle of the Heart


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Excitation of the Heart

Depolarization of the atria


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Depolarization of the ventricles


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Circulatory System -Gross and Cool Facts!

The body of an adult containsover 60,000 miles of blood vessels!An adult's heart pumps nearly4000 gallons of blood each day!Your heart beats some 30 million

times a year!The average three-year-old hastwo pints of blood in their body;the average adult at least fivetimes more!A "heartbeat" is really the soundof the valves in the heart closingas they push blood through itschambers.


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