Closed and Open Circulatory Systems

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley

Closed and Open Circulatory Systems

Closed system: Blood never leaves vessels.

Blood travelsthrough closedblood vessels

Single heart

Lymph travelsthrough closedlymph vessels


The Evolution of the Vertebrate Circulatory System

Fish

Two circulatory loops

1 circuit2-chambered heart

Frogs

Gills Lung

Turtles, lizards2 circuits3-chambered heart

Lung

2 circuits“5-chambered” heart

Crocodiles

Lung

2 circuits4-chambered heart

Birds

Lung


Mammals

Lung


Body Body BodyBody Body Body

Three-chambered heart

Ventricle divided into chambers

A AtriumV Ventricle

A V A

V

A A V

A A V

A V

A V

A

V

A

V

A

V


The Human Heart

AortaPulmonaryartery

Pulmonaryvein

Leftatrium

Semilunarvalves

Atrioventricularvalve

Leftventricle

Rightatrium

Atrioventricularvalve

Rightventricle

Inferiorvena cava

Superiorvena cava 6

Pulmonary circulation

4

1

25

3

Blood returns to heartfrom body, enters rightatrium.

Blood is pumpedfrom right ventricleto lungs.

Blood entersright ventricle.

Systemic circulation

Blood is pumped fromleft ventricle to body.

Blood returns to leftatrium from lungs.

Blood enters leftventricle.

6.

4.

1.

2.

5.

3.


Partial Pressures of Gases Vary throughout the Human Circulatory System

Pulmonary circulation

Systemic circulation

Venae cavae

Pulmonary arteryAorta

Blood leaving tissue capillariesPO2 40 mm HgPCO2 45 mm Hg

Pulmonary vein

Tissues PO2 40 mm HgPCO2 45 mm Hg

Blood enteringtissue capillariesPO2 140 mm HgPCO2 40 mm Hg

Inhaled air PO2 160 mm HgPCO2 0.3 mm Hg

Exhaled air PO2 120 mm HgPCO2 27 mm Hg

Blood enteringalveolar capillariesPO2 40 mm HgPCO2 45 mm Hg

Blood leavingalveolar capillariesPO2 104 mm HgPCO2 40 mm HgAlveoli of lungs

PO2 104 mm HgPCO2 40 mm Hg


Blood Pressure Changes during the Cardiac Cycle

Systolic blood pressure

Diastolic blood pressure

Ventricularpressure

Atrial pressure

Atrioventricularvalves open

Aortic pressure

Aortic valves closes

Atrioventricularvalves close

Aortic valve opens

Ventricular systole Ventricular diastole

Cardiac cycle


EKGs Record Electrical Events Associated with Cardiac Muscle Contraction

SA nodeactivatesatria

AVnodedelay

Electricalactivityin atria

Electrical activity in

ventricles

Ventricles recover


Patterns in Blood Pressure and Blood Flow

• Blood pressure is the force that blood exerts on the walls of arteries, capillaries, and veins.

• Blood pressure drops dramatically as blood moves through the capillaries, because the total cross-sectional area of blood vessels in the circulatory system increases greatly.

• The drop in blood pressure decreases the rate of blood flow to allow sufficient time for gases, nutrients, and wastes to diffuse between tissues and blood in the capillaries.

• Falling blood pressure is detected by baroreceptors in the walls of the heart and the major arteries.


Blood Pressure Drops Dramatically in the Circulatory System

From heart Capillaries Return to heart

Velocity

Total area


Patterns in Blood Pressure and Blood Flow

• When baroreceptors detect a major decrease in blood pressure, they trigger electrical signals that change the heart’s output and vessel diameter:

(1)Cardiac output is increased by an increase in both heart rate and the amount of blood pushed out by the ventricles.

(2)Arterioles serving the capillaries of noncritical tissues such as the skin and intestines are constricted to divert blood to more critical organs.

(3)The veins are constricted, shifting blood volume toward the heart and arteries to maintain blood pressure and flow to vital organs.

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Closed and Open Circulatory Systems