Circulation and Gas Exchange

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The heart rate, also called the pulse, is the number of beats per minute.

The stroke volume is the amount of blood pumped in a single contraction.

The cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume.

Slide 30

Four valves prevent backflow of blood in the heart:

The atrioventricular (AV) valves separate each atrium and ventricle.

The semilunar valves control blood flow to the aorta and the pulmonary artery.

The “lub-dup” sound of a heart beat is caused by the recoil of blood against the AV valves (lub) then against the semilunar (dup) valves.

Backflow of blood through a defective valve causes a heart murmur.

Slide 31

Maintaining the Heart’s Rhythic Beat

Some cardiac muscle cells are self-excitable = they contract without any signal from the nervous system.

The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which cardiac muscle cells contract.

Impulses from the SA node travel to the atrioventricular (AV) node. At the AV node, the impulses are delayed and then travel to the Purkinje fibers that make the ventricles contract.

Impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG). The pacemaker is influenced by nerves, hormones, body temperature, and exercise.

Slide 32

Control of heart rhyth

Signals spread

throughout

ventricles.

4

Purkinje Fibers:

ventricles contract

Pacemaker

generates wave of

signals to contract.

1

SA node

(pacemaker)

ECG

Signals are

delayed at

AV node.

2

AV

node

Signals pass

to heart apex.

3

Bundle

branches

Heart

apex

Slide 33

Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels

The physical principles that govern movement of water in plumbing systems also influence the functioning of animal circulatory systems.

The epithelial layer that lines blood vessels is called the endothelium.

Slide 34

Structure of blood vessels

Artery

Vein

SEM

100 µm

Endothelium

Artery

Smooth

muscle

Connective

tissue

Capillary

Basal lamina

Endothelium

Smooth

muscle

Connective

tissue

Valve

Vein

Arteriole

Venule

Red blood cell

Capillary

15 µm

LM

Slide 35