The

Mammalian

Heart

The Mammalian Circulatory System

Recall:

What are the 3 cycles of the mammalian circulatory

system? What are their functions?

What are the three main vessel types in the

mammalian circulatory system? What are their

functions?

What are the main components of blood? What are

their functions?

carotid artery

pulmonary vein

mesenteric arteries

aorta

renal artery

iliac artery

jugular vein

pulmonary artery

hepatic vein

superior vena cava

renal vein

iliac vein

inferior vena cava

hepatic portal vein

aorta

pulmonary artery

pulmonary veins

left atrium

atrioventricular valve

(bicuspid valve)

semilunar valve

left ventricle

septum

superior vena cava

inferior vena cava

atrioventricular valve

(tricuspid valve)

right atrium

right ventricle

semilunar valve

Cardiac Circulation

From the

upper body

From the

lower body

To the

lungs

From the

lungs

To the

upper body

To the

lower body

To the

lungs

From the

lungs

Directional Blood Flow

The heart itself is divided into 4 chambers and 2 sides separated by a septum.

Blood only flows in one direction in the circulatory system.

Blood returns to the heart through veins and exits the heart through arteries.

Veins bring blood to the atria. Blood then flows to the ventricles. The blood then exits the heart through arteries.

To keep blood flowing in one direction in the heart, there are valves that prevent backflow of the blood when the close. These valves only open in one direction.

Control of Heartbeat

A heartbeat is divided into periods of relaxations

(diastole) and contractions (systole).

During diastole, the heart muscles are relaxed.

Blood flows into the atriums through the veins.

The heart has two nodes which are responsible for

controlling contraction of the chambers which

results in a heartbeat.

Control of Heartbeat

The sinoatrial node (the pacemaker of the heart)

then sends out a signal that contracts the atriums

(atrial systole). This causes blood to flow past the

atrioventricular valves into the ventricles.

The atrioventricular node then sends out a signal

that contracts the ventricles (ventricular systole). This

causes the atrioventricular valves to close, and the

semilunar valves open.

The “lub-dub” sound of a heart beat is the sound of

first the atrioventricular valves closing and then the

semi-lunar valves closing.

Blood Pressure

Upon contraction of the ventricles (systole), blood

rushes out into the arteries. This produces high

pressure in the arteries.

When the heart muscles relax and blood is returning

to the heart, there is lower pressure in the arteries.

When blood pressure readings are given as two

numbers, they represent the pressure at systole and

at diastole.

E.g. 120

80mm Hg

Electrocardiogram

When the SA node and the AV node send out

signals, they are electrical impulses that travel along

the walls of the atria and ventricles, causing them to

contract.

An electrocardiogram (ECG) can measure the

change in voltage for these impulses which

produces an electrocardiograph which displays a

regular pattern for a heartbeat.

An irregular pattern indicates fibrillation, which is a

random contracting of muscles which can

sometimes be reset by a strong electrical current to

the heart.

Cardiac Output

Cardiac output is a measure of the volume of blood pumped from each ventricle per unit of time.

Cardiac output is affected by two factors: stroke volume and heart rate.

Cardiac output = stroke volume x heart rate

Stroke volume is the amount of blood pumped out of the heart in a heartbeat.

Heart rate is the number of beats per period of time.

Average stroke volume is around 70 mL and average resting heart rate is around 70 beats per minute. What is the cardiac output?

If an average person has 5L of blood, how long would it take to pump their total blood volume?

Heart Rate and Fitness

Maximum heart rate is the highest heart rate that

can be attained during high physical activity. This

rate is reduced with age.

However, maximum heart rate does not seem to

correlate with fitness. The time to return to a resting

heart rate seems to be a better indicator of physical

fitness.

A low resting heart rate is also associated with

general physical fitness as a lower number of beats

is needed to delivery blood to the body. This

indicate efficiency per pump.

Stroke Volume and Fitness

There are two factors that affect stroke volume:

1. How easily the heart fills with blood.

i. This is affected by distensibility (stretchiness) of the

ventricles.

2. How easily the heart empties the blood.

i. This is affected by the strength of ventricular

contractions.

Regular cardiovascular exercise can increase stroke

volume by enlarging and strengthening the

chambers. Cardiovascular exercise can also increase

distensibility of the ventricles.

Atherosclerosis

Build-up of fatty material forms a plaque through a

chain of reactions that blocks blood flow in the

artery.

Medication, an angioplasty or a coronary bypass

may be necessary to treat the problems of high

blood pressure and blood clots that are associated

with arteriosclerosis.