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11.4 The Cardiac Cycle and Circulation
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The Heart is a specialized organ that pumps blood though the body

In mammals, it is a 2-circuit system:
1) PULMONARY CIRCUIT – ___________________________________________
______________________________________________________________
2) SYSTEMIC CIRCUIT–_____________________________________________
______________________________________________________________

Location– it is situated ____________________________________________

Structure – the heart is enclosed in a sac, the _________, a two layered wall. The
space between the two walls is a lubricating fluid that allows the walls of the heart
to slide over one another as the heart beats without friction from other organs.

Heart is composed mostly of ________________ – a muscle type that is exclusive
to the heart only and has the ability to contract and relax quickly

The heart has 4 chambers: Left atrium, Right atrium, Left ventricle, Right ventricle
ATRIA


The atria are ____________________________________________________
o
Right atrium – receives blood from body
o
Left atrium – receives blood from lungs
Cardiac muscle that lines the walls of atria is ______ because the atria responsible
for pumping blood ________________________________________________
VENTRICLES

Ventricles have a _________________ and have _________________ that are
much more powerful than the atria. These thicker walls (especially left ventricle)
pump blood _____________________________________________________

The left and right side of the heart are separated by the __________________

The pumping action of the heart is synchronized (happen at the same time on right
and left side)

Blood flows in one-way (always in the same direction) with the help of __________
that __________________________________________________________

Note: there are two types of valves:
1) atrioventricular valves (AV valves):

_____________________________________

______________________________________________________
2) semilunar valves:

________________________________________

______________________________________________________
Heart Beat / Cardiac Cycle

Heart rate – ____________________________________________________
(measured by taking a pulse)

During a single heart beat, or cardiac cycle, the heart is pumping twice - 2
contractions)

Cardiac muscle is a myogenic muscle: it spontaneously ______________________
_________________________________; it doesn’t need the brain to control it!

The nerve impulses that generate heart contraction originate from a specific region
of the right atrium: the ______________________________, also known as the
_____________________.

The SA node sends out an “electrical signal” to both ________ causing them both
to _________________________. This causes blood to be pushed out of the
_________ and fill up the ______________________.

The ventricles need to now contract to push blood out into the _______________.

Within the right atrium is another area called the
_____________________________________________

The AV node receives a signal from the SA node when it sends its impulse

After 0.1 sec, the AV node sends out its “electrical” signal

The impulse is sent to the ____________________: special conducting fibres
that run down the septum

This causes both ventricles to simultaneously contract, _____________________
______________________________________________________________.

Systole (Systolic phase) – ___________________________

Diastole (Diastolic phase) – ____________________________

Using a stethoscope, you can hear the characteristic hear sounds: “lub-dub, lubdub, lub-dub…”

The “lub” sound is made by the closing of the atrioventricular valves (ventricular
systole)

The “dub” sound is made by the closing of the semilunar valves (ventricular
diastole).
CONTROL OF HEART RATE

The heart mainly controls itself, however, the brain and hormones can influence the
frequency of heart beats.

During times of increased body activity (such as exercise), heart rate needs to
increase to need demand for O2 by body cells and release accumulated CO2. The
brain sends a signal to the adjust frequency accordingly.

Hormones such as adrenaline (epinephrine) can also affect frequency
Analysing the Heartbeat

The cardiac cycle can be monitored using an ______________________ which
measures electrical signals and produces an _________________________ (ECG)