This document summarizes circulatory responses to exercise. It discusses how the cardiovascular system increases oxygen delivery to active muscles during exercise through two adjustments: increased cardiac output from higher heart rate and stroke volume, and redistribution of blood flow from inactive organs to active muscles. The heart is divided into four chambers that pump deoxygenated blood to the lungs and oxygenated blood to the body tissues through separate pulmonary and systemic circuits.

1. Circulatory Responses
To Exercise , 169

2. The primary purpose of the cardio
respiratory system is to deliver
adequate amounts of oxygen and
remove wastes from body tissues

3. One of the major challenges to
homeostasis posed by exercise is the
increased muscular demand for oxygen;
during heavy exercise the demand may be
fifteen to twenty-five times greater than at
rest.

4. To meet the increased oxygen demands of
muscle during exercise, two major adjustments
of blood flow must be made :
(I) an increased cardiac output (i.e, increased
amount of blood pumped per minute by the
heart) and
(2) a redistribution of blood flow from inactive
organs to the active skeletal muscles.

5. Organization of The Circulatory
System
The human circulatory system is a closed
loop that circulates blood to all body
tissues.
Blood travels away from the heart in
arteries and returns to the heart by way of
veins.

6. The system is considered "closed“
because arteries and veins are
continuous with each other through
smaller vessels

7. As the vessels become microscopic they form
arterioles, which eventually develop into "beds"
of much smaller vessels called capillaries.
 Capillaries are the smallest and most numerous
of blood vessels; all exchanges of oxygen,
carbon dioxide, and nutrients between tissues
and the circulatory system occur across
capillary beds.

8. Blood passes from capillary beds to small
venous vessels called venules.
As venules move back toward the heart.
they increase in size and become veins .
The mixture of venous blood from both the
upper and lower body that accumulates in
the right side of the heart is termed mixed
venous blood.

9. Structure of the Heart
The heart is divided into four chambers
and is often considered to be two pumps in
one .
The right atrium and right ventricle form
the right pump, and the left atrium and left
ventricle combine to make the left pump

11. The right side of the heart is separated
from the left side by a muscular wall
called the inter ventricular septum.
This septum prevents the mixing of
blood from the two sides of the heart.

12. Pulmonary and Systemic
Circuits
 The heart can be considered as two pumps in one.
 The right side of the heart pumps blood that is partially
depleted of its oxygen content and contains an
elevated carbon dioxide content as a result of gas
exchange in the various tissues of the body.
 This blood is delivered from the right heart into the
lungs through the pulmonary circuit.

13. At the lungs, oxygen is loaded into the
blood and carbon dioxide is released.
 This "oxygenated“ blood then travels to
the left side of the heart and is pumped
to the various tissues of the body via
the systemic circuit

14. HEART: MYOCARDIUM AND
CARDIAC CYCLE
Myocardium:
The wall of the heart is composed of three layers:
(I) An outer layer called the epicardium.
(2) A muscular middle layer, the myocardium ,
and
(3) An inner layer known as the endocardium

15. It is the myocardium, or heart muscle, that
is responsible for contracting and forcing
blood out of the heart.
The myocardium receives its blood supply
via the right and left coronary arteries.

16. Maintaining a constant blood supply to
the heart via the coronary arteries is
critical because, even at rest, the heart
has a high demand for oxygen and
nutrients.

17. When coronary blood now is disrupted (ie.,
blockage of a coronary blood vessel) for
more than several minutes, permanent
damage to the heart occurs .
 This type of injury results in the death of
cardiac muscle cells and is commonly
called a heart attack or myocardial
infarction.

18. Heart muscle differs from skeletal muscle in several
ways.
 First, cardiac muscle fibers are shorter than skeletal
muscle fibers and are connected in a tight series.
 Further, cardiac fibers are typically branched
,whereas skeletal muscle fibers are elongated and do
not branch .
 Also, cardiac muscLe contraction is involuntary,
whereas skeletal muscle contractions are under
voluntary control.

19. Heart muscle fibers are highly aerobic and
contain large numbers of mitochondria.
 Note, however, that cardiac muscle fibers
contain many more mitochondria than type
I, slow skeletal muscle fibers.
This fact highlights the importance of
continuous aerobic metabolism in the heart

20. Blood pressure can be increased by one or
all of the following factors :
A. Increase in blood volume,
B. Increase in heart rate,
C. Increased blood viscosity,
D increase in stroke volume, and/or
E. Increased peripheral resistance.

26. CARDIAC OUTPUT
Cardiac output (0) is the product of the
heart rate (HR) and the stroke volume (SV)
(amount of blood pumped per heartbeat)
(} =HR x SV
Thus, cardiac output can be increased due
to a rise in either heart rate or stroke
volume

27. Approximately 0.1 second after the
atrial contraction, the ventricles
contract and deliver blood into both the
systemic and pulmonary circuits.

28. CARDIAC CYCLE
The cardiac cycle refers to the
repeating pattern of contraction and
relaxation of the heart.
The contraction phase is called systole
and the relaxation period is called
diastole.

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