Transcript Nerve activates contraction

Chapter 11- Part 2
The Cardiovascular System
Coronary Circulation
 Blood in the heart chambers does not nourish
the myocardium
 The heart has its own nourishing circulatory
system
 Coronary Arteries
 Branch from the base of the aorta and encircle
the heart in the atrioventricular groove
 Cardiac Veins
 Blood empties into the right atrium via the
Coronary Sinus
Heart Attacks
 Angina Pectoris –
Crushing chest pain
 The result of a situation
in which the myocardium
is deprived of oxygen
 This pain is a warning
that should never be ignored, because if
angina is prolonged, the ischemic heart
cells may die.
Heart Attacks
 Myocardial
Infarction –
“Heart attack”;
Heart cells die
because of a
lack of oxygen
Amount of Work Done by the Heart
 The amount of work the heart does is
incredible!
 In one day it pushes the body’s supply of
~6 quarts of blood through the blood
vessels over 1000 times.
 It actually pumps about 6000 quarts of
blood in a single day!
The Heart: Conduction System
 Two types of controlling systems act to regulate
heart activity:
1. Autonomic Nervous System
 Act like “brakes” and “accelerators” to decrease or
increase the heart rate depending on which division
is activated
2. Intrinsic Conduction System (Nodal System)
 Built into the heart tissue
 Heart muscle cells contract (without nerve impulses)
in a regular, continuous, coordinated way
 Causes heart muscle depolarization in only one
direction – from the atria to the ventricles.
The Heart: Conduction System
 Special tissue sets the pace:
 Sinoatrial Node (SA Node) – Pacemaker
 Tiny cell mass located in the right atrium
 It starts each heartbeat and sets the pace for the
whole heart
 Atrioventricular Node (AV Node)
 Located at the junction of the atria and ventricles
 From the SA node, the impulse spreads through the
atria to the AV node, and then the atria contract
 At the AV node, the impulse is delayed briefly to give
the atria time to finish contracting
Heart Contractions
The Heart: Conduction System
 After the impulse travels through the AV node, it
then passes rapidly through the:
1. Atrioventricular Bundle (AV bundle)
•
Also called bundle of His
2. Bundle Branches
•
Right and left branches
•
Located in the interventricular septum
3. Purkinje Fibers
•
Spreads within the muscles of the ventricle
The Heart: Conduction System
1. First the impulse travels from the SA
Node → AV Node
• Causes the atria to contract
2. Then the impulse travels from the AV
Node → AV Bundle → Bundle Branches
→ Purkinje Fibers
• Results in the “wringing” contraction of
the ventricles that begins at the heart
apex and moves toward the atria.
Some Heart Problems
1. Damage to the SA node
• Can install artificial
pace-makers
2. Ischemia - Lack of blood flow to the heart
muscle
 May lead to fibrillation
 Fibrillation - A rapid uncoordinated
shuddering of the heart muscle
 It looks like a bag of worms
 Makes the heart totally useless as a pump and
is a major cause of death from heart attacks
The Heart: Cardiac Cycle
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
Atria contract simultaneously
Atria relax, then ventricles contract
Systole = Contraction of the ventricles
Diastole = Relaxation of the ventricles
The Heart: Cardiac Cycle
 Cardiac Cycle – Events of one complete
heart beat
 Average heart beats ~75 times per
minute
 The length of
the cardiac
cycle is
normally about
0.8 seconds
Heart Sounds
 You can hear two distinct sounds during
each cardiac cycle: “lub-dup”
1. The first heart sound (“lub”) is caused by
the closing of the AV valves
 Sound is longer and louder than the second
sound
2. The second heart sound (“dup”) is caused
by the closing of the semilunar valves
 Sound tends to be short and sharp
Heart Sounds
 Blood flows silently
as long as the flow
is smooth and
uninterrupted.
 If it strikes obstructions, its flow becomes
turbulent and generates sounds, which
can be heard with a stethoscope.
 Unusual heart sounds, or murmurs,
usually indicate valve problems.
The Heart: Cardiac Output
 Cardiac Output (CO) - Amount
of blood pumped by each side
of the heart in one minute
CO = (heart rate [HR]) x (stroke volume [SV])
 Stroke Volume - Volume of blood pumped by
each ventricle in one contraction
Regulation of Stroke Volume
 The more the cardiac muscle cells are
stretched, the stronger the contraction
will be.
 The important factor stretching the heart
muscle is venous return, the amount of
blood entering the heart and distending its
ventricles.
 Exercise speeds venous return because it
results in increased heart rate and force.
 Blood loss decreases venous return.
Cardiac Output Regulation
Figure 11.7
Regulation of Heart Rate
 Stroke volume tends to be relatively constant.
 However, when blood volume drops suddenly or
when the heart has been seriously weakened,
SV declines, and CO is maintained by a faster
heartbeat.
 Regulation of Heart Rate
1. Although heart rate does not depend on the
nervous system, its rate can be changed
temporarily by the autonomic nervous system.
2. Also modified by various chemicals, hormones,
and ions.
Congestive Heart Failure
 Congestive Heart Failure –
Occurs when the pumping
efficiency of the heart is
depressed so that circulation is
inadequate to meet tissue needs.
 Usually a progressive condition that
reflects weakening of the heart by
coronary atherosclerosis (clogging of the
coronary vessels), persistent high blood
pressure, or multiple myocardial infarcts.
Congestive Heart Failure
 Each side can fail independently of the other.
 Failure of one side puts a greater strain on the
opposite side, and eventually the whole heart fails.
1. Pulmonary Congestion – Failure of the left heart
 Left side is unable to eject the returning blood
 Blood vessels within the lungs become swollen and fluid
leaks into the lung tissue causing pulmonary edema. If
untreated, the person suffocates.
2. Peripheral Congestion – Failure of the right heart
 Blood backs up in the systemic circulation
 Edema is noticeable in the distal parts of the body (feet,
fingers)