Download A&P Chapter 16

The Circulatory
System – The Heart
Part 4: Regulation &
Maintenance
The Heart

The Heart: The pump that supplies force
critical to move blood through the
circulatory system.
 Located
in the thoracic cavity.
 10 ounces total, 12 cm long, 9 cm wide.
 Great vessels attach at superior end, inferior
end tapers off.

Mediastinum: Mass of tissue that extends
from sternum to vertebral column between
the lungs. Contains the heart!
The Heart

Pericardium: The double-walled membrane
surrounding the heart.
 Fibrous
Pericardium: Outer membrane made of
tough connective tissue providing protection &
preventing overstretching of the muscle.
 Serous Pericardium: Inner membrane.



Parietal Layer: Outer layer
Pericardial Cavity: Small gap that is filled with lubricating
paricardial fluid.
Visceral Pericardium aka Epicardium: Inner layer
The Heart

Heart Wall: Made up of 3 layers!
 Epicardium:
The outer layer (and layer of the
serous epicardium).

Composed of mesothelium & connective tissue.
Provides smooth & slippery texture.
 Myocardium:

Middle layer.
Cardiac muscle that makes up the bulk of the heart
& provide contraction force.
 Endocardium:
Smooth lining inside the
chambers & valves; composed of
endothelium.
The Heart

Chambers: 4 chambers total, 2 upper & 2 lower.
 Atria:


Upper chambers, both right & left.
Receive blood!
Auricle: A slight extension to each atria that increases the
total volume.
 Ventricles:



Lower chambers, both right & left.
Pump blood out to the body.
Interatrial Septum: Separates the right & left
atria.
Interventricular Septum: Separates the right &
left ventricles.
The Heart

Valves: Control the one-way flow of blood through the
chambers. 4 total:





Right Atrioventricular (A-V) Valve aka Tricuspid Valve:
Regulates blood flow into the right ventricle.
Left Atrioventricular (A-V) Valve aka Bicuspid Valve aka
Mitral Valve: Regulates blood flow into the left ventricle.
Aortic Valve: Regulates flow from the left ventricle to the aorta.
Pulmonary Valve aka Semi-lunar Valve: Regulates flow from
the right ventricle to the pulmonary trunk.
Chordae Tendineae: Connects the Right & Left A-V
Valves to the papillary muscles.
The Heart

Flow of Blood through the Heart:
 Deoxygenated
blood flows into the heart at the right
atrium.
 Blood passes from the right atrium to the right
ventricle via the Right A-V valve.
 Blood flows from the right ventricle through the
pulmonary valve into the pulmonary trunk (and off to
the lungs!).
 Oxygenated blood re-enters the heart through the
left atrium.
 Blood passes from the left atrium through the left AV valve to the left ventricle.
 Blood flows from the left ventricle through the aortic
valve into the aorta (and out to the body!).
The Heart

Flow of Blood Simplified:
 Pulmonary
Circuit: Right side of the heart
pumps blood to the lungs only.
 Systemic Circuit: Left side of the heart
pumps blood to the rest of the body.
Disorders of the Heart Valves
Stenosis: Failure of a heart valve to fully
open.
 Insufficiency: Failure of a heart valve to
fully close.
 Mitral Valve Prolapse (MVP): Blood leaks
back into the left atrium from the left
ventricle.

Coronary Circulation
Left & Right Coronary Arteries: The first
branches off the aorta that supply the left
& right halves of the heart with blood.
 Great & Middle Cardiac Veins: Return
blood from the heart muscle itself to the
coronary sinus & right atrium.
 Anastomoses: The point where two or
more branches of an artery serving the
same area meet.

Cardiac Muscle Contraction

Cardiac Muscle: Striated, involuntary muscle
specifically found in the heart.
 Rhythmicity:
Property of beating on a regular basis
even without electrical stimulation. This is unique to
cardiac muscle!
 Myocytes: Ends of cardiac muscle cells joined
together by intercalated discs.

Gap junctions between the discs allow for action potentials
(for communication) & desmosomes (to hold the fibers
together).
 Endomysium:
Surrounds the myocytes and supplies
access to capillaries. 10X as many mitochondria as
skeletal muscles.
Autorhythmic Conduction

Cardiac Conduction System: The electrical
conduction system that triggers cardiac muscle
contractions.
 Composed



of nodal tissue (special conductive tissue).
Sinoatrial (SA) Node: The pacemaker of the
heart – sets the heart rhythm at appx. 72 beats
per minute at rest.
Eptopic Pacemaker: Occurs when the heart
rhythm is set by some other site than the SA
node.
Arrhythmia: The term used for any abnormal
cardiac rhythm.
Autorhythmic Conduction

Steps of Autorhythmic Conduction:
 SA
nodes send signals to the
atrioventricular node.
 Atrioventricular node sends signals through
the atrioventricular bundle aka bundle of
his to the ventricles.
 Signal travels from the atrioventricular
bundle to the remainder of the heart via
Perkinje fibers.
Autorhythmic Conduction

Cardiovascular Center: Located in the
medulla oblongata – receives sensory
input from limbic system, cerebral cortex &
sensory systems & interprets the need to
decrease or increase heart rate.
 Cardioacceleratory
Center: Speeds the
heart up.
 Cardioinhibitory Center: Slow the heart
down.
Measuring Cardiac Output

Electrocardiogram aka EKG: Records the
electrical activity of the heart.
 Electrocardiograph:
The registered read out of the
heart rhythm. Only shows the depolarization, not
contraction of the muscle.

Three Deflections of the EKG:
 P-Wave:
Corresponds to the depolarization of the
atria (Atrial contraction).
 QRS-Wave: Corresponds to the depolarization of the
ventricles (Ventricle contraction).
 T-Wave: Corresponds to the ventricular
repolarization.
Cardiac Cycle

Cardiac Cycle: Consists of one complete
heartbeat.
 Systole:
The contraction phase.
 Diastole: The relaxation phase.
Cardiac Cycle

6 Phases of the Cardiac Cycle:

Rest: Atria are filling with blood; A-V valves open.
 Atrial Systole: Atrial depolarization prompted by depolarization of the
SA node. Forces blood into the ventricles (25 mL) over 0.1 seconds.
 Ventricular Systole: Rising blood pressure in the ventricle triggers
isovolumetric contraction, which leaves the volume the same but
raises pressure.
 Ventricular Ejection: When ventricular pressure is greater than aortal
pressure, the semi-lunar valves open.


Stroke Volume: Total amount of blood moving into the pulmonary trunk &
aorta (typically 70 mL).
Relaxation Period: Ventricular repolarization causes ventricular
diastole – all 4 valves close for isovolumetric relaxation.
 Ventricular Filling: A-V valve opens when ventricular pressure drops
back below atrial pressure, allowing the ventricles to fill again. Lasts 250
msec.
Heart Sounds
Heart Sounds: The sounds made by the
opening & closing of the valves & the rush
of blood.
 First Heart Sounds (S1): The closing of
the A-V valves, usually louder & longer
lasting.
 Second Heart Sounds (S2): The closing
of the semi-lunar valves, usually quieter &
quicker.

Heart Rhythm Disorders


Heart Murmer: Any abnormal clicking, gurgling,
or rushing noise accompanying the heartbeat.
Tachycardia: Persistent resting heart rate of
100 BPM or higher.
 Can
be caused by stress, heart diseases, drugs,
medications, or hyperthermia.

Bradycardia: Persistent resting heart rate of 60
BPM or less.
 Can
be caused by hypothermia; may be normal in
athletes.
Cardiac Output



Cardiac Output: The amount of blood volume pumped
by each ventricle per minute.
Cardiac Reserve: The difference between a resting
cardiac output & the maximum potential cardiac output.
Heart Rate: The number of times the heart goes through
one complete cardiac cycle per minute.





Adult males: 64-72 BPM resting.
Adult females: 72-80 BPM resting.
Infants: 120 BPM or more resting.
Cronotropic Agents: Anything that raises or lowers the
rate of contraction.
Inotropic Agents: Alters the stroke volume of the
ventricles.

Dopamine, epinephrine, & noreopinephine
Cardiac Output

Cardiac Output: Stroke volume X heart
rate CO (mL/min).
 SV
(mL/beat) X HR (beats/min)
Chemicals Impacting Heart Rate

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
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Sympathetic neurotransmitters & some
hormones of the adrenal glands can accelerate
the heart rate.
Hypernatremia: Excessive amounts of sodium can lower the heart rate.
Hyperkalemia: Excessive amounts of
potassium – can lower the heart rate and lead to
death.
Hypercalcaemia: Excessive amounts of calcium
– slows the heart rate.
Hypocalcaemia: Lowered amounts of calcium –
speeds the heart rate up.
Stroke Volume

Stroke Volume: The amount of blood
ejected by the ventricle during each
contraction. Mostly determined by the
amount of tension generated in the
ventricles.
Stroke Volume

Regulated by 3 factors:
 Preload:
The greater the tension of the cardiac
muscle prior to contraction, the greater the force of
the contraction & the more blood that is expelled.
Known as the Frank-Starling Law of the Heart.
 Contractility: Strength of the contraction is enhanced
by positive inotropic factors and decreased by
negative inotropic agents. (Anything that stimulates
or inhibits the sympathetic nervous system).
 Afterload: The amount of pressure in the semi-lunar
valves in the ventricles. The higher the pressure in the
arteries, the less stroke volume.
Blood Pressure

Blood Pressure: The pressure in the
heart and blood vessels.
 The
left side of the heart has higher blood
pressure than the right, but both have the
same volume of blood.
Pressure Gradient: The difference in
pressure of the two sides of the heart &
causes the valves to stay open.
 Sphygmomanometer: The device used
to measure the blood pressure.

Exercise & The Heart

Aerobic Exercise: Exercise that gets your
heart pumping!
 Can
be good for the heart.
 Increases cardiac reserve.