• Heart is about the
size of your fist
• Is a four chambered
pump
• Pumps over 1
million gallons per
year
• Over 60,000 miles
of blood vessels
Heart Location – Transverse Section
Anterior surface
of heart
• Heart is located in the mediastinum
– area from the sternum to the vertebral column and
between the lungs
Heart Orientation
• Apex - directed downwards and
to the left
• Base - directed upward and to
the right
• Anterior surface - deep to the
sternum and ribs
• Inferior surface - rests on the
diaphragm
• Right border - faces right lung
• Left border - faces left lung
Heart Enclosed in Pericardium
• Fibrous pericardium
– dense irregular CT
– protects and anchors the heart,
prevents overstretching
• Serous pericardium
– thin delicate membrane
– Made of two layers:
• parietal layer-outer layer
• visceral layer (epicardium)
• pericardial cavity with pericardial
fluid between the two layers.
Layers of Heart Wall
• Epicardium
– visceral layer of serous
pericardium
• Myocardium
– cardiac muscle layer is
the bulk of the heart
• Endocardium
– chamber lining & valves
Chambers of the Heart
• Four chambers
– Two upper atria (singular is atrium)
• Thin-walled
• Receive blood returning to heart and send it to ventricles
– Two lower ventricles
•
•
•
•
Thick-walled
Pump blood from heart
right ventricle supplies blood to the lungs (little flow resistance)
left ventricle wall is the thickest to supply systemic circulation
Heart Chambers and Vessels
Superior Vena Cava----Right Pulmonary Artery-----
------Aorta
-----------Left Pulmonary Artery
---------------Pulmonary Trunk
-------Left Pulmonary Vein (2)
Right Pulmonary Vein (2)---
--------Left Atrium
Right Atrium-------Right Ventricle-------------------
Inferior Vena Cava-------
-------Left Ventricle
Heart Interior and Valves
-----------Left Atrium
Pulmonary Semilunar Valve-------
---------Aortic Semilunar Valve
-----Bicuspid (mitral) Valve
Right Atrium------------Tricuspid Valve-----------------
Right Ventricle-------------------
--------Left Ventricle
Heart Valves
• AV valves close with ventricular contraction
– blood pressure forces cusps to close, preventing blood
from flowing from ventricle back into atria.
• SL valves close with ventricular relaxation
– prevent blood from returning to ventricles from
pulmonary artery and aorta. Blood fills valve cusps,
tightly closing the SL valves
Bicuspid (mitral) Valve
•When left ventricle contracts, the two cusps (leaflets)
snap shut. What causes them to close?
Flow of Blood Through the Heart
Vena Cavae
Right Ventricle
Pulmonary Valve
Pulmonary Veins
Right Atrium
Tricuspid Valve
Pulmonary Trunk
and Arteries
Lungs
Left Atrium
Bicuspid Valve
Aortic Valve to
Aorta
Left Ventricle
Cardiac Muscle Tissue
• Histology
•Striated
•Branched
•Intercalated discs
•Involuntary
•Aerobic
Two types of cardiac muscles
• CONTRACTILE CARDIAC MUSCLE:
- MAKE ALL THE MYOCARDIUM
- CAUSE CONTRACTION OF THE HEART
CHAMBERS.
• AUTORYTHMIC CARDIAC MUSCLE:
-SELF-EXCITABLE LIKE NERVES.
-FORM THE CONDUCTION SYSTEM
THROUGH THE HEART MUSCLES.
-FORM THE HEART PACEMAKER.
Electrical Events of the Heart
• Conducting system
•Consists of _______________
autorhythmic cells that initiate action
potential and then carry it through heart
•Components of Conducting System
•Sinoatrial (SA) Node - Pacemaker
•In right atrium near entrance of superior vena cava
•Automatically depolarizes and starts each heartbeat
•Atrioventricular (AV) Node
•Receives electrical signal from SA node, delays it then sends it
to ventricles
•AV Bundle (of His) receives signal from AV node
•Right and left Bundle Branches
•Formed by division of AV bundle
•Send signal to each ventricle
•Purkinje fibers spread signal throughout ventricles
Electrocardiogram (ECG or EKG)
Tracing of Heart’s electrical activity
•P wave – atrial depolarization
•QRS complex – ventricular
depolarization
•T wave – repolarization of Ventricles
•P-Q interval – time for signal to
travel from SA node to AV bundle
•Q-T interval – time for ventricular
depolarization and repolarization
Autorhythmicity
• Heartbeat intrinsic because it has its own
pacemaker that starts each beat
•____________
The SA node is the pacemaker that starts each
heartbeat by spontaneously depolarizing at the
heart rate
•Resulting action potential (signal)
spreads from conducting system to
contractile cells
Cardiac Cycle – How the Heart Beats
•Conducting system controls sequence of heartbeat
•_________
SA node depolarizes and stimulates contraction of atria
•_________
AV node receives signal, delays it, then passes it through rest of
conducting system to ventricles
•Assures that atria contract before ventricles
•This sequence of heartbeat called normal _____________
sinus rhythm
•Contraction phase of heartbeat called _______
systole
•Relaxation phase of heartbeat called _________
diastole
•Alternating contractions and relaxations allow heart to pump
blood then refill
•Diagram on next page shows steps of cardiac
cycle – events of one heartbeat
Animation of Heartbeat
Cardiac Cycle – Events of one Heartbeat
1. Atrial and Ventricular diastole
2. Atrial systole
3. Ventricular systole
•AV valves open
•Ventricles fill to 70%
•Completion of
ventricular filling
4. Atrial and Ventricular diastole
•Ventricles contract
•AV valves close – lubb (S1) sound
•SL valves open 50-60% of blood
ejected
•Ventricles relax – return to diastole
•SL valves close – dupp (S2) sound
Cardiac Output
•Definition: Amount of blood ejected by heart in one minute
•Factors affecting cardiac output
•Stroke volume: Milliliters of blood ejected by ventricle per beat
•Heart rate: Number of heartbeats per minute
•Formula: Cardiac output =
Stroke volume x Heart rate
Factors Affecting Stroke Volume
•Preload:
•End diastolic volume (EDV) or amount of blood in ventricle
before ejection
•More in, more out
•Contractility:
•Strength of contraction
•Affected by many factors including the nervous system and various
chemicals
Factors Affecting Stroke Volume Continued
•Afterload
•Tension or pressure ventricle must exert to open
semilunar valve and eject blood
•Determined by resting (diastolic) pressure in
pulmonary trunk or aorta
•Right ventricle must produce enough pressure to
open pulmonary semilunar valve
•Left ventricle must produce enough pressure to
open the aortic valve
•Does high blood pressure increase or decrease the
afterload?
•What long term effect might high afterload have on the
heart?
Factors Affecting Heart Rate
•Neural Control of Heart Rate
•Cardiac centers in __________________of
Medulla oblongata brain
•Cardiac acceleratory center
•Impulses through cardiac nerves of _________________________
sympathetic division of ANS
•Neurotransmitter ______________
norepinephrine accelerates heart rate
•Cardiac inhibitory center (CIC)
•Impulses through vagus nerve (CNX) of the ________________
parasympathetic
________________
division of ANS
•Neurotransmitter _______________
acetylcholine slows heart rate
•At rest, constant input by parasympathetic keeps heart beating
at resting rate – called _____________
vagal tone
Neural Control Diagram
Accelerator
Norepinephrine speeds-up
heart rate
Brake
Acetylcholine slows the heart rate
Factors Affecting Heart Rate Continued
•Blood chemistry
•Adrenaline (epinephrine) ___________________________________
increases rate and strength of heartbeat
•High levels of thyroid hormone will speed-up heart
•Changes in electrolytes (ion concentrations), especially potassium and
calcium
•Body temperature
•What happens when you have a fever?
•Changes in blood pressure
•Can slow-down or speed-up heart
•Will be discussed in next chapter
Clinical Terms
• Tachycardia: A heart
rate above 100/min.
• Bradycardia: A heart
rate below 60/min
• Asystole: Cardiac
standstill, no contraction
• coronary artery disease
(CAD): Narrowing of the
coronary arteries.
• Ischemia: Decreased
blood flow.
• Atherosclerosis:
Hardening of arteries.
• Angina pectoris: Chest
pain.
• Myocardial infarction:
Loss of living heart
muscle mass.
• Arteriosclerosis: Thickening
of the arterial walls.
• Arrhythmias: Irregularity of
heart rhythm.
• Heart failure: Reduced ability
of the heart to pump blood.
• Pericarditis: Inflammation of
the pericardium.