BIO 265 – Human A&P
Chapter 18
The Heart
The Heart
 Size
 Form
 Location – mediastinum
– Figure 18.1 and from other text
Heart Anatomy
 Pericardium (pericardial sac)
– Figures 18.1 and 18.2
Heart Anatomy
 Heart Wall
– Epicardium
– Myocardium
– Endocardium
– Figure 18.2
Heart Structure and Function
 What are the heart chambers?
 Overview of heart function
 Figure 18.5
Coronary Circulation
 In order for the heart to function, it must
have a constant supply of oxygen
 The coronary arteries carry the blood to the
heart
 Figure 18.7
Heart Attack
 What is a heart attack or myocardial
infarction?
 CD Animation
Heart Valves
 What are the 4 valves in the heart?
– Figure 18.8
Heart Valves
 Heart valve function – Figures 18.9 and
18.10
Heart Valves
 Heart sounds result from the closing of the
heart valves
 Heart murmurs occur when a valve does
not open or close properly
 CD Animation
Histology
 What are the characteristics of cardiac
muscle?
– Branched fibers
– Mitochondria
– T-tubules
– Intercalated disks with gap junctions
– Figure 18.11
Conducting System
 What are the components?
– Figure 18.14
Conducting System
 All cardiac muscle cells are autorhythmic
– They can generate spontaneous AP
– But the SA node is the pacemaker (it
depolarizes faster than other areas of the heart)
 Figure 18.13
Conducting System
 Once the AP is generated it spreads
through the atria to the AV node
 What role does the AV node play?
– Delays the AP for a split second
 The AP then passes very quickly through
the bundle branches
– The effect is contraction at the apex first
– Figure 18.14
Electrical Properties
 Cardiac muscle has an RMP similar to
skeletal muscle
 Differences between cardiac and skeletal
AP – Figure from other text
Cardiac Action Potentials
 Phases of AP in contractile cells:
– Depolarization
• Na+ channels (fast channels) open
• K+ channels are closed
• Ca2+ channels (slow channels) begin to open
– Early repolarization and plateau
• Na+ channels close
• Some K+ channels open
• Ca2+ channels stay open
– Figure from other text
Cardiac Action Potentials
– Final repolarization
• Ca2+ channels close
• many K+ channels open
– Figure from other text
Cardiac Action Potentials
 How would the AP in cardiac muscle
stimulate a contraction?
– Notice that Ca2+ comes from the extracellular
fluid as well as the SR
 Cool CD Animations! (my CD)
Electrocardiogram
 ECG wave patterns – Figures 18.16, 18.17,
and 18.18
The Cardiac Cycle
 The cardiac cycle refers to the repetitive
pumping process that occurs in the heart
– Systole – contraction of the heart
– Diastole – relaxation of the heart
– CD animation
The Cardiac Cycle
 Steps:
– Ventricular filling
• Passive – during complete diastole
• Active – during atrial systole
– Ventricular Systole
• Isovolumetric Contraction – closes AV valves and
opens semilunar valves
• Period of Ejection – blood leaves the ventricles
– Ventricular Diastole
• Isovolumetric relaxation – semilunar valves close
– Figure 18.20
The Cardiac Cycle
 Assuming an average 75 bpm:
– Cardiac Cycle = 0.8 s
– Atrial systole = 0.1 s
– Ventricular systole = 0.3 s
– Diastole = 0.4 s
 Awesome CD animation (my CD)
Cardiac Output
 Cardiac output (CO) =
Heart rate (HR) x Stroke volume (SV) of one
ventricle
 Calculations (p.698)
– Resting 75 bpm x 70 ml/beat = 5250 ml/min
– Or in other words your entire volume of blood
passes through each side of your heart each
minute!!!
– Exercise 20 liters/min to 35 liters/min
Regulation of the Heart
 Regulation of cardiac output is critical for
homeostasis
 Starlings law of the heart:
– The greater the venous return to the heart,
– The greater the stretch of the heart wall,
– This results in a more forceful contraction and
therefore a greater stroke volume
Regulation of the Heart
 Neural regulation:
– The heart is innervated by both sympathetic
and parasympathetic fibers
– Parasympathetic – decrease heart rate by
releasing acetylcholine
• It opens ligand-gated K+ channels
• Effect?
• Figure 18.15
Regulation of the Heart
– Sympathetic – increases heart rate and force of
contraction (stroke volume)
• Norepinephrine (a neurotransmitter) stimulates the
opening of the slow Ca2+ channels
• It works through a G-protein system that
synthesizes cAMP
• Figures 18.22 and 18.15
Regulation of the Heart
 Hormonal Control
– Epinephrine and norepinephrine – same effect
as above
 Problems in Regulation:
– Tachycardia – over 100 bpm
– Bradycardia – under 60 bpm (can be normal in
athletes)
Regulation of the Heart
– Congestive Heart Failure – cardiac output is
too low to meet body tissue needs
• Blood builds up in the veins (causing the
“congestion”)
– Causes:
• Coronary Atherosclerosis – decreases the hearts
pumping ability
• Hypertension (high blood pressure) – ventricles
can’t push the blood out into the arteries
• Myocardial infarction
Heart and Homeostasis
 How does the heart help maintain
homeostasis?
– Blood pressure example
• Baroreceptors, the cardioregulatory center, and
nerves
– Figures from other text
The Fetal Heart
 There are some interesting differences
between the fetal and adult hearts
 Why?
– Foramen ovalis in the atrial septum
– Ductus arteriosis between the pulmonary trunk
and the aorta
– Figures 18.4b and e