Transcript The Heart
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