Download The Heart

Chapter 20
Cardiovascular System
The Heart
20-1
The Heart
• The Heart is two pumps.
– Pulmonary circulation
• Carries blood to lungs
• Returns to the left side of
heart
– Systemic circulation
• Delivers oxygen and
nutrients to the body
• Returns to the right side of
the heart
20-2
Functions of the Heart
• Generating blood pressure
• Routing blood
– Heart separates pulmonary and systemic
circulations
– Ensures oxygenation of blood flowing to tissues.
• Ensuring one-way blood flow
– Heart valves ensure one-way flow
• Regulating blood supply
– Changes in contraction rate and force match
blood delivery to changing metabolic needs
20-3
Size, Shape, Location
of the Heart
• Size of a closed fist
• Shape
– Apex: rounded tip of
heart
– Base: Flat part at
opposite of end of cone
• Located in thoracic
cavity within the
mediastinum
20-4
Heart Cross Section
20-5
Pericardium
20-6
Heart Wall
• Three layers of tissue
– Epicardium: This serous membrane of smooth
outer surface of heart
– Myocardium: Middle layer composed of
cardiac muscle cell and responsibility for heart
contracting
– Endocardium: Smooth inner surface of heart
chambers
20-7
Heart Wall
20-8
External Anatomy
• Four chambers
– 2 atria
– 2 ventricles
• Auricles
• Major veins
– Superior vena cava
– Inferior vena cava
– Pulmonary veins
• Major arteries
– Aorta
– Pulmonary trunk
20-9
External Anatomy
20-10
Coronary Circulation
20-11
Heart Valves
• Atrioventricular
– Tricuspid
– Bicuspid or mitral
• Semilunar
– Aortic
– Pulmonary
• Prevent blood from
flowing back
20-12
Heart Valves
20-13
Function of the Heart Valves
20-14
Blood Flow Through Heart
20-15
Systemic and Pulmonary
Circulation
20-16
Heart Skeleton
• Consists of plate of
fibrous connective tissue
between atria and
ventricles
• Fibrous rings around
valves to support
• Serves as electrical
insulation between atria
and ventricles
• Provides site for muscle
attachment
20-17
Cardiac Muscle
•
•
•
•
•
Elongated, branching cells containing 1-2 centrally located nuclei
Contains actin and myosin myofilaments
Intercalated disks: Specialized cell-cell contacts
Desmosomes hold cells together and gap junctions allow action potentials
Electrically, cardiac muscle behaves as single unit
20-18
Conducting System of Heart
20-19
Electrical Properties
• Resting membrane potential (RMP) present
– Depends on low permiability to Na+ and Ca++
and high permiability to K+.
• Action potential
– Depolarization (Fast voltage gated Na+ channels)
– Early partial repolarization (Voltage gated Na+
channels close and a small number of K+ channels open.)
– Plateau phase - Prolonged period of slow
repolarization (Slow Ca++ channels are open)
– Rapid final repolarization phase (Voltage gated Ca++
channels close and more K+ channels open)
20-20
Action Potentials in
Skeletal and Cardiac Muscle
20-21
SA Node Action Potential
Permiability changes in the pacemaker cells (Autorhythmicity):
1.
2.
3.
Prepotential
• Small number of Na+ channels
open
• Voltage-gated K+ channels are
closing
• Voltage-gated Ca++ channels
begin to open
Depolarization Phase
• Voltage-gated Ca++ channels are
open
• Voltage-gated K+ channels are
closed.
Repolarization phase
• Voltage-gated Ca++ channels
close.
• Voltage-gated K+ channels open.
Note: Ca++ channel blockers like
verapamil are used to treat
tachycardia and arrhythmias.
20-22
Refractory Period
• Absolute: Cardiac muscle cell completely
insensitive to further stimulation
• Relative: Cell exhibits reduced sensitivity to
additional stimulation
• Long refractory period prevents tetanic
contractions
20-23
Electrocardiogram
• Action potentials through
myocardium during
cardiac cycle produces
electric currents than can
be measured
• Pattern
– P wave
• Atria depolarization
– QRS complex
• Ventricle depolarization
• Atria repolarization
– T wave:
• Ventricle repolarization
20-24
Cardiac Arrhythmias
• Tachycardia: Heart rate in excess of 100bpm
• Bradycardia: Heart rate less than 60 bpm
• Sinus arrhythmia: Heart rate varies 5%
during respiratory cycle and up to 30%
during deep respiration
• Premature atrial contractions: Occasional
shortened intervals between one contraction
and succeeding, frequently occurs in healthy
people
20-25
Alterations in Electrocardiogram
20-26
Cardiac Cycle
• Heart is two pumps that work together, right
and left half
• Repetitive contraction (systole) and
relaxation (diastole) of heart chambers
• Blood moves through circulatory system
from areas of higher to lower pressure.
– Contraction of heart produces the pressure
20-27
Cardiac Cycle
20-28
Cardiac Cycle
20-29
Heart Sounds
• First heart sound or “lubb”
– Atrioventricular valves and surrounding fluid vibrations as
valves close at beginning of ventricular systole
• Second heart sound or “dupp”
– Results from closure of aortic and pulmonary semilunar
valves at beginning of ventricular diastole, lasts longer
• Third heart sound (occasional)
– Caused by turbulent blood flow into ventricles and detected
near end of first one-third of diastole
• Clinical considerations:
–
–
–
–
Murmurs: abnormal heart sounds
Incompetent valve - leaks excessively (gurguling,swishing)
Stenosis: abnormally small valve openings (rushing sound before valve closes.
Causes: genetic or due to rhematic fever scaring or myocardial infarction 20-30
affecting the papillary muscles.
Location of Heart Valves
20-31
Mean Arterial Blood Pressure
• Stroke volume
– Volume of blood pumped during each cardiac cycle
• at rest ~70 ml
• can increase to ~200 ml during exercise
• Heart Rate
– ~72 BPM and can increase to over 120 BPM during exercise.
• Cardiac Output =stroke volume X heart rate
– Resting: 72 beats/min X 70 ml/beat = 5040 ml / min
– Exercise: 120 beats/min X 200 ml/beat = 24,000 ml/min.
• Cardiac reserve
– max cardiac output - resting cardiac output
– = 24,000-5040ml /min = 18960 ml
– C.O. is the major factor in determining blood pressure.
• Blood pressure
– Blood pressure reflects pressure changes in the aorta not the ventricle
– Normal BP 120 systolic / 80 diastolic
20-32
Factors Affecting MAP
20-33
Regulation of the Heart
• Intrinsic regulation: Results from normal
functional characteristics, not on neural or
hormonal regulation
– Starling’s law of the heart
– Stretching of the SA node.
• Extrinsic regulation: Involves neural and
hormonal control
– Parasympathetic stimulation
• Supplied by vagus nerve, decreases heart rate, acetylcholine
secreted
– Sympathetic stimulation
• Supplied by cardiac nerves, increases heart rate and force of
contraction, epinephrine and norepinephrine released
20-34
Heart Homeostasis
• Effect of blood pressure
– Baroreceptors monitor blood pressure
• Effect of pH, carbon dioxide, oxygen
– Chemoreceptors monitor
• Effect of extracellular ion concentration
– Increase or decrease in extracellular K+ decreases heart
rate
• Effect of body temperature
– Heart rate increases when body temperature increases,
heart rate decreases when body temperature decreases
20-35
Baroreceptor and Chemoreceptor
Reflexes
20-36
Baroreceptor Reflex
20-37
Chemoreceptor Reflex-pH
20-38
Effects of Aging on the Heart
• Gradual changes in heart function, minor
under resting condition, more significant
during exercise
• Hypertrophy of left ventricle
• Maximum heart rate decreases
• Increased tendency for valves to function
abnormally and arrhythmias to occur
• Increased oxygen consumption required to
pump same amount of blood
20-39