Download Circulatory System

Unit 9 – The Heart
Cardiovascular System
The Heart
20-1
Functions of the Heart
• Generating blood pressure
• Routing blood
– Heart separates pulmonary and systemic
circulations
• 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
20-2
The Closed Circulatory System
•Humans have a closed circulatory system, typical of
all vertebrates, in which blood is confined to vessels
and is distinct from the interstitial fluid.
–The heart pumps blood into large vessels
that branch into smaller ones leading into the organs.
–Materials are exchanged by diffusion between the blood
and the interstitial fluid bathing the cells.
20-3
The Cardiovascular System
Three Major Elements –
Heart, Blood Vessels, &
Blood
20-4
Size, Shape, Location
of the Heart
• Size of a closed fist
• Shape
– Apex: Blunt rounded
point of cone
– Base: Flat part at
opposite of end of cone
• Located in thoracic
cavity in mediastinum
20-5
Heart Cross Section
20-6
Pericardium
20-7
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
20-8
Heart Wall
20-9
External Anatomy
• Four chambers
– 2 atria
– 2 ventricles
• Auricles
• Major veins
– Superior vena cava
– Pulmonary veins
• Major arteries
– Aorta
– Pulmonary trunk
20-10
External Anatomy
20-11
Coronary Circulation
20-12
Heart Valves
• Atrioventricular
– Tricuspid
– Bicuspid or mitral
• Semilunar
– Aortic
– Pulmonary
• Prevent blood from
flowing back
20-13
Heart Valves
20-14
Function of the Heart Valves
20-15
Let’s Practice….
20-16
Did you get them all correct?
20-17
Blood Flow Through Heart
20-18
20-19
Systemic and Pulmonary
Circulation
Pulmonary circuit
The blood
pathway between
the right side of
the heart, to the
lungs, and back to
the left side of the
heart.
Systemic circuit
The pathway
between the left
and right sides of
the heart.
20-20
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
20-21
The Circulatory System
Blood Vessels -A network of tubes
–Arteriesarterioles move away from the heart
•Elastic Fibers
•Circular Smooth Muscle
–Capillaries – where gas exchange takes place.
•One cell thick
•Serves the Respiratory System
–VeinsVenules moves towards the heart
•Skeletal Muscles contract to force blood back from legs
•One way values
•When they break - varicose veins form
20-22
20-23
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
20-24
Conducting System of Heart
20-25
Electrical Properties
• Resting membrane potential (RMP) present
• Action potentials
– Rapid depolarization followed by rapid, partial
early repolarization. Prolonged period of slow
repolarization which is plateau phase and a
rapid final repolarization phase
– Voltage-gated channels
20-26
Action Potentials in
Skeletal and Cardiac Muscle
20-27
SA Node Action Potential
20-28
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
20-29
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
20-30
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
20-31
Alterations in Electrocardiogram
20-32
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
20-33
Cardiac Cycle
20-34
Events during Cardiac Cycle
20-35
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
20-36
Location of Heart Valves
20-37
Mean Arterial Pressure (MAP)
• Average blood pressure in aorta
• MAP=CO x PR
– CO is amount of blood pumped by heart per
minute
• CO=SV x HR
– SV: Stroke volume of blood pumped during each heart beat
– HR: Heart rate or number of times heart beats per minute
• Cardiac reserve: Difference between CO at rest and
maximum CO
– PR is total resistance against which blood must be
pumped
20-38
Factors Affecting MAP
20-39
Regulation of the Heart
• Intrinsic regulation: Results from normal
functional characteristics, not on neural or
hormonal regulation
– Starling’s law of the heart
• 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
20-40
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
20-41
Baroreceptor and Chemoreceptor
Reflexes
20-42
Baroreceptor Reflex
20-43
Chemoreceptor Reflex-pH
20-44
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
20-45