Transcript Heart and Circulation

Overview: Cardiovascular
System and the Heart
Circulatory System = heart,
BVs, and blood
Cardiovascular System =
passageways for blood =
heart, arteries veins, etc.
Two Hearts:
1. Pulmonary Circuit (right
side) - takes blood to lungs
for gas exchange
2. Systemic circuit (left
side)- takes oxygen rich
blood to the organs and
oxygen poor blood back to
the heart
• Right side of heart
gets O2 poor blood
– Pulmonary artery takes it
away from heart to lungs
– Pulmonary veins bring it
back O2 rich
• Left side of heart
serves systemic system
– Aorta takes O2 rich blood
out to organs
– Superior vena cava brings
it back from head, neck,
upper limbs
– Inferior vena cava brings
it back from organs below
diaphragm.
Pericardium
• Double walled sac
enclosing heart
• In the pericardial
cavity is pericardial
fluid that allows the
heart to beat
without friction
• Pericarditis is the
pain caused by
friction when the
membranes are dry
• Epicardium
– outer layer
– fatty
• Myocardium
– thickest layer
– cardiac muscle that
pulls against a
fibrous skeleton of
fibers
– focuses the
movement of
electricity
• Endocardium
– Smooth inner lining
Heart wall
Chambers
• Right and left
atria receive
returning blood
– have an easier
workload
• Right and left
ventricles eject
blood
• Ensure one way flow
• Made of flaps called cusps
• Open & close as a result of
pressure changes
• When ventricles relax,
valves are open
• Full ventricles contract
pressure pushes valves shut
AV valves = between atria + ventricles
Right AV – tricuspid valve
Left AV – bicuspid valve (aka,
mitral valve)
Semilunar valves = bet. ventricles +
the great arteries
Heart Valves
Coronary Circulation
• Getting blood to your heart
• ~3 billion beats over an 80 year
life span
• Heart needs 5% of body’s O2
– delivered by coronary arteries
• Myocardial Infarction: fat
deposits blocking arteries
leading to necrosis of tissue
– Anastomoses: our body’s defense
• Two arteries covering the same
area
• If the damage is extensive, the
heart beat becomes inefficient
- coronary bypass may be
necesssary
Cardiac Muscle and The Cardiac
Conduction System
• Cardiocytes: short, thick
branched cells
-mononucleated, striated
-myogenic –will beat rythmically
w/o CNS stimulation
-inherent contractile activity controlled
by the ANS
• Intercalated discs join cells end
to end
– Gap junctions allow ions to flow
between cells, keep electrical
current flowing from one cell to the
next
– The action potential travels thru all
cells connected together forming a
functional syncytium
Cardiac conduction system
• Our brain can modify the
heartbeat, but not
create it. Disembodied
hearts can beat for
hours.
• Sinoatrial (SA) node =
the pacemaker
-initiates heart beat and
determines heart rate
-damage to SA node results in
slower heart rate – implant an
artificial pacemaker
• Atrioventricular node =
sends signals to the
ventricles
Purkinje fibers arise from bundle branches
near the apex and then spread throughout
the myocardium.
Control of Heart Rate
• Without nervous system control, the heart would beat
about 100 times per minute
• Both sympathetic and parasympathetic nerves innervate
the SA node
• When you are relaxed, your parasympathetic nervous
system (via the vagus nerve) sets a resting heart beat
rate at about 70 beats/min
• When exercising or anxious, the sympathetic nervous
system ↑ heart beat via hormones like adrenaline – this ↑
flow of O2 blood to muscles
• Average maximum heart rate is 220 minus your age
Electrical & Contractile Activity
Contraction = systole
Relaxation = diastole
These can apply to parts (e.g., atrial systole), or just to
the ventricles
Sinus rhythm = normal beat triggered by SA node
Can have ectopic focus (alternate source of beat, instead
of SA node) called nodal rhythm
Arrhythmia = abnormal rhythm
Physiology of the SA node
• The nerves of the SA
node are always slowly
moving toward an action
potential
• As soon as the heart
beats it’s already
starting toward another
beat
• Avg. ~75 beats per
minute
• Cardiac muscle has a
sustained contraction,
and a longer refractory
period
– This prevents tetanus:
continual contraction
Membrane potential starts around -60mV.
Pacemaker potential is a gradual drift
upward (slow inflow of Na+ w/o outflow
of K+).
Fast calcium channels – inflow of Ca+.
Electrocardiogram (ECG/EKG)
• Composite reading of
many action potentials
• P wave: atria contract
• QRS complex: AV
node fires, ventricles
start to contract
• T wave: ventricles
repolarizing
• U wave: not always
seen – repolarization
of papillary muscles or
Perkinje fibers
Electrocardiogram
Cardiac cycle
“Lub-dub” sounds are made
when the heart valves that
separate the chambers of
the heart open and close in
sequence.
Now, you can…
• Identify the chambers and valves of the
heart
• Trace the flow of blood through the heart
chambers
• Contrast cardiac vs. skeletal muscle
• Describe the physiological properties of
cardiac muscle
• Describe the heart’s electrical conduction
system
• Describe the physiological mechanism of
control of rate of heart beat