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Chapter 18
Circulatory System
Heart (general)
• Size of a fist
• Almost one pound in
•
•
weight
Middle of chest points
to left
Just superior to
zyphoid process
Layers of Heart
• Epicardium (pericardial
sack)
– Protects heart
– Anchors it to surrounding
tissue
– Prevents overfilling of heart
with blood
– Pericarditis – hinders
production of serous fluid
sometimes under severe
friction inflammatory fluid
rushes in and can lead to
cardiac tamponade (heart
plug)
Myocardium (heart muscle)
• Fibers embedded in
•
layer form skeleton to
support and prevent
over dilation or
expansion.
More prevalent
around valves and
major vessels off of
heart.
Endocardium
• Thin tissue layer
which lines the inside
of the heart.
Chambers of the Heart (Atria)
• Atria – located on the top
•
•
•
of heart
Very thin relative to
ventricles.
Only have to pump to
ventricles.
Fossa ovalis – opening in
the fetal heart (seen as
shallow depression in
atrial septum.
Right Atrium
• Right atrium – receives
oxygen poor blood.
– superior vena cava –
diaphragm and above
– inferior vena cava – below
– Coronary sinus – vein from
heart
– Veins are any large vessel
moving blood toward heart.
Left Atrium
• Receives oxygen rich
blood from lungs
(pulmonary veins)
Ventricles
• Located on the bottom
• Right ventricle lies toward
•
•
•
the front
Left ventricle lies towards
the back (largest and
most muscular chamber)
Septum – portion that
divides the left from the
right chambers
Sulcus – groove formed
between atria and
ventricles
Circulatory Circuit
• Pulmonary circuit – right
•
•
side
Systemic circuit – left side
Coronary circuit – feeds
the heart to thick for
diffusion – blockages or
narrowing of these
vessels can be fatal if not
corrected (bi – pass)
Valves
• Atioventricular valves
– Tricuspid valve – 3 flaps of
tissue – right side
– Bicuspid valve (mitral valve) 2
flaps of tissue – left side
– Chordae tendinae –
connective tissue that
attaches to valves and inferior
muscle surface located in
ventricles.
– Blood flows into ventricles ventricles contract shoving
flaps upward – but the flaps
can only go so far up because
of the chords attached.
Semi – lunar valves
• Valves that prevent
•
backflow into
ventricles from major
arteries.
Valves have pockets
distal to heart – these
fill with blood and act
as sails slamming
shut to prevent
additional backflow.
Contraction
• As with skeletal muscle – a wave
•
•
of depolarization Na+ in elicits an
action potential. This causes the
sarcolemma to dump Ca ++ ions
out which binds to troponin sliding
tropomyosin out of the way sot
that myosin can interact with
actin. (sliding filament)
Cells are connected via gap
junctions so if one cell is
stimulated to fire all cells are
stimulated.
Rhythmic Control – nervous
system – see notes on generating
an action potential (nervous
system)
Excitable Fibers
• SA node –
– Located right atrial
wall just below
superior vena cava
– Fires about 100 times
per minute fastest
stimulated tissue so it
sets the pace (pace
maker)
Other excitable tissues
• Located in septum receives
message from SA node and
transmits down septum
stimulating ventricle to
contract
• Bundle of His – branches out
from AV node
• Purkinje fivers – runs along the
bottom of ventricles and
toward the lateral portions
causing stimulation.
• If SA node is damaged than AV
becomes pacemaker but it is
slower in its rate of contraction
(and so on)
EKG / ECG electrocardiogram
• P wave – atrial
•
•
depolarization
QRS complex –
ventricle
depolarization
T wave – ventricle
repolarization