Download (SA) node

Objective 8
Coronary Circulation
The function of coronary circulation is to supply the myocardium with blood.
Arterial Supply: The right coronary artery (RCA) and the left
coronary artery (LCA) originate from the aorta at
the sinuses of Valsalva
Branching of the RCA and LCA
Aorta
Right Coronary Artery
Marginal
Artery
Posterior Interventicular
Artery
serves the
right lateral
wall of the heart
serves the posterior wall
of both ventricles
Left Coronary Artery
Anterior
Interventricular Artery
serves the anterior walls
of both ventricles and
the interventricular septum
Circumflex
Artery
serves the lateral
left atrium and
and posterior
wall of the left
ventricle
Venous Drainage: Deoxygenated blood is collected by cardiac vein and
emptied into the right atrium
Right Atrium
Anterior Cardiac Veins
drains the anterior surface
Great Cardiac Vein
drains the anterior
surface
Coronary Sinus
Middle Cardiac Vein
drains the posterior
surface
Small Cardiac Vein
drains the inferior
right margin
C.
Terms:
anastomosis:
union or joining of two blood vessels (nerves or lymphatics)
collateral
alternative route of circulation to an area provided by an
circulation: anastomosis
ischemia:
infarction:
insufficient blood supply to an organ or a tissue,
usually due to a blocked artery
localized necrosis resulting from an obstruction of the blood
supply
Schematic drawing of the coronary artery circulation without (A) and
with interarterial anastomoses (B) between the right coronary artery
and the occluded left anterior descending artery (occluded
downstream of the third diagonal branch).
Traupe T et al. Circulation 2010;122:1210-1220
Copyright © American Heart Association
Changes in Infarcted Tissue:
1.
Bruised, cyanotic tissue
2. Edema, inflammation and leukocytosis with 24 hours
3. Cardiac enzymes (creatine kinase, lactate dehydrogenase) released
within 2-3 days
4. Tissue degradation and replacement by scar tissue
Scar tissue
Angina Pectoris:
thoracic pain resulting from
ischemia
Objective 9
Cardiac Muscle
A. Structure






Myocytes (cells) - small, branching, lightly striated fibers
One -two centrally located nuclei
Poorly developed sarcoplasmic reticulum; no triads
Large and abundant mitochondria
Myogobin present
Intercalated discs, made of gap junctions/desmosomes join cells
 allow small molecules and ions to pass between cells
 electrically couple the myocytes (functional syncytium,
note: no gap junctions between atrial and ventricular
cells)

 desmosomes prevent cell separation during contraction
High capillary density
B. Metabolism
• utilize aerobic respiration for ATP generation
• can use fatty acids for ATP production
In summary, what structural adaptations maximize the
cardiac myocytes capacity for aerobic respiration?
1.
2.
3.
4.
Many large mitochondria
Myoglobin
High capillary density
Can use fatty acids for fuel
C. Contraction Properties

slower speed of contraction than skeletal muscle

are autorhythmic (myogenic) and can contract in the
absence of a stimulus

receives dual innervation from the autonomic nervous
system (SNS
HR and force of contraction; PNS
HR
and force of contraction )
What is the neurotransmitter and receptor type for SNS?
Norepinephrine binds to adrenergic receptors
What is the neurotransmitter and receptor type for PNS ?
Acetylcholine binds to cholinergic receptors

cells respond to stretching with a more vigorous
contraction, remember the length-tension curve???

cells have a long absolute refractory period
What is the importance of this?
Objective 10
Autorhythmic and Contractile Cells
There are two populations of myocytes in
the heart:
autorhythmic cells
and
contractile cells
Location
Function
Autorhythmic Cells
Contractile Cells
Intrinsic conduction system:
SA node, AV node, AV
bundle, bundle branches,
purkinje fibers
All other myocytes
Initiate the action potentials
that stimulate contractile cells;
set heart rate
Contract and relax during
systole and diastole; they
serve as pumping cells
A Typical Action Potential for
Neurons, Skeletal Muscle Cells
Action potential of autorhythmic cells….
1.
Pacemaker potential:
gradual decrease in K+ efflux and
increased Na+ influx through slow
Na+ channels causes gradual
depolarization
3
2
2.
Threshold (-40mV);
Ca2+ channels open and Ca2+ enters
the cell from the ECF; this
causes depolarization
1
3.
Repolarization
occurs when Ca2+ channels close
and voltage regulated K+ open; K+
leaves the cell
Action Potential For Contractile Cardiac Cells (99% of cardiac myocytes)
0. Depolarization
Voltage regulated fast Na+ channels
open and Na+ enters from the ECF
causing depolarization
1. and 2. Plateau:
Ca2+ enters the sarcoplasm from the
SR and from the ECF through slow
Ca2+ ; channels; at the same time
there is a decrease in K+
permeability; this causes a prolonged
depolarization
3. Repolarization
Occurs as the Ca2+ channels close the
voltage regulated K+ channels open; K+
leaves the cell
4. Back to resting membrane potential
From AP to Contraction
AP travels down T-Tubules of the myocyte
Calcium enters cell
Calcium binds to troponin
Troponin tropomyosin complex exposes myosin
binding sites on actin
Thin filament slide toward toward center of the
sarcomere thick filaments
Contraction
Refractory Period of Contractile Cardiac Myocytes:
The long refractory period of contractile cardiac myocytes prevents
sustained contraction (tetany) in cardiac muscle and ensures that
filling time (diastole) occurs.
mV
time
absolute refractory period
atrial cells:
0.15 sec
ventricular cells
0.30 sec
Objective 11
The Intrinsic Conduction System
SA node
↓
AV node
↓
AV bundle
↓
Bundle branches
↓
Purkinje fibers
Element
Sinoatrial (SA) node
Location
right atrial wall,
just below the
SVC entrance
Comments
 inherent depolarization
rate is 100/minute
 normally slowed by
extrinsic factors
 is the normal
pacemaker for the
heart
SA node
↓
AV node
↓
AV bundle
↓
Bundle branches
↓
Purkinje fibers
Element
Location
Comments
Interatrial
Pathways
within the atrial
myocardium
Bachman’s Bundle delivers
the impulse to left
atrium; internodal
pathways deliver the
impulse through the right
atrium and to the AV node
and Internodal
Pathways
SA node
↓
AV node
↓
AV bundle
↓
Bundle branches
↓
Purkinje fibers
Element
Atrioventricular
(AV) node
Location
interatrial septum
above tricuspid
valve
Comments
impulse delayed
.01 sec
inherent rate
40-60/minute
SA node
↓
AV node
↓
AV bundle
↓
Bundle branches
↓
Purkinje fibers
Element
Atrioventricular Bundle
(of His)
Location
Superior
interventricular
septum
Comments
Only normal conduction
pathway from atria into
ventricles
SA node
↓
AV node
↓
AV bundle
↓
Bundle branches
↓
Purkinje fibers
Element
Right and left bundle
branches
Location
Interventricular
septum
Comments
Carries apex of the
heart
SA node
↓
AV node
↓
AV bundle
↓
Bundle branches
↓
Purkinje fibers
Element
Purkinje fibers
Location
Ventricular
myocardium
Comments
Stimulate papillary
muscles and ventricular
myocardial cells
Inherent rate is 15-30
depolarizations per
minute
A picture is worth a thousand words….
http://www.youtube.com/watch?v=bxKBQqe_Bo0