Review Heart Anatomy and Cardiac Muscle Cell Structure

Text: Chapter 14
Coloring Book: 26, 27, 29, and 30

CARDIAC CELL STRUCTURE

SMALL DISCRETE CELLS
INTERCALATED DISKS WITH DESMOSOMES
GAP JUNCTIONS = SYNCYTIUM
MANY MITOCHONDRIA
SR AND T TUBULES
STRIATED

Blood Flow

Systemic Capillaries --> Veins-->Vena Cava --> Right Atrium --> Right Ventricle
Pulmonary Artery --> Pulmonary Capillaries --> Pulmonary Vein
Left Atrium --> Left Ventricle --> Aorta --> Arteries --->Systemic Capillaries

Electrical Activity of the Heart

Note Differences in Conduction Velocity Due to Rates of Depolarization!

RECTIFICATION

Minimized efflux of K+ during AP plateau because of decreased K+ conductance at this positive Vm

TIME (in msec) <-50->

Ventricular action potential

Duration for complete contraction of the ‘pump’
Long AP with long refractory period to prevent fibrillation

Terminology

End Systolic Volume (ESV in ml)
End Diastolic Volume (EDV in ml))
Stroke Volume (SV in ml/beat)
SV = EDV - ESV
Heart Rate (in beats/min)
SV (ml/beat)
Cardiac Output (CO in ml/min)
CO = HR x SV

Starling’s Law of the Heart:

AS VENTRICULAR FILLING (EDV) INCREASES, STROKE VOLUME and STRENGTH OF BEAT) ALSO INCREASES

THE VENTRICLE PUMPS THE VOLUME THAT IT RECEIVES

STARLING’S LAW OF THE HEART

P = 2T/R

Starling’s Law of the Heart

Increased EDV or myocardial fiber length results in increased SV or increased strength of contraction.

Basis for Starling’s Law:

P = 2T/r

where

P = pressure in ventricle or aorta at ejection

T = myocardial tension required to generate that tension

r = radius of ventricle at beginning of systole

P = 2T/r

Which ventricle must develop more tension or contractile force, a large one or a small one?

SYMPATHETIC RESPONSE

b₁ receptors
On nodes and atrial and ventricular muscle cells
Increases rate
Increases Ca⁺⁺ released per beat via cyclic AMP

As heart rate increases,
filling time decreases

DIGITALIS:

DECREASE HR

BUT

INCREASE STRENGTH

POISEUILLE’S LAW

F = DPpr⁴

8 h L

TOTAL PERIPHERAL RESISTANCE (TPR)

FLOW in ml/min = K x DP
TPR = 1/K

F = DP / R
or
R = DP / F

P₁= 100 mm Hg P₂ = 10 mm Hg

FLOW = 10 ml / min

R = DP / F

= 90 mm Hg / 10 ml/min

= 9 mm Hg / min/ml

= 9 PRU

BLOOD PRESSURE IN mm Hg

BP = CO x TPR

Blood Pressure

Systolic
Diastolic
Average or Mean BP

Sympathetic Response on Heart

b1 receptors on pacemaker and atrial and ventricular muscle cells
Increase rate and strength

B1 receptor activation

G protein
adenylate cyclase --> cyclic AMP
cAMP-dependent protein kinase
phospholamban
myocardial SR takes up and releases more Ca++ per beat
result = more cross bridges = more tension

Vagus Nerve

Parasympathetic nerve
Right vagus to SA node
Left vagus to AV node and bundle
Decreases rate
No DIRECT influence on strength

PRESSURE MEASURED BY BARORECEPTORS

Why not measure blood flow (I.e., Cardiac Output)?

VAGUS NERVE

parasympathetic fibers
baroreceptors from aortic arch
stretch receptors from lungs