Physiology Exam 4

Stroke Volume

Amount of blood pumped each cycle

SV = End Diastolic Volume - End Systolic Volume

EDV = affected by the length of vent contraction & venous pressure (increased ventricular loading) 

ESV = affected by the arterial blood pressure and force of ventricular contraction 

Factors that effect SV

• Preload (EDV)

• Contractlity

• Afterload (ESV)

Cardiac Output

volume of blood pumped in each ventricle per minute 

CO = Heart Rate X SV

Resting CO= 5.25 L/Min

Max CO is 4-5 times resting

Maximal CO is met by increasing HR and SV 

Starlings Law

Preload

The SV of heart increases from an increase of volume of blood filling in heart.

Heart sarccomeres are extra overlapped

Greater filling = Greater force of contraction

Venous return is amount of blood returning to heart

Slow heart rate or increase in blood pressure (exercise) = increased venous return = increased contraction force.

Contractility

Contractile strength at given muscle length

Muscle length stays the same when contracting! 

Increased by sympathetic stimulation and positive inotropic agents. Ca2+

Decreased by negative inotropic agents (weaken contraction) 

Afterload

The pressure that the ventricles must overcome to eject blood through the semilunar valves 

Hypertension: High blood pressure in systemic circulation 

increases afterload = increased End Systolic Volume = decreased Stroke Volume 

Peristalsis

alternation contractions of smooth muscle layers that mix and squeeze substances through tube 

Single-unit (visceral) smooth muscle

Act like cardiac muscle

Gap junctions - synchronicity

spontaneous depolarization 

In all hollow organs besides the heart 

Autonomic nervous system (varicosities) 

Respond to multiple chemical stimuli

Multi-unit smooth muscle

Acts like skeletal muscle

Large airways, arteries, goosebumps, iris of eye

Rarely ever gap junctions or spontaneous depolarization 

independent muscle fiber innervated by the autonomic nervous system - graded potential 

 

Varicosities

autonomic nerves that innervate smooth muscle into diffuse junctions

Smooth muscle

thin and short 

only one nucleus

No sarcomreres, myofibrils, or T-tubules 

Thick filament has myosin heads all over

pouchlike infoldings called caveolae 

No troponin - calmodulin instead 

Calmodulin activates light chain kinase 

Dense bodies - like Z disks 

Can contract in the absence of electrical depolarization 

Relaxation only occurs after phosphate is removed from the myosin light chain 

contraction of smooth muscle

Slow ATPases

slow to contract but stays contracted for a long time

Either action or graded potential 

no electrical change (G-protein)

responds to stretch briefly, then adapts to new length 

Some smooth muscles have no nerve supply. depolarize spontaneously or respond to physical stimuli or chemical stimuli from G-protein-linked receptors.