“Little Cowboy”

Homeostasis and The Heart

Tissues and Organs Depend on Appropriate Blood Flow (Perfusion)

Supply = Demand

Starling’s Law: Intrinsic Control of HeartVenous Return determines “stretch”

of cardiac myocytes: Venous Return = Stretch Stretch = Force and Rate

Known as PreloadExercise Increases Venous

Return / Preload / Force & Rate

Extrinsic Control: Baroreceptor ReflexBaroreceptors: Sense stretch in

artery walls(Stretch = Pressure)Aorta Internal Carotid Artery

Afferent Signals to Cardioregulatory Centers: Medulla Oblongata

Perfusion homeostasis by addressing pressure problems:

Heart Rate Decreases

Pressure Increases

InhibitionOf PressureSignals

Baroreceptor Reflex…Efferent Signals from Autonomic

Nervous System:Parasympathetic: Decrease HRSympathetic: Increase HRAdrenal: Increase HR

How do you think pressure affects perfusion of vital tissues?

Decreased CO Threatens Vital OrgansCardiac Response:

Increase HR (to compensate for decreased pressure/SV)

Vascular Response:Direct more of the total blood

volume to vital tissuesAway from less vital tissues

Extrinsic Control: Chemoreceptor Reflexes Increased Metabolism produces more

CO2, acids, and Temp:

Chemoreceptors (mostly in the medulla oblongata) initiate:

SNS stimulation: Rescues from “metabolic buildup” by HR

PSNS stimulation: Slows the heart when CO2, acids and temp recover

Exercise = PreloadWorking muscles “squeeze” more

blood back to heart Increased Venous Return =

Increased PreloadStarling Law is important in

initial increases in Exercise CO

Exercise Stimulates SNSCardioregulatory centers + SNS:

Stimulate SA Node to increase HRStimulate Adrenal Medulla to

release Norepinepherine, which increases HR

Increase contractility and SVIncrease myocardial blood flow

Exercise increases CO2, H+ and Temperature

Chemoreceptors stimulate SNS and adrenal medulla

Increase HR and SV

Exercise Applications:Vital Organs: Heart, Lungs, Brain

(Kidney)How does Exercise affect the “Priority”

of blood flow to “vital organs”?What TWO tissues during exercise

have high priority for perfusion? (become vital organs)

Vital Tissues during Exercise:Working Muscles

Larger muscles = more blood volume = greater venous return

Skin (cooling)BrainHeartLungs

Meeting the Demand: More “Vital Organs”Cardiac Response:

Increased CO by Increased SV * HR

Preserving Blood flow to “HLB”Vascular Response:

Redistributing blood flow from less vital tissues…more later

Think About This: Explain the

difference between an “athlete’s” heart and an non-athlete’s heart:

Address Cardiac Output and Heart rate at rest and exercise.

Athlete vs. Non-Athlete

Ventricle Volume and Mass

Max SV = Max HR Max CO Resting HR Resting SV = Resting CO

More Thinking: How do you think

cardiac output is affected in paraplegic athletes?

What are the dominant muscles? Where?

Would swimmers be similar?

Upper Body Athletes:

Smaller Active Muscle Mass =

Venous Return SV = HR CO

At Maximum Exercise

Summarize: The HeartFunctions of the Heart:

Blood Pressure = PerfusionDirecting Blood: Lungs / Body

Anatomy – LocationLocation / OrientationChambers / ValvesTissues: Epicardium, myocardium,

endocardium

Summary: Anatomy, cont:

Coronary ArteriesPericardium

Blood Flow Through HeartBeginning at Right Atria…Relative O2 contents

Cardiac Myocytes:Anatomy and Action Potentials

Summary: Conduction System of Heart:

SA, AV nodes, AV bundles, bundle branches, purkinje fibers

ECGCardiac Cycle:

Atrial systole - diastoleVentricular systole and diastoleHeart Sounds / Murmurs

Summary: Regulation of Cardiac Output Intrinsic Regulation:

Starling’s Law Extrinsic Regulation:

SNS, PSNS, Endocrine Exercise and Homeostasis:

Perfusion to “VITAL ORGANS” Intrinsic and Extrinsic Controls