“Little Cowboy”

Homeostasis and The Heart Tissues and Organs Depend on Appropriate Blood Flow (Perfusion) Supply = Demand

Starling’s Law: Intrinsic Control of Heart Venous Return determines “stretch” of cardiac myocytes: Venous Return = Stretch Stretch = Force and Rate Known as Preload Exercise Increases Venous Return / Preload / Force & Rate

Extrinsic Control: Baroreceptor Reflex Baroreceptors: 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 Inhibition Of Pressure Signals

Baroreceptor Reflex… Efferent Signals from Autonomic Nervous System: Parasympathetic: Decrease HR Sympathetic: Increase HR Adrenal: Increase HR How do you think pressure affects perfusion of vital tissues?

Decreased CO Threatens Vital Organs Cardiac Response: Increase HR (to compensate for decreased pressure/SV) Vascular Response: Direct more of the total blood volume to vital tissues Away from less vital tissues

Extrinsic Control: Chemoreceptor Reflexes Increased Metabolism produces more CO 2, acids, and Temp: Chemoreceptors (mostly in the medulla oblongata) initiate: SNS stimulation: Rescues from “metabolic buildup” by HR PSNS stimulation: Slows the heart when CO 2, acids and temp recover

Exercise = Preload Working muscles “squeeze” more blood back to heart Increased Venous Return = Increased Preload Starling Law is important in initial increases in Exercise CO

Exercise Stimulates SNS Cardioregulatory centers + SNS: Stimulate SA Node to increase HR Stimulate Adrenal Medulla to release Norepinepherine, which increases HR Increase contractility and SV Increase myocardial blood flow

Exercise increases CO 2, 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) Brain Heart Lungs

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 Heart Functions of the Heart: Blood Pressure = Perfusion Directing Blood: Lungs / Body Anatomy – Location Location / Orientation Chambers / Valves Tissues: Epicardium, myocardium, endocardium

Summary: Anatomy, cont: Coronary Arteries Pericardium Blood Flow Through Heart Beginning at Right Atria… Relative O 2 contents Cardiac Myocytes: Anatomy and Action Potentials

Summary: Conduction System of Heart: SA, AV nodes, AV bundles, bundle branches, purkinje fibers ECG Cardiac Cycle: Atrial systole - diastole Ventricular systole and diastole Heart 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