Exercise Physiology Chapter 7

CV overall function

Transport

pulmonary circuit

pumps deoxygenated blood to the lungs 

Systemic circuit

pumps oxygenated blood from the lungs to the body

True or false: Right and left sides MUST each pump equal volumes per unit time

True

Blood flow through heart

• Inferior and superior vena cavae

• Right atrium 

• Tricuspid valve

• Right ventricle 

• Pulmonary semilunar valve 

• Pulmonary arteries 

• Lungs 

• Pulmonary veins 

• Left atrium 

• Bicuspid (mitral) valve 

• Left ventricle 

• Aortic semilunar valve 

• Aorta 

Epicardium

outer, connective tissue, protection 

Myocardium

middle, muscular layer, thick layer 

Endocardium

 inner, endothelium overlaying a thin connective layer

Septum

muscular wall separating L & R halves of heart 

Pericardium

triple layer bag that surrounds & protects heart (reduces friction)

Heart valves

purpose is to prevent back flow of blood, ensuring one-way blood flow, They open and close passively with pressure of blood against them 

AV Valves

thin walls, open when P in atria is higher than ventricles, close w/ retrograde P of blood against valves 

Chordae tendinae and Papillary muscles

prevent AV valves from reopening during ventricular contraction and causing leakage of blood into atria 

SL Valves

thicker walls, open and close when ventricular pressures exceed arterial pressures, close as blood flows backwards and fills cusps, no chordae tendinae or papillary muscles 

Lub sound

the closing of the two atrioventricular valves

Dub sound

the closing of semilunar valves 

3 classes of cardiac muscle

• Atrial contractile 

• Ventricular contractile 

• Specialized conductive

Myocardium characteristics

striated, sarcomere, and crossbridge cycle all the same as skeletal muscles 

Intercalated Disks

 join adjacent muscle cells together 

Desmosomes

adhering junctions 

Gap junctions

diffusion of ions between fibers with very little electrical resistance (almost free flow) 

Major importance of syncytial arrangement

1 impulse spreads to all fibers in syncytium to contract as a unit 

2 syncytia

atrial and ventricular 

Autoconduction

no need for innervation, creates own AP, no fiber type differences, fibers are highly oxidative 

Autoconduction + Syncytial arrangement

 = Autorhythimicity 

What allows us to autoconduct?

Pacemaker potentials or funny currents

What causes plateau in AP?

Opening of L type Ca++ channels, decreased membrane permeability to K+, delays repolarization

Significance of refractory periods

 they prevent tetany (involuntary contraction of muscles)

Increased extracellular Ca++ levels

enhance contraction 

Decreased extracellular Ca++ levels

inhibit contraction

SA Node

sinus rhythm 

SA Node - pacemaker

greatest permeability to Na+ 

AV Node pause duration and purposes

delays delivery of signal to ventricles by 0.13 s, allowing time for ventricular filling & AV valve closure

Net effects of specialized ventricular conduction system

allows simultaneous contraction of all parts of ventricles (6x normal ventricular fiber conduction speed) 

Ventricular conductive system: 

• Bundle of His (AV bundle) 

• Bundle Branches (R & L)

• Purkinje fibers

Chronotropic regulation

regulates heart rate 

Inotropic regulation

regulates contractive force 

Frank-starling Mechanism

increase in venous return, increase stretch on cardiac fibers, increase recoil upon contraction, increase contractive force 

PNS

vagus nerve, ACh

Increase in K+ permeability

hyperpolarizes membrane, decrease HR 

Vagal tone

 normal parasympathetic stimulation to control HR at rest 

Decrease in Ca++ entering through L type channels

decrease permeability, decrease force 

E/NE

released due to SNS stimulation, effects same as SNS 

Heart regulation - body temp 

Increase BT, increase membrane permeability to Na+ & Ca++, increase HR & contractive force 

Proprioceptors

increase HR at exercise onset 

Baroreceptors

stretch/pressure receptors in aorta and carotids 

Decreased BP

SNS stimulation

Increased BP

PNS stimulation 

Chemoreceptors

sensitive to chemical concentrations in blood; located in aorta and carotids 

Decreased O2, increased CO2 &/or decreased pH

SNS stimulation  

P-wave

atrial depolarization 

QRS complex

ventricular depolarization 

T-Wave

ventricular repolarization 

Diastole

phase of cardiac cycle when myocardium relaxed

Systole

phase of cardiac cycle when myocardium contracted

Atrial diastole

pressure ~ 0 mmHg, 70% of blood enters ventricles passively 

Atrial systole

last 30% filling (atrial kick), atria primer pumps for ventricles, closing of AV valves ends

Ventricular Systole 

Ventricular contraction increases pressure until semilunar valves open

Isovolumetric contraction

valves closed, builds pressure

Afterload

resistance against which left ventricle pumps 

Isovolumetric relaxation

valves closed again, most of our drop in pressure 

ESV

blood remaining in LV at end of ventricular systole, amount remaining after contraction

Ventricular diastole 

• 1st ⅓ rapid filling (70%) 

• 2nd ⅓ - not much 

• Last ⅓ - atrial systole (30%) atrial kick 

EDV

volume of blood in left ventricle at end of ventricular diastole

Preload

load to which a muscle is subjected before shortening (initiates frank starling) 

Stroke Volume

volume of blood pumped from LV with each beat 

SV formula

SV = EDV - ESV 

Ejection Fraction

proportion of blood pumped out of LV w/ each beat, 60-70% at rest, 80-90% when exercising

EF formula

EF = SV / EDV 

Cardiac Output (Q)

volume of blood pumped per unit time (per minute), 5 L/min at rest, 25 L/min while exercising

Q formula

Q = HR x SV 

Vascular system 3 wall layers

Itima, media, adventita

Itima

inner, contacts blood, single layer endothelial cells w/ thin basement membrane

Media

middle, smooth muscle

Adventita

outer, connective tissue

Arteries Function

carry blood away from heart 

Arteries characteristics

thick, elastic, high pressure 

Veins function

return blood to the heart

Veins characteristics

thin walls, low pressure 

Precapillary sphincter

controls blood flow into capillaries 

Capillaries

1 cell thick vessels for gas exchange 

Unidirectional valves

prevent back flow and aid venous return 

SBP

highest BP within vascular system, generated during cardiac systole

DBP

lowest BP within vascular system, generated during cardiac diastole

BF distribution

at rest, 64% of blood is in veins 

Venous reservoir

veins store blood and can constrict to increase venous return

BF from submax to max exercise

decrease BF to skin, compromise heat dissipation in favor of muscle contraction

Microvascular regulation

adjusting smooth muscle tone in vessel walls, especially arterioles at precapillary sphincter 

Acute control

changes in local concentrations of substances that act as vasodilators or vasoconstrictors

Long-term control

production of vascular growth factors that cause angiogenesis 

Oxygen effect

high oxygen - vasoconstriction

low oxygen - vasodilation

Endothelin

Released when endothelium damaged

Powerful vasoconstriction

prevents excessive blood loss in affected artery 

Increase SNS stimulation

constricts vessels further, increase arterial pressure

Decrease SNS stimulation

relieves some constriction, vessels dilate, decrease arterial pressure 

SNS stimulation to veins

causes venoconstriction, increase venous return 

Vasomotor tone

SNS continuously transmits frequent impulses to blood vessels, it keeps vessels in state of moderate constriction to maintain adequate BP 

Blood Volume Components

 plasma 55%, RBC 45%, WBC/PLatelets < 1%

Plasma 

• 55-60% of total blood volume

• 90% water w/ dissolved proteins (7%) & nutrients, electrolytes, hormones, antibodies, and waste (3%)

Hematocrit

% of total blood volume that consists of formed elements or RBCs