Exam 2: Heart physiology

how is basic heart rhythm modified

the ANS (parasympathetic/sympathetic)

what is the main function of coordinated heartbeat

• presence of gap junctions

• Intrinsic conduction system

what is the function of gap junctions for the heart

tunnels allow flow ions, flow of electricity in intercalated discs

what is the resting membrane potential for pacemaker cells, and why is it that way

unstable resting membrane potentials, due to opening of slow Na+ ion channels

What is the first occurance of pacemaker cells action potential

Slow depolarization is due to both the opening of Na+ channels and the closing of K+ channels

• The membrane is never at a flat line

what is the second occurance of pacemaker cells potential

• The action potential begins when the pacemaker potential reaches threshold’

• Depolarization is due to Ca2+ influx through Ca2+ channels

what is the last occurance of pacemaker cells action potential

• Ca2+ channels inactivating and K+ channels opening

• allows efflux of K+, which brings the membrane potential back to its most negative voltage

what is the sequence of heart excitation

• Sinoatrial (SA) node

• Atrioventricular (AV) node

• Atrioventricular (AV) bundle

• Right and left bundle branches

• Subendocardial conducting network

what is the secondary pacemaker

Atrioventricular node

how many impulses does the SA node complete per minute, without input from the nervous system

100x/minute

which ANS system has more control over heart rate

parasympathetic

where is the pacemaker located in the heart

right atrial wall

where is the atrioventricular (AV) node located

inferior interatrial septum

what does the AV node do

allows atria to finish their contraction before the ventricle begin to contract

what is the inherent rate for the AV node

50x/minute in absence of SA node input

where are the atrioventricular (AV) bundles located

superior interventricular septum

are the atria and ventricles connected by gap junctions

no, the are connected via AV bundles

how many pathways are there of AV bundles

two, right and left towards the apex of the heart

what is the function of the subendocardial conducting network

• complete pathway through interventricular septum to apex and up into ventricular walls

how does the ANS modify heart rate

cardiac centers in medulla oblongata

define cardioacceleratory

sympathetic output; to pacemakers and myocardium

define cardioinhibitory center

parasympathetic output; via vagus nerve; ONLY to pacemakers

what is the first part of action potential for contractile cells

• due to Na+ influx through fast voltage-gated Na+ channels

• A positive feedback cycle rapidly opens many Na+ channels, reversing the membrane potential

what is the second part of action potential for contractile cells

• due to Ca2+ influx through slow Ca2+ channels

• keeps the cell depolarized because few K+ channels are open

what is the third part of action potential for contractile cells

• due to Ca2+ channels inactivating and K+ channels opening

• allows K+ efflux, which brings membrane potential back to its resting voltage

what causes the plateau phase during action potential of contractile cells

Ca2+ surge prolongs the depolarization

define ECG

• electrocardiogram

• composite of ALL action potentials generated by intrinsic conduction syste, and contractile cells at given time

what are the three waves on a ECG

• P wave

• QRS complex

• T waves

what occurs during the P wave

atrial depolarization

what occurs during the QRS complex

ventricular depolarization, atrial repolarization

what occurs during the T wave

ventricular repolarization

define the cardiac cycle

blood flow through heart during one complete heartbeat: atrial systole and distole followed by ventricular systole and diastole

define systole

period of contraction

define diastole

period of relaxation

what are the two phenomenon that control blood flow through the heart

• contraction and relaxation sequences of the chambers

• opening and closing of the AV and SL valves

how does blood flow (think of concentration gradients)

• its controlled by pressure changes

• blood flows from an area of higher pressure to an area of lower pressure

what is related to the pressure development within a heart chamber

• volume of blood within the chamber

• size of chamber

what are the four phases of the cardiac cycle

• ventricular filling

• Isovolumetric contraction

• ventricular ejection

• Isovolumetric relaxation

what is the equation to getting the stroke volume

End diastolic volume (EDV) - End systolic volume (ESV) = Stroke Volume (SV)

define the End diastolic volume (EDV)

the most amount of blood in ventricles

define End systolic volume (ESV)

least amount of blood in ventricles

define isovolumetric

all valves are closed, the volume stays the same; ventricles are completely closed chambers, so volume remains constant

what occurs during the first stage of the cardiac cycle

• ventricular filling

• AV valves are open

• End diastolic volume, which is the volume of blood in each ventricular at the end of ventricular distole

describe passive in connection to the ventricular filling phase

80% of blood passively flows into ventricles

describe active in connection to ventricular filling phase

atrial systole occurs, delivering the remaining 20%

what occurs during ventricular systole

• atrial relaxation, ventricles begin to contract

• Closing of AV valves

• Consists of 2 phases

  • Isovolumetric contraction phase (all valves are closed)

  • Ventricular ejection phase

define ventricular ejection phase

ventricular pressure exceeds pressure in large arteries, forcing SL valves open

what occurs during isovolumetric relaxation

• ventricles relaxed; atria relaxed and filling

• ventricular pressure drops, backflow of blood in aorta and pulmonary trunk closes SL valved

• when atrial pressure exceeds that in ventricles → AV valves open; cycle begins

what is the time for one cardiac cycle

0.8 seconds

what is the time for atrial and ventricular systoles during one cardiac cycle

0.4 seconds

what is the amount of time where the heart relaxes during one cardiac cycle

0.4 seconds

describe the lub-dub sound (what valves are open and closed during the two sounds)

• First AV valves close; beginning of ventricular systole

• Second: AV valves close; beginning of ventricular diastole

define heart murmurs

abnormal heart sounds; usually indicate valves issues

what are the two types of heart murmurs

• incompetent (“leaky”) valves

• Stenotic valves

define incompetent (“leaky”) valves

don’t close completely, backflow of blood; lub-dub swish

define stenotic valves

fail to open completely; narrow opening restricts flow; described as high-pitched screeching

define cardiac output

volume of blood pumped by each ventricle in one minute (L/min)

what is the equation to find the CO

HR x SV

what is the stroke volume

volume of blood pumped out by one ventricle with each contraction or beat

what is the normal range of CO

5.25 L/min

what is the maximal amount of CO in a non-athletic person at resting

4-5x

what is the maximal amount of CO in an athletic person

7x resting

define cardiac reserve

difference between resting and maximal CO

if both the heart rate and stroke volume increase, does the CO increase

yes the CO will increase as a result of increase in HR and SV

How is end diastolic volume affected when it comes to regulation of stroke volume

it is affected by the length of ventricular diastole and venous return

how is end systolic volume affected when it comes to regulation of stroke volume

affected by force of ventricular contraction and arterial BP

what are the three main factors that affect stroke volume, and then more specifically does it affect EDV or SDV

• preload, affects EDV

• contractility affects ESV

• Afterload affects ESV

define preload

degree of stretch of cardiac muscle cells before they contract

how does preload affect EDV

• the cardiac muscle cells are naturally to close so venous return causes the stretch allowing optimal contraction in the cells

define venous return

amount of blood returning to heart

define contractility

contractile strength at given muscle length, independent of muscle stretch and EDV

what increases the contractility

• sympathetic stimulation → increased Ca2+ influx → more cross bridges

• Positive inotropic agents

  • thyroxine, glucagon, epinephrine, high extracellular Ca2+

what decreases contractility

• negative inotropic agents

  • acidosis, increased extracellular K+, calcium channel blockers

define afterload

pressure ventricles must overcome to eject blood from heart

what increases afterload

high blood pressure, which results in increased ESV and reduced SV

what are the three ways that heart rate is controlled

• neural

• chemical

• physical

How does the neural pathway affect heart rate

• sympathetic nervous system activated by emotional or physical stressors

  • Norepinephrine causes the pacemaker to fire more rapidly → faster HR → faster contraction and relaxation

• Parasympathetic nervous system opposes sympathetic effects

  • Acetylcholine hyperpolarizes pacemaker cells by opening K+ channels → slower HR

Does the parasympathetic nervous system affect the contractility of the heart muscles

no, the parasympathetic fibers only innervate pacemaker cells which affects the heart rate and not the contractility of heart muscles

How is heart rate regulated by chemicals

• hormones

• Ions

How is heart rate regulated by hormones

• epinephrine from adrenal medulla increases heart rate and contractility

• Thyroxine increases heart rate; enhances effects of norepinephrine and epinephrine

how do ions regulate heart rate

• Intra- and extracellular ion concentrations (Ca2+ and K+) must be maintained for normal heart function

  • Increased K+ decreases HR

  • moderate increase in Ca2+ increases HR

what are other factprs that influence heart rate

• age

• gender

• exercise

• body temperature

what are homeostatic imbalances of HR

• tachycardia (>100 bpm)

• Bradycardia (<60 bpm)

may result in grossly adequate blood circulation in non-athletes, may be desireable result of endurance training in athletes

what is the function of blood vessels

transport/delivery system of dynamic structures that begins and ends at the heart

what are the three types of blood vessels

• arteries

• capillaries

• veins

what is the function of arteries

• carry blood away from the heart

what is the function of capillaries

contact tissue cells; directly serve cellular needs

what is the function of veins

carry blood toward the heart

what is the direction of blood flow for the systemic circuit, include the veins

• left ventricle aorta

• large arteries

• smaller arteries

• arterioles

• capillaries

• venules

• small veins

• larger veins

• superior and inferior vena cava

• right atrium

what are the three tunic that make up the walls of the arteries and veins

• tunica intima

• tunica media

• tunica externa

describe the tunica intima

endothelium (simple squamous epithelium) lines the lumen of all vessels

describe tunica media

• smooth muscle and sheets of elastin

• innervated by sympathetic vasomotor nerve fibers of the ANS, control vasoconstriction and vasodilation of vessels

describe tunica externa

• areolar CT with collagen and elastic fibers - protects, reinforces, and anchors

• infiltrated with nerve fibers, lymphatics, and even tiny blood vessels

what has the bigger lumen, arteries or veins?

veins

what contains valves, arteries or veins?

veins

what are the contractility properties of arteries

• vasoconstriction

• vasodilation

what is the elasticity properties of arteries

ability to return to resting length after being stretched, stretch and recoil

what is the connection to potential and kinetic energy to arteries

• potential energy - surge of blood into the aorta stretches its elastin fibers, and allows it to “store” blood

• Kinetic energy - during diastole, the drop in blood pressure allows the elastin fibers to rebound and propel the blood forward

what are the three group that arteries can be divided into

• elastic arteries

• muscular arteries

• arterioles

describe elastic arteries, provide examples

• tunica media is rich in elastin

• pressure reservoirs

  • expand and recoil as blood is ejected from the heart

• Examples: aorta and its immediate branches