IFS WE3: CVS, Physio/CNS, Anatomy, BioM

CVP

Explain the anatomy of the heart

Overview of CVS:

-Closed system

*Heart as a pump

*Blood vessels

*Blood

Overview of CVS: Functions

-Transport of materials (Blood consist of nutrients, gases, water, hormones, antibodies + waste)

-Pathogen defense (antibodies + WBC's)

-Temperature control (vasodilation + vasoconstriction)

Heart location/parts

-Located in ventral aspect of thoracic cavity (between R/L lungs)

-Size of a fist

-Apex (lower pointed end of heart) Located inf. and positioned toward left (5th intercostal space)

-Base is broader, sup. and positioned behind sternum

Endocardium

Inner layer

Myocardium

Muscular middle layer

Epicardium

protective outer layer

Pericardium

Tough membranous sac

*filled with pericardial fluid that encases the heart and lubricates the heart

*permits to contract with min. friction

Anatomy of the Heart: Chambers

-4 chambers

*2 Atria

*2 Ventricles

**Ventricles separated by interventricular septum

Blood flow through Heart

*Atria receives blood to the heart and Ventricles pump blood out of heart

1) R atrium receives (deoxygenated blood from superior and inferior vena cava)

*pumps blood to R Ventricle

2) R Ventricle pumps (deoxygenated blood to the lungs via pulmonary a.)

3) L atria receives (oxygenated blood from the from the lungs via pulmonary v.)

*pump to L Ventricles

4) L Ventricle pumps (oxygenated blood through the aorta to systemic circulation)

Pulmonary circulation

-Blood flow from the heart to the lungs

-And from the lungs back to the heart

Systemic Circulation

-Blood flow from the aorta to the tissues

-And organs of the body back to the heart

Explain the location and names of the heart valves

Atrioventricular valves (AV)

Located between atria and ventricles

Between the R atria/R ventricle

Tricuspid Valve

Bicuspid/Mitral Valve

Between the L atria and L ventricle

Chordae tendineae

-Collagenous tendons

-attach to the flaps of the valves and anchor to papillary muscles in the ventricle

*preventing the valves from being pushed back into the atria when the ventricles contract

Semilunar valves (SL)

-Between ventricles and major a.

Pulmonary Valve

-Between the R ventricle and pulmonary a.

Aortic Valve

-Between L ventricle and aorta

Explain the blood flow through the heart

Flow chart

1) Sup./Inf. Vena Cava

2) R Atria

3) Tricuspid Valve

4) R Ventricle

5) Pulmonary valve

6) Pulmonary A.

7) Lungs

8) Pulmonary V.

9) L Atria

10) Mitral Valve

11) L Ventricle

12) Aortic valve

13) Aorta

14) Systemic A.

15) Capillaries

16) Veins

Explain the histology of the cardiac cells

Autorhythmic Cells

-Pacemakers

-1% of cardiac muscle fibers

-Generate electrical signal for contraction

-Smaller and fewer contractile fibers

-Lack of organized sarcomeres

Contractile Cells

-99% of cardiac muscle cells (lots of mitochondria)

-Striated fibers organized into sarcomeres

-Branched, single nucleus

-attached by specialized junctions=intercalated disks

Explain blood supply to the heart and the different branches of aorta

Explain pacemaker potential

Autorhythmic cells (pacemakers)

-1% of cardiac muscle fibers

-Generate AP spontaneously

-Sets Hr

Heart is Myogenic

-signal for contraction originates from the heart itself

*Occurs bc of the autorhythmic cells spontaneous AP

*Connections to the contractile cells to produce a contraction

Pacemaker Potential: Autorhythmic cells

-have unstable membrane potentials called pacemaker potentials

*spontaneous drift towards less negative values

Resting Membrane potential

-Drifts between -60 to -40 mv due to net influx of Na2+ ions

Pacemaker Potential: Depolarization

-Due to closure of Na2+ channels and opening of Ca2+ channels=Ca2+ influx

Pacemaker Potential: Repolarization

-Is due to closure of Ca2+ channels + opening of K+ channel=K+ outflux

Explain myocardial action potential

-Myocardial contractile cells

*Resting membrane potential -90mV

Myocardial Phases

Phase 0: Depolarization due to Na+ entry

Phase 1: Initial repolarization due to closure of Na+ channels

Phase 2: Plateau phase: Decrease K+ permeability + increased Ca2+ entry into the cell

Phase 3: Rapid repolarization: Ca2+ channels close + K+ permeability is increased

Compare and contrast between myocardial cells and autorhythmic cells

Similarities

-Ca2+ plays a unique role in each to generate an AP

*Autorhythmic cells-require Ca2+ influx/channel opening to cause depolarization

*Contractile cells: Ca2+ responsible for plateau phase of AP after initial influx of Na+

Differences

-Different resting membrane potentials for an AP

*Autorhythmic cells-unstable pacemaker potential- 60 mV, Ca2+ entry results in depolarization

*Myocardial Contractile cells- resting member potential-90 mV, Ca2+ results in plateau phase

Explain electrical conduction in the heart

SA node

-Sinoatrial

*first point of depolarization "pacemaker of heart"

Location: is in the superior and posterior walls of the R atrium

*near the opening of the superior vena cava + deep to epicardium

Autorhythmic cells in SA node

-Depolarize + send signal via an internodal pathway to AV node, located on floor of R atrium

*SA node also transmits electrical impulse to L atrium

Electrical conduction of the heart

1) SA node depolarizes

2) Electrical activity goes rapidly to AV node via internodal pathways

3) Conduction slows through AV node, a delay of 0.1 s occurs before excitation spread to ventricle

4) Depolarization moves rapidly through AV bundle

*bundle branches and Purkinje fibers to the apex of heart

5) Depolarization wave spreads upward from the apex

Explain EKG and terms such as waves, segments and intervals

Electrocardiogram ECG/EKG

Is the sum of multiple AP taking place in many heart cells

Wave

Parts of the trace that go above or below the baseline

Segment

Section of the baseline between 2 waves

Interval

Combination of waves and segments

P wave

Atrial depolarization

QRS complex

Ventricular depolarization

T wave

Ventricular repolarization

PR interval

Atrial depolarization + conduction through AV node

QT interval

Ventricular depolarization + repolarization

R-R interval

Represents the time between 2 consecutive heartbeats

P-R or PQ segment

Conduction through AV node

ST segment

Isoelectric line before ventricular repolarization

Explain cardiac muscle contraction

AP begins with pacemaker cells

-Voltage-gated L-type Ca2+ channels in the cell membrane open

-Ryanodine receptors open in the SR-Calcium enters cytoplasm

-Calcium binds to troponin

-Crossbridge cycle

Relaxation

-Calcium removed from cytoplasm: back into the SR with Ca2+ + ATPase

-Calcium removed from cell through the Na+ -Ca2+ exchanger in the cell membrane

Force generated

-is proportional to number of active crossbridges

*Determined by how much calcium is bound to troponin

-Sarcomere length affects force of contraction

Explain the terms such as a systole and diastole and the concept of blood flow and pressure in the heart

Systole

Cardiac muscle contraction

Diastole

Cardiac muscle relaxation

Principle blood flow

-Blood flows from areas of high pressure to low pressure

*Contraction increases pressure

*Relaxation decreases pressure

Explain Cardiac Cycle

Start: Late Diastole (relaxation)

Both chambers are relaxed, Semilunar valves are closed. AV valves are open, ventricles fill passively (-70% blood volume)

2) Atrial systole (contraction)

-Atrial contraction forces additional 30% of blood into ventricles (atrial kick)

*semilunar valves are closed and AV valves are open

3) Isovolumic Ventricular contraction

-1st phase of ventricular contraction, AV valves, closed

*Max blood volume in ventricles=EDV

*closure of AV valve results in S1 Heart sound

4) Ventricular ejection (SV=70 ml)

-Ventricular pressure rises, exciding pressure in the arteries + opening semilunar valves

*Blood is ejected

5) Isovolumic Ventricular relaxation

-Ventricles relax

-Blood flows back into semilunar valves closing them

-Min blood volume in ventricles (ESV=65 mL)

*closure of SL valve results in S2 heart sound

Know terms

End Diastolic Volume (EDV)

-Volume of blood in each ventricle at the end of diastole (ie before ventricular contraction) =135 mL

End Systolic Volume (ESV)

-Volume of blood in each ventricle at the end of ventricular systole=135-70=65 mL

Cardiac output

-Volume of blood pumped by each ventricle per minute =5-6 L/Min

Heart Rate

is the number of times a person's heart beats per minute; also

known as pulse. Average adult is 60-100 bpm

Ejection fraction values

-EF is the % of EDV ejected with one contraction

-Stroke Volume/EDV

-70/135=52%

Stroke Volume

-Amount of blood ejected out of each ventricle during systole=70 ml

Ejection Fraction

-Percentage of blood that leaves the ventricle with each contraction=SV/EDV=50-70% of the % EDV ejected per contraction of the ventricle

-Amount of blood pumped out of each ventricle during contraction/Amount of blood in each ventricle at the end of diastole

calculation

-SV=EDV-ESV

135ml-65 ml=70 ml

-EF=SV/EDV

70/135=52%

Explain the factors that influence SV

Contractility

-Affected by length of the muscle fiber

-Function of calcium interaction with contractile filaments

-Determined by the volume of blood at beginning of each contraction

-As stretch of the ventricle increases, so does SV

Frank Starling Law

-Relationship between stretch and force

-SV increases as EDV (End diastolic volume) increases

Preload

-Is the degree of stretch of the myocardium before contraction (depends on EDV)

*End diastolic volume

-Determined by venous return

-Venous return depend on:

*Skeletal muscle pump

*Respiratory pump

*Sympathetic innervation of veins

Venous return depend on: Skeletal Muscle pump

-Is a mechanism by which contracting muscles assist in the return of venous blood to the heat, LE

-One way venous valves prevent backflow

Ex: During exercise, skeletal muscle pump is highly active, leading to greater EDV

*increased SV

*improved CO

*supporting higher oxygen demands

Venous return depend on: Respiratory Pump

-Mechanism that enhances venous return to the heart by utilizing changes in intrathoracic + intra-abdominal pressure during breathing

*Inspiration (inhalation): Thoracic pressure decreases

*expanding vena cava + pulling more blood into the R atrium

*Abdominal pressure increases, compressing V. in the abdomen and pushing blood toward heart

-Expiration (Exhalation) Blood that accumulated in the pulmonary circulation moves into the L heart, aiding systemic circulation

Venous return depend: Sympathetic innervation of veins

-Sympathetic innervation of veins:

*Activation leads to venoconstriction (narrowing of v) reduces venous compliance

*forcing more blood to heart

Explain cardiac output and calculate CO using the formula

Cardiac Output

-Volume of blood pumped y one ventricle per min.

-A measure of Cardiac performance

-At rest, the heart pumps all of the blood in the body in only 1 min

Calculating CO

=HR x SV

-Resting CO

ex: 72 bpm x 70 ml=5040 ml/min

Avg: 5 L/min

-During exercising CO could increase 5-6 fold to 25-30 L/min

Calculate HR in a subject

EF=52%

EDV=135 ml

CO= 5L

Describe the autonomic innervation and its effects on the heart. Include neurotransmitters and receptors involved

Stimulation of Parasympathetic Nerves

-Decreases HR (Bradycardia)

-Ach (acetylcholine) on M receptor (Muscarinic)

Stimulation by Sympathetic Nerves

-Increases HR (Tachycardia)

-Increases Contractility (Inotropic)

-Sympathetic neuron (EPI, NE on B1 receptor)

EPI/NE=epinephrine/norepinephrine

Explain regulation of heart rate

Parasympathetic control "rest and digest"

-Responsible for typical resting HR

-Ach binds to Muscarinic receptors

-Increase potassium permeability + decrease calcium influx

-Reduced rate of depolarization

-Reduced HR

Sympathetic control "fight or flight"

-Responsible for increasing HR

-Norepinephrine bind with beta 1 receptors

-Increase sodium + calcium permeability

-Increase rate of depolarization

-Increased HR

Explain the anatomy of the blood vessels

-Each side of the heart acts as an independent pump

-Composition of vessels influence pressure + flow

-Resistance to flow influenced by:

*diameter

*length

*Viscosity of fluid

Arteries

-must withstand high pressure from the heart

-Act as pressure reservoir

*due to elastic + recoil ability

Arterioles

-major site of resistance

-diameter is regulated by local factors

-ANS + hormones which regulate BP + blood flow

Capillaries

-Exchange vessels consist of fenestrations or pores

-Precapillary sphincters