cardiovascular system

cardiac muscle characteristics and structure

- only found in the heart

-striations of repeating sarcomeres

-small w single nucleus

-arranged in layers and surround hollow cavities

-troponin and tropomyosin present

- T-tubules present

-SR present

-joined by intercalated discs

intercalated disks

link cardiac muscle cells together both mechanically and electrically

2 distinct features:

1. desmosomes: mechanically join cells with protein filaments

2. gap junctions: electrically join cells (allows ion flow)

functional syncytium

stimulation within a chamber results in a synchronous contraction of that chamber; each heart chamber functions as if it were one cell or a functional unit

L-type Ca2+ channels

(cardiac muscle excitation-contraction coupling)

specialized voltage-gated Ca2+ channels named for their long-lasting current

-located on sarcolemma and T-tubules (highly concentrated)

prolong cardiac muscle action potential and refractory period

Ryanodine Receptors

Ca2+ ch in cardiac SR

-opened by binding Ca2+ in cytosol rather tan by voltage as in skeletal muscle

-calcium-induced calcium release

Calcium-Induced Calcium Release

small initial influx of Ca2+ into the cell triggers the release of much larger quantity of Ca2+ from SR

tetanic contraction (tetanus)

sustained, maximum muscle contraction

-caused by high-frequency motor neuron stimulation, where muscles cannot relax between stimuli

can cardiac muscles exhibit tetanus? explain.

no because of L-type Ca2+ ch

-cardiac cells have a long refractory period of about 250ms

-cardiac cell contracts and relaces before it can be stimulated again which makes tetanic contraction impossible

cardiac muscle innervation (sympathetic and parasympathetic)

sympathetic:

-release NE

parasympathetic

-contained in vagus nerves (cranial nerve X)

-primarily release ACh

-muscarinic receptors

cardiovascular system overview and functions

heart + blood vessels

function: transports blood throughout the body

-delivery of O2, nutrients; removal of CO2, wastes

perfusion

delivery of blood per time per gram of tissue (mL/min/g)

adequate perfusion

sufficient delivery to maintain cells' health

-requires continual pumping of the heart and open, healthy vessels

what perfuses the heart?

heart is perfused by coronary arteries that supply muscle tissue

-blood inside the heart does not supply the heart w oxygen and nutrients

blood vessels

conduits of cardiovascular system that transport blood

three main types: arteries, veins, and capillaries

arteries (arterial trunks)

carry blood AWAY from heart

-most (not all) carry oxygenated blood

veins

carry blood back TOWARD the heart

-most (not all) carry deoxygenated blood

capillaries

sites of exchange (ex. of gases)

-b/w blood and air in lungs

-b/w blood and body cells

heart

hollow, four chambered muscular organ that pumps blood throughout the body

anatomic features vital to function:

-two sides

-great vessels

-valves

sides of heart and their functions

right side: receives deoxygenated blood from body and pumps it to lungs

left side: receives deoxygenated blood from lungs and pumps it to body

chambers of the heart

each side has two chambers

-atria (superior chamber)

-ventricles (inferior chamber)

interatrial septum

separates left atrium from right atrium

interventricular septum

separates left ventricle from right ventricle

pericardim

protective fibrous sac surrounding the heart

(a layer of the heart)

do the atria or ventricles have thicker walls?

ventricles (pumping chambers) have thicker walls then atria

is the left or right ventricle thicker?

left ventricle is thicker

-it must generate high pressure to to force blood through systemic circulation

-right just pumps to the nearby lungs

layers of the heart wall

epicardium, myocardium, endocardium (outside to inside)

epicardium

-outermost layer of the heart

-epi=upon

myocardium

-middle layer of heart wall (thickest)

-cardiac muscle cells that contract to pump blood

-myo=muscle

endocardium

-covers internal surface of heart and external surface of valves

-composed of endothelial cells

-continuous with lining of blood vessels

great vessels

transport blood directly to and from chambers of the heart

pulmonary trunk

transport blood away from heart to lungs (artery)

-branches into pulmonary arteries

aorta (descending and ascending)

transport blood away from heart to the rest of the body (artery)

-descending: to lower body

-ascending: to upper body

superior vena cava (SVC)

drain deoxygenated blood from superior body toward right atrium (vein)

inferior vena cava (IVC)

drain deoxygenated blood from inferior body toward right atrium (vein)

pulmonary veins

drain oxygenated blood into left atrium

what are the 2 sets of valves? Made of? function?

1. atrioventricular (AV) valves

2. semilunar valves

-made of endothelium-lined fibrous connective tissue cusps (flaps)

-ensure one-way flow of blood through heart

atrioventricular (AV) valves

sit b/w atrium and ventricle of each side

-right AV valve = tricuspid

-left AV valve = biscuspid or mitral valve

chordae tendineae (tendinous cords)

thin strands of collagen fibers attaching to AV valves

papillary muscles

cone-shaped projections extending from internal ventricle wall

-anchor chordae tendineae

semilunar valves

prevent backflow of blood into ventricles

each has 3 cusps

-pulmonary semilunar valve

-aortic semilunar valve

pulmonary semilunar valve

-located b/w right ventricle and pulmonary trunk

-prevent backflow of blood into ventricles

aortic semilunar valve

-located b/w left ventricle and aorta

-prevent backflow of blood into ventricles

heart sounds

S1 ("lubb") closing of AV valves

S2 ("dub") closing of semilunar valves

heart murmur

abnormal heart sound

-result of turbulence of blood passing through heart

-may be caused by valvular leakage, decreased valve flexibility, or a misshapen valve

basic pattern of circulation

right heart → lungs → left heart → systemic tissues → right heart

pulmonary circulation

the path of deoxygenated blood from the right side of the heart to the lungs

- right ventricle → lungs → left atrium

microcirculation

where exchange of gases, substrate, and waste products occurs b/w the blood and the extracellular fluid

- arterioles → capillaries → venules

-blood vessels return to left side of heart

systemic circulation

the path of oxygenated blood from the left side of the heart to systemic cells

-left ventricle → peripheral organs/tissues → right atrium

-at systemic cells (ex. skin, muscles), blood exchanges gases, nutrients, and wastes

-blood vessels return to right side of heart

1. heart contraction involves 2 events, what are they?

1. conduction system: initiates and propagates an action potential (excitation)

2. cardiac muscle cells: fire action potentials and contract (cross-bridge)

conduction system

initiates and conducts electrical events to ensure proper timing of contractions

-composed of specialized cardiac muscle cells that have action potentials but DO NOT contract

-activity influenced by autonomic NS

sinoatrial (SA) node

initiates heartbeat (pacemaker)

-located high in posterior wall of right atrium

atrioventricular (AV) node

located in floor of right atrium (near right AV valve)

atrioventricular (AV) bundle (bundle of his)

-extends from AV node through interventricular septum

-divides into left and right bundles

purkinje fibers

-extend from left and right bundles at heart's apex

-course through walls of ventricles

nodal cells

-nodal cells in the SA node initiate heartbeat

-exhibit autorhythmicity

-do not have a stable RMP

-common membrane proteins: Na+/K+ pumps, Ca2+ pumps, leak channels

-specific voltage-gated channels: slow ("funny") VG Na+ ch, fast VG Ca2+ ch, VG K+ ch

autorhythmmicity

spontaneously depolarize and generate an action potential

-aka spontaneous firing

resting membrane potential

about 60mV

pacemaker potential

ability to reach threshold without stimulation

cardiac muscle cells

- contain Na+/K+ pumps, Ca2+ pumps, Na+ and K+ leak channels

-resting membrane potential: -90mV

-contain specific VG Ca2+ ch

-fast VG Na+ ch

-L-type (slow) VG Ca2+ ch

-VG K+ ch

tetanic contraction (tetanus)

sustained, maximum muscle contraction

• caused by high frequency motor neuron stimulation, where muscles cannot relax b/w stimuli

cardiac muscles and tetanus

cardiac muscle cannot exhibit tetanus

• cardiac cells have a long refractory period = cell cant fire a new impulse

• plateau phase leads to refractory period of about 250ms

  • cardiac cell contracts and relaxes before it can be stimulated again

electrocardiogram (ECG/EKG) recording

• skin electrodes detect electrical signals of cardiac muscle cells

• tool used to diagnose

• measure summation fof many cardiac cell action potentials (APs) → not single AP

cardiac cycle

all events in the heart from the start of one heartbeat to the start of the next

• includes systole and diastole

• Contraction increases pressure; relaxation decreases it

  • blood moves down its pressure gradient (h → l)

  • Valves ensure that flow is forward / one-directional (closure prevents backflow)

ventricular activity

most important driving force

systole (ventricular contraction)

raises ventricular pressure

diastole (ventricular relaxation)

lowers ventricular pressure

4 main events of cardiac cycle

1. ventricular filling

2. isovolumetric ventricular contraction

3. ventricular ejection

4. isovolumetric ventricular relaxation

ventricular filling

• 1st event

• both AV valves open → blood floes into ventricles

• semilunar valves closed

• ventricles filled to end-diastolic volume (EDV)

  • amount of blood just before systole

isovolumetric ventricular contraction

• 2nd event

• beginning of systole

  • isovolumetric

    • all 4 valves are closed

      • no blood can be ejected

      • ventricular pressure increases

isovolumetric

associated with no volume change

• all 4 valves are closed

ventricular ejection

pressure in the ventricles exceeds pressure in aorta

and pulmonary trunk

→ semilunar valves open → blood ejected

from ventricles

• AV valves closed (chordae tendineae and

papillary muscles) to ensure one-directional

flow of blood

• Stroke volume (SV)

• Volume of blood ejected per cardiac

cycle

Isovolumetric ventricular relaxation

• 4th event

• beginning of diastole

• isovolumetric

  • all 4 valves are closed

• end systolic volume

end systolic volume

amount of blood remaining in ventricle after contraction finishes

• ESV=EDV-SV

cardiac output

amount of blood pumped by a single ventricle in one minute (e.g., L/min)

• measure of effectiveness of cardiovascular system

• determined by heart rate and stroke volume

  • HR x SV = CO

what influences HR

chronotropic agents

• autonomic NS

• hormones

what influences SV?

• preload

• inotropic agents

• afterload

chronotropic agents

external agents that change HR

• alter activity of nodal cells

• autonomic NS

  • parasympathetic : dec HR

  • sympathetic: inc HR

• hormones

  • epi: inc HR

preload

pressure stretching heart wall before shortening

• inc by filling heart w more blood (venus return)

  • inc EDV

frank starling mechanism

force of ventricular contraction directly proportional to the initial length (stretch) of myocardial fibers

• greater stretch (EVD/preload) → actin and myosin overlap in more optimal pattern → stronger contraction → higher SV

ionotropic agents

external agents that affect stroke volume by alterign contractility

• inc or dec avaliable Ca2+

  • sympathetic nerve stimulation : inc SV

  • epi : inc SV

contractility

force of contraction independent of stretch (EDV)

afterload

how hard the heart must work to eject blood from ventricles

• greater the “load” (pressure of blood in arteries) → inc work of cardiac muscle to eject blood → dec stroke volume

atherosclerosis

(plaque in vessel linings) increases afterload

• plaque dec artery diameter → inc resistance to blood flow

general structure of vessels

vessel walls are composed of 3 layers called tunics

• lumen : space inside of vessel where blood resides

tunica externa

outermost layer of vessel wall

• helps anchor vessel to other structures

tunica media

middle layer of vessel wall

• circularly arranged layers of smooth muscle cells w elastic fibers

• contraction causes vasoconstriction

• relaxation causes vasodilation

vasoconstriction

narrows lumen → inc pressure

vasodilation

widens lumen → dec pressure

tunica intima

innermost layer of vessel wall

• endothelium of simple squalamous epithelium

  • provides smooth surface for blood flow

arteries

heart ventricles → arteries → arterioles

• contain smooth muscle

• thick walled

• large quantity of elastic tissues → elasticity

• large diameter → low resistance

arteriole blood pressure depends on

• volume of blood

• how easily vessels can stretch → compliance

compliance

change in (Δ) volume/change in (Δ) pressure

systolic pressure

maximum arterial pressure just before ventricular ejection

diastolic pressure

min arterial pressure just before ventricular ejection

what is arterial pressure recorded as?

systolic/diastolic

capillaries

small vessels connecting arterioles to venules

• thin wall of endothelial cells and basement membrane (no surrounding smooth muscle or elastic tissue)

• small diameter : optimal for exchange between blood and tissue fluid

3 types of capillaries

1. continuous

2. fenestrated

3. sinusoid

capillary beds

groups of capillaries functioning together

• precapillary sphincter

precapillary sphincter

smooth muscle ring that helps determine volume of blood each capillary receives

veins

venules → veins → heart atria

• thinner, less eslatic fibers, and less muscle then arteries

• venous valves

  • prevent blood from pooling in the limbs; ensure blood flow toward heart