ch 18 heart

systemic circulation

left side of heart → body → right side of heart (oxygenated blood to tissues)

pulmonary circulation

right side of heart → lungs → left side of heart (deoxygenated blood to lungs)

Heart Chambers, Valves, and Blood Flow Order -

Blood Flow Through the Heart:

• Superior/Inferior vena cava →

• Right atrium →

• Tricuspid valve →

• Right ventricle →

• Pulmonary semilunar valve →

• Pulmonary trunk/arteries →

• Lungs (gas exchange) →

• Pulmonary veins →

• Left atrium →

• Bicuspid (mitral) valve →

• Left ventricle →

• Aortic semilunar valve →

• Aorta → body

3 layers of the heart wall

epicardium

myocardium

endocardium

epicardium

visceral layer of serous pericardium

epi- upon

myocardium

muscular, middle layer (contracts)

myo- muscle

endocardium

inner layer (lines chambers)

endo-inner

angina pectoris

a type of chest pain (thoracic pain) caused by a temporary (fleeting) lack of blood flow to the heart muscle (myocardium).

causes cells to be weakened

myocardial infarction

aka heart attack

caused by prolonged blockage of blood flow in a coronary artery.

causes of myocardial infarction

• Most commonly due to:

  • Atherosclerosis (plaque buildup in arteries)

  • Blood clot (thrombus) that forms at the site of the plaque rupture

early signs of heart attack

• pressure in center of chest

• pain in shoulders, neck or arms

• chest discomfort with fainting, sweating or nausea

intercalated discs

junctions between cells

anchor cardiac cells

desmosomes

prevents cells from separating during contraction

gap junction

allows ions to pass from cell to cell; electrically couple adjacent cells

-allows heart to be functional syncticum (behaved as single coordinated unit)

contractile cardiac cells

working muscle cells that are responsible for pumping blood

ex) ventricular muscle cells

rapid depolarization

Na+ in

Na+ influx thru fast voltage gated Na+ channels

rapid upstroke (membrane potential becomes positive)

positive feedback opens more Na+ channels

ends w/ na+ channels are inactive

plateau phase

Ca²⁺ in

Ca²⁺ influx thru slow voltage gated Ca²⁺ channels

only a few K+ channels open so flow is limited

maintains depolarization allows for sustained contraction

repolarization

K+ out

Ca²⁺ channels close & K+ channels open fully

K⁺ flows out and restores membrane potential to resting state

cell becomes negative inside again

pacemaker cells

cells set the rhythm of the heartbeat

-are self excitable (generate own electrical signals

found in SA node

pacemaker potential (slow depolarization)

caused by Na+ influx thru slow “funny” channels

followed by some Ca²+ entry

slowly drifts towards threshold w/o resting potential

pace maker:depolarization

at threshold fast CA²+ influx thru voltage gated Ca²+ channels

not Na+ like contractile cells

pace maker: repolarization

Ca²+ channels close

K+ channels open

K+ efflux restores negative resting potential

ap nerve cell depolarization

• Na⁺ influx via fast voltage-gated Na⁺ channels

ap nerve cell repolarization

• K⁺ efflux via voltage-gated K⁺ channels

ap nerve cells: no plateau phase

• Much faster than cardiac action potentials

• Resting potential restored quickly

sympathetic nervous system

fight or flight