Physio_09.txt

cardiac contraction lasts for a much longer duration

intercalate disk, specialized cell membranes with gap junctions that present small amounts of resistance to electrical impulses

• syncytium
• when one becomes excited they all become excited

• 105
• -85 to +20

• allows cardiac muscle contraction to last 15x longer then skeletal muscle
• last about 0.2 seconds
• immediately after the onset of the AP the cardiac muscle membrane permeability for K decreases, can occur due to Ca influx, prevents early depolarization
• K permeability returns to normal when the Ca channels close

• opening of fast Na channels and slow calcium channels (calcium-sodium channels)
• slow channels are slower to open and remain open for a longer duration, these cause the plateau phase
• the entering calcium ions are what cause the contraction of cardiac muscle
• The SA node's fast channels are inactivated because of its less negative resting state, The AP here is slower.

.25 - .3

• about .05 seconds in cardiac muscle
• muscle can be excited but it takes a much larger stimulus
• the atrial muscle is mush shorts refractory period then ventricular muscle, about .15 sec

• T tubules
• also release Ca ions into the muscle, determines the strength of contraction
• 5 times larger in cardiac muscle then in skeletal muscle
• calcium is made available in the T tubules by a large quantity of mucopolysaccharides that bind and store calcium

• in skeletal muscle it is stored in the cistern of SR
• on cardiac muscle calcium is in the extracellular fluid

0.2-0.3

• A is atrial contraction
• V is the passive flow of fluid into the atria while the AV valve is closed
• C is ventricular contraction causing a slight back flow of blood before the AV valves close increasing the pressure of the atria

• about 80% of blood passively flows from the atria to the ventricle
• the remaining 20% is forced into the ventricle by atrial contraction
• The body can function without this priming action while at rest, during exercise it can become pathological

• as soon as ventricular contraction is over the AV valves open
• flow is due to the amount of blood that has accumulated in the atria while the AV valve is closed

period of ventricular contraction when the AV valves have closed and the ventricle must build up enough pressure the open the Ao valve

• fast ejection is during the first third of ventricular contraction, 70% of volume
• slow ejection is last two thirds, 30% of volume

• systolic + 2x diostolic divided by 3
• diostolic + 1/3 pulse pressure

• 110-120 ml
• end diastolic volume

60%

septomarginal trabeculea

chordae tendineae

• occurs in the aortic pressure wave when the aortic valve closes
• dicrotic notch

• when the ventricles contract the AV valves close causing the sound
• low in pitch and long lasting

• closing of the semilunar valves
• rapid snap

• the amount of energy that the heart converts to work during each heartbeat
• Minute work output is how much energy is converted each minute, stroke work times heart rate

work done to move the volume from the veins to the arteries

• work done to propel the blood
• increases during aortic stenosis

• 150ml
• fibrous tissue can not stretch much more

250-300

60-80

• phase 1: period of filling, volume of LV increases by about 70ml and pressure rises from 0 to ~5
• Phase 2: isovolemic contraction; no volume change but pressure rises to equal the diastolic pressure of the aorta
• Phase 3: ejection; systolic pressure open Ao valve, volume of LV decreases, pressure continues to rise but then peaks and falls
• Phase 4: isovolemic relaxation; Ao valve closes, pressure falls to level of atrial pressure and mitral valve opens
• area within this loop is external work, this will increase when the heart pumps more volume

end diastolic pressure

the pressure of the aorta

oxidation of fatty acids

• ratio of energy converted to heat to energy converted to work
• normal heart this is 20-25%

• intrinsic, heart pumps out what it receives,
• control by the autonomic nervous system

• the greater the heart muscle is stretched during filling the greater the force of contraction and the greater the quantity of blood pumped into the aorta
• actin and myosin filiments are brought to a more optimal length

• directly increases heart rate 10-20 percent
• bainbridge reflex

• increase heart rate as well as contractile strength
• normal conditions has 30% stimulation

SA and AV nodes and atrial muscle

• causes the heart to become dilated
• can block conduction
• decreases the resting membrane potential

spastic contractions

increase rate

• the ease of flow through organs, venous return
• arterial pressure does not diminish CO until mean rises above 160