lab 4 - excercise 29: functions of the heart

cardiac output

how blood pressure changes

what happens when more oxygen is required?

cardiac output increases with an elevated heart rate or an increase in the volume ejected per contraction, or both

what is the hearts intrinsic control?

pacemaker in the heart located in the heart wall that determines heart rate

what are the hearts extrinsic controls?

from organs other than the heart such as hormones or input from the nervous system that control the heart rate or contraction strength

do cardiocytes, like neurons, undergo a normal polarization process?

yes! this produces a resting membrane potential

what are the three ion channels by which electrical impulses occur in the heart?

fast sodium channels, slow calcium channels, and potassium channels

what is polarization controlled by in cardiocytes?

sodium-potassium pump - holds an increase in sodium ions outside of the cell membrane and potassium ions inside the membrane

what happens when cardiocytes are stimulated?

fast sodium channels open, causing depolarization - causing a twitch of the muscle fiber

what’s the difference in twitch time between skeletal muscle and heart muscles and why is it there?

2 ms compared to 250 ms, caused by a plateau in the repolarization of the cell

what is the plateau in the repolarization of cardiocytes caused by?

slow movement of calcium into the cytosal

what is the job of the pacemaker in the sinoatrial SA node?

spontaneously and periodically depolarize, sending action potentials across the heart wall and causing the heart to contract

what is the depolarization process of the SA node?

due to the leaking of sodium ions into the pacemaker cells without the corresponding outflow of potassium ions

• when threshold is reached, fast calcium - sodium channels open and calcium and sodium ions flow into the cell

• when 0 millivolts (mV) is reached, the potassium channels open and potassium ions leave the cell

what happens when this occurs?

a field effect ! depolarizing cardiocytes adjacent to the pacemaker

what do action potentials from the sinoatrial node open?

voltage-gated slow calcium channels in the cardiocytes

what does this cause?

ligand gated calcium channels in the sarcoplasmic reticulum open and calcium moved into the cell, binding to troponin as it does to skeletal muscle

what system slows the heart rate?

parasympathetic nervous system

what nerve conveys parasympathetic fibers that innervate the SA node?

vagus nerve

what does the vagus nerve release?

acetylcholine - a neurotransmitter that promotes potassium (K+) leakage from the nodal cells of the heart to the interstitial fluid, increasing the flow of potassium ions to the outside of the membrane

why does this slow the heart rate?

by increasing the difference in voltage between the inside and the outside of the cells, it takes longer for the cells to reach threshold and depolarize

what is a parasympathometic substance?

one that mimics the effects of innervation by the parasympathetic nervous system

• acetylcholine

how can heart rate be elevated?

by increasing the firing rate of the SA node - includes the progressive inhibition of the parasympathetic nervous system, and the subsequent stimulation of the sympathetic nervous system

above 100 bpm, what is the heart rate controlled by?

the sympathetic nervous system

what happens when nerves from the cervical region of the spinal cord release nor epinephrine, which binds the beta adrenergic receptors?

calcium channels open, decreasing the threshold and causing more rapid firing of the SA node

what does epinephrine do to heart rate?

increases the heart rate and strength and contraction by making the calcium channels more permeable

sympathomimetic drug

One that mimics the effect of sympathetic, nervous innervation

• epinephrine

what is a stimulant?

has an effect on heart muscle; increases heart rate and the strength of contraction

• caffeine; High concentrations of caffeine cause arrhythmia’s

what does the addition of calcium chloride to heart tissue do?

increases the heart rate and contraction strength, but it can also produce pacemakers in region to the heart other than the SA node (ectopic foci)

ectopic foci

pacemakers and regions of the heart, other than the SA node

myogenic conduction

electrochemical transfer of impulses by cardiocytes

what does the lubb/dubb sounds of the heart reflect?

the closure of the heart valves

• lubb represents the closure of the atrioventricular valves

• dubb represents the closure of the semi lunar valves

heart murmur

extra whooshing sounds; attributed to the imperfect closure of the valves