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BIOL 141 notes 9

by: Camryn McCabe

BIOL 141 notes 9 Biol 141

Marketplace > Science > Biol 141 > BIOL 141 notes 9
Camryn McCabe
Penn State
GPA 3.81

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notes from lecture 9
Janelle Malcos
Class Notes
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This 4 page Class Notes was uploaded by Camryn McCabe on Friday February 26, 2016. The Class Notes belongs to Biol 141 at a university taught by Janelle Malcos in Spring 2016. Since its upload, it has received 22 views.

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Date Created: 02/26/16
Lecture 9 notes Volume and pressure • For a fixed volume of fluid, pressure depends on the volume of the space it occupies – Large space = lower pressure – Small space = high pressure – As the size of the space changes, so does the pressure – Apply this concept to heart chambers Pressure gradient: difference in pressures between 2 regions (P – P ) 1 2  Fluid flows from high pressure to low pressure o Pressure at first point will decrease; pressure at second point will increase o This holds true as long as the path is not blocked Volume and pressure  Volume of chambers change during a heartbeat  Also pay attention to pressure in vessels  Relaxation  Diastole o Space of chamber increases , volume of fluid remains constant  pressure decreases  Contraction  Systole o Space of chamber decreases, volume of fluid remains constant  pressure increases Cardiac Cycle = complete contraction and relaxation  Phase 1: Quiescent Period (before threshold, no action potential) o Atria and Ventricles are in diastole  Pressure of blood vessels > pressure in heart  No pressure in ventricles, therefore AV valves are open and semilunar valves are closed  Blood fills atria and flows through the AV valves to ventricles o Heart fills with blood from bottom up (through atria to ventricles)  Some blood is leftover from previous contraction  Ventricles contain about 90mL of blood (at this point)  NOT the maximum capacity of ventricle o SA node cells are depolarizing (but not to threshold yet) o Pressure in arteries in veins > pressure in chambers o Chambers are all relaxed, high volume  Phase 2: Atrial Systole Lecture 9 notes o SA node depolarizes to threshold (action potential across atria) o Atria contract (systole)  Pressure in atria > pressure in ventricles o Blood is forced into ventricles  About 40mL more blood  90mL + 40mL = 130mL total  This is the End Diastolic Volume (ventricles)  Phase 3: Isovolumetric contraction o Atria repolarize and relax (diastole)  Start to refill from veins o Ventricles depolarize and begin to contract (early systole)  Contract from bottom up  Blood forces AV valves closed  This makes first heart sound o Pressure in ventricles increases o Blood does not leave ventricles yet  Pressure in aorta and pulmonary artery > pressure in ventricles  Isovolumetric contraction: no change in volume of blood, but ventricles start to contract  Phase 4: Ventricular Ejection o Ventricles fully contract (full systole) o Pressure in ventricles > pressure in vessels  Forces pulmonary and aortic valves open  Semilunar valves are open; AV valves are shut  Blood leaves ventricles  Only 70mL leaves (stroke volume) o Stroke volume: amount that leaves after one stroke (contraction)  60 mL left behind (End Systolic Volume) o End Systolic volume: volume left when completely contracted o Atria are still in diastole  Continue to fill with blood  Phase 5: Isovolumetric Relaxation o Ventricles repolarize and relax (diastole) o Pressure decreases in ventricle  Pressure in pulmonary artery and aorta > pressure in ventricle  Blood tries to flow back, but valves shut and prevent this  This makes the second heart sound Lecture 9 notes o Both sets of valves are still closed so volume of blood in ventricles doesn’t change  Isovolumetric relaxation o When atria are filled, AV valves are forced open  cycle brings again with quiescent period End Diastolic Volume – End Systolic Volume = Stroke Volume About 130 mL - About 60 mL = About 70 mL  Cardiac Output (CO) o CO- the amount of blood pumped by the left ventricle in one minute (measures how efficiently our heart pumps blood) o Heart rate (beats/minute) X stroke volume (mL/beat) – HR X SV = CO o On average, total blood volume is pumped through the heart per minute o This is resting cardiac output  What affects heart rate? o Average heart rate = about 75 beats/minute o Autonomic nervous system modulates SA node activity  Without nervous system control, heart would beat about 100 beats/minute (SA node depolarization rate due to leak channels)  Visceral motor responses are initiated from interneurons in “brain centers” o Center- collection of interneurons that receive sensory input about a specific function and create motor output to alter that function o “Cardiovascular control center” (CVCC):  Cardiac control (heart)  Cardioacceleratory neurons  Cardioinhibitory neurons  Vasomotor control (vessels) o Together they regulate blood pressure and heart function  Why out body needs to alter heart rate? o Energy balance o O d2mand o Waste removal (CO ) 2 o Regulate blood pressure  Organ function Lecture 9 notes  Interneurons of the cardioacceleratory center will lead to an increased heart rate o Efferent neurons excited by this center are visceral motor neurons of the sympathetic system o Postganglionic neuron secretes norephinephrine (NE)  Adrenergic receptors on cells of the SA node bind NE  Cause an increase rate of action potentials of SA node o Maximum heart rate = 230 beats/minute  Limit of SA node excitation  Interneurons of the cardioinhibitory center will lead to an increased heart rate o Visceral motor neurons of the parasympathetic system o Postganglionic neuron secretes Ach  Cholinergic receptors on cells of the SA node bind Ach  Allow potassium to leave the cell  hyperpolarizing reaction  Rate of action potentials decrease o Normal heart rate = 70 beats/minute  Without nervous control the heart would beat about 100 beats/minutes  Sensory input is integrated to create motor output to SA node o Proprioceptors, baroreceptors, chemoreceptors are all integrated together o Proprioceptors (sensory input from muscles and tendons)  Informs brain on changes in physical activity o Baroreceptors (sensory input from blood vessels)  Informs brain on changes to pressure in vessels o Chemoreceptors (sensory input from blood vessels)  Informs brain on changes in CO or2O lev2ls in the blood (change in chemicals)  Important in respiratory system, but has some effect on heart rate)


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