IB 132 LECTURE 12 CHAP 12 CARDIOVASCULAR PHYSIOLOGY
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The circulatory system consists of:
Which of these two are part of the cardiovascular system?
The Heart and Blood Vessels
Functions of The Circulation System:
- •Supply O2and Nutrients
- •Remove ‘Wastes”
- •Temperature Regulation
- •Distribute hormones
Blood is made up of 3 parts:
- •Plasma ~55% of 5.5L = 3.0L
- •Cells and cell fragments ~45% of 5.5L–Erythrocytes > 99%–Leukocytes, platelets
- •Hematocrit: volume of erythrocytes/total blood volume; ~0.45 = 45%
What does Plasma include?
water, ions, proteins,nutrients, hormones,wastes, etc.
The hematocrit is a:
- rapid assessment of blood composition.
- It is the percent of the blood volume that is composed of RBCs (red blood cells).
The Circulatory System has:
4 heart chambers and 2 circuits
The Two circuits of the circulatory system are: Systemic and Pulmonary
Compare them below:
-The heart is the pumpthat propels theblood throughthe systemic andpulmonary circuits.
- -Left is fully oxygenated
- -Right is partially oxygenated
Pulmonary Trunk to Pulmonary Arteries to Capillaries of Lungs to Pulmonary Veins
TO Left Atrium to Left AV Valve to Left Ventricle to Aortic Valve
TO Aorta to Arteries to Arterioles to Capillaries to Venules to Veins to Vena Cavae
TO Right Atrium to Right AV Valve to Right Ventricle to Pulmonary Valve
ALL OVER AGAIN
- •The first heart sound (called S1, or ‘lub’) is caused by closure of the AV valves (onset of systole)
- •The second heart sound (called S1, or ‘dub’) is caused by closure of the pulmonary and aortic valves (onset of diastole)
- •Most are force-producing muscle cells (myocytes)–Striated muscle–Use myosin motors to produce force, motion on actintrack–Conduct action potentials on sarcolemma–Regulated by Ca-modulated thin filaments
- •~1% make up conducting system–Electrically excitable–Non force-producing
•Innervation from autonomic nervous system
–sympathetic fibers innervate entire heart (norepinephrine, beta-adrenergic) –speed HR
–parasympathetic fibers innervate the atria (Ach, muscarinic) –slow HR
Sequence of Excitation
- 1. Pacemakingin SA node
- 2. Conductionby gap jnsthrough atria
- 3. Excitation of AV node inR atrium
- 4. Conduction of action potentials down bundles of His
- 5. Spread alongPurkinje fibers
The rapid opening of voltage-gated Na channels is responsible for
the rapid depolarization phase.
The prolonged “plateau”of depolarization
is due to the slow but prolonged opening of voltage-gated L-type calcium channels and closure of potassium channels.
Opening of potassium channels causes
Mechanism of Pacemaker Potential:
- -13Na+ions “leaking”in through the F-type (funny) channels
- -Ca++ions moving in throughthe T-type (transient) channelscause a graded depolarization.
- -The rapid opening of L-type Ca++channels is responsible for the rapid depolarization phase.
- -Reopening of potassium channelsPLUSclosing of calcium channels are responsible for therepolarization
Mechanical events of the cardiac cycle
Systole:ventricular contractionblood ejection
Diastole:Ventricular relaxationblood filling
Cardiac output equals heart rate times stroke volume
-A small fraction of cardiac cells, called autorhythmicor pacemaker cells, determine the heart rate (HR).
-A much larger group, making up 99% of the total cells inthe heart, constitutes the force-producing cells. Theiractivity determines the stroke volume (SV).
Control of Heart Rate:
•Parasympathetic activity (vagusnerve) slows HR
•Sympathetic activity increases HR
To speed up the heart rate:
•deliver the sympathetic hormone, epinephrine, and/or
•release more sympathetic neurotransmitter (norepinephrine), and/or
•reduce release of parasympathetic neurotransmitter (acetylcholine).
The Frank-Starling Mechanism
To increase the heart’s stroke volume, fill it more fully with blood.
The increased stretch of the ventricle will produce more force by improving actin-myosin filament overlap.
1. Flow through capillary beds is slow because
their total cross-sectional area is large
Total area of capillary beds is huge because
there are billions of capillaries
Capillaries exchange nutrients and metabolic end products by
by diffusion(fast enough because distances are small)
A capillary network is filled from
arterioles and emptied by venules
Arterioles have smooth muscle that can
change their radii
3. How is homeostasis of ΔP maintained?
- •ΔP is the difference between mean arterial pressure (MAP) and capillary pressure
- •‘Mean’arterial pressure because arterial pressure varies between systolic and diastolic
- •Capillary pressure is approx. 0•So ΔP ~ MAP
Factors that determine MAP:
•Cardiac Output–Cardiac output = Heart Rate x Stroke Volume
- •Total Peripheral Resistance–Radius of arterioles–Blood viscosity
How does Blood get back to the heart?
1.Venous pressure < capillary pressure
3.Valves in veins
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