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Regulation of Blood Pressure

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... heart rate is 64 beats per minute (bpm) and the stroke ... If the heart is beating at 64 beats per minute (bpm) how much ATP does it need to keep pumping ... – PowerPoint PPT presentation

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Title: Regulation of Blood Pressure


1
Regulation of Blood Pressure
  • What determines your blood pressure?
  • What will cause it to increase or decrease?

2
Cardiac Output Blood Flow ? Blood Pressure
3
Cardiac Output
  • Cardiac Output heart rate x stroke volume
  • At rest, if the heart rate is 64 beats per minute
    (bpm) and the stroke volume is 80 mL, the cardiac
    output is 5.1 L/min. (An average human has 5 L of
    blood)
  • With exercise the heart rate can increase to 120
    bpm and the stroke volume to 125 mL, the cardiac
    output can increase to 15L/min.

4
The Beating Heart
  • The Heart Beat
  • What tissues compose the heart? How does a heart
    beat?
  • Certain cells of the heart are self-excitable
  • Although the heart is innervated, it will
    continue to beat even if the nerves are removed.
  • Cardiac cells will continue to beat even when
    they are isolated from the heart and placed in
    tissue culture.
  • In order to understand how heart cells beat we
    have to modify our understanding of an action
    potential

5
Action Potentials in the Heart
  • Special cardiac muscle cells, located in the
    right atria in a specialized region called the
    sinoatrial (SA) node, are considered the hearts
    pacemaker.
  • These muscle cells have an unstable resting
    potential due to changes in K permeability.
  • Slow depolarization of the cell results in the
    membrane potential drifting toward the threshold
    potential.
  • How will this affect the heart?
  • How do you think K permeability is altered in
    these cells?

6
Spread of Impulse
  • Cardiac muscle cells are interconnected by
    intercalated discs. How does this relate to how
    the heart beats? How does this relate to A-V
    contraction?

7
Spread of Impulse
Period of ventricular repolarization
8
How the Heart Beats (1)
  • Blood returning to the heart enters the atria,
    filling the atria
  • As the pressure in the atria rises, the AV valves
    are forced open, allowing blood to enter the
    ventricles
  • The contraction of the atria completely empties
    all blood into the ventricles
  • All this occurs while the ventricle is relaxed
    (diastole)

1
1
AV Valves
L
R
9
How the Heart Beats (2)
  • The ventricles then contract (systole)
  • The increased pressure in the ventricle causes
    the AV valves to close (lub), preventing backflow
    to the atria
  • The increased ventricular pressure forces the
    semilunar values (pulmonary and aortic) to open
  • As the ventricles relax the semilunar valves
    close (dub)

Semilunar Valves
1
1
2
AV Valves
2
L
R
10
How the Heart Beats (3)
  • The cycle repeats, with blood entering the atria.
  • The left and right atria contract in concert.
  • The left and right ventricle contract in concert.
  • This assures that same volume of blood is pumped
    through the pulmonary and systemic circulation.
  • However, the pulmonary and systemic circulation
    do not operate under the same pressures.
  • Which is greater? Why?

Semilunar Valves
1
1
2
AV Valves
2
L
R
11
Control of SA Node
  • The SA node sets the tempo for the entire heart
  • The SA node is influenced by two sets of nerves
  • One slows the heart rate down (parasympathetic-vag
    al)
  • One speeds the heart rate up (sympathetic nerves)
  • The heart rate is also influenced by hormones
    (epinephrine)

12
Cool Facts - ATP usage
  • If the heart is beating at 64 beats per minute
    (bpm) how much ATP does it need to keep pumping
  • 35 kg of ATP/day (77 pounds of ATP!!!)
  • Most ATP for cardiac function is generated by
    oxidative metabolism of fuels, which is why the
    heart needs a constant supply of oxygen.

13
Cool Facts - ATP usage
  • If the heart requires 35 kg of ATP/day how much
    total ATP does a person require each day?
  • 190 kg of ATP/day (420 pounds of ATP!!!)
  • How much ATP do we have in our bodies?
  • Only about 50g
  • This means that every molecule of ATP is recycled
    4000 times per day!

14
Cool Facts - ATP usage
  • In the absence of oxygen, the amount of ATP
    present in muscle cells is only enough to sustain
    muscle power for 5 or 6 seconds.
  • It is essential that ATP is synthesized
    constantly
  • Coronary ischemia (reduction in blood supply)
    greatly impairs the ability of the heart to
    produce ATP and can permanently damage the heart.

15
How much ATP does it take to move my finger?
  • Well I cant tell you that, but I can tell you
    how much ATP you need to jump an inch off the
    ground (www.madsci.org -the internet is amazing!)
  • It takes about 0.00015 moles
  • or 85 mg
  • or 9 x 1019 molecules

16
Cardiac Output Blood Flow ? Blood Pressure
17
Arteries - Capillaries - Veins
Do arteries always carry oxygenated blood?
18
Arteries and Veins
19
Why do arteries have thicker walls than veins?
  • The volume of blood in the arteries changes
    through the cardiac cycle and the increased
    elastic layer allows the arteries to stretch and
    recoil in response to these changes.
  • The volume of blood in the veins is more constant
    as it drains in the veins from the capillary
    beds.
  • Blood leaves the heart and enters the arteries
    under high pressure. The thick muscle walls
    allow the arteries to withstand the pressure
    without bursting.
  • The blood enters the veins at a much lower
    pressure due to the increased resistance of the
    capillary beds.

20
Lumen Diameter of Vessels
Although the wall thickness of arteries and veins
differ, the lumen size does not. The change in
vessel diameter will affect blood flow and blood
pressure
21
Blood flow-fluid dynamics
  • The flow of blood must be constant through the
    entire vessel system.
  • Blood will flow over 1000 times faster in aorta
    (30cm/sec) than in the capillaries (0.026cm/sec).
  • The increased total cross-sectional area of the
    capillaries compensates for the slower rate of
    flow.

22
Systemic Circulation
19 of blood is in pulmonary circulation
23
Systemic Circulation
  • Every cell in the body is within a 100 mm of a
    capillary.
  • Not every capillary bed has blood flowing through
    it all the time. The blood flow is controlled by
    precapillary sphincters
  • At any given time only 5-10 of the capillary
    beds have blood flowing through them.

24
Systemic Circulation
  • As the blood enters the capillaries, the high
    pressure pushes fluid out of the capillaries on
    the arterial side.
  • The proteins are too large to pass through the
    endothelial walls. This contributes to the
    osmotic pressure,which promotes return of fluid
    from the interstitial space at the venous side.
  • The decrease in pressure across the capillary bed
    also promotes return of fluid on the venous side.

25
Cardiac Output, Blood Flow and Blood Pressure
26
Blood Pressure
  • Blood pressure is determined by the cardiac
    output and the total peripheral resistance.
  • In a normal, healthy individual much of the
    resistance is generated by the millions of tiny
    arterioles and capillaries.
  • You can increase blood pressure by
  • Increasing heart rate
  • Increasing blood volume
  • Increasing vasoconstriction

27
Homeostasis of Blood Pressure
  • What are two ways to regulate blood pressure?
  • Control of vessel diameter
  • Vasoconstriction
  • Vasodilatation
  • Control of blood volume

28
Regulation of Vessel Diameter
  • A decrease in blood pressure is detected by
    baroreceptors located in the arch of the aorta.
  • When baroreceptors detect a change in blood
    pressure, they activate neurons in the medulla
    oblongata, which transmit signals to the smooth
    muscle in the arterioles.
  • In response, the smooth muscle will ____ (relax
    or contract?).

29
Regulation of Vessel Diameter
  • A decrease in blood pressure is detected by
    baroreceptors located in the arch of the aorta.
  • When baroreceptors detect a change in blood
    pressure, they activate neurons in the medulla
    oblongata, which transmit signals to the smooth
    muscle in the arterioles.
  • In response, the smooth muscle will ____ (relax
    or contract?).

contract
  • Is this a positive or negative feedback loop?

30
Hormonal Control of Blood Volume
31
Cardiovascular Disease
  • Leading cause of death in the US
  • Heart Attack
  • Decrease blood flow to the heart muscle due
    blockage of the coronary vessels by clot or
    atherosclerosis
  • Stroke
  • Decreased blood flow to the brain due to
    decreased blood flow or a bursting of a cerebral
    vessel, due to high blood pressure.
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