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.