The Cardiovascular System

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The Cardiovascular System

• blood vessels

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Blood Circulation

• Blood is carried in a closed system of vessels
  that begins and ends at the heart

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Human Cardiovascular System
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The 3 major types of vessels

• Arteries carry blood away from the heart
• Veins carry blood toward the heart
• Capillaries contact tissue cells (Serving
  cellular needs)

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Capillaries
     Very narrow (10 µm diameter, the red blood
cells that travel through capillaries are 6 µm in
diameter). Capillaries are made of thin
endothelial cells (one layer thick)
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Capillary Blood Flow

• Blood flow across the capillary bed is regulated
  by a sphincter muscle on the arteriole side.
  Whenever there is little need to supply blood to
  a given capillary bed, the sphincter closes and
  blood bypasses the capillary bed via an
  arterio-venal shunt.
• On the arterial side of the capillaries, blood is
  under high pressure, whereas the blood at the
  venal side is under low pressure.

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Hydrostatic Osmotic Pressures

• The high hydrostatic pressure on the arterial
  side squeezes water and nutrients out of the
  capillaries.
• Water leaving the capillaries builds up the
  osmotic pressure because the blood components
  have become more concentrated.
• Towards the venal end, water and waste materials
  are sucked into capillaries by the osmotic
  pressure.

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Capillary Dynamics
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Capillary Exchange

• Gases, nutrients, and wastes are exchanged
  between blood in the capillaries of tissues in 3
  ways
• 1. Diffusion
• a. most common
• b. substances including O2, CO2, glucose,
  hormones
• c. lipid-soluble substances pass directly
  through endothelial cell membrane
• d. water-soluble substances must pass
  through fenestrations or gaps between endothelial
  cells.
• 2. Vesicular transport (endo/exocytosis)
• 3. Bulk flow (filtration and absorption).

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Arteries arterioles

• (High pressure Low resistance)
• The blood vessels before the capillary beds
  have to bear high hydrostatic pressures created
  by the heart
• Arteries and smaller arterioles are thick
  walled tubes made of smooth muscle (to resist
  high pressure), containing a layer of collagen
  fibers (to give elasticity), and lined with
  endothelial cells (to protect red blood cells
  from mechanical damage).

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Tunicas
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Tunicas
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Veins venules

• (Low Pressure Low Resistance)
• Contain valves to prevent the backflow of blood
• Varicose veins result due to a failure of these
  valves

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Venous Blood Flow
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HEMODYNAMICS THE PHYSIOLOGY OF CIRCULATION

• Blood pressure pressure exerted by
  blood on the wall of blood vessels.
• In clinical use, we most commonly refer to mean
  (systemic) arterial blood pressure (MABP),
  because the blood pressure in the veins is
  essentially insignificant.
• The mean arterial blood pressure (MABP) rises to
  its maximum during systole (contraction) and
  falls to its lowest during diastole (relaxation).
• In a normal adult at rest, the MABP 120 mmHg/80
  mmHg

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Factors that Influence Arterial Blood Pressure

• Heart Action (cardiac output)
• Blood Volume (increase in blood volume increases
  BP)
• Peripheral Resistance (resistance R opposition
  to blood flow usually due to friction)
• So we can say CO MABP/R

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Blood Flow Friction

• This friction depends on 3 things
• 1.      Blood viscosity
• 2.    Total blood vessel length
• 3.    Blood Vessel Radius

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Regulation of BPBlood Flow

• F ?P/ R
• ?P change in pressure between arterial venous
  ends
• R Peripheral Resistance

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Hormonal Control

• Several hormones affect BP by
• acting on the heart
• altering blood vessel diameter
• adjusting blood volume.

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Hormones that increase BP

• Epinephrine and norepinephrine
• Increases CO (rate force of contraction)
  causes vasoconstriction of arterioles.
• Antidiuretic hormone (ADH)
• Causes vasoconstriction of arterioles during
  diuresis and during hemorrhage.
• Angiotensin II
• Causes vasoconstriction of arterioles and causes
  the secretion of aldosterone
• Aldosterone
• Increases Na and water reabsorption in the
  kidneys.

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Hormones that decrease BP

• Atrial natriuretic peptide (ANP)
• Causes vasodilation of arterioles and promotes
  the loss of salt and water in urine.
• Histamine
• Causes vasodilation of arterioles (plays a key
  role in inflammation)

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Regulation of Blood Pressure and Blood Flow

• Neural Regulation
• The cardiovascular (CV) center is located in the
  medulla oblongata
• CV Center Input
• Nerve impulses are sent to the CV center from
  three areas
• 1. Higher brain centers
• 2. Baroreceptors (or pressoreceptors) which
• detect changes in BP in aorta and carotid
  arteries
• 3. Chemoreceptors that detect changes in key
  blood chemical concentrations (H, CO2, and O2)

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Regulation of Blood Pressure and Blood Flow

• Neural Regulation
• CV Center Output
• Nerve impulses are sent from the CV center to
  either
• 1. The Sinoatrial (SA) Node of heart
• 2. The smooth muscle of peripheral blood vessels
  (i.e. arterioles).

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Regulation of Blood Pressure and Blood Flow

• Negative-Feedback Regulation
• If BP is too high
• 1.      Increase is detected by baroreceptors in
  the carotid artery or aorta
• 2.    Baroreceptors send an impulse to CV center
• 3.    CV center interprets that message and sends
  a signal to the SA Node and arterioles
• 4.    The SA Node decreases heart rate
• 5.    The arterioles dilate
• If BP is too low...
• 1.      SA Node increases hr
• 2.    Constriction of arterioles

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