Basic circulatory route

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Blood Vessels and Hemodynamics
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Chapter 21The Cardiovascular System Blood
Vessels and Hemodynamics

• Structure and function of blood vessels
• Forces involved in circulating blood
• Major types of circulation to be studied in lab

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Basic circulatory route
Heart
Arteries
Veins
Arterioles
Capillaries
Venules
Tissues
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Structure of Vessels

• Comparison of Arteries and Veins

• Blood flows away from heart in ________

arteries

• Blood flows toward heart in ______

veins

• Arteries are thicker than veins

• Veins have regularly spaced valves

• Which vessels have the highest pressure?

• Which vessels carry about 64 of the blood?

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Distribution of Blood
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Vessel Structure(Artery)
-----------------Tunica Interna
Endothelium, Basement Membrane Elastic Fibers
---------------Tunica Media
Smooth Muscle Elastic Fibers
------------Tunica Externa
Collagen Elastic Fibers
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Types of Arteries

• Elastic Arteries (gt1cm)

• Less muscle and more elastic tissue

• Larger arteries such as aorta

• Why do the larger arteries have more elastic
  tissue? What purpose do they serve?

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Types of Arteries Continued

• Muscular Arteries (0.1 10mm)

• Less elastic tissue and more muscle

• Medium size to smaller arteries

• Capable of greater vasoconstriction and
  vasodilation to adjust rate of flow

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Smaller Vessels

• Arterioles

-Smallest arteries (10 100 ?m)
- Deliver blood to capillaries
- Smallest ones lose tunica externa
- Called resistance blood vessels because their
vasoconstriction (decrease in diameter) increases
resistance, and their vasodilation (relaxation)
decreases resistance to blood flow in the arteries
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Capillaries (4 10 ?m)

• Microscopic vessels form microcirculation

• Tubes of endothelium and basement membrane

• Connect arterioles to venules

• Function in exchange of substances with tissues

• Interconnect like a net to form capillary beds

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Venules (10 100 ?m)

• Small veins that collect blood from capillaries

• Tunica media contains only a few smooth muscle
  cells scattered fibroblasts

• Rather porous endothelium

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MicrocirculationArterioles, Capillaries and
Venules
-------------------Arteriole
---------------Capillary
------Venule
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Anastomoses

• Union of 2 or more arteries supplying the same
  body region
• Alternate route of blood flow through an
  anastomosis is known as collateral circulation
• Can also occur in veins, arterioles and venules

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Physiology of Circulation-Blood Pressure

• Blood pressure (BP) is the force the blood exerts
  against vessel walls

• Difference in blood pressure (pressure gradient)
  along vessels causes blood to flow

• Blood flows from higher to lower pressure

• Pressure is highest in the aorta and lowest in
  the vena cavae

Though blood pressure is in every blood vessel,
most of our discussion will concern arterial
blood pressure
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Blood Flow

• Two factors are responsible for blood pressure
• Blood flow
• Resistance to blood flow

• Amount of blood flowing through vessels per unit
  of time (milliliters per minute)
• What is causes blood to flow?
• Which direction does it flow?

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Resistance (R) to blood flow

• Produced as the blood encounters friction and
  turbulence against the vessel and heart walls

• For blood to flow, blood pressure (BP) must
  overcome resistance (R)

• Increased resistance decreases blood flow

• Greatest resistance is in arterioles-called
  peripheral resistance (PR)

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Blood Pressure Formula

• Blood pressure Flow X Resistance

• ?Flow causes ?BP, ?Flow causes ?BP

• ?R causes ?BP, ?R causes ?BP

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Which of the following is true?

• Blood flows from lower to higher pressure
• 2. ? resistance causes ? blood pressure
• 3. ? resistance causes ? blood pressure
• 4. ? blood flow causes ? blood pressure

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Factors in Flow and Resistance

• Factors in Flow

• Cardiac Output (CO)

Amount of blood ejected by left ventricle in
one minute

• Blood volume

Total amount of blood in body

• More than 10 drop causes drop in BP

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Factors in Resistance

• Diameter of vessels, especially arterioles

vasoconstriction
Has arterial BP increased or decreased?

• Viscosity of blood

• Length of vessels

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Flow and Blood PressureBlood flow in redBlood
pressure in green
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Resistance and Blood PressureBlack arrows
represent vasoconstriction
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Measurements of Arterial blood pressure

• Systolic pressure(SP) and diastolic pressure (DP)

• Systolic pressure(SP)

• Pressure in arteries when left ventricle is
  contracting

• High number on blood pressure reading

• Diastolic pressure(DP)

• Pressure in arteries when left ventricle is
  relaxing

• Low number on blood pressure reading

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Measuring Arterial BP

• BP measured in millimeters of mercury (mm Hg)

• Use sphygmomanometer

• Usually taken in upper arm

• High number is systolic pressure

• Low number is diastolic pressure

• Typical reading is 120 mmHg/80 mmHg

• 140/90 or above considered high

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Sphygmomanometer
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The low number of a blood pressure reading occurs
when the _______________.
1. ventricle is pumping 2. ventricle is
relaxing 3. AV valves are closed 4. SLvalves
are open
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Other Pressures

• Pulse pressure (PP)

• Difference in Systolic and diastolic pressures or
  PPSP-DP

• High during exercise, anxiety, influence of
  certain drugs and with hardening of arteries

• Mean Arterial Blood Pressure (MAP or MABP)

• Single measure of arterial BP

• Formula

MAP Diastolic Pressure (Pulse Pressure ?3)
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The mean arterial blood pressure for a BP of
120/75 is _____________.
1. 80 mmHg 2. 90 mmHg 3. 95 mmHg 4. 100 mmHg
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Pressure Gradients Different Vessels

• Arterial Pressure Gradient

• Difference in arterial pressure from Aorta to
  capillaries

• Averages about 60 mmHg

• Capillary Pressure Gradient

• Difference in pressure from arteriole to venule
  side of capillary bed

• Averages about 20 mmHg

• Venous Pressure Gradient

• Difference in pressure from venules to Vena cavae

• Averages about 16 mmHg

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Blood Pressures in Various Vessels
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Capillary Exchange

• Passage of water and solutes between capillary
  plasma and interstitial fluid

• Three Methods

- Diffusion is movement of solute from ____ to
____ concentration
high
low
- Transcytosis is movement of large molecules
across capillary cells by ________________________
____
formation of pinocytotic vesicles
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Capillary Exchange Continued

• Bulk Flow Movement of water and solute between
  the blood and interstitial fluid because of
  differences in pressure.

- Movement of fluid and solute from capillaries
into interstitial fluid is _______
filtration
- Movement of fluid and solute from interstitial
fluid into capillaries is __________
reabsorption
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Bulk Flow continued

• Two opposing pressures at work

- Blood Hydrostatic Pressure (BHP) is the blood
pressure that pushes fluid out of blood. What
produces it?
- Blood Osmotic Pressure (BOP, AKA BCOP) is a
suction pressure that pulls fluid into blood
Opposing Pressures
BHP BOP
Blood pressure pushes fluid out
Blood osmotic pressure pulls fluid in
Capillary cross-section
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Capillary Exchange Continued
? means greater than

• Mechanism of Filtration and Reabsorption

?
- On arteriole side of capillary, BHP BOP
push pull
?
?
-On venule side of capillary, BOP BHP pull
push
?
- Higher BHP on arteriole side pushes water and
solute from capillary into interstitial fluid -
filtration
- Higher BOP on venule side pulls water and
solute from interstitial fluid into capillary -
reabsorption
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Capillary Exchange Diagram
Lymph Capillary
Filtration
Reabsorption
BHP (push) (35 mmHg)
BOP (pull) 26 mmHg
BOP (pull) (26 mmHg)
BHP (push) (16 mmHg)
Blood Capillary
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Which of the following causes capillary
filtration?
1 BOPgtBHP 2 BHPgtBOP 3 BHPBOP 4 vasoconstriction
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Venous pressure and venous return

• Venous pressure is very low and can not account
  for all of the return of blood to heart

• Factors that aid in venous return

- Contraction of skeletal muscles squeeze
veins and push blood toward
heart
- Breathing helps
- Venous valves prevent backflow of blood once
it is squeezed past them
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Illustration of Venous Return
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Blood Pressure Regulation

• Local regulation within tissues
• Central (neural) regulation by brain

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Local Regulation
Assures proper blood flow into capillaries
Tissues regulate blood flow to meet their
needs Changes in blood chemistry, and
temperature cause vasodilation or
vasoconstriction -What chemicals cause
vasodilation and increased blood flow into
capillaries? -What is relationship between
temperature and change of blood flow to
capillaries?
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Central Control of Blood Pressure Flow

• Role of Cardiovascular Centers -
  cardioacceleratory, cardioinhibitory vasomotor
  centers of the medulla oblongata

- Help regulate heart rate stroke volume
- Specific neurons regulate vessel diameter
- Regulate by input from sensory receptors and
output to heart
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Input to the Cardiovascular Center

• Higher brain centers such as cerebral cortex,
  limbic system hypothalamus

- anticipation of competition
- increase in body temperature

• Proprioceptors in muscles and tendons

- input during physical activity

• Baroreceptors in blood vessels

- changes in pressure within blood vessels

• Chemoreceptors in blood vessels and brain

- monitor concentration of chemicals in the blood
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Output from the Cardiovascular Center

• Heart

- Parasympathetic (vagus nerve) - decreased heart
rate
- Sympathetic (cardiac accelerator nerves) -
increased contractility rate

• Blood vessels

- Sympathetic vasomotor nerves

• Decreased stimulation produces dilation
  decreased BP

• Increased stimulation produces constriction
  increased BP

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Input and Output Summary
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Neural Regulation of Blood Pressure
Aortic/Carotid Reflexes

• Baroreceptor reflexes (AKA Left Heart Reflex)

- Carotid sinus reflex

• Receptors in carotid artery wall

• Sensory input to cardiovascular center in medulla

• Maintains normal BP in the brain

- Aortic reflex

• Receptors in wall of ascending aorta

• Sensory input to cardiovascular center in medulla

• Maintains general systemic BP

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Innervation of the Heart

• Sensory information from baroreceptors
• Speed up the heart with sympathetic stimulation
• Slow it down with parasympathetic stimulation (X)
• Cause vasodilation or vasoconstriction

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Baroreceptors monitor blood pressure. What
adjustments would occur if blood pressure to the
brain were to suddenly decrease?

• 1. ? cardiac output and widespread vasodilation
• 2. ? cardiac output and widespread
  vasoconstriction
• 3. ? cardiac output and widespread vasodilation
• 4. Nothing

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Chemoreceptor Reflexes

• Carotid bodies and aortic bodies
• Detect changes in blood levels of O2, CO2, and H
  (hypoxia, hypercapnia or acidosis )
• Cause stimulation of cardiovascular center
• Increases sympathetic stimulation to heart
  vessels
• ?Cardiac output and increase in blood pressure
• Also affect breathing rates

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Hormonal Regulation of Blood Pressure

• Renin-angiotensin-aldosterone (RAA) system
• Decrease in BP or decreased blood flow to kidney
• Release of renin results in 2 steps that form
  angiotensin II
• Systemic vasoconstriction increases resistance
• Causes ?NaCl (salt) reabsorption, and increased
  salt results in
• ________________________________________________
• Epinephrine norepinephrine
• Increases heart rate force of contraction
• Causes vasoconstriction in skin abdominal
  organs
• Vasodilation in cardiac skeletal muscle
• Antidiuretic hormone (ADH) causes
  vasoconstriction and water retention

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Carotid baroreceptors monitor pressure in the
__________________

• (A) kidneys
• (B) brain
• (C) heart
• (D) lungs

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• Which of the following maintains adequate blood
  pressure to the brain when a person stands up?
• (A) ?stimulation of carotid baroreceptors with
  reflex slowing of the heart and vasodilation
• (B) ?stimulation of carotid baroreceptors with
  reflex slowing of the heart and vasoconstriction
• (C) ?stimulation of carotid baroreceptors with
  reflex speeding-up of the heart and
  vasoconstriction
• (D) ?stimulation of carotid baroreceptors with
  reflex slowing of the heart and vasodilation

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Clinical Terms

• Hypertension
• Aneurysm

Hypertension and salt
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• Claudication
• Deep Venous Thrombosis
• Phlebitis
• Phlebotomist
• Venipuncture