Cardiovascular system: Blood vessels, blood flow, blood pressure

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Cardiovascular system Blood vessels, blood flow,
blood pressure
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Outline

• 1- Physical laws governing blood flow and blood
  pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes

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Outline

• 1- Physical laws governing blood flow and blood
  pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes

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Physical laws governing blood flow and blood
pressure

• Flow of blood through out body pressure
  gradient within vessels X resistance to flow
• - Pressure gradient aortic pressure central
  venous pressure
• Resistance
• -- vessel radius
• -- vessel length
• -- blood viscosity

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Factors promoting total peripheral resistance
(TPR)

• Total peripheral resistance TPR
• -- combined resistance of all vessels
• -- vasodilation ? resistance decreases
• -- vasoconstriction ? resistance increases

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Outline

• 1- Physical laws governing blood flow and blood
  pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes

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Vasculature
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Arteries and blood pressure

• Pressure reservoir
• Arterial walls are able to expand and recoil
  because of the pressure of elastic fibers in the
  arterial wall
• Systolic pressure maximum pressure occurring
  during systole
• Diastolic pressure pressure during diastole

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Arterial blood pressure
Figure 14.8
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Blood pressure values what do they mean?

• Pulse pressure
• PP SP-DP
• Mean arterial blood pressure MABP
• MABP SBP (2XDBP)
• 3
• CO MABP SV x HR
• TPR

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• Blood flow within each organ changes with body
  activities
• Reminder The ANS controls blood flow to the
  various organs

Figure 14.15
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Outline

• 1- Physical laws governing blood flow and blood
  pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes

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Capillaries

• Allow exchange of gases, nutrients and wastes
  between blood and tissues
• Overall large surface area and low blood flow
• Two main types
• - continuous capillaries narrow space between
  cells ? permeable to small or lipid soluble
  molecules
• - fenestrated capillaries large pores between
  cells? large molecules can pass

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Local control of blood flow in capillaries

• Presence of precapillary sphincters on the
  arteriole and beginning of capillaries
• Metarteriole no sphincter ? continuous blood
  flow ? controls the amount of blood going to
  neighboring vessels

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Movement of materials across capillary walls

• Small molecules and lipid soluble molecules move
  by diffusion through the cell membrane
• Larger molecules, charged molecules must pass
  through membrane channels, exocytosis or in
  between 2 cells
• Water movement is controlled by the capillary
  hydrostatic and osmotic pressures

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Forces controlling water movement

• Arterial side of the capillary
• High capillary hydrostatic pressure (BHP), lower
  capillary osmotic pressure (BOP, due to proteins
  and other molecules in the blood) ? Net
  filtration pressure pushes fluid from the blood
  toward the tissue (but the proteins remain in the
  capillary
• Venous side of the capillary
• - Lower hydrostatic pressure (due to resistance)
  and higher capillary osmotic pressure ? Net
  filtration pressure moves fluid back toward the
  capillary
• Interstitial fluid hydrostatic (IFHP) and osmotic
  pressures (IFOP) remain overall identical

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Fluid movement in the capillary

• Arteriole side fluid moves toward the tissues
• Venous side fluid reenters the capillary
• Overall for every 1 liter of fluid entering the
  tissues, only 0.85 l reenter the capillary
• The remaining 0.15 l is reabsorbed as lymph by
  lymphatic capillaries and eventually returned
  back to blood circulation
• When this system fails Edema

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Causes of edema

• Increased interstitial hydrostatic pressure
  (lymphatic capillary blockage)
• - breast cancer surgery, elephantiasis
• Leaking capillary wall
• - histamine release during allergic reaction

• Increased hydrostatic blood pressure
• - heart failure (left or right),
• - excess fluid in the blood
• Decreased blood osmotic pressure
• Liver, kidney diseases, malnutrition
  (kwashiorkor), burn injuries

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Outline

• 1- Physical laws governing blood flow and blood
  pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes

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Veins

• Veins are blood volume reservoir
• Due to thinness of vessel wall ? less resistance
  to stretch more compliance

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Factors influencing venous return

• 1- Skeletal muscle pump and valves
  ?
• 2- Respiratory pump
• 3- Blood volume
• 4- Venomotor tone

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Outline

• 1- Physical laws governing blood flow and blood
  pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes

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Lymphatic circulation

• Driven by factors similar to venous circulation
• - muscle activity
• - valves
• - respiration
• Lymph plasma-proteins
• Lymphatic circulation collects fluid not
  reabsorbed by the capillaries
• Lymph is filtered in nodes before return to blood
  circulation

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Outline

• 1- Physical laws governing blood flow and blood
  pressure
• 2- Overview of vasculature
• 3- Arteries
• 4. Capillaries and venules
• 5. Veins
• 6. Lymphatic circulation
• 7. Mean arterial pressure and its regulation
• 8. Other cardiovascular regulatory processes

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Mean arterial pressure and its regulation

• Regulation of blood flow in arteries
• - Intrinsic control
• - Extrinsic control
• -- Neural control
• -- Hormonal control
• Control of blood vessel radius
• Control of blood volume

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Mean arterial pressure and its regulation

• Regulation of blood flow in arteries
• - Intrinsic control
• - Extrinsic control
• -- Neural control
• -- Hormonal control
• Control of blood vessel radius
• Control of blood volume

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Regulation of blood flow in arteries

• It is important to adjust blood flow to organ
  needs ? Flow of blood to particular organ can be
  regulated by varying resistance to flow (or blood
  vessel diameter)
• Vasoconstriction of blood vessel smooth muscle is
  controlled both by the ANS and at the local
  level.
• Four factors control arterial flow at the organ
  level
• - change in metabolic activity
• - changes in blood flow
• - stretch of arterial smooth muscle
• - local chemical messengers

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Intrinsic control of local arterial blood flow

• Change in metabolic activity
• Usually linked to CO2 and O2 levels (? CO2 ?
  vasodilation ?? blood flow) intrinsic control
• Changes in blood flow
• - decreased blood flow ? increased metabolic
  wastes ? vasodilation

• Stretch of arterial wall myogenic response
• - Stretch of arterial wall due to increased
  pressure ? reflex constriction
• Locally secreted chemicals can promote
  vasoconstriction or most commonly vasodilation
• - inflammatory chemicals, (nitric oxide, CO2)

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Mean arterial pressure and its regulation

• Regulation of blood flow in arteries
• - Intrinsic control
• - Extrinsic control
• -- Neural control
• -- Hormonal control
• Control of blood vessel radius
• Control of blood volume

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Extrinsic control of blood pressure

• Two ways to control BP
• Neural control
• Hormonal control
• Use negative feedback

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Control of blood pressure

• Importance Blood pressure is a key factor for
  providing blood (thus oxygen and energy) to
  organs. SBP must be a minimum of 70 to sustain
  kidney filtration and adequate blood flow to the
  brain
• CO HR X SV MABP/TPR ?
• MABP HRxSVxTPR ? heart rate, stroke volume
• and peripheral
  resistance affect MABP
• Main factors controlling BP - Blood volume
• - Blood vessel radius

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Neural control of BP - 1

• Baroreceptors carotid and aortic sinuses sense
  the blood pressure in the aortic arch and
  internal carotid ? send signal to the vasomotor
  center in the medulla oblongata
• Other information are sent from the hypothalamus,
  cortex
• ?

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Neural control of BP - 2

• The vasomotor center integrates all these
  information
• The vasomotor sends decision to the ANS center
• Both parasympathetic and sympathetic innervate
  the S/A node ? can accelerate or slow down the
  heart rate
• The sympathetic NS innervates the myocardium and
  the smooth muscle of the arteries and veins ?
  promotes vasoconstriction

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Hormonal control of BP

• Control of blood vessel radius
• - Epinephrine
• - Angiotensin II
• - Vasopressin (?)
• Control of blood volume
• - Anti-diuretic hormone (vasopressin)
• - Aldosterone
• Control of heart rate and stroke volume
• - Epinephrine

• Hormones can control blood vessel radius and
  blood volume, stroke volume and heart rate
• On a normal basis, blood vessel radius and blood
  volume are the main factors
• If there is a critical loss of pressure, then the
  effects on HR and SV will be noticeable (due to
  epinephrine kicking in)

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Control of blood vessel radius

• Epinephrine secreted by the adrenal medulla and
  ANS reflex ? increase HR, stroke volume and
  promotes vasoconstriction of most blood vessel
  smooth muscles.
• Angiotensin II ? promotes vasoconstriction

• Angiotensin II secretion
• Decreased flow of filtrate in kidney tubule is
  sensed by the Juxtaglomerular apparatus (a small
  organ located in the tubule) ? secretion of renin
• Renin activates angiotensinogen, a protein
  synthesized by the liver and circulating in the
  blood ? angiotensin I
• Angiotensin I is activated by a lung enzyme,
  Angiotensin-Activating Enzyme (ACE), ?
  angiotensin II
• Angiotensin II is a powerful vasoconstricted of
  blood vessel smooth muscles

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Control of blood volume

• Anti-diuretic hormone ADH
• Secreted by the posterior pituitary in response
  to ?blood osmolarity (often due to dehydration)
• Promote water reabsorption by the kidney tubules
  ? H2O moves back into the blood ? less urine
  formed

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Control of blood volume

• Aldosterone
• Secretion by the adrenal cortex triggered by
  angiotensin II
• Promotes sodium reabsorption by the kidney
  tubules (Na moves back into the blood)
• H2O follows by osmosis
• Whereas ADH promotes H2O reabsorption only (in
  response to dehydration), aldosterone promotes
  reabsorption of both H2O and salt (in response to
  ? BP)

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Clinical application Shock

• Stage I Body reacts to maintain BP ? ?HR,
  vasoconstriction..? BP remains within normal
  range
• Stage II Body reacts to maintain BP ? ?HR,
  vasoconstriction..? BP drops below adequate range
  (SBP 70). Can be reversed by medical treatment
• Stage III Body is fighting to maintain adequate
  BP without success ? HR is very high ? not enough
  O2 for cardiac, brain cells to survive ? damages.
  Cannot be reversed by medical treatment

• Stage I reversible, compensated shock
• Stage II reversible, noncompensated shock
• Stage III irreversible shock
• Death