Chapter 18: Blood vessels and hemodynamics

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Chapter 18 Blood vessels and hemodynamics

• Structure and function of blood vessels
• Capillary exchange
• Hemodynamics
• Control of blood pressure
• Shock and homeostasis

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Types of blood vessels

• Arteries divide
• Elastic (conducting) arteries
• Muscular arteries
• Arterioles branch into
• Capillaries reunite to form
• Venules merge into
• Veins converge and convey blood back to the heart

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Arteries

• Elastic arteries or conducting arteries
• Pressure reservoirs
• Recoil of elastic fibers propels the blood.
• Muscular or distributing arteries
• Constrict or dilate to adjust blood flow.

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Arterioles

• Small arteries (10-300mm) that deliver blood to
  capillaries.
• Regulates blood flow
• Regulates blood pressure

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Continuous Capillaries
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Fenestrated capillaries
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Sinusoidal capillaries
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Capillary beds Microcirculation

• Vascular shunt
• True capillaries

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Venules and veins

• Capillaries unite and form venules
• Venules converge and form veins
• Veins
• No elastic layers
• Large lumen
• Valves
• Sinuses

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Arteries and Veins

• Anastomoses is the union of two or more branches
  of arteries.
• Varicose veins are caused by leaky venous valves
  that cause veins to become dilated and twisted.

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Physiology of blood

• Blood flow (ml/min)
• Blood pressure (mm Hg)
• Resistance
• Blood viscosity
• Vessel length
• Vessel diameter

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Blood pressure

• The pumping heart creates blood pressure.
• Pressure develops from resistance to flow
• Systolic pressure
• Diastolic pressure
• Pulse pressure
• Mean arterial pressure

MAPdiastolic BP1/3(systolic BP-diastolic BP)
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Venous return

• Overcoming resistance and the force of gravity.
• Skeletal muscle pump
• Respiratory pump
• Sympathetic control

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Maintaining blood pressure

• Cardiac output
• Peripheral resistance
• Blood volume

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Maintaining blood pressure

• Cardiac output
• Peripheral resistance
• Blood volume

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Maintaining blood pressure

• Cardiac output
• Peripheral resistance
• Blood volume

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Maintaining blood pressure

• Cardiac output
• Peripheral resistance
• Blood volume

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Pulse

• Pressure points

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Monitoring blood pressure

• Asculatory method uses the sphygmomanometer
• Sounds of Korotkoff
• Brachial artery is compressed and cuff pressure
  released
• First sound is systolic blood pressure
• Last sound is the diastolic blood pressure
• BP has a circadian rhythmpeaks in the morning

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Primary hypertension

• Diethigh intake of Na, saturated fats or
  deficiencies in K, Ca2, or Mg2
• Obesity
• Ageover 40
• Diabetes mellitus
• Heredity
• Stress
• Smoking

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Blood flow through tissues

• Delivers O2 and nutrients and removes waste
• Gas exchange
• Absorption of nutrients from digestive tract
• Urine formation in the kidney

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Velocity of blood flow

• Velocity is inversely related to the
  cross-sectional area.
• The greater the cross section, the slower the
  blood.
• Branching of blood vessels slows velocity.
• Veins coming together increases velocity

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Autoregulation of blood pressure
dilate
constrict
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Capillary exchange

• Vasomotion is slow and intermittent

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Bulk flow

• Bulk flow regulates fluid volumes in the blood
  and extracellular space.
• Hydrostatic pressurethe force of fluid on the
  capillary walls
• Colloid osmotic pressurethe force created by
  nondiffusible molecules
• Filtration--pressure driven movement from blood
  capillaries into interstitial fluid
• Reabsorption--pressure driven movement from
  interstitial fluid into blood capillaries

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Fluid flow in capillaries
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Hydrostatic-Osmotic Pressure Interactions

• Capillaries
• HPc is higher at arterial end
• OPc is constant
• Interstitial fluid
• HPif is typically close to zero
• OPif is close to 1mm Hg because of few
  extracellular proteins
• Net hydrostatic pressure is equal to HPc
• Net osmotic pressure OPc OPif
• Net filtration pressure NHP - NOP

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Shock and homeostasis

• Shock is the failure to deliver enough O2 to meet
  cellular metabolic needs.
• Four types of shock
• Hypovolemic shockdrop in fluid levels
• Cardiogenic shockfailure of heart to pump
• Vascular shockdecrease in vascular resistance
• Obstructive shockblood flow through a portion of
  the circulation is blocked.

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Signs and symptoms of shock

• Systolic blood pressure below 90mmHg
• Weak and rapid pulse
• Rapid heart rate
• Cool and damp skin
• Altered mental state
• Reduced urine formation
• Thirst
• Acidosis (low blood pH)
• Nausea

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