Blood vessels

• Arteries

  Carry blood away from a ventricle
• Veins

  Carry blood toward an atrium
• Capillaries

  Connect smallest arteries to veins and allow for exchange between the bloodstream and tissue cells
• Arteries

  • Have significant blood pressure inside
• Veins

  • Have little to no pressure inside
• Capillaries

  • The walls are thin and variably leaky
• Capillary Exchange - Diffusion

  1. Lipid soluble substances like steroid hormones, O2, CO2 diffuse easily

  2. Substances that do not dissolve in lipids like glucose and electrolytes must pass through channels, fenestrations or intercellular clefts

  3. Large particles like proteins are held back
• Capillary Exchange - Filtration and Reabsorption

  1. Blood (hydrostatic) pressure drives fluid out of capillary, high on arterial end, low on venous end

  2. Colloid osmotic pressure (COP) draws fluid into capillary, results from plasma proteins (albumin)

  3. Oncotic pressure = net COP (blood COP - tissue COP)
• Adrenergic receptors

  4 types of receptors for sympathetic nervous system: α1, α2, β1, β2
• Special Circulatory Routes

  • Skeletal Muscle
  • Brain
  • Lungs
• Blood Pressure

  Force that blood exerts against a vessel wall, measured at brachial artery of arm
• Systolic pressure

  BP during ventricular systole
• Diastolic pressure

  BP during ventricular diastole
• Normal blood pressure, young adult

  120/75 mm Hg
• Pulse pressure

  An important measure of stress exerted on small arteries
• Mean arterial pressure (MAP)


  An estimate of tissue perfusion, formula: MAP ≈ DP + ⅓(SP-DP)
• Hypertension


  Chronic resting BP > 140/90 or 130/80, can weaken small arteries and causes aneurysms, overworks the heart
• Hypotension

  Chronic low resting BP, or caused by blood loss, dehydration
• Edema

  Excess fluid in the extravascular compartment, often looks like 'swelling', can be caused by blood vessels that are too leaky or imbalance of osmosis
• Aneurysm


  A localized, blood-filled dilation (balloon-like bulge) of a blood vessel caused by disease or weakening of the vessel wall, most common in the aorta and the arteries at the base of the brain
• Afterload

  Pressure that must be overcome before a semilunar valve can open, increase in afterload causes stroke volume to decrease
• Parameters the body uses to regulate blood pressure and perfusion

  • Blood volume
  • Vascular resistance
  • Cardiac output
• Systems the body uses to regulate those parameters

  • Local
  • Neural
  • Hormonal
• RAAS - renin/angiotensin/aldosterone system

  1. Angiotensinogen (prohormone produced by liver)

  2. Renin (kidney enzyme released by low BP)

  3. Angiotensin I

  4. ACE (angiotensin-converting enzyme in lungs)

  5. Angiotensin II - a very potent vasoconstrictor
• Anti-hypertension drugs

  • ACE inhibitors
  • Diuretics
  • Beta-blockers
  • Angiotensin II receptor blockers
  • Calcium channel blocker
• CVA - cerebral vascular accident (stroke)

  Two types: brain infarction caused by ischemia, and hemorrhagic stroke caused by ruptured aneurysm
• TIA's - transient ischemic attacks

  Dizziness, loss of vision, weakness, paralysis, headache or aphasia, lasts from a moment to a few hours, often early warning of impending infarction-type stroke
• Mechanisms of Venous Return

  1. Pressure gradient from venules to central venous pressure

  2. Gravity draining blood from head and neck

  3. Skeletal muscle pump in the limbs

  4. Thoracic pump - inhalation expands thoracic cavity, pulling blood upward

  5. Cardiac suction of expanding atrial space
• Atherosclerosis causes heart attacks and strokes, and (along with diabetes) causes erectile dysfunction
• Aldosterone


  Promotes Na+ and water retention by kidneys, increases blood volume and pressure
• Atrial natriuretic peptide


  Causes generalized vasodilation and increase loss of salt in urine, decreases blood pressure
• ADH - Antidiuretic hormone


  Causes vasoconstriction and water retention, increases blood pressure
• Epinephrine and norepinephrine

  Constrict most blood vessels by binding to α-adrenergic receptors, causing vasoconstriction, but dilate skeletal and cardiac muscle blood vessels by binding to β-adrenergic receptors, causing vasodilation