Chapter 21
Blood Vessels
Direction of Flow
Heart to aorta to arteries to
arterioles to capillaries.
Capillaries to venules to veins to
vena cava to heart.
Veins
Arteries
• Capillaries form Microcirculation
• Microscopic vessels that connect arterioles to venules
• Found near every cell in the body but more extensive in
highly active tissue (muscles, liver, kidneys & brain)
•entire capillary bed fills with blood when tissue is active
•lacking in epithelia, cornea and lens of eye & cartilage
• Function is exchange of nutrients & wastes between
blood and tissue fluid
• Structure is single layer of simple squamous epithelium
and its basement membrane
Capillaries:
1. Continuous
2. Fenestrated
3. Sinusoid
Venous valves
Blood Distribution
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12% pulmonary vessels
8 % = heart
15% = systemic arteries and arterioles
5% = capillaries
60% = systemic veins and venules
Venous flow occurs by:
1. muscle contraction
2. respiratory pump
3. valve assistance
4. Ventricular relaxation
Varicose Veins
• Twisted, dilated superficial veins
– caused by leaky venous valves
• congenital or mechanically stressed from
prolonged standing or pregnancy
– allow backflow and pooling of blood
• extra pressure forces fluids into surrounding
tissues
• nearby tissue is inflamed and tender
• Deeper veins not susceptible because of
support of surrounding muscles
Anastomoses
• Union of 2 or more arteries supplying the same body
region
– blockage of only one pathway has no effect
• circle of willis underneath brain
• coronary circulation of heart
• Alternate route of blood flow through an anastomosis is
known as collateral circulation
– can occur in veins and venules as well
• Alternate routes to a region can also be supplied by
nonanastomosing vessels
Pulse Pressure
• Pulse pressure = systole - diastole
• MAP = diastolic pressure + pulse
pressure/3
• MAP = mean arterial pressure
• MAPB = diastole + 1/3 (systole – diastole)
• MAPB = mean arterial blood pressure
Blood Pressure
Influenced by:
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Peripheral resistance
Heart efficiency
Blood viscosity
Total blood vessel length
Arteriole elasticity
Blood volume
Hormones that affect BP
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Renin angiotensin
Epinephrine and norepinephrine
Antidiuretic hormone
Atrial natriuretic peptide
Autoregulation of BP
• Physical changes
• Vasodilating and constricting chemicals
Major Branches of the Aorta
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Coronary arteries
Brachiocephalic
Left common carotid
Left subclavian
Celiac
Superior mesenteric artery
Renals
Ovarian / testicular
Inferior mesenteric
Minor Branches of the Aorta
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Pericardial
Bronchial
Esophageal
Mediastinal
Intercostal
Phrenic
Thoracic
Lumbar
Suprarenal
Celiac circulation
Abdominal arteries
Arterial supply and venous
drainage of the liver
Hypertension
• Systole > 140
• Diastole > 90
• Causes: diet high in fat and sodium,
obesity, older age, race, heredity, stress,
and smoking.
Words to Learn
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Aneurysm
Angiogram
Diuretic
Phlebitis
Phlebotomy
Thrombophlebitis
Syncope
Tachycardia
Shock
Sphygmomanometer
Korotkoff sounds
Angiogenesis
Hypotension
Occlusion
White Coat Hypertension
Edema