TOPIC 3 Circulatory System – Blood Vessels
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Transcript of TOPIC 3 Circulatory System – Blood Vessels
Chapter 20pp. 718-747
TOPIC 3Circulatory System – Blood Vessels
Biology 221Anatomy & Physiology II
E. Lathrop-Davis / E. Gorski / S. Kabrhel
Blood Vessel Functions and Types
• Function– conduits for blood– separate systemic and pulmonary systems provide
more efficient delivery of oxygen and nutrients, removal of wastes
• Major Types of Vessels– Arteries – carry blood away from the heart– Capillaries – sites of exchange of materials between
blood and tissues– Veins – return blood to heart
Blood Vessel HistologyThree layers of blood vessel wall:• Tunica interna (tunica intima) inner layer
– endothelium (simple squamous epithelium)– subendothelial layer (areolar CT)
• Tunica media – middle layer– varying amounts of dense connective tissue– smooth muscle
° vasomotor tone– vasoconstriction– vasodilation
Fig. 20.1, p. 719
http://www.usc.edu/hsc/dental/ghisto/cv/d_1.html
Blood Vessel Histology• Tunica externa – outermost layer
– connective tissue– nerve fibers, lymphatic vessels– vasa varsorum – blood vessel system in tunica
externa of larger blood vessels (e.g., elastic arteries)
http://www.usc.edu/hsc/dental/ghisto/cv/d_2.html
http://www.usc.edu/hsc/dental/ghisto/cv/d_5.html
Elastic (Conducting) Arteries• Aorta and its major branches• Functions:
– carry blood rapidly away from heart toward capillary beds
– decrease blood pressure fluctuations during heart beat: ° expand during ventricular systole, which
decreases systolic pressure; and ° recoil during ventricular diastole, which maintains
pressure on blood
Elastic (Conducting) Arteries• Structure:
– large diameter, large lumen– thick walls – lots of elastic fibers (elastin)– vaso vasorum (see previous slide)
http://www.usc.edu/hsc/dental/ghisto/cv/d_2.html
Muscular (Distributing) Arteries• Account for most of the named arteries• Function: deliver blood to organs; control flow to
organs• Structure:
– internal diameter smaller than elastic arteries– thick tunica media with lots of smooth muscle
http://www.usc.edu/hsc/dental/ghisto/cv/d_12.html
Arterioles• Function: distribute blood to tissues within organs
major controller of blood flow into capillaries• Structure:
– branch and become smaller– walls’ thickness decreases as they near capillaries
° consists of endothelium and scattered smooth muscle cells near capillaries
http://www.usc.edu/hsc/dental/ghisto/cv/d_12.html
Capillaries• Function: sites of exchange between blood and
tissues• Structure: consist of tunica interna only
– some with scattered pericytes (smooth muscle cells)
• Three structural types: – continuous capillaries– fenestrated capillaries– sinusoids
Fig. 20.3, p. 724
http://www.usc.edu/hsc/dental/ghisto/cv/d_25.html
Continuous Capillaries• Endothelial cells continuous• cells may be held together by tight junctions
– intercellular clefts are gaps in tight junctions– tight junctions are continuous in brain (blood-brain
barrier)Fig. 20.3, p. 724
http://www.usc.edu/hsc/dental/ghisto/cv/d_25.html
Fenestrated Capillaries• Some endothelial cells have pores; most pores covered
with membrane• Very permeable – allow even large substances to pass• Found in small intestine, some endocrine glands,
kidney glomeruli
Fig. 20.3, p. 724
http://www.usc.edu/hsc/dental/ghisto/cv/d_26.html
Sinusoids• Large irregular lumens slows blood flow• Walls fenestrated or incompletely lined with endothelial
cells– in liver, endothelium is discontinuous where
macrophages (Kupffer cells) form part of vessel wall– in spleen, phagocytes on outside of endothelial lining
extend processes into lumen• Few tight junctions allow large molecules (e.g.,
proteins) to pass through• Located in liver, spleen, bone marrow, lymphoid tissue,
some endocrine glands
Fig. 20.3, p. 724
http://www.usc.edu/hsc/dental/ghisto/cv/d_34.html
Capillary Beds• Many capillary branches from arteriole• Microcirculation = flow of blood from arteriole to
venule through capillary bed• Metarteriole - thoroughfare channel
– fast, direct connection between arteriole and venule– terminal arteriole metarteriole thoroughfare
channel venule– by-passes capillary bed when tissue is inactive
Fig. 20.4, p. 725
Capillary Beds: True Capillaries• sites of exchange between blood and tissues• branches of metarteriole
– rejoin to thoroughfare channel– precapillary sphincter controls blood movement into
capillary bed• amount of blood entering depends on gross needs of
body (vasomotor nervous control) and local needs of tissue (local chemical cues)
Fig. 20.4, p. 725
Post-capillary Venules• Function: collect blood from capillary beds• Structure:
– formed by union of capillaries– leaky endothelium with few pericytes
• White blood cells (WBCs) abundanthttp://www.usc.edu/hsc/dental/ghisto/cv/d_36.html
Veins• Functions:
– carry blood under low pressure back toward heart– act as blood reservoirs = capacitance vessels;
° ~ 65% of body’s blood is in veinshttp://www.usc.edu/hsc/dental/ghisto/cv/d_39.html
Veins• Structure:
– gradually increase in size and thickness– all 3 tunics present, but thinner than in arteries of
corresponding size (external diameter)° little smooth muscle or elastin° relatively thicker tunica externa
– valves prevent backflow° varicose veins - blood pools because valves fail
causing venous walls to expand• Phlebitis – inflammation of vein
http://www.usc.edu/hsc/dental/ghisto/cv/d_39.html
Venous Sinuses• Function: collect blood under low pressure• Structure:
– flattened veins with walls of endothelium only– supported by surrounding tissues
• Examples: coronary sinus; dural sinuses
Vascular Anastomoses• Arterial anastomoses form collateral channels to
maintain flow in case of blockage– Examples:
° brain - circle of Willis° around joints° abdominal organs° heart
• Arteriovenous anastomoses– metarteriole thoroughfare channel
• Venous anastomoses– vein to vein– more common
Circulatory PatternsGeneral pattern:
Ventricles of heart elastic arteries muscular arteries arterioles capillaries venules veins atria of heart
See Table 20.1, p. 721
Circulatory PatternsTwo main systems:
Pulmonary circulation: – right ventricle pulmonary trunk R/L pulmonary
arteries alveolar capillaries of the lungs R/L pulmonary veins left atrium
– takes deoxygenated blood to lungs for exchange of gases
• Systemic circulation:– left ventricle aorta arteries capillaries of
body tissues superior and inferior venae cavae right atrium
– takes oxygenated blood to tissues, removes wastes
See Fig. 20.2, p. 720
Special Circulatory Patterns:• Hepatic Portal System - carries venous blood from
intestines, pancreas, stomach, spleen to liver; Fig. 20.27, p. 771
• Hypophyseal Portal System - carries blood with regulatory hormones from hypothalamus to anterior pituitary; Fig. 17.5, p. 617
Special Circulatory Patterns:• Coronary Circulation (covered with heart) - carries
oxygen-rich blood to heart and removes oxygen-poor blood; Fig. 19.7, p. 690
• Cerebral Circulation - carotid and vertebral arteries carry oxygen-rich blood to brain and jugular veins drain oxygen-poor blood from brain (details in lab); Fig. 20.20. p. 755 Fig. 20.25, p. 767
Special Circulatory Patterns:• Fetal Circulation - Fig. 29.13, p. 1136
– by-pass developing lungs° ductus arteriosus – carries blood from pulmonary
trunk to aorta° foramen ovale – allows blood to flow from right
to left atrium– Gas & material exchange at placenta
° umbilical arteries carry deoxygenated blood high in wastes to placenta
° umbilical vein brings oxygenated blood high in nutrients from placenta
– What do these fetal structures become?– What happens if they fail to close?
Vessel Disorders• Atherosclerosis: blood vessel walls are abnormally
thick and narrowed and less compliant
• Occlusive coronary atherosclerosis: narrowing of coronary arteries due to accumulation of cholesterol; often lead to ischemia and infarct
• Arteriosclerosis: late stage of atherosclerosis
• Aneurysm: localized dilation or out-pouching of a blood vessel or a cardiac chamber; rupture often leads to severe bleeding