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)

























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)


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













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













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













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


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


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


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


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

TOPIC 3 Circulatory System – Blood Vessels

Documents

Transcript of TOPIC 3 Circulatory System – Blood Vessels