CARDIOVASCULAR SYSTEM: VESSELS AND ROUTES

ANATOMY AND PHYSIOLOGY    SUMMER, 2002

COMPONENTS (GEN'L)

A. ARTERIES - carry blood away from heart

B. ARTERIOLES - smaller arteries

C. CAPILLARIES - connections between arterioles and venules; where exchange takes place

D. VENULES - smaller veins

E. VEINS - carry blood toward heart

F. VASA VASORUM - blood vessels in walls of blood vessels which provide oxygen and nutrients to
vessels

II       COMPONENTS (SPECIFIC)

A.      ARTERIES ANATOMY

1.      TUNICA INTERNA - inner layer; lined with endothelium + a basement membrane; has a layer of elastic tissue (Internal Elastic Membrane) outside basement membrane

2. TUNICA MEDIA - middle layer; thickest; consists of elastic fibers and smooth muscle
a.      External Elastic Membrane - separates media from externa tunic

3. TUNICA EXTERNA - outer layer; consists of elastic and collagen fibers

4. SPECIAL PROPERTIES -

a. ELASTICITY and CONTRACTILITY - regulated primarily by tunica media

b. VASODILATION - increase in lumen size; caused by removal of sympathetic
stimulation

c.      VASOCONSTRICTION - decrease in lumen size; caused by increase in sympathetic

stimulation

5. SPECIAL CASES

a.       E LAS TIC (CONDUCTING ) ARTERIE S –

1) Large arteries with thin walls; media layer has extensive elastic fibers and less

smooth muscle fibers (i.e. aorta, brachiocephalic, common carotid A.)

2)      Assists in providing continuous flow of blood from an intermittent source

b.        MUSCULAR (DISTRIBUTING) ARTERIES

1)      Medium sized arteries with more smooth muscle than elastic in the media layer (i.e.

axillary, brachial, femoral A.)

2)      Capable of greater adjustments (vasoconstriction/vasodilation) to volume of blood

which suits the needs of the structure supplied

c. ANASTOMOSES - junction of 2 or more vessels supplying same region

1)      COLLATERAL CIRCULATION - Provides alternate routes if occluded

2)      END ARTERIES - arteries which don't anastomose

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B.     ARTERIOLES

1. ANATOMY

a. Small arteries which deliver blood to capillary

b. Closest to artery end have similar tissue organization (3 layers); those closest to capillary
end consist of layer of endothelium surrounded by a few smooth muscle cells

2. PHYSIOLOGY

a.      Regulates blood flow from arteries to capillaries

C.      CAPILLARIES

1. ANATOMY

a. Connectors between arterioles and venules: found near most every body cell

b. Consist of single layer of cells (endothelium) and a basement membrane

c. Can form extensive branching networks thereby increasing surface area for diffusion

2. PHYSIOLOGY

a.       Permits the exchange of nutrients and wastes between blood and tissue cells

3. SPECIAL CASES

a. METARTERIOLE - vessel emerging from arterioles, transverses capillary network and
empties into venule

1) Proximal End - surrounded with smooth muscle - controls amount and force of
blood

2) Distal End (Thoroughfare Channels) - no smooth muscle so decrease in resistance
and increase in blood flow here

b. TRUE CAPILLARIES- emerge from metarterioles or arterioles; are not on the direct
flow route from arteriole to venule

1)      PRECAPILLARY SPHINCTER - ring of smooth muscle at site of origin which controls blood flow into capillary

c. CONTINUOUS CAPILLARIES - cytoplasm of endothelium cells is continuous except at

       endothelium junctions

                 1)        Common in muscle tissue

d. FENESTRATED CAPILLARIES – endothelium cells have numerous fenestrae (pores)
where cytoplasm is thin or absent; approx. 70-100nm in dia.;usually closed by a thin
diaphragm

1)      Common in SI villi, choroid plexuses of brain ventricles, ciliary processes of eyes and endocrine glands

e. SINUSOIDS - microscopic blood vessels; wider than capillaries; lined with phagocytic
cells rather than endothelium

1)      Common in liver; spleen, parathyroid and adrenal cortex

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C.      VENULES

1.      ANATOMY

a. Small veins formed when several capillaries unite

b. Area closest to capillary have interna layer composed of endothelium with externa layer
of connective tissue; at vein end, have media layer also

D.      VEINS

1.        ANATOMY

a. Similar to arteries with less elastic tissue and more white fibrous tissue

b. Contains VALVES to prevent back-flow; most common in extremities

c. Special Case

1)      VASCULAR (VENOUS) SINUS - vein with thin endothelium wall and no smooth muscle to alter it's diameter; surrounding tissue replaces media and externa layer (i.e. coronary sinus of heart, intracranial vascular sinus)

BLOOD RESERVOIR

59% - Veins, venules and venous sinuses

13% - .Arteries

12% - Pulmonary vessels

 9% - Heart

 7% - Arterioles and capillaries

III     CIRCULATION PHYSIOLOGY

A.      BLOOD PRESSURE (BP)

            1.         FACTORS AFFECTING ARTERIAL BP

a.    CARDIAC OUTPUT (CO) - approx. 5.25 L/min (70ml X 75 beats/min)

b.    BLOOD VOLUME - normally 5L

c.    PERPHERAL RESISTANCE

1)        Blood viscosity - relationship of RBC and solutes to fluid

2)        Changes in lumen size and elasticity

2.      DI RECT CONTROLS ON BLOOD VESSELS

a.      VASOMOTOR CENTER – cluster of neurons within medulla

         Controls blood vessel diameter (primarily arterioles)

Operates by increasing frequency of sympathetic impulses

b. BARORECEPTCORS – found within wall of carotid sinus and aorta; send impulses to

cardiac center and vasomotor center

c. CHEMORECEPTORS – receptors near/in the carotid sinus (Carotid bodies) and aorta
(Aortic Bodies; are sensitive to arterial blood gases and pH; directs impulses to
vasomotor center

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d. HIGHER BRAIN CENTERS - during high emotions; cerebral cortex stimulates
vasomotor center

e. CHEMICALS - Epinephrine and norepinephrine cause constriction of abdominal and
cutaneous arteries and dilate cardiac and skeletal muscle arteries; ADH causes general
vasoconstriction

f. AUTOREGULATION (LOCAL CONTROL )- regulated primarily by oxygen content
for the area in question

3.       FACTORS AFFECTING VENOUS RETURN

a. SKELETAL MUSCLE CONTRACTION AND VALVES - milking effect

b. BREATHING

1)      Movement of diaphragm down reduces chest cavity pressure and increases abdominal pressure

c. VELOCITY OF BLOOD FLOW -

1)      This is inversely proportional to the cross sectional area of the blood vessels (i.e. aorta cross sectional area (sq. cm) = 2.5 with a blood velocity (cm/sec) of 40; capillaries are 2,500 and less than 0.1 respectively)

B.     CAPILLARY EXCHANGE - a closed system

1.      PHYSIOLOGY

a. VASOMOTION - flow is intermittent due to contraction relaxation of smooth muscles of
metarterioles and precapillary sphincters; controlled by oxygen content in the tissue

b. TRANSPORT MECHANISM: DIFFUSION (water and dissolved substances)
1)      Based on Pressure Differences

a)      HYDROSTATIC PRESSURE - caused by pressure of water in fluids

b)      OSMOTIC PRESSURE - due to presence of non diffusible proteins in blood and interstitial fluid

BLOOD HYDROSTATIC PRESSURE (BHP) - tendency to move

fluid out of capillary and into interstitial spaces; 35mm Hg at arteriole

end., 18mm  Hg at venule end

-vs-

BLOOD OSMOTIC PRESSURE (BOP) - tendency to move fluid from interstitial spaces into capillaries; 28 mm Hg at arteriole and venule end

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INTERSTITIAL FLUID OSMOTIC PRESSURE (IFOP) - tendency to move fluid out of capillaries into interstitial fluid; 3mm Hg at both ends

-vs-

INTERSTITIAL FLUID HYDORSTATIC PRESSURE (IFHP) -tendency to move fluid into capillary from interstitial spaces; usually zero at either end

2) NET FILTRATION PRESSURE (NFP) = (BHP + IFOP) - (IFHP + BOP)

At arteriole end: (35 + 3) - ( 0 + 28) = +10mm Hg

At venule end: (15 + 3) - ( 0 + 28) = -7mm Hg

3)  STARLING LAW OF CAPILLARIES - A state of almost equilibrium exists with fluids from arteriole and venule ends of capillaries with the addition of fluid absorbed by lymphatic system.

C.     EVALUATION OF CIRUCULATION

1.      PULSE CHECKS: numerous locations

a. TACHYCARDIA - > 100 bpm

b. BRADYCARDIA - < 50 bpm

IV     CIRCULATION ROUTES

A.     SYSTEMIC CIRCULATION - distributes oxygenated blood throughout the entire body

1.  SIGNIFICANT SUBDIVISIONS

a.          CORONARY CIRCULATION - supplies myocardium of the heart

b.       HEPATIC PORTAL - communicates from GI tract to liver: 2 sources of blood to liver:

                   1)        Hepatic A.- carries oxygenated blood from systemic circulation

2)       Hepatic portal vein (formed by union of superior mesenteric and splenic veins) delivers deoxygenated blood from digestive organs; ultimately blood leaves through hepatic V. and into inferior vena cava

                        c.       FETAL CIRCULATION

                     1)      PLACENTA(AFTERBIRTH)- structure through which materials between fetal and maternal circulation are exchanged; attached to umbilicus of fetus by umbilical cord

2)      UMBILICAL CORD – consists of 2 arteries (carrying deoxygenated blood to

mother) and 1 vein (carrying oxygenated blood to fetus). Vein basically bypasses

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liver by flowing primarily into Ductus Venosus (ultimately becomes ligamentum venosum) and into the inferior Vena Cava

3) Oxygenated and deoxygenated blood mingle in inferior Vena Cava which empties
into right atrium: FORAMEN OVALE - opening in system between right and left
atria. becomes Fossa Ovalis

4) DUCTUS ARTERIOSUS - pulmonary shunt connects aorta enabling most blood
to bypass fetal lungs, becomes Ligamentum Arteriosum

d.      PULMONARY CIRCULATION - pulmonary trunk from right ventricle divides right side feeds right lung, left side feeds left lung; return via pulmonary vein back to left atrium.