The Peripheral Vascular System

ST120: Basic Sciences II

Concorde Career College, Portland

Cardiovascular System

Objectives:• Discuss the relevant vessels of the peripheral vascular

system

• Compare and contrast the structure of an artery and a vein

• Describe the mechanisms that regulate blood pressure

• Describe the etiology of atherosclerosis and arterial embolism and their treatments

• Compare and contrast bypass grafting and endarterectomy

Cardiovascular System

Blood Vessels and Circulation

Types of Blood Vessels

• Arteries– Arterioles

• Veins– Venules

• Capillaries

Blood Vessels

• Arteries: blood is pumped from the heart through a series of large distribution vessels. Largest artery = aorta

• Arteries divide into vessels that become progressively smaller and finally become tiny arterioles that control the flow into microscopic exchange vessels called capillaries

• Gas exchange occurs in capillary beds

Blood Vessels

• Blood Blood exits exits capillary bedscapillary beds and enters and enters venulesvenules

• VenulesVenules steadily steadily increase in sizeincrease in size to to eventually become eventually become veinsveins

• LargestLargest veinsveins are the are the superior and inferior superior and inferior vena cavavena cava

Blood Vessels

• Arteries carry blood away from the heart

• Veins carry blood toward the heart

• So do all arteries carry oxygen rich blood and all veins carry oxygen poor blood?

Structure• 3 tunics (coats) or layers of veins and arteries

– Tunica adventitia- outermost – made of connective tissue, which reinforce the vessel wall so it will not burst

– Tunica media- middle – contains smooth muscle

– Tunica intima- inner – endothelial cells --- endothelium lines the entire circulatory system

Structure

• Only Only arteriesarteries, , arteriolesarterioles, , veinsveins, and , and venulesvenules can be seen during surgery- can be seen during surgery- capillariescapillaries are are microscopicmicroscopic

• CapillariesCapillaries are only one are only one layer thick and layer thick and thin-walled-thin-walled- only tunica intima only tunica intima

• This allows for easy This allows for easy exchange of gasesexchange of gases and and nutrientsnutrients

Systemic and Pulmonary Circulation

• Systemic circulation: blood flow from left ventricle of the heart through blood vessels to all parts of the body and back to the right atrium

• Pulmonary circulation: venous blood moves from the right atrium to the right ventricle to the pulmonary artery to lung arterioles and capillaries. There the exchange of gases between the blood and the air takes place. This oxygenated blood then flows through lung venules into four pulmonary veins and returns to the left atrium

Pulmonary and Systemic Blood Circuits

Cardiovascular System

Veins contain valves to prevent the backward flow of blood:

A. External view of the vein shows wider area of valve.

B. Internal view with the valve open as blood flows through.

C. Internal view with the valve closed.

Blood Vessel Structure

Note the valve and the comparison of the artery, vein, and

capillary

Cardiovascular System

Ascending Aorta• Right Coronary• Left Coronary

Aortic Arch• Brachiocephalic

– Right Common Carotid– Right Subclavian

• Left Common Carotid• Left Subclavian

Cardiovascular System

Major veins and arteries of the neck

Branches of the Thoracic and Abdominal Aorta

Arterial System

Venous System

Blood Pressure

• Pressure on the blood vessel walls

• Highest in arteries, Lowest in Veins

• Blood pressure gradient: the graph looks like a hill… aorta is highest point and the venae cavae are the lowest. Defined as the difference between the mean BP in the aorta and the mean BP in the venae cavae.

Blood Pressure

• Blood pressure keeps the blood circulating

• No blood pressure = No blood circulating = death

• Average pressure is the MEAN BP

• Hypertension- high blood pressure; could rupture blood vessels

• Hypotension- low blood pressure; circulation can be too low to sustain life - Hemorrhage can cause hypotension

Factors That Influence Arterial Blood Pressure

• Blood volume• Strength of ventricular

contractions • Resistance• Blood viscosity• Heart rate

Blood Pressure• Blood Volume- volume of blood in the vessels

– Direct cause of blood pressure• Arterial blood volume is determined by how much the

heart pumps into them, which determines how much the arterioles drain out of them; the size of the arterioles are important in determining how much blood is drained from the arteries

• Larger the volume, the higher the pressure; conversely, lower blood volume, lower blood pressure; thus hemorrhage = lower blood pressure = not corrected = death

• Drop in BP is a major sign of hemorrhage

Strength of ventricular Contractions

–the the strengthstrength and and raterate of the of the heartbeat affects the heartbeat affects the stroke stroke volumevolume (amount of blood ejected by the LV into the aorta (amount of blood ejected by the LV into the aorta

with one contraction), with one contraction), which in turn affects which in turn affects cardiac output,cardiac output, which affects which affects blood volume,blood volume, therefore the therefore the BPBP

Blood Pressure

• Blood Viscosity- aka thickness. Blood that is too diluted causes BP to drop

– Less viscous than normal, BP decreases, so for hemorrhage treatment, whole blood or plasma is preferred

– More viscous than normal, BP increases

• Polycythemia increases viscosity thereby increasing BP

Blood Pressure

As blood leaves the LV and enters the aorta, its pressure falls progressively as the distance from the heart increases

Once in the venae cavae, the pressure is near zero

Blood Pressure

• Resistance is the hindrance of blood flow with in the CV system due to friction of the blood against the walls of the vessels

• Most resistance is in the aterioles, capillaries, and venules

• Vasoconstriction and vasodilation influence resistance

Blood Pressure

• Heart rate affects BP

• As the heart beats faster, each contraction of the LV leaves less time for the ventricle to refill, thus less blood is pumped into the aorta. This means less blood volume which is less blood pressure

Fluctuations in BP

• Doesn’t stay the same all the time.Doesn’t stay the same all the time.

• IncreasesIncreases during during exercise, fear, etc.exercise, fear, etc.

• DecreasesDecreases at night, while at night, while sleeping or relaxing.sleeping or relaxing.

• Normal is Normal is 120/80 for healthy adults (average)120/80 for healthy adults (average)

Central venous pressure

• BP within the RA

• CVP is low as it enters the RA

• If the heart is weakened, the CVP increases

5 mechanisms that keep venous blood moving

• Continued beating of the heart

• Adequate BP in the arteries

• Semilunar valves preventing backflow thus moving blood in the right direction

• Contraction of skeletal muscles squeezing veins with assistance of venous valves

• Changing pressures in the chest cavity during breathing acting as a pump

Pulse

• An An artery expandingartery expanding and and then recoilingthen recoiling– alternately is what you are feeling when you alternately is what you are feeling when you

take a take a pulsepulse..

• Provides information on the Provides information on the raterate, , strengthstrength, , and and rhythmrhythm of the heartbeat of the heartbeat

Major pulse points

• Temporal – over the temple anterior to the ear• Facial – lower margin of the mandible• Carotid – neck, along the sternocleidomastoid muscle• Axillary – inferiolateral axillary wall• Brachial – medial aspect of upper arm• Radial – at the wrist• Femoral – groin • Popliteal – behind and proximal to the knee• Dorsalis – dorsal surface of the foot• Apical – 5th left intercostal space (requires auscultation)

Hepatic Portal System

• Veins from the spleen, stomach, pancreas, gallbladder, and intestines send their blood to the liver by means of the hepatic portal vein.

Hepatic Portal Circulation

• Refers to the route of Refers to the route of blood flow through the blood flow through the liverliver..

• Liver cellsLiver cells remove and remove and detoxifydetoxify various various poisonous substances.poisonous substances.

• This is a variationThis is a variation ( (detourdetour) of the normal ) of the normal blood route blood route

• This means that this blood is sent through a This means that this blood is sent through a second set of second set of capillaries (in the liver)capillaries (in the liver)

Pathology

• Arteriosclerosis -thickening & loss of elasticity of the walls of the arteries Hardening of the arteries– Atherosclerosis -collection of fatty & other

substances on the inner lining of arteries, forming plaques, which progressively occlude the passageways; obstruction of the flow of blood

• Atheroma – prototypical lesion of atherosclerosis

Arteriosclerosis Obliterans

Diagnostic Procedures and Equipment

• Plethysmography

• Doppler probe

• Phleborheography

• CAT scan, MRI, and ultrasonography

• Angiography

Angiography

Pathology

• Arterial embolism– Treatment - Fogarty

catheter

Pulmonary Emboli Following Fogarty Embolectomy

– Carotid Endarterectomy - removal of arteriosclerotic plaque from an obstructed carotid artery

in order to restore circulation.

Endarterectomy