Vocabulary Blood Vessels

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1

Blood vessels

form a closed delivery system that begins and ends at the heart.

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Tunica Intima

the innermost tunic, in intimate contact with the blood in the lumen, forming a slick surface that minimizes friction as blood moves through the lumen.

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Subendothelial layer

in vessels larger than 1 mm, consisting of a basement membrane and loose connective tissue, supports the endothelium.

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Tunica Mediais

the middle tunic, mostly circularly arranged smooth muscle cells and sheets of elastin, the bulkiest layer in arteries, responsible for maintaining blood pressure and continuous blood circulation.

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Vasoconstriction

reduction in lumen diameter as the smooth muscle contracts

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Vasodilation

increase in lumen diameter as the smooth muscle relaxes

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Tunica Externa

the outermost layer is composed largely of loosely woven collagen fibers protect and reinforce the vessel, and anchor it to surrounding structures.

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Arteries

carry blood away from the heart, “branch,” “diverge,” or “fork” as they form smaller and smaller divisions.

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Veins

carry blood toward the heart, “join,” “merge,” and “converge” into the successively larger vessels approaching the heart.

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Capillaries

have intimate contact with tissue cells and directly serve cellular needs. Exchanges between the blood and tissue cells occur primarily through the gossamer-thin capillary walls.

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Elastic Arteries

conducting, thick-walled arteries near the heart—the aorta and its major branches.

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Muscular Arteries

distributing arteries, which deliver blood from elastic arteries to specific body organs

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Arterioles

smallest of the arteries delivers blood from the muscular arteries to the capillaries

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Continuous capillaries

abundant in the skin and muscles, are most common. They are continuous in the sense that their endothelial cells provide an uninterrupted lining, adjacent cells being joined laterally by tight junctions.

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Fenestrated Capillaries

are similar to the continuous variety except that some of the endothelial cells in fenestrated capillaries are riddled with oval pores, or fenestrations

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Sinusoids Capillaries

are highly modified, leaky capillaries found only in the liver, bone marrow, spleen, and adrenal medulla.

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Capillary beds

interweaving networks of capillaries

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Microcirculation

The flow of blood from an arteriole to a venule—that is, through a capillary bed

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Venules

are formed when capillaries unite.

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Postcapillary Venules

the smallest venules, consist entirely of endothelium around which pericytes congregate. They are extremely porous and fluid and white blood cells move easily from the bloodstream through their walls.

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Terminal Arteriole

feeds the capillary bed

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Metarteriole

a vessel structurally intermediate between an arteriole and a capillary

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Thoroughfare Channel

intermediate between a capillary and a venule.

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True Capillaries

number 10 to 100 per capillary bed, depending on the organ or tissues served. They usually branch off the metarteriole

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Precapillary Sphincter

surrounds the root of each true capillary at the metarteriole and acts as a valve to regulate blood flow into the capillary

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Vein Tunica Externa

is the heaviest wall layer, Consisting of thick longitudinal bundles of collagen fibers and elastic networks

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Venous valves

are formed from folds of the tunica intima, and resemble the semilunar valves of the heart in both structure and function

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Venous sinuses

such as the coronary sinus of the heart and the dural venous sinuses of the brain, are highly specialized, flattened veins with extremely thin walls composed only of endothelium.

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Vascular Anastomoses

interconnections where vascular channels unite

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Arterial Anastomoses

one arterial branch meets another supplying the same area.

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Collateral Channels

anastomoses provide alternate pathways

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Arteriovenous Anastomoses

the metarteriole–thoroughfare channel shunts of capillary beds that connect arterioles and venules.

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Venous Anastomoses

veins connect

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Blood flow

is the volume of blood flowing through a vessel, an organ, or the entire circulation in a given period (ml/min).

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Blood pressure (BP)

the force per unit area exerted on a vessel wall by the contained blood, is expressed in millimeters of mercury (mm Hg).

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Resistance

is opposition to flow and is a measure of the amount of friction blood encounters as it passes through the vessels.

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Peripheral Resistance

friction encountered in the peripheral (systemic) circulation, well away from the heart

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Blood viscosity

the internal resistance to flow that exists in all fluids and is related to the thickness or “stickiness” of a fluid.

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Total blood vessel length

the relationship between total blood vessel length and resistance is straightforward: the longer the vessel, the greater the resistance.

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Systolic Pressure

is the pressure peak, averages 120 mm Hg in healthy adults. Blood moves forward into the arterial bed because the pressure in the aorta is higher than the pressure in the more distal vessels

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Diastole Pressure

the aortic valve closes, preventing blood from flowing back into the heart, and the walls of the aorta (and other elastic arteries) recoil, maintaining sufficient pressure to keep the blood flowing forward into the smaller vessels. During this time, aortic pressure drops to its lowest level (approximately 70 to 80 mm Hg in healthy adults).

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Mean arterial pressure (MAP)

the pressure that propels the blood to the tissues. Diastole usually lasts longer than systole, so the MAP is not simply the value halfway between systolic and diastolic pressures. Instead, it is roughly equal to the diastolic pressure plus one-third of the pulse pressure.

MAP = diastolic pressure + (pulse pressure)/3

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Respiratory “Pump”

During inhalation, abdominal pressure increases, squeezing the local veins and forcing blood toward the heart. At the same time, the pressure in the chest decreases, entry into the right atrium.

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Muscular “Pump”

consisting of skeletal muscle activity. As the skeletal muscles surrounding the deep veins contract and relax, they “milk” blood toward the heart, and once blood passes each successive valve, it cannot flow back.

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Vasomotor Center

The neural center that oversees changes in the diameter of blood vessels, a cluster of neurons in the medulla.

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Vasomotor Fibers

postganglionic visceral efferent fibers innervating the smooth muscles of vessel walls.

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Vasomotor Tone

state of moderate constriction the arterioles are almost always in

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Baroreceptors

neural receptors located in the carotid sinuses (dilations in the internal carotid arteries, which provide the major blood supply to the brain).

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Carotid Sinus Reflex

slowing of the heart beat on pressure on the carotid artery at the level of the cricoid cartilage.

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Aortic Reflex

help maintain adequate blood pressure in the systemic circuit as a whole.

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Chemoreceptors

in the aortic arch and large arteries of the neck transmit impulses to the cardioacceleratory center, which then increases cardiac output, and to the vasomotor center, which causes reflex vasoconstriction. The rise in blood pressure that follows speeds the return of blood to the heart and lungs.

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Adrenal medulla hormones

during periods of stress, the adrenal gland releases norepinephrine (NE) and epinephrine to the blood, NE has a vasoconstrictive action. Epinephrine increases cardiac output and promotes generalized vasoconstriction.

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Angiotensin II

when blood pressure or blood volumes are low, the kidneys release the hormone renin. Renin acts as an enzyme, ultimately generating angiotensin II that stimulates intense vasoconstriction, promoting a rapid rise in systemic blood pressure

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Atrial Natriuretic Peptide (ANP)

Causes blood volume and blood pressure to decline.

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Antidiuretic Hormone

stimulates the kidneys to conserve water. It is not usually important in short-term blood pressure regulation, but when blood pressure falls to dangerously low levels (as during severe hemorrhage), much more ADH is released and helps restore arterial pressure by causing intense vasoconstriction.

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Vital Sign’s

pulse, blood pressure, respiratory rate and body temperature

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Pulse

pressure wave that is transmitted through the arterial tree.

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Pressure Points

clinically important arterial pulse points because they are compressed to stop blood flow into distal tissues during hemorrhage.

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Hypotension

or low blood pressure, is a systolic pressure below 100 mm Hg.

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Hypertension

high blood pressure.

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Tissue Perfusion

Blood flow through body tissues

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Autoregulation

the automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirements at any instant.

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Nitric oxide (NO)

is a powerful vasodilator which acts via a cyclic GMP second-messenger system.

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Endothelins

are among the most potent vasoconstrictors known.

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reactive hyperemia

refers to the dramatically increased blood flow into a tissue that occurs after the blood supply to the area has been temporarily blocked.

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Hyperemia

When muscles become active, blood flow increases

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Hydrostatic pressure

is the force exerted by a fluid pressing against a wall.

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Capillary hydrostatic pressure (HPc)

the pressure exerted by blood on the capillary walls.

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interstitial fluid hydrostatic pressure

acting outside the capillaries and pushing fluid in

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Colloid osmotic pressure

the force opposing hydrostatic pressure, is created by the presence in a fluid of large nondiffusible molecules, such as plasma proteins, that are unable to cross the capillary wall.

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hypovolemic shock

which results from large-scale loss of blood, as might follow acute hemorrhage, severe vomiting or diarrhea, or extensive burns. If blood volume drops rapidly, heart rate increases in an attempt to correct the problem. Thus, a weak, “thready” pulse is often the first sign of hypovolemic shock.

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vascular shock

blood volume is normal, but circulation is poor as a result of an abnormal expansion of the vascular bed caused by extreme vasodilation.

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Cardiogenic shock

or pump failure, occurs when the heart is so inefficient that it cannot sustain adequate circulation.

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vascular system

complex network of blood vessels

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systemic circulation

routes blood through a long loop to all parts of the body before returning it to the heart

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pulmonary circulation

is the short loop that runs from the heart to the lungs and back to the heart.

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Three important differences between systemic arteries and veins

Arteries run deep while veins are both deep and superficial.

Venous pathways are more interconnected.

The brain and digestive systems have unique venous drainage systems.

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blood islands

The endothelial lining of blood vessels is formed by mesodermal cells, which collect in little masses

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Pulmonary Trunk

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Pulmonary Arteries
Right & Left

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Pulmonary Veins

Right & Left
Superior & Inferior