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What are the The three major types of blood vessels?
arteries, capillaries, and veins
What are arterioles?
smallest artery branches
What are venules?
smallest veins
arteries always carry __ blood
oxygenated
Veins carry ___blood
oxygen poor
Arteries and veins have special jobs where?
In pulmonary circulation and in the umbilical of a fetus.
What happens in pulmonary circulation?
Arteries carry oxygen poor blood to the lungs and veins carry oxygen rich blood from the lungs to the heart.
only the __ have intimate contact with tissue cells and directly serve cellular needs
capillaries
Tunic definition
Coverings or vessel layers.
What is the innermost tunic?
Tunica intima
Endothelium definition
Single layer of squamous cells that line the heart, blood vessels, and lymphatic vessels.
Vessels larger than 1mm, _______, consisting of a basement membrane and loose connective tissue, supports the endothelium.
Subendothelial layer
The middle tunic is called__
the tunica media
The ____, is mostly circularly arranged smooth muscle cells and sheets of elastin.
tunica media
The activity of the smooth muscle is regulated by _____of the autonomic nervous system and a whole battery of chemicals.
vasomotor nerve fibers
Vasoconstriction definition
Narrowing of blood vessels
Vasodilation definition
Relaxation of the smooth muscles of the blood vessels, producing dilation.
Which tunica bears the chief responsibility for maintaining blood pressure and circulation?
Tunica media
The outermost layer of a blood vessel all is________
tunica externa
What is the tunica externa composed of?
loosely woven collagen fibers that protect and reinforce the vessel, and anchor it to surrounding structures.
What is inside the tunica externa?
nerve fibers, lymphatic vessels, elastic fibers.
In larger vessels, the tunica externa contains___
the vasa vasorum
What are the vasa vasorum?
tiny blood vessels that nourish the more external tissues of the blood vessel wall.
arteries can be divided into three groups
elastic arteries, muscular arteries, and arterioles.
What are elastic arteries?
the thick-walled arteries near the heart.
elastic arteries are sometimes called__
conducting arteries
Elastic arteries are______ expanding and recoiling as the heart ejects blood.
pressure reservoirs
without the pressure-smoothing effect of the elastic arteries, the walls of arteries throughout the body experience______
higher pressures
____deliver blood to specific body organs
Muscular arteries
Minute-to-minute blood flow into the capillary beds is determined by________________
arteriolar diameter
arteriolar diameter varies in response to
changing neural, hormonal, and local chemical influences.
What are capillaries?
the smallest blood vessels
What are pericytes?
contractile stem cells that can generate new vessels or scar tissue, stabilize the capillary wall, and help control capillary permeability
_____ lack capillaries but receive nutrients from blood vessels in nearby connective tissues.
Cartilage and epithelia
the avascular cornea and lens of the eye receive nutrients from the
aqueous humor.
there are three types of capillaries
continuous, fenestrated, and sinusoid.
What are intercellular clefts?
unjoined membrane which allow limited passage of fluids and small solutes.
capillary beds are
interweaving networks
The flow of blood from an arteriole to a venule—that is, through a capillary bed is called ______
the microcirculation
What forms the capillary bed?
10 to 20 capillaries
As blood flows through the capillaries, it takes part in exchanges
of gases, nutrients, and wastes with the surrounding tissue cells.
Veins carry blood from the capillary beds toward
the heart
The smallest venules,_______ consist entirely of endothelium around which pericytes congregate.
the postcapillary venules
fluid and white blood cells move easily from the bloodstream through their walls
Postcapillary venules
Veins are called capacitance vessels and blood reservoirs because they can hold up to_____
65% of the body’s blood supply at any time
their large-diameter lumens, which offer relatively little resistance to blood flow
veins
___ prevent blood from flowing backward in veins
Venous valve
Venous valves are most abundant in
the veins of the limbs
Varicose veins are
veins that are tortuous and dilated because of incompetent (leaky) valves.
resulting varicosities in the anal veins are called
hemorrhoids
Venous sinuses are
highly specialized, flattened veins with extremely thin walls composed only of endothelium
___are supported by the tissues that surround them, rather than by any additional tunics
Venous sinuses
vascular anastomoses are
Blood vessels form special interconnections
arteries supplying the same territory often merge, forming____
arterial anastomoses
Most organs receive blood from______arterial branch
more than one
anastomoses provide alternate pathways__________for blood to reach a given body region
called collateral channels
Arterial anastomoses occur________, where active movement may hinder blood flow through one channel.
around joints
thoroughfare channel shunts of some capillary beds that connect arterioles and venules are examples of
arteriovenous anastomoses
Because ____ are abundant, an occluded vein rarely blocks blood flow or leads to tissue death.
venous anastomoses
Blood flow is
the volume of blood flowing through a vessel, organ, or the entire circulation in a given period.
Blood pressure is
the force per unit area exerted on a vessel wall by the contained blood.
Resistance is
opposition flow and is a measure of the amount of friction blood encounters as it passes through vessels.
Why do we generally use the term total peripheral resistance(TPR)?
most friction is in the peripheral (systemic) circulation.
What are the three important sources of resistance?
blood viscosity, vessel length, and vessel diameter.
what is viscosity?
the internal resistance that exists in all fluids.
Polycythemia is
excessive numbers of red blood cells
the longer the vessel, the _____ the resistance
greater
the smaller the diameter, the _____ the resistance
greater
Blood vessel diameter _____________and _________ total peripheral resistance.
changes frequently, significantly alters
Blood viscosity and vessel length are normally _________ and so the influence is ______.
unchanging, constant
What is laminar flow or streamlining?
the relative speed and position of fluid in different regions of the tube’s cross section remain constant in a tube of a given size.
What are the major determinants of total peripheral resistance?
small-diameter arterioles
turbulent flow is
irregular fluid motion where blood from the different laminae mixes.
When blood encounters an abrupt change or a protruding area of the tube wall the smooth laminar blood flow is replaced by
turbulent flow
Turbulence dramatically ________ resistance
increases
Blood flow is directly proportional to the difference in
blood pressure
When blood pressure (P) ______, blood flow _______
increases
Blood flow is inversely proportional to
the peripheral resisitance.
TPR is far more important than ______ in influencing local blood flow.
blood pressure
______ can easily be changed by altering blood vessel diameter.
TPR
systemic blood pressure is ____ in the aorta
highest
systemic blood pressure declines throughout the pathway
The steepest drop in blood pressure occurs in
_______, which offer the greatest resistance to blood flow.
the arterioles
As long as______ exists blood continues to flow until it completes the circuit back to the heart.
a pressure gradient
Arterial blood pressure reflects two factors:
(1) how much the elastic arteries close to the heart can stretch(2) the volume of blood forced into them at any time.
blood pressure is pulsatile in the elastic arteries near the heart.
it rises and falls in a regular fashion
pressure peak generated by ventricular contraction is called
systolic pressure
During diastole, the aortic valve closes, preventing blood from flowing back into the heart.
diastolic pressure
The difference between the systolic and diastolic pressures is called the
pulse pressure.
mean arterial pressure (MAP)
the pressure that propels the blood to the tissues.
low capillary pressures are desirable because:
Capillaries are fragile and high pressures would rupture them.
even the low capillary pressure can force solute-containing fluids (filtrate) out of the bloodstream into the interstitial space.
venous blood pressure is ___ and changes ____ during the cardiac cycle.
steady, very little
three functional adaptations are critically important to venous return:
The muscular pump, respiratory pump, and sympathetic venoconstriction
As the skeletal muscles surrounding the deep veins contract and relax, they squeeze or “milk” blood toward the heart, and once blood passes each successive valve, it cannot flow back
The muscular pump
moves blood up toward the heart as pressure changes in the ventral body cavity during breathing.
The respiratory pump
reduces the volume of blood in the veins—the capacitance vessels (Venous volume is reduced and blood is pushed toward the heart.)
Sympathetic venoconstriction
Cardiovascular system homeostasis regulation involves three key variables:
Cardiac output, Total peripheral resistance,Blood volume
blood pressure varies directly with ____ and __
CO, TP
Anything that increases cardiac output or total peripheral resistance increases _____
blood pressure
Blood pressure also varies directly with blood volume because ____ depends on blood volume
CO
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