Test 4 Blood Vessels Flashcards
the blood vessels of the body form a
a closed circulatory system
powered by the pumping of the heart.
blood is carried in a?
closed
system of vessels that begins
and ends at the heart
the three major types of blood vessels
arteries, capillaries, and
veins.
the path of blood vessels
Heart → Arteries →
Arterioles → Capillaries →
Venules → Veins → Heart)
The walls of most blood vessels are composed of
three distinct layers
(tunics): 1) tunica intima, 2) tunica media, and 3) tunica externa
the tunics surrounding the central blood filled space of the blood vessel walls are called
the lumen
tunica intima
the innermost tunic, which contains the endothelium
(simple squamous epithelium) that lines the lumen of all vessels.
the endothelium froms a
smooth surface that minimizes the friction
of blood moving across them
in vessel larger than 1 mm in diameter
a thin layer of loose C.T.,
called the subendothelial layer, lies just external to the endothelium.
Tunic media
the middle tunic consists of circularly arranged sheets
of smooth muscle fibers that sandwich sheets of elastin and collagen
fibrils.
vasoconstriction
Contraction of the smooth muscle cells decreases the diameter of the
vessel
vasodilation
relaxation of the smooth muscle cells increases the vessel’s diameter of the vessel
the tunica media is thicker in?
arteries than in veins
tunica externa
the outermost layer of the vessel wall; composed of connective tissue (elastic and collagen fibers)
tunica externa function
protects the vessel, further strengthens its wall, and anchors
the vessel to surrounding structures.
arteries
vessels that carry blood away from the heart
the arterial system is divided into 3 parts
: elastic, muscular, arteriole
a) Elastic (conducting) arteries
(1cm-2.5 cm): thick-walled arteries
near the heart (aorta and its major branches)
- Large lumen allow low-resistance conduction of blood ; contains
elastin in all three tunics
- Withstands and dampends large blood pressure fluctuations to allow
blood to flow fairly continuously through the body
Muscular arteries
s (0.3mm to 1 cm): distal to elastic arteries and
deliver blood to body organs; have thick tunica media with more
smooth muscle and less elastic tissue; active in vasoconstriction
Arterioles
(10µm-0.3mm): smallest arteries; lead to capillary beds
and control flow into capillary beds via vasodilation and constriction
-Their tunica media contains only one or two layers of smooth muscle
cells
arteries
the passage of blood through the arteries proceeds from elastic arteries, to muscular arteries, to artrioles
capillaries
are the smallest blood vessels, with a diameter of 8-
10µm. just large enough to enable RBC’s to pass through in single file
capillaries are composed of
only a single layer of endothelial cells
surrounded by a basement membrane
pericytes
s: spider-shaped cells who form a network around the
periphery of the capillary and serve to strengthen and stabilize the
capillary
function of capillaries
Renew and refresh interstitial fluid with oxygen nutrients
cells need, and removes carbon dioxide and nitrogenous wastes that
cells deposit into the fluid
capillary bed
is a network of capillaries, which run throughout
most tissues….especially the loose connective tissues
capillary beds
terminal arteriole -> metarteriole -> (true capillaries) -> throughfare channel -> venule
precapillary sphincters
composed of smooth muscle cells, wrap
around the root of each true capillary where it leaves the metarteriole
the endothelial cells are held together by
tight junctions and
occasional desmosomes
tight junctions of capillaries do not…
do not surround the whole perimeter of the
endothelial cells…leaving gaps of unjoined membrane, called
intercellular clefts
the intercellular celfts
small molecules to exit and enter the
capillary
3 structural types of capillaries
Continuous, Fenestrated, and
Sinusoids
Continuous capillaries
most common; are abundant in the skin and
muscles, and have: endothelial cells that provide an uninterrupted
lining, adjacent cells that are held together with tight junctions but
have intercellular clefts of unjoined membranes that allow the passage
of fluids
blood brain barrier
the capillaries of the brain lack the structural
features that account for capillary permeability
blood brain barriers lacks
Complete tight junctions (intercellular clefts are absent)
-Vital molecules that must cross are “ushered through” via highly
selective transport mechanisms in the plasma membranes of the
endothelial cells.
fenestrated capillaries characterized by
an endothelium
riddled with fenestrations (pores) allowing greater permeability to
solutes and fluids than other capillaries
fenestrated capillaries found in
where there are high rates of exchange of small molecules
between the blood and the surrounding tissue fluid (e.g., small
intestines, endocrine glands, and kidneys)
sinusoidal capillaries characterized by
a twisted, leaky,
fenestrated capillaries with large lumens
sinusoidal capillaries allow
large molecules (proteins and blood cells) to pass between the
blood and surrounding tissues
- Blood flows sluggishly, allowing for many exchanges that occur
across the capillary walls
sinusoidal capillaries found in
liver, bone marrow, lymphoid tissue, and in some
endocrine organs
veins
are the blood vessels that conduct blood from the capillaries
toward the heart
-Because blood pressure in the venous part of the circulation is much
lower than in the arterial part
…the walls of veins are much thinner
than those of comparable arteries
venules
(8-100µm): the simplest veins that are formed when
capillary beds unite.
postcapillary venules
smallest venules, composed of endothelium
and a few pericytes; function like capillaries that leak fluid and
leukocytes during an inflammatory response
large venules have
one or two layers of smooth muscle (tunica
media)
veins are formed when
venules converge and are capacitance vessels
(blood reservoirs) that contain 65% of the blood supply; vei
in veins, the tunica externa is
thicker than the tunica media
(opposite in arteries)
veins:
Several mechanisms counteract the low venous blood pressure and
help move the blood along its course back to the heart:
a) Large-diameter lumens, which offer little resistance to flow
b) Valves (resembling semilunar heart valves), which prevent
backflow of blood; abundant in the veins of the limbs
vascular anastosomes
: merging blood
vessels, more common in veins than
arteries
vascular anastosomes example:
arterial anastomoses
: provide
alternate pathways (collateral channels)
for blood to reach a given body region
-If one branch is blocked, the collateral
channel can supply the area with adequate
blood supply (thoroughfare channels are
examples of arteriovenous anastomoses)
the walls of blood vessels contain
living cells and therefore require
a blood supply of their own
vasa vasorum
(“vessels of the vessels”): the tiny arteries, capillaries, and veins that supply and drain the walls of larger blood vessels
vasa vasorum located in?
in the tunica externa
vasa vasorum arise either as?
tiny branches from the same vessel or as small branches from other, nearby vessels and nourish the outer half of the wall of the larger vessel.
arteries vs veins:
delivery
arteries: Blood pumped into single
systemic artery – the aorta
veins:
Blood returns via superior and
interior venae cavae and the
coronary sinus
arteries vs veins location
arteries: deep, and protected by tissue
veins: both deep and superficial
arteries vs veins pathways
arteries: fair, clear, and defined
veins: convergent interconnection
arteries vs veins
supply/drainage
arteries: predictable supply
veins: dural sinuses and hepatic portal circulation
