A&P300 Chapter 21 (Blood vessels) Flashcards
blood vessels function
deliver blood to the organs and tissues in your body
help maintain homeostasis via vasoconstriction/vasodilation
note that many capillary sphincters are often constricted to make blood’s delivery of oxygen/nutrients efficient for tissues that require it most
..
how many km of blood vessel does left side pump through?
The left side of the heart pumps blood through an estimated 100,000 km of blood vessels
major types of BV
Arteries (efferent vessels)
Blood vessels that carry blood AWAY from the heart
Arterioles
Smaller than arteries, carries blood AWAY from the heart
Capillaries
Smallest blood vessels where O2 & CO2 can be exchanged
Venules
Smaller than veins, carries blood TOWARDS the heart
Veins (afferent vessels)
Blood vessels that carry blood TOWARDS the heart
arteries about
Also called efferent vessels
carry blood away from the heart to other tissues
High pressure/low volume reservoir
Have thick elastic walls.
characteristic of wall of arteries
thick elastic walls.
arterioles about
Small arteries that are less elastic
Have more smooth muscles
Provide the greatest resistance to the blood flow that help to regulate blood pressure
Regulate flow into capillary beds
arterioles vs arteries
arterioles less elastic
arterioles have more smooth muscle
which vessels contribute most to regulating BP
arterioles
Provide the greatest resistance to the blood flow that help to regulate blood pressure
capillaries about
The site of exchange with tissues
Exchange of gases and nutrients between blood and tissue cells
Compose of single layer of the endothelial cells, (thin flattened cells that line the inner wall of all vessels)
+
and basal membrane
venules and veins, about
Also called afferent vessels
carry blood away from the tissues to the heart
Low pressure/High volume reservoir
Regulate cardiac filling (how much blood is returning to the heart)
what is known as low pressure / high volume reservoire
veins / venules
how do veins regulate cardiac filling?
Neurohumoral mechanisms can mobilize the blood in veins to maintain filling pressure in the right heart when required.
3 layers of wall of blood vessel
Tunica interna
Innermost layer, adjacent to lumen
Tunica media
Middle layer of smooth muscle and elastic CT
Tunica externa
Outermost layer, CT outer covering
tunica interna aka
TUNICA INTIMA
more commonly known as “
tunica externa aka
tunica adventitia
we will refer to it as tunica externa
how are the 5 vessels structurally different?
some structural variations correlate to the different functions of the 5 major blood vessel types
about Tunica Intima (tunica interna)
Forms the inner lining of the blood vessel and is in direct contact with the blood
3 components of tunica intima
3 components:
Endothelium (simple squamous epithelium)
Basement membrane (reticular fibers)
Internal elastic lamina forming the boundary between the tunica interna and tunica media
—> (contributes to distensibility & stretch of vessel)
basement membranes function (general function – maybe not applicable here?)
Functionally, the BM is important for providing physical and biochemical cues to the overlying cells, sculpting the tissue into its correct size and shape.
tunica media – about
Muscular and CT layer that displays the greatest variation among the different vessel types
Composed of smooth muscle and elastic fibers
External elastic lamina separating the tunica externa from tunica media
which component of vessels has the greatest variation b/w the different types?
TUNICA MEDIA (esp because some vessels require more smooth muscle than others, depending on function)
Note external elastic lamina
shown as part of tunica externa in diagram, but notes include it as part of tunica MEDIA
more about role of tunica media
Regulates the diameter of the lumen, ultimately effecting the rate of blood flow and pressure
Helps limit blood loss with injury (VASOCONSTRICTION)
Allows stretch and recoil of the blood vessel
note hemostasis (vascular phase & tunica media)
(Helps limit blood loss with injury)
recall:
1) vascular phase
2) platelet phase
3) coagulation phase
tunica media contributes to vasoconstriction (during vascular phase)
tunica media and stretch/recoil
“Allows stretch and recoil of the blood vessel”
tunica externa (adventitia) – about
Consists of elastin and collagen fibers, numerous nerves and blood vessels (VASA VASORUM)
Contains the vasa vasorum
Small blood vessels that supply blood to the tissues of the vessels
Helps anchor vessel to surrounding tissues
vasa vasorum
Vasa vasorum are defined as small blood vessels that supply or drain the walls of the larger arteries and veins, and connect with a branch of the same vessel or a neighboring vessel to form a network of small blood vessels
Supply the vessel tissue with blood (oxygen and nutrients)
small arteries and veins in the tunica externa
NOTE diagram cmoparing vein vs artery
may not always be the case, but —>
in diagram shows that vein does not have internal/external ELASTIC LAMINA
otherwise, both have all the same components in diagram
SMOOTH MUSCLE (tunica media) layer is esp THICKER in artery
and Tunica externa is also considerably thicker in artery
tunica interna is roughly same
(all according to this diagram, in slides)
also note LUMEN
also note that LUMEN is much LARGER in vein
Seems that both are roughly same size externally, but due to increased mass of TUNICA MEDIA (smooth muscle layer) in ARTERY –> lumen size is relatively smaller
note differences
Arteries: thickest walls
Veins: largest lumens
Movement in vessel:
—> Arteries: pressure from heart
—> Veins: have valves and use skeletal muscle actions to move blood
vein valves
esp lower extremity
prevent backflow
as skeletal muscles assist in pushing blood upward, past valves, back to heart
arteries – HIGH COMPLIANCE
somewhat similar in concept to “plasticity”
Compliance:
“the ability of an organ to distend in response to applied pressure.”
why arteries high compliance
High compliance due to numerous elastic fibers
smooth muscle innervation in arteries
Smooth muscle innervated by autonomic nervous system
smooth muscle innervation vs VASOCONSTRICTION
Vasoconstriction:
—> sympathetics cause a decrease in the diameter of an artery or arteriole
—> increases BP or restricts blood flow to a damaged area
smooth muscle innervation vs VASODILATION
Vasodilation:
—> The process by which a decrease in sympathetics causes an increase in the diameter of the artery or arteriole.
—> via an increased need for blood supply or changes to body metabolism
(E.g. via effect of drugs)
are parasympathetics involved in vasodilation?
No
reduced sympathetic nervous signals is responsibly for vasodilation
also
what about effect of drugs?
E.g.
NO as mediator of vasodilation
medication vs vasodilation (E.g. NO)
NO and Vasodilation Mechanism
NO diffuses into the smooth muscle cells of blood vessels and activates an enzyme called guanylate cyclase,
which in turn increases the production of cyclic guanosine monophosphate (cGMP).
Elevated levels of cGMP cause the relaxation of smooth muscle cells, leading to vasodilation.
types of arteries
Elastic arteries (aka conducting arteries)
Muscular arteries (aka distributing arteries)
elastic arteries (aka conducting arteries)
LARGE DIAMETER
More elastic fibers, less smooth muscle
Function as pressure reservoirs
E.g. of elastic arteries
aorta and pulmonary arteries
contain much more elastic tissue in the tunica media than muscular arteries
high compliance of aorta
also note DICROTIC NOTCH and elasticity of AORTA
Muscular arteries (aka distributing arteries)
Medium diameter
More smooth muscle, fewer elastic fibers
smooth muscles allow vessels to regulate blood supply constricting or dilating.
Distribute blood to various parts of the body
more about elastic arteries
Largest diameter arteries in the body
Their walls are relatively THIN compared to their large DIAMETER.
internal and external lamina of ELASTIC ARTERIES
Well defined internal and external elastic lamina
(Elastic arteries)
thick tunica media, but primarily of which composition?
Thick tunica media made primarily of ELASTIC FIBRES called ELASTIC LAMELLAE
more about function of elastic arteries
they stretch & expand to accommodate a surge of blood during ventricular systole (E.g. Aorta)
Store mechanical energy – functioning as a “pressure reservoir”
When the ventricles of the heart are relaxed, these arteries may still propel the blood forward
—> VIA ELASTIC “recoil” (??)
again, E.g.
Examples: aorta, pulmonary trunk, aorta’s major initial branches
more about structure of muscular arteries (distributing arteries)
Medium-sized arteries
Tunica media contains more smooth muscle and fewer elastics fibers than elastic arteries
Well defined internal elastic lamina, thin external elastic lamina
—> external lamina that is part of tunica media does not need to be as thick
more about function of muscular arteries
Branch and ultimately distribute blood to each of the various organs
Capable of greater vasoconstriction and vasodilation
—> Responsible for control of blood flow rate
muscular arteries and “VASCULAR TONE”
Vascular tone
—> The ability of the smooth muscle to contract and maintain a state of partial contraction
—> Important in maintaining pressure and efficient blood flow
arterioles
Not much bigger than capillaries
Thin tunica interna
—> Thin fenestrated internal elastic lamina (disappears at terminal end)
Tunica media
—> consists of 1 to 2 layers of smooth muscle
Tunica externa
—> loose CT containing sympathetic nerves
(these impact blood flow and resistance via diameter changes)
more about important features related to function of arterioles
These vessels regulate the flow of blood into the capillary networks
METARTERIOLE & “Thoroughfare Channel”
Metarteriole (initial segment?) connects arteriole w/ venule —> VIA THOROUGHFARE CHANNEL (latter segment?)
the channels extending from metarteriole are capillaries
—> forming CAPILLARY BED(s)
a sphincter is at junctions of capillaries @ the metarteriole / thoroughfare channel
Precapillary-sphincters
at junction of arteriole and capillary
precapillary sphincter constriction?
Increase resistance:
—> Decrease diameter & vasoconstrict
—> Decreases blood flow into capillaries (E.g. when not needed)
Decrease resistance:
—> Increase diameter & vasodilate
—> Increases blood flow into capillaries
About Capillaries
Aka “exchange vessels”
Smallest of all vessels, but large total surface area
capillaries contact all body cells
—> The more metabolically active the cell the more capillaries serving it
primary function @ capillaries
Exchange of gases and nutrients between the blood and interstitial fluid
No metabolically active tissue is more than a few hundred micrometers from a capillary
capillaries structural characteristics
Lack both a tunica media and a tunica externa
Capillary walls are composed of only
—> a single layer of endothelial cells and
—> a basement membrane
average diameter of capillary
Average diameter = 8 µm
About the same as a single RBC
sometimes smaller –> requiring RBC to bend
capillary beds
interwoven network of many capillaries that supplies an organ or tissue
arises from a single arteriole
the more metabolically active the cells, the more capillaries in the capillary bed
metarterioles (AKA PRECAPILLARY ARTERIOLE)
Initial segment of the connection passageway
Contains smooth muscle that can change the vessel’s diameter and adjust flow rate through capillary bed
“Can be bypassed by arteriovenous shunt that directly connects arteriole to venule”
—> “Regulated by sympathetic innervation”
shunt define
SURGERY
an alternative path for the passage of the blood or other body fluid.
“shunt surgery”
what about arteriovenous shunt (???)
—> nothing found regarding surgery
—> *** MAY BE REFERRING TO THE METARTERIOLE “[serving] as vascular shunt when precapillary sphincters are closed”
Thoroughfare channel (?)
Most direct passageway through capillary bed (bypass)
Contains NO smooth muscle
thoroughfare channel vs metarteriole
Note that metarteriole and thoroughfare channel are continuous and connect arteriole with venule
—> however thoroughfare channel me be referring to the latter portion (venous portion?) which does NOT contain smooth muscle
precapillary sphincters
Precapillary sphincters:
Bands of smooth muscle that contract and relax to control flow into the capillary bed
more about capillary beds (Arterial collaterals)
Capillary bed may be supplied by more than one artery
Multiple arteries called COLLATERALS
—> (ARTERIAL COLLATERALS (via arterial anastomosis?) leading to arteriole?)
—> (collaterals?) fuse before giving rise to arterioles
fusion / arterial anastomosis
Fusion is an example of arterial anastomosis
Anastomosis is joining of blood vessels
why arterial anastomosis?
Allows continuous delivery of blood to capillary bed even if one artery is blocked or compressed
(note also arteriovenous anastomosis)
firectly b/w arteriole and venule
—> possibly also function as backup channels, in this case directly between arterioles and venules
(instead of from small arteries leading into an arteriole)
what about an artery that is the ONLY blood supply to a tissue/organ
An artery that is the only blood supply to a tissue or organ is called a terminal artery or an end artery
TERMINAL ARTERY / END ARTERY
Three types of capillaries
Continuous capillaries
Fenestrated capillaries
Sinusoids (sinusoidal capillaries)
Continuous capillaries
Continuous endothelium with intermittent breaks called intercellular clefts
where continuous capillaries?
Found in the brain, lungs, skeletal and smooth mm, CT
why continuous capillaries
Permits diffusion of water, small solutes, and lipid-soluble materials
Prevents loss of blood cells and plasma proteins
Some selective vesicular transport
specialized continuous capillaries –> where are they, and what do they do?
Specialized continuous capillaries in CNS and thymus have endothelial tight junctions
E.g.
Blood Brain Barrier (?)
Enables restricted and regulated permeability
Esp via vesciles (?)
Fenesterated capillaries
Contains “windows,” or pores, penetrating endothelial lining
Permits rapid exchange of
water and larger solutes
where found?
Capillaries of hypothalamus,
pituitary, pineal, and
thyroid glands
Absorptive areas of
intestinal tract
Kidney filtration sites
sinusoidal capillaries (aka sinusoids or “Discontinuous” capillaries)
Wider and more winding
Unusually large fenestrations
Missing a basement membrane
(OR INCOMPLETE BM w/ very large caps)
Large intercellular clefts
sinusoid etymology
sinus (q.v.) + -oid
sinusoidal capillaries – where?
Found in RBM, spleen, liver, anterior pituitary, parathyroid glands
Portal system?
Portal systems allow passage of blood from one capillary network to another through a portal vein
where are portal systems found?
There are 2 locations found in the body:
—> Liver (hepatic portal system)
—> Pituitary gland (hypophyseal portal system)
hepatic portal system
the venous system that returns blood from the digestive tract and spleen to the liver
why?
It supplies veins with metabolic substrates.
It also ensures that food ingested is processed by the liver first before entering the systemic circulation.
This way, ingested toxins are detoxified by hepatocytes
hypophyseal portal system
Capillary beds in the hypothalamus and the anterior pituitary are connected
(Important structures in the endocrine system)
why hypophyseal portal system?
Its main function is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland
3rd example?
google says renal portal system
venules
Small veins
Drain capillary blood and begins the return flow of blood back to the heart
about POSTCAPILLARY VEINS
Postcapillary venules:
Initially receive blood from capillaries
lack a tunica media and resemble expanded capillaries
Are very porous and therefore function as a site for exchange and WBC emigration
common site for WBC emigration (Diapedesis / extravasation)
POSTCAPILLARY VEINS
Microcirculation
The blood flow through the smallest vessels in the circulatory system
—> arterioles,
venules,
shunts (referring to metarteriole/thoroughfare channel)
and capillaries
which organs don’t have microcirculation?
exists in all tissues and organs except for the
cornea and epidermis
veins
Veins are formed from the union of several venules
Contain the characteristic 3 layers that make up arteries
how are layers different?
Tunica interna & tunica media is thinner in veins
much less smooth muscle and elastic fibers
—> veins look collapsed when dissected
veins vs elastic laminae?
vs recoil dynamics
Veins lack the internal and external elastic laminae
(They can increase and decrease in size to adapt to changes in volume & pressure but without the recoil dynamics of arteries.)