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Chapter 20:
Blood Vessels and Circulation
Circulatory routes:
Most common route
heart arteries arterioles
capillariesvenules veins
Portal system
blood flows throuh two
consecutive capillary networ!sbefore returnin to heart
hypothalamus " anterior pituitary
found in !idneys
between intestines " liver
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Circulation #outes: $nastomoses
$rteriovenous shunt
artery directly to vein
finers% toes% ears& heatloss% allows blood to bypass
e'posed areas durin cold
Venous anastomosis
more common
alternate drainae of orans
$rterial anastomosis
collateral circulation
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(he Vessel )all
(unica e'ternaoutermost layer
loose connective tissue
(unica mediamiddle layer
usually thic!est& smooth muscle% collaen% some elastic
smooth muscle for vasoconstriction and vasodilation
(unica interna
inner layer% e'posed to blood
simple s*uamous endothelium
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+are Vessels
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$rteries
Conductin ,elastic- arteries " larest
pulmonary% aorta and common carotid
tunica media consists of perforated sheets of elastic
tissue% alternatin with thin layers of smooth muscle%collaen and elastic fibers
e'pand durin systole% recoil durin diastole& lessens
fluctuations in BP .istributin ,muscular- arteries
distributes blood to specific orans& femoral and splenic
smooth muscle layers constitute /1 of wall thic!ness
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Medium Vessels
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$rteries and Metarterioles
#esistance ,small- arteries
arterioles control amount of blood to various orans
Metarterioles
short vessels connect arterioles to capillaries
muscle cells form a precapillary sphincter about
entrance to capillary
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mall Vessels
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Capillaries
(horouhfare channel " metarteriole continues
throuh capillary bed to venule
Precapillary sphincters control which beds are well
perfused
only 31 of the capillaries are open at a iven time
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Control of Capillary Bed Perfusion
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Control of Capillary Bed Perfusion
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(ypes of Capillaries
Continuous " occur in most tissues
endothelial cells have tiht 4unctions with intercellular
clefts ,allow passae of solutes-
5enestrated " !idneys% small intestineorans that re*uire rapid absorption or filtration&
endothelial cells have filtration pores ,fenestrations- "
allow passae of small molecules inusoids " liver% bone marrow% spleen
irreular blood"filled spaces& some have e'tra lare
fenestrations% allow proteins and blood cells to enter
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5enestrated Capillary
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5enestrated 6ndothelial Cell
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Veins
Venulespro'imal venule is *uite porous% e'chanes fluid with
tissues% li!e a capillary% at this point only
Venous sinuses: veins with thin walls% lare lumens%no smooth muscle
Veins have lower blood pressure: av77 30mm8
with little fluctuationthinner walls% less muscular and elastic tissue
e'pand easily% have hih capacitance
venous valves aid s!eletal muscles in upward blood flow
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Blood .istribution% #estin $dult
High
Capacitance
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Principles of Blood 5low
Blood flow: amountof blood flowin throuh a
tissue in a iven time ,mlmin-
Perfusion: rateof blood flow periven massof
tissue ,mlmin-
9mportant for delivery of nutrients and o'yen% and
removal of metabolic wastes
8emodynamics: physical principles of blood flow
based on pressure and resistance
5 P#% ,5 flow% P difference in pressure% #
resistance to flow
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Blood Pressure
Measured at brachial artery of arm
ystolic pressure: BP durin ventricular systole
.iastolic pressure: BP durin ventricular diastole
;ormal value% youn adult: 320
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Blood Pressure Chanes )ith .istance
More pulsatile
closer to heart
More pulsatile
closer to heart
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$bnormalities of Blood Pressure
8ypertension
chronic restin BP A 3100
can wea!en small arteries and cause aneurysms
8ypotension
chronic low restin BP
causes: blood loss% dehydration% anemia
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Blood Pressure 2
9mportance of arterial elasticity
e'pansion and recoil maintains steady flow of blood
throuhout cardiac cycle% smoothes out pressure
fluctuations and stress on small arteries BP rises with ae: arteries less distensible
BP determined by cardiac output% blood volume
and peripheral resistance
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Peripheral #esistance
Blood viscosity " by #BCs and albumin
viscosity with anemia% hypoproteinemia
viscosity with polycythemia % dehydration
Vessel lenth
pressure and flow decline with distance
Vessel radius " very powerful influence over flow
most ad4ustable variable% controls resistance *uic!ly
vasomotion: chane in vessel radius
vasoconstriction% vasodilation
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+aminar 5low and Vessel #adius
mall radius averae
velocity of flow is low
+are radius averae
velocity of flow is hih
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Peripheral #esistance
Vessel radius ,cont7-
laminar flow " flows in layers% faster in center
blood flow ,5- proportional to the fourth power of
radius ,r-% 5 r1 arterioles can constrict to 3/ of fully rela'ed radius
if r / mm% 5 ,/1- @3 mmsec& if r 3 mm% 5
3mmsec
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5low at .ifferent Points
5rom aorta to capillaries% flow for / reasonsreater distance traveled% more friction to flowsmaller radii of arterioles and capillaries
farther from the heart% reater the total cross sectionalarea
5rom capillaries to vena cava% flow aain
lare amount of blood forced into smaller channelsnever reains velocity of lare arteries
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#eulation of BP and 5low
+ocal control
;eural control
8ormonal control
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+ocal Control of BP and 5low
Metabolic theorytissue inade*uatelyperfused%wastesaccumulate
vasodilation
Vasoactive chemicalssubstances that stimulate vasomotion& histamine%
brady!inin
#eactive hyperemia
blood supply cut off then restored $nioenesis " rowth of new vessels
rerowthof uterine linin% around obstructions% e'ercise%malinant tumors
controlled by rowth factors and inhibitors
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;eural Control of BP and 5low
Vasomotor center of medulla oblonata:
sympathetic control stimulates most vessels to constrict%
but dilates vessels in s!eletal and cardiac muscle
interates three autonomic refle'esbarorefle'es
chemorefle'es
medullary ischemic refle'
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;eural Control: Barorefle'
Chanes in BP detected by stretch receptors%baroreceptors% in lare arteries above heart
aortic arch
aortic sinuses ,behind aortic valve cusps-
carotid sinus ,base of each internal carotid artery-
$utonomic negativefeedbac! response
baroreceptors send constant sinals to brainstem
BPcauses rate of sinals to rise% inhibitsvasomotorcenter% sympathetic tone% vasodilation causes BP
BPcauses rate of sinals to drop% excitesvasomotor
center% sympathetic tone% vasoconstriction and BP
B fl
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Barorefle'
;eative 5eedbac! #esponse
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;eural Control: Chemorefle'
Chemoreceptors in aortic body and carotid bodieslocated in aortic arch% subclavian arteries% e'ternal
carotid arteries
$utonomic response to chanes in blood chemistryp8% D2% CD2
primary role: ad4ust respiration
secondary role: vasomotion hypo'emia% hypercapnia and acidosis stimulate
chemoreceptors% instruct vasomotor center to cause
vasoconstriction% BP% lun perfusion and as e'chane
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Baroreceptors
Carotid body
Aortic bodyAortic body
Chemoreceptors E
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Dther 9nputs to Vasomotor Center
Medullary ischemic refle'inade*uate perfusion of brainstem
cardiac and vasomotor centers send sympathetic sinals to
heart and blood vessels: cardiac output and BP Dther brain centers
stress% aner% arousal can also BP
8 l C l f BP d 5l
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Angiotensinogen,prohormone produced by liver-
#enin ,!idney enFyme " low BP-
Angiotensin I
$C6 ,aniotensin"convertin enFyme in luns-
Angiotensin IIvery potent vasoconstrictor
8ormonal Control of BP and 5low
$niotensin 99
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8ormonal Control of BP and 5low 2
6pinephrine and norepinephrine effectsmost blood vessels
binds to "adreneric receptors% vasoconstriction
s!eletal and cardiac muscle blood vessels binds to "adreneric receptors% vasodilation
$.8 ,water retention-
patholoically hih concentrations% vasoconstriction $trial natriuretic factor ,urinary sodium e'cretion-
eneraliFed vasodilation
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#outin of Blood 5low
+ocaliFed vasoconstrictionpressure downstream drops% pressure upstream rises
enables routin blood to different orans as needed
$rterioles " most control over peripheral resistance
located on pro'imal side of capillary beds
most numerous
more muscular by diameter
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Blood 5low in #esponse to ;eeds
$rterioles shift blood flow with chanin priorities
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Blood 5low Comparison
.urin e'ercise
perfusion of luns% myocardium and s!eletal musclesperfusion of !idneys and diestive tract
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Capillary 6'chane
Dnly occurs across capillary walls between bloodand surroundin tissues
/ routes across endothelial cells
intercellular clefts
fenestrations
throuh cytoplasm
Mechanisms involveddiffusion% transcytosis% filtration and reabsorption
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Capillary 6'chane " .iffusion
Most important mechanism
+ipid soluble substances
steroid hormones% D2and CD2diffuse easily
9nsoluble substances
lucose and electrolytes must pass throuh channels%
fenestrations or intercellular clefts
+are particles " proteins% held bac!
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Capillary 6'chane " (ranscytosis
Pinocytosis% transport vesicles across the cell% e'ocytosis
9mportant for fatty acids% albumin and some hormones
,insulin-
Capillary 6'chane
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Capillary 6'chane "
5iltration and #eabsorption
Dpposin forcesblood ,hydrostatic- pressure drives fluid out of capillary
highonarterial endof capillary% lowonvenous end
colloid osmotic pressure ,CDP- draws fluid intocapillary ,same on both ends-
results from plasma proteins ,albumin-" more in blood
oncotic pressure net CDP ,blood CDP " tissue CDP-
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Capillary 5iltration E #eabsorption
7 in
13 out
Capillary filtration at arterial
end
Capillary reabsorption at
venous end
Variations
location,lomeruli"filter%
alveolar cap7" absorb-
activity% trauma,filtration-
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Causes of 6dema
Capillary filtration ,capillary BP or permeability-poor venous return
conestive heart failure " pulmonary edema
insufficient muscular activity!idney failure ,water retention% hypertension-
histamine ma!es capillaries more permeable
Capillary reabsorptionhypoproteinemia ,oncotic pressure blood albumin-
cirrhosis%famine%burns%!idneydisease
Dbstructed lymphatic drainae
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Conse*uences of 6dema
Circulatory shoc!e'cess fluid in tissue spaces causes low blood volume
and low BP
(issue necrosiso'yen delivery and waste removal impaired
Pulmonary edema
suffocation
Cerebral edema
headaches% nausea% seiFures and coma
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Mechanisms of Venous #eturn Pressure radient
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!eletal Muscle Pump
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Venous #eturn and Physical $ctivity
6'ercise venous return in many waysheart beats faster% harder " CD and BPvesselsofs!eletalmuscles%lunsandheartdilateflow
respiratory rate action of thoracic pump s!eletal muscle pump
Venous poolin occurs with inactivity
venous pressure not enouh force blood upward
with proloned standin% CD may be low enouh to
cause diFFiness or syncope
prevented by tensin le muscles% activate s!eletal m7 pump
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Circulatory hoc!
$ny state where cardiac output insufficient to meetmetabolic needs
cardioenic shoc! " inade*uate pumpin of heart ,M9-
low venous return ,+V#- shoc! " / principle forms
+V# shoc!
hypovolemic shoc! " most common
loss of blood volume: trauma% bleedin% burns% dehydration
obstructed venous return shoc! " tumor or aneurysm
ne't slide
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+V# hoc! 2
Venous poolin ,vascular- shoc!lon periods of standin% sittin or widespread
vasodilation
neuroenic shoc! " loss of vasomotor tone% vasodilation causes from emotional shoc! to brainstem in4ury
eptic shoc!
bacterial to'ins trier vasodilation and capillarypermeability
$naphylactic shoc!
severe immune reaction to antien% histamine release%
eneraliFed vasodilation% capillary permeability
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#esponses to hoc!
Compensated shoc!homeostatic mechanisms may brin about recovery
BP triers barorefle' and production of aniotensin
99% both stimulate vasoconstrictionif person faints and falls to horiFontal position% ravity
restores blood flow to brain& *uic!er if feet are raised
.ecompensated shoc! ,above mechanisms fail-ne't slide
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#esponses to hoc! 2
.ecompensated shoc!,life threatenin positive feedbac! loops occur-
CD myocardial ischemia and infarction CD
slow circulation disseminated intravascularcoaulation slow circulation
ischemia and acidosis of brainstem vasomotortone% vasodilation CD ischemia and acidosis of
brainstem
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pecial Circulatory #outes " Brain
(otal perfusion !ept constantfew seconds of deprivation causes loss of consciousness
1"= minutes causes irreversible brain damae
flow can be shifted from one active reion to another
#esponds to chanes in BP and chemistrycerebral arteries: dilate as BP % constrict as BP risesmain chemical stimulus: p8
CD2 > 82D 82 CD/8>> ,8CD/-" if CD2,hypercapnia- in brain% p8 % triers vasodilation
hypocapniap8%vasoconstriction%occurs withhyperventilation% may lead to ischemia% diFFiness and
sometimes syncope
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(9$s and CV$s
(9$s " transient ischemic attac!sdiFFiness% loss of vision% wea!ness% paralysis% headache
or aphasia& lasts from a moment to a few hours% often
early warnin of impendin stro!e CV$ " cerebral vascular accident ,stro!e-
brain infarction caused by ischemia
atherosclerosis% thrombosis% ruptured aneurysm
effects rane from unnoticeable to fatal
blindness% paralysis% loss of sensation% loss of speech common
recovery depends on surroundin neurons% collateral
circulation
pecial Circulatory #outes "
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pecial Circulatory #outes
!eletal Muscle
8ihly variable flow
$t rest
arterioles constrict% total flow about 3+min
.urin e'ercise
arterioles dilate in response to epinephrine and
sympathetic nerves
precapillary sphincters dilate due to lactic acid% CD2blood flow can increase 300 fold
Muscular contraction impedes flow
isometric contraction causes fatiue faster than isotonic
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pecial Circulatory #outes " +uns
+ow pulmonary blood pressureflow slower% more time for as e'chane
capillary fluid absorption
oncotic pressure overrides hydrostatic pressure
Ini*ue response to hypo'ia
pulmonary arteries constrict% redirects flow to better
ventilated reion
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Pulmonary Circulation
Pulmonary trun! to pulmonary arteries to each lun
lobar branches for each lobe ,/ riht% 2 left-
Pulmonary veins return to left atrium
increased D2 and reduced CD2 levels
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Pulmonary Capillaries ;ear $lveoli
Bas!etli!ecapillary beds
surround the
alveoli 6'chane of
ases with air at
alveoli
4 i i
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Ma4or ystemic $rteries
upplies o'yen and nutrients to all orans
$ i l i
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$rterial Pressure Points
ome ma4or arteries close to surface "" allows palpation for
pulse and serve as pressure points to reduce arterial bleedin
M 4 B h f h $
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Ma4or Branches of the $orta
$scendin aortariht E left coronary arteries supply heart
$ortic arch
brachiocephalic riht common carotid supplyin riht side of head
riht subclavian supplyin riht shoulder E upper limb
left common carotid supplyin left side of headleft subclavian supplyin shoulder and upper limb
.escendin aorta is thoracic aorta above
diaphram and abdominal aorta below diaphram
M 4 B h f h $
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Ma4or Branches of the $orta
$ i f h 8 d d ; !
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$rteries of the 8ead and ;ec!
Common carotid divides into internal E e'ternal carotids
e'ternal carotid supplies most e'ternal head structures
$ i l l f h B i
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$rterial upply of the Brain
Paired vertebral aa7 combine to form
the basilar artery on the pons
Circle of )illis on base of brain is
formed from anastomosis of basilar
E paired internal carotid aa
upplies brain% internal ear and
orbital structures
anterior% middle Eposterior cerebral
superior% anterior E
posterior cerebellar
$ t i f th I +i b
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$rteries of the Ipper +imb
ubclavian passes
between clavicle E
3st rib
Vessel chanes names
as passes to differentreions
subclavian to a'illary
to brachial to radial E
ulnarbrachial used for BP
and radial artery for
pulse
$ t i f th (h
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$rteries of the (hora'
(horacic aorta supplies viscera E body wallbronchial% esophaeal and mediastinal branches
posterior intercostal and phrenic arteries
9nternal thoracic% anterior intercostal E pericardiophrenic
arise from subclavian artery
M 4 B h f $bd i l $ t
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Ma4or Branches of $bdominal $orta
+ower limb+ower limb
JidneyJidney
H9H9
H9H9
H9H9
C li ( ! B h
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Celiac (run! Branches
Branches of celiac trun! supply upper abdominal viscera ""
stomach% spleen% liver E pancreas
M t i $ t i
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Mesenteric $rteries
$ t i f th + +i b
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$rteries of the +ower +imb
Branches to the lower limb arise from e'ternal iliac
branch of the common iliac artery
M 4 t i V i
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Ma4or ystemic Veins
.eep veins run parallel to arteries while superficial
veins have many anastomoses
. V i f 8 d d ; !
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.eep Veins of 8ead and ;ec!
+are% thin"walled dural sinuses form in between layers of
dura mater ,drain brain to internal 4uular vein-
fi i l V i f 8 d E ; !
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uperficial Veins of 8ead E ;ec!
Branches of internal and e'ternal 4uular veins drain the
e'ternal structures of the head
Ipper limb is drained by subclavian vein
e fi i l E .ee Vei f I e +i b
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uperficial E .eep Veins of Ipper +imb
9nferior Vena Cava E Branches
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9nferior Vena Cava E Branches
;otice absence of veins drainin the viscera """
stomach% spleen% pancreas and intestines
+ower limb+ower limb
JidneyJidney
+iver+iver
Veins of 8epatic Portal ystem
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Veins of 8epatic Portal ystem
.rains blood from viscera ,stomach% spleen and
intestines- to liver so that nutrients are absorbed
uperficial and .eep Veins of +ower +imb
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uperficial and .eep Veins of +ower +imb