Chapter 21 Blood Vessels and Circulation

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Chapter 21 Blood Vessels and Circulation

• BIO 211 Lab
• Instructor Dr. Gollwitzer

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• Today in class we will discuss
• General characteristics of blood vessels
• The anatomy of blood vessels
• The differences between arteries and veins
• The general functional patterns of blood vessels
• The types of arteries based on size, structure,
  and basic function
• Cardiovascular receptors
• And identify the major systemic arteries of the
• Aortic arch
• Head, brain, and neck
• Upper and lower extremities
• Trunk (thoracic and abdominal regions)

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Blood Vessels

• Arteries (aaway from heart)? arterioles?
  capillaries? venules? veins (to heart)
• Arteries branch repeatedly, decrease in diameter
• Arterioles smallest branches of arteries deliver
  blood to capillaries
• Capillaries smallest, thinnest vessels
• Site of all chemical and gaseous exchange between
  blood and interstitial fluid occurs
• Tissues rely on capillary diffusion to obtain
  nutrients and oxygen and to remove carbon dioxide
  and metabolic wastes
• Venules smallest venous branches collect blood
  from capillaries unite to form veins
• Veins return blood to heart
• Arteries and veins typically lie side by side in
  region being served

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Anatomy of Blood Vessels

• 3 layers to vessel walls
• Tunica interna/intima innermost layer
• Endothelium and CT with elastic fibers
• In arteries outer margin contains internal
  elastic membrane (thick layer of elastic fibers)
• Tunica media middle layer
• Concentric sheets of smooth muscle with loose CT
• When smooth muscle contracts?diameter decreases
  when relaxes?increases
• In arteries
• Thickest layer
• Outer margin contains external elastic membrane
  (thin band of elastic fibers)
• Larger arteries also contain layers of
  longitudinal smooth muscle cells
• Tunica externa outermost layer
• CT sheath around vessel
• In arteries contains collagen and elastic fibers
• In veins generally thicker than tunica media,
  contains elastic fibers and smooth muscle cells

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Fig. 21-1
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Fig. 21-1
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Differences Between Arteries and Veins
Feature Typical Artery Typical Vein
General Appearance in Cross Section Usually round (thick, strong walls so retain shape) Thicker wall Lumen constricted (elastic fibers recoil when no BP) Usually flattened or collapsed Thinner wall Lumen large
Tunica Interna Endothelium Internal Elastic Membrane Cant contract looks pleated when vessels constrict Present (on outer margin) Often smooth Absent
Tunica Media External Elastic Membrane Thick, dominated by more smooth muscle, elastic fibers resists pressure generated by heart Present (on outer margin) Thin, dominated by smooth muscle, collagen fibers Absent
Tunica Externa Collagen and elastic fibers Collagen, elastic, smooth muscle fibers
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Differences Between Arteries and Veins

• Arteries more resilient
• When stretched, elongate, keep shape snap back
  when released
• Veins contain valves to prevent backflow of blood
  toward capillaries

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Vasa Vasorum

• Vessels of vessels
• Walls of large vessels
• Too thick to allow diffusion between blood and
  blood vessel tissue
• Contain small arteries and veins that supply
  smooth muscle cells and fibroblasts of tunica
  media and tunica externa

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General Functional Patterns

• Distribution of arteries and veins on L and R
  sides usually identical
• L and R subclavian, axillary, brachial and radial
  arteries parallel veins
• NOT parallel near heart where largest vessels
  connect to atria or ventricles
• Single vessel may have several names as it
  crosses anatomical boundaries
• Descending aorta, thoracic aorta, abdominal aorta
• External iliac artery becomes femoral artery as
  it leaves the trunk and enters the lower limb

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Structural Characteristics of Vessels Change
Gradually as They Travel Away from/Toward Heart
Figure 21-2
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Arteries

• Thick, muscular walls, make arteries elastic and
  contractile
• Elasticity
• Permits passive changes in vessel diameter in
  response to pressure waves that come with each
  heart beat
• Allows arteries to absorb pressure pulses that
  accompanies contractions of ventricles
• Contractility ability to reduce diameter
  actively under control of sympathetic ANS
• Vasoconstriction contraction of arterial smooth
  muscle decreases vessel diameter
• Vasodilation relaxation of arterial smooth
  muscle increases vessel diameter
• Important in hemostasis contract to stop bleeding

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Arteries

• From heart to capillaries, arteries change
• From elastic arteries (large arteries)
• To muscular arteries (medium-sized arteries)
• To arterioles

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Fig. 21-2, right, p. 711
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Elastic Arteries

• AKA conducting arteries
• Large vessels
• Transport large volumes of blood away from heart
  (e.g., pulmonary trunk, aorta, and major
  branches)
• Walls very resilient
• Tunica media contains many elastic fibers and few
  smooth muscle cells
• Tolerate pressure changes during cardiac cycle
• Increase BP? arteries expand
• Decrease BP? arteries recoil to original shape
• Elasticity dampens pressure peaks and valleys
  that accompany the heartbeat

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Muscular Arteries

• AKA distribution arteries
• Medium-sized vessels are majority of arteries
• Distribute blood to skeletal muscle and internal
  organs (e.g., external carotid arteries of neck,
  brachial arteries of arms, femoral arteries of
  legs)
• Thick tunica media with more smooth muscle than
  elastic fibers
• By the time blood reaches arterioles
• Pressure oscillations have disappeared
• Blood flow is continuous

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Arterioles

• Smallest arterial vessels
• Have little or no tunica externa
• Tunica media
• In larger arterioles, only one or two layers of
  smooth muscle cells
• Smallest arterioles have scattered smooth muscle
  cells
• Respond to local conditions or to sympathetic or
  endocrine stimulation
• Vasodilate when O2 levels are low (passive)
• Vasoconstrict under sympathetic control
• Changes in diameter affect amount of force needed
  to push blood around CV system
• More pressure required to push blood though a
  constricted vessel than through a dilated one
• RESISTANCE force opposing blood flow
• Arterioles called resistance vessels

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Cardiovascular Receptors

• 2 Types
• Baroreceptors
• Chemoreceptors
• Chemoreceptors
• Respond to changes in O2, CO2, pH in blood
• Located in
• Carotid bodies (near carotid sinuses)
• Aortic bodies (near aortic arch)

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Cardiovascular Receptors

• Baroreceptors
• Located in
• Carotid sinuses (expanded chambers near base of
  internal carotid arteries) (Fig 21-23)
• Aortic sinuses (sac-like dilations at base of
  ascending aorta) (Fig 20-8b)
• Monitor amount of stretch in walls of
• Arteries
• R atrium
• Reflexes adjust CO and peripheral resistance to
  maintain normal arterial pressures
• Inc BP ? dec CO and peripheral vasodilation

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Locations of Cardiovascular Receptors
Figure 20-8b
Figure 21-23
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Aneurysm

• Bulge in weakened wall of artery
• Just like a bad tire can suffer a blow out
• Most dangerous in
• Arteries in brain ? stroke
• Aorta ? fatal bleeding
• Often painless, so go undetected
• Occurrence
• in individuals with arteriosclerosis (
  thickening or toughening of vessel walls) over
  time vessels become less elastic and weak spot
  develops
• in individuals with high BP puts great stress on
  vessel walls
• arterial inflammation or infection weakens
  arterial walls

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Major Systemic Arteries
Figure 21-21
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Systemic Arteries

• Ascending aorta
• Begins at aortic valve of left ventricle ?
• R and L coronary arteries (branch from base)
• Curves to form aortic arch
• Turns downward to become descending aorta ?
• Thoracic aorta ?
• Abdominal aorta
• Aortic arch ?
• L subclavian artery ?
• Vertebral
• Axillary
• L common carotid artery
• Brachiocephalic trunk/artery ?
• R common carotid artery
• R subclavian artery

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Figure 21-22 b
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Figure 21-22a
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Arteries of the Head and Neck

• Common carotid arteries (? head, neck)
• Each divides into
• External carotid artery
• ? neck, lower jaw, esophagus, larynx, pharynx,
  face
• Internal carotid artery
• ? brain, cranial nerves
• ? cerebral arterial circle/of Willis ring of
  arteries that encircles infundibulum of pituitary
  gland
• Circle is present because internal carotid
  arteries, middle cerebral arteries, and basilar
  artery are interconnected by anterior and
  posterior cerebral arteries and the anterior and
  posterior communicating arteries

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Cardiovascular Receptors

• Baroreceptors
• Monitor degree of stretch in walls of arteries
  and right atrium
• Located in carotid sinuses (expanded chambers
  near base on internal carotid arteries) and
  aortic sinuses (pockets in walls of ascending
  aorta adjacent to heart and wall of right atrium
  near entrance to vena cavae)
• Reflexes adjust CO and peripheral resistance to
  maintain normal arterial pressures
• Inc BP ? dec CO and peripheral vasodilation

Figure 21-23
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Arteries of the Brain

• Originate from
• Internal carotids (from common carotids)
• Vertebrals (from subclavians)
• Connected blood supply to brain
• Internal carotid arteries normally supply
  anterior half of cerebrum
• Vertebral arteries usually supply rest of brain
• Are interconnected (via anastomoses) ? ring of
  arteries around base of brain cerebral arterial
  circle (Circle of Willis)
• Encircles hypothalamus, influndibulum, pituitary
• Brain can receive blood from several vessels, so
  possibility of interruption of circulation is
  reduced ( collateral circulation)

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Cerebral Arterial Circle(Circle of Willis)
Figure 21-24a
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Strokes

• aka cerebrovascular accidents (CVAs)
• Usually affect middle cerebral arteries
• On right side ? loss of sensation and motor
  control on left side of body difficulty drawing
  or interpreting spatial relationships
• On left side ? aphasia and sensory and motor
  paralysis of right side of body
• Strokes affecting vessels that supply the brain
  stem also have distinctive symptoms
• Those affecting the lower brain stem are often
  fatal

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Arteries of the Chest andUpper Limbs

• Subclavian arteries
• Branch in thoracic cavity (Fig 21-24a) ?
• Vertebral arteries (? brain and spinal cord)
• Thyrocervical trunks (? muscles of neck,
  shoulder, upper back)
• Internal thoracic arteries (? pericardium and
  anterior chest wall)
• Leave thoracic cavity ?
• Axillary arteries (at axilla) ?
• Brachial arteries (as they enter brachium) ?
• Radial and ulnar arteries
• Radial and ulnar merge at wrist ?
• Palmar arterial arches ?
• digital arteries ? capillaries

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Figure 21-21 b
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Arteries of the Trunk
Figure 21-25
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Figure 21-22a
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Arteries of the Trunk

• Descending aorta
• Divided by diaphragm into
• Thoracic aorta
• Abdominal aorta

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Figure 21-25b, top
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Thoracic Aorta

• Begins at T5 and ends at diaphragm (T12)
• Visceral branches supply organs of chest
• Bronchial arteries ? tissues of lungs NOT
  involved in gas exchange
• Pericardial arteries ? pericardium
• Esophageal arteries ? esophagus
• Mediastinal arteries ? tissues of mediastinum
• Parietal branches supply chest wall
• Intercostal arteries ? chest muscles, vertebral
  column area
• Superior phrenic arteries ? superior surface of
  diaphragm

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Abdominal Aorta

• Abdominal aorta (from inferior diaphragm to L4)
• Unpaired branches
• to visceral organs
• Paired branches
• to body wall
• kidneys
• urinary bladder

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Arteries of the Abdominopelvic Organs
Figure 21-25
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Arteries of the Trunk
Figure 21-25
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Fig. 21-25b
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Unpaired Branches of the Abdominal Aorta

• Celiac trunk, divides into
• left gastric artery ? stomach, inferior esophagus
• splenic artery ? spleen, stomach, pancreas
• common hepatic artery ? liver (through proper
  hepatic artery, then the hepatic arteries),
  stomach, gall bladder, duodenum, pancreas
• Superior mesenteric artery ? pancreas, small
  intestine, appendix, upper 2/3 large intestine
• Inferior mesenteric artery ? last 1/3 large
  intestine

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Paired Branches of the Abdominal Aorta

• Inferior phrenic arteries ? inferior surface of
  diaphragm, inferior esophagus
• Suprarenal arteries ? adrenal glands
• Renal arteries ? kidneys
• Gonadal arteries ? gonads
• In males testicular arteries
• In females ovarian arteries
• Lumbar arteries ? vertebrae, spinal cord,
  abdominal wall

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Arteries of the Trunk
Figure 21-25
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Distal Branches of theAbdominal Aorta

• Abdominal aorta divides at terminal segment (L4)
  into
• L R common iliac artery
• Common iliac artery ?
• Internal iliac artery ? pelvic structures and
  organs
• External iliac artery ? lower limb

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Arteries of the Lower Limb

• External iliac arteries
• Pass through abdominal wall
• In thigh ?
• Femoral arteries
• ? deep femoral artery (skin and deep muscles of
  thigh)
• Posterior to knee ?
• Popliteal artery ?
• Anterior tibial artery ? dorsalis pedis ( ?
  foot/ankle)
• Posterior tibial artery ?
• Fibular (peroneal) artery (at ankle) ?
• Plantar arteries (plantar surface of foot)
• Plantar arteries and dorsalis pedis arteries
  anastomose to form plantar arterial arches ?
• Digital artery ? arterioles ? capillaries

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• Today in class we will discuss
• The structure of capillaries, different types of
  capillaries, and they function
• The types of veins based on size, structure, and
  basic function
• Blood distribution among the different type of
  blood vessels
• And identify the major systemic veins associated
  with
• Head, brain, and neck
• Upper and lower extremities
• Trunk (thoracic and abdominal regions)
• The hepatic portal system

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Capillaries

• Microscopic capillary networks in ALL active
  tissues no cell more than 5 cells from a
  capillary
• Thin walls permit 2 way exchange/diffusion
  between blood and interstitial fluids short
  distances, quick exchange
• Slow blood flow ? sufficient time for diffusion
  or active transport of materials across walls

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Capillary Structure

• Endothelial (simple squamous) tube simple inside
  delicate basement membrane
• No tunica externa or tunica media
• Diameter size of single RBC

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Figure 21-4
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Capillaries

• 2 major types
• Continuous
• One to several endothelial cells wrap around
  lumen
• Complete endothelium (no pores)
• Fenestrated
• Endothelium has pores (fenestrations)

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Continuous Capillaries

• Found In most regions of body
• In all tissues except epithelia and cartilage
• Permit diffusion of
• Water, small solutes, and lipid-soluble material
  into interstitial fluid
• Prevent loss of
• Blood cells and plasma protein

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Specialized Continuous Capillaries

• Found in
• CNS, thymus, testis
• Have tight junctions ? restricted permeability
  characteristics
• e.g., blood-brain barrier, blood-thymus barrier,
  blood-testis barrier

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Fenestrated Capillaries

• Pores permit rapid exchange of water and large
  solutes, e.g., small peptides, between plasma and
  interstitial fluid
• Found in
• Choroid plexus (brain)
• Endocrine organs (hypothalamus, pituitary,
  pineal, thyroid glands)
• Areas of reabsorption (GI tract, liver)
• Areas of filtration (kidneys)

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Sinusoids

• Venous structures that resemble fenestrated
  capillaries
• Flattened and irregular
• Have gaps (instead of pores) between adjacent
  endothelial cells
• Basement membrane is thinner or absent
• Permit free exchange of water and solutes as
  large as plasma proteins
• ? Slow blood flow, maximizing time for exchange
  across walls
• Found in liver, spleen, bone marrow, endocrine
  organs (pituitary and adrenal glands)

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Capillary Bed/Plexus

• Functional unit of capillaries
• Interconnected network of capillaries
• Single arteriole ? dozens of capillaries ?
  several venules (smallest venous vessels)

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Capillary Bed Structures

• Capillary sphincter
• Band of smooth muscle
• Guards entrance to each capillary
• Opens and closes, causing capillary blood to flow
  in pulses
• Thoroughfare channel
• Passageway between arterioles and venules
• Resembles typical capillary
• Metarteriole
• Initial segment of thoroughfare channel
• Wall contains smooth muscle capable of changing
  its diameter

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Figure 21-5
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Collaterals

• Multiple arteries that contribute to 1 capillary
  bed
• Fuse before giving rise to arterioles
• Allow circulation if 1 artery is blocked
  (detour)
• Anastomosis (joining of 2 tubes)
• Arterial anastomosis
• Fusion of 2 collateral arteries
• Arteriovenous anastomosis (joining of two tubes)
• Direct connection between arterioles and venules
• Bypasses capillary bed

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Vasomotion

• Alternating contraction and relaxation of smooth
  muscle in capillary sphincters (12x/min)
• Changes blood flow through capillary beds
• Blood flows in pulses vs. steady, constant stream
• Flow in each capillary is quite variable
• Blood may reach venules through one route one
  time and a different route the next time
• Controlled locally by changes in concentrations
  of chemicals and dissolved gases in interstitial
  fluid autoregulation
• e.g. when tissue O2 concentrations decrease,
  sphincters relax, blood flow to area increases

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Veins

• Collect blood from all tissues and organs and
  return it to the heart
• Veins vs. corresponding arteries
• Generally larger
• Walls thinner
• Blood pressure lower

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Veins

• 3 types of veins
• Venules (smallest)
• Collect blood from capillary beds
• Vary widely in size and character (smallest
  resemble expanded capillaries)
• Medium-sized veins
• Tunica media thin, few smooth muscle cells
• Tunica externa thickest layer contains bundles
  of elastic and collagen fibers
• Large veins
• Have all 3 tunica layers thin tunica media,
  thick tunica externa (elastic and collagen
  fibers)
• e.g. superior and inferior vena cavae and larger
  tributaries in abdominopelvic and thoracic
  cavities

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Figure 21-2, left
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Venous Valves

• BP in peripheral venules and medium-sized veins
  is 10-20 that in ascending aorta and continues
  to fall along venous system
• BP so low it cant oppose force of gravity
• Veins in limbs have valves
• Folds of tunica interna that project from vessel
  wall into lumen
• Point in direction of blood flow
• Ensure 1- way flow prevent backflow toward
  capillary
• Valves improve venous return
• Any movement of muscles that changes a veins
  shape squeezes/pushes blood toward heart

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Venous Valves
Figure 21-6
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Venous Valves

• Prolonged inactivity may cause a thrombus (clot)
  deep vein thrombosis (DVT)
• Can be fatal if clot dislodges and travels to
  heart, lung, brain, etc.
• When walls of veins near valves weaken or become
  stretched and distorted, valves may not work
  properly ? varicose veins
• Blood pools in veins, become distended

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Distribution of Blood

• Blood volume unevenly distributed among blood
  vessels
• Heart, arteries, capillaries 30-35 (1/3)
• Venous System 65-70 (2/3)
• Change in blood volume
• Large changes have little effect on BP
• If blood volume rises or falls, elastic walls
  stretch or recoil, changing volume of blood in
  venous system
• During hemorrhage
• Systemic veins constrict (venoconstriction)
• Decreases amount of blood in venous system,
  increases volume in arterial system and
  capillaries so at near normal levels despite
  significant blood loss
• Constriction of veins in liver, skin, and lungs
  redistributes total blood volume to delicate
  organs (brain, active skeletal muscle)
• Amount that can be shifted venous reserve
  (normally 20 total blood volume)

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Blood Distribution
Figure 21-7
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Major Systemic Veins
Figure 21-27
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Systemic Veins

• Eventually drain into either
• Superior vena cava (SVC) or
• Inferior vena cava (IVC)
• SVC collects blood from
• Head, neck
• Chest, shoulders
• Upper limbs
• IVC collects blood from
• Organs inferior to diaphragm
• Lower limbs
• SVC and IVC deliver blood to R atrium

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Venous Return from theHead and Neck

• Internal jugular veins
• Drain (collect blood from) cranial sinuses in
  dural folds (includes superior sagittal sinus,
  inferior sagittal sinus, straight sinus,
  occipital sinuses, transverse sinuses,sigmoid
  sinuses ), great cerebral vein (of Galen) and
  deep cerebral veins, facial veins, etc.
• External jugular veins
• Drain temporal and maxillary veins
• Vertebral veins
• Drain spinal cord and posterior surface of skull
• External jugular veins drain into subclavians,
  then into brachiocepalic veins (in chest)
• Internal jugular and vertebral veins drain into
  brachiocephalic veins

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Fig. 21-28b, p. 748
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Venous Return FromUpper Limbs

• Capillaries ? digital veins ? palmar venous
  arches (anastomoses) ?
• Superficial veins of arm
• Cephalic ?
• Subclavian
• Median cubital (branch to basilic)
• Median antebrachial ? basilic
• Basilic ? axillary (at junction with brachial) ?
  subclavian
• Deep veins of arm
• Radial and ulnar (at elbow) ? brachial vein
• Brachial and basilic veins ? axillary vein
• Axillary and cephalic veins (in shoulder) ?
  subclavian vein
• Subclavian vein ? brachiocephalic vein (after
  merge with vertebral, internal/external jugulars)

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Figure 21-29
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Superior Vena Cava

• Formed from
• Fusion of R and L brachiocephalic veins
• Tributaries (FYI)
• Mediastinal veins
• Azygos and/or hemiazygous veins drain
  mediastinals (partial), intercostals, esophageals

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Fig. 21-31a, part 1
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Figure 21-31a, part 2
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Inferior Vena Cava

• Collects venous blood from internal organs
  inferior to the diaphragm

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Venous Return from Lower Limbs

• Capillaries ? digital veins ? plantar venous
  arches (anastomoses) ?
• Superficial veins of leg
• Great saphenous ? femoral
• Small saphenous ? joins popliteal (in popliteal
  fossa) ? femoral (at femur)
• Deep veins of leg
• Anterior tibial
• Posterior tibial
• Fibular (peroneal)
• Union of 3 veins above ?
• popliteal ? femoral
• Femoral vein (inside pelvic cavity) ? external
  iliac vein ( internal iliac in pelvis) ? R L
  common iliac veins ? inferior vena cava (IVC)

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Figure 21-31b, p. 752
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Figure 21-32
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Veins Draining the AbdomenMajor Tributaries of
the IVC

• Lumbars
• Gonadals
• Hepatics
• Renals (largest tributary of IVC)
• Suprarenals
• Phrenics

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Figure 21-31
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Hepatic Portal System

• Portal vessel blood vessel connecting 2
  capillary beds
• Portal system network of portal vessels
• Connects capillaries in digestive tract with
  those in liver

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Blood Vessels of theHepatic Portal System

• Begins with capillaries of digestive system
• Drain into 5 tributaries of hepatic portal vein
• L R gastric veins (drain part of stomach)
• Splenic vein (drains spleen, part of stomach,
  pancreas)
• Inferior mesenteric vein (drains parts of large
  intestine)
• Superior mesenteric vein (drains part of stomach,
  small intestine, part of large intestine)
• Cystic vein (drains gall bladder)
• Hepatic portal vein (branches of) ? liver
  sinusoids ? central veins of liver lobules ? R
  L hepatic veins ? IVC

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Fig. 21-33
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Liver Histology
Figure 2420
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Hepatic Portal System

• Delivers nutrients (e.g., glucose, amino acids,
  etc.)
• Absorbed by capillaries of digestive organs
• To liver for
• Storage
• Metabolic conversion
• Excretion
• Blood passes through liver sinusoids ? hepatic
  veins ? IVC