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A&P 210: Chapter 20

Terms in this set (66)

general anatomy of blood vessels: arteries, veins, capillaries
arteries: carry blood away from heart

veins: carry blood back to heart

capillaries: connect arteries to veins
vessel wall: tunica interna + endothelium
tunica interna: lines blood vessel and is exposed to blood

endothelium: simple squamous epithelium overlying basement membrane and sparse layer of loose connective tissue

- selectively permeable barrier

- secretes chemicals that stimulate dilation or constriction

- repels blood cells + platelets

- when tissue around vessel inflame, cells produce cell-adhesion molecules that produce leukocytes
vessel wall: tunica media
- middle layer

- contains smooth muscle, collagen, elastic tissue

- strengthen vessels and prevent blood pressure from rupturing

- changes in diameter (vasomotion) of blood vessel
vessel wall: tunica externa
- outermost layer

- contains loose connective tissue that merge w/ blood vessels, nerves, etc.

- anchors vessel and provide passage for nerves + vessels

- vasa vasorum: small vessels that supply blood to outer half of large vessels
arteries
resistance vessels because have strong tissue structure that resists high blood pressure
arteries: conducting (elastic/large) arteries
- biggest arteries

- aorta, carotid, pulmonary trunk

- expand during systole (contract) + recoil during diastole (relax) = lessens fluctuations in blood pressure
arteries: distributing (muscular/medium) arteries
- distribute blood to organs

- brachial, femoral, renal, splenic arteries

- smooth muscle constitute wall thickness
arteries: resistance arteries (arterioles) + metarterioles
- arterioles: smallest arteries (control blood to organs)

- metarterioles: short vessels that link arterioles to capillaries
- muscle cells form pre-capillary sphincter to capillary (constriction of sphincters reduce blood flow through capillaries + divert blood to other tissues)
aneurysm
weak point in artery or heart wall

- thin-wall sac that pulsate w/ heartbeat which may rupture at any time

- dissecting aneurysm: blood accumulates b/w tunics of artery and separates them

- cause pain by putting pressure on other structures
sensory structures: carotid sinuses
baroreceptors (pressure sensors)

- in carotid artery

- monitors blood pressure that signal brainstem
sensory structures: carotid bodies + aortic bodies
carotid bodies:
- chemoreceptors
- oval bodies

aortic bodies:
- chemoreceptors
- wall of aortic arch

functions:
- monitor blood chemistry
- transmit signals to brainstem respiratory centers
- adjust respiratory rate to stabilize pH, CO2, O2
capillaries
where nutrients, wastes, and hormones pass b/w blood and tissue fluid through walls of vessels

- "business end" of cardiovascular system
3 types of capillaries: continuous capillaries
- in most tissues

- endothelial cells have tight junctions forming a tube w/ intercellular clefts

- allow passage of solutes like glucose

- pericytes wrap around capillaries that contain contractile protein like muscle (regulate blood flow)
3 types of capillaries: fenestrated capillaries
- kidneys, small intestine

- organs that require absorption or filtration

- endothelial cells have filtration pores (fenestrations)

- allow passage of small molecules
3 types of capillaries: discontinuous capillaries (sinusoids)
- liver, bone marrow, spleen

- irregular blood-filled spaces w/ large fenestrations

- allow proteins (albumin), clotting factors, and blood cells to enter circulation
capillary beds: thoroughfare channel + precapillary sphincters
thoroughfare channel: metarteriole that continue through capillary bed to venule

precapillary sphincters: control which bed are well perfused
- respond to local and hormonal control
capillary beds: when sphincters open
- capillaries are well perfused w/ blood + engage in exchanges w/ tissue fluid

- 3/4 of capillaries are shut down
capillary beds: when sphincters close
- blood bypass (go around) capillaries

- flows through thoroughfare channel to venule

- little to no blood flow (skeletal muscles at rest)
veins
- greater capacity for blood containment than arteries

- collapse when empty, expand easily
veins: postcapillary venules
smallest veins

- more porous than capillaries

- leukocytes emigrate from blood stream through venule walls
veins: muscular venules
- 1 mm in diameter

- 1-2 layers of smooth muscle in tunica media
veins: medium veins, venous sinuses, large veins
medium veins: up to 10 mm
- tunica interna forms venous valves; failure of valves = varicose veins

venous sinuses:
- dural venous sinus + coronary sinus of heart
- not capable of vasomotion

large veins: larger than 10 mm
veins: varicose veins
when people who stand for long periods = blood pools in leg and stretch veins, blood backflows and distend vessels > walls grow weak and develop varicose veins

- not enough venous pressure to force blood upward

- CO may be low to cause dizziness

- prevented by tensing leg muscles = activate skeletal muscle pump
circulatory routes: simplest pathway
common route: heart > arteries > arteriols > capillaries > venules > veins

blood passes through 1 capillary bed before return to heart
circulatory routes: portal system
blood passes through 2 capillary beds before return to heart

- b/w hypothalamus and pituitary
- kidneys
- b/w intestines and liver
circulatory routes: arteriovenous anastomosis (shunt)
anastomosis: point where 2 blood vessels merge

shunt: artery flows into vein by passing capillaries
venous and arterial anastomosis
venous anastomosis: most common
- one vein empties into another; make vein blockage less serious than arterial blockage

arterial anastomosis:
- two arteries merge
- provide collateral/alternative routes
blood flow and perfusion
at rest, flow is constant at 5.25 L/min
blood pressure
force that blood exerts against a vessel wall

- determined by CO, blood volume, peripheral resistance (resistance of blood flow in vessels away from heart)

- normal value in young adult: 120/75 mmHg
two blood pressures recorded
- measured at brachial artery of arm, using sphygmomanometer

systolic pressure: BP taken during ventricular contraction

diastolic pressure: minimum BP taken during ventricular relaxation b/w heart beats
pulse pressure + mean arterial pressure (MAP)
diff. b/w systolic and diastolic pressure
- measure stress exerted on arteries

MAP:
SBP + 2 (DBP) / 3
blood pressure: hypertension + hypotension
hypertension "silent killer": high blood pressure
- BP > 140/90
- weaken small arteries and cause aneurysms

hypotension: low resting BP
- caused by blood loss, dehydration, anemia
arterial elasticity
prevent high BP by ability of arteries to stretch and recoil - maintains steady flow in cardiac cycle, smooth pressure fluctuations, decrease stress on small arteries
peripheral resistance: rely on 3 variables
- blood viscosity/thickness

- vessel length: the farther liquid travels through tube, the more friction it encounters

- vessel radius: most powerful influence over flow

vasomotion: change in vessel radius
- vasoconstriction: smooth muscle contraction
- vasodilation: smooth muscle relaxation
from aorta to capillaries, blood velocity/speed decreases for 3 reasons
- greater distance = more friction

- smaller radii of arterioles and capillaries = more resistance

- far from heart = vessels and cross-sectional area become greater
from capillaries to vena cava, blood velocity/speed increase for 3 reasons
- less resistance from capillaries to veins

- large amount of blood forced into smaller channels

- never regains velocity of large arteries
2 purpose of vasomotion + 3 ways of controlling vasomotion
- raise/lower BP

- reroute blood from one region to another for perfusion:
ex: during exercise, sympathetic system reduces blood flow to kidneys + inc. blood flow to skeletal muscles

- ex: exercise dilates arteries in lungs, heart, and muscles > vasoconstriction in kidneys + digestive tract
- dozing in armchair after meal > vasoconstriction in lower limb raise BP above limbs = redirect blood to intestinal arteries

- local control
- neural control
- hormonal control
vasomotion: local control
autoregulation: ability of tissues to regulate own blood supply

- bloodstream delivers oxygen and removes metabolites

- when wastes are removed, vessels constrict
vasomotion: neural control pt. 1 - chemoreflex + chemoreceptors
vessels under control by central and autonomic nervous systems

- vasomotor center exerts sympathetic control (constrict)

chemoreflex: automatic response to change in blood chemistry (pH, O2, CO2)

chemoreceptors: aortic bodies and carotid bodies (located in aortic arch, subclavian + carotid arteries)
vasomotion: neural control pt. 2 - roles
primary role: adjust respiration

secondary role: vasomotion, stimulate breathing, inc. BP, etc.
medullary ischemic reflex
automatic response to drop in perfusion of brain

- medulla monitor own blood supply + activate reflexes when sense ischemia (insufficient perfusion)

- cardiac and vasomotor centers send sympathetic signal to heart and vessels = inc. heart rate + contraction, vasoconstriction, raise BP = restore normal perfusion to brain
vasomotion: hormonal control
influence BP through vasoactive effects + by regulating water balance
arterioles shift blood flow w/ changing needs
resting: mesenteric artery is dilated = inc. flow to intestines > common iliac artery is constricted = dec. flow to legs

exercise: mesenteric artery is constricted = dec. flow to intestines > common iliac artery is dilated = inc. flow to legs
capillary exchange: 3 routes + mechanisms involved
chemicals pass through capillary wall by 3 routes:
- endothelial cell cytoplasm
- intercellular clefts b/w endothelial cells
- filtration pores of fenestrated capillaries

mechanisms involved: diffusion, transcytosis, filtration + reabsorption
capillary: diffusion
most important form of capillary exchange

- glucose and oxygen more concentrated in blood diffuse out of blood
- carbon dioxide and other waste more concentrated in tissue fluid diffuse into blood

only occur if:
- solute can permeate plasma membrane
- solute can find passages large enough to pass through (like filtration pores + intracellular clefts)
capillary: diffusion - lipid-soluble substances + water-soluble substances
lipid-soluble substances: steroid hormones, O2 + CO2 diffuse through plasma membrane

water-soluble substances: glucose + electrolytes pass through filtration pores and intracellular clefts

large particles like proteins are held back
capillary: transcytosis
endothelial cells pick up material by pinocytosis or receptor-mediated endocytosis > transport vesicles across cell > discharge material on other side of plasma membrane by exocytosis

important for fatty acids, albumin, insulin
capillary: filtration and resabsorption
- fluid filters out of arterial end of capillary and osmotically reenters (reabsorption) at venous end

- delivers materials and removes wastes
capillary: filtration and reabsorption - opposing forces
blood hydrostatic pressure: draws fluid out of capillary
- high on arterial end, low on venous end

colloid osmotic pressure: draws fluid into capillary
- results from albumins
- oncotic pressure

hydrostatic pressure: force exerted against a surface by a liquid
- "holes in a tube"
- blood pressure
capillaries usually reabsorb most fluid they filter w/ exceptions
kidney capillaries: in glomeruli do not reabsorb

alveolar capillaries: in lung absorb completely to keep fluid out of air spaces
edema
accumulation of excess fluid in tissue

occurs when fluid filters into tissue faster than it is absorbed
edema: 3 causes
increased capillary filtration: kidney failure, histamine release, old age, poor venous return

reduced capillary absorption: hypoproteinemia, liver disease, protein deficiency

obstructed lymphatic drainage: surgical removal of lymph nodes
mechanisms of venous return
- pressure gradient

- gravity

- skeletal muscle pump

- thoracic (respiratory) pump: inhalation cause thoracic cavity to expand + cause thoracic pressure to dec. + cause abd. pressure to inc. = force blood upward = central venous pressure fluctuates

- cardiac suction: expand atrial space
exercise increases venous return in many ways
- heart beats faster + harder = inc. CO + BP

- vessels of skeletal muscles, lungs, and heart dilate and inc. flow

- increased respiratory rate = inc. action of thoracic pump

- increased skeletal muscle pump
circulatory shock, cardiogenic shock, low venous return
circulatory shock: state in which CO is insufficient to meet body's metabolic needs

cardiogenic shock: inadequate pumping of heart

LVR: CO is low bc too little blood returns to heart
circulatory shock: 3 principal forms
hypovolemic shock: most common
- loss of blood volume: trauma, burns, dehydration

obstructed venous return shock: tumor or aneurysm compresses a vein

venous pooling shock: long periods of standing, sitting, widespread vasodilation
neurogenic shock, septic shock, anaphylactic shock
neurogenic shock: loss of vasomotor tone, vasodilation
- causes from emotional shock or brainstem injury

septic shock: bacterial toxins trigger vasodilation + inc. capillary permeability

anaphylactic shock: immune reaction to antigen, histamine release, vasodilation, inc. capillary permeability
response to circulatory shock: compensated shock
homeostatic mechanisms bring about spontaneous recovery

ex: if a person faints and fall to horizontal position, gravity restores blood flow to brain
response to circulatory shock: decompensated shock
- triggers when compensated shock mechanism fails

- life-threatening positive feedback occur = cause damage to cardiac + brain tissue
brain
brain regulates own blood flow to match changes in BP and chemistry (700 mL/min.)

- cerebral arteries dilate as BP drops + constrict as BP rises

main chemical stimulus: pH
- hypercapnia: CO2 levels inc. in brain + pH decreases = vasodilation
- hypocapnia: raises pH = vasoconstriction
transient ischemic attacks + stroke or cerebral vascular accident
TIAs: episodes of cerebral ischemia
- spasms of diseased cerebral arteries
- dizziness, loss of vision, paralysis, aphasia
- warning of stroke

Stroke/CVA: death of brain tissue by ischemia
- blindness, paralysis, loss of sensation/speech
- recovery depends on neurons, collateral circulation
skeletal muscles
- varying flow depending on state of exertion

at rest:
- arterioles constrict
- capillary beds shut down
- flow about 1 L/min.

during exercise, arterioles dilate due to epinephrine and sympathetic nerves + precapillary sphincters dilate due to muscle metabolites (lactic acid, CO2)

- muscular contraction prevent flow
lungs
low BP (25/10 mmHg):
- slower flow = time for gas exchange
- capillary fluid absorption > oncotic pressure + prevent fluid accumulation

response to hypoxia: arteries constrict in diseased area > redirect flow to better ventilated area
Aorta and its major branches
ascending aorta:
- coronary arteries supply heart

aortic arch:
brachiocephalic:
- common carotid supply side of head
- subclavian supply shoulder and upper limb

descending aorta:
- thoracic aorta supply above diaphragm
- abdominal aorta supply below diaphragm
arteries of head and neck
- vertebral arteries form basilar artery

- circle of willis on base of brain is formed from anastomosis of basilar and carotid arteries
arteries of abdominal and pelvic region
regions of celiac trunk supply upper abdominal viscera (stomach, spleen, liver, pancreas)
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