CARDIOVASCULAR SYSTEM: Blood Vessels Chapter 21
Remember:
Blood is
Heart is the
Blood vessels are the “pipes”
transport blood, permit exchange of nutrients, hormones etc.
Types of Vessels
Arteries:
Arterioles: smaller diameter <.5 mm
Capillaries & Sinusoids:
Venules:
Veins:
Structure of Vessel Walls:
Lumen =
1. Tunica intima:
2. Tunica media:
3. Tunica externa or adventitia:
Internal elastic lamina (membrane):
External elastic lamina (membrane):
Differences between Arteries and Veins:
1. Artery walls are thicker
smooth muscle contracts or relaxes
vasoconstriction
vasodilation
2. Arterial lumens are smaller
3. Arteries are subject to higher pressure
arterial recoil:
aneurysm:
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4. Arteries carry blood away from the heart
5. Veins usually have valves
Comparison of vessel wall for arteries & veins:
ARTERIES:
ELASTIC ARTERIES:
•larger arteries closer to the heart (Aorta, LCC, L Subclavian, Brachiocephalic)
•composed of
tunics
•tunica media contains more
•large
•arterial pulse: stretch/recoil of arteries
MUSCULAR ARTERIES:
• most arteries of the body
• tunica media contains
• some are important pressure points
ARTERIOLES:
•diameter <.5 mm
•small lumen
•thick tunica media mostly smooth muscle cells
•regulate blood flow through vasoconstriction & vasodilation
resistance vessels
CAPILLARIES:
•most numerous
•extremely
•consist of
• site of exchange – slowest flowing blood
•Continuous & Fenestrated Capillaries
continuous:
fenestrated:
Capillary Beds:
Consists of 2 types of vessels:
1.) vascular shunt
2.) true capillaries
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metarteriole: (proximal end) at the beginning of direct
channel from arteriole to venule
precapillary sphincter: at entrance to each
capillary - open/close to control blood flow
through capillary bed – autoregulation
vascular shunt( thoroughfare channel):
true capillaries
SINUSOIDS:
•capillary like vessel – small space
VENULES:
•drain blood from capillaries
•small lumen
VEINS: (Reservoirs or Capacitance vessels)
• Medium & large veins
• Consists of same 3 layers as arteries but
tunica media is
•Some veins contain valves
-prevent
-mostly formed in
Varicose veins
•can be hereditary
•found in individuals
•if severe are removed and alternate venous
pathways take over.
Hemorrhoids:
Distribution of Blood
Heart, arteries and capillaries
contain 30-35% of blood volume
Veins contain 65-70%
termed capacitance vessels
because can easily stretch under low pressure
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Physiology of Circulation: (p. 720 table 21-1)
Blood flow:
Fastest flowing blood
Slowest flowing blood
Blood Pressure:
arterial blood pressure:
venous pressure:
circulatory pressure or MAP:
capillary hydrostatic pressure: forces molecules out of capillaries
Total Peripheral Resistance:
Sources of Resistance:
1. Vascular Resistance – friction b/w blood and vessel wall
a. Blood Viscosity:
b. Blood Vessel Length:
c. Blood Vessel Diameter
d. Turbulence: increases R
creates noise – (bruit) that can be heard with stethoscope
Relationship between Blood Flow, Blood Pressure, & Peripheral Resistance:
F = ∆P
R
F= Flow
P= Pressure
R= Resistance
R inversely proportional to r4
If R increases –what happens to F?
Why might this be beneficial?
If R increases and you need to maintain F, how does the body compensate?
Arterial Blood Pressure:
Systolic Blood Pressure (SBP):
SBP in aorta: 120 mmHg - in pulmonary artery 15 mmHg
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Diastolic Blood Pressure (DBP)
Pulse Pressure (PP): SBP - DBP
Mean Arterial Pressure (MAP)= DBP + PP/3
Factors Aiding Venous Return:
Venous pressure is very low
Muscular pump/compression: skeletal muscle contractions move blood
Respiratory pump: Boyle’s Law: V inversely related to P (V↓ = P↑)
during inspiration: diaphragm contracts, therefore thoracic cavity volume > abdominal cavity
volume
-Pressure in vena cava decreases and pressure in abdominal cavity increases so blood
flows from abdominal cavity into IVC
during expiration: diaphragm relaxes, therefore thoracic cavity volume < abdominal cavity
volume
-Pressure in thorax increases to push blood from IVC into RA
note: abdominal pressure drops & blood flows into IVC from lower extremities
Capillary Pressure and Exchange
Capillaries are the exchange vessels between blood and tissue cells
Very thin walls for diffusion
Filtration:
Hydrostatic Pressure:
Osmotic Pressure:
blood colloid osmotic pressure (BCOP) or oncotic pressure
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CHP = 35 mmHg at arterial end and
mmHg at venule end
COP or BCOP = 25 mmHg dependent on
Net Filtration Pressure (NFP):
When HP > OP
When OP > HP
However, the net pressure of fluid leaving at the arterial end is
of fluid entering the capillary at the venous end.
more than the net pressure
Fluid is lost to the interstitial space daily
Imbalances b/w HP and OP cause edema
Factors affecting CHP:
Factors affecting COP:
Cardiovascular Regulation:
Tissue Perfusion is dependent on Q, R and BP
Want active tissues to receive more blood
Autoregulation:
Vasodilation or vasoconstriction to control blood flow and blood pressure
1. Local vasodilators/constrictors: relax/constrict precapillary sphincter
Vasodilators:
Decreased tissue O2 or increased CO2
Lactic acid
Nitric oxide (NO)
Increased K or H ions in interstitial fluid
Increased local temperature
Vasoconstrictors:
PGs and thromboxanes
Myogenic Controls
Vascular smooth muscle contracts when stretched - so stretching causes
automatic vasoconstriction
When low pressure in vessel decreases stretch, vessel vasodilates
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Blood Pressure Regulation:
1.) Short-term Regulation: controls HR, contractility, or blood vessel diameter
2.) Long- term Regulation: controls BV via renal mechanisms
Nervous System (Neural) Controls:
vasomotor center
control vasoconstriction (NE): most arterioles in body
vasodilation (only in skeletal muscles and brain arterioles release NO)
all arterioles have vasomotor tone - always partially constricted
NE can either cause more or less constriction of smooth muscle
Reflex Control of Cardiovascular Function
Baroreceptor Reflex:
Baroreceptors: monitor stretch
Found in the carotid and aortic sinuses
BP depends on cardiac output (CO = HR X SV)
If BP increases they send info to BOTH the vasomotor and cardiac centers
Which would try to lower BP by
HR and
arterioles
If BP decreases how would the vasomotor and cardiac centers respond?
Note: sympathetic activation also triggers release of Epi & NE from adrenal medulla
Atrial baroreceptors – monitor stretch in right atrium
blood entering right atrium = amount blood pumped out of aorta
when activated – increase cardiac output
Valsalva maneuver: exhaling forcefully against a closed glottis
increases intrathoracic pressure which compresses aorta and vena cavae
decreases venous return = drop in BP and CO
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Chemoreceptor Reflex
Chemoreceptors
found in carotid and aortic bodies
Respond to blood CO2, pH and O2 levels in blood and CSF
when there is a ↓blood O2, pH or ↑CO2 they are excited and ↑BP
vasomotor center:
cardiac center:
Higher Brain Centers: Emotions
Chemical Controls – Hormones and Cardiovascular Regulation – mainly long-term regulation
Hormone
Adrenal Medulla
Hormones
Site of Release
Mechanism
Antidiuretic Hormone
(ADH)
Angiotensin II (renin)
Aldosterone
Atrial natriuretic factor
(ANF) or peptide (ANP)
EPO
Cardiovascular response to exercise:
HR: increased HR, increased venous return
BP: increases - SBP more than DBP
SV:
CO: 5 L/min up to 30 L/min
regular exercise lowers cholesterol, lowers resting HR, improves mood
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Blood Flow through Organs
1. Brain: receives 750 ml/min of blood
2. Heart: receives 250 ml/min at rest
3. Skin: varies from 250 ml/min to 2500 ml/min
4. Kidneys: 1200 ml/min
Clinical Stuff
1. Atherosclerosis & Arteriosclerosis
Atherosclerosis: deposit of fats/plaque
Arteriosclerosis:
2. Hypertension & Hypotension
Hypertension:
Prehypertension:
Stage 1:
Stage 2:
Consequences of untreated hypertension:
Causes:
-primary
-secondary
Hypotension
Reduced cardiac output: (hypovolemia, ↓HR, ↓ venous return)
Orthostatic hypotension:
3. Deep Vein Thrombosis (DVT)
usually in thigh or calf
more common in surgical patients
S/S: pain, swelling, redness
risk of clot breaking free and causing pulmonary embolism
Tx:
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4. Circulatory Shock ( pgs. 142-144 in Applications Manual: Shock)
Early stage: ↓ CO = ↓ BP = ↓ peripheral blood flow= ischemic tissues
Sympathetic N.S. responds: ↑HR, ↑CO to try to ↑ BP
if unsuccessful – tissues become ischemic, low BP ↓ venous return = ↓CO
Later stages (irreversible): damage to cardiac muscle, damage to tissues – vasodilation of blood
vessels = circulatory collapse
4. Meds used for BP treatment
those used for the heart because:
Beta-blockers:
Ca++ Channel blockers:
ACE Inhibitors:
Diuretics (diaqua, oretic, lasix, furoside)
Note: The applications manual has excellent clinical information for this unit. Read pages 118-142 for
additional information.
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Arteries and Veins of the Body – see ADAM packet 2
Pulmonary Circuit:
Systemic Circuit:
aorta: aortic arch, thoracic aorta, abdominal aorta
Circle of Willis or Cerebral Arterial Circle (pg. 743)
encircles the infundibulum
ensures brain gets adequate blood flow from either carotid or vertebral arteries
Cerbrovascular accident (CVA) or stroke:
middle cerebral artery most common site of a stroke
supplies temporal, frontal, parietal lobes: sensory/motor skills
damage occurs on opposite side of body as artery
Hepatic Portal System:
hepatic portal vein – drains venous blood into liver
receives blood from: inferior mesenteric, splenic and superior mesenteric veins
brings nutrient rich blood to liver for processing
liver processes and releases to hepatic vein which empties into IVC
Fetal Circulation: pgs. 755-758
Umbilical cord contains umbilical arteries & vein
Umbilical arteries: transports deoxygenated blood from fetus to placenta
Umbilical veins: transports oxygenated blood from placenta to fetus
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Shunts:
Foramen ovale: between R and L atria
Ductus arteriosus: between pulmonary
trunk and aorta
Ductus venosus: receives blood from
umbilical vein and shunts it to the inferior
vena cava.
pressure changes at birth due to breathing close foramen ovale and ductus arteriosus
left atrial/ventricular pressure increases and pulmonary pressure decreases
in adults have fossa ovalis and ligamentum arteriosum
patent foramen ovale:
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