Download 16 Unit 3

The Cardiovascular System:
Blood Vessels and Circulation
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Unit 3
Chapter 16
Blood Vessels
•
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Arteries- from heart
•
•
Capillaries- thin walled for diffusion
Veins- to heart
1. Venules => from capillaries
2. Veins from tissue to vena cavae to heart
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1. Elastic => large
2. Muscular => distribution to organs
3. Arterioles => distribution to capillaries- mostly
muscle
Figure 16.1ab
Figure 16.1c
Blood Vessel Structure
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• Three layers
• Arteries-> thicker tunica media
• Veins- bigger lumen and thinner walls
• Veins-> valves to prevent backflow
Venules very thin, no valves
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Elastic tissue and/or muscle
As they get smaller-> more muscle
Arterioles-> very muscular- control
• Muscular arteries & arterioles regulate flow
• Sympathetic activity to smooth muscle
vasoconstriction (narrowing)
• Decreased sympathetic activity or NO
causes relaxation or dilation
• Arterioles adjust flow into capillaries
• Systemic veins & venules serve as blood
reservoirs (~64% total blood volume)
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Vessel Functions
Capillary Details
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• Capillaries only have endothelium
Very thin cells & cell nuclei protrude into
lumen- easy diffusion
Sometimes direct route from arteriole to
venule
• Filling controlled by small arterioles
& precapillary sphincters
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• Connected from arterioles to
venules in networks
Figure 16.2a
Figure 16.2b
Capillary Exchange
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• Slow flow through capillaries
Allows time for exchange through wall
• Blood pressure 
filtration of fluid out of capillary
Mostly in first ½ of vessel length
Reabsorption of fluid from outside to inside
Mostly in last ½ of vessel length
• Balance determines fluid in circulation
Excess fluid returned via lymphatic system
Local signals can adjust capillary flow
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• Osmosis (protein concentration)
Figure 16.3
• Blood enters veins at very low
pressure.
• Needs more pumping to get back to
heart
• = action of heart; muscle pumps;
respiratory pump
• Some pressure from heart action
• Not enough to overcome gravity
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Venous Return
• Contracting skeletal muscles squeeze
veins emptying them
• Because of venous valves flow is toward
heart
• Respiratory pump has similar action
• Inhalation decreased thoracic pressure
& increased abdominal pressure
Blood flows toward heart
• Exhalation allows refilling of abdominal
veins
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Muscle & Respiratory Pumps
Figure 16.4
Blood Flow
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• from high pressure area to lower pressure area, i.e. down
pressure gradient
Greater gradient greater flow
• Ventricular contraction blood pressure (BP)
• Resistance= opposition to flow
• depends on lumen diameter & length & blood
viscosity
Smaller lumen  greater resistance
Higher viscosity greater resistance
viscosity of blood depends on Hct
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Highest in aorta and declines as flows through vessels
110-70 mmHg in aorta ~16 mmHg at venules
 0 at R. Atrium
Resistance
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• Depends on vessel lumen diameter
Smaller lumen  greater resistance
• And blood viscosity
Higher viscosity greater resistance
viscosity of blood depends on Hct
Longer the length of flow the more friction with
wall
Total body resistance increases with growth and
addition of tissue
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• And total vessel length
Anatomical Design
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• Length and pressure
• Design and local flow control- central
pressure
• Adult anatomy gives constant length
• If central blood pressure is controlled it
is constant
• Only variable is radius of the arterioles
• Each tissue can do it separately
• Review design in picture below
All tissues have the same pressure gradient
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Pressure Gradients
Pressure Gradients (Cont.)
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• Note pulse in aorta & large arteries
MAP
• pressure fall related to resistance
• Note low venous pressures
can’t get back to the heart!
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Note role of arterioles
Figure 16.5
• Fast responses: e.g. standing up
• Slower responses: e.g. blood volume
• Distribution: e.g. to working muscles
• Balance of CO with flow to body
• Interacts with many other control
systems
• Cardiovascular (CV) Center major
regulator
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Regulation of Blood Pressure &
Flow
Inputs
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• Higher centers:
• Sensory receptor input:
proprioceptors,
baroreceptors
chemoreceptors
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cerebral cortex,
limbic system,
hypothalamus
HR increases before race;
flow adjusted for body temperature
Inputs (Cont.)
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• Proprioceptors:
Start HR change as activity starts
• Baroreceptors: in aorta & carotid
• Chemoreceptors: in aorta & carotid
Low O2, high H+, CO2  
vasoconstriction  BP
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pressure   parasympathetic &
 sympathetic stimulation  CO
Figure 16.6
Output
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• ANS to heart
 Sympathetic  HR &  force of
contraction
 Parasympathetic  HR
to arterioles  vasomotor tone
To veins move blood to heart  BP
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• Vasomotor
Hormone regulation
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• Renin-Angiotensin system
Angiotensin II  vasoconstriction+ thirst
 aldosterone   Na+ & water loss in urine on
 constriction   BP
 Thirst & water retention in kidney BP
• ANP- from cells in atria
Vasodilation & loss of salt & water in urine BP
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• Epinephrine & Norepinephrine  CO
• ADH = Vasopressin
Figure 16.7
Checking Circulation- Pulse
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• Pulse in arteries = HR
• Tachycardia = rapid rest rate (>100
bpm)
• Bradycardia= slow rest rate (<50 bpm)
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Use radial artery at wrist,
carotid artery,
brachial artery
Blood Pressure
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• Use sphygmomanometer
Usually on brachial artery
• Raise pressure above systolicstop flow
• Lower pressure in cuff until flow just
starts
• Lower until sound suddenly gets faint
Diastolic pressure
• Normal values <120 mmHg for systolic &
< 80 mmHg for diastolic
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first sound  Systolic Pressure
Circulatory Routes
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• Two parts: Systemic & Pulmonary
• Systemic circulation- throughout body
• All systemic arteries branch from aorta
• All systemic veins empty into Superior
Vena Cava, Inferior Vena Cava or the
Coronary Sinus
Carry deoxygenated blood to heart
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Oxygenated blood deoxygenated as it goes
Figure 16.8
Figure 16.9
Figure 16.10a
Figure 16.10b
Figure 16.10c
Figure 16.11
Figure 16.12
Figure 16.13
Figure 16.14a
Figure 16.14b
Figure 16.14c
Figure 16.15
Pulmonary Circulation
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• From right ventricle pulmonary trunk
• R. & L. pulmonary arteries
Carry deoxygenated blood
•  R. & L. lungs
•  2 R. & 2 L. pulmonary veins
Carry oxygenated blood
•  L. atrium
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Gas exchange occurs
• Portal vein transports blood from one
capillary bed to another
• GI organs
•  Splenic & superior mesenteric veins
•  hepatic portal vein
• sinusoids in liver
Mixes with oxygenated blood
•  hepatic vein inferior Vena Cava
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Hepatic Petal Circulation
Figure 16.16a
Figure 16.16b
Fetal Circulation
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• Specialized for exchange of materials with
maternal blood and bypass of lungs
• Exchange in placenta umbilical vein
•  liver ductus venosus
•  inferior vena cava  R. atrium
•  foramen ovale L. Atrium
• Or  R. Ventricle Pulmonary trunk 
ductus arteriosus  aorta
•  internal iliacs  umbilical arteries
Placenta
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Mixes with deoxygenated blood from lower body
Figure 16.17
• Umbilical arteries medial umbilical
ligaments
• Umbilical vein  ligamentum teres
• Ductus venosus  ligamentum venosum
• Placenta expelled
• Foramen ovalis closes fossa ovale
• Ductus arteriosus  ligamentum
arteriosum
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At Birth
Aging
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• Stiffening of aortae
• Loss of cardiac muscle strength
• Coronary artery disease
• Congestive heart failure
• atherosclerosis
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Reduced CO & increased systolic
pressure