Transcript Cardiovascular

Chapter 16
The Cardiovascular
System: Blood Vessels
and Circulation
Blood Vessels
• arteries
• carry blood away from ventricles of heart
• arterioles
• receive blood from arteries
• carry blood to capillaries
• capillaries
• sites of exchange of substances between
blood and body cells
• venules
• receive blood from capillaries
• veins
• carry blood toward atria of heart
15-30
Blood Vessels
Three layers (tunica): external, middle, inner
Arteries: thicker
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Arterioles:
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Elastic: large
smooth muscle helps regulate blood pressure
Sympathetic activity to smooth muscle 
vasoconstriction (narrowing)
Decreased sympathetic activity or NONE
causes relaxation (dilation)
Capillaries lack muscle fibers
15-33
Metarteriole
• connects arteriole directly to venule
15-34
Walls of Artery and Vein
15-32
Blood Vessel Structure: Arteries, Veins
Blood Vessel Structure: Arteries, Veins
Capillaries
• smallest diameter blood vessels
• extensions of inner lining of arterioles
• walls are endothelium only
• semipermeable
• sinusoids – leaky capillaries
15-35
Capillary Network
15-36
Regulation of Capillary: Blood Flow
Precapillary sphincters
• may close a capillary
• respond to needs of the cells
• low oxygen and nutrients cause
sphincter to relax
Autoregulation: ability of a
tissue to adjust blood flow into
the area according to demands
15-37
Exchange in the Capillaries
• water and other substances leave capillaries because of net
outward pressure at the capillaries’s arteriolar ends
• water enters capillaries’ at the venular ends because of a net
inward pressure
• substances move in and out along the length of the capillaries
according to their respective concentration gradients
15-38
Capillary Details
Capillary Details
Capillary Exchange
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Colloid osmotic pressure (pulls into capillary)
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Plasma proteins create this “pulling” pressure
Causes reabsorption of fluid from outside to inside
Excess fluid returned via lymphatic system
Capillary Exchange
Blood Vessel Structure: Veins
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Venules
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Larger lumen, thinner walls
Valves prevent backflow
Very thin, no valves
Blood enters veins at very low pressure
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Inadequate to overcome gravity and return blood
to heart
Venous Valves
15-40
Venous Return: Two Mechanisms
Skeletal muscle contractions
1.
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Especially in lower limbs
squeeze veins - emptying them
Because of valves, flow is  heart
Systemic venules and veins serve as blood
reservoirs
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hold ~ 64% total blood volume
Venous Return: Two Mechanisms
Venous Return: Two Mechanisms
Respiratory pump
2.
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Inhalation decreases thoracic pressure
& increases abdominal pressure
 blood to heart
Exhalation allows refilling of abdominal veins
Blood Flow Through Vessels
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BP highest in aorta: 110/70 mm Hg
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Pulse in large arteries
BP declines as flows through more vessels
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Arterioles: major drop in BP due to smooth muscle
contraction  vasoconstriction
Capillary beds ~ 35-16 mm Hg 
16 mm Hg at venules  0 at right atrium
Blood Flow Through Vessels
Factors that regulate blood flow and BP
1. Blood volume and ventricular contraction 
cardiac output
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Under control of cardiovascular (CV) center (medulla)
2. Vascular resistance:
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lumen diameter
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vessel length
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Smaller lumen (with vasoconstriction)  greater
resistance
Greater vessel length (with weight gain)  greater
resistance
blood viscosity
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Higher viscosity (as with high hematocrit)  greater
resistance
Cardiovascular Center
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Located in medulla
Helps regulate
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Heart rate
Stroke volume
Blood pressure
Blood flow to specific tissues
Mechanisms
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By neural mechanisms
By hormonal mechanisms
Input to Cardiovascular Center (Medulla)
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Input from different parts of brain
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Cerebral cortex: thoughts, decisions
Limbic system: emotions
Hypothalamus: changes in temperature or blood
volume  blood flow adjusted accordingly
Input from sensory receptors and nerves
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Proprioceptors, baroreceptors, chemoreceptors
Input to Cardiovascular Center (Medulla)
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Proprioceptors:
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Baroreceptors in aorta and carotid: if BP 
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Cause  heart rate as exercise begins  
cardiac output (CO)   BP
 sympathetic stimulation   CO   BP
 parasympathetic   CO   BP
Chemoreceptors in aorta and carotid bodies
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If low O2, high CO2, or high H+ (acidity)  
resistance by  vasoconstriction   BP
Input to Cardiovascular Center (Medulla)
Output to Cardiovascular Effectors
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ANS nerves to heart
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 Sympathetic  HR and  force of contraction
  cardiac output (CO)   BP
 Parasympathetic   HR  CO   BP
Vasomotor (sympathetic nerves)
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To arterioles contract smooth muscle  
vasomotor tone   vascular resistance   BP
To veins contract smooth muscle  move blood
to heart   BP
Hormone Regulation of Blood Flow + BP
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Renin-angiotensin aldosterone (RAA) system
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Epinephrine + norepinephrine   CO  BP
ADH = vasopressin
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Angiotensin II  vasoconstriction   BP
 aldosterone  retain Na++ water   BP
 vasoconstriction   BP
Thirst + water retention in kidney   BP
ANP from cells in atria
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Vasodilation, loss of Na+ water in urine  BP
Hormone Regulation of Blood Flow + BP
Arterial Blood Pressure
Blood Pressure – force the blood exerts against the
inner walls of the blood vessels
• rises when ventricles contract
• falls when ventricles relax
• systolic pressure – maximum pressure
• diastolic pressure – minimum pressure
15-42
Checking Circulation: Pulse
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Pulse in arteries = heart rate (HR)
Press artery against bone or muscle.
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Radial artery (thumb side of wrist)
Carotid artery (neck)
Brachial artery (arm)
Tachycardia: rapid resting HR (>100 bpm)
Bradycardia= slow resting HR (<50 bpm)
Pulse
15-43
Central Venous Pressure
• pressure in the right atrium
• weakly beating heart increases central venous
pressure
• increase in central venous pressure causes blood to
back up into peripheral vein
15-49
Blood Pressure
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Device used: sphygmomanometer
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Inflate cuff to raise pressure > systolic BP
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First sound indicates systolic BP
Lower pressure further until sound become
faint
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Briefly stop blood flow there
Lower pressure in cuff until flow just starts
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Usually on brachial artery
Diastolic BP
Normal BP values <120 mm Hg for systolic
and < 80 mm Hg for diastolic
Circulatory Routes
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Two main routes: systemic + pulmonary
Systemic circulation
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Oxygenated blood travels from heart throughout
body, deoxygenating as it goes
All systemic arteries branch from aorta
All systemic veins empty into superior vena cava,
inferior vena cava, or the coronary sinus
Circulatory
Routes
Circulatory
Routes:
Aorta
Circulatory
Routes: Aorta
Circulatory Routes: Aorta
Circulatory Routes: Aorta
Circulatory
Routes: Pelvis,
Lower Limb
Circulatory
Routes:
Principle
Veins
Circulatory Routes: Principle Veins of
the Hands and Neck
Circulatory Routes: Principle Veins of
the Right Upper Limb
Circulatory
Routes:
Principle Veins
of the Pelvis
and Lower
Limbs
Pulmonary Circulation
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Carries blood from right side of heart to lungs
to get O2 and eliminate CO2
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Right ventricle (RV)  pulmonary trunk  R + L
pulmonary arteries  both lungs 
Carry “blue blood” low O2 in and high in CO2
Pulmonary capillaries: gas exchange 
R and L pulmonary veins  L atrium
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Carry “red blood” (high in O2 in and low in CO2)
Pulmonary Circuit
15-50
Blood Flow Through Alveoli
• cells of alveolar wall are tightly joined together
• the high osmotic pressure of the interstitial fluid draws water
out of them
15-51
Cerebral Arterial Circle
• Circle of Willis
• formed by anterior and posterior cerebral arteries, which join
the internal carotid arteries
15-58
Hepatic Portal Circulation
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Portal vein: transports blood from one organ’s
capillary bed to another
GI organs 
Splenic and superior mesenteric veins 
Hepatic portal vein (“blue blood”) 
Sinusoids (“leaky capillaries” in liver) 
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Mixes “blue blood” with “red blood”
Hepatic vein  inferior vena cava (IVC)
Hepatic Portal Circulation
Hepatic Portal Vein
15-68
Hepatic Portal Circulation
Fetal Circulation
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Specialized for exchange of materials with
maternal blood/bypass lungs
Exchange in placenta  umbilical vein
 ductus venosus (bypasses liver)
 inferior vena cava  R atrium (mixes with
deoxygenated blood from lower body)
 foramen ovale  L atrium
Or  R Ventricle  pulmonary trunk 
ductus arteriosus  aorta  internal iliac
arteries  umbilical arteries  placenta
Fetal
Circulation
Changes at Birth
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Umbilical arteries  medial umbilical
ligaments
Umbilical vein  ligamentum teres
Ductus venosus  ligamentum venosum
Placenta expelled after
Foramen ovalis closes  fossa ovale
Ductus arteriosus  ligamentum arteriosum
Aging
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Stiffening of aorta
Loss of cardiac muscle strength
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Reduced CO & increased systolic pressure
Higher risk for
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Coronary artery disease (CAD)
Congestive heart failure (CHF)
Atherosclerosis