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© Annie Leibovitz/Contact Press Images PowerPoint ® Lecture Slides prepared by
Human Anatomy & Physiology
Atlantic Cape Community Ninth Edition College
C H A P T E R
19
The Cardiovascular System: Blood Vessels: Part A
© 2013 Pearson Education, Inc.
Structure of Blood Vessel Walls
• Lumen – Central blood-containing space • Three wall layers in arteries and veins –
Tunica intima, tunica media, and tunica externa
• Capillaries –
Endothelium
with sparse basal lamina © 2013 Pearson Education, Inc.
Figure 19.1b Generalized structure of arteries, veins, and capillaries.
Tunica intima • Endothelium • Subendothelial layer • Internal elastic membrane Tunica media (smooth muscle and elastic fibers) • External elastic membrane Tunica externa (collagen fibers) • Vasa vasorum Lumen Artery Capillary Capillary network Lumen Vein Basement membrane Endothelial cells
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Valve
Tunics
• Tunica intima – Endothelium lines lumen of all vessels • Continuous with endocardium • Slick surface reduces friction –
Subendothelial layer
in vessels larger than 1 mm; connective tissue basement membrane © 2013 Pearson Education, Inc.
Tunics
• Tunica media – Smooth muscle and sheets of elastin – Sympathetic vasomotor nerve fibers control
vasoconstriction
and
vasodilation
of vessels • Influence blood flow and blood pressure © 2013 Pearson Education, Inc.
Tunics
• Tunica externa (tunica adventitia) – Collagen fibers protect and reinforce; anchor to surrounding structures – Contains nerve fibers, lymphatic vessels –
Vasa vasorum
of larger vessels nourishes external layer © 2013 Pearson Education, Inc.
Figure 19.2 The relationship of blood vessels to each other and to lymphatic vessels.
Venous system Arterial system Large veins (capacitance vessels)
Heart
Large lymphatic vessels Elastic arteries (conducting arteries) Lymph node
Lymphatic system
Muscular arteries (distributing arteries) Small veins (capacitance vessels) Arteriovenous anastomosis Lymphatic capillaries Sinusoid Arterioles (resistance vessels) Terminal arteriole Metarteriole
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Postcapillary venule Thoroughfare channel Capillaries (exchange vessels) Precapillary sphincter
Arterial System: Elastic Arteries
• Large thick-walled arteries with elastin in all three tunics • Aorta and its major branches • Large lumen offers low resistance • Inactive in vasoconstriction • Act as pressure reservoirs—expand and recoil as blood ejected from heart – Smooth pressure downstream © 2013 Pearson Education, Inc.
Arterial System: Muscular Arteries
• Distal to elastic arteries – Deliver blood to body organs • Thick tunica media with more smooth muscle • Active in vasoconstriction © 2013 Pearson Education, Inc.
Arterial System: Arterioles
• Smallest arteries • Lead to capillary beds • Control flow into capillary beds via vasodilation and vasoconstriction © 2013 Pearson Education, Inc.
Table 19.1 Summary of Blood Vessel Anatomy (1 of 2)
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Capillaries
• Microscopic blood vessels • Walls of thin tunica intima – In smallest one cell forms entire circumference •
Pericytes
help stabilize their walls and control permeability • Diameter allows only single RBC to pass at a time © 2013 Pearson Education, Inc.
Capillaries
• In all tissues except for cartilage, epithelia, cornea and lens of eye • Provide direct access to almost every cell • Functions – Exchange of gases, nutrients, wastes, hormones, etc., between blood and interstitial fluid © 2013 Pearson Education, Inc.
Capillaries
• Three structural types 1. Continuous capillaries 2. Fenestrated capillaries 3. Sinusoid capillaries (sinusoids) © 2013 Pearson Education, Inc.
Continuous Capillaries
• Abundant in skin and muscles – Tight junctions connect endothelial cells – Intercellular clefts allow passage of fluids and small solutes • Continuous capillaries of brain unique – Tight junctions complete, forming blood brain barrier © 2013 Pearson Education, Inc.
Figure 19.3a Capillary structure.
Pericyte Red blood cell in lumen Intercellular cleft Endothelial cell Basement membrane Tight junction Endothelial nucleus Pinocytotic vesicles Continuous capillary.
Least permeable, and most common (e.g., skin, muscle).
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Fenestrated Capillaries
• Some endothelial cells contain pores (fenestrations) • More permeable than continuous capillaries • Function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys) © 2013 Pearson Education, Inc.
Figure 19.3b Capillary structure.
Pinocytotic vesicles Red blood cell in lumen Fenestrations (pores) Endothelial nucleus Basement membrane Tight junction Intercellular cleft Endothelial cell Fenestrated capillary.
Large fenestrations (pores) increase permeability. Occurs in areas of active absorption or filtration (e.g., kidney, small intestine).
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Sinusoid Capillaries
• Fewer tight junctions; usually fenestrated; larger intercellular clefts; large lumens • Blood flow sluggish – allows modification – Large molecules and blood cells pass between blood and surrounding tissues • Found only in the liver, bone marrow, spleen, adrenal medulla • Macrophages in lining to destroy bacteria © 2013 Pearson Education, Inc.
Figure 19.3c Capillary structure.
Endothelial cell Red blood cell in lumen Large intercellular cleft Tight junction Incomplete basement membrane Nucleus of endothelial cell Sinusoid capillary. Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen).
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Capillary Beds
•
Microcirculation
– Interwoven networks of capillaries between arterioles and venules –
Terminal arteriole
metarteriole
– Metarteriole continuous with
thoroughfare channel
(intermediate between capillary and venule) – Thoroughfare channel
postcapillary venule
that drains bed © 2013 Pearson Education, Inc.
Capillary Beds: Two Types of Vessels
• •
Vascular shunt
(metarteriole — thoroughfare channel) – Directly connects terminal arteriole and postcapillary venule
True capillaries
– 10 to 100 exchange vessels per capillary bed – Branch off metarteriole or terminal arteriole © 2013 Pearson Education, Inc.
Blood Flow Through Capillary Beds
• True capillaries normally branch from metarteriole and return to thoroughfare channel •
Precapillary sphincters
regulate blood flow into true capillaries – Blood may go into true capillaries or to shunt • Regulated by local chemical conditions and vasomotor nerves © 2013 Pearson Education, Inc.
Figure 19.4 Anatomy of a capillary bed.
Precapillary sphincters Vascular shunt Metarteriole Thoroughfare channel True capillaries
Terminal arteriole Postcapillary venule
Sphincters open —blood flows through true capillaries.
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Terminal arteriole Postcapillary venule
Sphincters closed —blood flows through metarteriole – thoroughfare channel and bypasses true capillaries.
Venous System: Venules
• Formed when capillary beds unite – Smallest postcapillary venules – Very porous; allow fluids and WBCs into tissues – Consist of endothelium and a few pericytes • Larger venules have one or two layers of smooth muscle cells © 2013 Pearson Education, Inc.
Figure 19.5 Relative proportion of blood volume throughout the cardiovascular system.
Systemic arteries and arterioles 15% Pulmonary blood vessels 12% Heart 8% Capillaries 5% Systemic veins and venules 60%
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Veins
• Adaptations ensure return of blood to heart despite low pressure – Large-diameter lumens offer little resistance –
Venous valves
prevent backflow of blood • Most abundant in veins of limbs –
Venous sinuses
: flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain) © 2013 Pearson Education, Inc.
Table 19.1 Summary of Blood Vessel Anatomy (2 of 2)
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Figure 19.1a Generalized structure of arteries, veins, and capillaries.
Artery
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Vein
Vascular Anastomoses
• • • Interconnections of blood vessels
Arterial anastomoses
provide alternate pathways (
collateral channels
) to given body region – Common at joints, in abdominal organs, brain, and heart; none in retina, kidneys, spleen • Vascular shunts of capillaries are examples of arteriovenous anastomoses
Venous anastomoses
are common © 2013 Pearson Education, Inc.
Physiology of Circulation: Definition of Terms
•
Blood flow
– Volume of blood flowing through vessel, organ, or entire circulation in given period • Measured as ml/min • Equivalent to cardiac output (CO) for entire vascular system • Relatively constant when at rest • Varies widely through individual organs, based on needs © 2013 Pearson Education, Inc.
Physiology of Circulation: Definition of Terms
•
Blood pressure
(BP) – Force per unit area exerted on wall of blood vessel by blood • Expressed in mm Hg • Measured as systemic arterial BP in large arteries near heart – Pressure gradient provides driving force that keeps blood moving from higher to lower pressure areas © 2013 Pearson Education, Inc.
Physiology of Circulation: Definition of Terms
•
Resistance
(peripheral resistance) – Opposition to flow – Measure of amount of friction blood encounters with vessel walls, generally in peripheral (systemic) circulation • Three important sources of resistance – Blood viscosity – Total blood vessel length – Blood vessel diameter © 2013 Pearson Education, Inc.
Resistance
• Factors that remain relatively constant: – Blood viscosity • The "stickiness" of blood due to formed elements and plasma proteins • Increased viscosity = increased resistance – Blood vessel length • Longer vessel = greater resistance encountered © 2013 Pearson Education, Inc.
Resistance
• Blood vessel diameter – Greatest influence on resistance • Frequent changes alter peripheral resistance • Varies inversely with fourth power of vessel radius – E.g., if radius is doubled, the resistance is 1/16 as much – E.g., Vasoconstriction increased resistance © 2013 Pearson Education, Inc.
Resistance
• Small-diameter arterioles major determinants of peripheral resistance • Abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance – Disrupt laminar flow and cause turbulent flow • Irregular fluid motion increased resistance © 2013 Pearson Education, Inc.
Relationship Between Blood Flow, Blood Pressure, and Resistance
• Blood flow (F) directly proportional to blood pressure gradient ( P) – If P increases, blood flow speeds up • Blood flow inversely proportional to peripheral resistance (R) – If R increases, blood flow decreases: F = P/R • R more important in influencing local blood flow because easily changed by altering blood vessel diameter © 2013 Pearson Education, Inc.
Systemic Blood Pressure
• Pumping action of heart generates blood flow • Pressure results when flow is opposed by resistance • Systemic pressure – Highest in aorta – Declines throughout pathway – 0 mm Hg in right atrium • Steepest drop occurs in arterioles © 2013 Pearson Education, Inc.
Figure 19.6 Blood pressure in various blood vessels of the systemic circulation.
120 100 80 60 40 Diastolic pressure 20 0 Systolic pressure Mean pressure
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Arterial Blood Pressure
• Reflects two factors of arteries close to heart – Elasticity (compliance or distensibility) – Volume of blood forced into them at any time • Blood pressure near heart is
pulsatile
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Arterial Blood Pressure
• •
Systolic pressure
: pressure exerted in aorta during ventricular contraction – Averages 120 mm Hg in normal adult •
Diastolic pressure
: lowest level of aortic pressure
Pulse pressure
= difference between systolic and diastolic pressure – Throbbing of arteries (pulse) © 2013 Pearson Education, Inc.
Arterial Blood Pressure
• Mean arterial pressure (MAP): pressure that propels blood to tissues • MAP = diastolic pressure + 1/3 pulse pressure • Pulse pressure and MAP both decline with increasing distance from heart • Ex. BP = 120/80; MAP = 93 mm Hg © 2013 Pearson Education, Inc.
Capillary Blood Pressure
• Ranges from 17 to 35 mm Hg • Low capillary pressure is desirable – High BP would rupture fragile, thin-walled capillaries – Most very permeable, so low pressure forces filtrate into interstitial spaces © 2013 Pearson Education, Inc.
Venous Blood Pressure
• Changes little during cardiac cycle • Small pressure gradient; about 15 mm Hg • Low pressure due to cumulative effects of peripheral resistance – Energy of blood pressure lost as heat during each circuit © 2013 Pearson Education, Inc.
Factors Aiding Venous Return
1. Muscular pump
: contraction of skeletal muscles "milks" blood toward heart; valves prevent backflow
2. Respiratory pump
: pressure changes during breathing move blood toward heart by squeezing abdominal veins as thoracic veins expand
3. Venoconstriction
under sympathetic control pushes blood toward heart © 2013 Pearson Education, Inc.
Figure 19.7 The muscular pump.
Venous valve (open) Contracted skeletal muscle Venous valve (closed) Vein Direction of blood flow
© 2013 Pearson Education, Inc.
Maintaining Blood Pressure
• Requires – Cooperation of heart, blood vessels, and kidneys – Supervision by brain • Main factors influencing blood pressure – Cardiac output (CO) – Peripheral resistance (PR) – Blood volume © 2013 Pearson Education, Inc.
Maintaining Blood Pressure
• F = P/R; CO = P/R; P = CO × • Blood pressure = CO × PR (and CO depends on blood volume) R • Blood pressure varies directly with CO, PR, and blood volume • Changes in one variable quickly compensated for by changes in other variables © 2013 Pearson Education, Inc.
Cardiac Output (CO)
• CO = SV × HR; normal = 5.0-5.5 L/min • Determined by venous return, and neural and hormonal controls • Resting heart rate maintained by cardioinhibitory center via parasympathetic vagus nerves • Stroke volume controlled by venous return (EDV) © 2013 Pearson Education, Inc.
Cardiac Output (CO)
• During stress, cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation – ESV decreases and MAP increases © 2013 Pearson Education, Inc.
Figure 19.8 Major factors enhancing cardiac output.
Exercise BP activates cardiac centers in medulla Activity of respiratory pump (ventral body cavity pressure) Activity of muscular pump (skeletal muscles) Sympathetic venoconstriction Sympathetic activity Epinephrine in blood Parasympathetic activity Venous return EDV Contractility of cardiac muscle ESV Stroke volume (SV) Initial stimulus Physiological response Result Cardiac output (CO = SV x HR) Heart rate (HR)
© 2013 Pearson Education, Inc.
Control of Blood Pressure
• Short-term neural and hormonal controls – Counteract fluctuations in blood pressure by altering peripheral resistance and CO • Long-term renal regulation – Counteracts fluctuations in blood pressure by altering blood volume © 2013 Pearson Education, Inc.
Short-term Mechanisms: Neural Controls
• Neural controls of peripheral resistance – Maintain MAP by altering blood vessel diameter • If low blood volume all vessels constricted except those to heart and brain – Alter blood distribution to organs in response to specific demands © 2013 Pearson Education, Inc.
Short-term Mechanisms: Neural Controls
• Neural controls operate via
reflex arcs
that involve –
Baroreceptors
– Cardiovascular center of medulla – Vasomotor fibers to heart and vascular smooth muscle – Sometimes input from chemoreceptors and higher brain centers © 2013 Pearson Education, Inc.
The Cardiovascular Center
• Clusters of sympathetic neurons in medulla oversee changes in CO and blood vessel diameter • Consists of cardiac centers and vasomotor center • Vasomotor center sends steady impulses via sympathetic efferents to blood vessels moderate constriction called
vasomotor tone
• Receives inputs from baroreceptors, chemoreceptors, and higher brain centers © 2013 Pearson Education, Inc.
Short-term Mechanisms: Baroreceptor Reflexes
•
Baroreceptors
located in – Carotid sinuses – Aortic arch – Walls of large arteries of neck and thorax © 2013 Pearson Education, Inc.
Short-term Mechanisms: Baroreceptor Reflexes
• Increased blood pressure stimulates baroreceptors to increase input to vasomotor center – Inhibits vasomotor and cardioacceleratory centers, causing arteriolar dilation and venodilation – Stimulates cardioinhibitory center – decreased blood pressure © 2013 Pearson Education, Inc.
Short-term Mechanisms: Baroreceptor Reflexes
• Decrease in blood pressure due to – Arteriolar vasodilation – Venodilation – Decreased cardiac output © 2013 Pearson Education, Inc.
Short-term Mechanisms: Baroreceptor Reflexes
• If MAP low – Reflex vasoconstriction increased blood pressure increased CO – Ex. Upon standing baroreceptors of
carotid sinus reflex
protect blood to brain; in systemic circuit as whole
aortic reflex
maintains blood pressure • Baroreceptors ineffective if altered blood pressure sustained © 2013 Pearson Education, Inc.
Figure 19.9 Baroreceptor reflexes that help maintain blood pressure homeostasis.
3 Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory center) and inhibit vasomotor center.
4a Sympathetic impulses to heart cause HR, contractility, and CO.
2 Baroreceptors in carotid sinuses and aortic arch are stimulated.
4b Rate of vasomotor impulses allows vasodilation, causing R.
1 Stimulus: Blood pressure (arterial blood pressure rises above normal range).
5 CO and R return blood pressure to homeostatic range.
5 CO and R return blood pressure to homeostatic range.
4b Vasomotor fibers stimulate vasoconstriction, causing R.
1 Stimulus: Blood pressure (arterial blood pressure falls below normal range).
2 Baroreceptors in carotid sinuses and aortic arch are inhibited.
© 2013 Pearson Education, Inc.
4a Sympathetic impulses to heart cause HR, contractility, and CO.
3 Impulses from baroreceptors activate cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center.
Slide 1
Short-term Mechanisms: Chemoreceptor Reflexes
• Chemoreceptors in aortic arch and large arteries of neck detect increase in CO 2 , or drop in pH or O 2 • Cause increased blood pressure by – Signaling cardioacceleratory center increase CO – Signaling vasomotor center increase vasoconstriction © 2013 Pearson Education, Inc.
Short-term Mechanisms: Influence of Higher Brain Centers
• Reflexes in medulla • Hypothalamus and cerebral cortex can modify arterial pressure via relays to medulla • Hypothalamus increases blood pressure during stress • Hypothalamus mediates redistribution of blood flow during exercise and changes in body temperature © 2013 Pearson Education, Inc.
Short-term Mechanisms: Hormonal Controls
• Short term regulation via changes in peripheral resistance • Long term regulation via changes in blood volume © 2013 Pearson Education, Inc.
Short-term Mechanisms: Hormonal Controls
• Cause increased blood pressure – Epinephrine and norepinephrine from adrenal gland increased CO and vasoconstriction – Angiotensin II stimulates vasoconstriction – High ADH levels cause vasoconstriction • Cause lowered blood pressure – Atrial natriuretic peptide causes decreased blood volume by antagonizing aldosterone © 2013 Pearson Education, Inc.
Figure 19.10 Direct and indirect (hormonal) mechanisms for renal control of blood pressure.
Direct renal mechanism Indirect renal mechanism (renin-angiotensin-aldosterone) Arterial pressure Arterial pressure Initial stimulus Physiological response Result Inhibits baroreceptors Sympathetic nervous system activity Filtration by kidneys Angiotensinogen Renin release from kidneys Angiotensin I Angiotensin converting enzyme (ACE) Angiotensin II Urine formation Blood volume Adrenal cortex Aldosterone Secretes ADH release by posterior pituitary Sodium reabsorption by kidneys Water reabsorption by kidneys Thirst via hypothalamus Water intake Vasoconstriction; peripheral resistance Blood volume Mean arterial pressure Mean arterial pressure
© 2013 Pearson Education, Inc.
Long-term Mechanisms: Renal Regulation
• • • Baroreceptors quickly adapt to chronic high or low BP so are ineffective Long-term mechanisms control BP by altering blood volume via kidneys Kidneys regulate arterial blood pressure 1. Direct renal mechanism 2. Indirect renal (renin-angiotensin-aldosterone) mechanism © 2013 Pearson Education, Inc.
Direct Renal Mechanism
• Alters blood volume independently of hormones – Increased BP or blood volume causes elimination of more urine, thus reducing BP – Decreased BP or blood volume causes kidneys to conserve water, and BP rises © 2013 Pearson Education, Inc.
Indirect Mechanism
• The renin-angiotensin-aldosterone mechanism – Arterial blood pressure release of renin – Renin catalyzes conversion of angiotensinogen from liver to angiotensin I – Angiotensin converting enzyme, especially from lungs, converts angiotensin I to angiotensin II © 2013 Pearson Education, Inc.
Functions of Angiotensin II
• Increases blood volume – Stimulates aldosterone secretion – Causes ADH release – Triggers hypothalamic thirst center • Causes vasoconstriction directly increasing blood pressure © 2013 Pearson Education, Inc.
Figure 19.10 Direct and indirect (hormonal) mechanisms for renal control of blood pressure.
Direct renal mechanism Indirect renal mechanism (renin-angiotensin-aldosterone) Arterial pressure Arterial pressure Initial stimulus Physiological response Result Inhibits baroreceptors Sympathetic nervous system activity Filtration by kidneys Angiotensinogen Renin release from kidneys Angiotensin I Angiotensin converting enzyme (ACE) Angiotensin II Urine formation Blood volume Adrenal cortex Aldosterone Secretes ADH release by posterior pituitary Sodium reabsorption by kidneys Water reabsorption by kidneys Thirst via hypothalamus Water intake Vasoconstriction; peripheral resistance Blood volume Mean arterial pressure Mean arterial pressure
© 2013 Pearson Education, Inc.
Figure 19.11 Factors that increase MAP.
Activity of muscular pump and respiratory pump Release of ANP Conservation of Na + and water by kidneys Fluid loss from hemorrhage, excessive sweating Blood volume Blood pressure Crisis stressors: exercise, trauma, body temperature Vasomotor tone; bloodborne chemicals (epinephrine, NE, ADH, angiotensin II) Dehydration, high hematocrit Blood pH O 2 CO 2 Body size Blood volume Venous return Baroreceptors Chemoreceptors Activation of vasomotor and cardio acceleratory centers in brain stem Stroke volume Heart rate Initial stimulus Physiological response Result Cardiac output
© 2013 Pearson Education, Inc.
Diameter of blood vessels Mean arterial pressure (MAP) Blood viscosity Blood vessel length Peripheral resistance
Monitoring Circulatory Efficiency
•
Vital signs
: pulse and blood pressure, along with respiratory rate and body temperature •
Pulse
: pressure wave caused by expansion and recoil of arteries •
Radial pulse
(taken at the wrist) routinely used •
Pressure points
where arteries close to body surface – Can be compressed to stop blood flow © 2013 Pearson Education, Inc.
Figure 19.12 Body sites where the pulse is most easily palpated.
Superficial temporal artery Facial artery Common carotid artery Brachial artery Radial artery Femoral artery Popliteal artery
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Posterior tibial artery Dorsalis pedis artery
Measuring Blood Pressure
• Systemic arterial BP – Measured indirectly by
auscultatory method
using a
sphygmomanometer
– Pressure increased in cuff until it exceeds systolic pressure in brachial artery – Pressure released slowly and examiner listens for
sounds of Korotkoff
with a stethoscope © 2013 Pearson Education, Inc.
Measuring Blood Pressure
• •
Systolic pressure
, normally less than 120 mm Hg, is pressure when sounds first occur as blood starts to spurt through artery
Diastolic pressure
, normally less than 80 mm Hg, is pressure when sounds disappear because artery no longer constricted; blood flowing freely © 2013 Pearson Education, Inc.
Variations in Blood Pressure
• Transient elevations occur during changes in posture, physical exertion, emotional upset, fever.
• Age, sex, weight, race, mood, and posture may cause BP to vary © 2013 Pearson Education, Inc.
Alterations in Blood Pressure
•
Hypertension
: high blood pressure – Sustained elevated arterial pressure of 140/90 or higher –
Prehypertension
if values elevated but not yet in hypertension range • May be transient adaptations during fever, physical exertion, and emotional upset • Often persistent in obese people © 2013 Pearson Education, Inc.
Homeostatic Imbalance: Hypertension
• Prolonged hypertension major cause of heart failure, vascular disease, renal failure, and stroke – Heart must work harder myocardium enlarges, weakens, becomes flabby – Also accelerates atherosclerosis © 2013 Pearson Education, Inc.
Primary or Essential Hypertension
• 90% of hypertensive conditions • No underlying cause identified – Risk factors include heredity, diet, obesity, age, diabetes mellitus, stress, and smoking • No cure but can be controlled – Restrict salt, fat, cholesterol intake – Increase exercise, lose weight, stop smoking – Antihypertensive drugs © 2013 Pearson Education, Inc.
Homeostatic Imbalance: Hypertension
•
Secondary hypertension
less common – Due to identifiable disorders including obstructed renal arteries, kidney disease, and endocrine disorders such as hyperthyroidism and Cushing's syndrome – Treatment focuses on correcting underlying cause © 2013 Pearson Education, Inc.
Alterations in Blood Pressure
•
Hypotension
: low blood pressure – Blood pressure below 90/60 mm Hg – Usually not a concern • Only if leads to inadequate blood flow to tissues – Often associated with long life and lack of cardiovascular illness © 2013 Pearson Education, Inc.
Homeostatic Imbalance: Hypotension
• •
Orthostatic hypotension
: temporary low BP and dizziness when suddenly rising from sitting or reclining position •
Chronic hypotension
: hint of poor nutrition and warning sign for Addison's disease or hypothyroidism
Acute hypotension
: important sign of circulatory shock; threat for surgical patients and those in ICU © 2013 Pearson Education, Inc.
Circulatory Shock
• • •
Hypovolemic shock
: results from large scale blood loss
Vascular shock
: results from extreme vasodilation and decreased peripheral resistance
Cardiogenic shock
results when an inefficient heart cannot sustain adequate circulation © 2013 Pearson Education, Inc.
Figure 19.18 Events and signs of hypovolemic shock.
Acute bleeding (or other events that reduce blood volume) leads to: 1. Inadequate tissue perfusion resulting in O 2 and nutrients to cells 2. Anaerobic metabolism by cells, so lactic acid accumulates 3. Movement of interstitial fluid into blood, so tissues dehydrate Initial stimulus Physiological response Signs and symptoms Result Chemoreceptors activated (by in blood pH)
Major effect Minor effect
Baroreceptor firing reduced (by blood volume and pressure) Respiratory centers activated Cardioacceleratory and vasomotor centers activated Rate and depth of breathing Heart rate Tachycardia; weak, thready pulse Sympathetic nervous system activated Hypothalamus activated (by blood pressure) ADH released Neurons depressed by pH
Brain
Intense vasoconstriction (only heart and brain spared)
Adrenal cortex
Renal blood flow Renin released Angiotensin II produced in blood Aldosterone released Skin becomes cold, clammy, and cyanotic Kidneys retain salt and water Urine output
Kidneys
Water retention Central nervous system depressed Thirst Restlessness (early sign) Coma (late sign) CO 2 blown off; blood pH rises
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Blood pressure maintained; if fluid volume continues to decrease, BP ultimately drops. BP is a late sign.
Figure 19.15 Intrinsic and extrinsic control of arteriolar smooth muscle in the systemic circulation.
Vasodilators Metabolic O 2 CO 2 H + K + • Prostaglandins • Adenosine • Nitric oxide Neuronal Sympathetic tone Hormonal • Atrial natriuretic peptide Intrinsic mechanisms (autoregulation) • Metabolic or myogenic controls • Distribute blood flow to individual organs and tissues as needed Myogenic • Stretch Metabolic • Endothelins Vasoconstrictors Neuronal Sympathetic tone Hormonal • Angiotensin II • Antidiuretic hormone • Epinephrine • Norepinephrine
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Extrinsic mechanisms • Neuronal or hormonal controls • Maintain mean arterial pressure (MAP) • Redistribute blood during exercise and thermoregulation
Hydrostatic Pressures
•
Capillary hydrostatic pressure
(HP c ) (capillary blood pressure) – Tends to force fluids through capillary walls – Greater at arterial end (35 mm Hg) of bed than at venule end (17 mm Hg) •
Interstitial fluid hydrostatic pressure
(HP if ) – Pressure that would push fluid into vessel – Usually assumed to be zero because of lymphatic vessels © 2013 Pearson Education, Inc.
Colloid Osmotic Pressures
•
Capillary colloid osmotic pressure
(
oncotic pressure
) (OP c ) – Created by nondiffusible plasma proteins, which draw water toward themselves – ~26 mm Hg • Interstitial fluid osmotic pressure (OP if ) – Low (~1 mm Hg) due to low protein content © 2013 Pearson Education, Inc.
Hydrostatic-osmotic Pressure Interactions: Net Filtration Pressure (NFP)
• NFP—comprises all forces acting on capillary bed – NFP = (HP c + OP if ) – (HP if + OP c ) • Net fluid flow out at arterial end • Net fluid flow in at venous end • More leaves than is returned – Excess fluid returned to blood via lymphatic system © 2013 Pearson Education, Inc.
Capillary Exchange of Respiratory Gases and Nutrients
• Diffusion down concentration gradients – O 2 and nutrients from blood to tissues – CO 2 and metabolic wastes from tissues to blood • Lipid-soluble molecules diffuse directly through endothelial membranes • Water-soluble solutes pass through clefts and fenestrations • Larger molecules, such as proteins, are actively transported in pinocytotic vesicles or caveolae © 2013 Pearson Education, Inc.
© 2013 Pearson Education, Inc.
Figure 19.21b Major arteries of the systemic circulation.
Arteries of the head and trunk Internal carotid artery External carotid artery Common carotid arteries Vertebral artery Subclavian artery Brachiocephalic trunk Aortic arch Ascending aorta Coronary artery Celiac trunk Abdominal aorta Superior mesenteric artery Renal artery Gonadal artery Inferior mesenteric artery Common iliac artery Internal iliac artery Illustration, anterior view
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Arteries that supply the upper limb Subclavian artery Axillary artery Brachial artery Radial artery Ulnar artery Deep palmar arch Superficial palmar arch Digital arteries Arteries that supply the lower limb External iliac artery Femoral artery Popliteal artery Anterior tibial artery Posterior tibial artery Arcuate artery
Figure 19.22b Arteries of the head, neck, and brain.
Basilar artery Vertebral artery Internal carotid artery External carotid artery Common carotid artery Thyrocervical trunk Costocervical trunk Subclavian artery Axillary artery
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Arteries of the head and neck, right aspect Ophthalmic artery Branches of the external carotid artery • Superficial temporal artery • Maxillary artery • Occipital artery • Facial artery • Lingual artery • Superior thyroid artery Larynx Thyroid gland (overlying trachea) Clavicle (cut) Brachiocephalic trunk Internal thoracic artery
Figure 19.22d Arteries of the head, neck, and brain.
Anterior
Frontal lobe Optic chiasma Middle cerebral artery Internal carotid artery Mammillary body Temporal lobe Pons Occipital lobe Cerebral arterial circle
(circle of Willis)
• Anterior communicating artery • Anterior cerebral artery • Posterior communicating artery • Posterior cerebral artery Basilar artery Vertebral artery Cerebellum
Posterior
Major arteries serving the brain (inferior view, right side of cerebellum and part of right temporal lobe removed)
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Figure 19.24b Arteries of the abdomen.
Liver (cut) Diaphragm Inferior vena cava Celiac trunk Common hepatic artery Hepatic artery proper Gastroduodenal artery Right gastric artery Gallbladder Pancreas (major portion lies posterior to stomach) Esophagus Left gastric artery Stomach Splenic artery Left gastroepiploic artery Spleen Right gastroepiploic artery Duodenum Abdominal aorta Superior mesenteric artery The celiac trunk and its major branches.
The left half of the liver has been removed.
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Figure 19.24c Arteries of the abdomen.
Hiatus (opening) for inferior vena cava Hiatus (opening) for esophagus Adrenal (suprarenal) gland Celiac trunk Kidney Abdominal aorta Lumbar arteries Ureter Median sacral artery Major branches of the abdominal aorta.
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Diaphragm Inferior phrenic artery Middle suprarenal artery Renal artery Superior mesenteric artery Gonadal (testicular or ovarian) artery Inferior mesenteric artery Common iliac artery
Figure 19.24d Arteries of the abdomen.
Celiac trunk Superior mesenteric artery Branches of the superior mesenteric artery • Middle colic artery • Intestinal arteries • Right colic artery • Ileocolic artery Ascending colon Right common iliac artery Ileum Cecum Appendix Distribution of the superior and inferior mesenteric arteries.
The transverse colon has been pulled superiorly.
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Transverse colon Aorta Inferior mesenteric artery Branches of the inferior mesenteric artery • Left colic artery • Sigmoidal arteries • Superior rectal artery Descending colon Sigmoid colon Rectum
Figure 19.25b Arteries of the right pelvis and lower limb.
Common iliac artery Internal iliac artery Superior gluteal artery External iliac artery Deep artery of thigh Lateral circumflex femoral artery Medial circumflex femoral artery Obturator artery Femoral artery Adductor hiatus Popliteal artery
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Anterior tibial artery Posterior tibial artery Fibular artery Dorsalis pedis artery Arcuate artery Dorsal metatarsal arteries Anterior view
Figure 19.25c Arteries of the right pelvis and lower limb.
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Posterior tibial artery Lateral plantar artery Medial plantar artery Posterior view Popliteal artery Anterior tibial artery Fibular artery Dorsalis pedis artery (from top of foot) Plantar arch
Figure 19.26b Major veins of the systemic circulation.
Veins of the head and trunk Dural venous sinuses External jugular vein Vertebral vein Internal jugular vein Right and left brachiocephalic veins Superior vena cava Great cardiac vein Hepatic veins Splenic vein Hepatic portal vein Renal vein Superior mesenteric vein Inferior mesenteric vein Inferior vena cava Common iliac vein Internal iliac vein Veins that drain the upper limb Subclavian vein Axillary vein Cephalic vein Brachial vein Basilic vein Median cubital vein Ulnar vein Radial vein Digital veins Veins that drain the lower limb External iliac vein Femoral vein Great saphenous vein Popliteal vein Posterior tibial vein Anterior tibial vein Small saphenous vein Dorsal venous arch Dorsal metatarsal veins Illustration, anterior view.
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The vessels of the pulmonary circulation are not shown.
Figure 19.27b Venous drainage of the head, neck, and brain.
Ophthalmic vein Superficial temporal vein Facial vein Occipital vein Posterior auricular vein External jugular vein Vertebral vein Internal jugular vein Superior and middle thyroid veins Brachiocephalic vein Subclavian vein
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Superior vena cava Veins of the head and neck, right superficial aspect
Figure 19.27c Venous drainage of the head, neck, and brain.
Superior sagittal sinus Falx cerebri Inferior sagittal sinus Straight sinus Cavernous sinus Transverse sinuses Sigmoid sinus Jugular foramen Right internal jugular vein Dural venous sinuses of the brain
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Figure 19.28b Veins of the thorax and right upper limb.
Brachiocephalic veins Right subclavian vein Axillary vein Brachial vein Cephalic vein Basilic vein Median cubital vein Median antebrachial vein Cephalic vein Radial vein Basilic vein Ulnar vein Anterior view
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Deep venous palmar arch Superficial venous palmar arch Digital veins Internal jugular vein External jugular vein Left subclavian vein Superior vena cava Azygos vein Accessory hemiazygos vein Hemiazygos vein Posterior intercostals Inferior vena cava Ascending lumbar vein
Figure 19.29a Veins of the abdomen.
Cystic vein
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Hepatic portal system Suprarenal veins Renal veins Gonadal veins Lumbar veins R. ascending lumbar vein Common iliac veins Schematic flowchart.
Inferior vena cava Inferior phrenic veins Hepatic veins Hepatic portal vein Superior mesenteric vein Splenic vein Inferior mesenteric vein L. ascending lumbar vein External iliac vein Internal iliac veins
Figure 19.29b Veins of the abdomen.
Hepatic veins Inferior vena cava Right suprarenal vein Inferior phrenic vein Left suprarenal vein Renal veins Right gonadal vein Left ascending lumbar vein Lumbar veins Left gonadal vein Common iliac vein External iliac vein Internal iliac vein Tributaries of the inferior vena cava.
Venous drainage of abdominal organs not drained by the hepatic portal vein.
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Figure 19.29c Veins of the abdomen.
Hepatic veins Liver Hepatic portal vein Small intestine Rectum The hepatic portal circulation.
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Gastric veins Spleen Inferior vena cava Splenic vein Right gastroepiploic vein Inferior mesenteric vein Superior mesenteric vein Large intestine
Figure 19.30b Veins of the right lower limb.
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Popliteal vein Small saphenous vein Fibular vein Anterior tibial vein Dorsalis pedis vein Dorsal venous arch Dorsal metatarsal veins Anterior view Common iliac vein Internal iliac vein External iliac vein Inguinal ligament Femoral vein Great saphenous vein (superficial)