PowerPoint® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community Ninth Edition College

Human Anatomy & Physiology

CHAPTER

19

The Cardiovascular System: Blood Vessels: Part A © Annie Leibovitz/Contact Press Images

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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

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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

Valve

Tunica externa (collagen fibers) • Vasa vasorum

Lumen

Lumen

Artery

Capillary network

Vein

Basement membrane Endothelial cells

Capillary © 2013 Pearson Education, Inc.

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

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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

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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

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Figure 19.2 The relationship of blood vessels to each other and to lymphatic vessels.

Venous system

Large veins (capacitance vessels)

Arterial system

Heart Elastic arteries (conducting arteries)

Large lymphatic vessels Lymph node Lymphatic system Small veins (capacitance vessels)

Muscular arteries (distributing arteries)

Arteriovenous anastomosis Lymphatic capillaries Sinusoid Arterioles (resistance vessels) Terminal arteriole

Postcapillary venule © 2013 Pearson Education, Inc.

Thoroughfare channel

Capillaries (exchange vessels)

Precapillary sphincter

Metarteriole

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

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Arterial System: Muscular Arteries • Distal to elastic arteries – Deliver blood to body organs

• Thick tunica media with more smooth muscle • Active in vasoconstriction

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Arterial System: Arterioles • Smallest arteries • Lead to capillary beds • Control flow into capillary beds via vasodilation and vasoconstriction

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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

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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

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Capillaries • Three structural types 1. Continuous capillaries 2. Fenestrated capillaries 3. Sinusoid capillaries (sinusoids)

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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

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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). © 2013 Pearson Education, Inc.

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)

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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). © 2013 Pearson Education, Inc.

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

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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). © 2013 Pearson Education, Inc.

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

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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

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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

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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.

Terminal arteriole

Postcapillary venule

Sphincters closed—blood flows through metarteriole – thoroughfare channel and bypasses true capillaries. © 2013 Pearson Education, Inc.

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

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Figure 19.5 Relative proportion of blood volume throughout the cardiovascular system.

Pulmonary blood vessels 12% Systemic arteries and arterioles 15%

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)

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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

Vein

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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

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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

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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

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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

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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

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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 Systolic pressure 100 Mean pressure 80 60

40

Diastolic pressure

20 0

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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)

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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

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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

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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

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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

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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

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Maintaining Blood Pressure • F =  P/R; CO =  P/R;  P = CO × R • Blood pressure = CO × PR (and CO depends on blood volume) • Blood pressure varies directly with CO, PR, and blood volume • Changes in one variable quickly compensated for by changes in other variables

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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)

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Cardiac Output (CO) • During stress, cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation – ESV decreases and MAP increases

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Figure 19.8 Major factors enhancing cardiac output.

Exercise

BP activates cardiac centers in medulla

Activity of respiratory pump (ventral body cavity pressure)

Sympathetic activity

Parasympathetic activity

Activity of muscular pump (skeletal muscles)

Epinephrine in blood Sympathetic venoconstriction

Venous return

Contractility of cardiac muscle

ESV

EDV

Stroke volume (SV)

Heart rate (HR)

Initial stimulus Physiological response Result

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Cardiac output (CO = SV x HR)

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

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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

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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

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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

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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

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Short-term Mechanisms: Baroreceptor Reflexes • Decrease in blood pressure due to – Arteriolar vasodilation – Venodilation – Decreased cardiac output

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Short-term Mechanisms: Baroreceptor Reflexes • If MAP low –  Reflex vasoconstriction  increased CO  increased blood pressure – 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

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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.

1 Stimulus:

5 CO and R return blood pressure to homeostatic range.

Blood pressure (arterial blood pressure falls below normal range). 4b Vasomotor fibers stimulate vasoconstriction, causing R.

2 Baroreceptors in carotid sinuses and aortic arch are inhibited. 4a Sympathetic impulses to heart cause HR, contractility, and CO.

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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 CO2, or drop in pH or O2 • Cause increased blood pressure by – Signaling cardioacceleratory center  increase CO – Signaling vasomotor center  increase vasoconstriction

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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

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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

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Figure 19.10 Direct and indirect (hormonal) mechanisms for renal control of blood pressure. Direct renal mechanism

Arterial pressure

Indirect renal mechanism (renin-angiotensin-aldosterone) Initial stimulus

Arterial pressure

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

Adrenal cortex

ADH release by posterior pituitary

Thirst via hypothalamus

Secretes Aldosterone

Blood volume Sodium reabsorption by kidneys

Water reabsorption by kidneys

Water intake

Blood volume

Mean arterial pressure

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Mean arterial pressure

Vasoconstriction; peripheral resistance

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

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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

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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

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Functions of Angiotensin II • Increases blood volume – Stimulates aldosterone secretion – Causes ADH release – Triggers hypothalamic thirst center

• Causes vasoconstriction directly increasing blood pressure

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Figure 19.10 Direct and indirect (hormonal) mechanisms for renal control of blood pressure. Direct renal mechanism

Arterial pressure

Indirect renal mechanism (renin-angiotensin-aldosterone) Initial stimulus

Arterial pressure

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

Adrenal cortex

ADH release by posterior pituitary

Thirst via hypothalamus

Secretes Aldosterone

Blood volume Sodium reabsorption by kidneys

Water reabsorption by kidneys

Water intake

Blood volume

Mean arterial pressure

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Mean arterial pressure

Vasoconstriction; peripheral resistance

Figure 19.11 Factors that increase MAP. Activity of muscular pump and respiratory pump

Release of ANP

Fluid loss from hemorrhage, excessive sweating

Crisis stressors: exercise, trauma, body temperature

Conservation of Na+ and water by kidneys

Blood volume Blood pressure

Blood pH O2 CO2

Blood volume

Baroreceptors

Chemoreceptors

Venous return

Activation of vasomotor and cardioacceleratory centers in brain stem

Stroke volume

Heart rate

Vasomotor tone; bloodborne chemicals (epinephrine, NE, ADH, angiotensin II)

Diameter of blood vessels

Cardiac output

Physiological response

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Blood viscosity

Body size

Blood vessel length

Peripheral resistance

Initial stimulus

Result

Dehydration, high hematocrit

Mean arterial pressure (MAP)

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

Posterior tibial artery

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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

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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

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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

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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

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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

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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

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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

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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

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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 largescale blood loss • Vascular shock: results from extreme vasodilation and decreased peripheral resistance • Cardiogenic shock results when an inefficient heart cannot sustain adequate circulation

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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 O2 and nutrients to cells

Initial stimulus Physiological response Signs and symptoms Result

2. Anaerobic metabolism by cells, so lactic acid accumulates 3. Movement of interstitial fluid into blood, so tissues dehydrate

Chemoreceptors activated (by in blood pH)

Baroreceptor firing reduced (by blood volume and pressure)

Hypothalamus activated (by blood pressure)

Brain

Minor effect

Major effect Respiratory centers activated

Cardioacceleratory and vasomotor centers activated

Heart rate

Sympathetic nervous system activated

ADH released

Neurons depressed by pH

Intense vasoconstriction (only heart and brain spared)

Central nervous system depressed Kidneys

Renal blood flow

Adrenal cortex

Renin released

Angiotensin II produced in blood

Aldosterone released

Rate and depth of breathing

CO2 blown off; blood pH rises

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Tachycardia; weak, thready pulse

Kidneys retain salt and water

Skin becomes cold, clammy, and cyanotic

Blood pressure maintained; if fluid volume continues to decrease, BP ultimately drops. BP is a late sign.

Water retention

Urine output

Thirst

Restlessness (early sign)

Coma (late sign)

Figure 19.15 Intrinsic and extrinsic control of arteriolar smooth muscle in the systemic circulation. Vasodilators

Metabolic O2 CO2 H+ K+ • Prostaglandins • Adenosine • Nitric oxide

Neuronal Sympathetic tone

Hormonal • Atrial natriuretic peptide

Extrinsic mechanisms

Intrinsic mechanisms (autoregulation)

Vasoconstrictors

• Metabolic or myogenic controls • Distribute blood flow to individual organs and tissues as needed

Myogenic • Stretch

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Neuronal Sympathetic tone

Metabolic

Hormonal

• Endothelins

• Angiotensin II • Antidiuretic hormone • Epinephrine • Norepinephrine

• Neuronal or hormonal controls • Maintain mean arterial pressure (MAP) • Redistribute blood during exercise and thermoregulation

Hydrostatic Pressures • Capillary hydrostatic pressure (HPc) (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 (HPif) – 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) (OPc) – Created by nondiffusible plasma proteins, which draw water toward themselves – ~26 mm Hg

• Interstitial fluid osmotic pressure (OPif) – Low (~1 mm Hg) due to low protein content

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Hydrostatic-osmotic Pressure Interactions: Net Filtration Pressure (NFP) • NFP—comprises all forces acting on capillary bed – NFP = (HPc + OPif) – (HPif + OPc)

• 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

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Capillary Exchange of Respiratory Gases and Nutrients • Diffusion down concentration gradients – O2 and nutrients from blood to tissues – CO2 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

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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

Arteries that supply the upper limb Subclavian artery Axillary artery Brachial artery

Aortic arch Ascending aorta

Coronary artery Celiac trunk Abdominal aorta Superior mesenteric artery Renal artery Gonadal artery

Radial artery Ulnar artery Deep palmar arch Superficial palmar arch Digital arteries Arteries that supply the lower limb External iliac artery

Inferior mesenteric artery

Femoral artery

Common iliac artery

Popliteal artery

Internal iliac artery

Anterior tibial artery

Posterior tibial artery Illustration, anterior view © 2013 Pearson Education, Inc.

Arcuate artery

Figure 19.22b Arteries of the head, neck, and brain.

Ophthalmic artery

Basilar artery Vertebral artery Internal carotid artery External carotid artery Common carotid artery Thyrocervical trunk Costocervical trunk Subclavian artery Axillary artery

Arteries of the head and neck, right aspect © 2013 Pearson Education, Inc.

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 Cerebral arterial circle (circle of Willis)

Frontal lobe Optic chiasma

• Anterior communicating artery

Middle cerebral artery

• Anterior cerebral artery

Internal carotid artery

• Posterior communicating artery

Mammillary body

• Posterior cerebral artery Basilar artery

Temporal lobe

Vertebral artery

Pons

Occipital lobe Cerebellum Posterior Major arteries serving the brain (inferior view, right side of cerebellum and part of right temporal lobe removed) © 2013 Pearson Education, Inc.

Figure 19.24b Arteries of the abdomen.

Liver (cut) Inferior vena cava Celiac trunk Common hepatic artery Hepatic artery proper Gastroduodenal artery Right gastric artery

Diaphragm Esophagus Left gastric artery Stomach Splenic artery Left gastroepiploic artery Spleen

Gallbladder Pancreas (major portion lies posterior to stomach)

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

Diaphragm

Inferior phrenic artery

Adrenal (suprarenal) gland

Middle suprarenal artery

Celiac trunk

Renal artery

Kidney

Superior mesenteric artery

Abdominal aorta Lumbar arteries Ureter Median sacral artery

Major branches of the abdominal aorta.

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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

Transverse colon Aorta Inferior mesenteric artery Branches of the inferior mesenteric artery • Left colic artery • Sigmoidal arteries • Superior rectal artery Descending colon

Cecum Appendix

Distribution of the superior and inferior mesenteric arteries. The transverse colon has been pulled superiorly. © 2013 Pearson Education, Inc.

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

Anterior tibial artery Posterior tibial artery Fibular artery Dorsalis pedis artery Arcuate artery Dorsal metatarsal arteries © 2013 Pearson Education, Inc.

Anterior view

Figure 19.25c Arteries of the right pelvis and lower limb.

Popliteal artery Anterior tibial artery

Posterior tibial artery

Lateral plantar artery Medial plantar artery

© 2013 Pearson Education, Inc.

Posterior view

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. The vessels of the pulmonary circulation are not shown. © 2013 Pearson Education, Inc.

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 Superior vena cava Veins of the head and neck, right superficial aspect © 2013 Pearson Education, Inc.

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 © 2013 Pearson Education, Inc.

Figure 19.28b Veins of the thorax and right upper limb.

Brachiocephalic veins Right subclavian vein Axillary vein Brachial vein Cephalic vein Basilic vein

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

Median cubital vein Median antebrachial vein Cephalic vein Radial vein

Anterior view © 2013 Pearson Education, Inc.

Basilic vein Ulnar vein Deep venous palmar arch Superficial venous palmar arch Digital veins

Figure 19.29a Veins of the abdomen. Inferior vena cava

Cystic vein

Hepatic portal system

Inferior phrenic veins Hepatic veins

Hepatic portal vein Superior mesenteric vein Splenic vein

Suprarenal veins Renal veins

Inferior mesenteric vein

Gonadal veins

Lumbar veins

R. ascending lumbar vein

L. ascending lumbar vein

Common iliac veins External iliac vein Internal iliac veins Schematic flowchart. © 2013 Pearson Education, Inc.

Figure 19.29b Veins of the abdomen.

Hepatic veins

Inferior phrenic vein

Inferior vena cava

Right suprarenal vein

Left suprarenal vein Renal veins

Right gonadal vein

External iliac vein

Left ascending lumbar vein Lumbar veins Left gonadal vein Common iliac vein Internal iliac vein

Tributaries of the inferior vena cava. Venous drainage of abdominal organs not drained by the hepatic portal vein. © 2013 Pearson Education, Inc.

Figure 19.29c Veins of the abdomen.

Hepatic veins

Liver Hepatic portal vein

Gastric veins

Spleen Inferior vena cava Splenic vein Right gastroepiploic vein Inferior mesenteric vein Superior mesenteric vein

Small intestine Large intestine Rectum The hepatic portal circulation. © 2013 Pearson Education, Inc.

Figure 19.30b Veins of the right lower limb.

Common iliac vein Internal iliac vein External iliac vein Inguinal ligament Femoral vein

Great saphenous vein (superficial)

Popliteal vein Small saphenous vein

Fibular vein Anterior tibial vein Dorsalis pedis vein Dorsal venous arch Dorsal metatarsal veins

© 2013 Pearson Education, Inc.

Anterior view