principles of human anatomy and physiology, 11e 1 chapter 21 the cardiovascular system: blood...

Principles of Human Anatomy and Physiology, 11e

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Chapter 21

The Cardiovascular System: Blood Vessels and Hemodynamics

Lecture Outline


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INTRODUCTION

One main focus of this chapter considers hemodynamics, the means by which blood flow is altered and distributed and by which blood pressure is regulated.

The histology of blood vessels and anatomy of the primary routes of arterial and venous systems are surveyed.


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The Cardiovascular System: Blood Vessels and Hemodynamics

Structure and function of blood vessels

Hemodynamics forces involved in

circulating blood Major circulatory

routes


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STRUCTURE AND FUNCTION OF BLOOD VESSELS Angiogenesis: the growth of new blood vessels

It is an important process in the fetus and in postnatal processes

Malignant tumors secrete proteins called tumor angiogenesis factors (TAFs) that stimulate blood vessel growth to nature the tumor cells

Scientists are looking for chemicals that inhibit angiogenesis to stop tumor growth and to prevent the blindness associated with diabetes.


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Vessels

Blood vessels form a closed system of tubes that carry blood away from the heart, transport it to the tissues of the body, and then return it to the heart. Arteries carry blood from the heart to the tissues. Arterioles are small arteries that connect to capillaries. Capillaries are the site of substance exchange

between the blood and body tissues. Venules connect capillaries to larger veins. Veins convey blood from the tissues back to the heart. Vaso vasorum are small blood vessels that supply

blood to the cells of the walls of the arteries and veins.


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Arteries

The wall of an artery consists of three major layers (Figure 21.1).

Tunica interna (intima) simple squamous epithelium

known as endothelium basement membrane internal elastic lamina

Tunica media circular smooth muscle &

elastic fibers Tunica externa

elastic & collagen fibers


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Arteries

Arteries carry blood away from the heart to the tissues. The functional properties of arteries are elasticity and

contractility. Elasticity, due to the elastic tissue in the tunica internal

and media, allows arteries to accept blood under great pressure from the contraction of the ventricles and to send it on through the system.

Contractility, due to the smooth muscle in the tunica media, allows arteries to increase or decrease lumen size and to limit bleeding from wounds.


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Sympathetic Innervation

Vascular smooth muscle is innervated by sympathetic nervous system increase in stimulation causes muscle contraction or

vasoconstriction decreases diameter of vessel

injury to artery or arteriole causes muscle contraction reducing blood loss (vasospasm)

decrease in stimulation or presence of certain chemicals causes vasodilation

increases diameter of vessel nitric oxide, K+, H+ and lactic acid cause vasodilation


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Elastic Arteries Large arteries with more elastic fibers and less smooth muscle

are called elastic arteries and are able to receive blood under pressure and propel it onward (Figure 21.2).

They are also called conducting arteries because they conduct blood from the heart to medium sized muscular arteries.

They function as a pressure reservoir.


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Muscular Arteries

Medium-sized arteries with more muscle than elastic fibers in tunica media

Capable of greater vasoconstriction and vasodilation to adjust rate of flow walls are relatively thick called distributing arteries because they direct

blood flow


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Arterioles

Arterioles are very small, almost microscopic, arteries that deliver blood to capillaries (Figure 21.3).

Through vasoconstriction (decrease in the size of the lumen of a blood vessel) and vasodilation (increase in the size of the lumen of a blood vessel), arterioles assume a key role in regulating blood flow from arteries into capillaries and in altering arterial blood pressure.


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Arterioles Small arteries delivering blood to

capillaries tunica media containing few

layers of muscle Metarterioles form branches into

capillary bed to bypass capillary bed,

precapillary sphincters close & blood flows out of bed in thoroughfare channel

vasomotion is intermittent contraction & relaxation of sphincters that allow filling of capillary bed 5-10 times/minute


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Capillaries form Microcirculation Microscopic vessels that connect arterioles to venules Found near every cell in the body but more extensive in

highly active tissue (muscles, liver, kidneys & brain) entire capillary bed fills with blood when tissue is active lacking in epithelia, cornea and lens of eye & cartilage

Function is exchange of nutrients & wastes between blood and tissue fluid

Capillary walls are composed of only a single layer of cells (endothelium) and a basement membrane (Figure 21.1).


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Types of Capillaries Continuous capillaries

intercellular clefts are gaps between neighboring cells

skeletal & smooth, connective tissue and lungs

Fenestrated capillaries plasma membranes have many holes kidneys, small intestine, choroid plexuses,

ciliary process & endocrine glands Sinusoids

very large fenestrations incomplete basement membrane liver, bone marrow, spleen, anterior

pituitary, & parathyroid gland


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Venules

Small veins collecting blood from capillaries Tunica media contains only a few smooth

muscle cells & scattered fibroblasts very porous endothelium allows for escape of

many phagocytic white blood cells Venules that approach size of veins more

closely resemble structure of vein


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Veins

Veins consist of the same three tunics as arteries but have a thinner tunica interna and media and a thicker tunica externa less elastic tissue and smooth muscle thinner-walled than arteries contain valves to prevent the backflow of blood

(Figure 21.5). Vascular (venous) sinuses are veins with very thin

walls with no smooth muscle to alter their diameters. Examples are the brain’s superior sagittal sinus and the coronary sinus of the heart (Figure 21.3c).


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Veins Proportionally thinner

walls than same diameter artery tunica media less muscle lack external & internal

elastic lamina Still adaptable to

variationsin volume & pressure

Valves are thin folds of tunica interna designed to prevent backflow


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Varicose Veins Twisted, dilated superficial veins

caused by leaky venous valves congenital or mechanically stressed from prolonged

standing or pregnancy allow backflow and pooling of blood

extra pressure forces fluids into surrounding tissues nearby tissue is inflamed and tender

The most common sites for varicose veins are in the esophagus, superficial veins of the lower limbs, and veins in the anal canal (hemorrhoids). Deeper veins not susceptible because of support of surrounding muscles

The treatments for varicose veins in the lower limbs include: sclerotherapy, radiofrequency endovenous occlusion, laser occlusion, and surgical stripping


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Anastomoses Union of 2 or more arteries supplying the same body region

blockage of only one pathway has no effect circle of willis underneath brain coronary circulation of heart

Alternate route of blood flow through an anastomosis is known as collateral circulation can occur in veins and venules as well

Arteries that do not anastomose are known as end arteries. Occlusion of an end artery interrupts the blood supply to a whole segment of an organ, producing necrosis (death) of that segment.

Alternate routes to a region can also be supplied by nonanastomosing vessels

Table 21.1 summarizes the distinguishing features of the various types of blood vessels.


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Blood Distribution (Figure 21.6).

60% of blood volume at rest is in systemic veins and venules function as blood reservoir

veins of skin & abdominalorgans (liver and spleen)

blood is diverted from it intimes of need

increased muscular activityproduces venoconstriction

hemorrhage causes

venoconstriction to help

maintain blood pressure

15% of blood volume in arteries & arterioles


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Capillary Exchange Movement of materials in & out of a capillary

diffusion (most important method) Substances such as O2, CO2, glucose, amino acids,

hormones, and others diffuse down their concentration gradients.

all plasma solutes except large proteins pass freely across through lipid bilayer, fenestrations or intercellular clefts blood brain barrier does not allow diffusion of water-soluble materials

(nonfenestrated epithelium with tight junctions)

transcytosis passage of material across endothelium in tiny vesicles by

endocytosis and exocytosis large, lipid-insoluble molecules such as insulin or maternal antibodies

passing through placental circulation to fetus

bulk flow see next slide


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Bulk Flow: Filtration & Reabsorption Movement of large amount of dissolved or suspended

material in same direction move in response to pressure

from area of high pressure to area of low faster rate of movement than diffusion or osmosis

Most important for regulation of relative volumes of blood & interstitial fluid filtration is movement of material into interstitial fluid

promoted by blood hydrostatic pressure & interstitial fluid osmotic pressure

reabsorption is movement from interstitial fluid into capillaries promoted by blood colloid osmotic pressure

balance of these pressures is net filtration pressure


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Dynamics of Capillary Exchange

Starling’s law of the capillaries is that the volume of fluid & solutes reabsorbed is almost as large as the volume filtered (Figure 21.7).

910


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Net Filtration Pressure

Whether fluids leave or enter capillaries depends on net balance of pressures net outward pressure of 10 mm Hg at

arterial end of a capillary bed net inward pressure of 9 mm Hg at venous

end of a capillary bed About 85% of the filtered fluid is returned to

the capillary escaping fluid and plasma proteins are

collected by lymphatic capillaries (3 liters/day)


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Edema An abnormal increase in interstitial fluid if

filtration exceeds reabsorption result of excess filtration

increased blood pressure (hypertension) increased permeability of capillaries allows

plasma proteins to escape result of inadequate reabsorption

decreased concentration of plasma proteins lowers blood colloid osmotic pressure

inadequate synthesis or loss from liver disease, burns, malnutrition or kidney disease blockage of lymphatic vessels postoperatively or due to filarial worm infection

Often not noticeable until 30% above normal


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HEMODAYNAMICS: FACTORS AFFECTING BLOOD FLOW The distribution of cardiac output to various

tissues depends on the interplay of the pressure difference that drives the blood flow and the resistance to blood flow.

Blood pressure (BP) is the pressure exerted on the walls of a blood vessel; in clinical use, BP refers to pressure in arteries.

Cardiac output (CO) equals mean aortic blood pressure (MABP) divided by total resistance (R).


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Hemodynamics - Overview

Factors that affect blood pressure include cardiac output, blood volume, viscosity, resistance, and elasticity of arteries.

As blood leaves the aorta and flows through systemic circulation, its pressure progressively falls to 0 mm Hg by the time it reaches the right atrium (Figure 21.8).

Resistance refers to the opposition to blood flow as a result of friction between blood and the walls of the blood vessels.

Vascular resistance depends on the diameter of the blood vessel, blood viscosity, and total blood vessel length.

Systemic vascular resistance (also known as total peripheral resistance) refers to all of the vascular resistances offered by systemic blood vessels; most resistance is in arterioles, capillaries, and venules due to their small diameters.


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Hemodynamics

Factors affecting circulation pressure differences that drive the blood flow

velocity of blood flow volume of blood flow blood pressure

resistance to flow venous return

An interplay of forces result in blood flow


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Volume of Blood Flow

Cardiac output = stroke volume x heart rate

Other factors that influence cardiac output blood pressure resistance due to friction between blood

cells and blood vessel walls blood flows from areas of higher pressure to

areas of lower pressure


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Blood Pressure Pressure exerted by blood on walls of a

vessel caused by contraction of the ventricles highest in aorta

120 mm Hg during systole & 80during diastole

If heart rate increases cardiacoutput, BP rises

Pressure falls steadily insystemic circulation with distance from left ventricle 35 mm Hg entering the capillaries 0 mm Hg entering the right atrium

If decrease in blood volume is over 10%, BP drops

Water retention increases blood pressure


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Velocity of Blood Flow

The volume that flows through any tissue in a given period of time is blood flow.

The velocity of blood flow is inversely related to the cross-sectional area of blood vessels; blood flows most slowly where cross-sectional area is greatest (Figure 21.11).

Blood flow decreases from the aorta to arteries to capillaries and increases as it returns to the heart.


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Velocity of Blood Flow Speed of blood flow in cm/sec is inversely related to

cross-sectional area blood flow is slower in the

arterial branches flow in aorta is 40 cm/sec while

flow in capillaries is .1 cm/sec slow rate in capillaries allows for

exchange Blood flow becomes faster when vessels merge to

form veins Circulation time is time it takes a drop of blood to

travel from right atrium back to right atrium


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Venous Return (Figure 21.9). Volume of blood flowing back to the heart from the

systemic veins depends on pressure difference from venules (16

mm Hg) to right atrium (0 mm Hg) tricuspid valve leaky and

buildup of blood on venousside of circulation

Skeletal muscle pump contraction of muscles &

presence of valves Respiratory pump

decreased thoracic pressure and increased abdominal pressure during inhalation, moves blood into thoracic veins and the right atrium


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Clinical Application

Syncope, or fainting, refers to a sudden, temporary loss of consciousness followed by spontaneous recovery. It is most commonly due to cerebral ischemia but it may occur for several other reasons


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CONTROL OF BLOOD PRESSURE AND BLOOD FLOW


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Factors that Increase Blood Pressure


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Resistance

Friction between blood and the walls of vessels average blood vessel radius

smaller vessels offer more resistance to blood flow cause moment to moment fluctuations in pressure

blood viscosity (thickness) ratio of red blood cells to plasma volume increases in viscosity increase resistance

dehydration or polycythemia

total blood vessel length the longer the vessel, the greater the resistance to flow 200 miles of blood vessels for every pound of fat

obesity causes high blood pressure

Systemic vascular resistance is the total of above arterioles control BP by changing diameter


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Control of Blood Pressure & Flow Role of cardiovascular center

help regulate heart rate & stroke volume specific neurons regulate blood vessel diameter


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Cardiovascular Center - Overview The cardiovascular center (CV) is a group of neurons in the medulla

that regulates heart rate, contractility, and blood vessel diameter. input from higher brain regions and sensory receptors

(baroreceptors and chemoreceptors) (Figure 21.12). output from the CV flows along sympathetic and

parasympathetic fibers. Sympathetic impulses along cardioaccelerator nerves increase

heart rate and contractility. Parasympathetic impulses along vagus nerves decrease heart

rate. The sympathetic division also continually sends impulses to smooth

muscle in blood vessel walls via vasomotor nerves. The result is a moderate state of tonic contraction or vasoconstriction, called vasomotor tone.


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Input to the Cardiovascular Center

Higher brain centers such as cerebral cortex, limbic system & hypothalamus anticipation of competition increase in body temperature

Proprioceptors input during physical activity

Baroreceptors changes in pressure within blood vessels

Chemoreceptors monitor concentration of chemicals in the

blood


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Output from the Cardiovascular Center Heart

parasympathetic (vagus nerve) decrease heart rate

sympathetic (cardiac accelerator nerves) cause increase or decrease in contractility & rate

Blood vessels sympathetic vasomotor nerves

continual stimulation to arterioles in skin & abdominal viscera producing vasoconstriction (vasomotor tone)

increased stimulation produces constriction & increased BP


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Neural Regulation of Blood Pressure Baroreceptors are important pressure-sensitive

sensory neurons that monitor stretching of the walls of blood vessels and the atria. The cardiac sinus reflex is concerned with

maintaining normal blood pressure in the brain and is initiated by baroreceptors in the wall of the carotid sinus (Figure 21.13).

The aortic reflex is concerned with general systemic blood pressure and is initiated by baroreceptors in the wall of the arch of the aorta or attached to the arch.

If blood pressure falls, the baroreceptor reflexes accelerate heart rate, increase force of contraction, and promote vasoconstriction (Figure 21.14).


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Neural Regulation of Blood Pressure

Baroreceptor reflexes carotid sinus reflex

swellings in internal carotid artery wall glossopharyngeal nerve to

cardiovascular center in medulla maintains normal BP in the brain

aortic reflex receptors in wall of ascending aorta vagus nerve to cardiovascular center maintains general systemic BP

If feedback is decreased, CV center reduces parasympathetic & increases sympathetic stimulation of the heart


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Innervation of the Heart

Speed up the heart with sympathetic stimulation Slow it down with parasympathetic stimulation (X) Sensory information from baroreceptors (IX)


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Carotid Sinus Massage & Syncope

Carotid sinus massage can slow heart rate in paroxysmal superventricular tachycardia

Stimulation (careful neck massage) over the carotid sinus lowers heart rate paroxysmal superventricular tachycardia

tachycardia originating from the atria

Anything that puts pressure on carotid sinus tight collar or hyperextension of the neck may slow heart rate & cause carotid sinus

syncope or fainting


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Syncope Fainting or a sudden, temporary loss of consciousness

not due to trauma due to cerebral ischemia or lack of blood flow to the brain

Causes vasodepressor syncope = sudden emotional stress situational syncope = pressure stress of coughing,

defecation, or urination drug-induced syncope = antihypertensives, diuretics,

vasodilators and tranquilizers orthostatic hypotension = decrease in BP upon standing


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Chemoreceptor Reflexes

Carotid bodies and aortic bodies detect changes in blood levels of O2, CO2,

and H+ (hypoxia, hypercapnia or acidosis ) causes stimulation of cardiovascular center increases sympathetic stimulation to

arterioles & veins vasoconstriction and increase in blood

pressure Also changes breathing rates as well


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Hormonal Regulation of Blood Pressure Renin-angiotensin-aldosterone system

decrease in BP or decreased blood flow to kidney release of renin / results in formation angiotensin II

systemic vasoconstriction causes release aldosterone (H2O & Na+ reabsorption)

Epinephrine & norepinephrine increases heart rate & force of contraction causes vasoconstriction in skin & abdominal organs vasodilation in cardiac & skeletal muscle

ADH causes vasoconstriction ANP (atrial natriuretic peptide) lowers BP

causes vasodilation & loss of salt and water in the urine Table 21.1 summarizes the relationship between

hormones and blood pressure regulation.


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Local Regulation of Blood Pressure The ability of a tissue to automatically adjust its own blood

flow to match its metabolic demand for supply of O2 and nutrients and removal of wastes is called autoregulation.

Local factors cause changes in each capillary bed important for tissues that have major increases in activity

(brain, cardiac & skeletal muscle) Local changes in response to physical changes

warming & decrease in vascular stretching promotes vasodilation

Vasoactive substances released from cells alter vessel diameter (K+, H+, lactic acid, nitric oxide) systemic vessels dilate in response to low levels of O2 pulmonary vessels constrict in response to low levels of O2


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CHECKING CIRCULATION


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Evaluating Circulation Pulse is a pressure wave

alternate expansion & recoil of elastic artery after each systole of the left ventricle

pulse rate is normally between 70-80 beats/min tachycardia is rate over 100 beats/min/bradycardia under 60

Measuring blood pressure with sphygmomanometer Korotkoff sounds are heard while taking pressure systolic blood pressure is recorded during ventricular

contraction diastolic blood pressure is recorded during ventricular

relaxation provides information about systemic vascular resistance

pulse pressure is difference between systolic & diastolic normal ratio is 3:2:1 -- systolic/diastolic/pulse pressure


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Pulse Points


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Evaluating Circulation


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Blood Pressure

The normal blood pressure of a young adult male is 120/80 mm Hg (8-10 mm Hg less in a young adult female). The range of average values varies with many factors.

Pulse pressure is the difference between systolic and diastolic pressure. It normally is about 40 mm Hg and provides information about the condition of the arteries.


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SHOCK AND HOMEOSTASIS

Shock is an inadequate cardiac output that results in failure of the cardiovascular system to deliver adequate amounts of oxygen and nutrients to meet the metabolic needs of body cells. As a result, cellular membranes dysfunction, cellular metabolism is abnormal, and cellular death may eventually occur without proper treatment. inadequate perfusion cells forced to switch to anaerobic respiration lactic acid builds up cells and tissues become damaged & die


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Types of Shock

Hypovolemic shock is due to decreased blood volume. Cardiogenic shock is due to poor heart function. Vascular shock is due to inappropriate vasodilation. Obstructive shock is due to obstruction of blood flow. Homeostatic responses to shock include activation of the

renin-angiotensin-aldosterone system, secretion of ADH, activation of the sympathetic division of the ANS, and release of local vasodilators (Figure 21.16).

Signs and symptoms of shock include clammy, cool, pale skin; tachycardia; weak, rapid pulse; sweating; hypotension (systemic pressure < 90 mm HG); altered mental status; decreased urinary output; thirst; and acidosis.


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Types of Shock Hypovolemic shock due to loss of blood or body fluids

(hemorrhage, sweating, diarrhea) venous return to heart declines & output decreases

Cardiogenic shock caused by damage to pumping action of the heart (MI, ischemia, valve problems or arrhythmias)

Vascular shock causing drop inappropriate vasodilation -- anaphylatic shock, septic shock or neurogenic shock (head trauma)

Obstructive shock caused by blockage of circulation (pulmonary embolism)


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Homeostatic Responses to Shock

Mechanisms of compensation in shock attempt to return cardiac output & BP to normal activation of renin-angiotensin-aldosterone secretion of antidiuretic hormone activation of sympathetic nervous system release of local vasodilators

If blood volume drops by 10-20% or if BP does not rise sufficiently, perfusion may be inadequate -- cells start to die


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Restoring BP during Hypovolemic Shock


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Signs & Symptoms of Shock Rapid resting heart rate (sympathetic stimulation) Weak, rapid pulse due to reduced cardiac output & fast

heart rate Clammy, cool skin due to cutaneous vasoconstriction Sweating -- sympathetic stimulation Altered mental state due to cerebral ischemia Reduced urine formation -- vasoconstriction to kidneys

& increased aldosterone & antidiuretic hormone Thirst -- loss of extracellular fluid Acidosis -- buildup of lactic acid Nausea -- impaired circulation to GI tract


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CIRCULATORY ROUTES


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Introduction

The blood vessels are organized into routes that deliver blood throughout the body. Figure 21.17 shows the circulatory routes for blood flow.

The largest circulatory route is the systemic circulation.

Other routes include pulmonary circulation (Figure 21.29) and fetal circulation (Figure 21.30).


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Circulatory Routes Systemic circulation is left side

heart to body & back to heart Hepatic Portal circulation is

capillaries of GI tract to capillaries in liver

Pulmonary circulation is right-side heart to lungs & back to heart

Fetal circulation is from fetal heart through umbilical cord to placenta & back


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Systemic Circulation

The systemic circulation takes oxygenated blood from the left ventricle through the aorta to all parts of the body, including some lung tissue (but does not supply the air sacs of the lungs) and returns the deoxygenated blood to the right atrium.

The aorta is divided into the ascending aorta, arch of the aorta, and the descending aorta.

Each section gives off arteries that branch to supply the whole body. Blood returns to the heart through the systemic veins. All the veins of the

systemic circulation flow into the superior or inferior venae caveae or the coronary sinus, which in turn empty into the right atrium.

The principal arteries and veins of the systemic circulation are described and illustrated in Exhibits 21.1-21.12 and Figures 21.18-21.27.

Blood vessels are organized in the exhibits according to regions of the body. Figure 21.18a shows the major arteries. Figure 21.23 shows the major veins.


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Arterial Branches of Systemic Circulation

All are branches from aorta supplying arms, head, lower limbs and all viscera with O2 from the lungs

Aorta arises from left ventricle (thickest chamber) 4 major divisions of aorta

ascending aorta arch of aorta thoracic aorta abdominal aorta


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Aorta and Its Superior Branches

Aorta is largest artery of the body ascending aorta

2 coronary arteries supply myocardium arch of aorta -- branches to the arms & head

brachiocephalic trunk branches into right common carotid and right subclavian

left subclavian & left carotid arise independently thoracic aorta supplies branches to pericardium, esophagus,

bronchi, diaphragm, intercostal & chest muscles, mammary gland, skin, vertebrae and spinal cord


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Coronary Circulation

Right & left coronary arteries branch to supply heart muscle anterior & posterior

interventricular aa.


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Subclavian Branches Subclavian aa. pass superior

to the 1st rib gives rise to vertebral a. that

supplies blood to the Circle of Willis on the base of the brain

Become the axillary artery in the armpit

Become the brachial in the arm

Divide into radial and ulnar branches in the forearm


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Common Carotid Branches

External carotid arteries supplies structures external to skull as branches of maxillary

and superficial temporal branches Internal carotid arteries (contribute to Circle of Willis)

supply eyeballs and parts of brain

Circle of Willis


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Abdominal Aorta and Its Branches Supplies abdominal & pelvic viscera & lower extremities

celiac aa. supplies liver, stomach, spleen & pancreas superior & inferior mesenteric aa. supply intestines renal aa supply kidneys gonadal aa. supply ovaries

and testes Splits into common iliac

aa at 4th lumbar vertebrae external iliac aa supply

lower extremity internal iliac aa supply

pelvic viscera


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Visceral Branches off Abdominal Aorta

Celiac artery is first branch inferior to diaphragm left gastric artery, splenic artery, common hepatic artery

Superior mesenteric artery lies in mesentery pancreaticoduodenal, jejunal, ileocolic, ascending & middle colic aa.

Inferior mesenteric artery descending colon, sigmoid colon & rectal aa


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Arteries of the Lower Extremity

External iliac artery become femoral artery when it passes under the inguinal ligament & into the thigh femoral artery becomes popliteal artery behind the knee


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Veins of the Systemic Circulation

Drain blood from entire body & return it to right side of heart

Deep veins parallel the arteries in the region

Superficial veins are found just beneath the skin

All venous blood drains to either superior or inferior vena cava or coronary sinus


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Major Systemic Veins

All empty into the right atrium of the heart superior vena cava drains the head and upper extremities inferior vena cava drains the abdomen, pelvis & lower limbs coronary sinus is large vein draining the heart muscle back into

the heart


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Veins of the Head and Neck

External and Internal jugular veins drain the head and neck into the superior vena cava

Dural venous sinuses empty into internal jugular vein


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Venipuncture

Venipuncture is normally performed at cubital fossa, dorsum of the hand or great saphenous vein in infants


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Hepatic Portal Circulation

A portal system carries blood between two capillary networks, in this case from capillaries of the gastrointestinal tract to sinusoids of the liver.

The hepatic portal circulation collects blood from the veins of the pancreas, spleen, stomach, intestines, and gallbladder and directs it into the hepatic portal vein of the liver before it returns to the heart (Figure 21.28). enables nutrient utilization and blood detoxification

by the liver.


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Hepatic Portal System Subdivision of systemic

circulation

Detours venous blood from GI tract to liver on its way to the heart

liver stores or modifies nutrients

Formed by union of splenic, superior mesenteric & hepatic veins


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Arterial Supply and Venous Drainage of Liver


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Pulmonary Circulation The pulmonary circulation takes deoxygenated blood from the

right ventricle to the air sacs of the lungs and returns oxygenated blood from the lungs to the left atrium (Figure 21.29).

The pulmonary and systemic circulations differ from each other in several more ways. Blood in the pulmonary circulation is not pumped so far as

in the systemic circulation and the pulmonary arteries have a larger diameter, thinner walls, and less elastic tissue.

resistance to blood flow is very low meaning that less pressure is needed to move blood through the lungs.

normal pulmonary capillary hydrostatic pressure is lower than systemic capillary hydrostatic pressure which tends to prevent pulmonary edema.


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Pulmonary Circulation


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Pulmonary Circulation

Carries deoxygenated blood from right ventricle to air sacs in the lungs and returns it to the left atria

Vessels include pulmonary trunk, arteries and veins

Differences from systemic circulation pulmonary aa. are larger, thinner with less

elastic tissue resistance to is low & pulmonary blood

pressure is reduced


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Fetal Circulation

Oxygen from placenta reaches heart via fetal veins in umbilical cord. bypasses liver

Heart pumps oxygenated blood to capillaries in all fetal tissues including lungs.

Umbilical aa. Branch off iliac aa. to return blood to placenta.


84

Ductus arteriosus is shortcut from pulmonary trunk to aorta bypassing the lungs.

Lung Bypasses in Fetal Circulation

Foramen ovale is shortcut from right atria to left atria bypassing the lungs.


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DEVELOPMENT OF BLOOD VESSELS AND BLOOD Development of blood cells and blood vessels begins at

15 – 16 days. (Figure 21.31). It begins in the mesoderm of the yolk sac, chorion, and

body stalk. A few days later vessels begin to form within the embryo Blood vessels and blood cells develop from

hemangioblasts. Blood vessels develop from angioblasts which are

derived from the hemangioblasts Angioblasts aggregate to form blood islands Spaces appear and become the lumen of the vessel Blood cells develop from pluripotent stem cells which

are also derived from hemangioblasts.


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Developmental Anatomy of Blood Vessels

Begins at 15 days in yolk sac, chorion & body stalk

Masses of mesenchyme called blood islands develop a “lumen”

Mesenchymal cells give rise to endothelial lining and muscle

Growth & fusion form vascular networks

Plasma & cells develop from endothelium


87

Aging and the Cardiovascular System

General changes associated with aging decreased compliance of aorta reduction in cardiac muscle fiber size reduced cardiac output & maximum heart rate increase in systolic pressure

Total cholesterol & LDL increases, HDL decreases Congestive heart failure, coronary artery disease and

atherosclerosis more likely


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DISORDERS: HOMEOSTATIC IMBALANCES

Hypertension, or persistently high blood pressure, is defined as systolic blood pressure of 140 mm Hg or greater and diastolic blood pressure of 90 mm Hg or greater.

Primary hypertension (approximately 90-95% of all hypertension cases) is a persistently elevated blood pressure that cannot be attributed to any particular organic cause.

Secondary hypertension (the remaining 5-10% of cases) has an identifiable underlying cause such as obstruction of renal blood flow or disorders that damage renal tissue, hypersecretion of aldosterone, or hypersecretion of epinephrine and norepinephrine by pheochromocytoma, a tumor of the adrenal gland.


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DISORDERS: HOMEOSTATIC IMBALANCES High blood pressure can cause considerable damage to

the blood vessels, heart, brain, and kidneys before it causes pain or other noticeable symptoms.

Lifestyle changes that can reduce elevated blood pressure include losing weight, limiting alcohol intake, exercising, reducing sodium intake, maintaining recommended dietary intake of potassium, calcium, and magnesium, not smoking, and managing stress.

Various drugs including diuretics, beta blockers, vasodilators, and calcium channel blockers have been used to successfully treat hypertension.


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end

principles of human anatomy and physiology, 11e 1 chapter 21 the cardiovascular system: blood...

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