Cardiovascular System

Chapter 15The Cardiovascular System: The Heart & Blood Vessels

The Cardiovascular System

The cardiovascular system consists of:1. blood - The fluid which transports nutrients, respiratory gases, wastes etc.

to body tissues. 2. heart - The pump which moves the blood through the blood vessels.

I. Heart AnatomyA. size, location & orientation

1. mediastinum = medial cavity of thorax2. PMI = point of maximal intensity = between 5th & 6th ribs, just

below left nippleB. coverings

1. double-layered pericardiuma. fibrous pericardium = outer, tough, dense

connective tissue that protects heart, anchors heart to diaphragm and great vessels, and prevents

overfilling of heart with bloodb. serous pericardium = thin, two-layered serous

membrane(1) parietal pericardium lines internal surface

of the heart, the fibrous pericardium attaches to large arteries at base, then turns inferiorly to become the visceral pericardium

(2) visceral pericardium /epicardium = part of heart wall

(3) pericardial cavity = between serous layers, contains serous fluid for lubrication

pericarditis = inflammation of pericardium -->friction

cardiac tamponade = heart compressed by fluid (blood or excess serous fluid;

relieved by draining with needle)C. heart wall – consist of three, highly vascular layers

1. epicardium2. myocardium = mostly cardiac muscle, arranged in circular/spiral

bundles; connected to each other by a dense network of connective tissue fibers called the fibrous skeleton which reinforces/anchors, and electrically insulates.

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3. endocardium = squamous epithelium plus connective tissue; lines chambers, covers valves

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D. chambers & associated great vessels1. two atria = small, thin-walled, superior chambers, each with a

small, wrinkled protruding appendage called an auriclea. right atrium receives 3 veins (deoxygenated blood):

superior vena cava from upper body, inferior vena cava from lower body, coronary sinus from

myocardium itselfb. left atrium makes up most of the heart’s base and receives

four pulmonary veins from lungs (oxygenated)c. interatrial septumd. atrioventricular groove/coronary sulcus at A-V junctione. pectinate muscles (pectin = comb) = muscle bundles on

anterior internal walls of atriaf. fossa ovalis = depression in interatrial septum; was

foramen ovale in fetusg. functions - receives blood returning to heart; “pump” into

ventricles2. two ventricles = large, thick-walled, inferior chambers:

right ventricle forms most of anterior surface of heart;left ventricle dominates inferoposterior aspect, forms apex, and

has much thicker wallsa. pulmonary trunk carries deoxygenated blood from right

ventricle to lungsb. aorta carries oxygenated blood from left ventricle to bodyc. interventricular septumd. anterior interventricular sulcus/anterior

interventricular artery overlies anterior interventricular septum

e. posterior interventricular sulcus overlies posterior interventricular septum

f. trabeculae carneae = ridges of muscles on internal wallsg. papillary muscles = conelike muscle bundles which

anchor some of the valves (later)h. functions - discharge: Right ventricle --> pulmonary trunk

to lungs (deox)Left ventricle --> aorta to body (oxygenated)

i. ventricles make up most of the mass of the heartE. pathway of blood through heart

1. pulmonary circuit = short, low-pressure2. systemic circuit = long, much more resistance --> thicker walls

F. heart valves1. atrioventricular valves

a right atrioventricular (Rt. AV)/tricuspidb. left atrioventricular (L. AV)/bicuspid/mitralc. chordae tendineae = tiny collagen cords that anchor cusps

of AV valves to papillary muscles

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2. semilunar valvesa. aortic semilunar valveb. pulmonary semilunar valvec. no valves on vessels atria; little backflow because atria

compress/collapse these vessels when they contractII. Coronary Circulation: myocardium = too thick to be served by diffusion from

within A. right & left coronary arteries arise from base of aorta and encircle heart

in atrioventricular grooveB. cardiac veins & coronary sinusC. anastomosis = merging of nerves, blood vessels, or lymph vessels;

existence of many anastomoses among coronary arterial branches provides collateral routes for blood delivery

D. main coronary arteries lie in epicardium and send branches into myocardium; deliver when heart is relaxed (vessels are compressed

during contraction & partly blocked by open aortic semilunar valve)E. disorders

1. angina pectoris = thoracic pain due to temporary deficiency in blood to myocardium (due to stress-induced vessel spasms

or increased physical demands)2. myocardial infarction/heart attack/coronary = tissue death due

to prolonged coronary blockage (replaced by noncontractile scar tissue)Ill. Properties of Cardiac Muscle

A. microscopic anatomystriated, cells = short, fat, & branched, with abundant mitochondria;

intercalated discs hold cells together during contraction & electrically couple cells --> myocardium acts as single coordinated unit (functional syncytium) contracts by sliding filament

B. energy requirementsall aerobic respiration, using any nutrient supply available; therefore

damage from myocardial infarction is due to anoxia, not lack of fuel

C. mechanism & events of contraction1. differences between cardiac & skeletal muscle

cardiac muscle = 1 % autorhythmic (with ability to pace the heart) remainder = contractile muscle fibersa. all or none law

(1) in skeletal muscle = applies to each fiber(2) in cardiac muscle = whole organ

b. means of stimulationskeletal = 1 nerve ending/muscle fibercardiac = some cells = self-excitable (autorhythmicity)

c. absolute refractory period = much longer in cardiac --> prevents tetanic contractions which would stop

pumping action by preventing filling

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IV. Heart Physiology A. electrical events

two types of controlling systems regulate heart activity:• nerves of autonomic nervous system increase or decrease heart rate• the intrinsic conduction system, built into heart tissue, sends

depolarization one direction, from atria to ventricles1. intrinsic conduction system

a. cardiac muscle fibers can contract spontaneously, even if nerve connections are severed

b. different regions of heart have different rhythms (atria are faster), so need unifying control system for effective pumping

c. intrinsic conduction system sets basic rate of heart beat2. action potential generated by autorhythmic cells

a. autorhythmic cells produce pacemaker potentials = unstable resting potentials which continuously

depolarizeb. autorhythmic cells = localized in several areas; sequence

of excitation:1. sinoatrial (SA) node in right atrial wall -->

depolarizes 75x/min--> pacemaker --> produces sinus rhythm; depolarization spreads through atria

--> atrial contraction2. atrioventricular (AV) node = just above AV

junction small diameter fibers here delay impulse so atria complete contraction before ventricles contract

3. AV bundle of His in inferior part of interatrial septum = only electrical connection between

atria & ventricles (rest = insulated by fibrous skeleton

4. right & left bundle branches carry impulse along interventricular septum toward apex

5. Purkinje fibers continue through interventricular septum into apex, then turn superiorly into

the ventricular walls; more extensive on thicker, larger left side of heart; Purkinje fibers supply papillary muscles before lateral walls of ventricles to assure tension on AV valve cusps before full force of ventricular contraction

6. “wringing contraction” of ventricles begins at apex and moves toward atria, ejecting blood

superiorly into large arteries leaving ventricles

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c. defects/problems1. arrhythmias = irregular rhythms2. fibrillation = rapid, irregular shuddering (no

pumping)3. ectopic focus may take over after SA node damage

or may develop without damage--> extrasystole (premature contraction)

4. heart block damage to AV node--> no impulses to ventricles, intrinsic rate is too slow -->

implant pacemaker5. ischemia (is-) = inadequate blood to heart muscle6. tachycardia = heart rate over 1 00 beats/mm7. bradycardia = heart rate less than 60 beats/mm

3. extrinsic innervation of heartautonomic fibers (in medulla) modify activity of intrinsic system:a. sympathetic --> cardioacceleratory center --> increases

rate & force of heartbeatb. parasympathetic --> cardioinhibitory center --> slows

heart (via vagus nerves)4. electrocardiography – discussed in lecture

B. the cardiac cycle1. terms

a. systole = period of contractionb. diastole = relaxation period

(since ventricles do most of pumping, these terms refer to ventricles unless otherwise indicated)

c. cardiac cycle = 1 complete heartbeat (atrial systole/diastole & ventricular systole/diastole) = usually sec’s (at 75

beats/mm)(1) mid-to-late diastole heart relaxed, pressure in heart

= low; semilunar valves = closed; AV valves = open

blood flows passively into & thru atria into ventricles --> 70% of ventricular filling:

then atria contract, forcing remaining blood in atria--> ventricles

(2) ventricular systole ventricular contraction begins, pressure in ventricles rises sharply, closing

AV valves & then opening semilunar valves (meanwhile atria relax & again begin filling with blood)

(3) early diastole at end of systole, ventricles relax and semilunar valves close (prevent backflow);

then intraventricular pressure drops --> AV valves open, ventricles begin to refill (completes cycle)

C. heart sounds

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1. normal = lub-dup, pause lub-dup, pauselub = closing of AV valves; dup = closing of semilunar valves1. Second sound = longer/louder2. abnormal or unusual murmurs = due to turbulent blood

flow; may indicate valve problem

D. cardiac output (CO)1. cardiac output = amount blood pumped out by each ventricle/rnkj

stroke volume = volume blood pumped out of each ventricle/therefore:CO = heart rate(HR) X stroke volume(SV)average adult CO = (75 beats/mm) X (70m) = 5250 ml/mmnormal adult blood volume 5L (5000ml) so entire blood supply

passes thru each side of heart once each minuteCO varies with body’s demands; increases with increased SV or

HRcardiac reserve = difference between resting & maximal CO;

increases with training2. regulation of stroke volume

healthy heart pumps out -60% of blood which enters it, 70ml/beatmajor factor affecting SV = preload = degree of stretch of cardiac

muscle cells just before contractionFrank-Starling Law of the Heart = the greater the stretch --> the

stronger the contractionincreased stretch = due to increased venous return = due to slow

heartbeat (more filling), exercise (increased HR & force), muscular pump of active skeletal muscles

decreased venous return = due to severe blood loss, very rapid HR3. regulation of heart rate

a. autonomic nervous system regulation1. sympathetic NS increases HR during

emotional/physical stress2. parasympathetic NS (mostly vagus) resumes slow &

steady;normal resting conditions --> both divisions send impulses to SA

node; dominantinfluence = inhibitory, slows inherent rate of SA node stronger

stimulation of either division by sensory inputs (mostly from baroreceptors/pressoreceptors) --> temporarily inhibits the

alternate divisioneg: Atrial (Bainbridqe) reflexincrease in venous return --> blood congestion in atria -->

stretching of atrial walls --> increase in HR and force by directly stimulating the SA node AND by stimulating baroreceptors in atria that trigger reflexive increase in sympathetic stimulation of heart

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b. chemical regulation1. hormones

epinephrine mimics sympathetic stimulation to increase HR

thyroxine --> increases HR

c. other factors - age, gender. exercise, body tempresting fetal HR = 140-160 --> decreases throughout life female

HR = faster (72-80 vs 64-72 in male)heat increases HR (increases metabolic rate of heart cells/cold

decreases it)exercise acts through sympathetic division to increase HR

4. homeostatic imbalance of cardiac outputa. congestive heart failure pumping efficiency depressed -->

inadequate circulation to meet tissue needs (due to coronary atherosclerosis, high BP or Ml’s)

b. left side failure --> pulmonary congestion-- increased BP in lung vessels --> leak --> pulmonary edema

c. right side failure --> peripheral congestion --> distal edema (eg feet)

Blood Vessels

I. Structure & FunctionBlood vessels = closed circuit of tubes: arteries (away from heart), arterioles, capillary beds (exchange), venules, veins (toward heart)A. structure of walls

1. all blood vessels except capillaries = 3 layers; an inner endothelial lining, a middle layer of smooth muscle & elastic tissue,

and an outer layer of fibrous connective tissue; capillaries = 1 layer

lumen = blood-containing spaceB. arteries

1. much thicker-walled with more smooth muscle & elastic tissue than veins --> allows them to expand & recoil with blood

surges from heart, to maintain continuous pressure & continuous flow

2. arterioles = small arteries; regulate blood flow into capillary bedsC. capillaries = microscopic vessels with thin walls; diameter < 1 RBC 3

types:1. continuous capillaries have continuous walls with intercellular

clefts between cells; passage of fluids and small solutes = through clefts and through endothelial cells by vesicular transport; = most common; abundant in skin and muscles;

in brain = no clefts --> structural basis for blood-brain barrier

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2. fenestrated = with pores = in areas of active absorption or filtration

3. sinusoids = leaky capillaries with larger clefts to allow passage of larger molecules or blood cells

4. capillary beds = true capillaries (exchange vessels) plus metarteriole-thoroughfare channels (vascular shunts)

which directly connect arteriole and venule at opposite ends of bed;

precapillary sphincters regulate blood flow into capillaries5. veins

1. venules smallest venules = very porous

2. veins have larger lumens & thinner walls than arteries plus a system of venous valves (in limbs) to prevent

backflow3. skeletal muscle contractions aid venous return of blood to

heart4. most veins are usually only partially filled (blood reservoir)5. varicose veins = dilated due to incompetent valves

E. vascular anastomoses = merging of vessels1. arterial anastomoses provide collateral (alternate) channels to same

tissue/organ2. venous anastomoses = much more abundant

II. Physiology of Circulation A. terms:

1. blood flow = amount of blood through vessel/organ per unit time (ml/mm)

2. blood pressure (BP) = force/unit area of blood on vessel wall3. peripheral resistance (PR) = opposition to blood flow (friction)

sources = blood viscosity, vessel length, vessel diameter4. relationship between blood flow, BP, and PR:

blood flow = directly proportional to BP & inversely proportional to PR

B. systemic BP is highest in aorta; lowest in venae cavae1. arterial BP depends on compliance (distensibility) of arteries &

amount of blood forced into them, a BP peaks during systole (pressure BP is lowest during diastole) pressure = due to recoil of elastic arteries

pulse pressure = systolic minus diastolic2. mean arterial pressure (MAP = diastolic plus 1/3 pulse pressure);

keeps blood moving throughout cardiac cycle3. capillary BP = low to prevent rupture while still allowing

adequate exchange (capillaries are very permeable)4. venous BP steady (low) (due to resistance)

a. factors aiding venous return1. large lumens & venous valves

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2. respiratory & muscular pumps5. maintaining BP involves three major factors

a. cardiac output = volume/mm from left ventricleb. peripheral resistance = mainly due to vessel diameterc. blood volume

6. short-term neural controls of BPa. vasomotor center = sympathetic center (medulla) which

regulates blood vessel diameterb. baroreceptors = in carotids, aortic arch, & large arteries of

neck & thorax; prevent acute BP changes (eg from standing up), increase in BP --> baroreceptors inhibit vasomotor

center --> vasodilation, decreasing BP --> baroreceptors activate cardioinhibitory center --> reduce HR & force

decrease in BP --> baroreceptors stimulate vasomotor center --> vasoconstriction, increasing BP

--> baroreceptors activate cardioacceleratory center --> increase HR & force

c. chemoreceptors = in large arteries of neckincrease blood CO or decrease blood pH or O levels -->

chemoreceptors stimulate vasomotor center --> vasoconstriction which increases BP,

speeding blood to lungsd. higher brain centers (cerebrum & hypothalamus) may

modify neural controls of BP by influencing the medullary control centers. eg fight-or-flight response mediated by hypothalamus

7. short-term chemical controls of BPa. increase BP by promoting vasoconstriction

(1) adrenal medulla hormones (epinephrine & NE) - also increase HR & contractility

(2) antidiuretic hormone (from hypothalamus) - also stimulates kidneys to conserve water

(3) angiotensin II (generated in response to renin release by kidneys) - also stimulates release

of aldosterone(4) endothelium-derived factors = affect vascular

smooth muscleb. reduce BP by promoting vasodilation

(1) atrial natriurectic factor produced by atria- also causes decline in blood volume by causing

kidneys to excrete more sodium & water(2) nitric oxide (NO) released by vascular endothelium(3) inflammatory chemicals: ie. histamine(4) alcohol inhibits ADH release & depresses

vasomotor center --> vasodilation

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8. long-term controls of BP renal regulationkidneys regulate blood volume both directly and indirectly:a. direct mechanism

increased BP --> increases filtrate formation & fluid loss in urine

decreased BP --> kidneys retain more H increasing BPb. indirect decreased BP --> kidneys release renin, triggering

formation of angiotensin II (vasoconstrictor) & release of aldosterone (causes retention of salt & H)

9. monitoring circulatory efficiencya. alternating expansion & recoil of arterial walls with each

heartbeat; pulse points = pressure pointsb. BP: normal adult = 1 20/80 (systolic/diastolic)

BP cuff = sphygmomanometer10. variations in blood pressure

a. hypotension = systolic below 100 = usually due to conditioning

b. hypertension = 140/90 or higher; increases PR --> strains heart and may cause vascular complications,

especially in eyes and kidneysC. blood flow = tissue perfusion

1. velocity of blood flowfastest in aorta (smaller cross-sectional area);slowest in capillaries (large combined cross-sectional area), to

allow nutrient waste exchanges2. autoregulation - local adjustment of blood flow to individual

organs based on immediate requirementsa. metabolic controls = chemical factors (especially low 02)

that cause vasodilation of arterioles serving the area and open the precapillary sphincters

b. myogenic controls changes in BP directly stimulate vascular smooth muscle

c. long-term autoregulation increase in number and size of blood vessels in region in response to occluded

coronary vessel or high altitude3. blood flow in special areas in most instances, autoregulation is

controlled by oxygen deficits and accumulation of local metabolites. However, autoregulation in brain,

heart, and kidneys = extra efficient4. capillary dynamics

a. exchanges of respiratory gases & nutrients (small) = diffusion -solubles --> through clefts or

fenestrationsfat-solubles --> through lipid portion of endothelial cell

membraneb. fluid movements

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(1) hydrostatic pressures(2) osmotic pressures(3) hydrostatic-osmotic pressure interactions:

hydrostatic pressures dominate arterial end of capillary bed, forcing fluids out;

osmotic pressures dominate venous end, forcing fluids in

(4) small net loss of fluid & protein into interstitial space--> lymph vessels to cardiovascular

system5. circulatory shock = inadequate blood perfusion of tissues

a. hypovolemic shock = low blood volumeb. vascular shock = abnormal vasodilationc. cardiogenic shock = pump failured. orthostatic intolerance in returning astronauts

weightlessness --> decrease in blood volume --> inadequate perfusion of brain on reentry

Cardiovascular System: Heart & Blood VesselsReview Sheet

Heart1. Describe the size and shape of the heart, and indicate its location and orientation

in the thorax.2. Describe the structure, location, and function of the fibrous pericardium, parietal

pericardium, and visceral pericardium.3. Describe the structure and function of each of the three layers of the heart wall.4. Describe the structure and functions of the four heart chambers. Include

associated structures as well as the names and general routes of the great vessel(s) associated with each chamber.

5. Describe the structure, function and location of the skeleton of the heart.6. How do the right and left sides of the heart differ in structure and function?7. Trace the path of blood through the heart. Locate and describe the function of

each of the major vessels that enter and leave the heart. Which carry oxygenated blood?

8. Distinguish between the pulmonary and systemic circuits.9. Name the heart valves and describe their location and function.10. Describe how and when blood is delivered to the heart itself.11. Define the following: ischemia, angina pectoris, myocardial infarction.12. Describe the microscopic structure of cardiac muscle cells. What are intercalated

discs?13. Compare the contraction of cardiac muscle to that of skeletal muscle. Include the

all-or- none law and the absolute refractory period in your comparison. Define autorhythmic.

14. Name the elements of the intrinsic conduction system of the heart in order, beginning with the pacemaker. Trace the conduction pathway.

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15. Define the following: arrhythmia, fibrillation, heart block, tachycardia, bradycardia.

16. Distinguish between systole and diastole.17. Describe the timing and events of the cardiac cycle.18. Describe the normal heart sounds. What causes them?19. Define cardiac output. How does it relate to heart rate and stroke volume? What is

cardiac reserve?20. Name and explain the effects of the various factors involved in regulation of

stroke volume and heart rate.21. Explain the role of the autonomic nervous system in regulating cardiac output.

What is vagal tone?22. List several chemical factors which influence heart rate.23. Describe the effect of the following on heart rate: stimulation by the vagus nerve,

exercise, epinephrine, advanced age, and gender.24. Define congestive heart failure.25. Compare the effects of a failing right ventricle to those of a failing left ventricle.26. Describe several age-related changes in the heart.

Blood Vessels1. Describe the three layers that typically form the wall of a blood vessel, and state

the function of each.2. Define vasoconstriction and vasodilation.3. Compare the structure and function of arteries, arterioles, veins, venules, and

capillaries.4. Describe the structure and function of a capillary bed.5. How is blood flow into capillaries controlled?6. Define blood flow, blood pressure, and resistance, and explain the relationship

between these factors.7. List and explain the factors that influence blood pressure, and describe how blood

pressure is regulated.8. Define hypertension. Note both its symptoms and consequences.9. Explain how blood flow is regulated in the body in general. Describe the unique

features of arterial circulation of the brain and hepatic portal circulation.10. Define circulatory shock. Note several possible causes.11. Describe the forces responsible for the exchange of substances between blood and

the tissue fluid. Why do water and dissolved substances leave the arteriole end of a capillary and enter the venule end? How is excess interstitial fluid returned to venous circulation?

12. Define: atherosclerosis, ateriosclerosis, aneurysm , phlebitis , and varicose veins.13. List the major factors that promote the flow of venous blood.14. What changes occur in blood vessels as a person ages.

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