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Chapter 13 – Cardiovascular System
-consists of heart and blood vessels
-beats over 100,000 times per day
 2 closed pathways (circuits) of blood flow
-pulmonary circuit – sends oxygen-poor blood
to the lungs to pick up O2 and drop off CO2
- systemic circuit – sends oxygen-rich blood and
nutrients to body cells and removes waste
The Heart
 General Characteristics
- located between the lungs in the thoracic
cavity
- 2/3 on left side, 1/3 on right side
- triangular shape
- apex – pointed end that touches diaphragm,
points left
- base – flattened superior margin of heart
- size of clenched fist, 14cm x 9 cm
 Coverings of the Heart
- pericardium – double-layered serous
membrane that encloses heart and major blood
vessels
-outer layer called parietal pericardium or
pericardial sac
- 2 parts
1) thick outer fibrous layer (tough, dense
connective tissue; protects heart, anchors heart
to diaphragm, sternum, and major blood)
vessels attached to heart
2) thin serous layer (thin, squamous epithelium
underlaid by connective tissue)
- inner layer is called visceral pericardium or
epicardium
- firmly attached to surface of heart
- is both outer layer of heart wall and inner
layer of pericardium
- pericardial cavity – space between serous
layer of parietal pericardium and epicardium
-contains fluid secreted by serous cells of
pericardium, which reduces friction
between the membranes during heart
activity
-pericarditis – swollen pericardium
 Heart Wall
-3 layers
1) epicardium – thin, protective barrier,
contains fat deposits
2) myocardium – makes up most of heart wall,
composed of cardiac muscle tissue; cells are
arranged in spiral bundles interwoven w/
connective tissue fibers; links all parts of heart
together – forms network called the fibrous
skeleton
3) endocardium (endothelium) – smooth, white
membrane forming inner layer of heart wall,
lines internal spaces (chambers) of heart and
covers valves; composed of squamous
epithelium underlaid by a thin layer of
connective tissue; also lines inner layers of
blood vessels
Heart Chambers (internal spaces)
-2 superior atria (singular: atrium)
-2 inferior ventricles
 Atria
-receiving chambers for blood entering heart
-push blood into ventricles, don’t really “pump”
blood b/c walls are very thin w/ little
myocardium
-auricles – small, ear-like, hollow appendages
attached to atria (increase volume slightly)
-interatrial septum – divider separating left and
right atria
-fossa ovalis – oval depression on wall of
septum facing the right atrium (what remains
of an opening in fetal heart wall (foramen
ovale) where blood flowed from right to left
atrium to avoid lungs)
-right atrium collects incoming blood from the
superior vena cava (drains blood from all body
regions above heart), from the inferior vena
cava (drains blood from body regions below
heart), and the coronary sinus (drains blood
from the heart wall)
-left atrium – collects blood from the
pulmonary veins (drain blood from the lungs)
 Ventricles
-provide force necessary (contraction of
myocardium) to push blood out of heart, into
body, into vessels
-left ventricle contains thickest wall necessary
to push blood through all vessels of body,
except those supplying lungs
-trabeculae carnae – irregular folds of muscle
lined w/ endocardium, found on inner wall of
each ventricle
-papillary muscles – slender projections of folds
attached to certain valves
-interventricular septum – thick muscular
divider that internally separates the left and
right ventricles (groove on outer surface of
heart is known as interventricular sulcus)
-coronary sulcus – groove separating atria from
ventricles
-after ventricles receive blood from atria, right
ventricle pumps blood into pulmonary trunk
(carries blood to lungs) and left ventricle pumps
blood into aorta (carries blood to rest of body)
Heart Valves
-permit flow of blood in only one direction
 Atrioventricular (AV) Valves – located
between atria and ventricles; consists of 2 or 3
triangular flaps (cusps) that point downward
into ventricle
-tricuspid valve – 3 cusps, between right atrium
and right ventricle
-bicuspid (mitral) valve – 2 cusps, between left
atrium and left ventricle
-cusps of AV valves are dense connective tissue
covered by endocardium
-chordae tendinae – thin strands of connective
tissue that anchor cusps to papillary muscles in
walls of ventricles
-atrium contracts pushing blood downward
through opening in cusps, into ventricles
-ventricle contracts, pushing blood upward
against cusps, causing them to close
-heart murmur – valve defect that prevents
complete closure, allowing some blood to enter
atrium
 Semilunar (SL) Valves – 2 located between
ventricles and the major blood vessel each
empties into
-pulmonary valve – between right ventricle and
pulmonary trunk
-aortic valve – between the left ventricle and
aorta
-composed of dense connective tissue covered
w/ endocardium
-both SL valves consist of 3 half-moon shaped
cusps that resemble bowls, convex surfaces
face ventricle
-when ventricle contract, blood is pushed
against AV valves, closing them, pushing blood
against SL valves, opening SL valves, moving
blood through SL valves into vessels
-when ventricles relax, the drop in pressure
w/in causes SL valves to close, preventing blood
from returning to ventricles
-heart murmur not as common
Blood Flow Through the Heart
Blood enters right atrium from the superior
vena cava, inferior vena cava and coronary
sinus (low in O2 and high in CO2 because it has
circulated through the body)
Blood moves through the tricuspid valve into
right ventricle, through pulmonary valve,into
pulmonary trunk ( which divides into many
branches) and into the lungs where blood picks
up O2 and drops off CO2
Oxygenated blood enters left atrium through
the 4 pulmonary veins.
-Blood moves through mitral (bicuspid) valve
into left ventricle, through aortic valve, into
aorta and out to body (except lungs)
Supply of Blood to the Heart
-Coronary circulation: the flow of the blood
through the vessels in the heart wall.
Blood Vessels
-closed system consisting of arteries, arterioles,
capillaries, venules, and veins
Arteries and Arterioles
*Arteries – vessels that transport blood away
from the heart; strong, elastic tubes that begin
as major arteries of the heart (aorta, pulmonary
trunk)
- get thinner as they move farther away from
heart and eventually are classified as arterioleshave thinner walls, average diameter of .5mm
-3 layers of artery walls surrounding lumen –
hollow interior
1) tunica intima – inner layer, made of
endothelium surrounded by basement
membrane (connective tissue) rich in elastic
fibers
2) tunica media – thick smooth muscle layer w/
elastic fibers
3) tunica adventitia – outer layer – thin
connective tissue layer that anchors artery to
surrounding structures
- tunica media provides elasticity and
contractility
-vasomotor fibers – nerve fibers that stimulate
smooth muscles in vessels to contract
-vasoconstriction – when muscles in vessels
contract and lumen diameter decreases
-vasodilation – when muscles in vessels are
relaxed and lumen is normal size
-arterioles have the same 3 layers as arteries,
but thinner and smaller, eventually walls
consist of only endothelium, a thin layer of
smooth muscle, and an outer sheet of
connective tissue
Capillaries
-smallest vessels in body, average diameter of
.01mm (1 layer endothelium, 1 layer outer
connective tissue); allows only 1 RBC to pass
through at a time
-permit exchange of nutrients and gases
between blood and interstitial fluid b/c they are
so thin
-endothelium of capillary walls acts as a
semipermeable membrane barrier which allows
regulated movement of materials by diffusion,
osmosis, facilitated diffusion, and active
transport
-gases, ions, and waste diffuse in and out of
bloodstream
-kidneys and small intestines have larger pores
-blood-brain barrier has small or no pores
-most capillaries have intermediate size pores
which allow fluid from bloodstream to move
outside cells into interstitial fluid
-connect arteriole to venule
-usually form branching network called
capillary bed (10-100 capillaries per bed)
consisting of thoroughfare channels 
directly connect arteriole to venule
-precapillary sphincter – small band of
smooth muscle that surrounds the origin of
a branching group of capillaries; acts as a
valve to regulate blood flow into those
capillaries
Venules and Veins
-blood move from capillaries to venules after
change of materials
-venules increase in size as they merge together
to form veins; walls get thicker as they get
closer to the heart
*Veins – transport blood toward the heart
-walls of veins are thinner than artery walls and
lumens are larger
-less smooth muscle makes veins less elastic
and contractile than arteries
-veins can hold more blood b/c of larger lumen
diameters (65% of body’s blood at one time)
-usually only partially filled w/ blood and
slightly collapsed
-distensibility – walls expand (veins fill
completely) – allows for variations in blood
pressure
-veins have one-way valves that form folds in
the tunica intima (resemble SL valves of the
heart)
-frequent in veins of lower limbs, which must
return blood to the heart against the force of
gravity
-varicose veins – veins w/ weakened valves
causing blood to pool below them, causing vein
walls to become overstretched
-hemorroids – varicose veins in the anal canal
-other mechanisms for moving blood through
veins:
1) respiratory pump – activated when you
inhale b/c pressure increases w/in abdomen,
squeezing local veins pushing blood up
2) skeletal muscle pump – skeletal muscles
surrounding veins contract and relax during
body movement, pushing blood up
-venous sinuses – veins specialized for storing
blood; flattened w/ very thin walls composed of
only endothelium; supported by surrounding
tissue (not other tunica layers)
Blood Pressure
-force exerted by blood against inner walls of
vessels; keep blood moving
-clinically, refers to arterial pressure in major
branches of aorta
-BP lower in veins b/c other factors influence
blood flow in veins (valves, respiratory action,
and skeletal muscle activity)
-BP also lower in capillaries and venules causing
blood to move slower
Arterial BP
-blood flows from higher to lower pressure
areas
-highest pressure region is the aorta due to
pumping action of heart, which pushes a large
volume of blood through aorta
-elastic walls of aorta stretch to accommodate
surge of blood and pressure reaches maximum
value, called systolic pressure (peak – average
is 120 mm Hg)
-blood leaves aorta, moves through arteries,
down pressure gradient into smaller vessels
-aorta walls recoil to original shape and aortic
pressure drops to lowest point (70-80 mm Hg),
called diastolic pressure or ventricular diastole
(relaxation)
-measuring BP uses a sphygmomantometer
-cuff is wrapped around arm over brachial
artery
-air is pumped into cuff, which eventually
compresses brachial artery to the point where
no blood can pass
-release valve is opened slightly releasing
pressure in cuff and allowing small amount of
blood to pass through
-stethoscope detects sound when blood 1st
squeezes through artery  systolic pressure
-more blood spurts through artery making a
louder noise; no more noises are detected
when blood flows normally
-1st silent moment  diastolic pressure
-tapping noises called Korotkoff sounds and
represent turbulent blood flow through artery
Pulse
-artery walls expand and recoil the same way
that the aorta walls do
-pulse – rhythmic expanding and recoiling of an
arterial wall near skin surface; usually taken in
radial artery in wrist or common carotid artery
in neck
-pulse rate = heart rate (# of pulses counted = #
of heartbeats) b/c each pulse wave is
generated by contraction of heart
-average resting heart rate for adults is 70-90
beats per minute (bpm)
-children is 80-140 bpm; higher b/c of higher
metabolic rate
-adult pulse over 100 bpm is called tachycardia
-adult pulse rate below 60 bpm is called
bradycardia
Factors affecting blood pressure
1) cardiac output = heart rate x stroke volume
-change in how fast the heart beats or how
strongly ventricles contract (which affect how
much blood enters aorta) changes BP
-when increased, BP increases
-when decreased, BP decreases
2) Peripheral Resistance
-friction produced by blood as it contracts
vessel walls, which slows blood flow
-largely determined by diameter of lumen in
vessel
-smaller lumen= more resistance
-thicker blood = more resistance
-vasoconstriction – shrinks lumen diameter =
more resistance
-vasodilation = less resistance
- increase in PR – increase in BP
- deacrease in PR – decrease in BP
-arteriole diameter changes account for the
most important influence on BP in the body
3)Blood Volume
-measure of the amount of plasma and formed
elements are in cardiovascular system
-healthy = 5 liters
-changing amount changes BP
-injury and blood loss immediately lowers BP
Regulation of BP
1) Nervous system controls
-achieved by adjusting cardiac output and PR
-nerve impulses may speed up or slow down
heart rate
-vasomotor fibers constrict or relax smooth
muscles in tunica media of vessel walls
-baroreceptors detect changes in BP and send
message to medulla oblongata in brain
2) Hormonal controls
-norepinephrine (NE), epinephrine (E), atrial
natriuretic factor (ANF), antidiuretic factor
(ADF)
-NE and E are secreted by adrenal medulla in
times of stress, stimulate fight-or-flight
response
-E increases cardiac output by stimulating
heart rate and increases PR by promoting
arteriole vasoconstriction
-NE also increases PR
-ANF is secreted by atria of heart, reduces
blood volume, which decreases BP (causes
kidneys to excrete more water from body,
which can cause dehydration)
-ADF is produced by hypothalamus and
stimulates kidneys to conserve water increasing
blood volume and increasing BP
3) Kidney controls – long term BP control
-use water conservation or excretion
-release special chemicals
-when BP drops, kidney cells release the
enzyme renin, which triggers another chemical
called angiotensin II, which is a strong
vasoconstrictor – it also stimulates releasal of
hormone aldosterone which stimulates sodium
absorption by kidneys, causing more water to
be absorbed