The Cardiovascular
System
Chapter 11
Cardiovascular Overview
• Major function:
transportation
• Blood transports
oxygen, nutrients, cell
wastes, hormones, and
many other substances
vital for homeostasis to
and from the cells
The Heart: Anatomy
• Enclosed within the mediastinum
• Apex points toward the left at approximately
the 5th intercostal space
• Enclosed by double-walled pericardium (sac)
Cardiovascular System (The Heart)
• About the size of a fist
• In pericardial cavity
surrounded by
pericardium
Pericardium
• Outer Layer: fibrous pericardium
• Protection & anchors heart to surrounding
structures
• Inner Layer: serous pericardium
• slippery two-layer structure
• parietal layer – lines fibrous pericardium
• visceral layer – hugs heart and is part of heart wall
(also called epicardium)
• produces serous fluid
to allow the heart to beat
in a relatively frictionless
environment
Heart Wall
• Three layers
• Epicardium: visceral pericardium
• Protects by producing serous fluid
• Myocardium: thick bundles of
cardiac muscle twisted and
whorled into ringlike
arrangements
• Contractile layer of heart
• Endocardium: thin, glistening
sheet of endothelium that lines
the heart chambers
• Continuous with the linings of the
blood vessels leaving and entering
the heart
Heart Wall
Chambers of the Heart
• Four chambers: two left &
two right separated by
septum
• Each lined with
endocardium
• Upper: right & left atria receiving chambers for
blood from the body
• Lower: right & left
ventricles: thick-walled,
discharging chambers,
pumps blood from the
heart circulation
throughout the body
Circulation & Blood Flow
• Heart acts as a double pump
• Pulmonary circulation:
• Superior & inferior venae cavae brings blood to the
right atrium
• Flows into right ventricle and is pumped through
pulmonary trunk, which splits into pulmonary
arteries (right & left) to take blood to the lungs
• Oxygen & carbon dioxide are exchanged in the lungs,
and the blood is returned to the left atrium through
the four pulmonary veins
• Systemic circulation:
• Blood flows into the left ventricle from the left
atrium, and is pumped out of the heart into the
aorta
• Systemic arteries branch to supply body tissues and
oxygen-poor blood circulates via the systemic veins
back to the superior & inferior venae cavae to the
right side of the heart
Circulation
Systemic Circulation
Pulmonary Circulation
Systemic Circulation
link
Heart Valves
• Four valves allow blood to flow in only one
direction through heart chambers
• Atrioventricular (AV) valves: located between
atrial and ventricular chambers on each side
(open during heart relaxation)
• Bicuspid (mitral) valve – left AV valve (has two flaps
of endocardium)
• Tricuspid valve – right AV valve (has three flaps of
endocardium)
• Chordae tendinae – anchor flaps of valves to walls of
the ventricles so that valves can prevent backflow of
blood when ventricles contract
• Semilunar valves: guard bases of two large
arteries leaving the ventricular chambers (open
during heart contraction)
• Pulmonary semilunar valve: between right ventricle
and pulmonary artery
• Aortic semilunar valve: between left ventricle and
aorta
Heart Valves
Path of blood through heart
Venae cava and coronary sinus—
right atrium–- tricuspid---right
ventricle--- pulmonary arteries--lungs--- pulmonary veins--- left
atrium--- bicuspid--- left ventricle-- aorta to body
Cardiac Circulation
• Blood contained in the heart does
not nourish the myocardium
• Coronary arteries (right and left):
branch from the base of aorta and
encircle the heart as the functional
blood supply
• Oxygenates and nourishes the heart
muscle
• If blocked, causes ischemia (chest pain)
and eventually myocardial infarction
• Coronary veins: myocardium drains
into coronary veins, which empty
into an enlarged vessel (coronary
sinus)
• Coronary sinus empties into right
atrium
Physiology of the Heart
• In one day, pumps 6 liters of blood through the blood
vessels over 1000 times
• Made of cardiac muscle – contract spontaneously and
independently, even if all nervous connections are
severed
• Fibers shorter than skeletal muscle & branching with
striations
• One central nucleus
• Intercalated disc where cells join
• Involuntary muscle
• Muscle cells in different areas of the heart have
different rhythms, so need to be coordinated with a
control system
• Atrial cells = 60 bpm
• Ventricular cells = 20-40 bpm
• Two systems regulate heart activity:
• Autonomic nervous system: increase & decrease heart rate
• Intrinsic conduction system (nodal system): built into the
heart tissue & sets basic rhythm
Intrinsic Conduction System
• Tissue is a cross between muscle and nervous tissue
• Causes heart muscle depolarization in only one
direction – from the atria to the ventricles
• Contraction rate: 75 bpm as coordinated unit
• Sinoatrial node: located in right atrium; increases
rate of depolarization; starts heartbeat and sets pace
(pacemaker)
• Atrioventricular (AV) node: junction of atria &
ventricles; in septum between two atria; only way
impulse gets to ventricles (heart block if not
conducting impulse)
• Atrioventricular (AV) bundle (bundle of His) and
right and left bundle branches located in the
interventricular septum (wringing contraction of
ventricle)
• Purkinje fibers – spread within the muscle of the
ventricle walls (causes contraction from apex to atria
to eject blood superiorly)
Fig 11-7
Cardiac Cycle
• Based on pressure and
conduction of impulses
to cause contractions
• One complete heartbeat
• Recorded on
electrocardiogram (ECG)
• P wave: atrial
depolarization
• QRS wave: rapic ventricle
depolarization
• T wave: ventricle
repolarization
• Cardiac Cycle: Fig 11.8
page 366
• ECG: “A Closer Look”
pg. 367
Cardiac Cycle & ECG
Cardiac Cycle & Heart Sounds
• Atria contract simultaneously, then as they
relax the ventricles contract
• Systole: heart contraction (ventricular)
• Diastole: heart relaxation (ventricular)
• Cardiac cycle: events of one complete
heartbeat, during which both atria and
ventricles contract & relax
• Mid-to-late diastole: semilunar valves closed and
AV valves open
• Ventricular systole: AV valves close, semilunar valves
open
• Early diastole: semilunar valves shut and AV valves
forced open
• Heart sounds – “lub-dup”
• “lub” = closing of AV valves; “dup” = semilunar
valves close at end of systole
Cardiac Cycle
Cardiac Output
• Cardiac output (CO): amount of blood pumped
out by each side of the heart in 1 minute
• Stroke volume (SV): volume of blood pumped
out by a ventricle with each heartbeat
• CO = HR x SV
• Average CO = 75 bpm x 70 ml/beat = 5250 ml/min
• Entire blood supply passes through the body once
each minute (adult blood volume is approximately
6000 ml)
review
Blood Vessels
• Vascular system: closed transport system of
blood vessels
• Blood flows from arteries (0.1 mm-1 cm)
 arterioles (10-100 µm)  capillary beds
 venules (10-100 µm)  veins (0.1-1
mm)
Microscopic Anatomy of Blood Vessels
• Blood vessels have three
coats, or tunics (except
capillaries)
• Tunica intima: lines the
interior of the vessels;
thin layer of endothelium
• Tunica media: bulky
middle coat; smooth
muscle and elastic fibers
(constricts or dilates
blood vessels)
• Tunica externa
(adventitia): outermost
tunic; supports and
protects vessels
Structural Differences in Blood Vessels
Arteries
Veins
• Take blood away
• Take blood towards
from heart in
the heart in
circulation
circulation
• Thickest walls (thick • Thinner tunica
tunica media) to
media, so larger
withstand
lumen
continuous changes
• Veins have valves to
in pressure
prevent backflow of
• Have additional
blood and ensure
elastic membranes
that venous return
in the tunica media
equals cardiac
output (amount of
blood pumped out
of heart)
• Muscles surrounding
veins aid in venous
return as well
Capillaries
• Exchange of
materials between
blood and tissues
happens through
the walls of
capillaries
• Wall is one cell layer
thick (only tunica
intima)
• Form capillary beds
in tissues (flow from
arteriole to venule
through capillary
bed is called
microcirculation)
Capillary Exchange
• Number of capillaries in a tissue is related to
metabolic activity
• Types of capillary exchange:
• Diffusion (O2, CO2, glucose, amino acids, hormones)
& osmosis (water)
• high to low (slow process)
• Proteins & blood cells are too large to leave the vessel
• Transcytosis – active transport, material enclosed
in pinocytic vessels (large lipid insoluble molecules,
i.e. insulin)
• Bulk flow – pressure driven flow of particles that
regulates relative volume of blood and interstitial
fluid (faster process)
• Blood pressure pushes fluids out of the vessels; osmotic
pressure draws fluid back in (filtration and
reabsorption)
• Lymphatic system returns fluid left in the interstitial
fluid back to the blood
Capillary Exchange
• Pressure is higher
inside the
capillary at the
arteriole end
• Pressure is higher
outside the
capillary at the
venule end
Vital Signs: Physiology of Circulation
• arterial pulse, blood pressure (along with
respiratory rate & body temperature) are
vital signs taken in clinical setting
• Arterial pulse: arteries expand and recoil with
each beat of the left ventricle and creates a
pulse (pressure wave)
• normally equals heart rate: 70-76 bpm in normal
resting person
• influenced by activity, postural changes, emotions
• Blood pressure: pressure blood exerts against
the inner walls of blood vessels that keeps
blood circulating continuously even between
heartbeats
• Highest in arteries
• Systolic – peak of ventricular contraction; diastolic
– ventricles relaxing
• Normal is 120/80 mm Hg
Blood Pressure
Blood Pressure
Factors Affecting Blood Flow
• Blood flow: volume of blood
that flows through any
tissue/time (mL/min); moves
down pressure gradient
• Affected by:
• Blood pressure: decreases as
move away from aorta
• Resistance: friction increases as
size of lumen decreases;
differences in blood viscosity;
friction increases as blood vessel
length increases
• Venous return: valves keep
blood from backing up
• Velocity: flows faster in larger
vessels