A&P II (The Cardiovascular System)
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Cardiovascular System: The Heart
Chapter 17(I)
The heart is located in
the middle of thoracic
cavity – mediastinum,
within the pericardial
cavity
Apex
Base
Cardiovascular system Heart Blood Blood vessels
Heart has four
chambers: left &
right atria and left
& right ventricles
weight 250–350 g
beats ~100,000 times/day
pumps ~8,000 L of blood/day
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Position of heart in thoracic cavity
position of the apex in the 4th intercostal space
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- Atria – receive blood from veins
(vessels that bring blood TO heart)
- right atrium – from superior &
inferior venae cavae
- left atrium from pulmonary veins
- Blood drains from atria to ventricles
- Ventricles – pump blood into
arteries (vessels that carry blood
FROM the heart)
- right ventricle – to the pulmonary
trunk, then to pulmonary arteries
- left ventricle – to the aorta
Sup. vena cava
Inf. vena cava
Aorta
Pulm. trunk
Heart chambers & blood vessels
Pulmonary circuit
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Pulmonary arteries – deliver
deoxygenated (O2-poor & CO2-rich)
blood from right ventricle to lungs
Gas exchange occurs between
lung alveoli & pulmonary capillaries
O2 diffuses from air in alveoli into
capillary blood (oxygenation) & CO2
diffuses from blood in capillaries to
air in alveoli (to be exhaled)
Pulmonary veins – deliver
oxygenated (O2-rich) blood to left
atrium
Heart pumps blood through two circuits (loops of vessels)
In pulmonary circuit blood moves TO and FROM the lungs
Systemic circuit
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There, O2 diffuses from blood
into tissues & CO2 diffuses from
tissues into blood
After such exchange, blood is
deoxygenated; veins deliver it
to right atrium, to be pumped
into pulmonary circuit
pulmonary circuit carries blood
only to lungs & has low blood
pressure
Systemic circuit carries blood to
entire body & has high blood
pressure
Left side of heart – systemic pump: receives oxygenated
blood from pulmonary veins & pumps it to aorta & its branches
that serve rest of body – systemic circuit
Arteries deliver oxygenated blood from left ventricle to
systemic capillaries
Pericardium
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Pericardium – membranous
structure surrounding heart
Fibrous pericardium – outer layer
tough – collagen bundles anchor heart to diaphragm & great vessels
low distensibility – doesn’t change shape/size & prevent heart chambers from overfilling
Serous pericardium – thin inner serous membrane that
is composed of two layers & produces serous fluid
Parietal pericardium – fused to fibrous pericardium; encases heart like sac; at great vessels,
it folds under itself & forms ► ►
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cardiac tamponade
– fluid or blood
accumulates inside
pericardial cavity;
squeezes heart;
filling of ventricles &
amount of pumped
blood decreases
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The heart wall
Myocardium – thickest layer of wall; cardiac muscle cells
attached to inner fibrous skeleton
Endocardium – internal layer; simple squamous epithelium –
endothelium; continuous with lining of great vessels & valves
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Great vessels carry blood to & from the heart
- Major systemic veins – drain most of systemic circuit
- superior vena cava & inferior vena cava – drain deoxy-
genated blood from veins above & below diaphragm
- the veins open into posterior aspect of
right atrium
Pulmonary
trunk – largest
artery in circuit;
receives deoxy-
genated blood
from right
ventricle
splits into right &
left pulmonary
arteries; bring
blood to right &
left lungs
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Pulmonary arteries – branch extensively inside lungs, become
pulmonary capillaries where gases are exchanged
Oxygenated blood in pulmonary capillaries returns to left
atrium via pulmonary veins, two from each lung
Aorta supplies
entire systemic
circuit with
oxygenated blood
arises from left
ventricle as
ascending
aorta; curves as
aortic arch,
continues down
as thoracic &
abdominal
descending
aorta
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Inside heart chambers (1)
Four chambers in the heart ► two ventricles & two atria
Ventricles are larger than atria & have much thicker walls;
it makes ventricles much stronger pumps
Right atrium – larger
& thinner-walled than
left atrium
Each atrium has
muscular pouch –
auricle; right auricle is
much larger than left
auricle
Pectinate muscles –
muscular ridges on
anterior side of right
atrium; left atrium
walls are smooth
Inside heart chambers (2)
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Right ventricle – wider; has thinner walls than left ventricle
because of pressure differences in pulmonary & systemic
circuits; right ventricle pumps against slight resistance
Left ventricle – pumps against much
greater resistance & has to work harder;
so, it has greater muscle mass ~3 times
thicker than right ventricle
Interventricular septum –
thick, muscular wall; separates
ventricles; contracts with the rest
of ventricular muscle
Inside heart chambers (3)
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Trabeculae carneae – inside both ventricles; have ridged
surface made by irregular protrusions of cardiac muscle tissue
Papillary muscles – finger-like muscles in each ventricle
Chordae tendineae – tendon-like cords that attach papillary
muscles to valves between atria & ventricles
Blood flows through
heart in only one
direction ▬►
deoxygenated blood
– to pulmonary circuit
& oxygenated blood –
to systemic circuit
Two types of valves
prevent blood from
flowing backward
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The heart valves (1)
Atrioventricular valves – tricuspid & bicuspid valves that
prevent movement of blood backward into atria at the time of
ventricle contractions ▬►
Tricuspid valve – three cusps
between right atrium & right
ventricle
Bicuspid valve – two cusps
between left atrium & left ventricle;
also called mitral valve
Chordae tendineae – attached to
end of each cusp & to papillary
muscles, which contract before(!)
ventricles begin contraction; create
tension on chordae tendineae
keeping valves closed
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From mitre to mitral valve
Benedict XVI wearing an
embroidered mitre
Mitre simplex traditional style
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Backflow of blood from pulmonary artery & aorta to
ventricles – is prevented by semilunar pulmonary & aortic
valves
Pulmonary semilunar valve – between right ventricle &
pulmonary trunk
Aortic semilunar valve – between left ventricle & aorta
Valvular heart diseases – impaired function of one or
more valves; usually bicuspid (mitral) & aortic valves
insufficient valve – fails to close fully & allows blood to
leak backward – regurgitation
The heart valves (2)
stenotic valve –
cusps are impregnated
with calcium; hard &
inflexible; blood flows
through stenotic valve
with difficulty
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Blood flow through the heart: pulmonary circuit
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Blood flow through the heart: systemic circuit
Aortic arch
Brachiocephalic
trunk
Superior
vena cava
Right
pulmonary
arteries
Ascending aorta
Fossa ovalis
Left common carotid artery
Left subclavian artery
Ligamentum arteriosum
Pulmonary trunk
Pulmonary valve
Left pulmonary
arteries
Left pulmonary
veins
Left
atrium
Interatrial septum
Aortic valve
Cusp of left AV
(mitral) valve
Left ventricle
Interventricular
septum
Opening of
coronary sinus
Right atrium
Pectinate muscles
Conus arteriosus
Cusp of right AV
(tricuspid) valve
Chordae tendineae
Trabeculae
carneae
Moderator band
Descending aorta
Papillary muscles
Right ventricle
Inferior vena cava
Diagrammatic frontal section of the heart,
showing major landmarks & path of blood flow
(arrows) through atria, ventricles & associated vessels.
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almost all about heart anatomy…
a
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recognize blood vessels and heart structures
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name pointed heart structures &
great blood vessels
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The origin of coronary circulation
High blood pressure & elastic
rebound of ascending aorta
force blood through coronary
arteries between contractions
of left ventricle
In coronary circulation – cardiac
veins collect deoxygenated blood
Most cardiac veins – bring blood
to coronary sinus that opens
into right atrium
Coronary circulation – blood vessels that supply the heart
Right & left coronary arteries (very first branches of aorta!!)
– emerge from aortic sinuses – sacs in the base of ascending
aorta; they prevent cusps from sticking to walls of aorta
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Coronary arteries (1)
Right coronary artery
supplies blood to ►► right atrium; portions of both
ventricles; cells of sinoatrial & atrioventricular nodes
gives rise to ►► marginal artery & posterior inter-
ventricular artery
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Left coronary artery
- supplies blood to ►► left ventricle; left atrium; inter-
ventricular septum
- gives rise to ►► circumflex & anterior interventricular
arteries
- when blood flow to myocardium is insufficient, coronary
arteries grow arterial anastomoses (brunches that connect
them), forming collateral circulation
Coronary arteries (2)
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Most cardiac
veins empty into
large venous
structure on
posterior heart wall
– coronary sinus,
which drains into
right atrium
Right atrium –
final destination
for blood coming
from coronary
circulation
Cardiac veins
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Partial blockage of coronary circulation by fatty deposit
(atherosclerotic plaque) or thrombus reduces blood supply to
cardiac muscle & results in myocardial ischemia or
coronary artery disease (CAD)
Major symptom – chest pain = angina pectoris
When part of coronary circulation is completely blocked,
cardiac muscle cells die from the lack of oxygen & form
nonfunctional area of myocardial infarction – MI
Diagnosis – heart attack
Coronary artery disease & myocardial infarction
Normal artery
Narrowed artery
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Symptoms – chest pain that radiates to left arm or left side of neck, shortness of breath, sweating, anxiety, nausea & vomiting
Risk factors for CAD & MI – smoking, high blood pressure, poorly controlled diabetes, high levels of lipids in blood, obesity, age over 40 for males & over 50 for females, genetics
Survival depends on extent & location of damage; cardiac
muscle cells do not divide & dead cells are replaced with noncontractile scar tissue
Lethality – 25% of MI patients die before obtain medical help;
65% of deaths at age under 50 occur within one hour
Treatments include lifestyle modifications & medications; if these approaches fail, invasive treatments are considered
Atherectomy – long catheter is inserted into coronary artery & plaque can be removed; coronary angioplasty – balloon is inflated in blocked artery; piece of wire-mesh tubing – stent – may be inserted into artery
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1. Balloon angioplasty
Compressed & expanded
stents
2.
3.
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Coronary artery bypass surgery – small section is removed
from small artery or peripheral vein & used to create a detour
(bypass, shunt) around obstructed portion of coronary artery
CAD is diagnosed via angiography; small tube is fed through
artery in systemic circuit into ascending aorta & into coronary
arteries; special dye is injected into arteries; their & cardiac
muscle conditions & are examined by x-ray
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Cardiac muscle tissue
identify these muscle tissues
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Interacalated discs
Unique for cardiac muscle cells
◄ Striations ►
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Anatomy of a cardiac muscle cell
Specific properties of cardiac muscle cells
Small size
Single central
nucleus
Abundant
mitochondria
Branching
interconnections
between cells
Intercalated discs
LM x575
intercalated discs
mitochondria
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Intercalated discs
Intercalated discs – unique
structures that join adjacent
cardiac muscle cells
(pacemaker cells to contractile
cells & contractile cells to one
another)
Intercalated discs contain
intercellular junctions ►►
desmosomes – hold
cardiac muscle cells together
gap junctions – allow ions
to rapidly pass from one cell
to another, permitting
communication among
cells
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Tight junction
0.5 µm
1 µm
Desmosome
Gap junction
Extracellular
matrix
0.1 µm
Plasma membranes
of adjacent cells
Space
between
cells
Gap
junctions
Desmosome
Intermediate
filaments
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
Desmosomes
(or adhering
junctions) –
fasten cardiac
muscle cells
together into
strong sheets
Gap junctions – provide
cytoplasmic
channels
between
adjacent cells
Desmosomes & gap junctions
Gap junctions are electrical synapses between adjacent cardiac muscle cells
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Figure 6.32 Intercellular junctions in animal tissues
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Cardiac muscle cells (as any excitable cells) – contain
selective gated ion channels in sarcolemma; the channels
are responsible for generation of action potentials in both
pacemaker & contractile cardiac muscle cells
Voltage-gated sodium channels – open in response to
voltage changes across membrane
Voltage – difference in electrical potential between two points
Calcium channels – have voltage-gated mechanism for
opening & time-gated for closing
Potassium channels – all cardiac muscle cells have one or
more types of ligand-gated or voltage-gated channels
Nonspecific cation channels unique to pacemaker cells
Gated ion channels in sarcolemma of cardiac muscle cells
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Membrane potential – voltage (charge) difference that
exists across membranes of all cells
Resting membrane potential – membrane potential of
a non-stimulated excitable cell at rest; averages between
−60 mV and −90 mV; result of difference in concentration of
ions on both sides of plasma membrane
Biological current – flow of ions along chemical or
electrical gradients
Depolarization – change in resting membrane potential to
less negative value; occurs when positively charged ions
rush into cell or negatively charged ions leave cell
Hyperpolarization – change in resting membrane potential …
Repolarization – return of cell membrane to its negative
resting potential; occurs when positively charged potassium
ions leave cell (most common mechanism)
Cell electrophysiology
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- Concentrations of sodium & calcium ions outside cells
are higher than inside
- Sodium & calcium ions tend to follow their concentration
gradients to enter cell when their channels open
- Concentration of potassium ions inside cells is higher
than outside
- Potassium ions follow their concentration gradient & leave
cell when their channels open
- Sodium & potassium gradients are maintained by Na+/K+
pump; calcium ion gradient – by separate transport pump
Ion gradients across excitable membranes
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Chemical & electrical gradients ―►
unequal distribution of ions & charges inside & outside cell membrane
inside
(mM)
14
140
0.0004
10
outside
(mM)
142
4
2
110
high concentrations
of Na+, Ca2+ and Cl–
outside cells
high concentrations
of K+ and negatively
charged proteins
inside cells
K+
Na+
K+
Na+
positive
outside
negative inside
Na+
K+
Ca2+
Cl–
proteins‒
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Heart autorhythmicity
Conduction system & pacemaker cells
Cardiac muscle cells – unlike skeletal & smooth muscle
cells, do not require nerve stimulation to contract
Cardiac muscle sets its own rhythm without need for signals
from nervous system
Heartbeats ▬► spontaneous or automatic + regular or
rhythmic ▬► heartbeats are autorhythmic
Heart autorhythmicity – due to cardiac conduction system
Conduction system – is made of pacemaker cells which
rhythmically & spontaneously generate action potentials &
conduct them to contractile cells
In response – contractile cells generate their own action
potentials followed by their contractions
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Action potentials of pacemaker cell
repolarization
depolarization
level of the resting membrane potential
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Pacemaker cell action potentials
Pacemaker cells have no stable resting membrane
potential
They depolarize slowly from resting level of –60 mV to
threshold of –40 mV (“pacemaker potential” = 20 mV)
Slow depolarization is due to inflow of Na+ via nonspecific
leak channels
At threshold, fast depolarization occurs due to movement
of Ca2+ through voltage-gated channels into the cell
Repolarization – voltage-gated K+ channels open and K+
moves out of cell, increasing cell electronegativity
At –60 mV, K+ channels close, depolarization starts again
Each depolarization cycle creates one heartbeat
Heart pacemaker cells at rest fire at 0.8/sec or 75/min
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Pacemaker cell action potential
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- Your take-home (“prerequisite”) test is on “Canvas”, in the folder
“Quizzes”
- You may take the test between 12:00 PM (noon) Sunday, January
26, and 11:59 PM Tuesday, January 28 ONLY
- Make sure your computer and Internet work properly
- There are 35 questions on material of Chapters 10, 11, 14 in the
test (see p. 4 in my syllabus)
- After you open the test, you have one attempt ONLY to complete
and submit it
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answer
- You have 40 min to answer all questions and submit the test
- Don't forget to click the "Submit" button after the test is
completed
- You can see your result and correct answers between 8:00 AM
and 11:59 PM Wednesday, January 29
Take-home Test