Transcript Heart

Chapter 15
Cardiovascular System
Cardiovascular System
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Provides O2 & nutrients to all tissues
Removes CO2 & wastes
Consists of heart & b.v.
The heart is a 4 chambered,
hollow, muscular organ
• Avg. size: 9 cm wide,
14 cm long
Location
• Located in the
mediastinum, resting
on the diaphragm
• Base – top of heart
beneath 2nd rib
• Apex – point at bottom
(points toward left) at
5th intercostal space
• Bordered by lungs laterally
& sternum anteriorly
Coverings
1. Fibrous pericardium – tough, outer
layer
2. Parietal pericardium – inner lining of
pericardial cavity
Pericardial cavity – space filled
w/serous fluid; reduces friction
3. Visceral pericardium – membrane that
covers the heart (same as epicardium)
Coverings
Fibrous
pericardium→
Fibrous
pericardium
Visceral
pericardium
Layers of Heart Wall
1. Epicardium –
same as vis.
pericardium; thin
connective tissue;
protection &
secretes fluid
2. Myocardium – thick;
consists of cardiac muscle; contracts to pump blood
3. Endocardium – epithelial & connective tissue; lines all
chambers & valves; helps keep surfaces smooth
Heart – External Features
• Auricle – ext. flaps
• Sulci – grooves for
b.v.
• During an avg. lifetime,
the heart beats approx.
2.5 billion times
• It pumps an avg. of
approx. 300 million L of
blood
Internal Anatomy
• The heart has been
described as 2 pumps
that lie side by side
• The 2 sides of the
heart are separated by a
wall called the septum
• The 2 thinner-walled upper
chambers that receive
blood are called atria
• The 2 thicker-walled
bottom chambers that
pump blood are called ventricles
Internal Anatomy
• The atria are separated
from the ventricles by
valves
• Valves prevent the
backflow of blood
• Tricuspid – on rt.
• Bicuspid (mitral) on
left
• Rt. side of heart receives
deoxy. blood from body &
pumps it to the lungs to
get oxygenated (colored blue)
• Left side receives oxygenated
blood from lungs & pumps it to body
(colored red)
Heart Valves
• 2 types:
1. Atrioventricular valves
(A-V valves) –
located between the 2
atria & ventricles:
tricuspid & bicuspid (mitral)
2. Semilunar valves (S-L valves) – located in
the b.v. leading away from the heart:
pulmonary & aortic
Chordae Tendinae
• In the right and left ventricle chordae
tendinae are strong fibers attached to the
A-V valves.
• They prevent the valve from extending into
the atrium chamber.
• Attached to papillary muscles.
Heart Sounds
• Produced by the closing of the
heart valves
• A typical heartbeat is heard as
“lub-dup”
• A-V sounds:
• Mitral – heard at 5thintercostal
space
• Tricuspid – at tip of sternum
• S-L sounds:
• Aortic – at 2nd intercostal space
on rt.
• Pulmonary – 2nd intercostal space
on left
Blood Supply to the Heart
(anterior view)
• The left & rt.
coronary arteries
branch off the aorta
to supply blood
to the heart itself
• The l.c. art. branches
into circumflex &
left ant. descending
artery (or left
interventricular artery)
Blood Supply to the Heart
(anterior view)
• The rt. coronary
artery branches into
the marginal artery
& the posterior interventricular artery
(on posterior view –
next slide)
Coronary Circulation
Blood Supply to the Heart
• Blood leaves arteries &
passes through capillaries
of the myocardium
• Blood then passes into
cardiac veins
• Cardiac veins empty into
coronary sinus (lg. vein on
post. side of heart)
• Coronary sinus empties into
rt. atrium
Cardiac Conduction
System
• The heart has its
own pacemaker that
can initiate a heartbeat; called the
sinoatrial node (S-A
node)
• Located in the upper
rt.atrium; causes both
atria to contract almost
simultaneously
Cardiac Conduction
System
• Impulse travels to
the atrioventricular
node (A-V) located
in the interatrial septum
• Impulse then moves
to A-V bundle (or
bundle of His) & then
to bundle branches
• Purkinje fibers carry
impulse to distant parts
of ventricles
The Cardiac Cycle
• A series of
contractions &
relaxations that
constitute one
heartbeat
• Atria contract while
ventricles relax &
vice versa
• Diastole –
relaxation of a
heart chamber
• Systole – contraction of a heart chamber
Electrocardiograms (EKGs)
• Measures electrical activity of the heart
• Results from depolarization &
repolarization of the myocardium
• 12 electrodes are placed on various
places on the body
• Changes can indicate arrhythmias &
other heart-related conditions
Parts of an EKG
• P wave – contraction of
the atria
• QRS complex – contraction of ventricles
• T wave – relaxation of ventricles
• Relaxation of atria (repolarization) – not
seen (hidden by QRS complex)
EKG Measurements
• P wave to P wave 1 complete ♥ beat
• P-Q interval – time
it takes impulse to
travel from S-A
node to A-V node
EKG Measurements
• Q-T interval - the period from the
beginning of ventricular depolarization until
the end of ventricular repolarization
• The QT interval is
prolonged if it clearly
measures more than
half the R-R interval
• Called long QT syndrome
Abnormal EKGs
• Long QT syndrome
Bundle Branch Block
• The QRS complex is
the time required to
depolarize the ventricles.
• A normal QRS is 0.08-0.12 s
• > than 0.12 seconds is considered a BBB
(block in a bundle branche, or the
electrical impulse was conducted
abnormally)
Arrhythmias
• Normally the ♥ contracts about 60-100
times/min
• Each contraction represents one ♥ beat
• Abnormal ♥ rates & EKGs – called
arrhythmias
Arrhythmias
Sinus rhythm →
60-80 beats/min
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Tachycardia > 100
beats/min
Bradycardia < 60 beats/min
Arrhythmias
• Atrial Flutter – many
more P waves
compared to QRS
complexes
• Atrial Fibrillation – P
waves absent
Arrhythmias
• Junctional Rhythm –
S-A node nonfunctional;
P waves absent; heart being
paced by A-V node (40-60
beats/min)
• Ventricular Fibrillation –
Chaotic depolarization of
ventricles; extremely irreg. as
seen in heart attack, elec. shock
Blood Pressure
• Pulse – alternate expansion & relaxation
of arteries
• Pulse pressure – difference b/t systolic
& diastolic pressure
• Central venous pressure – pressure in
rt. atrium
Factors That Affect B.P.BP
An incr. in any of these causes an incr. in BP:
1. Heart Action
– Cardiac Output (CO) = Vol. of blood discharged
from the ventricles/min.
– Stroke Volume (SV) = Vol. of blood discharged
w/each contraction (approx. 70 ml at rest)
– Heart Rate (HR) = number of beats/min
– CO = SV X HR
– CO = 70 ml X 70 beats/min
– CO = 4900 ml/min
Factors That Affect B.P.P
2. Blood Volume = sum of formed elements
+ plasma (usually 5L); (ex. - hemorrhage
results in drop in B.P.)
3. Peripheral Resistance – force produced
from the friction on blood from b.v. walls
(expansion or dilation of b.v. changes
resistance)
4. Viscosity = ease w/which blood flows (an
incr. of RBCs incr. viscosity; anemia or
hemorrhage decr. it)
Blood Pressure
• Force blood exerts against inner walls
of b.v. (usually arteries)
• Avg. = 120/80
• Measured w/a sphygmomanometer
• 120 = systolic – maximum pressure
during ventr. contraction
• 80 = diastolic – lowest pressure during
ventr. relaxation
Measurement of BP
Blood Vessels
• Include arteries, veins & capillaries
• Arteries & veins have 3 layers:
1. tunica intima – single layer squamous cells;
secretes substances to stem blood flow
2. tunica media – makes up most of the b.v.;
mostly smooth muscle & some
connective tissue; allows for expansion
3. tunica externa – connective tissue;
provides attachment to surrounding tissue
Blood Vessels
• 2 differences b/t
arteries & veins:
1. thickness of
tunica media
2. veins have
valves
Capillaries
• Smallest b.v.; connect
arterioles to venules
• Resp. gases & other
substances are
exchanged in
capillaries thru
diffusion
Capillary Bed
Movement In Capillaries
• Water & other substances leave capillaries
at the arteriolar end b/c of a net outward
pressure
• Water & other substances leave at venular
end b/c of a net inward pressure
Movement in Capillaries
Capillaries
• Arrangement of capillaries control
permeability of substances
• In spleen, liver & red marrow,
capillaries have large openings
b/t cells; allow large subst. to
diffuse
• Blood-brain barrier –
tight arrangement of
capillaries around brain;
few substances pass thru;
protects brain