Cardiovascular System
Part I
Chapter 11
Anatomy of the Heart
Function:
– Transportation. Uses blood to carry oxygen, nutrients
and cell wastes.
Size:
– Approximately the size of your fist
– Weighs less than one pound
Location:
– Within the bony thorax between the lungs
Apex:
– Pointed end which is directed towards the left hip
and rest on the diaphragm.
Base:
– Posterosuperior aspect. Area where the blood vessels
of the body emerge. Points towards the right
shoulder and lies under the second rib.
Coverings and Wall of the Heart
Pericardium:
– Double sac/Serous membrane
Visceral Pericardium/Epicardium:
– Thin covering of the external surface of the heart
composing part of its wall
Parietal Pericardium:
– Loose covering which is reinforced on its superficial
face by connective tissue. Protects the heart and
anchors it to its surrounding structures.
– Serous Pericardial Membranes:
Produce a slippery lubricating fluid …
– Serous Fluid:
Allows the heart to beat easily and the pericardial layers to
slide smoothly across one another.
Coverings and Wall of the Heart
Myocardium:
– Thick bundles of cardiac muscle. This is
the layer of the heart which actually
contracts
Endocardium:
– Thin sheet of endothelium that lines the
hearts chambers
– Paricarditis:
Inflammation of the pericardium resulting in
a loss of serous fluid causing the layers to
form adhesions which interferes with the
movement of the heart.
Chambers and Associated Vessels
of the Heart
There are 4 chambers within the
heart. Each is lined with
endocardium to help blood flow
smoothly through the heart.
Atria:
– 2 of the chambers
Ventricles:
– 2 of the chambers
Chambers and Associated Vessels
of the Heart
Superior/Receiving Chambers:
– Composed of the atria
– Is not important in pumping blood through the heart
– Blood flows into these atria at a low pressure which
fills the two ventricles
Inferior/discharging Chambers:
– Composed of the ventricles
– In charge of actual pumping of blood through the
heart.
– They contract to propel blood out of the heart and
into circulation
– Right Ventricle:
Forms most of the anterior surface
– Left Ventricle:
Forms the apex
Chambers and Associated Vessels
of the Heart
Interventricular/Interarterial Septum:
– Divides the heart longitudinally
Superior and inferior Vena Cavae:
– Pump blood out through the pulmonary trunk.
Pulmonary Trunk:
– Splits into the right and left pulmonary arteries
Pulmonary arteries:
– Carry blood to the lungs, pick up oxygen, get rid of
CO2.
– Oxygen rich blood is then transported from the lungs
to the left side of the heart through the …
Pulmonary veins:
– Transport blood from the lungs to the left side of the
heart
Chambers and Associated Vessels
of the Heart
Pulmonary circulation:
– Circulation from the right side of the heart, to the lungs and
back to the left side of the heart.
– Its only function is to carry the blood to the lungs for gas
exchange and return it back to the heart.
Aorta:
– Blood from the left side of the heart is pumped out of the heart
and into the aorta
– From the aorta all the systemic arteries branch out and supply
the body tissues with blood.
Systemic Circulation:
– Circulation of oxygen poor blood circulating from tissues back
to the right atrium via the systemic veins which empty into the
superior or inferior vena cavae moving through the lefts side of
the heart through the body tissues and back to the right side of
the heart.
Valves
The heart has 4 valves allowing blood to
flow in only one direction through the
hearts chambers.
Atrioventricular/AV Valves:
– Between the atrial and ventricular chambers
on each side.
– Prevent back flow into the atria when
ventricles contract.
– Bicuspid/Mitral valve:
Left AV Valve consists of two flaps of endocardium
– Tricuspid valve:
Right AV valve consists of 3 flaps of endocardium
Valves
Chordae Tendinae:
– Tiny white cords which anchor the flaps of the valves
to the walls of the ventricles.
– When the heart is relaxed and blood is filling the
chambers the AV valve flaps hand loose into the
ventricle and when it contracts they are forced
upwards keeping the valve open.
Semilunar valves:
– Pulmonary & Aortic Valves: have three flaps which
lift all at once when the valves are closed and when
the ventricles contract they open
– As they open and close in response to pressure
changes they force blood to continually move
through the heart.
Valves
Incompetent Valve:
– Valve which is not working properly and
either stays open allowing blood to move
back and forth continuously or may stay shut
not allowing any blood to move through the
heart.
Valvular stenosis:
– Bacterial infection of the endocardium
causing the valves to become stiff forcing the
heart to contract more rigorously in order to
open the valve.
Cardiac Circulation
Coronary Arteries:
– Provides blood that oxygenates and nourishes the
heart.
– Branches from the base of the aorta and encircle the
heart
– They are compressed when the ventricles contract
and fill with blood when they are relaxed.
Cardiac Veins:
– Drain into the myocardium emptying into an
enlarged vessel on the backside of the heart called
the …
Coronary sinus:
– Empties into the right atrium
Cardiac Circulation
Angina Pectoris:
– Crushing chest pain due to the myocardium
being deprived of oxygen
– When the heart beats rapidly the
myocardium receives inadequate blood
supply because of the shortened relaxation
periods between heart beats
– If this condition is prolonged heart cells may
die causing…
Myocardial infarction:
– Heart attack!
Physiology of the Heart
In one day the heart pushes the body’s 6
quarts of blood through the blood vessels
over 1,000 times pumping 6,000 quarts
in a day!
Conduction system:
– Cardiac muscle cells contract spontaneously
and independently of nerve impulses. Muscle
cells in different areas of the heart then have
different rhythms.
Cardiac Conduction System
Nerves of the ANS: act as brakes to accelerate
or decelerate heart rate
Intrinsic conduction system/Nodal system:
– Composed of special tissue found only in the heart
and is a cross between muscle and nervous tissue.
– Causes the heart muscle depolarization from the
atria to the ventricles and enforces a contraction rate
of 75 bpm on the heart so that it beats as a unit.
– Atrial cells: beat at 60 bpm
– Ventricular cells: beat at 20-40 bpm
Conduction System of the Heart
Sinoatrial Node (SA node):
–
–
–
–
Crescent shaped tissue located in the right atrium
Has the highest rate of depolarization
It starts each heartbeat and sets the pace
It is our internal “pacemaker”
Atrioventricular Node (AV Node):
– Found at the junction of the atria and ventricles
– Impulses from the SA node cause the atria to
contract and is delayed by the AV node and passed
quickly to the AV bundle
– The bundle branches and purkinje fibers contract the
ventricles causing blood to be pumped out of the
heart
Conduction System of the Heart
Atrioventricular (AV) bundle:
– Sometimes referred to as the bundle of HIS
– Located in the interventricular septum
Bundle Branches:
– Right and left branches off the AV bundle
Purkinje Fibers:
– Thin fibers spread within the muscle of the
ventricular walls allowing them to contract
Conduction System of the Heart
Heart Block:
– Damage to the AV node releasing the ventricles from control of
the SA node and the ventricles begin to beat at their own rate –
usually slower
Ischemia:
– Lack of adequate blood supply to the heart leading to …
Fibrillation:
– Rapid, uncoordinated shuttering of the heart muscle making the
heart totally useless as a pump
– Major cause of death from a heart attack
Tachycardia:
– Rapid heart rate. Over 100 bpm (at rest)
Bradycardia:
– Heart rate that is slower than normal (below 50 bmp)
Cardiac Cycle and Heart Sounds
In a healthy heart the atria contract
simultaneously and as they relax the
contraction of the ventricles begins.
Systole:
– Contraction of the ventricles when the heart
is pumping blood
Diastole:
– Relaxation of the ventricles when the heart
is at rest
Cardiac Cycle and Heart Sounds
Cardiac Cycle:
– The events of one complete heart beat
– Occurs in less than 0.8 seconds
1. Mid to late Diastole
1. Heart is completely relaxed, pressure is low,
blood flows passively into the atria and into the
ventricles from the pulmonary and systemic
circulations.
2. Semilunar valves are closed, AV valves are open
3. Atria contracts forcing remaining blood into the
ventricles
Cardiac Cycle and Heart Sounds
2. Ventricular Systole:
- Ventricles contract, increase in pressure in
ventricles, AV valves close, when intraventricular
pressure is greater than the pressure I the large
arteries the semilunar valves open and blood
rushes out of the ventricles
- Atria are relaxed and begin to fill with blood.
3. Early Diastole:
- Ventricles relax, semilunar valves shut for a brief
moment the ventricles are completely closed
- Interventricular pressure decreases and when it
drops below the atrial pressure the AV valves are
forced open and ventricles refill with blood and the
cycle is complete!
Heart Sounds
During each cycle of the heart there are two
distinct sounds which can be heard:
– The first is the closing of the AV valves and is a
louder and longer sound
– The second is the closing of the semilunar valves and
the end of systole which is shorter and sharper
sounding
Murmurs:
– Abnormal or unusual heart sounds
– Common in young children
– Indicates a valve problem
(closed or narrowed valves)
Cardiac Output (CO)
Defined: the amount of blood pumped out by
each side of the heart in 1 minute. The product
of heart rate and stroke volume.
Stroke volume (SV):
– Volume of blood pumped out by a ventricle with each
heartbeat.
– Stroke volume increases as the force of the ventricle
contraction increases.
– Average is 70 ml/beat
– The entire blood supply passes through the body one
time each minute!
CO = HR (60-80 bpm) x SV (70 ml/beat)
CO = 5250 ml/min
Regulation of Stroke Volume
The healthy heart pumps out 60% of the blood
that enters it – approximately 70 ml with each
heartbeat!
Starlings Law of the Heart:
– States that the factor controlling SV is how much
cardiac muscle cells are stretched just before the
contraction. More stretch equals a stronger
contraction.
Venous Return:
The amount of blood entering the heart and
descending its ventricles keeps the amount pumped
out each side of the heart equal. This creates an
increase in venous return, increased stroke volume
and increase of the forcefulness of contraction.
Regulation of Heart Rate
Blood volume is decreased causing SV to
decrease and CO is maintained by increasing
the HR
HR can be changed by the ANS, various
chemicals and hormones
During physical and emotional stress the
nerves of the sympathetic system stimulate
the SA and AV nodes to increase HR which
leads to an increase in O2 and glucose
The demand then decreases and the
parasympathetic nerves slow and steady the
heart giving it a chance to rest
Irregularities of the Heart
Congestive Heart Failure (CHF):
– Heart is “worn out” because of age or hypertension and the
heart pumps weakly.
– Epinephrine: mimics the effects of the sympathetic system and
increases HR
– Thyroxin: hormone used to increase HR
Pulmonary congestion:
– The pumping efficiency of the heart is decreased and circulation
is inadequate to meet the needs of the tissues.
– Progressive weakening of the heart due to clogged coronary
vessels, increased BP or multiple myocardial infarctions causes
one side of the heart to fail (usually the L) and fluid leaks into
the lungs causing pulmonary congestion
Peripheral congestion:
– The right side of the heart fails edema