the cardiovascular system: the heart chapter 19. introduction the heart is the pump of our...
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The Cardiovascular System:The Heart
Chapter 19
Introduction The heart is the pump of our circulatory
system The cardiovascular system provides the
transport system of the body Using blood as the transport medium, the
heart continually propels oxygen, nutrients, wastes, and many other substances into the interconnecting blood vessels that move past the body cells
Heart Size, Location and Position The heart is about the
size of a fist It weighs between 250 -
350 grams (less than a pound)
Located in the medial cavity of the thorax, the mediastinum
It extends from the 2nd rib to 5th intercostal space
Rests on the superior surface of diaphram
Heart Size, Location and Position
The lungs flank the heart laterally and partially obscure it
Heart Size, Location and Position The heart lies anterior to
the vertebral column and posterior to the sternum
Two thirds of the heart lies to the left of the mid- sternal line; the balance projects to the right
Its broad flat base, or posterior surface, points to right shoulder
The apex points toward the left hip
Coverings of the Heart
The heart is enclosed in a double-walled sac called the pericardium
The loose fitting superficial part of the sac is the fibrous pericardium– This tough, dense connective tissue layer 1) protects the
heart; 2) anchors the heart; and 3) prevents overfilling
Coverings of the Heart
The loose fitting superficial part of the sac is the fibrous pericardium
This tough, dense connective tissue layer– Protects the heart
– Anchors it to surrounding structures (diaphragm/large vessels)
– Prevents overfilling of the heart with blood
Coverings of the Heart
Deep to the fibrous pericardium is the serous pericardium, a thin slippery serous membrane composed of two layers– Parietal layer
– Visceral layer
Coverings of the Heart
The parietal layer lines the internal surface of the fibrous pericardium
At the superior margin of the heart, the parietal layer attaches to the large arteries exiting from the heart
It then turns inferiorly and continues over the external heart surface as the visceral layer
Coverings of the Heart
The visceral layer, also called the epicardium, is an integral part of the heart wall
The layer membrane conforms around the heart much like pushing your fist into a double layer membrane with an air pocket in between
Coverings of the Heart
Between the two layers of serous pericardium is the slitlike pericardial cavity
The cavity contain pericardial fluid The serous membranes, lubricated by fluid, glide
smoothly against one another during heart activity, creating a relatively friction-free environment
Inflammation Inflammation of the heart can lead to
serious problems– Pericarditis / hinders production of serous
fluid production causing the heart to rub– Cardiac tamponade / inflammatory fluid
seep into the pericardial cavity, compressing the heart and limiting its ability to pump blood
Layers of the Heart Wall
The heart wall is composed of three layers– Superficial layer of epicardium
– Middle layer of myocardium
– Deep layer of endocardium All three layers are richly supplied with blood vessels
Layers of the Heart Wall
The epicardium is the visceral layer of the serous pericardium
The epicardium is often infiltrated with fat, especially in older people
Layers of the Heart Wall
The myocardium is the layer of cardiac muscle that forms the bulk of the heart
It is the layer that actually contracts
Layers of the Heart Wall Within the myocardium, the branching
cardiac muscle cells are tethered to each other by crisscrossing connective tissue fibers arranged in spiral or circular bundles
These interlacing bundles effectively link all parts of the heart together
Layers of the Heart Wall The connective tissue
forms a dense network called the internal skeleton of the heart
It reinforces the myocardium internally and anchors the cardiac muscle
This network of fibers is thicker in some areas than in others to rein- force valves and where the major vessels exit
Layers of the Heart Wall The internal skeleton
prevents overdilation of vessels due to the continual stress of blood pressure
Additionally, since connective tissue is not electrically excitable, it limits action potentials across the heart to specific pathways
Layers of the Heart Wall
The endocardium is a glistening white sheet of endothelium (squamous epithelium) resting on a thin layer of connective tissue
Layers of the Heart Wall Located on the inner myocardial surface, it
lines the heart chambers and covers the connective tissue skeleton of the valves
The endocardium is continuous with the endothelial linings of the blood vessels leaving and entering the heart
Chambers and Great Vessels The heart has four
chambers – Two superior atria
– Two inferior ventricles The longitudinal wall
separating the chambers is called the– Interartial septum
• Between atria
– Interventricular septum
• Between ventricles
Atria
Septum
Ventricles
Chambers and Great Vessels The right ventricle
forms most of the anterior surface of the heart
The left ventricle dominates the inferio- posterior aspect of the heart and forms the heart apex
Right Ventricle
LeftVentricle
Chambers and Great Vessels Two grooves visible
on the surface of the heart indicate the boundaries of its four chambers and carry the blood vessels that supply myocardium
The Atrioventricular groove or coronary sulcus encircles the junction of the atria and ventricles Coronary
Sulcus
Chambers and Great Vessels The anterior inter-
ventricular sulcus, separates the right and left ventricles
It continues as the posterior inter-ventricular sulcus which provides a similar landmark on the heart’s posterio- inferior surface
AnteriorInterventricular
Sulcus
PosteriorInterventricular
Sulcus
Atria: The Receiving Chambers Except for the small,
wrinkled, protruding appendages called auricles, the atria are free of distinguishing surface features
The auricles increase the atrial volume slightly
Auricles
Atria
Atria: The Receiving Chambers Internally, the
posterior walls are smooth, but the anterior walls are ridged by bundles of muscle tissue
These muscle bundles are called pectinate muscles
PectinateMuscle
Atria: The Receiving Chambers The interatrial
septum bears a shallow depression, the fovea ovalis
This landmark marks the spot where an opening, the foramen ovale, existed in the fetal heart
FoveaOvalis
Atria: The Receiving Chambers Functionally, the atria are receiving
chambers for blood returning to the heart from the circulation
Because they need to contract only minimally to push blood into the ventricles, the atria are relatively small, thin walled chambers
As a rule they contribute little to the propulsive pumping of the heart
Atria: The Receiving Chambers Blood enters the right
atrium via three veins– Superior vena cava
• Returns blood from body regions superior to diaphragm
– Inferiorn vena cava• Returns blood from
body areas below the diaphragm
– Coronary sinus• Collects blood draining
from the myocardium itself Inferior
vena cava
Superiorvenacava
Coronarysinus
Atria: The Receiving Chambers Blood enters the left
atrium via four veins– Right and left
pulmonary veins The pulmonary veins
transport blood from the lungs back to the heart
Posteriorview
Leftpulmonary
veins
RightPulmonary
veins
Ventricles: Discharging Chambers Marking the internal
walls of the ventricle chambers are irregular ridges of muscle called trabeculae carneae
The papillary muscles project into the cavity and play a role in valve function
Trabeculaecarneae
Papillarymuscles
Ventricles: Discharging Chambers The ventricles are
the discharging chambers of the heart
Note the difference in thickness of the wall
When the ventricles contract blood is propelled out of the heart and into circulation
Atrial Wall
VentricularWall
Ventricles: Discharging Chambers The right ventricle
pumps blood into the pulmonary trunk, which routes blood to the lungs for gas exchange
The left ventricle pumps blood into the aorta, the largest artery in the systemic circulation
Aorta
Leftventricle
Rightventricle
Pulmonarytrunk
Pathway of Blood: Heart The heart is actually
two pumps, each serving a separate blood circuit
Blood vessels that carry blood to the lung form the pulmonary circuit (gas exchange)
Vessels carrying blood to the body form the systemic circuit
Pathway of Blood: Heart The right side of the
heart forms the pulmonary circuit
Blood returning from the body enters the right atrium and passes into the right ventricle
The ventricle pumps the blood to the lungs via the pulmonary trunk
Pathway of Blood: Heart Blood in the
pulmonary circuit is oxygen poor and carbon dioxide rich
Once in the lungs the blood unloads carbon dioxide and picks up oxygen
Freshly oxygenated is carried back to the heart by the pulmonary veins
Pathway of Blood: Heart Note that the circulation of the pulmonary
circuit is unique Typically veins carry oxygen poor blood to
the heart and arteries carry oxygen rich blood
The pattern is reversed in the pulmonary circuit with the pulmonary arteries carrying oxygen poor blood to the lungs and the pulmonary veins carrying oxygen rich blood back to the heart
Pathway of Blood: Heart The left side of the
heart is the systemic system pump
Freshly oxygenated blood leaving the lungs enters the left atrium and passes into the left ventricle
The left ventricle pumps blood into the aorta and from there into many distributing arteries
Pathway of Blood: Heart Smaller distributing
arteries carry the blood to all parts of the body
Gases, wastes and nutrients are exchanged across capillary walls
Blood then returns to the right atrium of the heart via systemic veins and the cycle continues
Pathway of Blood: Heart Although equal volumes of blood are
flowing in the pulmonary and systemic circuits at any one moment the two ventricles have very unequal work loads
The pulmonary circuit, served by the right ventricle, is a low pressure circulation
The systemic circuit, served by the left ventricle, circulates through the entire body and encounters about five times as much resistance to blood flow
Ventricles: Discharging Chambers The difference in
system work load is revealed in the comparative anatomy of the two ventricles
The walls of the left ventricle are three times as thick as those of the right ventricle
Leftventricle
Ventricles: Discharging Chambers The cavity of the left
ventricle is circular The right ventricle
wraps around the left and is crescent shaped
The left can generate much more pressure than the right and is a far more powerful pump
Leftventricle
Pathway of Blood: System Blood flows through the heart and other
parts of the circulatory system in one direction– Right atrium right ventricle pulmonary
arteries lungs– Lungs pulmonary veins left atrium left
ventricle body This one way flow of blood is controlled by
four heart valves
Heart Valves Heart valves are
positioned between the atria and the ventricles and between the ventricles and the large arteries that leave the heart
Valves open and close in response to differences in blood pressure
Bicuspid(mitral)
valve
Aorticvalve
Pulmonaryvalve
Tricuspidvalve
Heart Valves The valves of the
heart allow for the blood to flow in only one direction
Note: View of the heart with the superior atria removed
Atrioventricular (AV) Valves The AV valves are
located at each atrial-ventricular junction
The valves are positioned to prevent a backflow of blood into the atria when the ventricles are contracting
The valves are the– Tricuspid valve
– Bicuspid valve
Bicuspid(mitral)
valve
Tricuspidvalve
Atrioventricular (AV) Valves The right AV valve,
the tricuspid, has three flexible cusps
The left AV valve, the bicuspid, has two flexible cusps
The cusps are flaps of endocardium reinforced by connective tissue
Bicuspid(mitral)
valve
Tricuspidvalve
Atrioventricular (AV) Valves Attached to each of
the AV valve flaps are tiny collagen cords called chordae tendoneae
The cords anchor the cusps to the papillary muscles protruding from the ventricular walls
Chordaetendoneae
Papillarymuscles
Atrioventricular (AV) Valves When the heart is
completed relaxed, the AV valve flaps hang limply into the ventricular chambers
Blood flows into the atria and then through the open AV valves into the ventricles
Atria contract, forcing additional blood into ventricles
Atrioventricular (AV) Valves When the ventricles
begin to contract, compressing the blood in the chambers, intra- ventricular pressure rises forcing blood superiorly against the valve flaps
The chordae tendoneae and the papillary muscles anchor the flaps in their closed position
Semilunar (SL) Valves The aortic and
pulmonary semilunar valves are located at the bases of the large arteries exiting the ventricles
The valves prevent backflow of blood from the aorta and pulmonary trunk into the associated ventricles
Aorticvalve
Pulmonaryvalve
Semilunar (SL) Valves Each semilunar valve
is made up of three pocketlike cusps
Their mechanism of closure differs from that of the AV valves
When the ventricles contract intra- ventricular pressure exceeds the blood pressure in the aorta and pulmonary trunk
Semilunar (SL) Valves Blood pressure from
the ventricle forces the semilunar valves open and blood is forced past the valve and into the artery
When the ventricles relax, and the blood flows backward toward the heart it fills the cusps which closes the valves
Coronary Circulation The coronary
circulation, the functional blood supply of the heart, is the shortest circulation in the body
The arterial supply of the coronary circulation is provided by the right and left coronary arteries
Coronary Circulation The left coronary
artery runs toward the left side of the heart and then divides into its major branches
Anterior interventricular artery follows the sulcus and supplies blood to the inter- ventricular septum and walls of ventricle
Coronary Circulation The right coronary
artery courses to the right side of the heart where it divides
The marginal artery serves the myo-cardium of the lateral part of the right side of the heart
The posterior inter-ventricular artery runs to the apex of the heart
Coronary Circulation There are many merging blood vessels
that delivery blood to the heart muscle This explains how the heart can receive
an adequate supply when one of its coronary arteries is almost entirely occluded
Coronary Circulation The coronary arteries provide an inter-
mittent pulsating flow to the myocardium These vessels and their main branches lie
in the epicardium and send branches inward to nourish the myocardium
Although the heart represents only about 1/200 of body weight, it requires 1/20 of the body’s blood supply
The left ventricle receives the largest proportion of the blood supply
Coronary Circulation After passing
through the myo- cardium, the venous blood is collected by the cardiac veins
The veins join together to form an enlarged vessel called the coronary sinus which empties into the right atrium
End of Material
Chapter 19