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