Anatomy of the
Cardiovascular
System
Chapter 18
pages 677 - 724
Heart


Location of the heart

Lies in the mediastinum

ribs 2 through 6

approximately two thirds of
its mass is to the left of the
midline

Apex lies on the diaphragm,
pointing to the left

Base lies just below the
second rib
Boundaries of the heart are
clinically important as an
aid in diagnosing heart
disorders
Coverings of the heart

Pericardium
Fibrous pericardium

tough, loose-fitting
inextensible sac
Serous pericardium



parietal layer lies inside
fibrous pericardium
visceral layer
(epicardium) adheres to
outside of the heart
provides protection
against friction
Layers of the heart

Epicardium


Myocardium



outer layer of heart wall
thick, contractile middle
layer of heart wall
compresses the heart
cavities, and the blood
within them,
with great force
Endocardium

delicate inner layer of
endothelial tissue
Chambers of the heart

Atria (2)
 “receiving chambers”
 because they receive
blood from veins

Myocardial wall of
each atrium is not
very thick
Chambers of the heart


Ventricles
 “pumping chambers”
 because they push blood
into the large network of
vessels
Ventricular myocardium is
very thick
 because great force must
be generated to pump
blood a large distance
 myocardium of left
ventricle is thicker than
the right
 because it must push
blood much further
Heart Valves
Atrioventricular (AV) valves

prevent blood from flowing
back into the atria from the
ventricles when the ventricles
contract
Tricuspid valve (right AV valve)


guards the right atrioventricular
orifice
free edges of three flaps of
endocardium are attached to
papillary muscles by chordae
tendineae
Bicuspid, or mitral, valve (left AV
valve)

similar in structure to tricuspid
valve except only two flaps
present
Heart Valves
Semilunar (SL) valves


Pulmonary semilunar
valve


Half-moon shaped valves
that prevent back flow
into the heart
at entrance of pulmonary
artery
Aortic semilunar valve

at entrance of aorta
Blood supply of heart tissue

Myocardial cells receive
blood from right and left
coronary arteries





First branches to come off aorta
Ventricles receive blood from
branches of both right and left
coronary arteries
Each ventricle receives blood
only from a small branch of
corresponding coronary artery
Most abundant blood supply
goes to myocardium of left
ventricle
The right coronary artery is
dominant in approximately 50%
of all hearts and the left in about
20%; in approximately 30%,
neither coronary artery is
dominant
http://www.youtube.com/watch?v=TS0Je1m9Q8A&feature=player_detailpage
Blood supply of heart tissue

Veins of the coronary
circulation



As a rule, veins follow a
course that closely
parallels that
of coronary arteries
After going through
cardiac veins, blood
enters coronary sinus to
drain into right atrium
Several veins drain
directly into right atrium
Conduction system of the heart


Key Components
Sinoatrial node


Atrioventricular node


small mass of special cardiac
muscle in right atrium along lower
part of interatrial septum
Atrioventricular bundle


hundreds of cells in right atrial
wall near opening of superior
vena cava
AV bundle originates in AV node,
extends by two branches down
the two sides of the
interventricular septum
Purkinje fibers

extend out to papillary muscles
and lateral walls of ventricles
Nerve supply of the heart

Cardiac plexuses
located near arch of
aorta, made up of the
combination of
sympathetic and
parasympathetic fibers



Most fibers end in the
SA node, but some end
in the AV node and in
the atrial myocardium
Sympathetic nerves
accelerator nerves
Vagus fibers inhibitory,
or depressor, nerves
Blood Vessels

Arteries


Veins


Carry blood away from
heart
Carry Blood toward the
heart
Capillaries

Carry blood to cells of the
body
Arteries

Elastic arteries




Able to stretch without
injury
Accommodate surge of
blood when heart
contracts and able to recoil
when ventricles relax
aorta and its major
branches
Muscular (distributing)
arteries



Smaller in diameter than
elastic arteries
Muscular layer is thick
brachial, gastric

Arterioles (resistance
vessels)



Smallest arteries
Important in regulating
blood flow to endorgans
Metarterioles


Short connecting vessel
between true arteriole
and 20 to 100 capillaries
Encircled by precapillary
sphincters
Capillaries
True
capillaries
receive
blood flowing from
metarteriole with input regulated by
precapillary sphincters
Continuous
Continuous
capillaries
lining of endothelial
cells
Openings called intercellular clefts
exist between adjacent endothelial
cells
Fenestrated
capillaries
Have
both intercellular clefts and
“holes” to facilitate exchange
functions

Sinusoids
Large
lumen and tortuous course
Absent or incomplete basement
membrane
Veins

Veins




Carry blood toward the
heart
Act as collectors and as
reservoir vessels
capacitance vessels
Types


Veinules
Veins
Blood Vessel Layers

Three Main layers

Tunica adventitia


Tunica media


found in arteries and veins
found in arteries and veins
Tunica intima


found in all blood vessels
only layer present in
capillaries
Building Blocks of Blood Vessels

Lining endothelial cells


Only lining found in
capillary
Line entire vascular tree



Provide a smooth luminal
surface—protects against
intravascular coagulation
Capable of secreting a
number of substances
Capable of reproduction
Building Blocks of Blood Vessels

Collagen fibers

Exhibit woven
appearance


Have only a limited ability
to stretch (2% to 3%)
under physiological
conditions
Function to strengthen
and keep lumen of vessel
open

Building Blocks of Blood
Vessels
Elastic fibers



Fibers can stretch over 100%
under physiological
conditions
Play important role in
creating passive tension to
help regulate blood pressure
throughout cardiac cycle
Smooth muscle fibers



Present in all segments of
vascular system except
capillaries
Most numerous in elastic
and muscular arteries
Exert active tension in
vessels when contracting
Circulatory routes

Systemic circulation




Left sided pump
blood flows from the
left ventricle of the
heart through blood
vessels to all parts of
the body
except gas exchange
tissues of lungs
back to right atrium
Circulatory routes

Pulmonary circulation




Right Sided pump
venous blood moves
from right atrium to
right ventricle to
pulmonary artery to
lung arterioles and
capillaries
gases are exchanged
oxygenated blood
returns to left atrium via
pulmonary veins
Systemic circulation

Arterial anastomosis


open into other branches
of the same or other
arteries
Arteriovenous
anastomoses

shunts occur when blood
flows from an artery
directly into a vein
Systemic circulation


Superior Vena Cava

Venous blood from the
head, neck, upper
extremities, and thoracic
cavity

except lungs
Inferior vena cava

Venous blood from lower
extremities and abdomen



Fetal circulation
Two umbilical arteries
 extensions of internal iliac
arteries;
 carry fetal blood to placenta
Placenta
 attached to uterine wall
 where exchange of oxygen
and other substances
between the separated
maternal and fetal blood
occurs
Umbilical vein
 returns oxygenated blood
from placenta to fetus
 enters body through
umbilicus continues as
ductus venosus

Ductus venosus


Foramen ovale


continuation of umbilical
vein, drains into inferior
vena cava
opening in septum
between right and left
atria
Ductus arteriosus

small vessel connecting
pulmonary artery with
descending thoracic aorta
Diagram of Fetal Blood Flow
Fetal circulation

Changes in circulation at birth

When umbilical cord is cut, the two
umbilical arteries, the placenta and
the umbilical vein no longer
function




Umbilical vein within the baby’s body
becomes the round ligament of the
liver
Ductus venosus becomes the
ligamentum venosum of the liver
Foramen ovale

functionally closed shortly after a
newborn’s first breath and pulmonary
circulation is established

structural closure takes approximately
9 months
Ductus arteriosus

contracts with establishment of
respiration, becomes ligamentum
arteriosum
Changes over time

Birth


Childhood to adulthood



Exercise thickens myocardium
increases blood supply
Adulthood through later
adulthood


change from placenta-dependent
system
degenerative changes
Atherosclerosis


blockage or weakening of critical
arteries
Heart valves and myocardial tissue
degenerate - reduces pumping
efficiency