The document describes the structure and function of the heart and Purkinje fibers. It discusses the layers of the heart wall, the four chambers, and valves. It explains that Purkinje fibers are specialized cardiac muscle cells that rapidly conduct electrical impulses from the ventricles to contract the myocardium and eject blood from the heart. The document provides details on the histological appearance of Purkinje fibers and their role in ventricular conduction when pacemaker function is compromised.

1. Name : RATHER ALI MOHMAD
SEMEY STATE MEDICAL
UNIVERSITY
SIW
Topic:Descripition of heart and
purkinje fibres

2. The heart is an in-line pump for the cardiovascular system, so it is continuous with the
veins and arteries that are attached to it (vena cava, pulmonary veins, pulmonary artery,
and aorta). As you know, the heart has four chambers; right atrium, left atrium, right
ventricle, left ventricle. Atrioventricular valves separate the atria from the ventricles,
while semilunar valves separate the ventricles from the pulmonary trunk / aorta.

3. Heart – "four
chambered"
Right atrium &
ventricle
Pulmonary circuit
Left atrium & ventricle
Systemic circuit

4. Similar to the vessels, the wall of the heart is organized into three layers;
1. Endocardium – which is a simple squamous endothelium (plus basement
membrane) with an underlying subendocardial region consisting of connective
tissue, smooth muscle, nerves.
2. Myocardium – cardiac muscle (with connective tissue elements)
3. Epicardium – mostly adipose tissue, with an outer visceral pericardium

5. In case it’s not obvious, the three layers are found in the walls of the heart. In the atrial and
ventricular septa and papillary muscles, only the endocardium and myocardium are
present. As we will see, valves have only structures from the endocardium (i.e. endothelium
plus connective tissue).

6. The section below is similar to the boxed region in the
drawing to the left. The atrium, ventricle, and
atrioventricular valve (arrows) are indicated. This
slide was stained using a special stain (Trichrome) that
is similar to H&E, but also gives connective tissue
fibers an “aqua” color. This staining highlights
connective tissue in the endocardium and valve.
Lumen of
ventricl
eatrium
Note that:
1. the myocardium in the
ventricle is thicker than
in the atrium
2. the endocardium is
thicker in the atrium
than in the ventricle
3. there are vessels in the
epicardium…these are
the coronary arteries and
cardiac veins that supply
the heart

7. The section below is similar to the boxed region in the
drawing to the left, so that it includes the wall of the
right ventricle and pulmonary artery as indicated, as
well as a semilunar valve (arrows).
Right
ventricle
Pulmonary artery
Actually,the regionin the boxappearsto include the atrialwall and the mitral
valve,which are not on the slide. Thisis because the sectionis actuallya sagittal
slice takenof the anterior wallof theventricle and artery(yellowline in image
below).

8. The section below is more difficult to visualize. The cut is similar to the yellow dotted
line in the drawing, but the line runs posterior to the pulmonary artery. Recall that the
aorta passes posterior to the pulmonary artery. This section is through the anterior wall
of the left ventricle, aorta, and (aortic) semilunar valve (arrows), but includes the
posterior wall of the pulmonary artery, as well as the connective tissue that is shared
between these great vessels.
Lumen of
heart
Left
ventricl
e
Lumen of aorta
Of course,thiscould be the right ventricle,withthe vesselsswitched,but again,nothing to worryabout.
Lumen of
pulmonary artery

9. A magnified view of a valve shows
that it has a core of connective
tissue, covered by endothelial cells
(arrows) that are continuous with
the endothelium of the chambers.

10. At the base of the valve, there is a
thickening of connective tissue called
the annulus fibrosus.
We’llshowyou the annulus fibrosus on
the slidesnow,followedby a more
detaileddescription of its structure and
function.

11. The four valves are in approximately the same plane within the heart. More
specifically, it’s the base of the valves that are in this same plane. Note that this is at
the level of the coronary (atrioventricular) sulcus.

13. SERIES AND
PARALLEL CIRCUITS

15. Purkinje fibers are specialized for the
transmission of excitation. They are larger
than ordinary muscle fibers. The bulk of
the sarcoplasm is occupied by glycogen
that is not preserved in most histological
preparations; consequently, Purkinje fibers
have a clear empty appearance in most
preparations.
PURKINJE FIBRES

16. The Purkinje fibers are further specialized to
rapidly conduct impulses (numerous fast voltage-
gated sodium channels and mitochondria, fewer
myofibrils than the surrounding muscle tissue).
Purkinje fibers take up stain differently from the
surrounding muscle cells because of relatively
fewer myofibrils than other cardiac cells and the
presence of glycogen around the nucleus causes
Purkinje fibers to appear, on a slide, lighter and
larger than their neighbors, arranged along the
longitudinal direction (parallel to the cardiac
vector) . They are often binucleated cells.
PURKINJE FIBRES

17. Heart rate is governed by many influences from the
autonomic nervous system. The Purkinje fibers do not
have any known role in setting heart rate but are
influenced by electrical discharge from the sinoatrial
node.
During the ventricular contraction portion of the
cardiac cycle, the Purkinje fibers carry the contraction
impulse from both the left and right bundle branch to
the myocardium of the ventricles. This causes the
muscle tissue of the ventricles to contract and
generate force to eject blood out of the heart, either
to the pulmonary circulation from the right ventricle
FUNCTION

18. Purkinje fibers also have the ability of firing at a
rate of 15-40 beats per minute if upstream
conduction or pacemaking ability is
compromised. In contrast, the SA node in
normal state can fire at 60-100 beats per
minute. In short, they generate action
potentials, but at a slower rate than sinoatrial
node. This capability is normally suppressed.
Thus, they serve as the last resort when other
pacemakers fail. When a Purkinje fiber does
fire, it is called a premature ventricular
contraction or PVC, or in other situations can be
a ventricular escape. It plays a vital role in the
circulatory system
FUNCTIO
N

19. The conducting system of the heart transmits electrical stimuli to
cardiac muscle in a systematic fashion to maximize directional
pumping of blood.
The stimulus is initiated by the sinoatrial (SA) node near the
superior vena cava. Because cardiac muscle cells are connected
by gap junctions, the impulse spreads from the SA node through
the atria toward the ventricles (purple wave in image to the right).
This causes a contraction wave that propels blood through the AV
valves. However, this impulse does not pass directly to the
ventricles due to the presence of the fibrous tissue of the annulus.
Impulses reach the atrioventricular (AV)
node, which passes the impulse through
the annulus fibrosus, and down the
ventricular septum via the AV bundle and
bundle branches, and finally into the
remainder of the ventricular wall via
Purkinje fibers. In this manner,
ventricular contraction spreads as a wave
from the apex toward the great arteries,
propelling blood superiorly.

20. In this slide, don’t worry about orientation or
chamber identification. Suffice it to say that the
region within the rectangle and shown below is
part of the endocardium of a ventricle.
The cells in the outlined
region are Purkinje
fibers, modified cardiac
muscle cells. They are
easily identified because
they have striations, and
the cytoplasm near the
nucleus contains
glycogen, which washes
away during tissue
preparation.

25.  Taber, Clarence Wilbur; Venes, Donald (2009).
Taber's cyclopedic medical dictionary. F a Davis
 Hall, John (2011). Guyton and Hall textbook of
medical physiology (12th ed.). Philadelphia, Pa.:
Saunders/Elsevier. p. 157.. Cite error: Invalid
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