Transcript 3 layers

2006 clinical medicine
Circulatory System
Department of Histology and
Embryology Li jinxin No.1020603
CIRCULATARY SYSTEM
In this chapter, the following are examined:
1. Organisation of the heart , including
the three-layered structure of the
heart wall and the conducting system.
2. Histological characteristics of the
various segment of the arteries and
veins.
3. Correlation between the structure
of the three types of capillary and
their major functions.
1.General description
--- closed tubular
system consisting
of cardiovascular and
lymphatic vascular
system.
1.1 The cardiovascular system
includes the heart, arteries,
capillaries and veins. They are
hollow organs, wall of which is
composed of 3 tunics and lined
with endothelium.
1.2 The lymphatic vascular system
begins in blind-ended lymphatic
capillaries, which anastomose in
lymphatic vessels and then empty
into the large veins near the heart
by lymphatic ducts.
2.Heart – a pump
The wall of the heart
– 3 layers:
endocardium
myocardium
epicardium
endocardium
myocardium
epicardium
2.1 Endocardium – thin inner lining
composed of 3 layers
a. Endothelium
b. Subendothelial layer is a thin sheet of
connective tissue.
c. Subendocardial layer consists of loose
connective tissue and the conducting
system of the heart.
Endothelium
Subendothelial
layer
Subendocardial
layer
2.2 Myocardium
a. Composed of cardiac muscle
richly supplied with capillaries.
b. Thicker in ventricles than in atria,
and thickest in the left ventricle.
c. Atrial myocardial fibers contain
specific atrial granules secreting
atrial natriuretic factor (ANF).
This hormone increases excretion
of water and sodium and
potassium ions and decreases
blood pressure.
2.3 Epicardium – visceral
layer of the pericardium
a. Consists of a thin layer of
loose connective tissue covered
by mesothelium ( 间皮 ).
b. Numerous adipose cells in
the subepicardial layer.
2.4 Conducting system of the heart
2.4.1 Composed of
 the sinoaterial
node (SA),
 atrioventricular
node (AV),
 AV bundle and
the network
 Purkinje fibers.
2.4.2 Three types of specialized
cardiac muscle cells:
P-cells
(pacemaker cells),
 transitional cells
 Purkinje fibers.

2.4.3 Purkinje fibers – terminal
branches of conducting system
a. Broader and shorter than ordinary
cardiac muscle fibers.
b. Pale stained and rich in sarcoplasm.
c. Few myofibrils.
d. Well-developed intercalated discs
between Purkinje fibers.
3.Arteries
General structure of blood vessels
---- three layers (except for capillaries)

Tunica intima
– inner tunic
Tunica media
– middle layer
Tunica adventitia
– outer layer
A. Tunica intima
consisting of 3 layers
 Endothelium :simple
squamous epithelium.
 Subendothelial layer
is loose connective
tissue.
 Internal elastic
membrane is made up
of elastin.
B. Tunica media
Consists mainly of smooth muscle cells
and fenestrated elastic membranes,
among which variable amounts of
fibers and matrix are interposed.
 There are no fibroblasts. Smooth
muscle cells are responsible for
production of the fibers and matrix.

C. Tunica adventitia
Outer layer of loose connective tissue
with vasa vasorum (营养血管)and
nerve.
 The external elastic membrane
may be found between media and
adventitia.

Arteries
– classified according to size into 3 groups:
A. Large arteries
(conducting arteries)
B. Medium-sized arteries
( distributing arteries)
C. Small arteries
( resistance vessels)
3.1 Large


arteries
The large arteries include the aorta,
the pulmonary trunk and their main
branches.
40 –70 layers of elastic membranes
in the tunica media. (elastic arteries)
Subendothelial layer
Endothelium
Tunica
intima
Tunica
media
Tunica
adventitia
vasa vasorum
Tunica media
Function

They carry the blood from the heart to
the middle arteries.
3.2 Medium-sized arteries
Thin tunica intima with distinct internal
elastic membrane.
 Tunica media is composed of 10 - 40
layers of smooth muscle cells (muscular
arteries).
 Tunica adventitia is as thick as the tunica
media. A definite external elastic
membrane is situated between the tunica
media and the tunica adventitia.

1.Endothelium 2.internal elastic membrane
3.Tunica media 4.Tunica adventitia
Function

These vessels regulate the distribution
of the blood to various parts of the
body. They are therefore also termed
distributing arteries.
3.3 Small arteries



With a diameter less than 1mm. Called
arterioles if less than 300 µm.
The internal elastic membrane is
prominent. When the diameter is less
than 50µm, The internal elastic
membrane disappears
The tunica media is mainly composed
of 3 - 5 layers of smooth muscle cells
(muscular arteries).
Small
arteries
Small vein
arteriole
Function
These vessels regulate the distribution
of the blood to various parts of the
body tissue.
 Resistance vessels.

4. Capillaries




The smallest blood vessels with diameter
of 5 -10 µm.
The thinnest wall composed of
endothelium resting on a basal lamina,
within which pericytes are enclosed.
Distribute widely in the body and form a
network with different density according
to metabolism.
Great surface area (6000 m2) facilitates
substance exchange.
2
1
1. Basement
Membrane
2. Pericyte
3. Endothelial
cells
3
Classification



based on ultrastructures
Continuous capillaries
Fenestrated capillaries
Sinusoids (discontinous capillary)
4.1 Continuous capillaries




A continuous layer of endothelial cells
joined by tight junctions.
A continuous layer of basal lamina.
A large number of pinocytotic vesicles in
the cytoplasm of endothelial cells.
Present in the muscular tissue,
connective tissue, nervous tissue and
lungs.
tight junction
pinocytotic vesicles
4.2 Fenestrated



capillaries
The continuous endothelium and basal lamina
is the same as that of the continuous type.
Characterized by pores, usually closed by a
diaphragm.
Present in tissues in which rapid exchange of
substances occurs between the tissues and the
blood, such as in the renal glomerulus,
submucosa of stomach and intestine, and some
endocrine glands.
pore
4.3 Sinusoids (discontinous capillary)
An enlarged and irregular lumen
(diameter of 30 - 40µm).
 Wide gaps (discontinuous) between
endothelial cells.
 The basal lamina may be incomplete or
lack at all.
 Found in the liver, spleen, bone marrow,
and certain endocrine glands.

5.Veins – capacitance vessels




Larger diameter, thinner wall and fewer
smooth muscles than accompanying arteries.
Internal and external elastic membranes are
absent.
The adventitia is the thickest consisting of
longitudinally oriented smooth muscle cells,
collagenous and elastic fibers.
Lumen frequently appears irregular, with
valves (folds of intima) in small and mediumsized veins to prevent blood flow in reverse
direction.
Exercise:
1.Describe the structure and function of
the heart wall.
2.Compare the structure features and
function of the three sizes of artery.
3. Describe the general structure of the
capillaries and the features of three
types of capillary.
4.What are the structural features of
veins compared with arteries?