Circulatory system
Shiping Ding (丁世萍), Ph. D
School of Medicine, Zhejiang University
Learning Objectives
• To be familiar with the type of capillary.
• To be familiar with the type of artery and vein.
• To distinguish with all the types of blood
vessels.
Concepts of organs and systems
 Organ: composed of four kinds of the tissues
in a particular way
Types
Hollow organs: studied from inside to outside
parenchyma
Substantial organs:
interstitium
 System: composed of many organs which
have relationship with each other in
structure and function.
General outline
---Closed tubular system
According to the circulating
fluid in the tubes, blood or lymph:
•Blood vascular system
(cardiovascular system)
•Lymphatic vascular system
Cardiovascular System
The histological study of the cardiovascular system
includes two major components
• Heart – mainly functions as a pump to move blood
(and all the things blood carries) through the body.
• Blood vessels – are the tubes that distribute the blood
to the cells and then back to the heart.
The blood vessels include three major divisions:
Arteries –
deliver blood from heart to capillaries
Capillaries –
the smallest blood vessels and closest to
body cells, the interchanges between blood
and tissues occur there
Veins –
carry blood from body to the heart
Histological Structure of Blood Vessels
Structural feature of
Arteries and Veins:
Tunica intimae
1. Endothelium
2. Subendothelial layer
3. Internal elastic membrane
Tunica media
Mainly smooth muscle
Tunica adventitia
external elastic membrane
Mainly connective tissue
medium-sized A
Artery
 transport blood from heart to capillaries
 according to their size, structure and function
are classified
Large artery
Medium-sized artery D>1mm
Small artery D>0.3~1mm
Arteriole D<0.3mm
Structure features of artery
• The wall of Arteries consist of three
layers or “coats” often referred to as
tunics.
– Tunica intimae – is the inner coat
– Tunica media – is the middle layer
– Tunica adventitia or tunica externa is
the outer layer of the wall of the blood
vessel
• Layers of arteries wall differ in
different size blood vessels. The
structure and function of arteries
change as their diameter decreases.
Tunica intimae
•
is the inner coat and it
consists of
1)inner endothelial layer
2)subendothelial layer: a layer
of loose connective tissue
3)internal elastic membrane
(often very distinct)
•
This layer is relatively
constant within different size
arteries.
Tunica media
• This layer makes up the greatest part of the wall of the
artery.
• It is comprised primarily of smooth muscle.
• In small arteries or arterioles it may be only 1-3 cells thick
but in larger arteries may comprise hundreds of layers of
muscle cells.
• In large arteries, there in increased amounts of elastin
fibers.
Tunica adventitia
• This is the outer layer of the wall of the artery.
• It consists primarily of connective tissue and serves to
attach the blood vessel into the surrounding connective
tissue.
• Often contains adipose tissue and often contains blood
vessels (vasa vasorum) that supply the walls of the blood
vessels.
Medium-sized artery (Muscular artery):
 muscular artery: diameter larger than 1mm
Tunica intima
Endothelium
Subendothelial layer: LCT
Internal elastic lamina: clear
Tunica media: contain 10~40 layers of circular
smooth muscle
Tunica adventitia
External elastic lamina
LCT: contain vasa vasorum
Medium-sized artery
Tunica
Adventitia
Tunica
Media
Tunica
intima
Classic muscular artery- elastic stain
Large (elastic) artery:
 contains aorta, the pulmonary trunk and
their main branches
With a large lumen relative to wall thickness
 subendothelial layer is thicker with a few
smooth muscles
 tunica media is thick, contains a 40-70
concentrically-arranged elastic lamina
 internal and external elastic lamina are not
distinguished
 tunica adventitia are thinner, abundant vasa
vasorum
PT stain
Elastic artery
Muscular artery
Small artery:
 muscular artery and peripheral resistance vessel
 internal elastic lamina is clear, while external elastic lamina is
not distinguished
 the tunica media contains 3~9 layers of smooth muscles
Arterioles:
Less than 0.3mm in
diameter. Have similar and
simpler structure as that of
muscular artery.
Several layers of smooth
muscle in tunica media.
Responsible
for
the
presence of blood pressure.
Vein
 large lumen, thin wall,
irregular
 internal and external
elastic lamina are not clear
 tunica media is thin, with
a few elastic fibers and
smooth muscles
 tunica adventitia is thick
(best-developed)
 some veins have valves
Large veins
D>10mm
Medium-sized vein
D=2~9mm
Vein valves: Bag-like protrusion of
tunica intima, which prevents the
blood flow from running to opposite
direction. Exists only in the vein that
has low position or far away from
heart.
Vein with valve
A Comparison of a Typical Artery and a Typical Vein
Artery, vein, nerve, elastin stain
elastic tissue is colored dark purple, cytoplasm (in smooth muscle
and nerve) is lighter purple, and collagen is pale pink.
Artery, vein, nerve, elastin stain
elastic tissue is colored dark brown, collagen is pale pink and cytoplasm
(in smooth muscle and nerve) is purple.
Artery, vein, nerve, trichrome stain
collagen is colored blue and smooth muscle is red. Red blood cells in
the venous lumen are brighter red.
Capillaries
• Capillaries are the site where materials carried in the
blood are unloaded and other materials are loaded into the
blood.
• In many organs the capillaries form a network.
• Consist of a single layer of simple squamous epithelium.
the average diameter about 8um.
Capillaries
1) L/M:
• A single layer of endothelial
cells
• Pericyte
• A basement membrane
Pericyte:
long cytoplasmic processes
have a contractile function, participating
in the repair process
Capillary - pericyte
 E/M
The types of Capillaries
Continuous C.
Fenestrated C.
Sinusoid
The types of Capillaries
Continuous
capillary
Structure
endothelial cell:
large number of
pinocytotic vesicles
cell junctions
between the
endothelia (tight
junction)
no pores, no gaps
Fenestrated capillary
Sinusoid
endothelial cells: present
abundant perforated pores (6080nm in D, with 4-6 nm
diaphragm)
a greatly enlarged diameter (30~40um)
have or haven’t diaphragm
on them
 absence of a continuous basement
membrane
basement membrane:
continuous
endothelial cell: intercellular clefts are
large between cells, many pores without
diaphragm
macrophages are located either among
or outside the cells of the endothelium
basement
membrane: integrity
Location
distributed in muscle
tissue, brain, lung
and
connective
tissue, etc.
distributed in tissues where
rapid interchange of substances
occurs between the tissue and
the blood, as in the kidney
glomerulus, mucosa of
gastrointestine, some endocrine
glands
distributed in tissues where interchange of
substance in big size occurs, as in the liver,
spleen, and some endocrine glands
Continuous capillary
Fenestrated capillary
Sinusoid
Heart
 a hollow muscular organ that contracts rhythmically
 pump blood through the circulatory system
The wall of heart
 epicardium
 myocardium
 endocardium
The wall of heart
E
SE
endocardium
subendocardial layer
Purkinje fibers
myocardium
epicardium
endocardium
Endothelium
Subendothelial layer: fined CT
Subendocardial layer: LCT, blood vessels, nerves and
the impulse-conducting system of the heart
myocardium thickest layer, consists of cardiac muscle, is
richly supplied with capillaries
three layers are divided roughly, cardiac
muscle arrange spirally.
闰盘
线粒体
Cardiac muscle:HE×100
epicardium
LCT: contain adipose cells, blood vessels and
nerves
Methothelium
构成心包脏层
心包受损
影响心脏功能
Conducting System
components:
sinoatrial node (SA node):
the primary pacemaker of the heart
located in epicardium of right atrium
atrioventricular node( AV node)
bundles( AV bundles) located in
subendocardial layer.
network of Purkinje fiber
Impulse generating and conducting
system of the heart:
Pacemarker
cell
Transitional cell
Purkinje cell
Location
SA / AV
SA / AV /AV
bundle
AV bundle / branches
Structure
small, fusiform or
polygonal in shaped
thinner and shorter than
caridac muscle
shorter, boarder than caridac muscle,
with 1-2 centrally located nuclei
less myofibril
more myofibril than P cell
rich in mitochondria, glycogen, less
myofibril
well-developed intercalated disks
Function
heartbeat
generating
transmit impulse
Transmit impulse into the
ventricle quickly
transitional cell
Purkinje cell
Purkinje cell
Cardiac cell
Purkinje cells both broader and shorter than
ordinary cardiac muscle fibers, rich in
sarcoplasm, two nuclei can be found, welldeveloped intercalated disks.
Purkinje fiber
Purkinje fibers
The core of dense connective tissue
cardic valve
endothelium
prevent the back flow of blood
Question
1. To describe the difference between
large artery and medium-sized artery.
2. To describe the types of capillary.
Good-bye!
Thank you for your attention!