Download Tunica media

Cardiovascular System
Overview of the cardiovascular
system


The cardiovascular system is a
transport system.
The cardiovascular system includes
the heart, blood vessels, and
lymphatic vessels.
General features of arteries and veins

The walls of
arteries and veins
are composed of
three layers, from
the lumen outward,
which are tunica
intima, tunica
media and tunica
adventitia.
Tunica intima

It consists of three components:
endothelium, basal lamina,
subendothelial layer( loose connective
tissue) and internal elastic membrane.
Internal elastic membrane


Structure: A sheet-like layer or
lamella of fenestrated elastic
material.
Function: Fenestrations enable
substances to diffuse readily
through the layer and reach cells
deep within the wall of the vessel.
Tunica media



This layer consists primarily of layers
of elastic tissue or of smooth muscle.
Some connective tissue is usually
present.
Variable amounts of elastin, reticular
fibers, and proteoglycans are
interposed between the smooth muscle
cells of the tunica media. All of the
extracellular components of the tunica
media are produced by the smooth
muscle cells.
Tunica adventitia


It is composed primarily of longitudinally
arranged collagenous tissue and a few
elastic fibers.
In addition, the tunica adventitia of large
arteries and veins contains a system of
vessels, called vasa vasorum, that supply
blood to the vascular walls themselves, as
well as a network of autonomic nerves,
called nervi vascularis, that contral
contraction of the smooth muscle in the
vessel wall.



Contraction and relaxation of
smooth muscle cells in the tunica
media influence blood flow and
pressure.
Contraction of smooth muscle in
the tunica media reduces the
luminal diameter of vessels,
increasing the vascular resistance.
Leading to an increase in the blood
pressure.
Relaxation of smooth muscle cells
increases the luminal diameter of
the vessels, decreasing vascular
resistance and blood pressure.
Arteries

Arteries are classified into three
types on the basis of size and the
characteristics of the tunica media:
Large or elastic arteries
Medium or muscular arteries
Small arteries and arterioles
Elastic arteries


Elastic arteries have multiple
sheets of elastic lamellae in their
walls.
Function: elastic arteries serve
pimarily as conduction tubes,
however, they also facilitate the
continuous and uniform movement
of blood along the tube.
Elastic arteries-tunica intima

The tunica
intima
consists of
endothelium,
basal lamina,
subendothelial
connective
tissue, and an
inconspicuous
internal
elastic
Elastic arteries-tunica intima

Endothelial cells
possess rod-like
inclusions, called
Weibel-Palade
bodies, which are
present in the
cytoplasm.
Elastic arteries-tunica intima


Weibel-Palade bodies are electrondense structures and contain von
Willebrand factor (also called
coagulating factorⅧ).
von Willebrand factor can combine with
collagen fibers and platelets
simultaneously, when vessels broken,
platelets adhere to collagen fibers to
form thrombus through von Willebrand
factor .
Elastic arteries-tunica intima


Subendothelial layer
is connective
tissue.The main cell
type is the smooth
muscle cell.
The internal elastic
membrane is usually
identified only
because it is the
innermost elastic
Elastic arteries-tunica media


The tunica media
consists of multiple
layers of smooth
muscle cells
separated by elastic
lamellae.
Elastin in the form
of fenenstrated
sheets or lamellae
between the muscle
cell layers. They are
Elastic arteries-tunica media


Smooth muscles
arranged in layers.
Fibroblast are not
present in the
tunica media.
Collagen fibers and
ground substance
are synthesized
and secreted by the
smooth muscle
Elastic arteries-tunica adventitia


The tunica adventitia
is a relatively thin
connective tissue
layer. It is usually
less than half the
thickness of the
tunica media.
Collagen and elastic
fibers are in the form
Elastic arteries-tunica adventitia


Fibroblast and
macrophages are
the principal cells
of the tunica
adventitia.
It consists of blood
vessels and nerves.
Muscular arteries

Muscular
arteries have
more smooth
muscle and
less elastin in
the tunica
media than do
elastic arteries.
Muscular arteries- tunica intima



The tunica intima is
thinner and
contains a
prominent internal
elastic membrane.
Subendothelial
layer is sparse.
In histologic
sections, the
internal elastic
membrane usually
appears as a well-
Muscular arteries- tunica media



The tunica media is
composed almost
entirely of smooth
muscle amid collagen
fibers, with little
elastic material.
The smooth muscle
cells are arranged in a
spiral fashion.
There are no
fibroblasts in this
layer.
Muscular arteries- tunica adventitia

The tunica
adventitia is
relatively thick and
is often separated
from the tunica
media by a
recognizable
external elastic
membrane.
Muscular arteries- tunica adventitia



It consists of
fibroblasts,
collagen fibers,
elastic fibers, and
scattered adipose
cells.
It is about the
same thickness as
the tunica media.
Nerves and small
vessels travel in it.
Small arteries and arterioles


They are distinguished from one
another by the number of smooth
muscle cell layers in the tunica
media.
Arterioles have only one or two
layers of smooth muscle in their
tunica media; a small artery may
have up to about eight layers.
Small arteries and arterioles


Typically, the tunica intima of a
small artery has an internal elastic
membrane, whereas this layer
may or may not be present in the
arteriole.
Both the tunica adventitia is a thin,
ill-defined sheath of connective
tissue.
Veins-characteristics:

Veins are divided into three types
on the basis of size:
Small veins or venules
( postcapillary
and muscular
venules)
Medium veins
Large veins
Veins-characteristics:


Veins have thinner walls than their
accompanying arteries, and the lumen of
the vein is larger than that of the artery.
The tunica media contains a much larger
quantity of collagen than in arteries. The
amount of elastic tissue or of muscle is
much less.
Veins-characteristics:



The wall of a vein is easily compressed.
In arteries the tunica media is usually
thicker than the adventitia. In contrast the
adventitia of veins is thicker than the media.
The tunics of veins are not as distinct or
well defined as the tunics of arteries.
Veins-characteristics:

Many veins, especially those that
convey blood against gravity, contain
valves that allow blood to flow in only
one direction, back toward the heart.
The valves are semilunar flaps
consisting of a thin connective tissue
core covered by endothelial cells.
Summary



Understand the general features of
arteries and veins.
Emphasis: understand the structure of
arteries (elastic, muscular, small
arteries and arterioles).
Know the characteristics of veins.
Homework


Review the structure of arteries and
veins.
Prepare for the next lesson-the
structure of capillaries,
microcirculation, and the heart.
Wish you have a good time!
Capillaries-general structure


Capillaries are the smallest diameter
blood vessels.
Capillaries form blood vascular
network that allow fluids containing
gases, metabolites, and waste
products to move through their thin
walls.
Capillaries-general structure

The wall of a capillary is formed
essentially by endothelial cells which
are lined on the outside by a basal
lamina. Overlying the basal lamina
there may be isolated branching
perivascular cells (pericytes), and a
delicated network of reticular fibers and
cells.
Capillaries- pericytes

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Pericyte with branching
cytoplasmic processes, is
enclosed by a basal
lamina that is continuous
with that of the
endothelium.
It displays features of a
unspecialized cell with a
large nucleus.
It can give rise to
endothelial cells and
smooth muscle cells
Capillaries-classification

Based on their
morphology, three
types of capillaries
are described:
continuous
capillaries,
fenestrated
capillaries, and
discontinuous
Continuous capillaries


Seen in the skin,
connective tissue,
muscle lungs and
brain.
The edges of
endothelial cells
fuse completely
with those of
adjoining cells to
form a continuous
wall.
Continuous capillaries


The pericyte
surrounds the
capillary with
branching
cytoplasmic
processes.
Numerous
pinocytotic vesicles
underlie both the
luminal and basal
plasma membrane
Fenestrated capillaries


Found in endocrine
glands and sites of
fluid and
metabolite
absorption, such as
the gallbladder and
intestinal tract.
Fenestrations
provide channels
across the capillary
wall.
Fenestrated capillaries


They also have
pinocytotic
vesicles, basal
lamina and
pericytes.
A fenestration
may have a
thin,
nonmembrano
us diaphragm
across its
Discontinuous capillaries (sinusoids)



Found in the liver,
spleen, and bone
marrow.
They are larger in
diameter and more
irregularly shaped
than other capillaries.
The wall consists
only of endothelium
supported by a thin
layer of connective
tissue. The wall may
be incomplete at
places.
Capillaries –functional aspects



Two important points: blood flow and
richness of the capillary network.
Blood flow is controlled through local
and systemic signals.
The richness of the capillary network
is related to the metabolic activity of
the tissue.
Microcirculation-arteriovenous shunts
arteriole
metarteriole
venule

Precapillary
sphincters
capillaries

venule
Direct routes
between the
arterioles and
venules that divert
blood from the
capillaries.
Commonly found in
the skin of the
fingertips, nose and
lips.
Microcirculation-arteriovenous shunts
arteriole
metarteriole
venule

Precapillary
sphincters
capillaries

venule

Contraction of the
arteriole smooth
muscle of the AV
shunt sends blood to
a capillary bed;
relaxation of the
smooth muscle
sends blood to a
venule, bypassing
the capillary bed.
AV shunts serve in
thermoregulation.
Microcirculation-Thoroughfare channel
arteriole
metarteriole
venule

Precapillary
sphincters
capillaries
venule

Its proximal
segment is called
a metarteriole,
also allow some
blood to pass
more directly
from arteriole to
venule.
Capillaries arise
from both
arterioles and
Thoroughfare channel
arteriole
metarteriole
venule

Precapillary
sphincters
capillaries
venule

A sphincter of
smooth muscle,
called the
precapillary
sphincter, is located
at capillaries’origin
from either an
arteriole or a
metarteriole.
These sphincters
control the amount
of blood passing
Heart

epicardium
myocardium
The wall of the
heart is composed
of three layers.
From the outside
to the inside they
are epicardium,
myocardium, and
endocardium.
endocardium
Epicardium
Mesothelium
Consisting of a
layer of
mesothelial cells
and its underlying
connective tissue.
The blood vessels
and nerves that
supply the heart
lie in the
epicardium.

Fibroelastic
tissue
Adipose tissue
Myocardium

epicardium
myocardium
endocardium
Consist of
cardiac
muscle, the
principle
component of
the heart.
Endocardium

Consist of an inner
layer of endothelium
and subendothelial
connective tissue, a
middle layer of
connective tissue and
smooth muscle cells,
and a deeper layer of
connective tissue, also
called the
subendocardial layer.
The impulseconducting system of
the heart is located in
A fibrous skeleton


At the junction of the atria and
ventricles, and around the openings of
aorta and pulmonary trunk there are
rings of dense connective tissue. Similar
dense connective tissue is also present
in the membranous part of the
interventricular and interartrial septum.
These masses of dense connective
tissue constitute the skeleton of the
heart. They give attachment to fasciculi
of heart muscle. They also act as an
electrical insulator by preventing the
Heart valves

Heart valve
epicardium
myocardium
endocardium
The valves of
the heart are
folds of
endocardium
that enclose a
plate like layer
of dense
connective
tissue.
Impulse-conducting system

The pace of the
beating action in the
heart is initiated at
the sinuatrial (S-A)
node, a group of
specialized cardiac
muscle cells located
near the junction of
the superior vena
cava and the right
atrium.
Impulse-conducting system

The S-A node
initiates an impulse
that spreads along
the cardiac muscle
fibers of the atria and
along internodal
tracts composed of
modified cardiac
muscle fibers.
Impulse-conducting system

The impulse is then
picked up at the
atrioventricular (A-V)
node and conducted
across the fibrous
skeleton to the
ventricles by the
atrioventricular (A-V)
bundle.
Impulse-conducting system

The bundle divides
into smaller right
and left bundle
branches and then
into subendothelial
branches
commonly called
Purkinje fibers.
Purkinje fibers

N
N
N
N
They are chains of
cells, united by
desmosomes, and
intercalated discs
are absent. These
cells have a larger
diameter, and are
shorter, than
typical cardiac
myocytes.
Purkinje fiber has
a central nucleus
surrounded by
clear cytoplasm.
Nodal myocytes

Nodal myocytes (present in the AV node and the S-A node) are
narrow, rounded, or cylindrical
cells with single nuclei. They are
responsible for pace-maker
functions.
Transitional myocytes

They are present in the A-V node
and the S-A node, and in the stem
and main branches of the A-V
bundle.They are similar to cardiac
myocytes except that they are
narrower. Conduction through them
is slow.
Summary



Understand the structure of three
kinds of capillaries.
Know the structure and function of
every segment of microcirculatory
vessel.
Understand the structure of Purkinje
fibers, Nodal myocytes, and
Transitional myocytes
Homework


Review three structure of capillaries ,
Purkinje fibers, Nodal myocytes, and
Transitional myocytes.
Prepare for the next lessonlymphatic system.
Wish you have a good time!