Download Dr. Maha Cardiovascular system 2nd stage Cardiovascular system is

Dr. Maha
Cardiovascular system
2nd stage
Cardiovascular system is closed system of tubes with an endothelial
lining from the heart through the arteries into capillaries and baek through
the veins.
Blood vessels :
The blood vessels consist of vaniously sized tubes arranged in circuit
through which blood is delivered from the heart to the tissues. Then back
to the heart from all parts of the body, oxygen from the lungs, nutrients
from the intestine and liver, regulatory agents such as hormones are
dislributed to all organs and tissues, waste products also empty into the
circulation.
The blood vessels are usually composed of the following layers or
Tunics:A) Tunica in tima: - it consist of a layer of endothelial cells lining the
vessel's these cells rest on basal lamina beneath the endothelium is
the sub endothelial layer , consisting of loose connective tissue.
B) Tunica media:- it consist of concentric layers of arranged smooth
musele cells and among them are variable a mount of elastic and
reticular fibers , the tunica media separated from tunica in tima by
internal elastic lamina , in larger arteries , atlinner external elastic
lamina is found separating the media from outer tunica adventitia.
C) Tunica Adventitia : - The adventitia consist principally of
longitudinally oriented collage and elastic fibers , the collage in
adventitia is type 1 , the adventitia gradually becomes continuous
with the connective tissue of organ through which the vessel is
running.
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Dr. Maha
Cardiovascular system
2nd stage
Type of Arteries
Arteries classified according to their size into arterioles , muscular
arteries of medium or large diameter and large elastic arteries. In general
the wall of arteries thicker than the walls of veins .
Histology
A) Large lastic Arteries : These include aorta and it's large branches this type of arteries has
the following characteristics , the intima is thicker than the corresponding
tunica of a muscular artery the sub endothelial layer is thick , an internal
elastic lamina also present , the media consist of series of perforated elastic
laminae , whose number increases with age between the elastic lamina the
smooth muscle cells , reticular fiber and ground substance.
The tunica adventitia which does not shown an external limiting
lamina, is relatively developed and contine collagen and elastic fibers.
B) Muscular Arerties : The intima contain endothelial cells which lined the lumen and sub
endothelial layer is thicker than the corresponding of arteriotes and few
smooth muscle cells may be present an internal elastic lamina is
prominent , the media may contain up to (40) layers of smooth muscle
cells , although the number of layers diminishes as the artery become
smaller , between these cells we see variable , number of elastic lamellae ,
as well as reticular fibers and protcoglgcause and an external elastic
lamina is present in large muscular arteries , the adventitia consist of
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Dr. Maha
Cardiovascular system
2nd stage
collage and elastic fibers , a few fibroblasts and adipose cells present
also. , lymphalics , vasavasorum , and nervs also found in the adventitia.
C) Arterioles :
These are generally less than 0.5 mm in diameter and have relatively
narrow lumens the lumen is lined by endothelial cells, the sub endothelial
layer is very thin and an internal elastic lamina is lacking except in the
largest arterioles.
The media is muscular and genelly composed of 7-5 circular
arranged layers of smooth muscle cells. he advenilitia thin and hasn't
external lamina.
Types of veins : A) Large veins : It such as venae cava , renal , external iliac , splenic and mesenteric
veins.
1. Tunica adventitia :- is thick and form the greater part of wall , it
consist of loose connective tissue with thick longitudinal oriented
bundles of collagen and elastic fibers, smooth muscle layers also
longitudinal arranged , vasa vasorum also present and may extend to
tunica media.
2. Tunica media :- is thin and poorly developed and my be absent.
3. tunica intima :- consist of endothelial cells resting on basal lamine ,
sub endothelial connective tissue may be prominent.
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Dr. Maha
Cardiovascular system
2nd stage
B) Medium veins : They vary is size form 1-10 mm in diameter
1. tunica intima : thin consist of endothelial cells resting on basal
lamina , present scattered collagen fibers and fine elastic fibers ,
external elastic lamina poorly defined.
2. Tunica media : - is thinner than the corresponding arteries .
3. tunica adventitia : - is thickler than the media , it consist of collage
and elastic fibers and frequentally longitudinal smooth muscle cell ,
vasa vasorum present in large vessels of this class , also conn .
most medium veins provid with valves so , the tunica intima that
project into lumen consist of connective tissue covered the surfaces
of endothelial cells , rich network of elastic fibers present in C.T
beneath the endothelium .
C) Venules : It rang from 10 to 50 Um in diameter
1. tunica intima consist of thin continuous endothelium , the thin basal
lamina is penetrated by pericytes.
2. Tunica media:- is absent in smallest venules
3. Adventitia:- consist of few collagen fibers scattered fibroblasts ,
mast cells, macrophages and plasma cells .
When the vessels increase in size to reach 50 um m scattered smooth
muscle cells present and from incomplete tunica media , and the
adventitia increase , thickness and collagen fibers also present and
irregular fibroblasts.
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Dr. Maha
Cardiovascular system
2nd stage
Types of capillaries : There are two type of capillaries according to appearance of the
endothelium and basal lamina
1. continuous capillaries .
2. penestrated capillaries.
The basic structure of capillaries is the tunica intima consist of
endothelium and basal lamina , the tunica media absent and the tunica
adventitia greatly reduced .
1. Continuous capillaries:These form the common type of capillaries and the wall consist of
continous endothelium and thin tunica adventitia the lumen arranged from
5-10 Mm the endothelial cells rest on continous basal lamina , the tunica
adventitia is thin and containe some collagen and elastic fibers.
Embedded in small amount of ground substance , fibroblasts ,
macrophages and mast cells also present.
Pericytes cell also present enclosed by basal lamina
2- Fenestrated capillaries : Have the same structure of continous capillaries but differ that the
endothelial cells. Contain numerous gaps (pores) which appear between
adjoining cells 70-10 nm in diameter .
The fenestrate (gaps) are closed by thing diaphragm that show central
knob-like thickenings the diaphragm is single layer stricture the basal
lamina is continous a cross the fenestrate .
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Dr. Maha
Cardiovascular system
2nd stage
Fenestrated capillaries occur in intestinal villi , cillary processes of
eye are found in liver, spleen , bone marrow and adenohypophysis , their
has wide lumia are lined by endothelial cells interspersed with fixed
macrophages of mononuclear phagocytes similar thin venous sinuses are
found in endocrine glands.
Arleriovenous anastomoses
Arteriovenous anastomosis are special areas of skin of the nose , lips
and pads where the arterile opens directly into a venule without going
through the capillaries bed. This provide an althernative channel of blood
supply and regulation of heat loss.
The wall of the heart : the cardiac wall consist of three layers :1. endocardium (inner layer).
2. myocardium (middle layer).
3. epicardium (outer layer)
* The endocardium :- contains sequamous endothelial cells , vascular
arealar conncctive tissue and conducting fibers.
* The myocardium : - is composed of cardiac muscle and also contain
vascular areolar connective tissue ,
* The epicardium :- is thicker than the endocardium and fat adeposits in
the rather than connective tissue and coronary blood vessels are often
found.
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Dr. Maha
Cardiovascular system
2nd stage
Cardiac Valves :There several valves into the heart they are :1. right atrioventricular valve (bicuspid or mitral valve) , this valve
between right atrium and right ventricle
2. left atrioventricular valve ctricuspid or mitral valve between the left
atrium and left ventricle .
The function of two valves are (during contraction of ventricle
(systole) prevent flowing of blood back into atria.
3. Aortic valve :- this valve between the left ventricles and aorta.
4. Pulmonary valve:- this valve between right ventricle and pulmonary
arlery.
The valves are similar in structure. The atrioventricular valves are attached
to (fibrosa) it's a dense fibrocollagenous central plate , which is an
extention of fibrocollagenous tissue of central fibrous body and
fibrocollagenous valve ring. (Central fibrous body is a fibrocollagenous
skelelon located in heart at level of valves)
(valve ring is extention of central fibrous body surround the heart valve)
the valves are coverd on both sides by endocardium which is thicker , on
venlricular side , the valves connected to the papillary muscle by thing
tendinous cords called chordae tendinae. Valves of pulmonary arteries and
aorta are thinner and shown the sam structure of atrio ventricular valve.
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Dr. Maha
Cardiovascular system
2nd stage
Conducting system : The conducting system of heart consist of specialized cardiac muscle
fibers and is responsible for initiating and maintaining cardiac rhythm and
for ensuring coordination of atrial and ventricular contraction.
This system consist of muscle fibers which are modified to act as
transducers rather than contractile cells. Tcatriorenlrical (bundle) and SA
node (sinoatrial node) and AV node catrioventricular node)
The SA node located in epicardium , the impulse intiated in this node and
spread through the cardiac muscle of atrium to reach the atrioventricular
node which located in interatrial septum then intiates the later contraction
of ventricles. The impulse pusses rapidly through the atrioventricular
bundles to interventricular septum and this bundles branching into two
trunk (R+L) and pass in to venlricles, this the impulse is conducted to all
parts of ventricles. The atrioventricular bundles and it's branching called
purkinje fibers.
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