Transcript Tunica Media

Circulatory System
Dr. Maria Zahiri
Cardiovascular System
Consists of:
 Blood vessels
Lymphatic vessels
Heart
Blood vessels
 Arteries:
transport blood away from heart
 Veins:
drain microvascular beds, returnining blood to heart
 Microvascular
•
•
•
bed:
Arterioles
Capillaries
postcapillary venules
 Arterioles
regulate volume of blood flow
 Capillaries
have small diameter, thin walled, and are where
gas/nutrient exchange take place
 Postcapillary
venules
are the site of passage of blood cells to connective
tissue
Tunics of Vessels
Walls of blood vessels are composed of 3layers:
Tunica
intima
Tunica
media
Tunica
adventitia
 Tunica
intima is
composed of:
•
a simple squamous
epithelium(endothelium)
•
the subendothelial (loose
connective tissue)
 Tunica
media usually is
the thickest layer of the
vessel wall
is composed of:
•
helically disposed layers
of smooth muscle cells
•
occasionally elastic and
reticular fibers (collagen
III)

Tunica adventitia
is the outermost
layer that blends into
surrounding
connective tissue

Collagen type I
Arteries
There is 3 types of arteries in human body:
 large(elastic)
 medium(muscular)
 small arteries
arterioles
Elastic Artery )Aorta)
Special characteristics of
elastic arteries are:
 Internal elastic lamina
 External elastic lamina
 Several elastic
membranes known as
fenestrated membranes
alternating with smooth
muscle cells located in
tunica media
Tunica intima
simple
squamous endothelial cells
(resting on a basal lamina )
The
cells are joined by tight junctions and gap
junctions
Tunica intima
subendothelial
•
•
•
connective tissue
collagen
elastin fibrils
smooth muscle cells
dense
internal elastic lamina
Tunica Media
It
is the thickest layer
is composed of many fenestrated elastic
lamellae, collagen and smooth muscle cells
The
wavy sheets of elastic membranes are
located between the smooth muscle fibers of
the tunica media (stretching )
Tunica Media
The
extracellular matrix of tunica media, is
composed of :
• chondroitin sulfate
• collagen
• reticular
• elastic fibers
( is synthesized and secreted by the smooth
muscle cells)
Few
fibroblasts also exist in tunica media
Tunica adventitia
 is
the outermost layer of the vessel wall which merges
with the connective tissue of the body wall
It consists of :
• Fibroblasts
• Collagen
• thin elastic fibers
• small blood vessels
• the vasa vasorum
 This layer is thinner than tunica media
 Prevents over-stretch of the arterial wall
 It also contains nervi vascularis
vasa vasorum

("the vessels of the vessels") is a network of small blood vessels that
supply the walls of large blood vessels, such as elastic arteries (aorta) and
large veins (vena cava).
Vascular nerves
are nerves which innervate arteries and veins.
 control vasodilation and vasoconstriction,
which in turn lead to the control and
regulation of temperature and homeostasis

Muscular arteries
•
•
distribute blood to the organs and tissues
They have less elastic lamina and more smooth muscle cells
than elastic arteries
Muscular arteries
•
•
•
The muscle is arranged so that its contraction narrows the
lumen of the vessel
Internal and external elastic lamina are present
Have smaller diameter than large elastic arteries
Tunica Intima
•
•
•
Endothelial lining with basal lamina
Little subendothelial connective tissue
Internal elastic lamina which is a fenestrated sheet of elastic fibers
Tunica media
Consists of:
• smooth muscles(are arranged in spiral
pattern)
•collagen type III
•few elastic fibers
•There is No fibroblasts
•External elastic lamina is also present
Tunica adventitia
 is
continuous with the connective tissue of the organ which is
supplied by this vessel
 Thick connective tissue layer about equal to tunica media in
thickness
 High collagen content with fibroblasts
 Elastic fibers concentrated in external elastic lamina
Small Arteries and Arterioles
 Arteriole
has a diameter less than 0.1 mm and has 1-3 layers of
smooth muscle in tunica media
 Arterioles are key control points for blood flow
 Small
media
artery has up to 8 layers of smooth muscle cells in tunica
Small Arteries and Arterioles
 Small
arteries and large arterioles have fenestrated internal elastic
lamina, but in smaller arterioles it is absent
 Tunica adventitia is sparse and poorly developed
Veins
 Veins
are classified as large, medium and small size
 Large and medium veins usually accompany with large and
medium arteries
 Large and medium veins have tunica intima, tunica media and
tunica adventitia
Veins
 Tunica
media of veins are thinner than arteries of the same size
 Wall of a vein is much thinner than artery with the same size
 Some veins may have valves to prevent backflow of blood
Large Veins
 Vena
cava is a good example of
a large vein
 Tunica intima
• Endothelium
• basal lamina
• thin subendothelial connective
tissue
• internal elastic lamina
Large Veins
 Tunica
media consists of 4-5
layers of smooth muscle with
no distinct border, collagen and
fibroblasts
 Tunica adventitia is thick
with some smooth muscle;
many collagen fibers,
fibroblasts and some elastic
fibers
Medium veins
 Tunica
intima: endothelium, basal lamina, subendothelial
connective tissue and internal elastic lamina
 Tunica media: very thin, smooth muscle and some fibroblasts,
reticular and elastic fibers
 Tunica adventitia: thicker than media, is composed of collagen
bundles and a few scattered smooth muscle
Venules
 Their
wall consists of endothelium, basal lamina and pericytes
(contractile) in postcapillary venules
 In larger venules, pericytes are replaced by smooth muscle cells
 Venules are sensitive to histamine and serotonin, increased
permeability to fluid and WBC during allergic and inflammatory
reactions
Venules
 They
have No real tunica media, just have 1-2 layers of smooth muscle
 Some collagen and a few fibroblast
 Endothelial cells of venules are cuboidal in certain lymphoid tissue
and are called high-endothelial venules
Capillaries
 Single
layer of endothelial cells with basal lamina
 7-9 micrometer
 Pericytes are located along the outside of the capillaries and small
venules, forming gap junctions with endothelial cells
 Site of most nutrient and gas exchange between tissue and blood
 Longest: in muscle
Pericytes
are contractile cells
 wrap around the endothelial cells of
capillaries and venules throughout the body.
 Also known as Rouget cells or mural cells

Capillaries
 Continuous
(nonfenestrated) capillaries
 Discontinuous
(fenestrated) capillaries have pores are 80-100 nm in
Capillaries
 Continuous
•
•
•
(nonfenestrated= somatic) capillaries
have no pores in their wall, have tight junctions: CNS, PNS, muscle,
connective tissue, exocrine gland
Have 70 nm vesicles
CNS capillaries have No vesicles
Capillaries
•
•
•
•
Discontinuous (fenestrated= visceral)
capillaries 60- 80 nm pores
covered by a pore diaphragm,
(endocrine glands, intestines,
In renal glomerulus that fenestrated
capillaries lack diaphragms
Sinusoidal capillaries
 Special
thin-walled,
incomplete capillaries with
irregular large diameter
 Discontinuous endothelial
wall contain many large
fenestrae without diaphragms
 Found in liver, lymph nodes
and hemopoietic tissues such
as bone marrow and spleen
Metarteriole




is a short vessel
links arterioles and venules.
Instead of tunica media, they have individual smooth
muscle, each forming a precapillary sphincter
that encircles the entrance to that capillary bed.
arteriovenous anastomoses (AVA)
are direct vascular connections between arterioles and venules
that bypass the capillary bed
Intermediate segment has a thickened tunica media, Its
subendothelial layer is composed of plump modified polygonal
smooth muscle cells
Are useful in thermoregulation
are abundant in skin
Glomus
 Vascularize
 This
nail beds and tips of fingers and toes
small organ receives an arteriole without elastic lamina
and richly innervated smooth muscle cell layer,which surround
the lumen, thus directly control blood flow to region before
emptying into a venous plexus
the carotid sinus





(or carotid bulb)
is a dilated area at the base of the internal carotid
just superior to the bifurcation of the common carotid
is sensitive to pressure changes in the arterial blood at this level.
It is the major baroreception site in humans and most mammals.
Carotid body

(carotid glomus or glomus caroticum)

is a small cluster of chemoreceptors and supporting cells located near the
bifurcation of the carotid artery

It detects changes in the composition of arterial blood flowing through it
(pressure of oxygen,carbon dioxide, pH and temperature)
Necrosis
is a form of cell injury which results in the
premature death of cells in living tissue by autolysis.
 Necrosis is caused by factors external to the cell or tissue,
such as infection, toxins, or trauma which result in the
unregulated digestion of cell components.

apoptosis
is a naturally occurring programmed and targeted
cause of cellular death.
 While apoptosis often provides beneficial effects to
the organism, necrosis is almost always detrimental
and can be fatal

Aneurism
Atherosclerosis
Heart
Heart wall is composed of 3layers:
• endocardium,
• myocardium
• epicardium
Endocardium
 composed
of endothelium with subendothelial (fibroelastic
connective tissue)
 Middle layer is dense connective tissue with smooth muscle and
elastic fibers
 Outer layer called
subendocardium and is
continuous with connective
tissue of myocardium,
containing small blood vessels
and purkinje fibers
Myocardium
Thick middle layer of the heart, is composed of cardiac
muscle cells
Epicardium
 The
outermost layer, composed of mesothelial cells with
underlying loose connective tissue contains coronary vessels and
nerves and ganglia,and usually has adipose tissue too
 Homologue of the tunica adventitia of the vessels
Heart Valve
 Endothelial
lining on surface
 Core of dense irregular connective tissue with many
elastic fibers
Purkinje Fibers
 Large diameter cardiac muscle cells that are pale staining,
conduct electrical impulses
Lymphatic Vessels
 Lymphatic
vessels are thin walled, unidirectional, carry excess
interstitial fluid from tissues back to vascular system
 Lymphatic capillaries begin as blind tubes and converge into
larger vessels
 2 main vessels empty into vascular system at base of neck
Lymphatic Vessels
 Fluid
passes through lymph nodes before returning to vascular
system
 Lymph capillaries have incomplete basal lamina and are very
permeable
Lymphatic Vessels
 Bundles
of anchoring filaments terminate on the plasma membrane
 Lymphatic capillaries are slightly larger in diameter than blood
capillaries
 The ends of the endothelial cells that make up the wall of a
lymphatic capillary overlap
Lymphatic ducts
Lymphatic ducts are similar to large veins
Tunica intima composed of endothelium and several layers of
elastic and collagen fibers
In tunica media smooth muscle cells are oriented circularly
and longitudinally
Tunica adventitia contains smooth muscle and collagen fibers
Angiosarcoma


is a malignant neoplasm (cancer) of endothelial-type cells
that line vessel walls.
This may be in reference to blood (hemangiosarcoma) or
lymphatic vessels (lymphangiosarcoma).
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