Histology
Lecture 11: Circulatory System
Cardiovascular System
 pulmonary and systemic circuit
 heart, blood vessels, lymphatic vessels, blood
Arteries transport blood away from heart
Veins returnining blood to heart
Microvascular:arterioles, capillaries, and
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
Tunica intima: simple squamous
epithelium and the subendothelial
connective tissue
Tunica media: helically disposed layers of
smooth muscle cells, and occasionally elastic
membranes
Tunica adventitia: outermost layer that
blends into surrounding connective tissue
Tunica Intima
simple squamous endothelial cells resting on a
basal lamina
tight junctions and gap junctions
Beneath the lining membrane is a
subendothelial connective tissue
The subendothelial layer contains collagen and
a few elastin fibrils and occasional smooth
muscle cells
Tunica intima of elastic arteries is relatively
thick
Tight junctions prevent paracellular transport,
Tunica Intima
 Endothelial lining with basal lamina
 Little subendothelial connective tissue
 Internal elastic lamina (fenestrated)
Tunica media
 smooth muscles, collagen type III, few
elastic fibers
 Smooth muscle(spiral pattern)
 There is No fibroblasts
 External elastic lamina
Tunica adventitia
 Outermost layer of the vessel wall
(connective tissue)
 Fibroblasts,collagen, thin elastic
fibers, and small blood vessels; the
vasa vasorum
 Thinner than tunica media
 It also contains nervi vascularis
Capillaries
Single layer of endothelial cells with
basal lamina
Pericytes, forming gap junctions with
endothelial cells
Site of most nutrient and gas exchange
between tissue and blood
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
Elastic Artery
 Aorta is a good example
 Special characteristics of elastic
arteries are:
 Internal elastic lamina
 External elastic lamina
 Several elastic membranes with
smooth muscle cells located in tunica
media
Muscular Arteries
Distribute blood to the organs and tissues
Elastic lamina and more smooth muscle
cells than elastic 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
‫تا انقثاض ریتمیک‬
‫خون را ته گردش‬
‫در می آورد و‬
‫شامل‪:‬‬
Heart
• Endocardium
Inner layer 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
Its encirculated covered each camber
Its thicker in ventricles especially left
Epicardium
The outermost layer, mesothelial cells with
underlying loose connective tissue contains
coronary vessels and nerves and ganglia,
adipose tissue
Homologue of the tunica adventitia of the vessels
‫اسکلت فیثروی قلة‪:‬‬
‫عملکرد‪:‬‬
‫ناهنجاری های ساختمانی‬
‫قلة‬
‫ترمیم دریچه های‬
‫معیوب‬