Download LAB 11 Practical Histology Cardiovascular system Introduction: The

LAB 11

Practical Histology
Cardiovascular system
Introduction: The cardiovascular system is subdivided into two functional
parts
 Blood vascular system:
1. The blood vascular system distributes nutrients, gases, hormones to all parts of
the body; collects wastes produced during cellular metabolism.
2. The blood vascular system consists of a continuum of blood vessels (arteries,
arterioles, capillaries, venules, veins) and a muscular pump (heart).
 Lymph vascular system
1. The lymph vascular system collects tissue fluid from tissues and returns it to
the blood vascular system.
2. The lymph vascular system consists of blind-ended capillaries (lymphatic
capillaries) connected to venous vessels (lymphatic vessels) and various
lymphoid organs (e.g., lymph nodes).
 Organization of blood vascular system
1. The heart wall can be viewed as a three-layered structure.
a) Inner layer = endocardium
b) Middle Layer = myocardium
c) Outer layer = epicardium (also called the pericardium)
2. Except for the smallest vessels, blood and lymphatic vessel walls can also be
viewed as three-layered structures.
a) Inner layer = tunica intima
b) Middle layer = tunica media
c) Outer layer = tunica adventitia
 Structure of the heart wall
1. The endocardium is the inner layer of the heart wall and consists of the
endothelial lining and the underlying connective tissue layers.
2. The myocardium is the middle layer of the heart wall and contains the cardiac
muscle throughout most of the heart.
3. The epicardium is the outer layer of the heart and consists of a connective
tissue region covered by a mesothelium on its outer surface.
 Blood Vessels:
Most larger blood vessel walls contain three major layers with sublayering.
1. The tunica intima is the luminal layer, consist of endothelium (simple
squamous epithelium), subendothelial layer (loose connective tissues).
2. Internal elastic lamina (elastica interna) marks the boundary between the
tunica intima and the tunica media.
3. The tunica media contains layers of either elastic laminae/lamellae
(fenestrated sheets) or CT alternating with layers of smooth muscle.
4. If present, the external elastic lamina (elastica externa) marks the boundary
between the tunica media and the tunica adventitia.
5. The tunica adventitia contains loose to moderately dense CT.
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LAB 11
Practical Histology
Cardiovascular system
 Types of arteries
Character
Large arteries (elastic
arteries or conducting
arteries)
Medium to small arteries
(muscular arteries)
thin
Arterioles
Tunica intima
thin
very thin consisting only of
endothelium
Internal elastic
lamina
not as distinct as in other very distinct, usually folded
arteries
usually present except in
smaller arterioles
Tunica media
Thick 40 - 60
Thick 5 - 40 layers
thin 1 to 5 layers
Tunica adventitia
thin
thick
thin
Example
aorta
Branchial artery
Coronary arteriole
Function
conduct blood from the
heart to smaller arteries
and to even out blood
pressure and flow.
Regulate blood pressure and
blood distribution by
contraction and relaxation of
smooth muscle in the tunica
media.
regulate blood pressure and
deliver blood under low
pressure to capillaries.
 Types of veins:
Character
Large veins
muscular venules
Small to medium veins
Tunica intima
thicker
thin
thin
Internal elastic
lamina
usually distinguishable
Absent
Absent
Tunica media
thin
thin; 1 - 3 layers
thin
Tunica adventitia
very thick
thick
well developed
Example
vena cava
most named veins are in this
category.
found in many of the
lymphatic tissues.
Function
collect blood from
medium sized veins and
return it to heart
collect blood from postcapillary venules
collect blood from smaller
venous vessels
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LAB 11
Practical Histology
Cardiovascular system
 Differences between artery and vein
Artery
carrying blood at high pressure
Vein
carrying blood at very low pressure
Smooth muscle and/or elastic fibers predominate over
collagen fibers in tunica media
Collagen fibers are relatively abundant among the
smooth muscle cells in the tunica media
components are arranged circularly in tunica media allows change in diameter to regulate blood pressure
and blood flow
components arranged longitudinally - prevents excess
stretching of vessel wall
No valves
Valves present; prevent backflow
Regular diameter, narrow lumen, and thick wall
Irregular diameter, wide lumen, and thin wall
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