Histology for Pathology
Circulatory System
Theresa Kristopaitis, MD
Associate Professor
Director of Mechanisms of Human Disease
Kelli A. Hutchens, MD, FCAP
Assistant Professor
Assistant Director of Mechanisms of Human Disease
Loyola Stritch School of Medicine
OBJECTIVES
1. Given a histologic section of a large or medium sized artery, identify the
a) tunica intima
b) tunica media
c) tunica adventitia
2. Identify the following structures in a histologic section of an artery
a) Endothelium
b) Internal elastic lamina
c) External elastic lamina
d) Vasovasorum
3. Distinguish the characteristics which separate large, medium and small
arteries and arterioles.
4. In a tissue section, distinguish a medium sized artery from a medium sized
vein
5. In a tissue section identify capillaries, describe their structure and function
6. Compare and contrast general structural features of the arterial vs venous
system
7. Describe the structure and function of a lymphatic vessel
Vessel Types
• Arteries
–
–
–
–
Large artery
Medium artery
Small artery
Arteriole
• Veins
–
–
–
–
Large Vein
Medium Vein
Small Vein
Venule
• Capillaries
– Continuous
– Fenestrated
– Discontinuous
Overall Structure of Vessels
• Three layers (tunica)
– Tunica intima(inner most layer)
• Endothelium
• Subendothelium
• Internal elastic lamina (IEL) in arteries
– Tunica media
• Smooth muscle layer
• External elastic lamina (EEL) in arteries
– Tunica adventitia (outer most layer)
• Connective tissue and fibroblasts
• Longitudinal smooth muscle in veins
• Vasovasorum in large vessels
Structure of Vessels
Large Artery
Subendothelium
Endothelium
b
a
Elastic fibers
c
Vasa vasorum
a = tunica intima - endothelial lining plus thin layer of underlying connective tissue called
the subendothelium.
b = tunica media - alternating layers of elastic membranes (elastic lamina) and smooth
muscle.
c = tunica adventitia - fairly dense connective tissue carrying small blood vessels,
the vasa vasorum
High Power of AortaTunica Media
Endothelium
Endothelium: Composed of single layer of squamous cells, provides a permeable
barrier, angiogenesis, release of single molecules.
Medium Artery
Also called muscular artery because the wall is dominated by smooth muscle.
Similar to large artery but internal and external elastic lamina are well defined
and lack prominent vasovasorum.
Small Artery & Arterioles
Arteriole
Small Arteries: Generally have same structure as medium artery but have a smaller
diameter and no external elastic lamina. The tunica media also has fewer layers of
smooth muscle cells.
Arterioles: The smallest arteries, lead blood flow into capillary beds. Only two layers
of smooth muscle cells. Internal elastic lamina, external elastic lamina, and
subendothelial layers usually absent.
Large Arteries
Medium
Arteries
Small arteries
Arterioles
Tunica Media Smooth muscle
cells + Large
quantity of elastic
fibers
Dominated by
multiple layers
of smooth
muscle cells
(6-40)
2-6 layers of
smooth muscle
1-2 layers of
smooth muscle
cells
Function
Conduct blood
from heart.
Walls recoil.
Accommodate
pressure changes.
Maintain
continuous blood
flow during
diastole.
Distributing
arteries
Help control
and modulate
blood pressure
Control blood
flow to
capillaries.
Important role
in regulating
blood pressure.
Examples
Aorta and its large
branches –
subclavian,
carotid, iliac
Coronary, Renal
Within
substance of
tissues and
organs
Within
substance of
tissues and
organs
Capillary
• Smallest vessels
• Connect arterioles and
venules
• One layer of endothelial
cells with a basal lamina
*
A capillary lying in the endomysium
between skeletal muscle fibers. This
one shows very dark endothelial
nuclei and has 3 pink red blood
cells* lined up in a row inside
Venules and Small Veins
Similar except
• Small veins may have
slightly larger lumen
and more visible
smooth muscle layer
• Venules have small
lumens, thin walls,
and only single layer
of endothelum. Have
surrounding
connective tissue
Vein
Medium-sized vein with a much less compact
muscle layer than in arteries.
a - tunica media
b – tunica adventitia, which is at least as wide
as the media, and often even wider.
LUMEN
(filled with
RBCs)
Medium Vein
Tunica intima
Smooth
muscle
bundles
Tunica media
Tunica
adventitia
Quite similar to a large vein but smaller lumen, tunica adventitia contains fewer
bundles of longitudinal smooth muscle and vasa vasorum is not prominent.
Valves
• Folds in the intima seen
in medium and larger
veins
• Number of valves
increase with size of
vessel
• Prevent backflow of
blood
• Also present in the
lymphatic vessels
Large Veins
Vasa vasorum
a
c
b
Smooth muscle
bundles
a. Tunica intima
b. Tunica media with a circular smooth muscle
layer
c. Tunica adventitia: thickest layer with many
longitudinal smooth muscle bundles and
vasa vasorum.
Artery vs Vein
Vein
Artery
Arterial system
Venous system
Lumen
Smaller, rounder.
Prominent internal
elastic lamina
Larger, flatter
Tunica media
Thicker than tunica
adventitia
Tunica adventitia
Valves
Thicker than tunica media
Longitudinal smooth muscle
bundles present
No
Yes
Lymphatic system
• Composed of lymphatic capillaries, vessels, and
ducts
• Collect and drain interstitial fluid from tissue in
the large veins
• Have large lumens and relatively thin walls
• Single layer of endothelium
• Connective tissue outer layer with few smooth
muscle cells
• Also have valves
Lymphatics
Valve
Thinned walled vessels with large lumens and valves. There are some
fat cells and lymphocytes in the surrounding connective tissue.