VASCULAR PATHOLOGY

1. SAMOEI – EGERTON
UNIVERSITY
MBChB
Y3

2. 2
CONTENTS
1. HISTOLOGY REVIEW
2. NORMAL STRUCTURE AND TYPES OF ARTERIES, VEINS, CAPILLARIES &
LYMPHATICS
3. BLOOD SUPPLY OF ARTERIES

3. 3
HISTOLOGY REVIEW
• Blood vessels differ from each other in their
structure and function.
NORMAL STRUCTURE
ARTERIES
Divided into 3 types depending on the caliber
and certain histological features
1. Large (Elastic) Arteries
2. Medium-sized (Muscular) Arteries
3. Small-sized Arteries (Arterioles)
Histologically, the major arteries of the body
have 3 layers in their walls, namely:
1. Tunica intima
2. Tunica media
3. Tunica adventitia
The layers progressively decrease with
diminution in size of the vessels

4. 4
Inner coat of the artery
Composed of:
1. Endothelium (inner lining)
2. Subendothelial connective tissue
3. Internal elastic lamina
ENDOTHELIUM
 Simple squamous epithelium
 Has narrow junction between cells which
certain materials pass.
 Integrity of vascular endothelium is of
paramount importance in the maintenance of
vascular functions – damage to it initiates
thrombus formation at the site
SUBENDOTHELIAL CONNECTIVE
TISSUE
 Consists of loose connective tissue which
includes; myoepithelial cells, collagen,
proteoglycans, elastic tissue & matrix
glycoproteins
INTERNAL ELASTIC LAMINA
 Is a layer of elastic fibres
 Have minute fenestrations

5. 5
TUNICA MEDIA
Middle coat of arterial wall
Bounded by:
Internal elastic lamina, internally
External elastic lamina, externally
Is the thickest
Consists mainly of:
Smooth muscle cells
Elastic fibres
The external elastic lamina consists of
condensed elastic tissue and is well defined
than internal elastic lamina
TUNICAADVENTITIA
Outer coat of arteries
Consists of:
Loose mesh of connective tissue
Some elastic fibres (which merge with
adjacent tissues)
It is rich in:
Lymphatics
Autonomic nerve fibres

6. 6
As the caliber of arteries decrease, the 3 layers
progressively diminish.
LARGE (ELASTIC) ARTERIES
 Include: Aorta, innominate artery, common
carotid, major pulmonary & common iliac
arteries.
Have:
Tunica media with very high content of
elastic fibres
Thick elastic laminae
All its layers being thicker than in
muscular arteries
MEDIUM-SIZED (MUSCULAR) ARTERIES
 Include: Large branches of elastic arteries
Have:
Tunica media primarily composed of smooth
muscle cells & SOME elastic fibres
IEL appears as a single wavy line while EEL is
less prominent
All its layers being thinner than in elastic arteries
SMALL-SIZED ARTERIES (ARTERIOLES)
 3 layered
 Layers are much thinner and cannot be distinguished
Consists of:
Single layer of epithelial cells in intima
1 or 2 layers of smooth muscle cells in media
Elastic laminae are lost
Small amount of collagen and elastic tissue
in adventitia

7. 7
Layers of arterial wall receive nutrition and oxygen from two sources:
1. Tunica intima & inner 1/3 of tunica media are nourished by direct
diffusion of blood present in the lumen.
2. Outer 2/3 of tunica media & tunica adventitia are supplied by vasa
vasora (vessels of vessels) – the nutrient vessels arising from the
parent artery

8. 8
• The structure of normal veins is
basically similar to that of arteries.
• The walls of the veins are thinner.
• The three tunicae (intima, media and
adventitia) are less clearly demarcated,
elastic tissue is scanty and not clearly
organised into internal and external
elastic laminae.
• The media contains very small amount
of smooth muscle cells with abundant
collagen.
• All veins, except vena cavae and
common iliac veins, have valves best
developed in veins of the lower limbs.
• The valves are delicate folds of intima,
located every 1-6 cm, often next to the
point of entry of a tributary vein.
• They prevent any significant
retrograde venous blood flow.

9. 9
• Capillaries are about the size of an
RBC (7-8μm).
• Have 1-2 endothelial cells but NO
MEDIA.
• Blood from capillaries returns to the
heart via post-capillary venules and
from there into venules and then
drained into veins.
3 TYPES OF CAPILLARIES
FENESTRATED
Have small pores & allow small
molecules to pass through them
Found in: intestines, kidneys, endocrine
glands
CONTINUOUS
No perforations, allow only small
molecules to pass through (are the most
common type)
Found in: skin, nerve tissue, respiratory
organs, exocrine glands
SINUSOIDAL/DISCONTINUOUS
Have large open pores, large enough to
allow blood cell through it.
Found in: BM, liver, spleen, lymph nodes
Are the “leakiest” of all

10. 10
Lymphatic capillaries, lymphatic vessels and lymph nodes comprise
the lymphatic system.
Lymphatic capillaries resemble blood capillaries, and larger
lymphatics are identical to veins.
However, lymphatics are lined by a single layer of endothelium have
thin muscle in their walls than in veins of the same size and the valves
are more numerous.
Lymphatic capillaries and lymphatics form plexuses around tissues
and organs.
The walls of lymphatic capillaries are permeable to tissue fluid,
proteins and particulate matter.

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