Description
Cardiovascular System
Blood & lymphatic vessels in the
connective tissue
Constituents
• Heart
• Blood vessels:
(a) Arteries
(b) Capillaries
(c) Veins
elastic arteries
large vein
muscular arteries
medium-sized vein
arterioles
venules
capillaries/sinusoids
Arteries – ALWAYS carry blood away from the heart
Veins – ALWAYS return blood to the heart
All are lined on their inner surface by endothelial cells (simple squamous)
Gross Anatomy of Circulatory System
Pulmonary &
Systemic Circulations
Pulmonary Circuit
• Right ventricle into
pulmonary trunk to
pulmonary arteries to
lungs.
• Return by way of 4
pulmonary veins to left
atrium.
Systemic Circuit
Basic structure of arteries
1. Tunica interna or intima:
consists of-
a. Endothelium
b. Basal lamina
c. Subendothelial connective
tissue
d. Internal elastic lamina
2. Tunica media
3. Tunica externa or adventitia
Classification of Arteries
• Elastic (conducting/ large size arteries):
e.g. aorta, pulmonary trunk, carotids,
subclavian, axillary, iliac.
• Muscular (distributing/ medium size
arteries)
• Arterioles
Elastic arteries
• Internal elastic lamina is ill-
defined.
• Tunica media is
predominantly made up of
elastic fibres.
• Tunica adventitia contains
blood vessels (vasa
vasorum).
Diameter: > 1 cm
Elastic artery
Muscular arteries
(Medium sized arteries)
• Internal elastic lamina is
clearly visible.
• Tunica media is
predominantly made up
of smooth muscle cells.
• Tunica adventitia is
thicker than of elastic
artery.
Diameter: 2-10 mm
Arterioles
• Arterioles less than 50 μm
diameter are called terminal
arterioles.
• The smallest terminal
arteriole is < 12 μm
• Internal elastic lamina is
poorly developed.
• Thin layer of smooth muscle
in tunica media.
• Precapillary sphincter
• Tunica adventitia is thin.
• Metarterioles Diameter: < 100 μm
Veins
• Classified as large,
medium & small (venules).
• All the 3 tunics are present
but not well defined.
• T. intima: endothelial cells,
basal lamina,
subendothelial connective
tissue & few smooth
muscle cells
• T. media: larger amount of
collagen, thinner
• T. adventitia: thicker
Large vein
Largest conducting arteries – lead
directly from heart, subject to high
pressure
Superior & inferior Pulmonary trunk & aorta
vena cava and their and their major branches
tributaries
2 – 9 mm ~ 4 mm
External and internal External and internal
jugular, brachial & carotids, brachial &
femoral veins femoral arteries
~ 10-50 µm
~ 30 µm
Capillaries
• Thin-walled endothelial-lined microscopic vessels that
connect arterioles & venules.
• Extensive network
• Diameter: 5-10 μm
• Flow of blood through capillary is called Microcirculation.
• Absence of T. media & adventitia.
Types of capillaries
• Continuous capillaries
• Fenestrated capillaries
• Sinusoids
Capillaries Only endothelium
Variably permeable
~ 8 µm
Characterized by circular fenestrae or
pores that penetrate the endothelium –
permit exchange of larger molecules.
somewhat
permeable
Intestinal mucosa, choroid plexus,
Most body regions
endocrine glands, kidneys
Sinusoids
• Resemble fenestrated capillaries but have:
a. irregular shapes
b. longer pores
c. thinner (or no) basement membrane
• Blood flow is sluggish
• Found in the liver, bone marrow, spleen etc.
• Sometimes called as sinusoidal capillary.
References
1. diFiore’s Atlas of Histology with functional
Correlations, 12th Edition.
2. Textbook of Human Histology. Inderbir
Singh, 1st Edition.
3. Textbook of Histology. GP Pal, 3rd
Edition.
MCQ
• Prominent external elastic lamina is a
feature of:
1. Elastic artery
2. Muscular artery
3. Arteriole
4. Vein
MCQ
• Tunica media is thinner than adventitia in:
1. Elastic artery
2. Muscular artery
3. Arteriole
4. Vein
MCQ
• All are components of Tunica intima
except:
1. Endothelium
2. Subendothelial layer
3. Internal elastic lamina
4. Cell junction
MCQ
• Internal elastic lamina is poorly developed
in:
1. Elastic artery
2. Muscular artery
3. Arteriole
4. Vein
MCQ
• All are present in Tunica adventitia of
arteries except:
1. Collagen fibres
2. Elastic fibres
3. Plasma cells
4. Vasa vasorum