Cardio-Vascular System
Angiology is the description of the organs of circulation of the blood and lymph. It includes the heart and vessels(blood and lymph vessels) including spleen and thymus.
Circulatory System
The circulatory system consists of the blood vascular system and the lymphatic system.
The blood vascular system is made up of the heart, arteries, veins and capillaries.
Cardio-Vascular System
Cardio-vascular system is the branch of Angiology which deals with microscopic form and structure of heart and blood vessels(artery, vein, and capillary)
Artery
Thick wall tubes which carry blood away from the heart to the organs, tissues, and cells.
It carries oxygenated(pure) blood except pulmonary artery.
Arteriole
Smallest terminal arteries with diameter less than 0.5 mm and narrow lumen are called arterioles.
Arterioles divide into smaller branches and form successively terminal arterioles and meta-arterioles.
The meta-arterioles terminate into capillaries.
Vein
Thin walled tubes that carry blood away from the cells, tissue, and organs to the heart.
It carries deoxygenated(impure) blood except pulmonary vein.
General structure of blood vessels
The wall of blood
vessels consists of three layers, except capillaries;
1.
Tunica
intima (innermost layer)
2.
Tunica
media (middle layer)
3.
Tunica
adventitia (outer layer)
(Note:-Figure for practical note book)
Fig: Small artery and vein, x.s., eyelid, pig
4. Internal elastic lamina, 7. small artery, 8. Small vein, 9. Sweat gland,
10. Tunica adventitia, 11. Tunica media
10. Tunica adventitia, 11. Tunica media
1. Tunica
intima
The tunica intima of the
arteries, vein and that of the heart (the endocardium) are essentially
identical.
It consists of three layers(from inside to outside)
i) Endothelial
layer: It is the inner most layer of tunica intima consists of simple squamous epithelium rest on a
basal lamina lining the lumen of the blood vessels and lymph vessels
ii) Sub-endothelial
layer: Consists of loose connective tissue and a few scattered smooth muscle cells.
iii) Internal
elastic lamina: Composed of elastic fiber, which has gaps (fenestrae) that
allow diffusion of substance into the deeper regions of the arterial wall to
nourish the cells.
2. Tunica
media
Consists chiefly
of smooth muscle cells, variable amount of elastic and reticular fibers are also present.
Smaller
artery- chiefly muscular tissue
Medium size artery- smooth muscle and elastic fiber
Larger
trunk- elastic tissue exclusively
3. Tunica
adventitia
Consists chiefly
of type-I collagen and elastic fibers.
Superficially- chiefly
fibrous connective tissue
In deeper
parts- some elastic fiber
In some
arteries- smooth muscle fiber
Fig: Small artery, vein, and nerve
1. Adipose tissue, 2. Artery, 5. External elastic lamina, 6. Internal elastic lamina, 7. Nerve,8. Pancreas, 9. Tunica adventitia, 11. Tunica media, 12. Vein
Differences between artery & vein
Artery
|
Vein
|
||
1.
|
Diameter
|
Small
|
Large
|
2.
|
Lumen
|
Small
|
Large
|
3.
|
Wall
|
Thick
|
Thin
|
4.
|
Tunica
intima
|
Relatively
thick
|
Thinner
|
5.
|
Internal elastic lamina
|
Distinct
|
Not
distinct
|
6.
|
Externalelastic lamina
|
Distinct
|
Not
well distinct
|
7.
|
Tunica
media
|
Much
thick (2/3 of thickness of wall)
|
Thinner
(1/3 of thickness of wall)
|
8.
|
Tunica
adventitia
|
Thinner
(1/3 of thickness of wall). It contains more elastic & less collagen fiber
|
Thicker
(2/3 of thickness of wall). It contains more collagen & less elastic
fiber
|
9.
|
Valves
|
Absent
|
Present
|
10.
|
Extend of vasavasorum
|
Tunica
adventitia and outer 2/3 of tunica media
|
Upto tunica media
|
Capillaries
Capillaries are
the network of microscopic tubes composed of single layer of endothelial cells,
interposed between the meta-arteriole and venules.
Sinusoids
Sinusoids are
large, irregular tubular spaces found in certain organs in place of
capillaries.
Location- Liver,
spleen, bone marrow, adrenal cortex, parathyroid gland etc.
Difference between
sinusoids & capillaries
Capillaries
|
Sinusoids
|
||
1.
|
Diameter
|
Small (7-9 um)
|
Large (30-40 um)
|
2.
|
Lumen
|
Regular
|
Irregular,
tortuous
|
3.
|
Wall
|
Thicker
|
Thinner,
may be incomplete
|
4.
|
Endothelial
lining
|
Continuous
and fenestrated
|
Discontinuous and may
be fenestrated
|
5.
|
Phagocytic
cell
|
Absent
|
Present
|
6.
|
Basal
lamina
|
Present
|
Absent
|
7.
|
Surrounding
sheath
|
A
thin sheath of loose connective tissue
|
A
thin layer of reticular fiber
|
8.
|
Size
of pore
|
Small
(20-60 nm)
|
Large (about 100 nm) |
9.
|
Distribution
|
All
over the body
|
Liver,
spleen etc.
|
The heart
- The heart is the central hollow muscular organ which function as a suction and force pump.
- It is situated in the middle mediastinum space of the thorax and is enclosed in a fibro-serous sac called pericardium.
- The pericardium encloses the heart and in part, the great vessels connected with it.
Fig: Parietal and visceral pericardium, cat
1. Adipose tissue, 4. Myocardium,(Rt. ventricle), 9. Pericardial cavity, 10. Parietal pericardium, 11. Visceral pericardium
Structure
GROSS
GROSS
- The heart wall consists mainly of peculiar striated muscle, the myocardium, which is covered externally by the visceral part of serous pericardium, or epicardium, and is lined internally by the endocardium.
- So, the wall of heart (from inward to outward) consists of following three layers, namely;
- Endocardium (innermost layer)
- Myocardium (middle layer)
- Epicardium (outer layer)
Fig: Right auricle, pig
4. Collagenous fibers, 6. Endocardium, 7. Myocardium, 9. Smooth muscle HISTOLOGY
Endocardium (innermost layer)
- It is the innermost layer of heart, is homologous to the tunica intima of blood vessels.
- It is composed of simple squamous epithelium(endothelium)cells resting on delicate connective tissue.
- Under this tissue there is a thick stratum consisting mostly of flat nets of elastic fibers which becomes more numerous towards the myocardium. They are specially prominent in the atria.
- A sub-endocardial layer of connective tissue binds the myocardium with the endocardium, by a sub-endocardial elastic tissue containing vessels, nerves and purkinje fibers.
- It is the middle and thickest layer of heart, is homologous to the tunica media of blood vessels.
- It consists of layers of cardiac muscles fibers in a connective tissue framework which is continuous with both the endocardium and epicardium.
- It contains elastic fibers, vessels, nerves, and terminal purkinje fibers.
- The cardiac muscle fibers are connected in a narrow-meshed syncytium. The bundles have a complex course.
- It is the outermost layer of heart and constitutes the visceral serous layer of pericardium which is a tough serous membrane of varying thickness.
- It contains numerous elastic fibers which are laid down densely in laminae, specially in the deeper portions.
- The outer free pericardial surface is lined with simple squamous epithelium(mesothelium) to low columnar cells.
- It is closely attached to the myocardium and also covers vessels, nerves, and adipose tissue.
- The fat is distributed in a definite manner and is specially abundant in the grooves of the heart.
Fig: Venacava, x.s., dog
1. Adipose tissue, 3. Cardiac muscle, 12. Tunica intima, 13. Tunica media, 14. Vasavasorum If you have any questions you can ask me on :
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