1. THE CIRCULATORY SYSTEM
DEFINITION/DESCRIPTION
This is the composite body system that is
responsible for the continuous movement of
all body fluids and their contents.
It is subdivided into:
Blood vascular (Cardiovascular) system and
Lymphatic vascular system.

2. The Cardiovascular System
Functions: The functions of the CVS include:
Continuous movement of body fluids
Oxygen transport to body tissues
CO2 transport from body tissues
Transport of metabolic wastes
Transport of hormones
Transport of drugs and other biologically active
substances
7. Transport of blood cells
8. Thermoregulation
9. Electrolyte regulation
10. Body defense
11. Biosynthesis of biologically active substances
12. Inactivation of biologically active substances

3. Component Parts of the CVS
The CVS is composed of a circuit of a hollow muscular organ (The heart) and vascular channels through which blood flows to and from the body tissues.
It is composed of:
The heart
The arterial vascular system
The capillary vascular system
The venous vascular system

6. Microscopic Anatomy of the CVS
All the component parts of the CVS share a common basic microstructure which is found in their walls.
The wall is composed of three main layers, viz.
Tunica intima (Tunica internus): This is the mucous
membrane which lines the cavities of the heart and
the lumen of the vessels.
2. Tunica media (Tunica intermedus): This is composed
of striated and smooth muscle fibres which
contract to propel blood through the heart and
blood vessels.
3. Tunica adventitia (Tunica externus): This is the
fibrous connective tissue layer which supports and
protects the heart and vessels.

10. Variations occur in the 3 layers from one
part of the body to another on the basis of
functional requirements of various tissues of
the body.
The most variable layer is the tunica media.

11. Microscopic Anatomy of the Heart
The cardiac wall is composed of:
Tunica intima (Endocardium): This is lined by squamous cell and contains blood vessels, nerve fibres and conducting tissue in its connective tissue
2. Tunica Media (Myocardium): This is composed
of several layers of cardiac muscle fibres (Striated muscle).
3. Tunica Adventitia (Epicardium): This is lined by
serous squamous cells and contains blood
vessels, nerve fibres and adipocytes in its
connective tissue
Furthermore, the heart is enclosed in a coat of fibrous tissue which is lined by serous squamous cells (Fibrous and Serous Pericardium)

13. The Arterial Vascular System
Functions:
a. Blood distribution to tissue capillaries
b. Control of Pressure and rate of blood flow to
the tissues.
Organization:
There are three types of arteries;
Elastic arteries: These include the aorta and its
main branches
2. Muscular arteries: These include the named
arteries supplying regions and organs of the body
3. Arterioles: These are vessels found in the walls
and substances of organs of the body

14. The Microcirculation
The microcirculation consists of a network of vessels at which:
Exchange of substances occurs between the blood vascular system and the tissues of the body
Blood flow into tissues is controlled.
The microcirculation is composed of:
Metarterioles.
Precapillary sphincters.
Capillaries
Post-capillary venule
Collecting venule
Small muscular venule
Arteriovenous shunts

16. The Capillary (Exchange Vessels)Vascular system
 The capillary is an endothelial-lined vessel which also has a basement membrane.
Functions:
a. Permits selective passage of molecules.
Serves as the exchange site between blood
and tissues of the body.
c. It metabolizes substrates through the
endothelial cells.
d. Serves as an Antithrombogenic channel for
blood

17. Classification of capillaries:
There are four types of capillaries viz.
Continuous (Somatic) capillaries (Pharynx,
Brain and Muscles)
2. Fenestrated capillaries with diaphragm
(Stomach and Endocrine glands)
3. Fenestrated capillaries without diaphragm
(Kidney glomeruli)
Discontinuous capillaries (Liver, Spleen
and Bone marrow )

19. The Venous Vascular System (Capacitance Vessels)
Functions:
Collection of blood from the capillary system
Return of blood to the heart for recirculation
Characteristic features of Veins:
a. Low pressure blood flow.
b. Valve assisted blood flow.
c. Skeletal muscle assisted blood flow.
d. Inspiration assisted blood flow.
e. Larger capacity than the arterial vascular
system hence retains 70 of total blood volume.

20. Classification of Veins:
Muscular venule. Smallest vein (connecting venous system to the microcirculation)
Small veins
Medium-sized veins and
Large-sized Veins

21. The Lymphatic Vascular System
The vessels of the lymphatic vascular system are blind-ended tubes arising from tissue spaces.
The functions of the lymphatic system are:
Drainage of excess tissue fluid (Lymph)
Passive transport of lymph, lymphocytes and
other immunologic factors
3. Release of lymph into the blood vascular
system

22. Characteristic features of the lymphatic system: This system is characterized by: 
Unidirectional flow of fluid towards the heart
Valves and muscle assisted flow of fluid
Filtration of fluid through lymph nodes
Vessels formed from blind-ended lymph
capillaries

23. Microstructure of the Lymphatic System:
This comprises:
Blind-ended, thin-walled, endothelial-lined
capillaries
2. Non-fenestrated endothelium
3. Rudimentary basement membrane
4. Large vessels posses circular and longitudinal
layers of smooth muscles
5. Fine elastic filaments (Anchoring fibres) attach
endothelium to surrounding connective tissue
6. The large vessels contain vasa vasorum and
nerve fibres

26. Lymphatic vessels are not found in the following areas/structures:
Central nervous system (CNS)
Cornea
Teeth
Bone
Cartilage
Bone Marrow
Thymus gland
Placenta.