The circulatory system transports fluids throughout the body; it consists of the cardiovascular and lymphatic systems. The heart and blood vessels make up the blood transportation network, the cardiovascular system. Through this system, the heart pumps blood through the body’s vast system of blood vessels. The blood carries nutrients, oxygen, and waste products to and from the cells. VASCULAR CIRCUITS The heart consists of two muscular pumps dividing the circulation into two components: pulmonary circulations systemic circulations or circuit Pulmonary Circulation Rt ventricle propels low O2 blood into the lungs via the pulmonary arteries. CO2 is exchanged for O2 in the capillaries of the lungs. Then the O2 -rich blood is returned via the pulmonary veins to the Lft atrium. This circuit, from the right ventricle through the lungs to the left atrium, is the pulmonary circulation. Systemic Circulation Left ventricle propels the O2 -rich blood through systemic arteries (the aorta and its branches), exchanging O2 and nutrients for CO2 in the remainder of the body’s capillaries. Low- O2 blood returns to right atrium via systemic veins (tributaries of the superior and inferior vena cava). This circuit, from left ventricle to right atrium, is the systemic circulation.

1. The Cardiovascular System:
Blood Vessels
By Dr.SOMAL

2. INTRODUCTION
 The circulatory system transports fluids throughout the body;
 it consists of the cardiovascular and lymphatic systems.
 The heart and blood vessels make up the blood transportation
network, the cardiovascular system.
 Through this system, the heart pumps blood through the body’s
vast system of blood vessels.
 The blood carries nutrients, oxygen, and waste products to and from
the cells.

3. VASCULAR CIRCUITS
The heart consists of two
muscular pumps dividing the
circulation into two
components:
 pulmonary circulations
 systemic circulations or
circuit

4. Pulmonary Circulation
 Rt ventricle propels low O2
blood into the lungs via the
pulmonary arteries.
 CO2 is exchanged for O2 in the
capillaries of the lungs.
 Then the O2 -rich blood is
returned via the pulmonary
veins to the Lft atrium.
 This circuit, from the right
ventricle through the lungs to
the left atrium, is the pulmonary
circulation.

5. Systemic Circulation
 Left ventricle propels the O2 -
rich blood through systemic
arteries (the aorta and its
branches),
 exchanging O2 and nutrients for
CO2 in the remainder of the
body’s capillaries.
 Low- O2 blood returns to right
atrium via systemic veins
(tributaries of the superior and
inferior vena cava).
 This circuit, from left ventricle to
right atrium, is the systemic
circulation.

6. Blood Vessels
 Arteries – under high pressure
leaves the heart and is
distributed to the body
 Arterioles – final distributing
vessels
 Capillaries – site of exchange
 Venules – from the capillary bed
passes into thin-walled venules
 Veins – carry blood to the heart

7. Basic structure
 3 layers or tunics
1. Tunica interna (intima)
2. Tunica media
3. Tunica externa
 Modifications account for 5 types of blood
vessels and their structural/ functional
differences

8. Structure
 Tunica interna (intima)
 Inner lining consisting of
a single layer of flattened
epithelial cells, the
endothelium
 Capillaries consist only
of this tunic, having a
supporting basement
membrane.

9. Structure
 Tunica media
 Middle layer consisting
primarily of smooth muscle
 The most variable coat
 Arteries, veins, and
lymphatic ducts are
distinguished by the
thickness of this layer
 In the case of arteries, the
presence of variable
amounts of elastic fibers.
 Regulates diameter of
lumen.

10. Structure
 Tunica externa
 Outer connective
tissue layer or
sheath
 Vasa vasorum
 Helps anchor vessel
to surrounding
tissue

11. Arteries
 Carry blood under relatively high
pressure from the heart and distribute it
to the body
 3 layers of typical blood vessel
 There are three types of arteries
 The different types of arteries are
distinguished from each other on the
basis of overall size, relative amounts of
elastic tissue or muscle in the tunica
media
 Artery size and type are a continuum

12. Elastic Arteries
(Large arteries)
 Initially receive the cardiac
output.
 Have many elastic layers in
their walls. (minimizing the
pressure change, and
return to normal size
between ventricular
contractions)
 Also known as
conducting arteries –
conduct blood to
medium-sized arteries

13. Muscular Arteries
(Medium arteries)
 Tunica media contains more smooth
muscle and fewer elastic fibers than
elastic arteries
 Walls relatively thick consist chiefly of
circularly disposed smooth muscle fibers.
 Capable of great vasoconstriction/
vasodilatation to adjust rate of blood flow
 Regulates the flow of blood to different
parts of the body
 Also called distributing arteries

14. Small Arteries and arterioles
(Resistance vessels)
 relatively narrow lumen and thick
muscular walls.
 The degree of filling of the capillary
beds and level of arterial pressure
within the vascular system are
regulated mainly by the degree of
tonus (firmness) in the smooth
muscle of the arteriolar walls.
 If the tonus is above normal,
hypertension (high blood pressure)
results

15. Arterioles
 Abundant microscopic vessels
 Metarteriole has precapillary sphincter which monitors blood flow
into capillary
 Sympathetic innervation and local chemical mediators can alter
diameter and thus blood flow and resistance
 Resistance vessels – resistance is opposition to blood flow

16. Terms related to Arteries
 Anastomoses
 communications between the branches of 2 or more arteries
supplying the same body region
 provide numerous potential detours for blood flow in case the
usual pathway is obstructed by compression due to the position
of a joint, pathology, or surgical ligation.
 Collateral circulation
 Provide alternate routes
 If a main channel is occluded collateral circulation ensures the
blood supply to structures distal to the blockage.
 collateral pathways require time to open adequately; they are
usually insufficient to compensate for sudden occlusion or
ligation.

17. Terms related to Arteries
 Terminal arteries (end arteries)
 Arteries that do not anastomose with adjacent arteries are true
(anatomical) terminal arteries.
 True terminal arteries supply the retina. Occlusion results in
blindness
 Functional terminal arteries (arteries with ineffectual
anastomoses) supply segments of the brain, liver, kidneys,
spleen, and intestines

18. Capillaries
 Smallest blood vessels connect arterial outflow and venous
return
 Microcirculation – flow from metarteriole through capillaries and
into postcapillary venule
 Capillary beds – arise from single metarteriole
 arteriovenous(AVS) anastomoses —Direct connections between
the small arterioles and venules proximal to the capillary beds
 AVS—permit blood to pass directly from the arterial to the
venous side of the circulation without passing through capillaries.
 Arteriovenous (AV) shunts are numerous in the skin, where they
have an important role in conserving body heat.

19. Arteries, Capillaries, and Venule

20. Types of Capillaries
 3 types
1. Continuous
 Endothelial cell
membranes from
continuous tube
2. Fenestrated
 Have fenestrations or
pores
3. Sinusoids
 Wider and more
winding
 Unusually large
fenestrations

22. Veins
 Veins generally return low-pressure
blood from the capillary beds to the
heart.
 Thin walls in relation to total diameter
 Same 3 layers
 low-oxygen blood gives the veins a dark
blue appearance.
 veins do not pulsate and do not spurt
blood when severed.

23. Venules and Small Veins
 Thinner walls than arterial counterparts
 Postcapillary venule – smallest venule
 Venules are the smallest veins.
 Magnification is required to observe
venules.
 Venules drain capillary beds and join
similar vessels to form small veins.
 Small veins are the tributaries of larger
veins that unite to form venous plexuses
(networks of veins), such as the dorsal
venous arch of the foot

24. Medium veins
 Drain venous plexuses and accompany medium
arteries
 Valves – folds on tunica interna forming cusps
 In the limbs, and in some other locations where the flow of
blood is opposed by the pull of gravity
 Aid in venous return by preventing backflow, making flow
unidirectional.
 The valvular mechanism also breaks columns of blood in the
veins into shorter segments, reducing back pressure.
 Both effects make it easier for the musculovenous pump to
overcome the force of gravity to return blood to the heart.

26. Large veins
 Characterized by wide bundles of longitudinal smooth
muscle and a well-developed tunica adventitia.

27. Characterstics of veins
 Although their walls are thinner,
their diameters are usually
larger than those of the
corresponding artery.
 The thin walls allow veins to
have a large capacity for
expansion
 Although often depicted as
single vessels in illustrations for
simplicity, veins tend to be
double or multiple.

28. Characterstics of veins
 Those that accompany deep arteries— accompanying veins (L.
venae comitantes)—surround them in an irregular branching
network.
 This arrangement serves as a countercurrent heat exchanger, the
warm arterial blood warming the cooler venous blood as it returns to
the heart from a cold limb.

29. Characterstics of veins
 The accompanying veins occupy a relatively unyielding fascial
vascular sheath with the artery they accompany.
 As a result, they are stretched and flattened as the artery expands
during contraction of the heart, which aids in driving venous blood
toward the heart —an arteriovenous pump.
 venous anastomoses —natural communications, direct or indirect,
between two veins—occur more often between them

30. Proximal
valve
Distal
valve
1
Proximal
valve
Distal
valve
1 2
Proximal
valve
Distal
valve
1 2 3
Characterstics of veins
 Skeletal muscle pump – (milking) The outward expansion of the
bellies of contracting skeletal muscles in the limbs, limited by the
surrounding deep fascia, compresses the deep veins within and
around the skeletal muscle inside the deep fascia,pushes the blood
superiorly toward the heart; another (musculovenous) type of
venous pump

31. Blood Distribution
 Veins are more abundant
than arteries.
 Largest portion of blood
at rest is in systemic
veins and venules
 Blood reservoir
 Venoconstriction reduces
volume of blood in
reservoirs and allows
greater blood volume to
flow where needed

32. THANK YOU