Blood vessels.2.

Blood vessels.2.

1. 1
SMS 1053SMS 1053
Dr. Mohanad R. AlwanDr. Mohanad R. Alwan

2. Blood vessels
2
Learning Objectives:
Compare and contrast the structure and function
of
Arteries
Veins
Capillaries

3. Blood Vessels
Closed circulatory
system
Arteries
Arterioles
Capillaries
Venules
Veins
3 tunics
Lumen
3

4. The Vessels
Functions:
Distribution of blood
Exchange of materials with tissues
Return of blood to the heart
Structure:
Most have the same basic structure:
– 3 layers surrounding a hollow lumen

5. General Structure of Blood Vessels
Arteries and veins are composed of three tunics:
 tunica interna
 tunica media
 tunica externa
Capillaries are composed of endothelium.

6. Generalized Structure of Blood Vessels
Arteries and veins are composed of three tunics
– tunica interna, tunica media, and tunica
externa
Lumen – central blood-containing space
surrounded by tunics
Capillaries are composed of endothelium with
sparse basal lamina

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The Anatomy Of Blood Vessels
Layers:
2.Tunica interna (intima):
•Endothelial layer that lines the lumen of all vessels.
•In vessels larger than 1 mm, a subendothelial connective tissue
basement membrane is present
2. Tunica media:
•Smooth muscle and elastic fiber layer, regulated by sympathetic
nervous system
•Controls vasoconstriction/vasodilation of vessels
3. Tunica externa (adventitia):
•Collagen fibers that protect and reinforce vessels
•Larger vessels contain vasa vasorum

8. General Structure

9. The Vessels
1. Tunica Intima
Innermost smooth layer
Simple squamous epithelium
Continuous with the endocardium
Present in all vessels

10. The Vessels
2. Tunica Media
layer of smooth muscle - circular arrangement –
contains elastin
Supplied by sympathetic division of the ANS
Depending on body’s needs – lumen is narrowed
(vasoconstriction) or widened (vasodilation)

11. The Vessels
3. Tunica Externa (Adventitia)
Thin layer of CT
Elastic & collagen fibres

12. The Vessels
Types of Vessels:
Arteries – carry blood away from the heart
Veins – carry blood towards the heart
Capillaries – the most important part of the
vascular system; site of exchange of materials

13. The Blood Vessels and the
Cardiovascular System
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Arteries: blood from heart
Strong & Elastic
Conduct blood to capillaries
Sphincters
Capillaries: exchange with cells
Veins
Return blood to heart
Valves

14. Histological Structure of Blood Vessels
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15. Make Up of Blood Vessels: Arteries and
Arterioles
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Endothelium
Elastic tissues
Rebounds
Evens flow
Smooth muscles
Fibrous tissue
Tough
Resists stretch
Figure 15-2: Blood vessels

16. Artery with thick wall
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Connective tissue
Muscle layer
Endothelium

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1
2
3
ELASTIC ARTERY (AORTA)
Stained with orsein
1 - tunica intima
2 - tunica media
3 - tunica externa

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19. Types of Blood vessels: Arteries
Elastic Arteries:
Thick-walled arteries near the heart; the aorta and its
major branches.
Large lumen allows low-resistance conduction of blood.
Contain lots of elastin in all three tunics.
walls stretch and recoil to propel blood
Withstand and regulate large blood pressure
fluctuations.
Allow blood to flow fairly continuously through the body

20. Muscular (Distributing) Arteries and Arterioles
Muscular arteries – distal to elastic arteries;
deliver blood to body organs
Have thick tunica media with more smooth muscle
and less elastic tissue
Active in vasoconstriction
Arterioles – smallest arteries; lead to capillary
beds
Control flow into capillary beds via vasodilation and
constriction

21. Types of Blood vessels: Arteries
Muscular (distributing) arteries
 medium sized vessels
 tunica media more smooth muscle; less
elastin
 major area of vaso-constriction &
dilation to regulate blood flow

22. The Vessels
Arterioles (diameter of 0.3 mm or less)
 smallest arteries; lead to capillary beds.
 close to capillaries - single layer of muscle
spiralling around the endothelial lining
 regulates blood flow to capillary

23. General Structure

24. Venous System: Venules
Are formed when capillary beds unite
Allow fluids and WBCs to pass from the bloodstream
to tissues
Postcapillary venules – smallest venules,
composed of endothelium and a few pericytes
Large venules have one or two layers of smooth
muscle (tunica media)

25. Venous System: Veins
Veins are:
Formed when venules converge
Composed of three tunics, with a thin tunica
media and a thick tunica externa consisting of
collagen fibers and elastic networks
Capacitance vessels (blood reservoirs) that
contain 65% of the blood supply

26. Venous System: Veins
Veins have much lower blood pressure and thinner
walls than arteries
To return blood to the heart, veins have special
adaptations
Large-diameter lumens, which offer little resistance to
flow
Valves (resembling semilunar heart valves), which
prevent backflow of blood
Venous sinuses – specialized, flattened veins with
extremely thin walls (e.g., coronary sinus of the
heart and dural sinuses of the brain)

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28. Make Up of Blood Vessels:
Veins and Venules (Contrasted to Arteries)
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Thinner walls
Larger diameter
Closer to skin
Less muscle
Less elastic
Figure 15-3: Metarterioles

29. Anatomy of Vessels
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30. Comparison of Veins and Arteries
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Arteries: Veins:

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•They also have semi-lunar
valves to stop the blood flowing
backwards

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•This is a medium
sized vein,
recognizable as such
by its scanty wall and
the presence of a
valve inside it.
•The valve flaps are
marked by arrows.

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Artery and a vein

39. Vascular Anastomoses
Merging blood vessels, more common in veins
than arteries
Arterial anastomoses provide alternate pathways
(collateral channels) for blood to reach a given
body region
If one branch is blocked, the collateral channel can
supply the area with adequate blood supply
Thoroughfare channels are examples of
arteriovenous anastomoses

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A capillary wall is very thin and composed of (endothelium
only)
single layer of cells as it does not have to withstand high
internal pressure.
A capillary wall is often highly permeable, partly because
its very thin and partly because of holes in and between cells
in some capillaries (particularly those with high demand of
exchange e.g endocrine glands)
Capillaries

41. Capillaries
Capillaries are the smallest blood vessels
Walls consisting of a thin tunica interna, one cell thick
Allow only a single RBC to pass at a time
Pericytes on the outer surface stabilize their walls
There are three structural types of capillaries:
continuous, fenestrated, and sinusoids

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lumen
endothelium
(one cell thick)
cell

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A capillary bed

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48. Make Up of Blood Vessels: Capillaries
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Figure 15-16: Types of capillaries

49. Continuous Capillaries
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Continuous capillaries are abundant in the skin
and muscles, and have:
Endothelial cells that provide an uninterrupted
lining
Adjacent cells that are held together with tight
junctions
Intercellular clefts of unjoined membranes that
allow the passage of fluids

50. Continuous Capillaries
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Continuous capillaries of the brain:
Have tight junctions completely around the
endothelium
Constitute the blood-brain barrier

51. Continuous Capillaries
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Figure 19.3a

52. Fenestrated Capillaries
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Found wherever active capillary absorption or
filtrate formation occurs (e.g., small intestines,
endocrine glands, and kidneys)
Characterized by:
An endothelium riddled with pores (fenestrations)
Greater permeability to solutes and fluids than
other capillaries

53. Fenestrated Capillaries
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Figure 19.3b

54. Sinusoids
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Highly modified, leaky, fenestrated capillaries
with large lumens
Found in the liver, bone marrow, lymphoid tissue,
and in some endocrine organs
Allow large molecules (proteins and blood cells)
to pass between the blood and surrounding
tissues
Blood flows sluggishly, allowing for modification
in various ways

55. Sinusoids
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56. Capillary Beds
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A microcirculation of interwoven networks of
capillaries, consisting of:
Vascular shunts – metarteriole–thoroughfare
channel connecting an arteriole directly with a
postcapillary venule
True capillaries – 10 to 100 per capillary bed,
capillaries branch off the metarteriole and return
to the thoroughfare channel at the distal end of
the bed

57. Capillary Beds
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Figure 19.4a

58. Capillary Beds
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Figure 19.4b

59. Blood Flow Through Capillary Beds
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Precapillary sphincter
Cuff of smooth muscle that surrounds each true
capillary
Regulates blood flow into the capillary
Blood flow is regulated by vasomotor nerves
and local chemical conditions, so it can either
bypass or flood the capillary bed

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61. Capillary Exchange
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Diffusion:
Filtration:
Reabsorption:

62. Capillary Exchange
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At the arteriole end of a capillary, water moves
out of the blood due to the force of blood
pressure.
At the venule end, water moves into the blood
due to osmotic pressure of the blood.
Substances that leave the blood contribute to
tissue fluid, the fluid between the body’s cells.

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In the midsection of the capillary, nutrients
diffuse out and wastes diffuse into the blood.
Since plasma proteins are too large to readily
pass out of the capillary, tissue fluid tends to
contain all components of plasma except it has
lesser amounts of protein.
Excess tissue fluid is returned to the blood
stream as lymph in lymphatic vessels.
Capillary Exchange

64. Capillary exchange
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65. Capillary exchange
At the arterial end of a capillary, the blood
pressure is higher than the osmotic pressure;
therefore, water tends to leave the bloodstream.
 In the midsection, oxygen and carbon dioxide
follow their concentration gradients.
At the venous end of a capillary, the osmotic
pressure is higher than the blood pressure;
therefore, water tends to enter the bloodstream.
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66. Capillary Exchange
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67. Blood Flow in Capillaries
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Blood moves slowly in capillaries because there
are more capillaries than arterioles.
This allows time for substances to be exchanged
between the blood and tissues.

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72. Major arteries and veins of the systemic circuit
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