1. Principles of Physiology
BLOOD VESSELS

2. Blood vessels Arteries – away from the heart
Capillaries – within the body tissues
Veins – toward the heart

3. Structure of Artery and Veins
Three layers except for capillaries and venules
Tunica intima (interna)
Endothelium
Tunica media (Smooth muscle)
Vasoconstriction
Vasodilation
Tunica adventitia (externa)
Merges with connective tissue surrounding blood vessels

4. Structure of Artery and Veins
Arterioles
Veinules

5. Structure of Artery and Veins

6. Arteries
Elastic – lots of elastin in tunica media especially “conducting arteries” cm diameter
Muscular – “distributing arteries” BP and pulse sites – large tunica media smooth muscular layer – 1cm diameter
Arterioles – 0.3 – 10µm diam. less smooth muscle
Capillaries – µm diam.

7. Elastic (Conducting) Arteries
Thick-walled arteries near the heart; the aorta and its major branches
Large lumen allow low-resistance conduction of blood
Contain elastin in all three tunics
Withstand and smooth out large blood pressure fluctuations
Serve as pressure reservoirs

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

9. 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

10. Blood vessels

11. Capillary Beds
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

12. Capillary Bed

13. Blood Flow Through Capillary Beds
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

14. Venous System: Venules
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)

15. 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

16. Veins have much lower blood pressure and thinner walls than arteries
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)

17. Merging blood vessels, more common in veins than arteries
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

18. S. No.
Arteries
Veins 1
Most arteries are located deep in the body
Veins are situated superficially 2.
They appear pink (وردي) in color
They appear dark red in color 3.
They contain oxygenated blood except pulmonary artery
They contain deoxygenated blood except pulmonary vein 4.
They carry blood away (بعيدا) from heart into various organs and tissue
They bring blood from various organs and tissues into or towards (نحو) heart 5.
Their wall is thick, strong, and less distensible (قابل للنفخ)
Their wall is thin, weak and more distensible 6.
They are non collapsible
They are collapsible (قابلة للطي) 7.
Lumen of arteries is small
Lumen (تجويف عضو) of veins is large 8.
The flow (تدفق) of blood is fast, jerky and with great pressure
The flow of blood is slow, steady and with less pressure 9.
Valve absent
Valve present and prevents back flow of blood
10.
They become empty after death
They contain blood even after death

19. Circulatory Physiology
Blood flow = CO, constant at rest in the body, but organs may vary (in mL/min.)
Blood Pressure = force, mostly refers to arterial system near the heart [in millimeters of mercury (mm Hg)]
Resistance = opposition to flow, friction, called peripheral resistance

20. Resistance Factors: Blood Vessel Diameter
Small-diameter arterioles are the major determinants of peripheral resistance
Fatty plaques from atherosclerosis:
Cause turbulent blood flow
Dramatically increase resistance due to turbulence

21. Systemic Blood Pressure
The pumping action of the heart generates blood flow through the vessels along a pressure gradient, always moving from higher- to lower-pressure areas
Pressure results when flow is opposed by resistance

22. Systemic Blood Pressure
Systemic pressure:
Is highest in the aorta
Declines throughout the length of the pathway
Is 0 mm Hg in the right atrium
The steepest change in blood pressure occurs in the arterioles

23. Systemic Blood Pressure
Arterial - systolic is ~120mmHg and diastolic is ~80mmHg