1. Topic 3
Circulation

2. Objective 1 Blood Vessel Structure/Function
General Histological Features of Blood Vessels:
Arteries/Veins
 arteries and veins have three layers (tunics)
 the central blood filled opening is called the lumen

3. Intima (Interna)
: simple squamous epithelium which lines the lumen
Subendothelial layer:
loose areolar CT located external to the endothelium in vessels with a diameter > 1 mm
Endothelial cell products:
Nitric oxide: relaxes vascular smooth muscle
Prostacyclin: relaxes vascular smooth muscle and repels platelets
Endothelin: contracts vascular smooth muscle causing vasoconstriction
Endothelium

4. Smooth muscle cells arranged in a circular fashion
Elastic fibers organized into sheets
Muscle fibers cause vasoconstriction (contracted cells) and vasodilation (relaxed cells)
 they are controlled by
SNS vasomotor nerves
and chemical factors
Elastic fibers provide elasticity (stretch and recoil)
Media
Aorta Small Artery

5. Vasa Vasorum Adventitia (Externa)
Collagen fibers with nerve fibers, lymphatic vessels and elastic fibers in large vessels
: small blood vessels that nourish the wall of larger blood vessels
Protect, reinforce vessels and attach them to surrounding structures
Vasa Vasorum
Blue arrow: vasa vasorum
Green arrow: tunica media

6. Comparing Arteries and Veins
Thick tunica media
Thin tunica adventitia
No valves
Round lumen
Veins
Thin tunica media
Thick tunica adventitia
Valves present
Irregular lumen

7. Recall the vessels of the cardiovascular system ………

8. Comparing Blood Vessels
Internal diameter is 2.5 cm – 1 cm
Well developed tunica media rich in elastic fibers; adventitia is thin
conducting artery:
drives the circulation of blood into smaller vessels
during systole, the artery fills with a stroke volume and is stretched
during diastole the artery maintains pressure as it recoils on the blood, propelling it further along
Elastic Artery

9. Distributing Artery elastic arteries supply pressure
Muscular Artery
External diameter is 1 cm to 0.3 mm
Well developed tunica media rich in smooth muscle fibers
Internal elastic lamina and external elastic lamina are sheets of elastic fibers that separate the tunica intima/tunica media and tunica media/tunica adventitia
dilate and constrict to control the distribution of blood to organs
vasoconstriction reduces the diameter of the artery and decreases the flow of blood to an organ
vasodilation increases the diameter of the artery and increases the flow of blood to an organ
Distributing Artery
elastic arteries
supply pressure
stomach skin kidney heart
Muscular arteries dilate and constrict to direct blood flow

10. Arteriole External diameter is < 0.3 mm
Internal elastic lamina present in most cases
Tunica media is a single layer of smooth muscle cells
vasoconstriction and vasodilation controls the distribution of blood to capillary beds
Arteriole

11. Arterioles deliver blood to capillary beds

12. Pericytes Capillary External diameter averages 8-10 μm
Single layer of endothelium (simple squamous epithelium) resting on a basement membrane
No elastic laminae are present
are connective tissue cells that stabilize the capillary wall
Thin walls permit the exchange of gases, nutrients and wastes with interstitial fluid
Pericytes

14. Precapillary sphincters
Capillary Beds:
 smooth muscle sphincters that open and close to regulate
the distribution of blood through capillary beds
Precapillary sphincters

15. Structural Types of Capillaries:
: endothelial cells are joined by tight junctions but may be interrupted in some places by intercellular clefts
Continuous Capillaries
Fenestrated Capillaries
like continuous capillaries, but the endothelial cells have pores (fenestrations) covered by thin membranes; these capillaries are more permeable than continuous capillaries

17. Sinusoids
: leaky capillaries that have large lumens and are usually fenestrated; few tight junctions and intracellular clefts; found in liver, bone marrow, lymphoid tissues and some endocrine organs
Spleen sinusoids and liver sinusoids are lined with macrophages (called Kupffer Cells)

18. External diameter ranges from 8-100 m
Postcapillary venule (small): consists of endothelium with a few pericytes; are extremely porous
Larger venules:
Contain endothelium, a thin tunica media and a thin tunica adventitia
Collect blood from tissue capillaries and carry it to veins
Venule

19. Vein Capacitance Vessel Jugular Vein
External diameters vary, but they are larger than their corresponding arteries
Lumen has an irregular shape
All three tunics are present
 tunica externa is thick
 tunica media is generally thin
Valves, formed from endothelium, are present in some places to prevent the backflow of blood
Collect blood from venules and carry it to the heart
Veins hold up to 50% of the total blood volume
Capacitance Vessel
Jugular Vein

20. Valves prevent the backflow of blood…….
Venous vales are formed from folds of the:
They are abundant in veins of the limbs and are absent in veins of the ventral body cavity
endothelium

21. Venous Sinuses large diameter veins
endothelium
They are made of
Examples of venous sinuses:
Coronary Sinus Cranial Sinuses

22. The Distribution of Blood Volume In the Vascular Tree:
Location
% of Total Blood Volume
Aorta 2
Other Systemic Arteries 8
Systemic Arterioles 1
Systemic Capillaries 5
Systemic Veins 50
Heart Chambers 12
Pulmonary Circulation 18
Sinusoids 4

23. Objective 2 Vascular Disorders
Arteriosclerosis
Causes: aging, hypertension, diabetes, smoking, hereditary factors, elevated cholesterol
Characteristics:
abnormal thickening and abnormal hardening of the vessel walls in the arterial system
 smooth muscle cells and collagen fibers migrate into the tunica media
 lumen becomes narrowed
Hyperplastic arteriosclerosis

24. Atherosclerosis Most common cause of arteriosclerosis:
Endothelial cells are injured; inflammation occurs
Macrophages release free radicals and enzymes that further damage the vessel wall
LDL becomes oxidized and ingested by macrophages (foam cells)
Foam cells invade the wall and accumulate (fatty streak)
Smooth muscle cells proliferate, secrete collagen and form a fibrous plaque
Vessel becomes narrowed and obstructed; platelets adhere and lead to thrombus formation
Atherosclerosis

27. Varicose Veins Damage to one or more valves in a vein
Venous distention and pooling of blood; veins become tortuous and palpable
Surrounding tissue may become edematous
Varicose Veins

28. Localized dilation or outpouching of a blood vessel or cardiac chamber
Arterial walls become weakened and may rupture; common sites are the abdominal aorta, renal arteries and cerebral arteries
Aneurysm

29. Aneurysm in a Basilar Artery Aortic Aneurysm

30. Phlebitis Thrombophlebitis Inflammation of a vein usually due to
Infection or trauma
May lead to pooled blood and edema
Inflammation of a vein associated with a blood clot
Redness, heat, swelling and pain in the affected area; the clot may break off and become an embolus that blocks smaller vessels in other areas
Phlebitis
Thrombophlebitis
Superficial thrombophlebitis is an inflammation of a vein just below the surface of the skin, which results from a blood clot. This condition may occur after recently using a intravenous (IV) line, or after trauma to the vein. It involves an inflammatory response associated with a clot in the vein. Some symptoms can include pain and tenderness along the vein and hardening and feeling cord-like. Superficial thrombophlebitis is usually a benign and short-term condition. Symptoms generally subside in 1 to 2 weeks, but hardness of the vein may remain for much longer.