BIOL 2304 Vasculature and Circulation
Circulatory System
Three basic components:
Heart – serves as pump that establishes the pressure gradient needed for blood to flow to tissues
Blood – transport medium within which materials being transported are dissolved or suspended
Blood vessels – passageways through which blood is distributed from heart to all parts of body and back to heart
Circulatory Circuits
Pulmonary circuit – takes blood to and from the lungs
Systemic circuit – vessels transport blood to and from body tissues
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Pulmonary Circulation
Pulmonary Circulation
– consists of blood vessels that take the blood to and from the lungs for the purpose of gas exchange
Pulmonary Trunk
– O
2
-poor blood leaves the right ventricle via the pulmonary trunk; large artery that branches to left and right pulmonary arteries
Pulmonary Arteries
– take the blood to the lung where O
2
is picked up and CO
2
is left off
Pulmonary Veins – blood returns to the heart via four pulmonary veins that go to the left atrium
Systemic Circulation
Systemic Circulation – consists of blood vessels that extend to and from the heart; delivers O
2
and nutrients to body tissues; picks up CO
2
and waste products from tissues
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Types of Blood Vessels
Arteries
– large; carry blood away from heart
Arterioles – small arteries that deliver blood to capillaries
Capillaries
– thin-walled, microscopic vessels that allow for gas and solute exchange between vessels and tissue cells
Venules
– small veins that collect and drain blood into veins
Veins – large; return blood to heart
Heart → Arteries → Arterioles → Capillaries → Venules → Veins → Heart
Anatomy of a Blood Vessel
Composed of three layers called tunics :
Tunica intima – composed of simple squamous epithelium
Tunica media – sheets of smooth muscle
Vasoconstriction – Contraction of smooth muscle in vessel wall (tunica media)
Vasodilation – Relaxation of smooth muscle in vessel wall (tunica media)
Tunica externa (tunica adventitia) – composed of connective tissue
Lumen
Central, blood-filled space of a vessel
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Anatomy of Blood Vessels
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Cross Section of Blood Vessels
The thick tunica media of arteries allow them to remain open during histological preparation.
The thin tunica media of veins allow them to collapse when blood is not present to hold them open.
Types of Arteries
Elastic arteries
– the largest of the arteries
Diameters range from 2.5 cm to 1 cm
Examples:
Aorta
Brachiocephalic trunk (artery)
Pulmonary trunk
Sometimes called conducting arteries
High elastin content withstands high blood pressure and provides recoil to help propel blood forward
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Types of Arteries
Muscular arteries
Lie distal to elastic arteries
Diameters range from 1 cm to 0.3 mm
Includes most named arteries
Sometimes called distributing arteries
Tunica media is thick
Unique features:
Internal elastic laminae
External elastic laminae
Arterioles
Smallest arteries
Larger arterioles possess all three tunics
Diameter of arterioles controlled by:
Local factors in the tissues
Sympathetic nervous system
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Capillaries
Smallest blood vessels
Diameter from 8 –10 µm
RBCs pass through capillary lumen single file
Capillary beds run through tissues
Pre-capillary sphincters constrict or dilate to control blood flow into a capillary bed
Vasa vasorum ("vessels of the vessels")
Capillaries that supply large blood vessels
Found in large arteries and veins such as the aorta and vena cavas
Capillary Bed
(Open & Closed Pre-capillary Sphincters)
Capillary Permeability
Endothelial cells – held together by tight junctions and desmosomes; form wall of vessel
Intercellular clefts – clefts between endothelial cells
Size of cleft varies; dictates size of molecules allowed to enter and exit the vessel
Fenestrations – (“window”) large pores through an endothelial cell
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Veins
Venules form from merging capillaries
Diameters from 8 –100  m
Venules join veins
Tunica externa is the thickest tunic in veins
Specific Circulatory Routes
Coronary circulation
Supplies blood to heart tissue
Cerebral arterial circle (Circle of Willis)
Supplies blood to brain
Hepatic portal system
Carries nutrient-filled blood from Gastrointestinal tract to liver for detoxification and nutrient storage
Fetal circulation
F etus blood reaches placenta so that it may obtain nutrients from the mother’s uterus, release wastes
Fetal lungs do not require as much blood supply as those of a newborn
Coronary Circulation
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Cerebral Arterial Circle (Circle of Willis)
Circle of Willis serves the brain
Vertebral artery branches into basilar artery , which forms the Circle of Willis
Portal Systems
Portal System
– a system in which a capillary bed leads to another capillary bed through veins, without first going through the heart
Hepatic portal system
– carries blood from GI tract to liver for removal of toxins and storage of some nutrients
Organization :
Non-portal system : Arteries  Capillary bed  Veins  Heart
Portal Systems: Arteries  Capillary bed  Veins  Capillary bed  Veins  Heart
Hepatic Portal System
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Fetal Circulation
Fetal circulation
All major vessels in place by month three of development
Differences between fetal and postnatal circulation
Fetus must supply blood to the placenta to obtain nutrients
Very little blood is sent through the pulmonary circuit
Umbilical vessels run in the umbilical cord
Paired umbilical arteries
Single umbilical vein
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BIOL 2304 Blood Vessels of the Body
The Aorta
Ascending aorta
– arises from the left ventricle; branches to form coronary arteries
Aortic arch – lies posterior to the manubrium; aortic branches form:
Brachiocephalic trunk
Left common carotid
Left subclavian arteries
Descending aorta – continues from the aortic arch
Thoracic aorta –extends from T
5
– T
Abdominal aorta – extends from T
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vertebrae
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– L
4 vertebrae
Divides into right and left common iliac arteries
Vena Cava
Superior & Inferior vena cava returns blood from the systemic veins to the heart
Superior Vena Cava – drains venous blood from head, arms, and chest (body regions superior to the diaphragm)
Inferior Vena Cava – drains venous blood from the lower half of the body (body regions inferior to the diaphragm)
Superior and inferior vena cava both empty into the right atrium of the heart
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Vena Cava
Cerebral Arterial Circle (Circle Of Willis)
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Arteries Of The Head And Neck, Right Aspect
Arteries Of The Right Upper Arm & Thorax
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Arteries Of The Right Lower Arm
Major Branches Of The Abdominal Aorta
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The Celiac Trunk And Its Main Branches
Arteries Of The Right Pelvis And Lower Limb
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Major Arteries of the Systemic Circulation
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Dural Sinuses In The Cranium
Veins
Veins of the Head and Neck
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Veins Of The Right Upper Arm And Thorax Wall
Veins Of The Right Upper Limb And Thorax Wall
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Veins Of The Right Lower Arm
Antecubital Fossa
Form anastomoses frequently
Median cubital vein is used to obtain blood or administer IV fluids
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Veins of the Abdomen
Lumbar veins
Gonadal (testicular or ovarian) veins
Renal veins
Suprarenal veins
Hepatic veins
Tributaries Of The Inferior Vena Cava
Veins Of The Hepatic Portal System
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Veins of the Pelvis and Lower Limbs
Deep veins
Share the name of the accompanying artery
Superficial veins
Great saphenous vein empties into the femoral vein
Small saphenous vein empties into the popliteal vein
Veins Of The Right Lower Limb And Pelvis
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Major Veins of the Systemic Circulation
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Continuous Capillary
Fenestrated Capillary
Sinusoidal Capillary
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