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: oxygen-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 oxygen is picked up and CO2 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 oxygen and
nutrients to body tissues picks up CO2 and waste products
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Types of Blood Vessels
Arteries - carry blood away from heart
Arterioles - small arteries that deliver blood to capillaries
Capillaries – thin walled vessels allow for exchange between blood and tissue cells
Venules - collect and drain blood into veins
Veins - return blood to heart
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Arteries → Arterioles → Capillaries → Venules → Veins
Anatomy of a Blood Vessel
Composed of three layers called tunics:
Tunica intima – composed of simple squamous epithelium
Tunica media – sheets of smooth muscle
Contraction – vasoconstriction
Relaxation – vasodilation
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.
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Types of Arteries
Elastic arteries – the largest arteries
Diameters range from 2.5 cm to 1 cm
Largest arteries: the aorta and its major branches
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 and 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
Red blood cells pass through lumen single file
Capillary beds run through tissues
Pre-capillary sphincters constrict to control blood flow
Vasa vasorum ("vessels of the vessels")
Capillaries that supply large blood vessels.
Found in large arteries and veins such as the aorta and its branches.
Capillary Bed
Open & Closed Precapillary Sphincters
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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
Capillaries
Capillaries classified by diameter & permeability
Three Types of Capillaries
Continuous capillary –
Least permeable
Do not have pores
Only small molecules, water,& ions diffuse through tight junctions
Fenestrated capillary –
Large fenestrations (pores)
Small molecules and limited proteins diffuse
Sinusoidal capillary –
Most permeable
Discontinuous basement
Allow passage of proteins and cells as necessary
Continuous Capillary
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Fenestrated Capillary
Sinusoidal Capillary
Veins
Venules form from capillaries
Diameters from 8 –100 m
Venules join veins
Tunica externa is the thickest tunic in veins
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Specific Circulatory Routes
Coronary circulation
supplies blood to heart tissue
Cerebral arterial circle
supplies blood to brain
Hepatic portal system
carries nutrient-filled blood from gastrointestinal tract to liver for detoxification and nutrient
storage
Fetal circulation
fetus blood reaches placenta so that it may obtain nutrients from the mother’s uterus; fetal lungs
do not require as much blood supply as newborn
Coronary Circulation
Functional blood supply
Coronary arteries
Arise from the aorta
Located in the coronary sulcus
Main branches
Left and right coronary arteries
Coronary Circulation
Left coronary artery
Anterior interventricular
artery
Circumflex artery
Rjght coronary artery
Posterior interventricular
artery
Marginal artery
Coronary sinus
Great cardiac vein
Middle cardiac vein
Small cardiac vein
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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
Unpaired umbilical vein
Fetal vessels and structures
Ductus venosus
Ligamentum teres
Ligamentum venosum
Medial umbilical ligaments
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