20 PART 1
Blood Vessels
Types of Blood Vessels
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Three major types of blood vessels are
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Arteries
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Capillaries
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Veins
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Arteries—carry blood away from the heart
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Arterioles—the smallest arteries
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Capillaries—the smallest blood vessels
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Venules—receive blood from capillaries
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Veins—receive blood from venules
Structure of Blood Vessels
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Composed of three layers (tunics)
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Tunica intima
• Innermost tunic
• Contains the endothelium
• Simple squamous epithelium
• Vessels  than 1 mm also have a subendothelial layer
Structure of Blood Vessels
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Composed of three layers (tunics)
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Tunica media—sheets of smooth muscle
• Contraction—vasoconstriction
• Relaxation—vasodilation
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Tunica externa
• Composed of connective tissue
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Lumen
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Central blood-filled space of a vessel
Types of Arteries
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Elastic arteries—the largest arteries
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Diameters range from 2.5 cm to 1 cm
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Includes the aorta and its major branches
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Sometimes called conducting arteries
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High elastin content dampens surge of blood
pressure
Types of Arteries
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Muscular (distributing) arteries
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Lie distal to elastic arteries
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Diameters range from 1 cm to 0.3 mm
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Includes most named arteries
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Tunica media is thick
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Unique features
• Internal and external elastic laminae
Types of Arteries
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Arterioles
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Smallest arteries
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Diameters range from 0.3 mm to 10 µm
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Larger arterioles possess all three tunics
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Diameter of arterioles controlled by
• Local factors in the tissues
• Sympathetic nervous system
Capillaries
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Smallest blood vessels
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Diameter from 8 to 10 µm
• Red blood cells pass through single file
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Site-specific functions of capillaries
• Lungs—oxygen enters blood, carbon dioxide leaves
• Small intestines—receive digested nutrients
• Endocrine glands—pick up hormones
• Kidneys—remove of nitrogenous wastes
Continuous Capillaries
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Most common type of capillary
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Occur in most organs
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Tight junctions and desmosomes join epithelial cells
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Intercellular clefts
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Gaps of unjoined membranes
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Allow small molecules in and out of capillaries
Fenestrated Capillaries
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Joined by tight junctions and desmosomes
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Have pores in their endothelium
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Occur where high rates of exchange occur
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Intestines
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Glomeruli of kidneys
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Endocrine glands
Sinusoids
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Wide, leaky capillaries found in some organs
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Usually fenestrated
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Intercellular clefts are wide open
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Occur in bone marrow and spleen
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Sinusoids have a large diameter and twisted course
Capillary Permeability
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Four routes into and out of capillaries
Direct diffusion
Through intercellular clefts
Through cytoplasmic vesicles
Through fenestrations
Low-Permeability Capillaries
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Blood brain barrier
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Capillaries have complete tight junctions
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No intercellular clefts are present
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Vital molecules pass through
• Highly selective transport mechanisms
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Not a barrier against:
• Oxygen, carbon dioxide, and some anesthetics
Capillary Beds
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Network of capillaries running through tissues
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Precapillary sphincters
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Regulate the flow of blood to tissues
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Tendons and ligaments—poorly vascularized
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Epithelia and cartilage—avascular
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Receive nutrients from nearby connective tissue
Venous Vessels
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Conduct blood from capillaries toward the heart
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Blood pressure is much lower than in arteries
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Venules are the smallest veins
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Diameters from 8 to 100 m
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Smallest venules—called postcapillary venules
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Venules join to form veins
Veins
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Structural differences from arteries
Lumens are larger
• 65% of blood in veins at any given time
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Tunica externa is thicker
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Less elastin in walls
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Walls are thinner than those of comparable arteries
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Mechanisms to Counteract Low Venous Pressure
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Valves in some veins
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Particularly in limbs
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Prevent backflow of blood
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Not located in veins of thoracic and abdominal cavities
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Skeletal muscle pump
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Muscles press against thin-walled veins
Vascular Anastomoses
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Vessels interconnect to form vascular anastomoses
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Organs receive blood from more than one arterial source
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Neighboring arteries form arterial anastomoses
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Provide collateral channels
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Veins anastomose more frequently than arteries
Pulmonary Circulation
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Pulmonary trunk
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Leaves the right ventricle
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Divides into right and left pulmonary arteries
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Superior and inferior pulmonary veins
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Carry oxygenated blood into the left atrium
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Vessels of pulmonary circuit
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Thinner walls than systemic vessels
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Maximum arterial pressure lower in pulmonary circuit
Systemic Circulation
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Systemic arteries
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Carry oxygenated blood away from the heart
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Aorta—largest artery in the body
The Aorta
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Ascending aorta—arises from the left ventricle
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Branches—coronary arteries
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Aortic arch—lies posterior to the manubrium
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Branches
• Brachiocephalic trunk
• Left common carotid
• Left subclavian arteries
The Aorta
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Descending aorta—continues from the aortic arch
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Thoracic aorta—in the region of T5–T12
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Abdominal aorta—ends at L4
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Divides into right and left common iliac arteries
20 PART 2
Blood Vessels
Arteries of the Head and Neck
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Pairs of arteries supplying head and neck
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Carotid arteries
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Branches of subclavian arteries
• Vertebral arteries
• Thyrocervical trunk
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Costocervical trunk
Common Carotid Arteries
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Located in the anterior triangle of the neck
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Two branches of the common carotid artery
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External carotid artery
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Internal carotid artery
Common Carotid Arteries
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External carotid artery branches
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Superior thyroid artery
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Lingual artery
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Facial artery
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Occipital artery
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Posterior auricular artery
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Superficial temporal artery
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Maxillary artery
Common Carotid Arteries
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Internal carotid artery branches
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Ophthalmic artery
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Anterior cerebral artery
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Anterior communicating artery
• Forms part of the cerebral arterial circle
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Middle cerebral artery
Subclavian Arteries
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Right subclavian artery
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Originates from brachiocephalic trunk
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Left subclavian artery
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Arises as third branch from the aortic arch
Vertebral Arteries
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Vertebral arteries
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Supply posterior brain
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Join to form the basilar artery
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Basilar artery
• Divides into two posterior cerebral arteries
• Posterior communicating arteries
• Connect posterior cerebral arteries to middle cerebral arteries
Thyrocervical and Costocervical Trunks
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Thyrocervical trunk
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Sends two branches posteriorly over scapulae
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Sends one branch anteriorly to the inferior part of the thyroid gland
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Costocervical trunk
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Sends a branch superiorly to deep muscles of the neck
Sends a branch inferiorly to intercostal spaces
Arteries of the Thorax
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Internal thoracic arteries
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Supply anterior thoracic walls
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Anterior intercostal arteries
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Branches of internal thoracic arteries
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Posterior intercostal arteries
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Inferior nine pairs arise from thoracic aorta
Arteries of the Upper Limb
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Subclavian artery
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Enters the axilla as the axillary artery
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Axillary artery becomes the brachial artery at the inferior border of teres major
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Brachial artery divides into
• Radial artery and ulnar artery
Arteries of the Abdominal Aorta
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Inferior phrenic arteries
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Celiac trunk
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Superior mesenteric artery
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Suprarenal arteries
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Renal arteries
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Gonadal (testicular or ovarian) arteries
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Inferior mesenteric artery
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Common iliac arteries
20 PART 3
Blood Vessels
Arteries of the Pelvis and Lower Limbs
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Internal iliac arteries
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External iliac artery
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Femoral artery
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Popliteal artery
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Anterior tibial artery
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Posterior tibial artery
Systemic Veins
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Three major veins enter the right atrium
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All medium and large arteries have deep locations accompanied by deep veins
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Superficial veins lie just beneath the skin
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Multivein bundles—venous plexuses
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Unusual patterns of venous drainage
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Dural sinuses
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Hepatic portal system
Venae Cavae and Tributaries
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Superior vena cava
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Returns blood from body regions superior to the diaphragm
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Inferior vena cava
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Returns blood from body regions inferior to the diaphragm
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Superior and inferior vena cava
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Join the right atrium
20 PART 4
Blood Vessels
Veins of the Head and Neck
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Dural sinuses
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Superior and inferior sagittal sinuses
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Straight sinus
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Transverse sinuses
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Sigmoid sinus
Veins of the Head and Neck
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Internal jugular veins
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Drain blood from brain
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Superiorly it lies lateral to the internal carotid artery
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Inferiorly it lies lateral to the common carotid artery
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External jugular veins
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Tributaries drain scalp
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Empty into subclavian vein
Veins of the Thorax
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Azygos vein
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Hemiazygos vein
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Accessory hemiazygos vein
Veins of the Upper Limbs
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Deep veins
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Follow the paths of companion arteries
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Have the same names as the companion arteries
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Superficial veins
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Visible beneath the skin
• Cephalic vein
• Basilic vein
• Median cubital vein
• Median vein of the forearm
Superficial Veins
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Form anastomese frequently
Median cubital vein is used to obtain blood or administer IV fluids
Veins of the Abdomen
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Lumbar veins
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Gonadal (testicular or ovarian) veins
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Renal veins
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Suprarenal veins
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Hepatic veins
The Hepatic Portal System
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A specialized part of the vascular circuit
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Picks up digested nutrients
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Delivers nutrients to the liver for processing
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Two capillary beds
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First capillary bed in stomach and intestines
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Second capillary bed is in liver sinusoids
The Hepatic Portal System
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Tributary veins of the hepatic portal vein
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Superior mesenteric vein
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Splenic vein
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Inferior mesenteric vein
20 PART 5
Blood Vessels
Portal Systemic Anastomoses
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Scarring and degeneration of liver
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Leads to blockage of liver sinusoids
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Raises blood pressure in hepatic portal system and leads to portal hypertension
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Portal hypertension leads to emergency anastomoses for portal blood
• Veins of inferior esophagus, hemorrhoidal veins, veins of superficial abdominal
wall
Veins of the Pelvis and Lower Limbs
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Deep veins
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Share the name of the accompanying artery
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Superficial veins
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Great saphenous vein empties into the femoral vein
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Small saphenous vein empties into the popliteal vein
Disorders of the Blood Vessels
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Aneurysm
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Deep vein thrombosis of the lower limb
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Venous disease
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Microangiopathy of diabetes
Arteriovenous malformation
Blood Vessels Throughout Life
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Fetal circulation
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All major vessels in place by month 3 of development
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Differences between fetal and postnatal circulation
• Fetus must supply blood to the placenta
• Very little blood is sent through the pulmonary circuit
Vessels to and from the Placenta
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Umbilical vessels run in the umbilical cord
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Paired umbilical arteries
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Unpaired umbilical vein
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Fetal vessels and structures
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Ductus venosus
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Ligamentum teres
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Ligamentum venosum
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Medial umbilical ligaments
Shunts Away from the Pulmonary Circuit
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Foramen ovale
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Ductus arteriosus
Blood Vessels in Adulthood
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Atherosclerosis begins in youth
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Consequences evident in middle to old age
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Males
• Between ages 45 and 65, more males than females experience atherosclerosis
• Experience heart disease and atherosclerosis later in life