Tunics Tunica intima –Endothelium lines lumen of all vessels Tunica media –Smooth muscle and sheets of elastin –Sympathetic vasomotor nerve fibers control vasoconstriction and vasodilation of vessels: Influence blood flow and blood pressure Tunica externa –Collagen fibers protect & reinforce; anchor to surrounding structures –Contains nerve fibers, lymphatic vessels –Vasa vasorum of larger vessels nourishes external layer
Types of Arteries (depending on size & shape): –Elastic –Muscular –Arterioles
Arterial System: Elastic Arteries Large thick-walled arteries with elastin in all three tunics Aorta and its major branches Large lumen offers low resistance Act as pressure reservoirs—expand and recoil as blood ejected from heart –Smooth pressure downstream
Arterial System: Muscular Arteries Distal to elastic arteries –Deliver blood to body organs Thick tunica media with more smooth muscle Active in vasoconstriction
Arterial System: Arterioles Smallest arteries Lead to capillary beds Control flow into capillary beds via vasodilation and vasoconstriction of the arterioles (influenced by hormones and other chemicals)
Capillaries Microscopic blood vessels Walls of thin tunica intima Pericytes help stabilize their walls and control permeability Diameter allows only single RBC to pass at a time
Capillaries In all tissues except for cartilage & epithelia ( receive nutrients from nearby blood vessels ), cornea & lens of eye ( receive nutrients from aqueous humor) Provide direct access to almost every cell Functions –Exchange of gases, nutrients, wastes, hormones, etc., between blood and interstitial fluid Three structural types Continuous capillaries Fenestrated capillaries Sinusoid capillaries (sinusoids)
Pericyte Red blood cell in lumen Intercellular cleft Endothelial cell Basement membrane Tight junction Endothelial nucleus Pinocytotic vesicles Continuous capillary. Least permeable, and most common (e.g., skin, muscle). Continuous Capillaries –Tight junctions connect endothelial cells –Intercellular clefts allow passage of limited passage of fluids and small solutes Continuous capillaries of brain unique –Tight junctions complete, forming blood brain barrier
Pinocytotic vesicles Red blood cell in lumen Fenestrations (pores) Intercellular cleft Endothelial cell Endothelial nucleus Basement membrane Tight junction Fenestrated capillary. Large fenestrations (pores) increase permeability. Occurs in areas of active absorption or filtration (e.g., kidney, small intestine). Fenestrated Capillaries Some endothelial cells contain pores (fenestrations) More permeable than continuous capillaries Function in absorption or filtrate formation (small intestines, endocrine glands, and kidneys)
Endothelial cell Red blood cell in lumen Large intercellular cleft Nucleus of endothelial cell Incomplete basement membrane Sinusoid capillary. Most permeable. Occurs in special locations (e.g., liver, bone marrow, spleen). Tight junction Sinusoid Capillaries Fewer tight junctions; usually fenestrated; larger intercellular clefts; large lumens Large molecules and blood cells pass between blood and surrounding tissues Found only in the liver, bone marrow, spleen, adrenal medulla In the liver, hepatic macrophages in lining to destroy bacteria
Capillary Beds Def.: Interwoven networks of capillaries – blood flows thru arterioles-> venules (microcirculation) Capillary Beds: Two Types of Vessels Vascular shunt (metarteriole—thoroughfare channel) –Directly connects terminal arteriole and postcapillary venule True capillaries –10 to 100 exchange vessels per capillary bed –Branch off metarteriole or terminal arteriole
True capillaries normally branch from metarteriole and return to thoroughfare channel Precapillary sphincters regulate blood flow into true capillaries –Blood may go into true capillaries or to shunt Regulated by local chemical conditions and vasomotor nerves Example: Eating and relaxing – blood flow in the digestive system; abdominal cramps and indigestion when running and eating!!! Vascular shunt Precapillary sphincters Metarteriole Thoroughfare channel Terminal arteriole True capillaries Postcapillary venule Sphincters open —blood flows through true capillaries. Terminal arteriole Postcapillary venule Sphincters closed —blood flows through metarteriole – thoroughfare channel and bypasses true capillaries. Blood Flow Through Capillary Beds
Venous System: Venules Formed when capillary beds unite –Smallest postcapillary venules: very porous; allow fluids and WBCs into tissues –Consist of endothelium and a few pericytes Larger venules have one or two layers of smooth muscle cells
Veins Venules join to form veins Have thinner walls, larger lumens compared with corresponding arteries Thin tunica media; thick tunica externa of collagen fibers and elastic networks Called capacitance vessels (blood reservoirs); contain up to 65% of blood supply Blood pressure lower than in arteries (walls don’t burst!) => Adaptations ensure return of blood to heart despite low pressure –Large-diameter lumens offer little resistance –Venous valves prevent backflow of blood Most abundant in veins of limbs –Venous sinuses: flattened veins with extremely thin walls (e.g., coronary sinus of the heart & dural sinuses of the brain)
Circulatory Pathways: Blood Vessels of the Body Two main circulations –Pulmonary circulation: short loop that runs from heart to lungs and back to heart –Systemic circulation: long loop to all parts of body and back to heart
Common carotid arteries to head and subclavian arteries to upper limbs Capillary beds of head and upper limbs Aorta Superior vena cava Aortic arch RALA RV LV Azygos system Thoracic aorta Venous drainage Arterial blood Capillary beds of mediastinal structures and thorax walls Inferior vena cava Diaphragm Abdominal aorta Capillary beds of digestive viscera, spleen, pancreas, kidneys Inferior vena cava Capillary beds of gonads, pelvis, and lower limbs Figure Schematic flowchart showing an overview of the systemic circulation.
Figure 19.21a Major arteries of the systemic circulation. R. external carotid artery R. internal carotid artery L. external carotid artery L. internal carotid artery R. vertebral R. common carotid – right side of head and neck L. common carotid – left side of head and neck L. vertebral R. axillary R. subclavian – neck and R. upper limb Brachiocephalic – head, neck, and R. upper limb Aortic arch L. subclavian – neck and L. upper limb L. axillary Arteries of L. upper limb Ascending aorta – L. ventricle to sternal angle Thoracic aorta T 5 –T 12 (diaphragm) L. and R. coronary arteries Arteries of R. upper limb L. ventricle of heart Visceral branches Parietal branches Mediastinal – posterior media- stinum Esophageal – esophagus Bronchial – lungs and bronchi Pericardial – pericardium Posterior intercostals – intercostal muscles, spinal cord, vertebrae, pleurae, skin Superior phrenics – posterior and superior diaphragm Diaphragm Abdominal aorta T 12 (diaphragm)–L 4 Visceral branches Parietal branches Gonadal – testes or ovaries Suprarenal – adrenal glands and Renal – kidneys Superior and inferior mesenterics – small intestine – colon Celiac trunk – liver – gallbladder – spleen – stomach – esophagus – duodenum Inferior phrenics – inferior diaphragm Lumbars – posterior abdominal wall Median sacral – sacrum – coccyx R. common iliac – pelvis and R. lower limb L. common iliac – pelvis and L. lower limb Arteries of R. lower limb Arteries of L. lower limb
Aorta Ascending arteryAortic ArchDescending aorta Left coronary artery brachiocephalic Right coronary artery Left common carotid arteryLeft subclavian artery Thoracic aortaAbdominal aorta Left & right common iliac arteries Right common carotid artery Right subclavian artery Major arteries of the systemic circulation.
Figure 19.22d Arteries of the head, neck, and brain. Cerebral arterial circle (circle of Willis) Anterior communicating artery Posterior communicating artery Posterior cerebral artery Cerebellum Basilar artery Vertebral artery Posterior Major arteries serving the brain (inferior view, right side of cerebellum and part of right temporal lobe removed) Frontal lobe Optic chiasma Middle cerebral artery Internal carotid artery Mammillary body Temporal lobe Pons Occipital lobe Anterior cerebral artery
Figure 19.25b Arteries of the right pelvis and lower limb. Common iliac artery Internal iliac artery Superior gluteal artery External iliac artery Deep artery of thigh Lateral circumflex femoral artery Medial circumflex femoral artery Obturator artery Femoral artery Adductor hiatus Popliteal artery Anterior tibial artery Posterior tibial artery Fibular artery Dorsalis pedis artery Arcuate artery Dorsal metatarsal arteries Anterior view
Figure 19.26b Major veins of the systemic circulation. Veins of the head and trunk Dural venous sinuses External jugular vein Vertebral vein Internal jugular vein Right and left brachiocephalic veins Superior vena cava Great cardiac vein Hepatic veins Splenic vein Hepatic portal vein Renal vein Superior mesenteric vein Inferior mesenteric vein Inferior vena cava Common iliac vein Internal iliac vein Veins that drain the upper limb Subclavian vein Axillary vein Cephalic vein Brachial vein Basilic vein Median cubital vein Ulnar vein Radial vein Digital veins Veins that drain the lower limb External iliac vein Femoral vein Great saphenous vein (longest vein; issue from dorsal venous arch) Popliteal vein Posterior tibial vein Anterior tibial vein Small saphenous vein Dorsal venous arch Dorsal metatarsal veins Illustration, anterior view. The vessels of the pulmonary circulation are not shown.
Figure 19.27b Venous drainage of the head, neck, and brain. Ophthalmic vein Superficial temporal vein Facial vein Occipital vein Posterior auricular vein External jugular vein Vertebral vein Internal jugular vein Superior and middle thyroid veins Brachiocephalic vein Subclavian vein Superior vena cava Veins of the head and neck, right superficial aspect
Figure 19.28b Veins of the thorax and right upper limb. Brachiocephalic veins Right subclavian vein Axillary vein Brachial vein Cephalic vein Basilic vein Median cubital vein Median antebrachial vein Cephalic vein Radial vein Basilic vein Ulnar vein Deep venous palmar arch Superficial venous palmar arch Digital veins Anterior view Internal jugular vein External jugular vein Left subclavian vein Superior vena cava Azygos vein Accessory hemiazygos vein Hemiazygos vein Posterior intercostals Inferior vena cava Ascending lumbar vein
Figure 19.29b Veins of the abdomen. Hepatic veins Inferior vena cava Right suprarenal vein Right gonadal vein External iliac vein Inferior phrenic vein Left suprarenal vein Renal veins Left ascending lumbar vein Lumbar veins Left gonadal vein Common iliac vein Internal iliac vein Tributaries of the inferior vena cava. Venous drainage of abdominal organs not drained by the hepatic portal vein.
Figure 19.29c Veins of the abdomen. Hepatic veins Liver Hepatic portal vein Small intestine Rectum Gastric veins Spleen Inferior vena cava Splenic vein Right gastroepiploic vein Inferior mesenteric vein Superior mesenteric vein Large intestine The hepatic portal circulation.
Figure 19.30b Veins of the right lower limb. Common iliac vein Internal iliac vein External iliac vein Inguinal ligament Femoral vein Great saphenous vein (superficial) Popliteal vein Small saphenous vein Fibular vein Anterior tibial vein Dorsalis pedis vein Dorsal venous arch Dorsal metatarsal veins Anterior view