Blood VesselsI. Structure of Blood Vessels Walls 

A. Three layers1. Tunica intera            a. Inner most layer            b. Endothelium                        i. Simple squamous            c. Some larger vessels have subendothelium                        i. Loose connective tissue                        ii. Basement membrane2. Tunica media            a. Middle layer            b. Circularly arranged smooth muscle            c. Chemical and nervous control of degree of contraction                        i. Sympathetic NS            d. Change in diameter                        i. Vasoconstriction                        ii. Vasodilation3. Tunica externa            a. Made of collagen fibers

            b. Function                        i. Protection                        ii. Reinforcement                        iii. Anchor to surrounding tissue            c. Accessory tissues                        i. Nerve fibers                        ii. Lymphatic vessels                        iii. Elastic network                        iv. Tiny blood vessels within layer-vasa vasorum II. Arterial SystemA. Classification based on size and function1. Elastic (conducting) arteries            a. Characteristics                        i. Thick-walled                        ii. Near heart                        iii. Largest diameter                        iv. More elastic                        v. Large lumen            b. Properties                        i. Dampen BP changes associated with heart contraction                        ii. Passive accommodation results in smooth flow of blood            c. 1.0 - 2.5 cm2. Muscular arteries-distributing arteries            a. Distal to elastic arteries            b. Deliver blood to specific organs            c. Thick media layer                        i. More smooth muscle            d. 0.3 - 1.0 cm3. Arterioles            a. Determine flow into capillary beds            b. Mostly smooth muscle            c. 10 µm - 0.3 cm4. Capillaries            a. Smallest blood vessels                        i. 8 - 10 µm            b. Tunica interna only            c. Exchange of materials B. Types of capillary1. Continuous            a. Uninterrupted endothelial cells            b. Incomplete tight junctions                        i. Intercellular clefts2. Fenestrated            a. Endothelial cells have oval pores

                        i. Fenestrations            b. Pores permit greater permeability3. Sinusoidal            a. Modified, leaky capillaries            b. Large molecules can pass through C. Capillary beds 

1. Capillaries act as networks-capillary beds2. Microcirculation            a. Arteriole to venule3. Parts of a capillary bed            a. Vascular shunt                        i. Connects arteriole with venule            b. True capillariesD. Sequence of blood movement through capillary bed1. Terminal arteriole2. Metateriole            a. True capillaries branch off                        i. Pre-capillary sphincter controls blood flow into capillary3. Thoroughfare channel

            a. Capillaries rejoin4. Post-capillary venule  III. Venous SystemA. Types of vessels1. Venules            a. 8 - 100 µm            b. Characteristics vary with size                        i. Little muscle                        ii. Thin externa2. Veins            a. Formed from venules            b. Thinner walls and less muscle than arteries            c. Little muscle in media                        i. Mostly elastin            d. Externa is thickest wall layerB. Capacitance vessels1. Veins act as reservoirs            a. Large lumens            b. Low blood pressure allows walls to thin2. Venous valves            a. Prevent backflow            b. Folds of interna  IV. Physiology of CirculationA. Terms1. Blood flow-volume flowing through a given structure per unit time (ml/min)2. Blood pressure-force per unit area (mm Hg)3. Resistance-opposition to flow; generally encountered in the systemic circuit-peripheral resistance (PR)            a. Sources of resistance                        i. Blood viscosity-thickness related to formed elements                        ii. Total blood vessels length-longer the vessels, the greater the resistance                        iii. Blood vessel diameter-flow is inversely related to diameter; the larger the diameter, the less resistance (1/r4)            b. In healthy humans, diameter is the greatest source of resistanceB. Relationship between flow, pressure and resistance  Blood Flow (F) = ∆P/PR (Difference in blood pressure between two points/peripheral resistance V. Systemic Blood PressureA. Background

1. Heart pumping generates blood flow2. Pressure results when flow opposed by resistance3. Blood flows along a pressure gradient            a. From higher to lower pressure                        i. Highest in aorta                        ii. Lowest in right atriumB. Arterial blood pressure 

1. Factors affecting arterial pressure            a. Stretching of arteries near heart                        i. Compliance                        ii. Distensibility            b. Volume of blood forced into the arteries near heart2. Changes associated with systole            a. Aorta is stretched by blood leaving left ventricle                        i. Kinetic energy            b. Blood moves toward periphery because peripheral pressure is lower than aortic pressure                        i. Systolic pressure: 120 mm Hg3. Changes associated with diastole            a. Semilunar valve closes

            b. Aorta recoils            c. Pressure is maintained by reducing volume                        i. Diastolic pressure: 70 - 80 mm Hg4. Pulse pressure            a. Difference between systolic and diastolic pressure5. Mean arterial pressure (MAP)            a. Diastolic pressure + 1/3 pulse pressureC. Capillary blood pressure1. 40 mm Hg entering2. 20 mm Hg exitingD. Venous blood pressure1. Characteristics            a. Relatively steady throughout cardiac cycle            b. Gradient from venules to vena cava                        i. 20 mm HG (60 from aorta to arterioles)2. Venous return            a. Venous pressure is too low to promote adequate return            b. Need additional functional modifications3. Functional modification            a. Respiratory pump                        i. Abdominal (ventral body cavity) pressure increases squeeze local veins                        ii. Backflow is prevented by valves                        iii. Blood is forced toward the heart                        iv. Chest cavity pressure decreases                        v. Thoracic veins expand                        vi. Blood enters right atrium            b. Muscular pump (more important)                        i. Contraction of skeletal muscle surrounding veins compress vein                        ii. Backflow is prevented by valves                        iii. Blood moves in direction of heart VI. Regulation of Blood PressureA. Factors influences blood pressure1. Cardiac output2. Peripheral resistance3. Blood volumeB. Blood pressure = Cardiac output X Peripheral resistance1. Cardiac output is directly related to blood volume2. Blood pressure is directly related to CO, BV and PRC. CO = Stroke volume X HR D. Factors that enhance CO  1. Reduce parasympathetic controla.         Reduce effect of vagus nerve

                        i. HR increases2. Increase sympathetic activity            a. Increases contractility of heart                        i. Reduces ESV                        ii. Increases stroke volume            b. Releases Epi into blood stream from adrenal medulla                        i. Increases heart rate3. Increase activity of respiratory and muscular pumps            a. Increases venous return                        i. Increases EDV                        ii. Increases stroke volumeE. Neural control of blood pressure1. Short-term mechanisms2. Nervous control of peripheral resistance            a. Alter blood distribution            b. Alter blood vessel diameter 3. Vasomotor center 

            a. Regulation of blood vessel diameter            b. Vasomotor fibers

                        i. Sympathetic efferents                        ii. Innervate smooth muscle of blood vessels                        iii. Primarily arterioles                        iv. Release NE                        v. Vasoconstrictor            c. Vasomotor tone                        i. Tonic vasoconstriction4. Baroreceptors 

            a. Detect changes in arterial blood pressure                        i. Pressure sensitive mechanoreceptors                        ii. When BP rises, receptors are stretched            b. Located in carotid sinuses, aortic arch and walls of all large vessels            c. Stretching increases signaling to vasomotor center                        i. Inhibits vasomotor center                        ii. Causes dilation of arteries and veins            d. Arteriole dilation reduces peripheral resistance            e. Venodilation shifts blood to venous reservoirs                        i. Venous return decreases                        ii. Cardiac output declines            f. Baroreceptors also send efferent signals to cardiac centers in the medulla

                        i. Inhibit sympathetic NS                        ii. Stimulate parasympathetic NS                        iii. HR and contractile force decrease            g. Respond to acute changes in blood pressure                        i. Carotid sinus reflex protects blood supply to brain                        ii. Aortic reflex maintains supply to systemic circuit5. Chemoreceptors 

            a. Respond to changes in O2 and CO2 concentrations and pH            b. Located in carotid and aortic arch and carotid sinus            c. Primarily involved in control of respiratory rate and depth (see Respiration Lecture)F. Chemical control of blood pressure1. Short-term2. Levels of O2 and CO2 (see Respiration Lecture)3. Blood-borne chemicals 

            a. Adrenal medulla hormones                        i. NE and EPI (nicotine is a monoamine agonist)                        ii. NE is a vasoconstrictor                        iii. EPI increase cardiac output by increasing cardiac muscle contractility            b. Atrial natriuretic peptide (ANP)                        i. Atrial peptide hormone                        ii. Reduces blood pressure by antagonizing aldosterone                        iii. Increases water excretion from kidney            c. Antidiuretic hormone (ADH)                        i. Posterior pituitary hormone                        ii. Increases blood pressure by increasing water absorption by distal tubule                        iii. At high concentrations, causes vasoconstriction            d. Angiotensin II                        i. Mediated by release of renin by JGA of kidney tubule                        ii. When amount of blood entering kidney tubule is too low, renin is released                        iii. Renin catalyzes the conversion of angiotensinogen into angiotensin II                        iv. Angiotensin II causes vasoconstriction of systemic arterioles                        v. Increases BP                        vi. Angiotensin II also causes release of aldosterone from adrenal cortex                        vii. Aldosterone increases absorption of water by kidney tubules

            e. Endothelium-derived factors                        i. Endothelin-vasoconstrictor                        ii. Prostaglandin-derived growth factor (PDGF)-vasoconstrictor                        iii. Nitrous oxide (NO)-fast acting, local vasodilator            f. Inflammatory chemicals-vasodilators                        i. Histamine, etc. (see Immune Lecture)                        ii. Increase capillary permeability            g. Alcohol                        i. Reduces blood pressure                        ii. Inhibits ADH release-increases loss of water in urine                        iii. Increases vasodilation (skin) by depressing vasomotor centerG. Renal regulation of blood pressure1. Long-term mechanisms for blood pressure regulation2. Kidney controls blood volume by regulating water loss in urine3. Blood volume affects cardiac output via:            a. Venous pressure            b. Venous return            c. EDV            d. Stroke volume4. Blood pressure change parallels change in blood volume            a. Increase in volume increases BP                        i. Kidney responds by eliminating water to reduce volume            b. Decrease in volume decreases BP                        i. Kidney responds by absorbing water to increase volume 5. Direct action of the kidney            a. Alteration to rate of fluid filtration from blood stream to kidney tubules                        i. Increased BP increases amount of filtrate entering tubules                        ii. Filtrate entering is greater than the amount that can be processed                        iii. Fluid leaves body in the form of urine                        iv. Blood volume decreases and therefore BP            b. Indirect renal mechanisms 

                        i. Renin-angiotensin mechanism (see above)                        ii. Aldosterone also causes Post. Pituitary to release ADH                        iii. ADH promotes water reabsorption from by kidney  VII. Tissue PerfusionA. Blood flow is distributed to body tissue in an exacting fashion1. At rest            a. Brain: 13%            b. Heart 4%            c. Kidney: 20%            d. Abdominal organs: 24%2. During exercise:            a. Skin, muscles and heart increase            b. Remaining tissues either remain same or decreaseB. Blood flow velocity 

1. Inversely proportionate to cross-sectional area of blood vessels to be filled            a. Flow is fastest through vessels with smallest cross-sectional area                        i. Aorta has a cross-sectional area (2.5 cm2) and an average velocity of 40-50 cm/s                        ii. Capillaries have a total cross-sectional area of 4500 cm2 and a very slow flow (0.03 cm/s)C. Blood flow through individual organs is intrinsically controlled (i.e., autoregulation)1. Diameter of arterioles feeding a given organ is controlled by that organD. Intrinsic control mechanisms1. Metabolic controls-Levels of nutrients, particularly oxygen, act as autoregulation stimuli2. Myogenic controls            a. Excessive or inadequate blood pressure can damage or cause the death of an organ            b. Such blood pressure changes stimulate myogenic responses VIII. Capillary Dynamics 

A. Gases and nutrients diffuse from capillary to interstitial fluid1. Water-soluble solutes pass through clefts and fenestrations2. Lipid-soluble diffuse through the plasma membranes of capillary epithelial cells B. Forces responsible for the direction and amount of fluid crossing capillary walls1. Hydrostatic and osmotic pressure            a. Forces opposeC. Hydrostatic pressure1. Force exerted by a fluid against a vessel wall            a. In the capillary bed                        i. Hydrostatic pressure is the same as capillary blood pressure2. Capillary hydrostatic pressure (HPc) forces fluid through capillary wall            a. Greater at arterial end (35 mm Hg)            b. Lower at venous end (17 mm Hg)3.  HPc is opposed by interstitial fluid hydrostatic pressure (Hpif)            a. Hpif is assumed to be zero                        i. Interstitial fluid is withdrawn by lymphatic tissue4. Net effective hydrostatic pressure is equal to HPc (HPc  - Hpif)D. Osmotic pressure1. Net movement of water from an area of low to high solute concentration            a. Solute concentration in relatively high in capillary blood

                        i. High concentration of plasma proteins                        ii. Capillary colloid osmotic pressure (OPc)                        iii. 26 mm Hg            b. Interstitial osmotic pressure (OPif) is much lower                        i. 0.1 to 5 mm Hg            c. Net osmotic pressure                        i. Approximately 25 mm HgE. Net filtration pressure (NFP)1. Reflects interaction between hydrostatic and osmotic pressure2. Arterial end            a. NFP = (HPc  - Hpif) - (OPc - OPif)                        i. 35 - 25 = 10 mm Hg3. Venous end            a. NFP = (HPc  - Hpif) - (OPc - OPif)                        i. 17 - 25 = -8 mm Hg  Circulatory SystemI. Pulmonary CirculationA. Function1. Gas exchange onlyB. Sequence1. Pulmonary trunk            a. Bifurcates into rt. and lt. pulmonary arteries2. Pulmonary arteries              a. In the lungs, arteries subdivide into lobar arteries                        i. Three in right                        ii. Two in left3. Lobar arteries branch to form arterioles4. Further branching to form pulmonary capillaries5. Capillaries drain into venules6. Venules join to form two pulmonary veins per lung7. Four pulmonary veins drain into left atrium  II. Overview of Systemic CirculationA. Aorta and Major Arteries of the Systemic Circulation 

B. Aortic arch (branches in sequence relative to lt. ventricle)1. Coronary arteries2. Brachiocephalic            a. R. common carotid                        i. R. internal carotid                        ii. R. external carotid            b. R. subclavian                        i. R. vertebral                        ii. R. axillary3. L. common carotid            a. L. internal carotid            b. L. external carotid4. R. subclavian            a. L. vertebral            b. L. axillaryC. Thoracic aorta (above the diaphragm)1. Parietal branches2. Visceral branchesD. Abdominal aorta (below diaphragm)1. Parietal branches2. Visceral branches

3. R. common iliac4. L. common iliac III. Arteries of Head and Neck 

A. Brachiocephalic artery branches off aortic arch1. R. subclavian artery branches off brachiocephalic artery2. R. vertebral artery branches off R. subclavian artery3. R. vertebral joins with L. vertebral to form Basilar artery            a. Basilar artery is part of Circle of Willis (see below)4. Basilar artery divides to form R. and L. posterior cerebral arteries            a. Supply occipital and inferior temporal lobes of brainB. After R. subclavian artery branches, Brachiocephalic artery is the R. common carotid arteryC. R. common carotid bifurcates to form R. external and internal carotid arteriesD. R. external carotid branches as it runs superiorly1. Superior thyroid            a. Supplies thyroid and larynx2. Linguala. Supplies tongue3. Facial

            a. Supplies skin and muscles of anterior face4. Occipital            a. Supplies posterior scalp5. R. external carotid splitsa. Maxillary                        i. Supplies upper and lower jawb. Superficial temporal            a. Supplies most of scalpE. R. Internal carotid1. Enters the skull and services the brain2. Opthalmic branches off            a. Supplies eyes, orbits, forehead and nose3. R. internal carotid divides to form            a. R. anterior cerebral artery                        i. Supplies medial surface of brain            b. R. middle cerebral artery                        i. Supplies lateral parts of temporal and parietal lobesF. Circle of Willis 

1. R. and L. posterior communicating arteries connect posterior cerebral arteries with R. and L. anterior cerebral arteries

2. Anterior communicating artery connects R. and L. anterior cerebral arteriors                                    IV. Arteries of Upper Limb and Thorax  

A. After giving rise to the R. vertebral artery, R. subclavian courses laterally and gives off branches to neck (do not need to know these vessels)B. R. subclavian artery passes under clavicle1. Name changes to axillary arteryC. Axillary artery gives off a number of branches1. Thoracoacromial            a. Supplies superior shoulder and pectoral region2. Lateral thoracic            a. Supplies lateral chest wall and breast3. Subscapular            a. Supplies scapula, latissimus dorsi and thorax wall4. Anterior and posterior circumflex arteries            a. Supply deltoid and shoulder jointD. As axillary artery enters arm, name changes to brachial arteryE. Brachial artery gives off a branch

1. Deep brachial artery            a. Supplies triceps brachii (posterior arm)2. Brachial artery supplies anterior flexor muscles of armF. Brachial artery splits to form two arteries1. Radial artery            a. Supplies lateral muscles of forearm2. Ulnar artery            a. Supplies medial muscles of forearm(Do not need to know arteries of wrist and hand)G. Arteries of the thorax wall1. Internal thoracic artery branches off the subclavian arterya. As the internal thoracic artery descends it gives off anterior intercostals arterires            i. Supplies anterior intercostals spaces2. Costocervical trunk gives rise to the first two posterior intercostals arteries3. The thoracic aorta gives rise to the next nine pairsa. Supplies posterior intercostals spaces and deep muscles of back, vertebral columns and spinal cord  V. Arteries of the Abdomen 

A. Abdominal artery lies below the level of the diaphragmB. As abdominal aorta descends it gives the inferior phrenic arteries1. Supply the diaphragmC. Abdominal aorta descends and gives off the celiac trunk D. Celiac trunk divides into three branches1. Common hepatic            a. Gives off branches to stomach, small intestine and pancreasb. After giving off gastroduodenal artery, common hepatic becomes hepatic artery            i. Right gastroepiploic branches off gastroduodenal artery            ii. Supplies stomachc. Hepatic splits into right and left branches            i. Supplies liver2. Splenic            a. Sends branches to stomach and pancreas            b. Splenic terminates in the spleen            c. Left gastroepiploic branches of splenic arteryi. Supplies stomach3. L. gastric artery            a. Supplies stomach and inferior esophagusE. Abdominal aorta descends and gives off the suprarenal arteries  1. Supply adrenal glandsF. Abdominal aorta descends and gives off the superior mesenteric artery1. Superior mesenteric gives off branches that supply mesenteric organs            a. Intestinal                        i. Supply large intestine            b. Ileocolic                        i. Supply appendix, colon            c. R. and middle colic                        i. Supply transverse colonG. Abdominal aorta descends and gives off the paired renal arteries1. Supply kidneys on each side of the bodyH. Abdominal aorta descends and gives off the gonadal arteries (Testicular or ovarian)I. Abdominal aorta descends and gives off the inferior mesenteric artery1. Inferior mesenteric gives off branches that supply distal part of the colon            a. L. colic            b. Sigmoidal arteries            c. Superior rectal arteriesJ. Abdominal aorta descends and gives off the lumbar arteries1. Supply posterior abdominal wallK. Aorta terminates giving rise to three arteries1. Median sacral2. R. and L. common iliacs 

VI. Arteries of Pelvis and Leg 

A. Common iliac divides into two branches1. Internal iliac            a. Supply pelvis and visceral organs                        i. Bladder, rectum, uterus and vagina (prostate and ductus deferns)            b. Divides to serve muscles of gluteal muscles and external genitalia2. External iliacB. As external iliac enters thigh it becomes the femoral arteryC. Femoral artery gives off branches as it descends down the thigh1. Deep femoral artery            a. Serves posterior thigh            b. Deep femoral artery gives off branches that supply head and neck of femur                        i. Lateral and medial circumflex arteriesD. Femoral artery descends and passes through adductor hiatus and enters popliteal fossaE. Femoral artery becomes the popliteal artery1. Supplies knee region F. Popliteal artery divides1. Posterior tibial artery            a. Gives off peroneal artery

                        i. Supplies lateral muscles of the leg2. Anterior tibial artery            a. Supplies extensor muscles(Do not need to know arteries of ankle or foot) VII. Major Veins of the Systemic Circulation 

A. Superior vena cava runs from union of brachiocephalic veins (L. and R.) to R. atriumB. Veins that drain into R. brachiocephalic vein1. R. internal jugular vein2. R. vertebral vein3. R. subclavian vein            a. R. external jugular vein empties into R. subclavian vein*Left side corresponds to right sideC. Inferior vena cava runs from junction of common iliac veins to R. atriumD. Veins that drain into inferior vena cava1. Hepatic veins (R. and L.)2. R. suprarenal vein3. Renal veins (R. and L.)4. R. gonadal vein5. Lumbar veins

 VIII. Veins of Head and Neck 

A. Drainage of blood from brain1. Most veins drain into dural (meningial) sinuses            a. Superior sagittal            b. Straight            c. Cavernous            d. Transverse2. Most blood from the brain drains into internal jugular veinsB. Deep veins of the face drain into inferior jugular veins 

1. Facial2. Superficial temporal IX. Veins of Upper Limbs and Thorax 

A. Azygous system drains thoracic tissues1. Azygous vein drains into superior vena cava            a. Posterior intercostal veins drain into azygous2. Azygous veins that drain into azygous vein            a. Hemiazygous            b. Accessory hemiazygous veinB. Deep drainage of upper limb1. Distal veins of the arm drain into ulnar and radial veins2. Ulnar and radial veins unite to form brachial vein3. As brachial vein enters shoulder, it becomes axillary vein4. At level of first rib, axillary vein becomes subclavian veinC. Superficial drainage of upper limb1. Median vein of the forearm lies between ulna and radius            a. Connects either to basilic or cephalic veins2. Cephalic vein joins with axillary vein3. Basilic vein joins with brachial vein4. Median cubital vein connects basilic and cephalic veins            a. Commonly used to obtain blood samples X. Veins of Abdomen 

A. Hepatic portal system1. Multiple hepatic veins carry blood from liver to inferior vena cava2. Cystic veins drain gall bladder and join the hepatic veinsB. Hepatic portal vein receives drainage from digestive viscera            a. Hepatic portal vein carries blood to liver                        i. Nutrients are removedC. Visceral veins draining into hepatic portal vein1. Superior mesenteric2. Inferior mesenteric            a. Drains large intestine and rectum                        i. Joins splenic3. Splenic            a. Drains spleen, parts of the stomach, and pancreas                        i. Joins superior mesentericD. Other veins draining into inferior vena cava1. Lumbar veins            a. R. and L. ascending lumbar veins2. Gonadal veins            a. R.: ovariaries or testes on right side of body                        i. Drains directly into vena cava            b. L.: ovariaries or testes on left side of body

                        i. Drains into L. renal vein3. Suprarenal            a. R: right adrenal gland                        i. Drains directly into vena cava            b. L: left adrenal gland                        i. Drains into left renal vein4. Renal veins            a. Drain kidneys E. Common iliacs join to form inferior vena cava XI. Veins of Pelvis and Lower Limbs 

A. Anterior and posterior tibial veins joins to form poplitealB. Above the knee the popliteal becomes the femoral veinC. As the femoral vein enters the pelvis it becomes the external iliacD. External iliac joins with internal iliac to form common iliacE. Saphenous veins            a. Great                        i. Drains medial aspects of the leg                        ii. Longest vein in the body

                        iii. Empties into femoral vein            b. Small                        i. Drains deep fascia of calf                        ii. Empties into popliteal vein