1. Blood Vessels Part 2 Slides by Barbara Heard and W. Rose. figures from Marieb & Hoehn 9 th eds. Portions copyright Pearson Education

2. K.A.A.P. Monitoring Cardiovascular Performance Vital signs: HR, blood pressure, respiratory rate, body temperature Radial artery routinely used for HR Other locations also work: where arteries are close to body surface – Carotid, femoral, dorsalis pedis, posterior tibial

3. © 2013 Pearson Education, Inc. Figure 19.12 Body sites where the pulse is most easily palpated. Superficial temporal artery Facial artery Common carotid artery Brachial artery Radial artery Femoral artery Popliteal artery Posterior tibial artery Dorsalis pedis artery

4. K.A.A.P.

6. © 2013 Pearson Education, Inc. Measuring Blood Pressure Systemic arterial BP –Measured indirectly by auscultatory method using a sphygmomanometer –Pressure increased in cuff until it exceeds systolic pressure in brachial artery –Pressure released slowly and examiner listens for sounds of Korotkoff with a stethoscope

7. © 2013 Pearson Education, Inc. Measuring Blood Pressure Systolic pressure, normally less than 120 mm Hg, is pressure when sounds first occur as blood starts to spurt through artery Diastolic pressure, normally less than 80 mm Hg, is pressure when sounds disappear because artery no longer constricted; blood flowing freely

8. © 2013 Pearson Education, Inc. Alterations in Blood Pressure Hypertension: high blood pressure Systolic pressure >=140 mmHg or Diastolic pressure >=90 (or both) Chronic (sustained) hypertension Increased risk of MI (heart attack), heart failure, stroke, peripheral vascular disease…

9. © 2013 Pearson Education, Inc. Primary or Essential Hypertension Most (90% of) hypertension is “Essential hypertension” No obvious other cause (such as endocrine disorder, etc.) Risk factors: family history, diet, obesity, age, diabetes mellitus, stress, smoking No cure but can be controlled –Restrict salt, fat intake –Increase exercise, lose weight, stop smoking –Antihypertensive drugs

10. © 2013 Pearson Education, Inc. Homeostatic Imbalance: Hypertension Secondary hypertension less common –Due to identifiable disorders including obstructed renal arteries, kidney disease, and endocrine disorders such as hyperthyroidism and Cushing's syndrome –Treatment focuses on correcting underlying cause

11. © 2013 Pearson Education, Inc. Alterations in Blood Pressure Hypotension: low blood pressure –Blood pressure below 90/60 mm Hg –Usually not a concern Only if leads to inadequate blood flow to tissues –Often associated with long life and lack of cardiovascular illness

12. © 2013 Pearson Education, Inc. Homeostatic Imbalance: Hypotension Orthostatic hypotension: temporary low BP and dizziness when suddenly rising from sitting or reclining position Chronic hypotension: hint of poor nutrition and warning sign for Addison's disease or hypothyroidism Acute hypotension: important sign of circulatory shock; threat for surgical patients and those in ICU

13. © 2013 Pearson Education, Inc. Blood Flow Through Body Tissues Tissue perfusion involved in –Delivery of O 2 and nutrients to, and removal of wastes from, tissue cells –Gas exchange (lungs) –Absorption of nutrients (digestive tract) –Urine formation (kidneys) Rate of flow is precisely right amount to provide proper function

14. © 2013 Pearson Education, Inc. Figure 19.13 Distribution of blood flow at rest and during strenuous exercise. Brain Heart Skeletal muscles Skin Kidneys Abdomen Other 750 250 1200 500 1100 1400 600 750 12,500 1900 600 400 Total blood flow at rest 5800 ml/min Total blood flow during strenuous exercise 17,500 ml/min

15. © 2013 Pearson Education, Inc. Velocity of Blood Flow Changes as travels through systemic circulation Inversely related to total cross-sectional area Fastest in aorta; slowest in capillaries; increases in veins Slow capillary flow allows adequate time for exchange between blood and tissues

16. © 2013 Pearson Education, Inc. Relative cross- sectional area of different vessels of the vascular bed Total area (cm 2 ) of the vascular bed Velocity of blood flow (cm/s) 50 Arterioles 40 30 20 0 10 5000 4000 3000 2000 0 1000 Aorta Arteries Veins Capillaries Venules Venae cavae Figure 19.14 Blood flow velocity and total cross-sectional area of vessels.

17. Autoregulation Automatic adjustment of blood flow to tissues to meet metabolic requirements Controlled intrinsically (i.e. locally) by modifying arteriolar diameter - does not require autonomic nervous system activity Organs regulate their own blood flows by varying resistance of their own arterioles

18. Autoregulation Two types of autoregulation Metabolic control Myogenic control Combination of both determines overall response

19. Autoregulation Keeping flow constant when pressure gradient changes. In a rigid pipe: Resistance (R) does not change. The equation Flow = ΔP / R predicts that when pressure changes, flow will change by the same percent as pressure. In an elastic tube: A pressure change causes a diameter change, and hence a resistance change: pressure ↑ ⇒ diameter ↑ ⇒ resistance ↓ As a result, a pressure change will cause a larger flow change than what you’d get in a rigid pipe. In a vascular bed with autoregulation: Flow changes little when the pressure gradient changes. Percent change in flow is smaller than percent change in pressure.

20. Graph shows pressure-flow relation (vertical axis=change in flow, horiz. axis=change in pressure) for rigid pipes ( ), elastic tubes ( ), “perfect” autoregulation ( ), and actual measurements in dogs whose neural reflexes are temporarily blocked ( ). We expect “passive “ blood vessels to look like. The fact that they look like shows they are not passive – they autoregulate. Coleman, Granger, Guyton 1971 Measurements in animals with neural reflexes blocked Autoregulation Keeping flow constant when pressure gradient changes.

21. © 2013 Pearson Education, Inc. Metabolic Autoregulation Vasodilation of arterioles and relaxation of precapillary sphincters occurs in response to – Declining tissue O 2 – Substances from metabolically active tissues (H +, K +, adenosine, and prostaglandins) and inflammatory chemicals

22. © 2013 Pearson Education, Inc. Metabolic Autoregulation Effects – Relaxation of vascular smooth muscle if flow is insufficient for demand – Release of NO (powerful vasodilator) by endothelial cells Endothelins released from endothelium are potent vasoconstrictors NO and endothelins balanced unless blood flow inadequate, then NO wins Inflammatory chemicals also cause vasodilation

23. Myogenic Autoregulation How it seems to work: Pressure ↑ ⇒ tension in vessel wall ↑ ⇒ vascular smooth muscle constricts ⇒ diameter ↓ ⇒ resistance ↑ Therefore, a pressure change causes a resistance change that prevents flow from changing as much as it would have, if resistance had just stayed the same (or worse, if resistance had changed in the way you’d expect for an elastic tube) P.C. Johnson, Circ Res. 1986.

24. © 2013 Pearson Education, Inc. Figure 19.15 Intrinsic and extrinsic control of arteriolar smooth muscle in the systemic circulation. Vasodilators MetabolicNeuronal Intrinsic mechanisms (autoregulation) Vasoconstrictors Extrinsic mechanisms Myogenic Metabolic Neuronal Hormonal Sympathetic tone Neuronal or hormonal controls Maintain mean arterial pressure (MAP) Redistribute blood during exercise and thermoregulation Metabolic or myogenic controls Distribute blood flow to individual organs and tissues as needed Stretch Angiotensin II Antidiuretic hormone Epinephrine Norepinephrine Endothelins Hormonal Sympathetic tone Atrial natriuretic peptide O 2 CO 2 H + K + Prostaglandins Adenosine Nitric oxide

25. © 2013 Pearson Education, Inc. Long-term Autoregulation Occurs when short-term autoregulation cannot meet tissue nutrient requirements Angiogenesis –Number of vessels to region increases and existing vessels enlarge –Common in heart when coronary vessel occluded, or throughout body in people in high-altitude areas

26. © 2013 Pearson Education, Inc. Blood Flow: Skeletal Muscles Varies with fiber type and activity –At rest, myogenic and general neural mechanisms predominate - maintain ~ 1L /minute –During muscle activity Active or exercise hyperemia - blood flow increases in direct proportion to metabolic activity Local controls override sympathetic vasoconstriction Muscle blood flow can increase 10 

27. © 2013 Pearson Education, Inc. Blood Flow: Brain Blood flow to brain constant as neurons intolerant of ischemia; averages 750 ml/min Metabolic controls –Decreased pH of increased carbon dioxide cause marked vasodilation Myogenic controls –Decreased MAP causes cerebral vessels to dilate –Increased MAP causes cerebral vessels to constrict

28. © 2013 Pearson Education, Inc. Blood Flow: Brain Brain vulnerable under extreme systemic pressure changes –MAP below 60 mm Hg can cause syncope (fainting) –MAP above 160 can result in cerebral edema

29. © 2013 Pearson Education, Inc. Blood Flow: Skin Blood flow through skin –Supplies nutrients to cells (autoregulation in response to O 2 need) –Helps regulate body temperature (neurally controlled) – primary function –Provides a blood reservoir (neurally controlled)

30. © 2013 Pearson Education, Inc. Blood Flow: Skin Blood flow to venous plexuses below skin surface regulates body temperature –Varies from 50 ml/min to 2500 ml/min, depending on body temperature –Controlled by sympathetic nervous system reflexes initiated by temperature receptors and central nervous system

31. © 2013 Pearson Education, Inc. Temperature Regulation As temperature rises (e.g., heat exposure, fever, vigorous exercise) –Hypothalamic signals reduce vasomotor stimulation of skin vessels  –Warm blood flushes into capillary beds  –Heat radiates from skin

32. © 2013 Pearson Education, Inc. Temperature Regulation Sweat also causes vasodilation via bradykinin in perspiration –Bradykinin stimulates NO release As temperature decreases, blood is shunted to deeper, more vital organs

33. © 2013 Pearson Education, Inc. Blood Flow: Lungs Pulmonary circuit unusual –Pathway short –Arteries/arterioles more like veins/venules (thin walled, with large lumens) –Arterial resistance and pressure are low (24/10 mm Hg)

34. © 2013 Pearson Education, Inc. Blood Flow: Lungs Autoregulatory mechanism opposite that in most tissues –Low O 2 levels cause vasoconstriction; high levels promote vasodilation Allows blood flow to O 2 -rich areas of lung

35. © 2013 Pearson Education, Inc. Blood Flow: Heart During ventricular systole –Coronary vessels are compressed Myocardial blood flow ceases Stored myoglobin supplies sufficient oxygen During diastole high aortic pressure forces blood through coronary circulation At rest ~ 250 ml/min; control probably myogenic

36. © 2013 Pearson Education, Inc. Blood Flow: Heart During strenuous exercise –Coronary vessels dilate in response to local accumulation of vasodilators –Blood flow may increase three to four times Important–cardiac cells use 65% of O 2 delivered so increased blood flow provides more O 2

37. © 2013 Pearson Education, Inc. Blood Flow Through Capillaries Vasomotion –Slow, intermittent flow –Reflects on/off opening and closing of precapillary sphincters

38. © 2013 Pearson Education, Inc. Capillary Exchange of Respiratory Gases and Nutrients Diffusion down concentration gradients –O 2 and nutrients from blood to tissues –CO 2 and metabolic wastes from tissues to blood Lipid-soluble molecules diffuse directly through endothelial membranes Water-soluble solutes pass through clefts and fenestrations Larger molecules, such as proteins, are actively transported in pinocytotic vesicles or caveolae

39. © 2013 Pearson Education, Inc. Figure 19.16 Capillary transport mechanisms. (1 of 2) Red blood cell in lumen Endothelial cell Fenestration (pore) Intercellular cleft Tight junction Endothelial cell nucleus Pinocytotic vesicles Basement membrane

40. © 2013 Pearson Education, Inc. Figure 19.16 Capillary transport mechanisms. (2 of 2) Pinocytotic vesicles Caveolae Intercellular cleft Transport via vesicles or caveolae (large substances) Movement through fenestrations (water-soluble substances) Basement membrane Movement through intercellular clefts (water- soluble substances) Diffusion through membrane (lipid-soluble substances) Endothelial fenestration (pore) Lumen 1 2 3 4

41. © 2013 Pearson Education, Inc. Fluid Movements: Bulk Flow Fluid leaves capillaries at arterial end; most returns to blood at venous end –Extremely important in determining relative fluid volumes in blood and interstitial space Direction and amount of fluid flow depend on two opposing forces: hydrostatic and colloid osmotic pressures

42. © 2013 Pearson Education, Inc. Hydrostatic Pressures Capillary hydrostatic pressure (HP c ) (capillary blood pressure) –Tends to force fluids through capillary walls –Greater at arterial end (35 mm Hg) of bed than at venule end (17 mm Hg) Interstitial fluid hydrostatic pressure (HP if ) –Pressure that would push fluid into vessel –Usually assumed to be zero because of lymphatic vessels

43. © 2013 Pearson Education, Inc. Colloid Osmotic Pressures Capillary colloid osmotic pressure (oncotic pressure) (OP c ) –Created by nondiffusible plasma proteins, which draw water toward themselves –~26 mm Hg Interstitial fluid osmotic pressure (OP if ) –Low (~1 mm Hg) due to low protein content

44. © 2013 Pearson Education, Inc. Hydrostatic-osmotic Pressure Interactions: Net Filtration Pressure (NFP) NFP—comprises all forces acting on capillary bed –NFP = (HP c + OP if ) – (HP if + OP c ) Net fluid flow out at arterial end Net fluid flow in at venous end More leaves than is returned –Excess fluid returned to blood via lymphatic system

45. © 2013 Pearson Education, Inc. The big picture Fluid filters from capillaries at their arteriolar end and flows through the interstitial space. Most is reabsorbed at the venous end. For all capillary beds, 20 L of fluid is filtered out per day—almost 7 times the total plasma volume! Due to fluid pressing against a boundary HP “pushes” fluid across the boundary In blood vessels, is due to blood pressure Due to nondiffusible solutes that cannot cross the boundary OP “pulls” fluid across the boundary In blood vessels, is due to plasma proteins Piston Boundary Solute molecules (proteins) Boundary “Pushes” “Pulls” Hydrostatic pressure (HP)Osmotic pressure (OP) 17 L of fluid per day is reabsorbed into the capillaries at the venous end. Lymphatic capillary Venule About 3 L per day of fluid (and any leaked proteins) are removed by the lymphatic system (see Chapter 20). Arteriole Fluid moves through the interstitial space. Net filtration pressure (NFP) determines the direction of fluid movement. Two kinds of pressure drive fluid flow: Figure 19.17 Bulk fluid flow across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments, and maintains the interstitial environment. (1 of 5)

46. © 2013 Pearson Education, Inc. Figure 19.17 Bulk fluid flow across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments, and maintains the interstitial environment. (3 of 5) Net filtration pressure (NFP) determines the direction of fluid movement. Two kinds of pressure drive fluid flow: Due to fluid pressing against a boundary HP “pushes” fluid across the boundary In blood vessels, is due to blood pressure Due to nondiffusible solutes that cannot cross the boundary OP “pulls” fluid across the boundary In blood vessels, is due to plasma proteins Piston Boundary Solute molecules (proteins) Boundary “Pushes” “Pulls” Hydrostatic pressure (HP)Osmotic pressure (OP)

47. © 2013 Pearson Education, Inc. Figure 19.17 Bulk fluid flow across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments, and maintains the interstitial environment. (4 of 5) How do the pressures drive fluid flow across a capillary? Net filtration occurs at the arteriolar end of a capillary. Capillary Boundary (capillary wall) Hydrostatic pressure in capillary “pushes” fluid out of capillary. Osmotic pressure in capillary “pulls” fluid into capillary. HP c = 35 mm Hg OP c = 26 mm Hg OP if = 1 mm Hg HP if = 0 mm Hg NFP = 10 mm Hg Interstitial fluid Hydrostatic pressure in interstitial fluid “pushes” fluid into capillary. Osmotic pressure in interstitial fluid “pulls” fluid out of capillary. To determine the pressure driving the fluid out of the capillary at any given point, we calculate the net filtration pressure (NFP) ––the outward pressures (HP c and OP if ) minus the inward pressures (HP if and OP c ). So, NFP As a result, fluid moves from the capillary into the interstitial space. = (HP c + OP if ) – (HP if + OP c ) = (35 + 1) – (0 + 26) = 10 mm Hg (net outward pressure)

48. © 2013 Pearson Education, Inc. Figure 19.17 Bulk fluid flow across capillary walls causes continuous mixing of fluid between the plasma and the interstitial fluid compartments, and maintains the interstitial environment. (5 of 5) Hydrostatic pressure in capillary “pushes” fluid out of capillary. The pressure has dropped because of resistance encountered along the capillaries. Osmotic pressure in capillary “pulls” fluid into capillary. HP c = 17 mm Hg OP c = 26 mm Hg Hydrostatic pressure in interstitial fluid “pushes” fluid into capillary. Osmotic pressure in interstitial fluid “pulls” fluid out of capillary. HP if = 0 mm Hg OP if = 1 mm Hg NFP= –8 mm Hg Capillary Boundary (capillary wall) Interstitial fluid Again, we calculate the NFP: Notice that the NFP at the venous end is a negative number. This means that reabsorption, not filtration, is occurring and so fluid moves from the interstitial space into the capillary. = (HP c + OP if ) – (HP if + OP c ) = (17 + 1) – (0 + 26) = –8 mm Hg (net inward pressure) NFP Net reabsorption occurs at the venous end of a capillary.

49. © 2013 Pearson Education, Inc. Circulatory Shock Any condition in which –Blood vessels inadequately filled –Blood cannot circulate normally Results in inadequate blood flow to meet tissue needs

50. © 2013 Pearson Education, Inc. Circulatory Shock Hypovolemic shock: results from large- scale blood loss Vascular shock: results from extreme vasodilation and decreased peripheral resistance Cardiogenic shock results when an inefficient heart cannot sustain adequate circulation

51. © 2013 Pearson Education, Inc. Figure 19.18 Events and signs of hypovolemic shock. Acute bleeding (or other events that reduce blood volume) leads to: 1. Inadequate tissue perfusion resulting in O 2 and nutrients to cells 2. Anaerobic metabolism by cells, so lactic acid accumulates 3. Movement of interstitial fluid into blood, so tissues dehydrate Initial stimulus Physiological response Signs and symptoms Result Chemoreceptors activated (by in blood pH) Baroreceptor firing reduced (by blood volume and pressure) Hypothalamus activated (by blood pressure) Respiratory centers activated Cardioacceleratory and vasomotor centers activated Sympathetic nervous system activated ADH released Neurons depressed by pH Central nervous system depressed Heart rate Intense vasoconstriction (only heart and brain spared) Renal blood flow Renin released Angiotensin II produced in blood Aldosterone released Kidneys retain salt and water Water retention Rate and depth of breathing Tachycardia; weak, thready pulse Skin becomes cold, clammy, and cyanotic Urine output Thirst Restlessness (early sign) Coma (late sign) CO 2 blown off; blood pH rises Blood pressure maintained; if fluid volume continues to decrease, BP ultimately drops. BP is a late sign. Major effect Minor effect Adrenal cortex Kidneys Brain

52. © 2013 Pearson Education, Inc. 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

53. © 2013 Pearson Education, Inc. Figure 19.19a Pulmonary circulation. Pulmonary capillaries of the R. lung R. pulmonary artery L. pulmonary artery Pulmonary capillaries of the L. lung From systemic circulation R. pulmonary veins Pulmonary trunk L. pulmonary veins RA RV LV LA Schematic flowchart. To systemic circulation

54. © 2013 Pearson Education, Inc. Figure 19.19 Pulmonary circulation. Pulmonary capillaries of the R. lung R. pulmonary artery L. pulmonary artery Pulmonary capillaries of the L. lung From systemic circulation R. pulmonary veins Pulmonary trunk L. pulmonary veins RA RV LV LA Left pulmonary artery Aortic arch Pulmonary trunk Right pulmonary artery Three lobar arteries to right lung Right atrium Pulmonary veins Right ventricle Left ventricle Two lobar arteries to left lung Pulmonary veins Left atrium Pulmonary capillary Air-filled alveolus of lung Schematic flowchart. Illustration. The pulmonary arterial system is shown in blue to indicate that the blood it carries is oxygen-poor. The pulmonary venous drainage is shown in red to indicate that the blood it transports is oxygen-rich. Gas exchange To systemic circulation

55. © 2013 Pearson Education, Inc. 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 19.20 Schematic flowchart showing an overview of the systemic circulation.

56. © 2013 Pearson Education, Inc. ArteriesVeins DeliveryBlood pumped into single systemic artery—the aorta Blood returns via superior and inferior venae cavae and the coronary sinus LocationDeep, and protected by tissuesBoth deep and superficial PathwaysFairly distinctNumerous interconnections Supply/drainagePredictable supplyUsually similar to arteries, except dural sinuses and hepatic portal circulation Differences Between Arteries and Veins