Figure 21-8 An Overview of Cardiovascular Physiology Cardiac Output Venous Return Arterial Blood Pressure Regulation (Neural and Hormonal) Venous Pressure Peripheral Resistance Capillary Pressure Capillary exchange Interstitial fluid 1

Pressure and Resistance Total capillary blood flow Equals cardiac output Is determined by pressure and resistance in the cardiovascular system

Pressure and Resistance An Overview of Cardiovascular Pressures Systolic pressure Peak arterial pressure during ventricular systole Diastolic pressure Minimum arterial pressure during diastole Pulse pressure Difference between systolic pressure and diastolic pressure Mean arterial pressure (MAP) MAP = diastolic pressure + 1/3 pulse pressure

Vessel diameter Vessel diameter (cm) Figure 21-10a Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit Vessel diameter (cm) Vessel diameter 4

Total cross-sectional area of vessels Figure 21-10b Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit Cross- sectional area (cm2) Total cross-sectional area of vessels 5

Average blood pressure Figure 21-10c Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit Average blood pressure (mm Hg) Average blood pressure 6

Velocity of blood flow Velocity of blood flow (cm/sec) Figure 21-10d Relationships among Vessel Diameter, Cross-Sectional Area, Blood Pressure, and Blood Velocity within the Systemic Circuit Velocity of blood flow (cm/sec) Velocity of blood flow 7

Figure 21-11 Pressures within the Systemic Circuit Systolic Pulse pressure Mean arterial pressure Diastolic mm Hg 8

Pressure and Resistance Capillary Pressures and Capillary Exchange Vital to homeostasis Moves materials across capillary walls by Diffusion Filtration Reabsorption

Pressure and Resistance Diffusion Movement of ions or molecules From high concentration To lower concentration Along the concentration gradient

Pressure and Resistance Diffusion Routes Water, ions, and small molecules such as glucose Diffuse between adjacent endothelial cells Or through fenestrated capillaries Some ions (Na+, K+, Ca2+, Cl-) Diffuse through channels in plasma membranes

Pressure and Resistance Diffusion Routes Large, water-soluble compounds Pass through fenestrated capillaries Lipids and lipid-soluble materials such as O2 and CO2 Diffuse through endothelial plasma membranes Plasma proteins Cross endothelial lining in sinusoids

Pressure and Resistance Filtration Driven by hydrostatic pressure Water and small solutes forced through capillary wall Leaves larger solutes in bloodstream

Pressure and Resistance Reabsorption The result of osmosis Blood colloid osmotic pressure Equals pressure required to prevent osmosis Caused by suspended blood proteins that are too large to cross capillary walls

Figure 21-12 Capillary Filtration Capillary hydrostatic pressure (CHP) Amino acid Blood protein Glucose Ions Interstitial fluid Small solutes Hydrogen bond Water molecule Endothelial cell 1 Endothelial cell 2 15

Pressure and Resistance Capillary Exchange At arterial end of capillary Fluid moves out of capillary Into interstitial fluid At venous end of capillary Fluid moves into capillary Out of interstitial fluid Transition point between filtration and reabsorption Is closer to venous end than arterial end Capillaries filter more than they reabsorb Excess fluid enters lymphatic vessels

Pressure and Resistance Interplay between Filtration and Reabsorption Hydrostatic pressure Forces water out of solution Osmotic pressure Forces water into solution Both control filtration and reabsorption through capillaries

Pressure and Resistance Net Hydrostatic Pressure Is the difference between Capillary hydrostatic pressure (CHP) And interstitial fluid hydrostatic pressure (IHP) Pushes water and solutes Out of capillaries Into interstitial fluid

Pressure and Resistance Net Colloid Osmotic Pressure Is the difference between Blood colloid osmotic pressure (BCOP) And interstitial fluid colloid osmotic pressure (ICOP) Pulls water and solutes Into a capillary From interstitial fluid

Pressure and Resistance Net Filtration Pressure (NFP) The difference between Net hydrostatic pressure And net osmotic pressure NFP = (CHP – IHP) – (BCOP – ICOP)

Figure 21-13 Forces Acting across Capillary Walls KEY CHP (Capillary hydrostatic pressure) BCOP (Blood colloid osmotic pressure) Arteriole NFP (Net filtration pressure) Venule Filtration Reabsorption No net fluid movement 20.4 L/day 24 L/day 35 mm Hg 25 mm Hg 25 mm Hg 25 mm Hg 18 mm Hg 25 mm Hg NFP  10 mm Hg NFP  0 NFP  7 mm Hg CHP  BCOP Fluid forced out of capillary CHP  BCOP No net movement of fluid BCOP  CHP Fluid moves into capillary 21

Figure 21-14 Short-Term and Long-Term Cardiovascular Responses Autoregulation Autoregulation is due to opening and closing precapillary sphincters due to local release of vasodilator or vasoconstrictor chemicals from the tissue. HOMEOSTASIS RESTORED Local decrease in resistance and increase in blood flow HOMEOSTASIS Local vasodilators released Normal blood pressure and volume Inadequate local blood pressure and blood flow HOMEOSTASIS DISTURBED • Physical stress (trauma, high temperature) • Chemical changes (decreased O2 or pH, increased CO2 or prostaglandins) • Increased tissue activity Start 22

Figure 21-14 Short-Term and Long-Term Cardiovascular Responses Central Regulation Central regulation involves neuroendocrine mechanisms that control the total systemic circulation. This regulation involves both the cardiovascular centers and the vasomotor centers. Short-term elevation of blood pressure by sympathetic stimulation of the heart and peripheral vasoconstriction Stimulation of receptors sensitive to changes in systemic blood pressure or chemistry Activation of cardiovascular centers Neural mechanisms Stimulation of endocrine response Long-term increase in blood volume and blood pressure Endocrine mechanisms If autoregulation is ineffective HOMEOSTASIS RESTORED 23

Figure 21-15 Baroreceptor Reflexes of the Carotid and Aortic Sinuses Cardioinhibitory centers stimulated Cardioacceleratory centers inhibited Decreased cardiac output Responses to Increased Baroreceptor Stimulation Vasomotor centers inhibited Baroreceptors stimulated Vasodilation occurs HOMEOSTASIS DISTURBED HOMEOSTASIS RESTORED Rising blood pressure Blood pressure declines Start HOMEOSTASIS Normal range of blood pressure 24

Figure 21-15 Baroreceptor Reflexes of the Carotid and Aortic Sinuses HOMEOSTASIS Normal range of blood pressure Start HOMEOSTASIS DISTURBED HOMEOSTASIS RESTORED Falling blood pressure Blood pressure rises Vasoconstriction occurs Baroreceptors inhibited Vasomotor centers stimulated Increased cardiac output Responses to Decreased Baroreceptor Stimulation Cardioacceleratory centers stimulated Cardioinhibitory centers inhibited 25

Figure 21-16 The Chemoreceptor Reflexes Respiratory centers in the medulla oblongata stimulated Respiratory Response Respiratory rate increases Increasing CO2 levels, decreasing pH and O2 levels Effects on Cardiovascular Centers Cardiovascular Responses Cardioacceleratory centers stimulated Reflex Response Increased cardiac output and blood pressure Chemoreceptors stimulated Cardioinhibitory centers inhibited Vasomotor centers stimulated Vasoconstriction occurs Start HOMEOSTASIS DISTURBED HOMEOSTASIS RESTORED Elevated CO2 levels, decreased pH and O2 levels in blood and CSF Decreased CO2 levels, increased pH and O2 levels in blood and CSF HOMEOSTASIS Normal pH, O2, and CO2 levels in blood and CSF 26

Factors that compensate for decreased blood pressure and volume Figure 21-17a The Hormonal Regulation of Blood Pressure and Blood Volume HOMEOSTASIS Normal blood pressure and volume HOMEOSTASIS DISTURBED HOMEOSTASIS RESTORED Start Blood pressure and volume fall Blood pressure and volume rise Decreasing blood pressure and volume Short-term Long-term Combined Short-Term and Long-Term Effects Sympathetic activation and release of adrenal hormones E and NE Increased blood pressure Increased blood volume Endocrine Response of Kidneys Increased cardiac output and peripheral vasoconstriction Renin release leads to angiotensin II activation Erythropoietin (EPO) is released Angiotensin II Effects Angiotensin II Antidiuretic hormone released Aldosterone secreted Factors that compensate for decreased blood pressure and volume Thirst stimulated Increased red blood cell formation 27

Factors that compensate for increased blood pressure and volume Figure 21-17b The Hormonal Regulation of Blood Pressure and Blood Volume Responses to ANP and BNP Increased Na loss in urine Increased water loss in urine Combined Effects Reduced thirst Natriuretic peptides released by the heart Inhibition of ADH, aldosterone, epinephrine, and norepinephrine release Reduced blood volume Peripheral vasodilation HOMEOSTASIS DISTURBED HOMEOSTASIS RESTORED Rising blood pressure and volume Declining blood pressure and volume HOMEOSTASIS Increasing blood pressure and volume Normal blood pressure and volume Factors that compensate for increased blood pressure and volume 28

Table 21-2 Changes in Blood Distribution during Exercise 29

21-4 Cardiovascular Adaptation Table 21-3 Effects of Training on Cardiovascular Performance Subject Heart Weight (g) Stroke Volume (mL) Heart Rate (BPM) Cardiac Output (L/min) Blood Pressure (systolic/ diastolic) Nonathlete (rest) 300 60 83 5.0 120/80 Nonathlete (maximum) 104 192 19.9 187/75 Trained athlete (rest) 500 100 53 5.3 Trained athlete (maximum) 167 182 30.4 200/90* *Diastolic pressures of athletes during maximum activity have not been accurately measured.

Figure 21-18 Cardiovascular Responses to Hemorrhaging and Blood Loss HOMEOSTASIS Normal blood pressure and volume HOMEOSTASIS RESTORED HOMEOSTASIS DISTURBED Blood pressure and volume rise Extensive bleeding reduces blood pressure and volume Falling blood pressure and volume Responses coordinated by the endocrine system Elevation of blood volume Responses directed by the nervous system Long-Term Hormonal Response Cardiovascular Responses ADH, angiotensin II, aldosterone, and EPO released Peripheral vasoconstriction; mobilization of venous reserve Increased cardiac output Stimulation of baroreceptors and chemoreceptors Pain, stress, anxiety, fear Higher Centers Stimulation of cardiovascular centers General sympathetic activation 31