The Blood Vessels and Blood Pressure Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Blood Flow Blood is constantly reconditioned so composition remains relatively constant Reconditioning organs receive more blood than needed for metabolic needs Digestive organs, kidneys, skin Adjust extra blood to achieve homeostasis Blood flow to other organs can be adjusted according to metabolic needs Brain can least tolerate disrupted supply Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Distribution of Cardiac Output at Rest Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Blood Flow Flow rate through a vessel (volume of blood passing through per unit of time): Directly proportional to the pressure gradient Inversely proportional to vascular resistance F = ΔP R F = flow rate of blood through a vessel ΔP = pressure gradient R = resistance of blood vessels Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Blood Flow Pressure gradient is pressure difference between beginning and end of a vessel Blood flows from area of higher pressure to area of lower pressure Resistance is measure of opposition of blood flow through a vessel Depends on 3 things: Blood viscosity Vessel length Vessel radium Major determinant of resistance to flow is vessel’s radius Slight change in radius produces significant change in blood flow R is proportional to 1 r4 Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Relationship of Resistance and Flow to Vessel Radius Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Animation: Measuring blood pressure

Animation: Arteries as pressure reservoir

Vascular Tree Closed system of vessels Consists of Arteries Arterioles Carry blood away from heart to tissues Arterioles Smaller branches of arteries Capillaries Smaller branches of arterioles Smallest of vessels across which all exchanges are made with surrounding cells Venules Formed when capillaries rejoin Return blood to heart Veins Formed when venules merge Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Basic Organization of the Cardiovascular System Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Animation: Flow velocity

Animation: Vein function

Arteries Specialized to Serve as rapid-transit passageways for blood from heart to organs Due to large radius, arteries offer little resistance to blood flow Act as pressure reservoir to provide driving force for blood when heart is relaxing Arterial connective tissue contains Collagen fibers Provide tensile strength Elastin fibers Provide elasticity to arterial walls Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arteries as a Pressure Reservoir Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Blood Pressure Force exerted by blood against a vessel wall Depends on Volume of blood contained within vessel Compliance of vessel walls Systolic pressure Peak pressure exerted by ejected blood against vessel walls during cardiac systole Averages 120 mm Hg Diastolic pressure Minimum pressure in arteries when blood is draining off into vessels downstream Averages 80 mm Hg Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Blood Pressure Can be measured indirectly using sphygmomanometer Korotkoff sounds Sounds heard when determining blood pressure Sounds are distinct from heart sounds associated with valve closure Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Blood Pressure Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Pulse Pressure Pressure difference between systolic and diastolic pressure Example If blood pressure is 120/80, pulse pressure is 40 mm Hg (120mm Hg – 80mm Hg) Pulse that can be felt in artery lying close to surface of skin is due to pulse pressure Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Mean Arterial Pressure Average pressure driving blood forward into tissues throughout cardiac cycle Formula for approximating mean arterial pressure Mean arterial pressure = diastolic pressure + ⅓ pulse pressure At 120/80, mean arterial pressure = 80 mm Hg + ⅓ (40 mm Hg) = 93 mm Hg Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arterioles Major resistance vessels Radius supplying individual organs can be adjusted independently to Distribute cardiac output among systemic organs, depending on body’s momentary needs Help regulate arterial blood pressure Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arterioles Mechanisms involved in adjusting arteriolar resistance Vasoconstriction Refers to narrowing of a vessel Vasodilation Refers to enlargement in circumference and radius of vessel Results from relaxation of smooth muscle layer Leads to decreased resistance and increased flow through that vessel Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arteriolar Vasoconstriction and Vasodilation Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arterioles Only blood supply to brain remains constant Changes within other organs alter radius of vessels and adjust blood flow to organ Local chemical influences on arteriolar radius Local metabolic changes Histamine release Local physical influences on arteriolar radius Local application of heat or cold Chemical response to shear stress Myogenic response to stretch Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Magnitude and Distribution Of the Cardiac Output at Rest and During Moderate Exercise Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arterioles Specific local chemical factors that produce relaxation of arteriolar smooth muscle Decreased O2 Increased CO2 Increased acid Increased K+ Increased osmolarity Adenosine release Prostaglandin release Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arterioles Local vasoactive mediators Endothelial cells Release chemical mediators that play key role in locally regulating arteriolar caliber Release locally acting chemical messengers in response to chemical changes in their environment Among best studied local vasoactive mediators is nitric oxide (NO) Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Functions of Endothelial Cells Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Functions of Nitric Oxide (NO) Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arterioles Extrinsic control Accomplished primarily by sympathetic nerve influence Accomplished to lesser extent by hormonal influence over arteriolar smooth muscle Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Arterioles Cardiovascular control center In medulla of brain stem Integrating center for blood pressure regulation Other brain regions also influence blood distribution Hypothalamus Controls blood flow to skin to adjust heat loss to environment Hormones that influence arteriolar radius Adrenal medullary hormones Epinephrine and norepinephrine Generally reinforce sympathetic nervous system in most organs Vasopressin and angiotensin II Important in controlling fluid balance Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Capillaries Thin-walled, small-radius, extensively branched Sites of exchange between blood and surrounding tissue cells Maximized surface area and minimized diffusion distance Velocity of blood flow through capillaries is relatively slow Provides adequate exchange time 2 types of passive exchanges Diffusion Bulk flow Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Capillaries Narrow, water-filled gaps (pores) lie at junctions between cells Permit passage of water-soluble substances Lipid soluble substances readily pass through endothelial cells by dissolving in lipid bilayer barrier Size of pores varies from organ to organ Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Capillaries Under resting conditions many capillaries are not open Capillaries surrounded by precapillary sphincters Contraction of sphincters reduces blood flowing into capillaries in an organ Relaxation of sphincters increases blood flow Metarteriole Runs between an arteriole and a venule Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Lymphatic System Extensive network of one-way vessels Provides accessory route by which fluid can be returned from interstitial to the blood Initial lymphatics Small, blind-ended terminal lymph vessels Permeate almost every tissue of the body Lymph Interstitial fluid that enters a lymphatic vessel Lymph vessels Formed from convergence of initial lymphatics Eventually empty into venous system near where blood enters right atrium One way valves spaced at intervals direct flow of lymph toward venous outlet in chest Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Lymphatic System Functions Return of excess filtered fluid Defense against disease Lymph nodes have phagocytes which destroy bacteria filtered from interstitial fluid Transport of absorbed fat Return of filtered protein Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Lymphatic System Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Edema Swelling of tissues Occurs when too much interstitial fluid accumulates Causes of edema Reduced concentration of plasma proteins Increased permeability of capillary wall Increased venous pressure Blockage of lymph vessels Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Veins Venous system transports blood back to heart Capillaries drain into venules Venules converge to form small veins that exit organs Smaller veins merge to form larger vessels Veins Large radius offers little resistance to blood flow Also serve as blood reservoir Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Veins Factors which enhance venous return Driving pressure from cardiac contraction Sympathetically induced venous vasoconstriction Skeletal muscle activity Effect of venous valves Respiratory activity Effect of cardiac suction Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Factors that Influence Venous Return Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Mean Arterial Pressure Blood pressure that is monitored and regulated in the body Primary determinants Cardiac output Total peripheral resistance Mean arterial pressure = cardiac output x total peripheral resistance Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Determinants of Mean Arterial Pressure Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Mean Arterial Pressure Constantly monitored by baroreceptors (pressure sensors) within circulatory system Short-term control adjustments Occur within seconds Adjustments made by alterations in cardiac output and total peripheral resistance Mediated by means of autonomic nervous system influences on heart, veins, and arterioles Long-term control adjustments Require minutes to days Involve adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Baroreceptor Reflexes to Restore Blood Pressure to Normal Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Blood Pressure Additional reflexes and responses that influence blood pressure Left atrial receptors and hypothalamic osmoreceptors affect long-term regulation of blood pressure by controlling plasma volume Chemoreceptors in carotid and aortic arteries are sensitive to low O2 or high acid levels in blood reflexly increase respiratory activity Associated with certain behaviors and emotions mediated through cerebral-hypothalamic pathway Exercise modifies cardiac responses Hypothalamus controls skin arterioles for temperature regulation Vasoactive substances released from endothelial cells play role Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Blood Pressure Abnormalities Hypertension Blood pressure above 140/90 mm Hg 2 broad classes Primary hypertension Secondary hypertension Hypotension Blood pressure below 100/60 mm Hg Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Hypertension Most common of blood pressure abnormalities Primary hypertension Catchall category for blood pressure elevated by variety of unknown causes rather than by a single disease entity Potential causes being investigated Defects in salt management by the kidneys Excessive salt intake Diets low in K+ and Ca2+ Plasma membrane abnormalities such as defective Na+-K+ pumps Variation in gene that encodes for angiotensinogen Endogenous digitalis-like substances Abnormalities in NO, endothelin, or other locally acting vasoactive chemicals Excess vasopressin Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Hypertension Secondary hypertension Accounts for about 10% of hypertension cases Occurs secondary to another known primary problem Examples of secondary hypertension Renal hypertension Endocrine hypertension Neurogenic hypertension Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Hypertension Complication of hypertension Congestive heart failure Stroke Heart attack Spontaneous hemorrhage Renal failure Retinal damage Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Hypotension Low blood pressure Occurs when There is too little blood to fill the vessels Heart is too weak to drive the blood Orthostatic (postural) hypotension Transient hypotensive condition resulting from insufficient compensatory responses to gravitational shifts in blood when person moves from horizontal to vertical position Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Hypotension Circulatory shock Occurs when blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained 4 main types Hypovolemic (“low volume”) shock Cardiogenic (“heart produced”) shock Vasogenic (“vessel produced”) shock Neurogenic (“nerve produced”) shock Chapter 10 The Blood Vessels and Blood Pressure Human Physiology by Lauralee Sherwood ©2010 Brooks/Cole, Cengage Learning

Animation: Pattern of blood circulation

Animation: Lymph vessels and lymph nodes

Animation: Blood vessel anatomy