CVS3Final - Cardiovascular Cardiovascular System Blood...

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Unformatted text preview: Cardiovascular Cardiovascular System: Blood Vessels Blood Vessels Blood is carried in a closed system of vessels that begins and ends at the heart Blood Vessels Blood Vessels The three major types of vessels are arteries, capillaries, and veins Blood Vessels Blood Vessels Arteries carry blood away from the heart, veins carry blood toward the heart Blood Vessels Blood Vessels Capillaries contact tissue cells and directly serve cellular needs Generalized Structure of Blood Generalized Structure of Blood Vessels Arteries and veins are composed of three tunics – tunica interna, tunica media, and tunica externa Generalized Structure of Blood Generalized Structure of Blood Vessels Lumen – central blood­containing space surrounded by tunics Generalized Structure of Blood Generalized Structure of Blood Vessels Capillaries are composed of endothelium with sparse basal lamina Tunics Tunics Tunica interna (tunica intima) Endothelial layer that lines the lumen of all vessels In vessels larger than 1 mm, a subendothelial connective tissue basement membrane is present Tunics Tunics Tunica media Smooth muscle and elastic fiber layer, regulated by sympathetic nervous system Controls vasoconstriction/vaso dilation of vessels Tunics Tunics Tunica externa (tunica adventitia) Collagen fibers that protect and reinforce vessels Larger vessels contain vasa vasorum Elastic (Conducting) Arteries Elastic (Conducting) Arteries Thick­walled arteries near the heart; the aorta and its major branches Large lumen allow low­resistance conduction of blood Withstand and smooth out large blood pressure fluctuations DEMONSTRATES THE INTIMAL CHANGES IN THE VASA VASORUM (SYPHILITIC AORTITIS THAT EVENTUALLY EFFETCS THE AORTA AS THE VASA VASORUM GETS THROMBOSED DUE TO ARTERITIS). Psyphilitic Aortitis – RUPTURED Psyphilitic Aortitis – RUPTURED SYPHILITIC ANEURYSM Dissecting Aneurysm – The elastic Dissecting Aneurysm – The elastic element of the arch arteries gets fragmented and the wall undergoes dissection. This was a case of uncontrolled hypertension Takayasu’s arteritis Takayasu’s arteritis Diseases of the arch arteries typically present as a “Pulseless disease” Muscular (Distributing) Arteries and Arterioles Muscular (Distributing) Arteries and Arterioles Muscular arteries – distal to elastic arteries; deliver blood to body organs Have thick tunica media with more smooth muscle and less elastic tissue Kawasaki’s disease Kawasaki’s disease Commonest cause of Coronary artery disease and Myocardial infarction in children Muscular (Distributing) Arteries and Arterioles Muscular (Distributing) Arteries and Arterioles Muscular arteries – distal to elastic arteries; deliver blood to body organs Have thick tunica media with more smooth muscle and less elastic tissue Renal artery stenosis Renal artery stenosis Renal artery stenosis Renal artery stenosis Muscular (Distributing) Muscular (Distributing) Arteries and Arterioles Muscular arteries – distal to elastic arteries; deliver blood to body organs Active in vasoconstriction Muscular (Distributing) Muscular (Distributing) Arteries and Arterioles Arterioles – smallest arteries; lead to capillary beds Control flow into capillary beds via vasodilation and constriction Vasculitis of the small arteries Vasculitis of the small arteries presents as palpable Purpura Vasculitis of the small arteries presents Vasculitis of the small arteries presents as palpable Purpura Vasculitis of the small arteries Vasculitis of the small arteries presents as palpable Purpura Capillaries Capillaries Capillaries are the smallest blood vessels Walls consisting of a thin tunica interna, one cell thick Allow only a single RBC to pass at a time Capillaries Capillaries Capillaries are the smallest blood vessels Pericytes on the outer surface stabilize their walls Capillaries Capillaries There are three structural types of capillaries: a. Continuous, b. Fenestrated, and c. Sinusoids Continuous Capillaries Continuous Capillaries Continuous capillaries are abundant in the skin and muscles, and have: uninterrupted lining tight junctions Intercellular clefts of unjoined membranes that allow the passage of fluids Continuous Continuous Capillaries Continuous capillaries of the brain: Have tight junctions completely around the endothelium Constitute the blood­brain barrier Fenestrated Capillaries Fenestrated Capillaries Found wherever active capillary absorption or filtrate formation occurs (e.g., small intestines, endocrine glands, and kidneys) Characterized by: An endothelium riddled with pores (fenestrations) Greater permeability to solutes and fluids than other capillaries Fenestrated Capillaries Fenestrated Capillaries Fenestrated Capillaries Fenestrated Capillaries Sinusoids Sinusoids Highly modified, leaky, fenestrated capillaries with large lumens Found in the liver, bone marrow and in lymphoid tissue, Allow large molecules (proteins and blood cells) to pass between the blood and surrounding tissues Sinusoids Sinusoids Capillary Beds Capillary Beds A microcirculation of interwoven networks of capillaries, consisting of: Vascular shunts – metarteriole–thoroughfare channel connecting an arteriole directly with a postcapillary venule Capillary Beds Capillary Beds A microcirculation of interwoven networks of capillaries, consisting of: True capillaries – 10 to 100 per capillary bed, capillaries branch off the metarteriole and return to the thoroughfare channel at the distal end of the bed Capillary Beds Capillary Beds Figure 19.4b Blood Flow Through Capillary Beds Blood Flow Through Capillary Beds Precapillary sphincter Cuff of smooth muscle that surrounds each true capillary Regulates blood flow into the capillary Venous System: Venules Venous System: Venules Postcapillary venules – smallest venules, composed of endothelium and a few pericytes Venous System: Veins Venous System: Veins Veins are: Capacitance vessels (blood reservoirs) that contain 65% of the blood supply Venous System: Veins Venous System: Veins Veins have much lower blood pressure and thinner walls than arteries To return blood to the heart, veins have special adaptations Large­diameter lumens, which offer little resistance to flow Venous System: Veins Venous System: Veins Valves (resembling semilunar heart valves), which prevent backflow of blood Venous System: Veins Venous System: Veins Venous sinuses – specialized, flattened veins with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain) Blood Pressure (BP) Blood Pressure (BP) Force per unit area exerted on the wall of a blood vessel by its contained blood Expressed in millimeters of mercury (mm Hg) Blood Pressure (BP) Blood Pressure (BP) Force per unit area exerted on the wall of a blood vessel by its contained blood Measured in reference to systemic arterial BP in large arteries Resistance Resistance Resistance – opposition to flow Measure of the amount of friction blood encounters as it passes through vessels Referred to as peripheral resistance (PR) Mean Arterial Pressure Parasympathetic Arterial baroreceptors Sympathetic SA Node Ventricular Myocardium Veins Arteries Action Potential Contractility Venomotor tone Vasoconstriction Heart Rate Feedback Stroke Volume Mean Arterial Pressure Total Peripheral Resistance Resistance Resistance The three important sources of resistance are: a. Blood viscosity, b. Total blood vessel length, and c. Blood vessel diameter Resistance Factors: Resistance Factors: Viscosity Resistance factors that remain relatively constant are: Blood viscosity – thickness or “stickiness” of the blood Resistance Factors: Vessel Length Resistance Factors: Vessel Length Resistance factors that remain relatively constant are: Blood vessel length – the longer the vessel, the greater the resistance encountered Resistance Factors: Blood Resistance Factors: Blood Vessel Diameter Changes in vessel diameter are frequent and significantly alter peripheral resistance Resistance Factors: Blood Resistance Factors: Blood Vessel Diameter Resistance varies inversely with the fourth power of vessel radius (one­half the diameter) For example, if the radius is doubled, the resistance is 1/16 as much Resistance Factors: Blood Resistance Factors: Blood Vessel Diameter Small­diameter arterioles are the major determinants of peripheral resistance Blood Flow, Blood Pressure, Blood Flow, Blood Pressure, and Resistance Blood flow (F) is directly proportional to the difference in blood pressure (∆ P) between two points in the circulation If ∆ P increases, blood flow speeds up; if ∆ P decreases, blood flow declines Blood Flow, Blood Pressure, Blood Flow, Blood Pressure, and Resistance Blood flow is inversely proportional to resistance (R) If R increases, blood flow decreases Blood Flow, Blood Pressure, Blood Flow, Blood Pressure, and Resistance R is more important than ∆ P in influencing local blood pressure Systemic Blood Pressure Systemic Blood Pressure Arterial Blood Pressure Arterial Blood Pressure Arterial BP reflects two factors of the arteries close to the heart Their elasticity (compliance or distensibility) The amount of blood forced into them at any given time Arterial Blood Pressure Arterial Blood Pressure Blood pressure in elastic arteries near the heart is pulsatile (BP rises and falls) Arterial Blood Pressure Arterial Blood Pressure Mean arterial pressure (MAP) – pressure that propels the blood to the tissues Arterial Blood Pressure Arterial Blood Pressure MAP = diastolic pressure + 1/3 pulse pressure Venous Blood Pressure Venous Blood Pressure A cut vein has even blood flow; a lacerated artery flows in spurts Factors Aiding Venous Factors Aiding Venous Return Venous BP alone is too low to promote adequate blood return and is aided by the: Respiratory “pump” – pressure changes created during breathing suck blood toward the heart by squeezing local veins Factors Aiding Venous Factors Aiding Venous Return Venous BP alone is too low to promote adequate blood return and is aided by the: Muscular “pump” – contraction of skeletal muscles “milk” blood toward the heart Factors Aiding Venous Factors Aiding Venous Return Valves prevent backflow during venousreturn Maintaining Blood Pressure Maintaining Blood Pressure Maintaining blood pressure requires: Cooperation of the heart, blood vessels, and kidneys Supervision of the brain Maintaining Blood Pressure Maintaining Blood Pressure Blood pressure = CO x PR Maintaining Blood Pressure Maintaining Blood Pressure Blood pressure varies directly with CO, PR, and blood volume Cardiac Output (CO) Cardiac Output (CO) Controls of Blood Pressure Controls of Blood Pressure Short­term controls: Are mediated by the nervous system and bloodborne chemicals Counteract moment­to­ moment fluctuations in blood pressure by altering peripheral resistance Kidney Kidney Controls of Blood Pressure Controls of Blood Pressure Long­term controls regulate blood volume Short­Term Mechanisms: Short­Term Mechanisms: Neural Controls Neural controls of peripheral resistance: Alter blood distribution to respond to specific demands Maintain MAP by altering blood vessel diameter Short­Term Mechanisms: Short­Term Mechanisms: Neural Controls Neural controls operate via reflex arcs involving: Baroreceptors Vasomotor centers of the medulla and vasomotor fibers Vascular smooth muscle Short­Term Mechanisms: Short­Term Mechanisms: Vasomotor Center Vasomotor center – a cluster of sympathetic neurons in the medulla that oversees changes in blood vessel diameter Maintains blood vessel tone by innervating smooth muscles of blood vessels, especially arterioles Short­Term Mechanisms: Short­Term Mechanisms: Vasomotor Center Cardiovascular center – vasomotor center plus the cardiac centers that integrate blood pressure control by altering cardiac output and blood vessel diameter Short­Term Mechanisms: Short­Term Mechanisms: Vasomotor Activity Sympathetic activity causes: Vasoconstriction and a rise in blood pressure if increased Blood pressure to decline to basal levels if decreased Short­Term Mechanisms: Short­Term Mechanisms: Vasomotor Activity Vasomotor activity is modified by: Baroreceptors (pressure­sensitive), chemoreceptors (O2, CO2, and H+ sensitive), higher brain centers, bloodborne chemicals, and hormones Short­Term Mechanisms: Short­Term Mechanisms: Baroreceptor­Initiated Reflexes Increased blood pressure stimulates the cardioinhibitory center to: Increase vessel diameter Decrease heart rate, cardiac output, peripheral resistance, and blood pressure Short­Term Mechanisms: Baroreceptor­Initiated Reflexes Declining blood pressure stimulates the cardioacceleratory center to: Increase cardiac output and peripheral resistance Low blood pressure also stimulates the vasomotor center to constrict blood vessels Baroreceptor Reflexes Baroreceptor Reflexes Short­Term Mechanisms: Short­Term Mechanisms: Chemical Controls Blood pressure is regulated by chemoreceptor reflexes sensitive to oxygen and carbon dioxide Short­Term Mechanisms: Short­Term Mechanisms: Chemical Controls Prominent chemoreceptors are the carotid and aortic bodies Short­Term Mechanisms: Short­Term Mechanisms: Chemical Controls Reflexes that regulate blood pressure are integrated in the medulla Short­Term Mechanisms: Short­Term Mechanisms: Chemical Controls Higher brain centers (cortex and hypothalamus) can modify BP via relays to medullary centers Short­Term Mechanisms: Short­Term Mechanisms: Chemical Controls Higher brain centers (cortex and hypothalamus) can modify BP via relays to medullary centers Chemicals that Increase Blood Chemicals that Increase Blood Pressure Adrenal medulla hormones – norepinephrine and epinephrine increase blood pressure Chemicals that Increase Blood Chemicals that Increase Blood Pressure Antidiuretic hormone (ADH) – causes intense vasoconstriction in cases of extremely low BP Chemicals that Increase Blood Chemicals that Increase Blood Pressure Angiotensin II – kidney release of renin generates angiotensin II, which causes intense vasoconstriction Chemicals that Increase Blood Chemicals that Increase Blood Pressure Endothelium­derived factors – endothelin and prostaglandin­derived growth factor (PDGF) are both vasoconstrictors Chemicals that Decrease Chemicals that Decrease Blood Pressure Atrial natriuretic peptide (ANP) – causes blood volume and pressure to decline Chemicals that Decrease Chemicals that Decrease Blood Pressure Nitric oxide (NO) – has brief but potent vasodilator effects Chemicals that Decrease Chemicals that Decrease Blood Pressure Inflammatory chemicals – histamine, prostacyclin, and kinins are potent vasodilators Chemicals that Decrease Chemicals that Decrease Blood Pressure Alcohol – causes BP to drop by inhibiting ADH Long­Term Mechanisms: Renal Long­Term Mechanisms: Renal Regulation Long­term mechanisms control BP by altering blood volume Long­Term Mechanisms: Long­Term Mechanisms: Renal Regulation Baroreceptors adapt to chronic high or low blood pressure Increased BP stimulates the kidneys to eliminate water, thus reducing BP Long­Term Mechanisms: Long­Term Mechanisms: Renal Regulation Baroreceptors adapt to chronic high or low blood pressure Decreased BP stimulates the kidneys to increase blood volume and BP Kidney Action and Blood Kidney Action and Blood Pressure Kidneys act directly and indirectly to maintain long­term blood pressure Direct renal mechanism alters blood volume Kidney Action and Blood Kidney Action and Blood Pressure Kidneys act directly and indirectly to maintain long­term blood pressure Indirect renal mechanism involves the renin­ angiotensin mechanism Kidney Action and Blood Kidney Action and Blood Pressure Declining BP causes the release of renin, which triggers the release of angiotensin II Kidney Action and Blood Kidney Action and Blood Pressure Angiotensin II is a potent vasoconstricto r that stimulates aldosterone secretion Kidney Action and Blood Kidney Action and Blood Pressure Aldosterone enhances renal reabsorption and stimulates ADH release Monitoring Circulatory Monitoring Circulatory Efficiency Efficiency of the circulation can be assessed by taking pulse and blood pressure measurements Monitoring Circulatory Monitoring Circulatory Efficiency Vital signs – pulse and blood pressure, along with respiratory rate and body temperature Monitoring Circulatory Monitoring Circulatory Efficiency Pulse – pressure wave caused by the expansion and recoil of elastic arteries Radial pulse (taken on the radial artery at the wrist) is routinely used Variations in Blood Pressure Variations in Blood Pressure Blood pressure cycles over a 24­hour period Variations in Variations in Blood Pressure Extrinsic factors such as age, Variations in Variations in Blood Pressure Extrinsic factors such as sex Variations in Blood Pressure Variations in Blood Pressure Extrinsic factors such as weight Variations in Blood Variations in Blood Pressure Race Variations in Variations in Blood Pressure Extrinsic factors such as race Variations in Blood Pressure Variations in Blood Pressure Mood Variations in Variations in Blood Pressure Posture Alterations in Blood Pressure Alterations in Blood Pressure Hypotension – low BP in which systolic pressure is below 100 mm Hg Alterations in Blood Pressure Alterations in Blood Pressure Hypertension – condition of sustained elevated arterial pressure of 140/90 or higher Alterations in Blood Pressure Alterations in Blood Pressure Transient elevations are normal and can be caused by fever, physical exertion, and emotional upset Alterations in Alterations in Blood Pressure Chronic elevation is a major cause of heart failure, vascular disease, renal failure, and stroke Hypotension Hypotension Orthostatic hypotension – temporary low BP and dizziness when suddenly rising from a sitting or reclining position Hypotension Hypotension Chronic hypotension – hint of poor nutrition and warning sign for Addison’s disease Hypotension Hypotension Acute hypotension – important sign of circulatory shock Threat to patients undergoing surgery and those in intensive care units Hypertension Hypertension Hypertension maybe transient or persistent Hypertension Hypertension Primary or essential hypertension – risk factors in primary hypertension include diet, obesity, age, race, heredity, stress, and smoking Hypertension Hypertension Secondary hypertension – due to identifiable disorders, including excessive renin secretion, arteriosclerosis, and endocrine A thickening and hardening of the arteries, disorders appears in various forms and can be related to a number of different causes Velocity of Blood Flow Velocity of Blood Flow Autoregulation: Local Autoregulation: Local Regulation of Blood Flow Autoregulation – automatic adjustment of blood flow to each tissue in proportion to its requirements at any given point in time Metabolic Controls Metabolic Controls Declining tissue nutrient and oxygen levels are stimuli for autoregulation Metabolic Controls Metabolic Controls Hemoglobin delivers nitric oxide (NO) as well as oxygen to tissues Metabolic Controls Metabolic Controls Nitric oxide induces vasodilation at the capillaries to help get oxygen to tissue cells Metabolic Controls Metabolic Controls Other autoregulatory substances include: potassium and hydrogen ions, adenosine, lactic acid, histamines, kinins, and prostaglandins Myogenic Controls Myogenic Controls Inadequate blood perfusion or excessively high arterial pressure: Are autoregulatory Provoke myogenic responses – stimulation of vascular smooth muscle Myogenic Controls Myogenic Controls Vascular muscle responds directly to: Increased vascular pressure with increased tone, which causes vasoconstriction Reduced stretch with vasodilation, which promotes increased blood flow to the tissue ...
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