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56 Cards in this Set
- Front
- Back
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Blood vessel structure and function |
More than pipes for blood, vessels are dynamic, interactive and essential components of the cardiovascular organ system. |
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Blood vessel types |
Arteries: Carry blood away from the heart --Large elastic arteries: Thicker than 1 cm --Medium muscular arteries: Between 0.1-10 mm --Arterioles: Less than 0.1 mm Capillaries: Site of nutrient and gas exchange Veins: Carry blood toward the heart --Venules: Veins smaller than 0.1 mm |
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Vessel wall layers |
Tunic interna (intima): Inner lining in direct contact with the blood. The epithelium of the intima is the same endothelium that makes up the endocardial lining of the heart. Plays an active role in vessel-related activities. Tunic media: Middle layer, chiefly composed of smooth muscle that regulates the diameter of the vessel lumen. Tunic externa: Outer layer, helps anchor vessel to surrounding tissue through use of elastic and collagen fibers. |
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Large elastic arteries |
Best exemplified by the aorta, which is the size of a garden hose. Walls of elastic arteries are thin compared to their overall size. Store mechanical energy during ventricular systole then transmit that energy to keep blood moving after the aortic and pulmonary valves close. |
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Medium muscular arteries |
Smooth muscles help maintain proper vascular tone to ensure efficient blood flow to the distal tissue beds. |
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Arterioles (resistance vessels) |
Deliver blood to capillaries and have the greatest collective influence on both local blood flow and on overall blood pressure. They are "adjustable nozzles" across which the greatest drop in pressure occurs. |
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Anastomosis |
A union of vessels supplying blood to the same body tissue. It is a fail-safe that provides collateral circulation in the case that one branch is blocked. |
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Capillaries |
The only sites in the entire vasculature where gasses, water, and other nutrients are exchanged. The terminal end of an arteriole tapers toward the capillary junction to form a single metarteriole. At the metarteriole-capillary junction the distal muscle cell forms the precapilary sphincter which monitors and regulates blood flow in the capillary bed. The metarteriole becomes the thoroughfare channel to the postcapillary venule and then to the vein. |
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Capillary walls |
Different from other vascular structures in that they are made of only one layer of endothelial cells sitting on a very thin basement membrane. There are no other tunicas, layers or muscles. This allows them to be freely permeable to many substances (gasses, fluids, small ionic molecules). |
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Capillary types |
1. Continuous capillaries: The most common, with endothelial cells forming a continuous tube, interrupted only by small intercellular clefts (gaps between neighboring cells). Found in CNS, lungs, muscles, skin. 2. Fenestrated capillaries: Have fenestrations (pores) that make capillaries more porous. Found in kidney, villi of small intestines, and endocrine glands. 3. Sinusoids: Wider and more winding in shape with large porous channels through with proteins and blood cells can pass from tissue to blood and back. For example, newly formed blood cells enter bloodstream through sinusoids of red bone marrow. |
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Veins |
Compared to arteries of similar size, veins have thinner walls, less muscle and elastic tissue and are designed to operate at much lower pressure. -Intravenous pressure in venules (16 mmHg) is less than half that of arterioles (35 mmHg) and drops to just 1-2 mmHg in some large veins. -Because pressure is so low, veins have valves to keep blood flowing in only one direction. -When exposed to higher than normal pressure, veins can become incompetent (varicose veins) |
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Capillary exchange (diffusion/transcytosis) |
Substances enter and leave capillaries by diffusion, transcytosis and bulk flow. -Diffusion: Most important method. Substances such as O2, CO2, glucose, amino acids, hormones, and others diffuse down their concentration gradients. All plasma solutes except proteins pass freely through across most capillary walls. The exception is the brain where the blood-brain barrier exists. Transcytosis: Some materials cross the capillary membrane via enclosure of substances within vesicles that enter cells by endocytosis. |
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Capillary exchange (bulk flow) |
This is filtration (out of capillaries) and reabsorption (into capillaries) of ions, molecules and particles at a rate faster than diffusion. -Diffusion is more important for solute exchange between plasma and interstitial fluid, bulk flow is more important for regulation of the relative volumes of blood and interstitial fluid. -The movement of water and dissolved substances (except proteins) through capillaries is dependent on hydrostatic and osmotic pressure. -Most of the fluid that leaves at the arterial end of a capillary and returns at the venous end. This is Starling's law of the capillaries. Filtration is the movement of blood through the walls of the capillary into the interstitial fluid. Reabsorption is the movement of fluid from the interstitial fluid back into the capillary. |
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Pressures promoting filtration (out of capillary) |
Blood hydrostatic pressure (BHP): Generated by the pumping action of the heart. Decreases from ~35 to ~16 mmHg from arterial end to venous end of capillary. Interstitial fluid osmotic pressure (IFOP): Constant at 1 mmHg. FBHIO-Federal Bureau of horny intern operations |
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Pressures promoting reabsorption (into capillary) |
Blood colloid pressure (BCOP): Due to the presence of plasma proteins too large to cross the capillary, averages 26 mmHg at each end of capillary. Interstitial fluid hydrostatic pressure (IFHP): Close to 0 mmHg and is only a significant factor in states of edema. RBCIH-Royal Bank of Canada interest hikes |
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Capillary exchange (mechanism) |
Generally filtration outpaces reabsorption slightly. -At the arterial end, net pressure is 10 mmHg and fluid leaves the capillary via filtration. -At the venous end, net pressure is -9 mmHg and fluid enters the capillary via reabsorption. -On average, 85% of filtered fluid is reabsorbed. -Fluid that is not reabsorbed (3L/day for entire body) enters the lymphatic vessels to be eventually returned to the blood. |
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Capillary exchange (mathematics) |
Net filtration pressure = (BHP+IFOP) – (BCOP+IFHP). Really the only variable is BHP, which ranges from 35 to 16. IFOP is steady at 1, BCOP is steady at 26, IFHP is steady at 0. The net will always depend on whether BHP is greater or lower than 25. The BHP variance is caused by the heartbeat and gets lower toward the venous end of the capillary. |
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Hemodynamics (factors affecting blood flow) |
Blood flow: The volume of blood that moves through the entire body or a specific organ during a given time (often in mL/min). -Caused by contractions of the heart and the pressure that is generated as a result. -Blood always flows from areas of high pressure to low pressure. This pressure gradient is needed or blood flow stops. -Blood pressure is highest as it leaves the ventricles and gets lower the farther away it is. |
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Hemodynamics (resistance) |
While the pressure generated by the heart's contractions causes blood to move, the movement is opposed by a factor called resistance. There are 3 factors: 1. Blood viscosity: A high ratio of RBCs in blood can increase blood viscosity as can high plasma protein levels. 2. Total blood vessel length: More vessels = more length = more resistance. Extra blood vessels with adipose tissue tied to higher resistance in obese individuals. 3. Size of blood vessel lumen: Diameter is inversely related resistance and small changes have big effect on resistance. This is the easier factor for the body to change. Adjusting lumen size of arterioles is principal way body controls blood flow to specific organs and tissues. This happens through vasoconstriction/vasodilation. |
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Ohm's Law |
Blood flow = pressure divided by resistance Increasing pressure or decreasing resistance will increase blood flow. Increasing resistance or decreasing pressure will decrease blood flow. |
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Distribution of total blood flow |
Blood flow around the entire body is called total blood flow, this is the same thing as cardiac output. The body can influence how much blood goes to certain regions via the autonomic nervous system's ability to control smooth muscle in blood vessels. For example, during sympathetic response, blood vessels supplying digestive organs constrict while those supplying skeletal muscles dilate. |
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Arterial blood pressure |
When people talk about blood pressure they are talking about arterial blood pressure. It represents pressure in the arteries (but not the arterioles). |
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Blood pressure measurement |
Expressed as systolic pressure over diastolic pressure. The systolic pressure is the level at which blood vessels can begin to pump against pressure. The diastolic pressure is when they no longer register against lower pressure. The systolic pressure is while the ventricles are contracting. The diastolic pressure is while the ventricles are relaxed. |
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Mean arterial pressure |
MAP=SP + 2DP/3 Because the heart spends more time in diastole, they MAP is closer to diastolic pressure. MAP=COxSVR MAP is directly related to cardiac output and systemic vascular resistance. |
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Factors influencing cardiac output |
-Increased heart rate -Increased stroke volume -Increased venous return -Increased sympathetic impulses/hormones from adrenal medulla -Decreased parasympathetic impulses -Increased blood volume -Skeletal muscle pump -Respiratory pump -Venoconstriction |
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Factors influencing systemic vascular resistance |
-Increased blood viscosity -Increased blood vessel length -Vasoconstriction -Increased number of RBCs -Increased body size (obesity) |
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Venous return (overview) |
The volume of blood flowing back to the heart through the systemic veins. Venous return impacts stroke volume, and thus cardiac output. Venous return is due to pressure generated by contractions of the left ventricle. There is only a small difference between the venules (16 mmHg) and the right ventricle (0 mmHg). |
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Venous return (3 factors) |
1. Valves: Found in all but the largest veins, they ensure blood only flows in one direction. 2. Skeletal muscle pump: Uses the actions of muscles to milk blood back to heart 3. Respiratory pump: During normal breathing, alternating negative pressures in the thoracic and abdominal cavities work to pull venous blood toward the heart. |
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Velocity of blood flow |
Velocity is inversely related to the total cross-sectional area of blood vessels. The aorta is wide but its only one vessel. When compared to all the capillaries its cross-sectional area is small. Thus aorta is fastest and capillaries are slowest. |
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Cardiovascular center |
A group of neurons in the medulla that regulates heart rate, contractility, and blood vessel diameter. Receives input from higher brain and sensory receptors, and output flows from the CV system flows along sympathetic and parasympathetic fibers. |
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Cardioaccelerator nerves |
Sympathetic impulses from CV center increase heart rate and contractility |
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Vasomotor nerves |
Sympathetic impulses continuously sent to smooth muscle in blood vessels via vasomotor nerves that dictate state of tonic contraction or vasoconstriction, aka vasomotor tone. |
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Vagus nerves |
Parasympathetic impulses from CV center flow through vagus nerve and decrease heart rate. |
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Baroreceptors |
Important pressure-sensitive sensory neurons that monitor stretching of the walls of the blood vessels and atria. If blood pressure falls, baroreceptor reflexes accelerate heart rate, increase force of contraction and promote vasoconstriction -- all of which increase blood pressure. |
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Carotid sinus reflex |
Baroreceptors in carotid sinus maintain normal blood pressure in the brain and is initiated by baroreceptors in the walls of the carotid sinus. |
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Aortic reflex |
Baroreceptors in wall of ascending aorta and aorta arch that monitor general systemic blood pressure. |
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Blood pressure chemoreceptors |
Located close to baroreceptors, these receptors monitor levels of O2, CO2, pH in blood and send signals to CV center and respiratory center. |
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Hormonal regulation of blood pressure |
Hormones in blood alter cardiac output, systemic vascular resistance or total blood volume. 4 hormones/systems at play: 1. RAA system (aldosterone) 2. Epinephrine, norepinephrine 3. Antidiuretic hormone 4. Atrial natriuretic peptide |
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RAA system |
Renin is released by kidneys when blood volume falls or blood flow decreases. This leads to the formation of angiotensin II while raises BP by vasoconstricting and stimulating secretion of aldosterone from the adrenal glands, which raises BP by causing kidneys to retain Na+ and water. |
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Epinephrine/norepinephrine |
Released from adrenal medulla in response to sympathetic stimulation. Increase cardiac output by increasing rate and force of contractions. Vasoconstriction to GI tract organs and vasodilation to skeletal and cardiac muscle. |
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Antidiuretic hormone |
Released from posterior pituitary in response to dehydration or decreased blood volume. Causes increased water retention, which raises BP. |
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Atrial natriuretic peptide |
Released by cardiac atria when BP is high and lowers BP by vasodilation and reducing blood volume by promoting loss of Na+ and water in urine. |
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Autoregulation of blood pressure |
The ability of tissue to automatically adjust its own blood flow to match its metabolic demand for supply of O2 and nutrients and removal of waste. Oxygen is usually the stimulus for autoregulation. Temperature changes can also cause autoregulation. Warm temps vasodilate, cool temps vasoconstrict. Additionally, WBCs, platelets and endothelial cells can release chemicals that vasodilate/vasoconstrict |
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Checking circulation |
Accomplished by checking the pulse. It is a result of the alternating expansion and recoiling of elastic arteries after each systole. Normal resting heart rate is 70-80 BPM. |
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Tachycardia |
Resting heart rate over 100 BPM |
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Bradycardia |
Resting heart rate below 50 BPM |
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Pulse points |
Wrist: radial artery Bicep: brachial artery Neck: common carotid artery Corner of mouth: facial artery Ear: Superficial temporal artery Thigh: Femoral artery Back of knee: Popliteal artery Top of foot: Dorsalis pedis artery |
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Measurement of blood pressure |
Blood pressure is measured with a sphygmomanometer, usually at one of the brachial arteries. The various sounds that are heard are the Korotkoff sounds. Normal BP in males is 120/80. In females its 8-10 mmHg less. |
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Pulse pressure |
The difference between the systolic and diastolic pressure. Average is 40. |
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Shock and homeostasis |
Shock is the failure of the cardiovascular system to deliver adequate amounts of oxygen and nutrients to meet the metabolic needs of body cells. As a result, cell membrane dysfunction occurs, cellular metabolism is abnormal and cellular death may occur. Signs of shock include clammy, cool, pale skin; tachycardia; weak, rapid pulse; sweating; hypotension; systolic pressure less than 90 mmHg; altered mental state; decreased urinary output; thirst |
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Hypovolemic shock |
Due to decreased blood volume. Response would be activation of RAA system, secretion of ADH, activation of the sympathetic division of ANS and release of local vasodilators. |
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Cardiogenic shock |
Due to poor heart function |
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Obstructive shock |
Due to obstruction of blood flow |
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Vascular shock |
Due to excess vasodilation. Seen in cases of massive allergy or sepsis. Septic shock causes more than 100K deaths per year and is the most common cause of death in hospital critical care units. |
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Circulatory routes |
Pulmonary circulation leaves the right ventricle and carries deoxygenated blood to the lungs to offload CO2 and pick up O2. Systemic circulation leaves left ventricle and supplies oxygenated blood to the entire body. Includes various subdivisions such as coronary circulation, cerebral circulation and hepatic portal circulation. |
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Hepatic portal circulation |
Collects blood from the veins of the pancreas, spleen, stomach, intestines, and gallbladder and directs it into the hepatic portal vein of the liver before it returns to the heart. This allows for nutrient utilization and blood detoxification in the liver. Splenic vein and superior mesenteric vein come together as hepatic portal vein. This feeds into the liver and into hepatic vein and then inferior vena cava. |
