Ch 15
Regulation of Blood Pressure: Identify locations of arterial baroreceptors and their functions (fig. 15.14). Explain how the baroreceptor reflex operates in response to (a) increased blood pressure & (b) decreased blood pressure. [refer to the figures to see if you answered (a) correctly; the figures may help you with the answer to part (b)].
Baroreceptors are located in the walls of the carotid artery and aorta. They continuously monitor the pressure of blood flowing to the brain, and fire action potentials at normal blood pressure to the CVCC. (a) Increase in blood pressure will result in AP's firing rate to increase. The CVCC will then increase parasympathetic activity (more ACh released) and lower sympathetic activity (less NE released) to lower heart rate and dilate arterioles. Dilated arterioles will allow for more blood to flow through, and this lowers the MAP. (b)Decrease in blood pressure will result in AP's firing rate to decrease. The CVCC will then decrease parasympathetic activity (decrease in ACh release) and increase sympathetic activity (more NE released). This will constrict the arterioles causing less blood to flow, and this will increase the MAP.
Explain how arterioles regulate the distribution of blood to organs as needed and how vasoconstriction affects resistance and blood flow.
Blood flow to organs is set to some degree by the number and size of arterioles feeding a specific organ. Vasoconstriction of an arteriole will decrease blood flow causing an increase in resistance. This allows for the blood to divert to an arteriole with lower resistance. Blood traveling through arterioles will take the path of least resistance.
Explain how transient (orthostatic) hypotension might occur (refer to pg. 527; p. 535 5th ed.).
When going from a flat position to standing, gravity will pull blood to the lower extremities. This pooling can create a decrease in venous return, so that less blood is in the ventricles at the beginning of the next contraction. Cardiac output will fall, causing arterial blood pressure to decrease. This is orthostatic hypotension. This will normally trigger your baroreceptor reflex, resulting in increased peripheral resistance and increased cardiac output, which together will increase your mean arterial pressure bringing everything back to normal within two heartbeats.
Discuss how the following 3 factors affect resistance of blood vessels to flow: (also a review from Chapter 14). Also see figure 15.11b.
a) blood viscosity - blood viscosity is determined by the ratio of RBC to plasma, and by how much protein is in the plasma. Resistance increases with viscosity. b) resistance to flow - the tendency of the cardiovascular system to oppose blood flow. An increase in the resistance of the blood vessels results in a decrease in flow through that vessel, therefore, blood will take the path of least resistance. c) length of vessels - the resistance to fluid flow increases as the length of the vessel increases.
Discuss how arteries, arterioles, capillaries and veins anatomy relates to their specific functions, with respect to presence of endothelium, elastic tissue, and smooth muscle and one-way valves in the veins (refer to fig. 15.2 & 15.4
All blood vessels contain a thin layer of endothelium, a type of epithelium. Arteries: carry blood AWAY from the heart and are considered to be the pressure reservoir due to their elastic tissue present in the tunica intima. The presence of vascular smooth muscle maintains a state of partial contraction, aka muscle tone, to assist with vasoconstriction (artery diameter narrows) or vasodilation (artery diameter widens) when necessary. Arterioles: blood enters arterioles from the arteries. They create a high-resistance outlet for arterial blood flow. Arteriole walls are thinner than arterial walls, and do not consist of elastic tissue or fibrous tissue. The smooth muscle present helps with vasoconstriction and vasodilation. Capillaries: site of nutrient and gas exchange between the plasma, ISF and cells of the body. The walls consists of only endothelium, making them the smallest vessels in the cardiovascular system. Diffusion and bulk flow occur in the capillaries. Veins: carry blood BACK to the heart from capillaries, and are considered the volume reservoir due to the fact that veins are more numerous than arteries (they hold more than half of the blood in the circulatory system). Vein walls consist of endothelium, elastic tissue, smooth muscle and fibrous tissue, and can easily expand when filled with blood. Some veins contain valves to prevent blood from flowing backwards through the system.
Distinguish between the location, chemical mediator, and action of alpha and beta-2 adrenergic receptors in arterioles; also discuss the purpose of vasogenic (myogenic) tone (fig. 15.11) & how it is maintained.
Alpha Receptor: Located in blood vessel walls such as SM of arterioles of the Gi tract and skin (and some in SKM arterioles). High sensitivity to Norepinephrine(NE) and low sensitivity to Epinephrine(Epi). Function for vasoconstriction (SM contraction) Beta 1 Receptor: Located in myocardium such as cardiac conduction and contractile cells. High sensitivity to Epi and NE. Functions to enhance cardiac muscle contraction force and increase BPM by increasing rate of depolarization. Beta 2 receptor: Located in blood vessel walls such as the SM of the arterioles in the heart, liver, SKM and also found in SM of bronchioles. High sensitivity to Epi and low sensitivity to NE (not innervated by sympathetic neurons, thereby limiting their exposer to NE). Function to vasodilate arterioles (relaxation of SM in blood vessels) and bronchodilation in lungs.
Explain why arterial blood pressure fluctuates in relation to systole and diastole of the left ventricle (fig. 15.6) & how blood volume may affect the BP (fig. 15.9).
Arterial blood pressure fluctuates due to left ventricular systole and diastole. As the blood is pumped into the arteries, the pressure is at its highest, and falls slightly as the left ventricle relaxes. The decrease in pressure is not as much as in the ventricle itself, mainly because the arteries are able to capture and store the energy in their elastic walls. Changes in blood volume will affect blood pressure, i.e. higher blood volume will increase blood pressure and vice versa. Cardiac output would fluctuate depending on an increase or decrease in blood volume.
Briefly describe the functions of arteries, arterioles, capillaries and veins. Discuss how their anatomy relates to their specific functions, with respect to presence of endothelium, elastic tissue, and smooth muscle and one-way valves in the veins (refer to fig. 15.2 & 15.4
Artery: Low amount of Endotheliium, some Elastic tissue, the most Smooth Muscle, and some Fibrous Tissue Arteriole: Low endothelium, some smooth muscle, no elastic tissue or fibrous tissue. Capillary: Low endothelium, no elastic tissue, smooth muscle or fibrous tissue Venule: Low endothelium and fibrous tissue, no elastic tissue or smooth muscle Vein: Low Endotheliium, some Elastic tissue, Smooth Muscle, and Fibrous Tissue
Describe the anatomy of a capillary (Figs. 15.16).
Capillaries have the thinnest walls of all blood vessels allowing the exchange of nutrients and gases across the vessel wall. The wall is composed of a single layer of flattened endothelial cells supported on a basal lamina. Cell junctions between the cells allow for leak channels to be present, and vary within different tissues depending on their need for exchange. There are two types of capillaries, continuous and fenestrated. Continuous capillaries are those whose endothelial cells are connected by leaky junctions, while fenestrated capillaries have large pores that allow high volumes of fluid to pass rapidly between the ISF and plasma.
Explain the concept of compliance of arteries (p. 471 7th ed.; p.500 6th ed.). Describe how it is affected by arteriosclerosis and atherosclerosis (also refer to p. 502 in 7th ed)
Concept of compliance: Arterial compliance is an index of the elasticity of the large arteries C (compliance) = ΔV (change in arterial blood volume) / ΔP (change in arterial blood pressure) Arteriosclerosis: occurs when the blood vessels that carry oxygen and nutrients from your heart to the rest of body (arteries) become thick/stiff — sometimes restricting blood flow to organs & tissues Atherosclerosis: specific type of arteriosclerosis, refers to the buildup of fats, cholesterol and other substances in and on artery walls (plaques), which can restrict blood flow
Compare and contrast the 3 means of capillary exchange: 1) diffusion, 2) transcytosis (vesicle transport) and 3) bulk flow [filtration (=movement out of capillary into ISF) & absorption (=movement into the capillary blood from ISF)].
Diffusion allows for most small dissolved solutes and gases to easily flow between or through endothelial cells. Transcytosis allows for larger proteins and molecules to be transported through the endothelial cells by creating vesicles from caveolae and non-coated pits on the cell surface. In some instances, a chain of vesicles will fuse together to create an open channel that extends across the endothelial cell. Bulk Flow allows for mass movement of fluids through the endothelium as a result of hydrostatic or osmotic pressure gradients. If the direction of bulk flow in into the capillary, then the fluid movement is called absorption, and if the flow is out of the capillary, it is known as filtration
Explain why the velocity of blood flow decreases in the capillaries and then increases when funneling from capillary beds into venules (Fig 15.17).
Due to the cross-sectional area of the capillaries, the velocity of blood flow will decrease. Total cross-sectional area of the capillaries is large, therefore the velocity of blood flow is low. Once the blood flow leaves the capillaries, the cross-sectional area decreases, which will increase velocity of the blood flow. Since nutrient and gas exchange occurs on the capillaries, the slow velocity is ideal for maximum explosive exchange.
Describe how elastic and muscular arteries act as "pressure reservoirs" (fig. 15.5).
Due to the presence of elastic tissue and smooth muscle within the arterial walls, the vessel is able to expand after left ventricular contraction, and release the pressure build up through elastic recoil, thereby sending blood forward through the circulatory system.
Discuss factors that may lead to edema.
Edema - an accumulation of fluid in the interstitial space. Hypovolemia, a decrease in blood volume Blockage of lymphatic system Excessive vasodilation, blood vessels widen decreasing blood pressure
Explain how bulk flow is regulated by hydrostatic pressure and osmotic pressure. Be able to calculate the difference in capillary hydrostatic pressure and colloid osmotic pressure (refer to fig. 15.18).
Hydrostatic pressure is the lateral pressure component of blood flow within the capillary that pushes the blood through the capillary pores. This will decrease along the length of the capillary as energy is lost to friction. The hydrostatic pressure in the ISF is very low, so we consider it to be zero. This means water movement due to hydrostatic pressure will be directed out of the capillary. Osmotic pressure, or more accurately colloid osmotic pressure, is the pressure created by proteins. Since proteins are found in the plasma and not in the ISF, the colloid osmotic pressure will be higher in the plasma, and virtually zero in the ISF. This will favor water movement by osmosis from the ISF into the plasma. The net pressure driving fluid flow across the capillary is determined by the difference between hydrostatic pressure and colloid osmotic pressure. A positive value for the net pressure indicates net filtration, while a negative value indicates net absorption.
Define the terms hypotension and hypertension.
Hypotension - abnormally low blood pressure Hypertension - abnormally high blood pressure
Describe "hypovolemic shock" (see Clinical focus on p. 487 7th ed.; p.519 6th ed.; p. 521 5th ed.), its cause, consequences and how it must be treated.
Hypovolemic shock is a result of the decrease in circulating blood volume. The consequences of hypovolemic shock are low cardiac output and falling peripheral blood pressure. To treat, one must administer oxygen, fluids, and norepinephrine to the patient. NE stimulates vasoconstriction and increases cardiac output.
Describe local controls (refer to Fig. 15.10) over variation in arteriolar resistance to blood flow: myogenic autoregulation, paracrine signals.
Local (Intrinsic) controls affecting arteriolar resistance Myogenic autoregulation is the ability for vascular smooth muscle to regulate its own state of contraction. As blood pressure increases within the arteriole, the smooth muscle fibers within the wall are stretched, and causes the wall to constrict, thereby reducing the blood flow. Paracrine signals can also be used to change arteriole resistance. As an example, when aerobic metabolism increases, tissue O2 levels decrease while CO2 levels increase. The change in gas levels dilates the arterioles and increases blood flow, bringing in more O2 and taking CO2 away. When increase in blood flow is accompanied by an increase in metabolic activity, this is known as active hyperemia.
Compare and contrast lymph and blood.
Lymph is a clear fluid consisting of interstitial fluid, interstitial proteins, and particulate matter such as bacteria. Lymph removes waste from the system. Lymph movement is in a single direction. Lymph is moved along by the normal function of the body. Lymph is purified by lymph nodes. Blood is a red fluid consisting of red blood cells, white blood cells, and platelets suspended in plasma. Blood transports oxygen throughout the body. Blood flows in a circulatory system. Blood is pumped through the circulatory system by the heart. Blood is purified by the kidneys.
List and describe the determinants of MAP (Fig. 15.8). Explain why arterioles act as the major site of variable resistance to blood flow.
Mean arterial pressure (MAP): the driving force for blood flow - Balance between blood flow into the arteries and out of the arteries 1. Inflow → dependent on the force of the left ventricle 2. Outflow → affected by peripheral resistance (from the arterioles) - MAP is α CO x R (R is resistance of arterioles) Arterioles act as the major site of variable resistance due to the large amounts of smooth muscle in the arteriole walls. As the smooth muscle contracts or relaxes, the radius of the arteriole changes.
Microcirculation: Describe the function of metarterioles (figure 15.3) and precapillary sphincters.
Metarterioles can act as a bypass channel, helping to divert blood from the capillary beds and directly into the venous circulation. Precapillary sphincters can close off capillaries in response to local signals. This directs blood to travel from arterioles, to metarterioles, and then directly into the venous circulation. When precapillary sphincters are open, blood will travel through the normal path of arteries, to capillaries, and then to the venous circulation.
Be able to calculate pulse pressure (PP) and mean arterial pressure (MAP) (fig. 15.6 & see p. 483 in 7th ed.).
Pulse Pressure (PP) = SP - DP Mean Arterial Pressure (MAP) = DP + [ (SP-DP) / 3 ] SP = Systolic Pressure DP = Diastolic Pressure Example: SP = 120 DP = 80 PP = 120 - 80 ---> PP = 40 (Yay!) MAP = 80 + (40 / 3) ---> 80 + 13 ---> MAP = 93 (Yay!) Fun Fact! MAP will be closer to DP due to the fact that diastole lasts almost twice as long as systole.
Describe the reflex/extrinsic controls (p. 490 7th ed.; refer to fig. 15.11a) over variation in arteriolar resistance to blood flow.
Sympathetic neurons can secrete NE and Epi to bind to alpha receptors and beta2 receptors respectively. NE binds to alpha receptors causing vasoconstriction, while Epi binding to beta2 receptors causes vasodilation. Constriction will increase resistance while dilation decreases resistance. Which tissues have which receptors? Think of the FFF response. Alpha receptors can be found in GI tract and skin, and Beta2 receptors are found in heart, liver and skeletal muscles. During FFF, blood flow to those organs that will help with reactions is increased, while non-essential organs can have a decrease.
Summarize the association between the cardiovascular system and the lymphatic system. Then explain how the fluid volume of the ECF is maintained in health by capillary exchange and lymphatic activity.
The lymphatic and cardiovascular systems include a network of capillaries and vessels that assist in circulating the body fluids. The lymphatic vessels transport excess fluid away from the interstitial spaces of tissues and return it to the bloodstream. Lymphatic activity is responsible for restoring fluid lost from the capillaries to the circulatory system. Lymph vessels lie close to capillaries and allow for one-way movement of the ISF from the tissues into the circulation. The pathway consists of lymph vessels joining one another, creating lymphatic vessels that progressively increase in size. Lymph nodes are found along the way which contain immunologically active cells including lymphocytes and phagocytes, to rid the fluid of bacteria. The fluids empty through lymph ducts into the internal jugular veins, and return it to the circulatory system.
Identify the determinants of venous pressure & how venous return of blood is enhanced during exercise. (2 of the determinants are discussed in the textbook (p. 483 7th ed.). One other will be discussed in lecture (cardiac suction).
Venous pressure is considered low. Pressure has been dropped leading up to the capillaries to ensure a smooth flow for nutrient exchange. The steady flow of blood from the capillaries helps to push the blood through the veins. During exercise, venous blood is aided by the skeletal muscle pump and the respiratory pump. Muscle contractions help push the venous blood by compressing the veins and forcing blood through the valves within the veins. Also, as your breathing increases, the diaphragm applies pressure on your liver to help propel blood through the veins. A third determinant is when the ventricles relax, they create suction, thereby pulling blood into themselves.
