Cardiovascular Study Guide (Week 5) PDF

Study Guide Cardiovascular System (Week 5) NOTE – The nature of this material is a bit “circular” – so there are areas of this study guide that introduce a topic, and then separate sections which expend further upon it. Sections 5A (Fluid Compartm...

Study Guide Cardiovascular System (Week 5) NOTE – The nature of this material is a bit “circular” – so there are areas of this study guide that introduce a topic, and then separate sections which expend further upon it. Sections 5A (Fluid Compartments) and 5B (Filtration and Reabsorption) A. Fluid volumes and compartments 1. Organize the body’s fluid into compartments, and rank the volume within each compartment i. Intracellular fluid (MOST FLUID IN BODY) ii. Extracellular Fluid (a) Vascular Compartment (THIRD LARGEST FLUID COMPARTMENT) (a) Plasma is the fluid in this compartment (i) 99% of plasma is water 1. Electrolytes are dissolved in this water (ii) Remaining 1% is proteins (“plasma proteins”) 1. Albumin (most abundant) a. Transports various hormones and drugs 2. Globulins a. Incudes immunoglobulins (like IgG) 3. Fibrinogen a. For blood clotting (b) Interstitial Fluids (SECOND LARGEST FLUID COMPARTMENT – DETAILS IN NEXT SECTION) (a) Water and dissolved electrolytes (i) Remember, these water molecules are in between the various structural molecules which make up the interstitial space (collagen, proteoglycans, etc.) (ii) Because this fluid is between these proteins, it is in “gel” form (b) Normally, no protein in the fluid itself B. Interstitium 1. Define interstitium, interstitial fluid, and tissue gel i. Interstitium – Space between cells ii. Interstitial fluid – Fluid in the interstitium iii. Tissue gel – Combination of proteoglycans and the fluid trapped within them 2. Describe the role of proteoglycans in the interstitial space i. Provide structure to the interstitum, along with collagen ii. Interact with water molecules to create a gel (a) Slow diffusion of water molecules rather than rapid movement 3. Compare free fluid concentration in normal tissue versus edematous tissue i. Normal tissue or mild edema (a) Very little free fluid (b) Most of fluid is in the form of tissue gel ii. Moderate to severe edema (a) Considerable free flowing fluid, not trapped between proteoglycans C. Basics of fluid movement between compartments 1. Briefly describe how fluid moves between the VASCULAR and INTERSTITAL compartments i. Water (with electrolytes) is FILTERED out of the capillaries into the interstitial fluid ii. Water (with electrolytes) is REABSORBED from the interstitial fluid back into the capillaries (a) 90% of the fluid that is FILTERED from the capillaries is then REABSORBED (b) Remaining 10% goes back via lymphatic vessels iii. Starling’s forces determine this movement (see Separate section) iv. Electrolytes are NOT a major influence of movement between VASCULAR and INTERSTITIAL compartments 2. Briefly describe how fluid moves between the INTERSTITIAL and INTRACELLULAR compartments i. Fluid (including electrolytes) moves between interstitium and the cell via various CHANNELS and TRANSPORTERS ii. Electrolyte concentration DOES influence fluid movement (a) Concentration gradients influence if electrolytes move into or out of cells (b) Water movement is dependent on cell osmolarity (which is dependent on ions inside and outside the cells) D. Fluid Filtration 1. Briefly describe the role of plasma proteins in maintaining blood volume, including the relative contribution of albumin to this i. Cause osmotic pressure (also known as “oncotic pressure”) (a) “Colloid osmotic pressure” is specific to plasma proteins (b) Plasma proteins do not diffuse through capillaries (a) Plasma proteins in the capillaries “pull” fluid (water + electrolytes) from the interstitium back into the plasma ii. Albumin is responsible for 80% of colloid osmotic pressure (a) Remember, albumin is made in the liver! (b) If we have any sort of liver dysfunction, it can influence how much albumin is in the blood, and thus influence fluid movement! 2. Describe the four Starling forces acting on fluid in blood, including their normal direction i. Capillary hydrostatic pressure (a) Generally outward (promotes filtration) (b) Think of this as “mechanical pressure” (a) The physical force of the fluid in the capillaries pressing against the walls of the capillaries (i.e., to escape out of the capillaries) (b) In other words, the higher the “blood pressure” in the capillary, the higher the capillary hydrostatic pressure will be ii. Interstitial fluid pressure (a) Generally inward (promotes absorption) (a) Think of this as the physical force of the fluid in the interstitium pushing against the walls of the capillaries (i.e., to go back into the capillaries) iii. Plasma colloid osmotic pressure (a) Generally inward (promotes absorption) (a) Think of this as a “magnet” in the capillaries pulling fluid out of the interstitium back into the capillaries  iv. Interstitial fluid colloid osmotic pressure [USUALLY NOT PRESENT] (a) Generally outward (promotes filtration) (a) This would only happen if there are proteins within the interstitial fluid, and that is normally not the case (b) If there were proteins in the interstitial fluid, this force would be like a “magnet” pulling fluid out of the capillaries and into the interstitium 3. Relate arterial and venous capillary pressure to net filtration and net reabsorption of fluid i. Net filtration pressure at the venous end of the capillary (the distal end) is lower than at the arterial end of the capillary (the proximal end) (a) Fluid is generally FILTERED out of the capillary near arterial end (proximal end) (a) Capillary hydrostatic pressure is MUCH higher than interstitial fluid pressure and colloid osmotic pressure (b) This high hydrostatic pressure pushes fluid out of the capillary and into the interstitium (b) Fluid is generally REABSORBED back into blood near the venous end (distal end) (a) Capillary hydrostatic pressure is lower at the venous end (distal end) (i) In part, this is because a bunch of fluid in the capillary was previously pushed out from the proximal end! So (b) Plasma colloid osmotic pressure is higher at the venous end (i) This is because the proteins are more concentrated, since fluid was pushed out of the capillary (c) Interstitial pressure is also higher towards the venous end (i) This is because fluid has been pushed out the capillary at the proximal part and into the interstitium – since there is more fluid in the interstitium, that means pressure is higher (d) So, the combination of high plasma colloid osmotic pressure (pulls fluid into capillary) and increased interstitial fluid pressure (pushes fluid into capillary) ultimately means more fluid moves from the interstitium into the capillary at the venous end ii. Greater arterial pressure generally yields greater net filtration by increasing capillary hydrostatic pressure (a) In other words, pressure in the aorta is increased, that would increase pressure in the arteries, which would increase pressure in the arterioles, which will increase capillary hydrostatic pressure – and thus, increase filtration iii. Increased venous pressure can ultimately reduce reabsorption of fluid in the venous capillaries, thus increasing net filtration of fluid (a) If venous pressure is elevated, it is harder for fluid to get out of the interstitium and back into the capillaries 4. Compare the general magnitude of fluid reabsorbed through venous capillaries to that entering lymphatic vessels i. Under normal conditions, ~90% of fluid which was filtered out at the arterial end of the capillaries is reabsorbed at the venous end ii. Thus, only about 10% of the fluid filtered out from the arterial end of the capillaries is circulated through the lymphatic system E. Lymphatic System 1. Relate changes in interstitial fluid volume and pressure to lymph flow i. Greater interstitial fluid volume causes greater interstitial fluid pressure (a) Increased interstitial fluid pressure causes greater lymph flow (a) However, interstitial fluid pressure >~2mmgHg fails to increase flow further (i) So, when the interstitium is packed with LOTS of fluid, there becomes a point at which the lymphatic vessels are running at full capacity and cannot keep up with removing the fluid (ii) This will result in edema 2. Name the factors which are responsible for lymphatic pumping i. Contraction of lymph vessel walls (a) Smooth muscle automatically contracts when lymphatic vessels stretched ii. Rhythmic compression of lymphatic vessels (a) Skeletal muscle contraction (b) Movement (c) Arterial pulsation (d) External compression F. Edema 1. State the two VERY broad causes of extracellular edema, and provide clinical examples of edema for each i. Increased fluid filtration (a) Examples – Anything which increases vascular permeability (more “leakage” from capillaries) (a) Example – histamine (i) Think of somebody having an allergic reaction and having a puffy face – THAT is in part from histamiine (b) Example – inflammatory response (c) Example – capillary damage (burns) ii. Decreased fluid reabsorption (a) Examples – Anything which increases venous resistance (and thus pressure) (a) Blood clots (b) Heart failure (blood can’t get out of heart, so it backs up in the veins, which backs up to the capillaries) (c) Localized external compression (e.g., applying a tourniquet) (b) Examples – Anything which slows / stops lymphatic flow (a) Tumors which block lymph flow (b) Surgery which removes lymph vessels (mastectomy is common example) (c) Parasitic worms in lymphatic vessels (elephantitis) iii. (Or a combination of both of these) 2. Differentiate between pitting edema and non-pitting edema, including the mechanism accounting for differences in tissue compliance i. Edema – accumulation of fluid in the interstitial space (a) NOTE: We are talking about EXTRAcellular edema here. It is also possible to have INTRAcellular edema, but we are not covering that here  ii. Pitting Edema – so much fluid has accumulated in the interstitium that the fluid is no longer in gel form, but rather as free fluid (a) Remember, normally the proteoglycans and water bind to form gel (b) Pitting edema is like having “puddles” of water in the interstitial space (c) It is called “pitting” because if you press your finger into the site of edema, hold it a few seconds, and then remove it, the area remains indented (the “pit”) (a) The reason for this is because the pressure from the finger pushed those “puddles” out into the surrounding area Section 5c (Vascular Function) G. Relate how distensibility of arteries and veins relates to their respective anatomy and how a change in volume influences a change in pressure 1. Arteries and arterioles have more (thicker) smooth muscle layer compared to veins and venules 2. Thinner walls in veins means that veins have greater distensibility than arteries and arterioles i. In other words, veins expand more for a given blood pressure than arteries do ii. Thus, veins serve as a reservoir for blood (a) More blood is found within veins in our body than in the arteries H. Compare the relationship between volume and pressure in the arterial and venous systems 1. Small changes in volume have a major effect in arterial pressure i. In other words, if we add more blood to the body, this will ultimately cause a significant increase in arterial blood pressure, since the arteries are not as distensible 2. Large changes in volume have a small effect on venous pressure i. In other words, if we add more blood to the body, this will ultimately have LITTLE effect on venous blood pressure, since the veins will just expand outwards I. Briefly describe how aortic distensibility influences systemic circulation 1. Aorta fills with blood during systole and distends 2. During diastole, the aorta recoils i. This recoil means that the aorta is applying inward pressure against the blood ii. This forces blood to move to sites of lower pressure iii. Because of the aortic value, blood can only move away from the heart iv. So, the elastic recoil of the aorta keeps blood moving throughout the systemic circulation even during cardiac diastole (i.e, blood continues to move in the arteries even when the heart is “relaxed”) J. Define pulse pressure 1. The difference between systolic arterial blood pressure and diastolic arterial blood pressure 2. For example, if systolic arterial blood pressure is 120mmHg and diastolic arterial blood pressure is 80mmHg, pulse pressure is 40mmHg (120-80=40) K. Briefly describe how pulse pressure is clinically interpreted 1. A high pulse pressure is called a “bounding” pulse i. It means there is a large difference between systolic and diastolic arterial pressure, but does not tell us why: (a) This could be a high systolic with normal diastolic (a) Example: A healthy exercise BP of 140/80 (pulse pressure 60)  (b) This could be elevated systolic and diastolic, but systolic is elevated way more than diastolic (a) Example: Hypertension with a BP of 150/90 (pulse pressure 60) (c) This could be a normal systolic with low diastolic (a) Example: Normotensive with a BP of 120/60 (pulse pressure of 60) 2. A low pulse pressure is called a “thready” pulse i. It also does not tell us why, similar to above ii. Clinically, it is MOST likely to be due to a LOW SYSTOLIC pressure, rather than a high diastolic pressure L. Name the two MAJOR factors which influence arterial pulse pressure, and relate how changes in these ultimately influence pulse pressure 1. Stroke volume i. Greater SV means greater rise and fall of pressure ii. Remember, stroke volume depends on a few factors (covered separately in greater detail): (a) Cardiac contractility (how hard the heart is contracting) (b) Afterload (how much resistance the ventricle has to overcome to get the blood out into the aorta) 2. Compliance of the arterial tree i. Noncompliance increases arterial pressure ii. This is related to sympathetic nervous system activation (covered in greater detail separately) (a) Sympathetic nervous system activation generally causes arterial/arteriolar vasoconstriction (b) This means the arteries/arterioles become LESS distensible (MORE rigid) (c) This generally increases systolic arterial pressure (more than diastolic arterial pressure) (a) That increases pulse pressure M. Explain why mean arterial pressure is not simply the average of systolic and diastolic pressure at rest, and how this changes with high heart rates (e.g. during exercise) 1. More time is spent in diastole than systole i. This means that diastole contributes more to the average pressure than systole does 2. During exercise, the relative time spent in diastole decreases N. State the normal value for right atrial pressure, and briefly describe why this matters 1. Approximately