PSL301 Lecture 7 2022 PDF

EXERCISE, CAPILLARY EXCHANGE, AND THE LYMPHATIC SYSTEM Silverthorn, 7th ed. pp 496-502 Silverthorn, 8th ed. pp 495-502  Cardiovascular Responses to Exercise 1) Increase in venous return and respiratory pump 2) Increase in sympathetic activity, withdrawal of parasympathetic activity - Neuro...

EXERCISE, CAPILLARY EXCHANGE, AND THE LYMPHATIC SYSTEM Silverthorn, 7th ed. pp 496-502 Silverthorn, 8th ed. pp 495-502  Cardiovascular Responses to Exercise 1) Increase in venous return and respiratory pump 2) Increase in sympathetic activity, withdrawal of parasympathetic activity - Neuromuscular junctions in skeletal muscle send signals to the CCC - effects on HR + contractility, resistance arterioles in metabolically inactive tissues 3) Local metabolites mediate profound vasodilation in skeletal muscle (reduced TPR) Cardiovascular responses to Exercise Review: think about how blood flow gets divided as it passes through the CV system Capillaries have the slowest velocity of blood – WHY? Velocity of flow depends on total cross-sectional area of ALL the vessels at that same level in the CV system. Figure 15-18 Practical Example- this tube shows how blood velocity is inversely proportional to the cross-sectional area Flow rate (Q) = 12 cm3/min Flow rate (Q) 12 cm3 Velocity (v) = Cross-sectional area (A) At point X At point Y Flow 12 cm3/min 12 cm3/min v= v= X 1 cm2 12 cm2 A = 1 cm2 Y v = 12 cm/min v = 1 cm/min A = 12 cm2 The narrower the vessel, the faster the velocity of flow. FIGURE QUESTION If the cross-sectional area of this pipe is 3 cm2, what is the velocity of the flow? Capillaries: exchange site for nutrients and waste exchange materials occurs across the very thin capillary wall Capillary density is related to metabolic activity of cells [Bone marrow, liver and spleen do not have typical capillaries but sinusoids]; LARGE openings Over 10 billion capillaries with surface area of 500-700 m2 performing solute and fluid exchange. Two Types of Capillaries Continuous: Nucleus Muscle, brain Endothelial cells Endothelial cell junctions Basement Transcytosis membrane vesicles (a) Continuous capillaries have leaky junctions. Figure 15-17a Two Types of Capillaries Fenestrated ‘Leaky’: high volumes Fenestrated Kidney, intestine pores Basement membrane (cut) Transcytosis vesicles Fenestrations or pores Endothelial cell junction Basement membrane (b) Fenestrated capillaries have large pores. Figure 15-17b Capillary Exchange: HOW do substances move?? Exchange between plasma and interstitial fluid can occur by paracellular (in between cells- through cell-cell junctions) pathways Larger solutes and proteins move by vesicular transport (transcellular- through apical and bosolateral membranes of cells) In most capillaries, large proteins are transported by transcytosis Small dissolved solutes, H2O, and gases move by DIFFUSION Solute and Fluid Exchange Across Capillaries Most important means by which substances are transferred between plasma and interstitial fluid is by diffusion. Lipid soluble substances diffuse directly through cell membrane of capillaries (i.e.,CO2, O2). Lipid insoluble substances such as H2O, Na+, Cl-, and glucose cross capillary walls via intercellular clefts. Concentration differences across capillary enhances diffusion. Effect of Molecular Size on Passage Through Capillary Pores The width of capillary intercellular slit pores is 6 to 7 nanometers. The permeability of the capillary pores for different substances varies according to their molecular diameters. Relative Permeability of Muscle Capillary Pores to Different-sized Molecules Substance Molecular Weight Permeability Water 18 1.00 NaCl 58.5 0.96 Urea 60 0.8 Glucose 180 0.6 Sucrose 342 0.4 Insulin 5000 0.2 Myoglobin 17,600 0.03 Hemoglobin 69,000 0.01 Albumin 69,000.0001 Capillary Exchange: final forces for transfer Bulk flow = Mass movement of fluid as a result of hydrostatic or osmotic pressure gradients Absorption: fluid movement into capillaries Filtration: fluid movement out of capillaries hydrostatic pressure Net filtration at arterial end Determinants of Net Fluid Movement across Capillaries Capillary hydrostatic pressure (Pc): forces fluid outward through the capillary membrane. Interstitial fluid pressure (Pif): opposes filtration when value is positive. Determinants of Net Fluid Movement across Capillaries Plasma colloid osmotic pressure (π p/c): opposes filtration causing osmosis of water inward through the membrane Interstitial fluid colloid pressure (π if): promotes filtration by causing osmosis of fluid outward through the membrane Overall ‘Net Pressures’ = (Pc + Pif) + (π p/c + π if) Fluid Exchange at a Capillary Hydrostatic pressure and osmotic pressure regulate bulk flow Net Flow Out > 3 L/day Figure 15-19a Example- Typical Net Forces in Capillaries Net filtration pressure of 0.3 mmHg Filtration coefficient of 10 ml/min/mmHg Results in net filtration rate of (10*0.3) = 3ml/ min for entire body = 4.32 L/day Where does all that fluid go ??? Review Question: In a patient with left-side heart failure, the pulmonary capillary pressure is 27 mmHg, the average interstitial pressure is -1 mmHg, and the colloid osmotic pressure gradient is 19 mmHg in favor of absorption. What is the direction of fluid movement and the net driving pressure? A) absorption, 7 mmHg B) Absorption, 9 mmHg C) Filtration, 7 mmHg D) Filtration, 9 mmHg E) there is no net fluid movement Hint: pressures have directionality (think of vectors with +/- signs) Net pressure= (Pc + Pif) + (π p/c + π if) If we set outward pressure vector (filtration) as positive Net pressure = (27 + 1) + (-19) = 9 mmHg or 9 mmHg filtration (outward) Fluid Exchange at a Capillary Venule Arteriole Net filtration Net absorption Lymph vessels (b) Relationship between capillaries and lymph vessels Figure 15-19b Lymphatic System: multifunctional! Returning fluid and proteins to circulatory system Picking up fat absorbed and transferring it to circulatory system Serving as filter for pathogens Lymphatic System Thoracic (left lymph) duct Lymphatics of A route by which fluid and Cervical lymph nodes upper limb protein can flow from Right lymph duct interstitial spaces to the blood Thymus Axillary lymph nodes Thoracic duct Lymphatics of prevent edema mammary gland Lumbar lymph nodes Spleen Lymph is derived from Pelvic lymph nodes interstitial fluid Inguinal lymph nodes Plays important role in the Lymphatics immune system of lower limb Eventually drain into the Blind-end lymph capillaries in the tissues Subclavian veins à heart. remove fluid and filtered proteins. Lymph fluid empties into the venous circulation. Edema: Fluid buildup/swelling High Pcap Causes Inadequate drainage of lymph Filtration >>> absorption Can happen in XX ANY vascularized tissue Think about what would happen if pressure in the peripheral veins increased – for example as might happen in heart failure Edema: one case of pathology Elephantiasis: abnormal enlargement of any part of the body due to obstruction of the lymphatic channels in the area small parasitic roundworms Reside in lymph channels! Transmitted by mosquito ~20 million people worldwide Edema: one case of pathology XX Obstruction of the lymphatic channels in the area Ascites: Fluid in the abdomen (peritoneal cavity) Kwashiorkor: "the sickness of the child who is displaced from the breast." Mechanism? Ascites: Fluid in the abdomen (peritoneal cavity) XX Ascites Liver Cirrhosis: 1. alcoholism, Hepatitis, fatty liver disease, acetaminophen 2. Decreased function of the liver: 3. liver is the major producer of what ??! Mechanism? Ascites Liver Cirrhosis: XX Capillary exchange summary Two main types of capillaries; sinusoids are variant Pressure gradients in the capillaries drive filtration and absorption Protein concentrations in the capillary and interstitium are critical Be able to calculate the pressure forces that result in fluid movement Lymphatic tissues operate to return/reclaim fluid from the interstitial space Alterations along the way: pathology