Cardiovascular System Lecture 12: Exercise, Capillary Exchange and the Lymphatic System PDF

Cardiovascular System Lecture 12: Exercise, Capillary Exchange and the Lymphatic System Cardiovascular Responses to Exercise  Local effects on the tissues that need to be fed with nutrients and oxygen  Global sympathetic effect that is driving the blood faster 1. Increase in venous return and resp...

Cardiovascular System Lecture 12: Exercise, Capillary Exchange and the Lymphatic System Cardiovascular Responses to Exercise  Local effects on the tissues that need to be fed with nutrients and oxygen  Global sympathetic effect that is driving the blood faster 1. Increase in venous return and respiratory pump a. Skeletal and respiratory pump bring blood back to the heart to increase filling 2. Increase in sympathetic activity, withdrawal of parasympathetic activity a. Neuromuscular junctions in skeletal muscle send signals to the CCC b. Effects of HR and contractility, resistance arterioles in metabolically inactive tissues 3. Local metabolites mediate profound vasodilation in skeletal muscle (reduced TPR)  Net Effect: reduction in the total peripheral resistance o Opening all the vessels in the skeletal muscles causes the global total peripheral resistance to be reduced Cardiovascular Responses to Exercise  Resting vs. Exercising the blood flow is redistributed o Profound redistribution of an enhanced cardiac output o Purpose of the system during exercise is to drive blood to the skeletal muscles (88%) and the heart (4%) o Body has taken the materials (metabolites) to open the blood vessels in the tissues that are metabolically active  Opening the blood vessels causes tissues that are not active to be closed o Sympathetic nervous system squeezes down on the capillary beds that don’t need the blood right away  Treadmill o Early in the workout, individuals will experience cold and clammy hands and arms  Directly due to the sympathetic activity as the skin arterioles squeeze in response to the increase of blood needed elsewhere in the body  Swimming o When you eat a meal all of the gut arterioles open up o Swimming causes individuals to activate the skeletal muscles o The gut will shut down and have reduced blood flow resulting in severe cramping  Ventricular Filling o “If you increase heart rate you reduce the amount of time to fill the ventricles”  effects the ventricular filling and the stroke volume o When you are exercising the sympathetic system is activated  Venous return is higher – pushing more blood into the heart  Frank-Starling means more blood will be pumped out  Will be able to pump more forcefully during systole as contractility has increased  Stroke volume has increased despite the heart having less time during ventricular filling o Counter balance with all the other factors  Mean arterial pressures increase during exercise o What happens to the baroreceptors?  The more you exercise the more you tune your body to an exercised state o Resetting of the baroreceptors o Behave differently because the body recognizes not o bring the BP down to resting right away as it is a benefit when exercising to have a higher MAP  Better profusion through the tissues  Three theories to how this happens o Sympathetic activity causes them to think higher pressures are normal  Body gets used to the changes in BP This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:52 GMT -06:00 https://www.coursehero.com/file/31079957/Lecture-12docx/ Cardiovascular System Baroreceptor transmission is blocked during exercise  May be sending the signals but the brain is not receiving the signals o Chemoreceptor (low pH) signals outweigh baroreceptor signals  Other section of the medulla that is sensitive to chemicals rather than temperature  Recognize the lower pH that is generated during exercise due to increased CO2 concentration  May counter the baroreceptor signals One or all of these factors could be working together to make the baroreceptors think that the increased MAP during exercise is normal o  Capillaries: Exchange  Primary place in the body where nutrients are exchanged  Exchange materials across thin capillary wall – 1 cell layer thick composed of flattened endothelial cells supported on a basal lamina o Oxygen is in very close proximity to the tissues that it needs to get into  Capillary density is related to metabolic activity of cells o More metabolically active tissues have denser capillary networks o Muscles and glands have the highest capillary density while subcutaneous tissue and cartilage have the lowest  Bone marrow, liver, and spleen do not have typical capillaries but sinusoids; LARGE openings o Fenestrated o Proteins and nutrients that these organs needs are different than the rest of the body so must have different types of capillaries to accommodate  Over 10 billion capillaries with surface area of 500-700m2 performing solute and fluid exchange Two Types of Capillaries Continuous  These capillaries are found in muscle, connective tissue, and neural tissue  Made up of 1 type of cell – endothelial cell o Lines the rest of the blood vessels throughout the body o 1-cell layer thick o Tube made up of endothelial cells that are joined together  The cells are joined together through cell-cell junctions o Points where the two endothelial cell contact one another  Have a basement membrane o Cells produce this sort of matrix that holds the capillary together  Vesicles are used for transport, move materials from the apical side of the cell to the basolateral side o Basolateral is near the basement membrane and the apical side is near the capillary and blood o Transport materials from one side to the other  The continuous capillaries of the brain have evolved to form the blood-brain barrier, with tight junctions that protect the neural tissue from toxins that may be in the bloodstream Fenestrated This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:52 GMT -06:00 https://www.coursehero.com/file/31079957/Lecture-12docx/ Cardiovascular System        Non-continuous and leaky Fenestrated—have pores large enough to allow high volumes of fluid to pass through Majority of capillaries don’t allow proteins to escape into the extracellular fluid In tissues like the liver (important in processing and handling proteins) have specialized capillaries Also have vesicles and endothelial junctions, primary difference are the fenestrations Found in the kidney and intestines where they are associated with absorptive transporting epithelia The bone marrow, liver, and spleen have modified vessels called sinusoids o Sinusoids have large fenestrations that allow extremely large proteins to cross the endothelium barrier into the blood Capillary Exchange  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 basolateral membranes of cells) o Ensures that proteins do not interact with parts of the membrane o In most capillaries, large proteins are transported by transcytosis  Small dissolved solutes, H2O, and gases move by DIFFUSION o Diffusion rate for dissolved solutes id determined primarily by the concentration gradient between the plasma and the interstitial fluid o Important to have the capillary at 1 cell layer thick o Can occur paracellularly for molecules that cannot pass through the membrane of the cell Capillary Exchange: Final Forces for Transfer  Important in the CV system to ensure that everything gets where it needs to be o All of the fluid returns back to the CV o Ensure that we don’t lose any blood volume  Bulk Flow: Mass movement of fluid as a result of hydrostatic or osmotic pressure gradients – has 2 components o Absorption: fluid movement into capillaries o Filtration: fluid movement out of capillaries  Fluid movement is driven by pressure gradients o Hydrostatic pressure (blood pressure)  Pressure of the blood at the arterial end of the capillary  Input pressure of the capillary is driven by the arteriolar pressure o Net filtration at the arterial side of the capillary o Net absorption at the venous side of the capillary 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 the cell membrane of capillaries (i.e. CO 2, O2)  Lipid insoluble substances such as H2O, Na, Cl, and glucose cross capillary walls via intercellular clefts  Concentration differences across capillaries 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  Capillaries in different tissues have extreme differences in their permeability’s o Water has maximum permeability (very small) o As size and polarity increases the permeability decreases o Hemoglobin and albumin need to stay in the blood and cannot pass through the capillary wall This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:52 GMT -06:00 https://www.coursehero.com/file/31079957/Lecture-12docx/ Cardiovascular System Determinants of Net Fluid Movement across Capillaries  Main determinants of bulk flow or movement across the capillary are: o Capillary Hydrostatic pressure (Pc):  Forces fluid outward through the capillary membrane o Pressure in the interstitial fluid (Pif):  Opposes filtration when value is positive  These two forces oppose one another  Pressure on the outside (interstitial fluid) and the pressure in the capillary (blood pressure)  Colloid osmotic pressure: pressure gradient that is set up between the interstitial fluid and the plasma in the blood vessels, effectively describes the fact that water is attracted to proteins o Protein concentration in plasma is much higher than the interstitial fluid o Water wants to absorb BACK into the capillary because it is attracted to the high protein concentration o Proteins present in the interstitial fluid are at extremely low levels  Draw water out  Plasma colloid osmotic pressure: o Opposes filtration causing osmosis of water inward though the membrane  Interstitial fluid colloid pressure: o Promotes filtration by causing osmosis of fluid outward through the membrane  Net effect: -25mmHg absorption (back into the capillary) o Negative as the water is going back into the capillary  Difference between interstitial pressure and capillary pressure is that it varies between 32mmHg and 15mmHg depending on which end of the capillary you are at o Arteriolar end is high: 32mmHg o Venous end is low: 15mmHg  Variances from one end to the other creates a pressure gradient that allows the filtration at the arteriolar end and absorption at the venous end  Net pressure refers to the balance between the capillaries and the interstitial pressures o Balance between the colloid osmotic pressure in the capillaries and the colloid osmotic pressure in the interstitial fluid  Establish 2 gradients o One gradient that is trying to drive fluid out of the capillary in the forward direction o One gradient that is trying to drive fluid back in the negative direction o Balance between the pressure will determine the bulk flow in the system This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:52 GMT -06:00 https://www.coursehero.com/file/31079957/Lecture-12docx/ Cardiovascular System Fluid Exchange at a Capillary  Hydrostatic pressure and osmotic pressure regulate bulk flow o If the direction of bulk flow is into the capillary  absorption o If the direction of bulk flow is out of the capillary  filtration  Blue arrows are the filtration out of the capillaries  Red arrows are the colloid osmotic gradient of 25mmHg o Water being absorbed into the capillary by the high protein concentration in the plasma o Stays the same across the capillary because the protein concentration also does not change  Hydrostatic pressure changes, as there is resistance in the capillary so it is decreasing across the length  Capillary filtration is caused by hydrostatic pressure that forces fluid out of the capillary through leaky cell junctions  Critical point that tips the balance o Arterial side favors filtration of the water o Nothing happens in the center o Colloid osmotic pressure gradient overcomes the hydrostatic pressure gradient  Fluid/water flow into the capillary at the venous end (absorption)  Net filtration at the arteriolar end and net absorption at the venous end  Balance of all of this: o Net flow out of about 3L/day o ~2/3 of your blood supply (water) gets recycled through this process Net Pressure =Hydrostatic Pressure−colloid osmotic pressre  A positive value for the net pressure indicated net filtration and a negative value indicates net absorption This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:52 GMT -06:00 https://www.coursehero.com/file/31079957/Lecture-12docx/ Cardiovascular System Net Starting Forces in Capillaries  Net Filtration pressure of 0.3mmHg o Filtration coefficient of 10ml/min/mmHg o Results in net filtration rate of (10*0.3) = 3mk/min for entire body Fluid Exchange at a Capillary  When water leaves the capillary it goes into the interstitial spaces  The interstitial spaces are connected to the lymphatic system o Lymph vessels collect excess water and bring it back to the CV system  Comes in through the venous system and is recycled back into the blood volume Lymphatic System  Has multiple functions: o Returning fluid and proteins to circulatory system o Picking up fat absorbed and transferring it to circulatory system o Serving as a filter for pathogens  Serves as a route by which fluid and proteins can flow from interstitial spaces to the blood o Lymph system parallels the CV system – wherever there are capillaries there are lymph nodes  Prevents edema o Swelling, accumulation of fluid in the interstitial space  Lymph is derived from interstitial fluid  Plays important role in the immune system o Lymph vessels can enter lymph nodes, which have a collection of immunologically active cells like lymphocytes and macrophages  Eventually drain into the subclavian veins which join the internal jugular veins  heart Edema: fluid buildup/swelling  Fluid buildup and swelling is caused by inadequate drainage of the lymph or the blood capillary filtration greatly exceeds the capillary absorption o Overwhelm the lymph’s ability to bring materials back o Blockage in the lymphatic system that produces the block  Can happen in ANY vascularized tissue  If there is a blockage in a lymph vessel the fluid will continue to buildup in the interstitial space  Three factors can disrupt the normal balance between capillary filtration and absorption o An increase in capillary hydrostatic pressure o Decrease in plasma protein concentration o An increase in interstitial proteins Elephantiasis  Abnormal enlargement of any part of the body due to obstruction of the lymphatic channels in the area  Caused by small parasitic round worms This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:52 GMT -06:00 https://www.coursehero.com/file/31079957/Lecture-12docx/ Cardiovascular System o Worms get stuck in the lymph channels o Transmitted by mosquito o ~20 million people worldwide Ascites – fluid in the abdomen (peritoneal cavity)  Kwashiorkor: “the sickness fo the child who is displaces from the breast.” o There are many proteins in breast milk that would benefit the child as they would contribute to their colloid osmotic pressure o Babies that don’t get enough proteins have low colloid osmotic pressure and cannot withdraw the bulk flow back into the capillaries  Fluid gets stuck in the abdomen causing ballooning Liver Cirrhosis  Causes: o Alcoholism, Hepatitis, Fatty Liver Disease, Acetaminophen o Decreased function of the liver:  Liver is important in producing proteins  If the liver is not functioning properly it cannot produce high amounts of plasma proteins  Will not generate the colloid osmotic pressure gradient and will not be able to draw fluid back into the capillaries and will result in a distended stomach due to fluid excess This study source was downloaded by 100000818475141 from CourseHero.com on 02-07-2024 15:05:52 GMT -06:00 https://www.coursehero.com/file/31079957/Lecture-12docx/ Powered by TCPDF (www.tcpdf.org)