this lecture covers the circulatory system and the lymphatic system. the main types of blood vessels are reviewed (we covered this in organ systems already in much greater detail). arteries supply oxygenated blood to tissues and have three basic layers: the innermost layer is the tunica intima and has a squamous endothelium, subendothelial CT, and internal elastic lamina. the middle layer is the tunica media and has smooth muscle and external elastic lamina. the outermost layer is the tunica adventitia which has connective tissue that blends in with surrounding CT, with a network of blood vessels (vasa vasorum) and nerves (nervi vascularis). arterioles are the next level after arteries, which have a thicker smooth muscle tunica media layer which aids in their function, which is mainly to regulate blood flow to capillary beds. there are three types of capillaries which are distinguished by size and continuity of the endothelium: type 1 continuous, which have a tight endothelium which do not allow much leakage, type 2 fenestrated, which allow for some leakage and are present in the renal glomerulus, and type 3 discontinuous, which are much larger and have huge holes that allow for entire cells to pass through- found in the bone marrow, spleen, and liver. after the capillaries come the venules and veins, which are different from arteries in that they have no internal elastic lamina, a thinner tunica media, and rely on the contraction of skeletal muscle and a series of valves for blood flow back to the heart.
the lymphatic system is a sort of complementary system to the circulatory system in that it recirculates body fluids which have been picked up from the interstitial space outside of capillaries. it also functions in red blood cell production and destruction, aids in immunodefense (in the production and circulation of lymphocytes), and aids in fat absorption in the GI tract (think of the central lacteal in the lamina propria of the small intestine). there are several orders of lymphatic organization, the first of which is diffuse lymph tissue, which is just a scattering of lymphocytes in a general area, such as right underneath the epidermis in the airways or GI tract. next is nodular lymph tissue, which are more discrete aggregations of lymphocytes which might have germinal centers in the middle for profilerating new cells- such as the Peyer's patches in the ileum. next is a lymph node, which is an encapsulated "inline filter" for lymph vessels, a small container into which lymph gets poured in through many afferent lymphatic vessels, filtered through the subcapsular and medullary sinuses, and poured back out through a larger efferent lymphatic vessel.
finally, we get to the lymph organs, which are large scale lymph and blood filtering factories. first is the spleen, the functional part of which is called the splenic pulp, which comes in two varieties- red and white. the red is the bulk of the spleen and is filled with RBC's, and white pulp are little islands of lymphocytes that are found alongside blood vessels. the tonsils are another lymph organ, consisting of a series of lymphatic tissue masses covered by a stratified squamous epithelium which is thrown into "crypts". the thymus is the third and last lymph organ, and is a bi-lobed organ beneath the sternum in which t-lymphocytes are trained to differentiate self from non-self.
questions
1. what are the three basic layers to arteries?
2. describe the tunica intima layer of arteries.
3. describe the tunica media layer of arteries.
4. describe the tunica adventitia layer of arteries.
5. what is an arteriole?
6. what are three major differences between veins and arteries?
7. what is a venule?
8. what are the three types of capillaries?
9. describe type I capillaries.
10. describe type II capillaries.
11. describe type III capillaries.
12. what are the main functions of the lymphatic system?
13. describe lymphatic vessels.
14. what are the two types of lymphoid tissue?
15. describe diffuse lymphoid tissue.
16. describe nodular lymphoid tissue.
17. what are the four examples of lymph organs?
18. describe the structure of a lymph node.
19. what is the flow through a lymph vessel?
20. describe the structure of the spleen.
21. what is the thymus?
22. describe the structure of the tonsils.
answers
1. tunica intima, tunica media, tunica adventitia.
2. tunica intima is the innermost layer of an artery and contains squamous endothelium, sub endothelial CT, and internal elastic lamina.
3. tunica media is the middle, thickest layer that contains smooth muscle with elastin.
4. tunica adventitia is the outermost layer containing CT with a network of blood vessels (vasa vasorum) and nerves (nervi vascularis)
5. an artery with a luminal diameter of less than 100um that plays a role in distributing and controlling entry of blood into capillary beds.
6. no internal elastic lamina, relatively thin tunica media, and endothelium is thrown into valves to prevent backflow.
7. a vein with a luminal diameter of less than 200um.
8. type 1 continuous, type 2 fenestrated, type 3 discontinuous.
9. the most common capillary in the body, the endothelium is held tightly together and is relatively leak proof.
10. small holes in endothelium allow some leakage, seen in glomerulus, exocrine ducts, choroid plexus.
11. larger (up to 30um) diameter with large holes in endothelium that allow entire cells to pass, seen in liver, bone marrow, spleen.
12. recirculation of body fluids, defense, hematopoeisis (adding lymphocytes), recycling RBC's (spleen), absorption of fat in GI tract. recirculate blood in defense of fat recycling.
13. vessels that gather and remove excess tissue fluid from capillaries and circulate back into venous system. rely on skeletal muscle and valve system for pumping (much like veins).
14. diffuse and nodular
15. scattering of lymphocytes; often associated with epithelial linings of GI tract and respiratory airways.
16. semi discrete (but unencapsulated) mass of lymphocytes, sometimes with a germinal center where new cells proliferating.
17. lymph nodes, spleen, tonsils, thymus.
18. encapsulated mass of lymph nodules that serves as an in line filter (for lymph) with multiple afferent "feeder" lines and one or two efferent "drainer" lines.
19. afferent lymph vessel, subcapsular sinus, medullary sinus, efferent lymphatic vessel.
20. inline filter (for blood) with two types of "pulp" in the parenchyma: red pulp is the bulk of the spleen and has masses of RBC's, white pulp is small lymphocytes islands associated with blood vessels.
21. a bilobed t-lymphocyte manufacturing center underneath the sternum
22. series of masses of lymphoid tissue with stratified squamous epithelium thrown into crypts that cover aggregations of nodules.
Showing posts with label arteries. Show all posts
Showing posts with label arteries. Show all posts
Wednesday, December 3, 2008
Saturday, November 15, 2008
11.08.08 organ systems: vascular physiology and hemodynamics part 1
this was a long introduction to the more intricate details of blood flow dynamics. the beginning of the lecture introduced the larger structures of the circulatory system: the major arteries and aortas: the aortic arch, which branches into the braciocephalic, left common carotid, and left subclavian, with the braciocephalic branching off into the right subclavian and right common carotid. the thoracic aorta, which has intercostal, brachial, and esophageal branches. finally, the abdominal aorta, which has a visceral branch that is divided into the renal, suprarenal, and the GI branch, as well as a common iliac and femoral artery. other details of larger architecture: the right pulmonary artery goes underneath the aortic arch. the ligamentum arteriosum is the vestigial remains of the ductus arteriosum in the developing heart, which shunted blood from the pulmonary artery directly to the aorta, past the non-functioning lungs. the superior vena cava is a combination of the right and left brachiocephalic veins, which are each a convergence of the right and left internal jugular and subclavian veins.
we then zoom in and look at the smaller architecture of arteries, arterioles, capillaries, veins and venules. arteries have three layers, a tunica intima which has endothelium, sub endothelial CT, and an internal elastic lamina. tunica media is the middle layer with smooth muscle and external elastic lamina. tunica adventitia is the outermost layer, with fibrocollagen. arterioles have extensive smooth muscle (which, as it is explained later, helps create a large resistance which causes the largest pressure drop in the circulatory system), running 1-5 layers deep in the tunica media with less fibrous tissue in the tunica intima and adventitia. capillaries are described as the place for nutrient exchange, either through the membrane for lipid soluble solutes such as gas, or through the extensive pore network for water soluble solutes. veins and venules have thinner walls and less elastin, allowing them to function as a reservoir for the blood, containing up to 64% of the circulating blood.
then we shift to blood flow dynamics and begin with a simple equation describing blood flow: Q=P/R. blood flow equals pressure gradient divided by vascular resistance. blood flow is essentially cardiac output, which is stroke volume times heart rate, and is regulated by neural and endocrine systems. resistance is related to vascular resistance and is regulated by metabolic and neurohumoral systems. pressure is described as an "emergent property" which arises from the interaction of flow and resistance. which seems like just a fancy way of saying P=Q*R. pressure difference is then defined as Paorta-Pvenacava, but since Pvenacava is negligible, P=Paorta. we later find out that Paorta is essentially mean arterial pressure (the formal definition / estimation of which is diastolic pressure plus 1/3 of the difference between systolic and diastolic pressure). thus the most useful, applicable form of this flow equation seems to be (cardiac output) = (mean arterial pressure) / (vascular resistance)
several more terms are introduced in the discussion of blood flow. resistance is elucidated in the poiseuille equation as being proportional to the viscosity of the blood and length of the vessel while being inversely proportional to the radius^4. velocity is the measure of flow taking into account surface area; it can also be described as the speed at which the blood flows along the length of the vessel (as opposed to the flow, which does not account for this). capillaries have the greatest total surface area, making the velocity of blood drop considerably, allowing time for nutrient exchange. viscosity is used as a segue into the idea of laminar flow, which occurs as a result of blood/blood friction and also blood/vessel wall friction, causing the velocity to be greatest in the center of the vessel. finally, turbulence is described as proportional to the reynold's number, which is proportional to diameter of the vessel, density of blood, and velocity, and inversely proportional to the viscosity.
there are a few different aspects of blood pressure that are looked at in this last section. the first is the act of taking blood pressures via a sphygmanometer, which can measure systolic and diastolic pressure by listening for the pressure at which the korotkow sound appears, which represents the turbulence caused by the systolic pressure briefly opening up the occluded brachial artery. the diastolic pressure can then be determined when the korotkow sounds disappear, since the artery will be continuously open when diastolic pressure is slightly greater than the pressure of the cuff. the second is the idea of the two different types of blood pressure on the microscopic level: pressure that arises from blood/blood interaction, going along the length of the vessel, is described as perfusion pressure and is related to kinetic energy. the blood pressure that arises from blood/vessel wall interaction is called transmural pressure and is related to potential energy (in this case stored as pressure in the arteries).
the next aspect of pressure that is looked at is the pulse pressure, which is defined as the difference between the systolic and diastolic pressures, and as such is directly related to both stroke volume and compliance. we learn that in healthy circulation, there is a certain level of compliance in the aortas which allows for some of the stroke volume to be effectively "stored" in the arteries during systole, and the pressure created from this storage allows blood to flow in the capillaries even during diastole. in contrast, in arterial dysfunction involving low compliance, the stroke volume translates directly into the capillaries, not allowing for any additional flow during diastole. this is displayed graphically on the pressure vs. stroke volume graph, in which compliance is a line with a positive slope; where decreased compliance increases the slope of the compliance line, thereby increasing systolic pressure and reducing diastolic pressure. finally, three pathologies relating to pulse pressure are described: artherioscerlosis is a disease in which the arteries have lower compliance, causing higher systolic pressure and therefore larger pulse pressure. hypothyroidism and aortic stenosis are both diseases in which the stroke volume is reduced, which also leads to an reduced pulse pressure.
we then zoom in and look at the smaller architecture of arteries, arterioles, capillaries, veins and venules. arteries have three layers, a tunica intima which has endothelium, sub endothelial CT, and an internal elastic lamina. tunica media is the middle layer with smooth muscle and external elastic lamina. tunica adventitia is the outermost layer, with fibrocollagen. arterioles have extensive smooth muscle (which, as it is explained later, helps create a large resistance which causes the largest pressure drop in the circulatory system), running 1-5 layers deep in the tunica media with less fibrous tissue in the tunica intima and adventitia. capillaries are described as the place for nutrient exchange, either through the membrane for lipid soluble solutes such as gas, or through the extensive pore network for water soluble solutes. veins and venules have thinner walls and less elastin, allowing them to function as a reservoir for the blood, containing up to 64% of the circulating blood.
then we shift to blood flow dynamics and begin with a simple equation describing blood flow: Q=P/R. blood flow equals pressure gradient divided by vascular resistance. blood flow is essentially cardiac output, which is stroke volume times heart rate, and is regulated by neural and endocrine systems. resistance is related to vascular resistance and is regulated by metabolic and neurohumoral systems. pressure is described as an "emergent property" which arises from the interaction of flow and resistance. which seems like just a fancy way of saying P=Q*R. pressure difference is then defined as Paorta-Pvenacava, but since Pvenacava is negligible, P=Paorta. we later find out that Paorta is essentially mean arterial pressure (the formal definition / estimation of which is diastolic pressure plus 1/3 of the difference between systolic and diastolic pressure). thus the most useful, applicable form of this flow equation seems to be (cardiac output) = (mean arterial pressure) / (vascular resistance)
several more terms are introduced in the discussion of blood flow. resistance is elucidated in the poiseuille equation as being proportional to the viscosity of the blood and length of the vessel while being inversely proportional to the radius^4. velocity is the measure of flow taking into account surface area; it can also be described as the speed at which the blood flows along the length of the vessel (as opposed to the flow, which does not account for this). capillaries have the greatest total surface area, making the velocity of blood drop considerably, allowing time for nutrient exchange. viscosity is used as a segue into the idea of laminar flow, which occurs as a result of blood/blood friction and also blood/vessel wall friction, causing the velocity to be greatest in the center of the vessel. finally, turbulence is described as proportional to the reynold's number, which is proportional to diameter of the vessel, density of blood, and velocity, and inversely proportional to the viscosity.
there are a few different aspects of blood pressure that are looked at in this last section. the first is the act of taking blood pressures via a sphygmanometer, which can measure systolic and diastolic pressure by listening for the pressure at which the korotkow sound appears, which represents the turbulence caused by the systolic pressure briefly opening up the occluded brachial artery. the diastolic pressure can then be determined when the korotkow sounds disappear, since the artery will be continuously open when diastolic pressure is slightly greater than the pressure of the cuff. the second is the idea of the two different types of blood pressure on the microscopic level: pressure that arises from blood/blood interaction, going along the length of the vessel, is described as perfusion pressure and is related to kinetic energy. the blood pressure that arises from blood/vessel wall interaction is called transmural pressure and is related to potential energy (in this case stored as pressure in the arteries).
the next aspect of pressure that is looked at is the pulse pressure, which is defined as the difference between the systolic and diastolic pressures, and as such is directly related to both stroke volume and compliance. we learn that in healthy circulation, there is a certain level of compliance in the aortas which allows for some of the stroke volume to be effectively "stored" in the arteries during systole, and the pressure created from this storage allows blood to flow in the capillaries even during diastole. in contrast, in arterial dysfunction involving low compliance, the stroke volume translates directly into the capillaries, not allowing for any additional flow during diastole. this is displayed graphically on the pressure vs. stroke volume graph, in which compliance is a line with a positive slope; where decreased compliance increases the slope of the compliance line, thereby increasing systolic pressure and reducing diastolic pressure. finally, three pathologies relating to pulse pressure are described: artherioscerlosis is a disease in which the arteries have lower compliance, causing higher systolic pressure and therefore larger pulse pressure. hypothyroidism and aortic stenosis are both diseases in which the stroke volume is reduced, which also leads to an reduced pulse pressure.
Subscribe to:
Posts (Atom)