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.
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