Exam 2 Review:  Chapter 20:  Gross Anatomy of the Lymphatic System

lymphatic system - The interconnected system of spaces and vessels between cells in the body's connective tissues and the specialized organs (bone marrow, thymus, spleen, lymph nodes, tonsils, and diffuse and nodular lymphatic tissues) through which lymph circulates throughout the body; its functions include transport of absorbed lipids from the meals, the return of excess extracellular/interstitial fluid to the cardiovascular system, and a variety of immune defense functions.

lymph - The specific name give to the clear, yellowish protein-poor fluid located between cells in all tissues except blood after it has been collected into the vessels of the lymphatic drainage system; it may also be referred to as lymph before* it is collected into those vessels; its functions include transport of absorbed lipids from the meals, the return of excess extracellular/interstitial fluid to the cardiovascular system, and a variety of immune defense functions.  [Note*:  Therefore, it is functionally equivalent to the interstitial fluid = intercellular fluid = tissue fluid.]

lymph capillary - The smallest lymph vessels which are open at the distal end to admit lymph (interstitial fluid = intercellular fluid = tissue fluid) from the tissue spaces; the walls consist of a simple squamous endothelium with a poorly developed basement membrane.

lymph vessel - Any of the delicate thin-walled vascular tubes, lined with endothelium and a very thin outer areolar connective tissue wrapping, which transport lymph (interstitial fluid = intercellular fluid = tissue fluid) from the tissue spaces back to the systemic circulation; some of the larger vessels have valves to prevent backflow; these vessels anastomose freely with one another; these vessels are interrupted in various locations by lymph nodes.  aka -- lymphatic vessels, lymphatics

anchoring filaments - Collagen fiber which attach the endothelial cells of lymph capillaries to the surrounding tissue structures so that any increase in interstitial fluid volume opens the minivalves (loose connections between endothelial cells), rather than causing the lymph capillaries to collapse. 

lacteal - Any of the numerous minute lymph capillaries, located in the intestinal villi, which convey chyle (lymph containing lipids absorbed from the meal and packaged in chylomicrons) from the intestine to the lymphatic circulation and thereby to the thoracic duct and then to the systemic blood circulation.

chyle - A milky fluid consisting of lymph and emulsified fat packaged in chylomicrons, extracted from chyme (the liquid contents of the small intestine) by the lacteals during digestion, and passed to the bloodstream through the lymphatic system to the thoracic duct and then to the systemic blood circulation.

lymph trunks - The next-to-largest lymphatic vessels which collect lymph fluid from the various regional lymphatic collecting ducts and unit to form the two largest lymphatic vessels, the right lymphatic duct and the thoracic duct = left lymphatic duct; these vessels are delicate thin-walled vascular tubes, lined with endothelium and a thin outer areolar connective tissue wrapping.

thoracic duct = left lymphatic duct - The main lymphatic channel of the body which drains lymph back to the systemic circulation from entire body except for the right arm, thorax, head and neck; it begins as a continuation of the cisterna chyli at the level of the T12 (12^th thoracic vertebra) and runs parallel to the aorta for much of its length until it turns to merge with the left subclavian vein or one of its branches; this vessel is a delicate thin-walled vascular tube, lined with endothelium and a thin outer areolar connective tissue wrapping.

cisterna chyli - the distal (inferior) portion of the thoracic duct, sometimes slightly enlarged in diameter, which collect lymph fluid from the various  lymph trunks of the legs and lower abdominal cavity; it is located at the level of L2 (2^nd lumbar vertebra).

right lymphatic duct  - The minor lymphatic channel of the body which drains lymph back to the systemic circulation from only the right arm, thorax, head and neck; it is quite short, forming from several of the nearby lymphatic trunks, and usually merging with the right jugular vein; this vessel is a delicate thin-walled vascular tube, lined with endothelium and a thin outer areolar connective tissue wrapping.

resistance (to disease) - The general term for all body defenses against injury and disease which are non-specific in the sense of not being generated in response to specific foreign antigen(s); examples include surface barriers (skin and mucous membranes) and their protective secretions (sweat and sebum, cerumen, tears, saliva, the acidity of urine, vaginal and gastric secretions), the processes of vomiting (to expel toxins), inflammation, phagocytosis, and fever, various antimicrobial  proteins (lysozyme, complement, transferrins, interferons) and mediators of inflammation and fever (histamine, kinins, protaglandins, leukotrienes, etc.) and the actions of Natural Killer (NK) lymphocytes.

susceptibility (to disease) - The property of an individual, an organ system, organ or tissue to be affected by disease; it is affected by environmental factors as well as genetic, developmental, and nutritional factors which lower one's resistance.

List:

1. The functions of the lymphatic system.

          (1)  to return excess interstitial fluid (lymph) and its dissolved solutes (electrolytes, nutrients, wastes, regulatory substances, immune system molecules) to the systemic circulation.
          (2)  to transport dietary fats/lipids (in the form of chylomicrons) absorbed from the meal at the intestines to the adipocytes via the systemic circulation.
          (3)  to contribute to specific immune defenses by (a) serving as a route for leukocyte movements, (b) filtering lymph at the lymph nodes, (c) filtering blood at the spleen, (d) providing the location and opportunity for specific leukocytes, especially lymphocytes, to encounter and respond to foreign and tumor antigens.

6. the three means/mechanisms by which lymph flow (returning lymph fluid to the circulatory system) is facilitated.

          (1)  valves in lymphatic vessels which prevent backflow within the lymphatic drainage system.
          (2)  skeletal muscle pump - the contraction of skeletal muscles in the limbs assists with lymph return from the limbs because lymph vessels are guarded by valves to prevent back flow of lymph; as a result, skeletal muscle contraction provides an extravascular compression on these lymph vessels which moves the lymph forward (and against gravity) back toward the systemic circulation.
          (3)  respiratory pump - the contraction of the diaphragm and intercostal muscles in the thoracic cavity assists with lymph return to the systemic circulation because each time a person inhales, there is a slight but significant drop in internal thoracic pressure which creates a pressure gradient which assists in the flow of lymph moving forward (and against gravity) back toward the systemic circulation.

Sketch and label:

1. The structure of lymph vessels. How are lymph vessels similar to and different from blood vessels?

 

The Structure of Lymph Vessels: These six figures illustrate the microscopic architecture of lymph vessels.  Valves are present in lymph vessels to prevent backward flow of lymph through the lymph drainage system.  You can see valves in the three micrographs. Your sketch might be based on the drawing below with the black background.  You would label the endothelial cells, the valves, and the flap at the blind end of the lymph capillary, and you would indicate the direction of the lymph flow.

How are lymph vessels similar to and different from blood vessels? They are similar in that they are (1) lined with a simple squamous endothelium, (2) have varying amounts of fibrous connective tissue adventitia wrapping their outer surfaces, and (3) transmit a fluid in a single direction with little or no backflow permitted. The are different in that (1) lymph vessels are delicate and thin walled and lack a tunica media with smooth muscle, while blood vessels are thicker walled and always have some amount of smooth muscle in their walls; (2) lymph vessels transmit lymph, while blood vessels transmit blood; (3) all lymph vessels have valves while only some veins, and no arteries, have valves; and (4) lymph vessels form a functionally open system in that tissue fluid can be passed directly from the tissue space into the interior of the lymph vessels, while blood vessels form a functionally closed system and tissue fluid never enters the interior of the blood vessel unless an injury has occurred.

Describe:

1. the basic components of lymphatic tissue.
 

capsule	a dense irregular fibrous connective tissue sheath external to the lymphatic tissue; present in the thymus, the lymph nodes, and the spleen, but absent in the red bone marrow and in MALT (mucosa-associated lymphatic tissue)
stroma	a meshwork of fine reticular fibers embedded in a gelatinous connective tissue ground substance
parenchyma	a dense collection of leukocytes (WBCs), primarily T and B lymphocytes, but also a significant minority of moncyte-derived macrophages, and insignificant numbers of granulocytes; certain immunologically regions will be organized into follicles with pale germinal centers
vessels	the delicate thin-walled vascular tubes, lined with endothelium and a very thin outer areolar connective tissue wrapping, which transport lymph (interstitial fluid = intercellular fluid = tissue fluid) from the tissue spaces back to the systemic circulation; some of the larger vessels have valves to prevent backflow; these vessels anastomose freely with one another; these vessels are interrupted in various locations by lymph nodes

 Explain:

1. How the lymphatic system functions to restore fluid lost from the circulatory system.

More fluid exits blood capillaries by diffusion than returns by reabsorption (Starling's Law of the Capillaries); approximately 3L of lymph is generated per day.  The lymphatic vessel drainage system recaptures this fluid and returns it to the systemic circulation along with its dissolved solutes.