Lymphatic System (Start Exam 3) Flashcards
Lymphatic system Includes:
lymph, lymph vessels, lymph nodes, tonsils, thymus, and spleen
Primary Functions (Lymphatic System)
A. Aids in returning fluid to the circulation from interstitial spaces. Also returns proteins that escape from capillaries and are not readily reabsorbed.
B. Transports fats from the digestive tract to the blood.
C. Produces lymphocytes - which are blood cells active in our body’s immune response.
Lymphatic Vessels: Lymph capillaries
- tiny closed-ended vessels which have their beginnings in interstitial spaces adjacent to capillaries. These are present in every tissue of the body with the exception of the central nervous system, and avascular tissues (e.g. cartilage)
- similar to blood capillaries but usually form less extensive plexuses, have a slightly larger diameter, and are more permeable.
Lymphatic Vessels: Lymphatics
- lymph capillaries flow together to form these larger lymph vessels
- lymphatics are very similar to veins except they are much smaller in diameter than the average vein. They also have much thinner walls. In addition, lymphatics at various intervals flow in and out of tiny glands called lymph nodes.
- like veins, lymphatics have valves. These give them a “beaded” appearance and are present in greater numbers than in veins.
- lymphatics tend to follow blood vessels. In subcutaneous tissue one will find them in closer proximity to veins where as in the abdominal cavity or in viscera they tend to be located closer to arteries and form plexuses around them. Groupings of lymph nodes are often found near major arteries.
Lymphatic Vessels: Ducts (2)
- Ultimately - all lymphatics flow into 2 major ducts:
1. Right lymphatic duct - this receives tributaries from the right side of the head, the right arm, and the right shoulder area. Flows into right subclavian vein.
2. Thoracic duct - receives tributaries from all other parts of the body. Flows into left subclavian vein.
The Scheme of Lymph Circulation
A. The basic plan of blood circulation is to have fluid containing the important nutrients for cells pass out of arteriolar capillaries - supply the cells with what they need - and then pass back into the venous capillaries carrying the cell’s waste products. However, not all the fluid passing out of the artery end of the capillary passes back directly into the venous end. Thus the lymphatic system aids in the return of fluids to the circulation.
B. Fluid from interstitial spaces flows into lymph capillaries
- at this point it is now called lymph.
- Lymph - overflow fluid from tissue spaces.
C. Lymph flows from lymph capillaries to lymphatics to lymph nodes.
D. Lymph nodes actually filter lymph and remove particulate matter before allowing it back into the circulation.
E. Lymphatics to Ducts to Venous general circulation.
F. Return of Proteins to the Circulation - normally proteins are too large to pass through capillary membranes, but there is occasional leakage. It is important to maintain a specific concentration of protein in the blood, to maintain a proper colloid osmotic pressure. Otherwise one would lose fluid from the circulation to the tissue. Thus proteins must be returned to the circulation.
- Lymphatics are much more permeable than blood vessels and can more readily pick up proteins from the interstitial fluid.
- This becomes especially important in inflammation when capillaries become more permeable to proteins in order to combat the problem (e.g. infection) in the tissue. If more protein leaves the capillary than can be returned by the lymphatics then Edema will result due to an increase in the colloid osmotic pressure of the interstitial fluid. Tissues will tend to swell with fluid.
- 3 causes of edema:
1. increased hydrostatic pressure in blood circulation.
2. decreased colloid osmotic pressure in blood.
3. increased colloid osmotic pressure in interstitial space.
Flow of Lymph in Lymphatics
A. Interstitial fluid pressure - when this rises fluid is more actively forced into lymphatics. The greater this pressure - the more lymph formed.
B. Lymphatic Pump - this is caused by an intrinsic mechanism in the lymph vessels themselves. All lymph vessels have valves so that lymph can only flow in one direction. Smooth muscle in the walls of the lymphatics contracts periodically, and this forces the lymph along. When a lymph vessel becomes stretched with excess lymph, it automatically contracts and pushes the lymph past the next lymphatic valve, etc., etc.
C. This pumping action is aided by contractions of surrounding skeletal muscle during normal movement.
D. Lymph flow varies tremendously - but on an average, one pumps approximately 1 - mls/minute through the lymphatic system back to the circulation
Lymph Nodes
A. Shaped similar to kidney bean - have a hilus on one side, and covered by a capsule of fibrous connective tissue which extends into the gland as trabeculae. Anywhere from 1 mm to 25 mm (1 inch) long. Parencyma can be divided into a cortex and medulla
- cortex - dense groupings of lymphocytes called lymph nodules
- in the center of these nodules one often see germinal centers where lymphocytes are formed.
- medulla - contain sinuses through which the lymph circulates and has lymphocytes arranged in strands called medullary cords.
Afferent lymphatic vessels - enter on the convex side in several locations - contain valves so lymph cannot return to afferents.
- lymph then circulates through sinuses in the cortex and then into sinuses in the medulla between the medullary cords. Lymph then leaves the node via efferent lymphatic vessels located at the hilus (hilum) of the node.
B. Function of Node - large molecules are absorbed by the lymphatics and pass into the nodes. Often these things which are picked up by the lymph system are harmful if put back into circulation (example: tetanus toxin or bacteria). Many of these elements are filtered out by:
1. Phagocytic cells called macrophages or reticuloendothelial cells.
- lymph nodes are also the site of:
2. formation of lymphocytes which aid in the body’s defense.
Plasma cells (type of lymphocyte) produce antibodies.
- sometimes a node itself can become infected - it may swell and become tender. This is evidence of a possible infection in the area drained by the afferent lymphatics of that node.
Tonsils
- these are masses of lymphoid tissue embedded within a mucous membrane. 3 pairs:
1. Pharyngeal Tonsils - posterior wall of nasopharynx, near opening of eustachian tube. Called the “adenoids”.
2. Palatine Tonsils - found in tonsilar cavity at back of oral cavity between the “tonsilar pillars” (glossopalatine and pharyngopalatine arches). This is usually what refers to when they say “tonsil”. These are the ones usually removed in a “tonsillectomy”.
3. Lingual tonsils - located posteriorly at the base of the tongue - also sometimes removed in a tonsillectomy.
Spleen
- largest mass of lymphatic tissue in the body.
1. Morphology - about 5 inches (12 cm) long - located just below the diaphragm, posterior and lateral to the stomach adjacent to the ribs.
- has both a diaphragmatic and a visceral surface
- capsule - made up of fibroelastic tissue and some smooth muscle. This is covered by a visceral peritoneum - Like Lymph Nodes it also has trabeculae and a hilus = stroma of organ.
- has two types of tissue in parenchyma
(parenchyma = functional tissue of an organ)
(stroma = structural tissue of an organ)
a. Red pulp - arranged in strands called splenic or Billroth’s cords - these have a function of phagocytosis of things bad for the body - including bad blood cells, and bacteria. Associated with veins.
b. White pulp - this is lymphoid tissue in clusters surrounding arteries. Forms lymphocytes. Associated with arteries.
2. Function - spleen also functions as a blood storage depot. - during times of physical exertion or hemorrhage, the spleen can contract and release many RBC’s into the circulation.
Thymus
- a ribbed mass of lymphoid tissue located just posterior to the sternum.
- relatively large in children - reaches its maximum size at puberty and then begins to regress.
- in the older adult it is replaced mostly with adipose and connective tissue
Peyer’s Patches
- lymphoid accumulations in the wall of the intestines - primarily in the submucosa of the wall of the ileum.
