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LYMPHATIC SYSTEM
The 2 most important functions of the lymphatic system:
1. Maintain fluid balance in the internal environment
2. Immunity
Plasma filters out of the arterial end of capillaries into the space between cells
(interstitialspace) because of the pressure there.
Most of this interstitial fluid is (1) absorbed by the cells or (2) reabsorbed by the blood before
it flows out of the tissue. A small percentage of it remains behind in the spaces If more
remained, there would be (1) massive swelling-EDEMA and possible death destruction (2)
SHOCK because of loss of fluid in the circulatory system.
The lymphatic vessels drain the excess fluid and return it to the venous blood just before it
reaches the heart
COMPONENTS OF THE LYMPHATIC SYSTEM
1. Lymph/Lymphatic vessels
2. Lymph nodes
3. Lymph nodules-Peyer’s Patches in intestinal tract
4. Specialized lymphatic organs-tonsils, spleen, and thymus
Lymph and interstitial fluid are similar to blood plasma EXCEPT that they have a lower % of
proteins than plasma does -The thoracic duct has a much higher % of protein because it flows
from the liver and the small intestine before it reaches the Thoracic duct Since lymph doesn’t
clot, if damage to main lymphatic trunks occurs death can occur-because it is impossible to
maintain adequate serum protein concentration by dietary means-If significant loss of lymph
continues, emaciation occurs and is potentially fatal…
Lymphatic vessels differ from blood vessels
1. Not a closed ring/Begin blindly in the intercellular spaces of soft tissues of the body
2. Originate as lymphatic capillaries or in the villi of the SI as lacteals
3. Independent of but lie side by side with blood capillary networks
4. Have lymph nodes located along their course
5. Have small openings-clefts-between cells in walls so they are very permeable
6. Most have capacity for repair or regeneration when damaged
7.Smaller than veins
8. Thinner walls than veins
9. Have more valves than veins-to keep lymph flowing in one direction
Lacteals in villi absorb fats and other nutrients->milky lymph CHYLE
Each day about 50% of total blood proteins leak out of the capillaries into tissue fluid
andreturn to blood via lymphatics
LYMPHATIC PUMP
Return 3 L/day to circulatory system
No HEART TO PUMP LYMPH SO LYMPHOKINETIC ACTIONS-similar to what
makesvenous blood return to heart
1. Breathing movements-changes in pressure between thoracic and abdominal
cavities
2. Skeletal muscle contractions
**Contraction of smooth muscle plays a minor role
**Also, arterial pulsations, postural changes, and massage of body soft tissues
STRUCTURE OF LYMPH NODES
Oval or bean shaped-small as a pinhead or large as a lima bean
When infection is present, germinal centers form and node begins to release lymphocytes
B-lymphocytes-begin final stages of maturation here in the GC and then finish to
become antibody producing plasma cells in the denser outer layers
The center, or MEDULLA of a lymph node is composed of sinuses and medullary cordsBoth Cortical and Medullary sinuses are lined with macrophages for phagocytosis
FUNCTIONS OF LYMPH NODES
1. Defense
a. Lymph flows slowly thru them
b. Gives time to remove microbes and other injurious particles (soot) .. phagocytosis
c. Sometimes overwhelmed and infection of the node (adenitis) results
d. Cancer cells often break away from malignant tumor and travel to the lymph nodes and
they become cancerous-can block lymph flow and cause edema in the area
2. Hematopoiesis
a. Final stages of maturation for some types of lymphocytes and monocytes (B cells)
LYMPHATIC DRAINAGE OF THE BREAST
Cancer of the breast is one of the most common forms of malignancy in women
Often metastasize from this “primary” site to rest of body thru lymphatic system
Surgical procedures mastectomies-all or some of breast tissue removed
Lymphedema may occur because lymph flow is interrupted by removal of lymph
vesselsusually restored by growth of new lymphatic vessels in area
Anastomoses (connections) occur between lymphatics from both breasts across midline
Results in spread from one breast to the other
TONSILS
Help protect against bacteria invading nasal and oral cavities
1. PALATINE TONSILS-on each side of throat
2. PHATYNGEAL TONSILS-adenoids-near posterior opening of nasal cavity
3. LINGUAL TONSILS-near base of tongue
Tonsilitis (Inflammation of tonsils)
Tonsillectomy (Removal of tonsils)-controversial because of their critical immunological role
THYMUS
PRIMARY ORGAN OF THE LYMPHATIC SYSTEM
Unpaired with 2 lobes-in the mediastinum-behind the sternum and extending up into
the neck
Relative size largest in 2 year old Absolute size largest at puberty
Gradually atrophies and may be replaced by fat as age-probably completes its essential work
early in childhood
INVOLUTION (shrinkage of an organ)
Did not understand its role until 1961-plays a critical part in body’s immune system
TWO FUNCTIONS
1. Final site of lymphocyte development before birth
2. Secretes hormones called thymosin that enable lymphocytes to develop into
mature T cells-T cells attack foreign or abnormal cells and regulate immune
function
SPLEEN
Located below diaphragm above L kidney, colon and stomach
HYPERTROPHIES during infectious diseases and atrophies in old age
SPLENOMEGALY-abnormal spleen enlargement is observed in various disorders-scarlet
fever, syphilis, and typhoid fever, also in hypertension and hemolytic anemia
Surgical removal of the spleen may be required for some of these
FUNCTIONS:
1. Defense-as blood passes thru, removes microbes and phagocytoses them
2. Hematopoieses-Some WBCs complete development and become activated hereAlso, before birth RBCs are formed in spleen-later, only in extreme hemolytic anemia
3. RBC and Platelet destruction-remove and phagocytize worn out RBCs and
imperfect platelets-breaks apart hemoglobin and salvage iron and globin and
returns to bloodstream to store in bone marrow and liver
4. Reservoir for blood-has normal volume of about 350 ml of blood-can empty to
200 ml in less than a minute to help body-“self-transfusion”-response to stress
from hemorrhage
DISORDERS OF THE LYMPHATIC SYSTEM
1. LYMPHEDEMA-swelling because of obstruction of the lymphatics and accumulation of
lymph
a. Congenital lymphedema-women 15->25-1st soft->firm and painful-Diuretics or
surgery
b. Fliaria-parasitic worms seen in the tropics-elephantiasis
2. LYMPHANGITIS-inflammation of lymphatic vessel-from invasion of infectious
organism-red streaks extenD from infected are up arm or leg->NECROSIS
(tissue death) may occur-ABSCESS (collection of fluid) can occur—infectious
agents may spread into bloodstream causing SEPTICEMIA (blood poisoning)
3 LYMPHOMA-tumor of cells of lymphoid tissue-usually malignant-usually originate in
isolated lymph nodes and spread from node to node thru anastomoses of the lymphatic
vessels
a. Hodgkin’s and non-Hodgkin’s lymphoma –
1. Hodgkin’s is malignancy with uncertain etiology-may be viral induced tumor
of T cells-no evidence to support that usually begins as painless enlarged
lymph nodes in neck or axilla->spreads-may cause anemia, lymphedema,
leukocytosis, fever and weight loss-potentially curable with radiation
therapy if it hasn’t spread beyond lymphatic system-Chemotherapy is used in
more advanced cases-Infection is common complication
2. Non-Hodgkin’s-malignancy of lymphoid tissue other than Hodgkin’s
lymphoma-etiology uncertain-maybe virus-Patients with immunodeficiencies
such as AIDS often develop this-NOT NECESSARILY-Usually a more
generalized involvement of lymph nodes-Central NS also often involvedRadiation and chemotherapy are treatments of choice
4. TONSILITIS-already discussed-may extend to middle ear by way of Eustachian
tubes-maybe tonsillectomy