The Lymphatic System & Immunity
Lymphatic System

Describe the structure & functions of the lymphatic system.
Structure: lymphatic vessels & lymphoid organs & closely associated with circulatory system

Vessels: collect extracellular fluid & return it to circulation via one way-valved vessels that
get larger & larger until entering thoracic duct or the right lymphatic duct.
o Thoracic duct is much larger – serves lower extremities, abdomen, left arm & left side
of the head & neck. It is on the left and fluid enters the left subclavian vein.
o Right lymphatic duct – serves only the right arm and the right side of the head &
neck. It is on the right and fluid enters the right subclavian vein

Lymphoid organs: Spleen, lymph nodes, thymus, red bone marrow
Function –
1. Lymphatic vessels take up excess tissue fluid & return it to the bloodstream
2. Lymphatic capillaries absorb fats at the intestinal villi & transport them to the bloodstream
3. The lymphatic system helps to defend the body against disease

Describe the structure & function of the lymph nodes.
o Lymph nodes-fibrous connective tissue capsule divided into nodules with sinuses
(spaces) filled with lymphocytes & macrophages & as lymph passes through it is
cleansed of debris & infectious organisms
i. Nodules can occur singly or in groups = tonsils (adenoids, palatine &
lingual)
ii. Peyer’s patches in intestinal wall
iii. Groups in groin, armpit

Describe the structure & functions of the thymus, spleen & red bone marrow.
o Spleen – sinus containing lobules filled with blood instead of lymph
i. Vessels within can expand & serve as a blood reservoir
ii. Lobules – red pulp: rbc, lymphocytes, macrophages
iii. Lobules – white pulp: lymphocytes & macrophages only
iv. Both types cleanse blood of bacteria
o Thymus – located along trachea atop heart & is larger during childhood (may
disappear)
i. Divided into lobules by connective tissue where T-lymphocytes mature
1. T-lymphocytes have passed test to “self” recognize
2. Secretes thymosin – believed to cause pre-T cells to become Tcells
o Red bone marrow – site of origin for all blood cells red & white
i. Adults – skull, sternum, ribs, clavicle, pelvis & spinal column, ends of
femur & humerus
Immunity

Describe the body’s nonspecific defense mechanisms.
o Useful against all types of pathogens
i. Barriers to entry (skin & mucous membranes)
1. sebaceous glands in skin secrete oils that are antibacterial
2. ciliated cells of respiratory tract sweep mucus and trapped particles
into mouth to be expectorated or swallowed
3. acidic pH of stomach is antibacterial
4. resident fauna of gut and vaginal area prevent colonization of
pathogens
ii. Inflammation (inflammatory reaction) = reddening & swelling of site of
injury
1. `capillaries & tissue cells erupt & release histamine = dilates
capillaries  more permeable
2. increased permeability allows proteins & fluids to escape 
swelling
3. increased fluid pressure stimulates nerve endings  pain
4. skin break allows pathogens to enter & amoeboid neutrophils &
monocytes squeeze though cap walls to tissue fluid & phagocytize
invaders
5. pus forms indicating the body is trying to overcome and infection
iii. Protective proteins
1. the complement system – one C protein is activated when a
pathogen enters the body & domino effect activates many others
2. together army of proteins form holes in bacteria cell walls &
membranes allowing fluids & salt to enter  rupture
3. complement completes certain immune responses = name
4. when viruses enter cells the infected cell protein secretes interferon
which binds to noninfected cells causing them to prepare for attack
by producing substances that interfere with viral replication

Contrast antibody-mediated immunity with cell-mediated immunity.
Immunotherapy

Describe how to provide an individual with active & passive immunity.

Give examples of immunotherapeutic drugs.
Immunological side effects & illnesses

Give examples of how the immune system overdefends & underdefends the body.
Effects of Aging

Describe the anatomical & physiological changes that occur in the lymphatic system as
we age.