Essentials of Anatomy and Physiology

SUMMARY

The preceding discussions of immunity will give you a
small idea of the complexity of the body’s defense sys-
tem. However, there is still much more to be learned,
especially about the effects of the nervous system and
endocrine system on immunity. For example, it is

known that people under great stress have immune

systems that may not function as they did when stress

was absent.

At present, much research is being done in this

field. The goal is not to eliminate all disease, for that

would not be possible. Rather, the aim is to enable

people to live healthier lives by preventing certain

diseases.

338 The Lymphatic System and Immunity

STUDY OUTLINE

Functions of the Lymphatic System

1. To return tissue fluid to the blood to maintain
   blood volume (see Fig. 14–1).


2. To protect the body against pathogens and other
   foreign material.

Parts of the Lymphatic System

1. Lymph and lymph vessels.


2. Lymphatic tissue: lymph nodes and nodules,
   spleen, and thymus; lymphocytes mature and pro-
   liferate.

Lymph—the tissue fluid that enters lymph
capillaries

1. Similar to plasma, but more WBCs are present,
   and has less protein.


2. Must be returned to the blood to maintain blood
   volume and blood pressure.

Lymph Vessels

1. Dead-end lymph capillaries are found in most tis-
   sue spaces; collect tissue fluid and proteins (see Fig.
   14–2).


2. The structure of larger lymph vessels is like that of
   veins; valves prevent the backflow of lymph.


3. Lymph is kept moving in lymph vessels by:
   
   
   • constriction of the lymph vessels
   
   
   • the skeletal muscle pump
   
   
   • the respiratory pump
   
   
   
   


4. Lymph from the lower body and upper left quad-
   rant enters the thoracic duct and is returned to the
   blood in the left subclavian vein (see Fig. 14–3).


5. Lymph from the upper right quadrant enters the
   right lymphatic duct and is returned to the blood in
   the right subclavian vein.

Lymph Nodes—encapsulated masses of lym-

phatic tissue

1. Found in groups along the pathways of lymph ves-
   sels.


2. As lymph flows through the nodes:
   
   
   • foreign material is phagocytized by fixed macro-
     phages
   
   
   • lymphocytes are activated and fixed plasma cells
     produce antibodies to foreign antigens (see Fig.
     14–4)
   
   
   
   


3. The major paired groups of lymph nodes are the
   cervical, axillary, and inguinal groups. These are
   at the junctions of the head and extremities with
   the trunk; remove pathogens from the lymph from
   the extremities before the lymph is returned to the
   blood.

Lymph Nodules—small unencapsulated

masses of lymphatic tissue

1. Found beneath the epithelium of all mucous mem-
   branes, that is, the tracts that have natural openings
   to the environment.


2. Destroy pathogens that penetrate the epithelium of
   the respiratory, digestive, urinary, or reproductive
   tracts.


3. Tonsils are the lymph nodules of the pharynx;
   Peyer’s patches are those of the small intestine.

Spleen—located in the upper left abdominal

quadrant behind the stomach

1. The fetal spleen produces RBCs.


2. Functions after birth:
   
   
   • contains lymphocytes to be activated and fixed
     plasma cells that produce antibodies
   
   
   • contains fixed macrophages (RE cells) that