LYMPHATIC SYSTEM (Chapter 16)
Lymphatic system collects fluid that has escaped from the cardiovascular system and returns it back to the
1. The lymphatic system consists of:
i. a fluid called lymph
ii. lymphatic vessels (highly permeable)
iii. several structures and organs that contain lymphatic tissue
iv. bone marrow (the site of lymphocyte production)
2. Lymph is interstitial fluid that has entered and flows through lymphatic vessels.
3. Lymphatic tissue is a specialized form of reticular connective tissue that contains large numbers of
4. The lymphatic system has the following major functions:
i. draining interstitial fluid
ii. transporting dietary fat
iii. protecting against invasion by foreign or abnormal substances via immune responses
5. Formation and Flow of Lymph:
i. More fluid is filtered out of blood capillaries than is reabsorbed by them.
ii. Each day, about 3 liters of this interstitial fluid drains into lymphatic capillaries.
iii. This lymph flows through lymphatic vessels and eventually into the blood of the subclavian veins.
iv. One major function of lymphatic vessels is to return fluid and any leaked plasma proteins to the
v. The flow of lymph toward the subclavian veins is maintained primarily by the compressive
contractions of skeletal muscles and the actions of one way valves within lymphatic vessels; respiratory
movements also help to maintain lymph flow.
6. Lymphatic Trunks and Ducts:
i. Lymph drains into the thoracic duct on the left side or the right lymphatic duct.
ii. Thoracic duct: a. is the main collecting duct of the lymphatic system
b. receives lymph from the left side of the head, neck, and chest, the left upper extremity, and the
entire body below the ribs
iii. Right lymphatic duct:
a. drains lymph from the upper right side of the body
A. Immune System and lymphatic tissue:
The main defense cells of the Immune System are called LYMPHOCYTES. They are important for
recognition of specific foreign molecules and destroys pathogens.
There are two main types of Lymphocytes:
B lymphocytes (produced mainly in the bone marrow and mature there) produce antibodies against
specific antigens on foreign cells
T lymphocytes (mature mainly in the thymus gland) recognize foreign antigen bearing cells and
penetrate their cell membrane and program cell death
(Also helper T cells enhance the activity of T and B cells).
Effector and Memory cells. Effector cells are shortlived and attack antigens; memory cells remain
in the system lying dormant until another antigen is presented at a later date and the memory cell elicits a
rapid and large response (basis of acquired immunity and vaccinations).
Lymphocytes can be organized into lymphatic organs and tissue:
PRIMARY LYMPHATIC ORGANS: where ste