HUMAN BIOLOGY

158 Chapter 9

the Lymphatic system

n    Link to blood vessel function 7.6

As you’ve just read, the lymphatic system does several

things in the body. It works with the cardiovascular sys-

tem by picking up fluid that is lost from capillaries and

returning it to the bloodstream. The lymphatic system’s

lymph trickles past

arrays of lymphocytes

in the lymph node

valve (prevents

backflow)

B Cross section of a lymph node

9.2

other key task is defense. As sketched in Figure 9.3, the

system consists of drainage vessels, lymphoid organs such

as the spleen and lymph nodes, and lymphoid tissues. The

tissue fluid that has moved into lymph vessels is aptly

called lymph.

Tonsils

Defense against

bacteria and other

foreign agents

Right lymphatic duct

Drains right upper portion

of the body

T hymus gland

Site where certain

T lymphocytes acquire means

to chemically recognize

specific foreign invaders

T horacic duct

Drains most of the body

Spleen

Major site of antibody

production; disposal

site for old red blood cells

and foreign debris; site of

red blood cell formation

in an embryo

Some lymph vessels

Return excess tissue

fluid and reclaimable

solutes to the blood

Some lymph nodes

Filter bacteria and

many other agents of

disease from lymph

Bone marrow

Red marrow in some

bones is where white

blood cells are produced

(also red blood

cells and platelets)

A

Figure 9.3 Animated! The lymphatic system

collects fluid and functions in defense. A The small

green ovals show where some of the major lymph

nodes are located. The system also includes patches

of lymphoid tissue in the small intestine and in the

appendix. B Cutaway diagram of a lymph node. Its

inner chambers are packed with infection-fighting

white blood cells. (© Cengage Learning)

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