NOTES: The Lymphatic /

Immune Immune System

(Ch 12, part 1)

The lymphatic system is closely

associated with the cardiovascular

system.

Functions of the Lymphatic

System:

● transports excess fluid to the bloodstream

● absorbs fats

● helps defend the body against disease-causing agents

LYMPHATIC PATHWAYS

Lymphatic capillaries

● microscopic, closed-end

tubes that extend

into intercellular spaces

● receive LYMPH through ● receive LYMPH through

their thin walls

(LYMPH = the fluid of the lymphatic system… more later!)

● lymphatic capillary networks parallel blood capillary networks

Lymphatic vessels:

● have walls similar to

those of veins, but thinner,

and have valves to

prevent backflow of

lymph

● become larger and lead to LYMPH NODESand then merge into LYMPHATIC TRUNKS

Lymphatic Trunks and Collecting Ducts:

● lymphatic trunks lead to two collecting ducts:

-THORACIC DUCT

� larger and longer duct;

� receives lymph from the lower limbs,

abdominal regions, left upper limb, left side of

thorax, head, and neck

-RIGHT LYMPHATIC DUCT

� receives lymph from the R side of the head &

neck, R upper limb, R thorax

● collecting ducts join the SUBCLAVIAN VEINS

Tissue Fluid & Lymph:

● LYMPH is essentially tissue fluid that has entered a lymphatic capillary

● tissue fluid originates from blood plasma and is composed of:

-water-water

-dissolved substances that leave blood capillaries (small molecules, nutrients, gases, hormones)

**NOT present are larger plasma proteins (too large to pass through capillary walls)

Functions of lymph:

1) returns to the bloodstream small proteins that leaked out of blood capillaries

2) transports foreign particles, such as 2) transports foreign particles, such as bacteria or viruses, to lymph nodes

Lymph Movement● lymph, like venous blood,

is under low pressure and may not flow readily

● movement of lymph is ● movement of lymph is affected

by skeletal muscle

contraction and pressure

changes associated

with breathing

**if lymph movement is impaired, it may

accumulate within the intercellular

spaces and produce EDEMA, or

swelling

(example: after surgery, the lymphatic vessels and lymph nodes around the wound may be damaged, causing fluid to wound may be damaged, causing fluid to accumulate around the surgery site and lead to swelling)

Lymph Nodes:

Structure of a Lymph Node:

● lymph nodes are subdivided into nodules

● nodules contain

masses of

lymphocytes

and macrophages

Locations of Lymph Nodes:

● lymph nodes aggregate in groups or chains along the paths of larger lymphatic vessels

Functions of Lymph Nodes:

● filter potentially harmful foreign particles from lymph

● are centers for the production of lymphocytes(attack invading viruses, bacteria, parasites, etc.)etc.)

● contain phagocytic cells

(engulf and destroy foreign

substances, damaged

cells, cellular debris)

THYMUS AND SPLEEN

Thymus:

● located anterior to aorta

and posterior to upper

part of sternum

● shrinks slowly after puberty● shrinks slowly after puberty

● contains large numbers of

LYMPHOCYTES which

mature into T CELLS (T lymphocytes) –important in providing immunity (more on these later…)

Spleen:

● largest lymphatic organ

● located in upper left portion of abdominal cavity (just inf. to diaphragm and lat./post. to stomach)to stomach)

● resembles a large lymph node (divided into lobules)

Spleen:

● spaces within splenic

lobules are filled with blood

● contains many macrophages, which destroy/remove foreign which destroy/remove foreign particles and damaged RBCs from the blood

**the spleen filters blood as the lymph nodes filter lymph!**