Chapter 22: Lymphatic system and immunity

Define lymph:

• Interstitial fluid that has entered the lymphatic vessels.  

Describe the functions of the lymphatic system:

• Maintains tissue fluid balance→ excess interstitial fluid enters lymphatic capillaries and becomes lymph. **This is what keeps us from being swollen all the time. (about 3L of fluid/day becomes lymph)

• Absorbs fat→ transports fats from the small intestine to the veins via lacteals, specialized lymph capillaries present in the interstitial mucosa which absorb digested fat and deliver chyle (fatty lymph) to the blood.

• Aids in defense→ microorganisms and other foreign substances are filtered from lymph by lymph nodes and from blood by the spleen.

List the organs and tissues of the lymphatic system:

• Lymphatic nodules, lymph nodes, tonsils, spleen, and thymus

Describe the location, structure, and function of lymphatic capillaries: 

• Lymphatic capillaries are MORE permeable than blood capillaries. 

• Can withstand interstitial pressure and remain open. 

•  Epithelium functions as a series of one-way valves

• Found in all parts of the body EXCEPT: nervous system, bone marrow, and avascular tissues like cartilage, cornea, and the epidermis. 

• Lymph flows from capillaries into the larger lymphatic vessels. 

Explain how lymph is formed and subsequently transported through lymphatic vessels:

• Fluid moves from the blood capillaries into tissues. Most is returned to the blood capillaries but the remainder moves from the tissues into the highly permeable lymphatic capillaries to form lymph.

• overlap of epithelial cells of the lymphatic capillary allows easy entry of interstitial fluid but prevents movement back into the tissue. The valves also ensure the one-way flow of lymph.

Lymphatic vessels:

• contain valves that ensure the one-way flow of lymph: 

****Contraction of lymphatic vessels, smooth muscle, skeletal muscle contraction, and thoracic pressure changes.

• Lymph in the lymphatic vessels is filtered by the lymph nodes that are distributed along vessels.

• Lymph in the lymphatic vessels is delivered into one of the lymphatic trunks. 

Distinguish between the thoracic duct and right lymphatic ducts (indicating where lymph from different regions of the body would drain):

**Lymph is delivered from the lymph trunks into one of two large ducts that then drains and moves lymph back into the venous system.

Right lymphatic duct:

• drains lymph from the right upper arm and the right side of the head and thorax. 

Thoracic duct:

• drains lymph from the rest of the body

Lymphatic vessels: flow

One-way system:

• carries fluid away from the tissues

• fluid moves from blood capillaries into the intersitial space

**Most (90%) fluid returns to the blood, but some (10%) is moved into the lymphatic capillaries to become lymph

• Lymphatic capillaries —> vessels —> trunks —> ducts