Chapter 21 - The Lymphatic System and Immunity

Functions of the lymphatic system

- draining excess interstitial fluid (fluid recovery)

- transporting dietary lipids

- immune responses

Draining excess interstitial fluid (fluid recovery)

the excess fluid is returned to the blood for usage or removal in the body

Lymphedema

occurs when lymphatic drainage is diminished leading to swelling. blockage of lymphatic vessels can lead to this condition

Transporting dietary lipids

this occurs through lacteals in the lining of the small intestine

- lymphatic vessels transport lipids and lipid-soluble vitamins (A, D, E, and K) absorbed in the gastrointestinal tract through the body

Immune response

the lymphatic system often times picks up pathogens with fluid in the body. these pathogens are removed in lymph nodes

3 primary parts of the lymphatic system are?

lymphatic vessels, lymphatic organs, lymphatic

Lymphatic vessels

transports fluids back to the blood that have escaped from the blood

Lymphatic organs

are scattered throughout the body

Lymph

the fluid contained in lymphatic vessels

Types of lymphoid cells

lymphocytes, macrophages, dendritic cells, reticular cells, neutrophils

Lymphocytes

serve as the primary cells of the immune system. these develop in red bone marrow and mature into two types of immunocompetent cells

T cells (T lymphocytes)

these manage immune responses and some directly attach and destroy foreign cells

B cells (B lymphocytes)

protect the body by producing plasma cells. plasma cells secrete antibodies into the blood. antibodies attach to and immobilize antigens until they can be destroyed

Lymphatic macrophages

protect the body by phagocytizing foreign substances and by activating T cells

Dendritic cells

are also phagocytes on foreign substances that

Reticular cells

produce a network of protein fibers that support cells in the lymphoid organs

Neutrophils

aggressively attack and kill bacteria

Lymphatic capillaries

small vessels located in the spaces between cells. these are typically closed at one end (unlike capillaries in blood)

Where lymphatic capillaries are NOT found

bone marrow and nervous tissue

Composition of lymphatic capillaries

made of very thin endothelial cells whose ends overlap one another

How fluid enters a lymphatic capillary

when fluid pressure is greater on the outside, the overlapping ends of the endothelial cells are pushed open, allowing fluid to enter

How fluid is prevented from leaving a lymphatic capillary

when fluid pressure is greater on the inside, the overlapping endothelial cell ends are forced shut, preventing fluid from leaking back into tissue spaces

What can enter lymphatic capillaries

proteins from surrounding tissue spaces, cell debris, and pathogens. all can enter lymphatic capillaries for transport through the body

Lacteals

special lymphatic capillaries that transport fat from the small intestine to the bloodstream

Chyle

fatty lymph

Lymph flows from lymphatic capillaries into what?

lymphatic collecting vessels

Lymphatic collecting vessels

these are wider than lymphatic capillaries. these vessels in the skin tag along with superficial veins and the deep lymphatic vessels of the body travel with deep arteries

Lymphatic collecting vessels vs veins

these have the same tunics as veins, but they have thinner walls and more valves than veins

Lymphatic trunks

formed by the union of the largest lymphatic collecting vessels. these drain large areas of the body. these are named for the area of the body that they drain; lumbar trunk, subclavian trunk, and intestinal trunk

Lymphatic ducts

receive lymph from lymphatic trunks

2 major lymphatic trunks

right lymphatic duct and thoracic duct

Right lymphatic duct

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

Thoracic duct

large, receives lymph from the rest of the body

What does the lymphatic system lack?

a pump to push fluid into and through lymphatic vessels

What moves fluid through the lymphatic system

1. milking action of skeletal muscles

2. pressure changes in the thorax during breathing

3. numerous valves in lymphatic vessels

4. pulsations of nearby arteries

Lymph nodes

cluster along the major lymphatic vessels of the body. these are the most numerous of the lymphatic organs. these act to filter lymph as it moves through the lymphatic system

Where are lymph nodes located

they are located throughout the body, but they cluster in the inguinal, axillary, and cervical regions of the body (these are areas where lymphatic collecting vessels converge to form lymphatic trunks)

2 primary functions of lymph nodes

filtering lymph and activating immune system

Filtering lymph

MACROPHAGES in the nodes act to destroy and remove microbes and foreign debris that is carried by lymph

Activating the immune system

LYMPHOCYTES in the nodes monitor the lymphatic system for foreign invaders and they attack such creatures when they are present

Structure of a lymph node

- they are typically small, and bean shaped

- each node is surrounded by a thick CAPSULE. TRABECULAE (connective tissue strands) extend inward to divide the lymph node into a number of chambers or compartments.

Cortex of a lymph node

outer portion of a node. this area contains follicles where dividing B cells are located

Medulla of a lymph node

contains MEDULLARY CORDS which are inward extensions of lymphatic tissue

Medullary cords

contain plasma cells

Lymph sinuses

fill the central portion of the node. these sinuses contain numerous lymphocytes and macrophages, both of which provide protection to the body

Circulation in the lymph nodes

afferent lymphatics --> subcapsular sinus --> trabecular sinus --> medullary sinus --> hilus (an indentation near the efferent lymphatics)

Efferent vs afferent lymphatic vessels

generally, there are fewer efferent lymphatic vessels than afferent lymphatic vessels; therefore, lymph flow slows substantially. this allows time for macrophages and lymphocytes to cleanse and filter lymph of foreign debris and bacteria

How does lymph get cleaned

has to pass through several lymph nodes before it is completel cleansed

Lymph nodes are often the first sites to capture what?

metastatic cancer cells

Lymphoma

cancer of the lymph nodes

Lymphadenitis

inflammation of a lymph node. this typically occurs due to some type of infection

Hodgkin's disease

malignancy of a lymph node

Spleen

the largest lymphoid structure in the body. located in the left side of the abdominal cavity beneath the diaphragm

What is the spleen the primary site for

primary site of lymphocyte proliferation and immune response. it also has a role in cleansing the blood by removing old and worn blood cells and platelets from the body

Other functions of the spleen

- storage of red blood cell breakdown products for future use and processing

- serving as the site of red blood cell production in the fetus (this function ends after birth)

- storing blood platelets

Structure of the spleen

it is surrounded by a CAPSULE. the spleen contains TRABECULAE that support large numbers of macrophages and lymphocytes. these lymphocytes are primarily stored in a region known as the WHITE PULP

Red pulp

involved primarily in removing red blood cells. these structures contain macrophages that aid in the breakdown of red blood cells

Splenic cords

make up much of the red pulp of the spleen

Splenectomy

surgical removal of the spleen

- this usually occurs following trauma to the spleen. the liver often assumes the functions of the removed spleen. surgeons try to leave some of the spleen in the body because in some cases, the spleen can regenerate

Splenomegaly

enlarged spleen. this can be an indicator of cancer or mononucleosis

Thymus gland

located in the inferior neck and extending into the superior thorax

What does the thymus gland secrete

hormones thymosin and thymopoietin. these two hormones force T lymphocytes to fight specific pathogens in the immune response (a property known as immunocompetence)

When is the thymus gland most active

most active during childhood. follow adolescence, its growth stops and it gradually starts to atrophy

The thymus gland is primarily composed of what

densely packed lymphocytes. these lymphocytes are located in the cortex.

What does the thymus not contain

B cells

Tonsils

are considered to be the simplest of all the lymphoid organs. these form a ring around the pharynx and they are named according to location

Types of tonsils

palatine, lingual, pharyngeal, tubal

Palatine tonsils

paired, located on either side of the posterior end of the oral cavity

- these are the largest and most commonly infected tonsils

Lingual tonsils

paired, located at the base of the tongue

Pharyngeal tonsil

located at the posterior wall of the nasopharynx. these are referred to as the adenoids if they are enlarged

Tubal tonsils

surround the openings of the eustachian tubes into the pharynx

What are the purpose of tonsils

gather and remove pathogens entering the pharynx via food or inhaled air

What do tonsils contain

contain invaginations known as CRYPTS. the walls of these crypts are covered by epithelial tissue. bacteria and other pathogens are often trapped and destroyed in the epithelial cells covering the crypts

Peyer's patches

structurally similar to tonsils, these are located in the small intestine.

- these are involved in destroying bacteria that enter into the small intestine and generating memory lymphocytes that provide long-term immunity

Vermiform appendix

located in the large intestine, is structurally similar to Peyer's Patches

Red bone marrow

located in the open spaces of spongy bone

- red bone marrow plays a critical role in the formation of new, healthy blood cells

- the tonsils gather and remove pathogens entering the pharynx via food or inhaled air