Lymphatic System

Three main components of the lymphatic system

1. Network of lymphatic vessels (lymphatics) 2. Lymph: fluid in vessels 3. Lymph nodes: cleanse lymph.

Primary function of the lymphatic system

To return fluids leaked from blood vessels back to the blood.

Lymphoid organs and tissues

Provide the structural basis of the immune system by housing phagocytic cells and lymphocytes.

Structures that are considered lymphoid organs and tissues

Spleen, thymus, tonsils, lymph nodes, and other lymphoid tissues.

The interstitial fluid the lymphatic system circulate per day

Approximately 3 liters.

Interstitial fluid when it enters lymphatic vessels

It is called lymph.

Type of system do lymphatic vessels provide for lymph flow

A one-way system, ensuring lymph flows only toward the heart.

Lymphatic capillaries

Blind-ended vessels that weave between tissue cells and blood capillaries.

Lymphatic capillaries are absent

In bones, teeth, and bone marrow.

Specialized structures increase the permeability of lymphatic capillaries

1. Overlapping endothelial cells forming one-way minivalves 2. Minivalves anchored by collagen filaments to matrix, so increases in ECF volume opens minivalves even more

Lacteals

Specialized lymph capillaries present in the intestinal mucosa that absorb digested fat and deliver fatty lymph (chyle) to the blood (transport digestive fats).

Larger lymphatic vessels

They have thinner walls, more internal valves, and anastomose more frequently.

Collecting lymphatic vessels drain into

They drain into increasingly larger vessels called lymphatic trunks, vessels, and ducts

The names of the paired lymphatic trunks

Paired lumbar, paired bronchomediastinal, paired subclavian, paired jugular trunks.

Right lymphatic duct

Drains right upper arm and right side of hear and thorax

Thoracic duct

Drains rest of body. In about half of individuals, starts out as an enlarged sac (cisterna chyli).

Both lymphatic ducts and thoracic duct

Empties lymph into venous circulation at junction of internal jugular and subclavian veins on its own side of the body.

Function of lymph nodes in the lymphatic system

To cleanse lymph (lymphatic ducts)

The significance of the increased permeability of lymphatic capillaries

It allows them to take up larger molecules and particles that blood capillaries cannot, such as proteins, cell debris, pathogens, and cancer cells.

The role of minivalves in lymphatic capillaries

They open to allow increased interstitial fluid volume to enter and close when the volume decreases.

The relationship between collecting vessels and veins in the skin

Collecting vessels in the skin travel with superficial veins.

Deep lymphatic vessels travel with

They travel with arteries.

The single intestinal trunk responsible for

Draining lymph from the intestinal area.

The primary purpose of lymphatic vessels

To transport lymph back to the bloodstream.

Two large lymphatic ducts that lymph is delivered into

The right lymphatic duct and the thoracic duct.

Type of system is the lymphatic system compared to

It is a low-pressure system, similar to the venous system.

Mechanisms propel lymph through the lymphatic system

The milking action of skeletal muscle, pressure changes in the thorax during breathing, valves to prevent backflow, pulsations of nearby arteries, and contractions of smooth muscle in the walls of lymphatics.

Physical activity affect lymph flow

Physical activity increases the flow of lymph.

Lymphedema

Severe localized edema caused by anything that prevents normal return of lymph to blood.

Some causes of lymphedema

Tumors blocking lymphatics or removal of lymphatics during cancer surgery.

May improve lymphedema

If some lymphatic pathways remain and enlarge.

Two main types of lymphoid cells

Immune system cells: T Cells (lymphocytes), B cells (macrophages), dendritic cells and supporting cells (reticular cells).

Lymphocytes

Cells of the adaptive immune system that mature into T cells and B cells.

Macrophages

They phagocytize foreign substances and help activate T cells.

Dendritic cells

They capture antigens and deliver them to lymph nodes, also helping to activate T cells.

Reticular cells

Produce reticular fibers called stroma in lymphoid organs.

Function of stroma in lymphoid organs

It acts as a network-like support that scaffolds immune cells.

Main functions of lymphoid tissue

To house and provide proliferation sites for lymphocytes and offer surveillance vantage points for lymphocytes and macrophages.

type of connective tissue largely composes lymphoid tissue

Reticular connective tissue.

What is diffuse lymphoid tissue?

A loose arrangement of lymphoid cells and some reticular fibers found in virtually every body organ (Found in lamina propria of mucous membranes).

What are lymphoid follicles (nodules)?

Solid, spherical bodies consisting of tightly packed lymphoid cells and reticular fibers, containing germinal centers of proliferating B cells. Isolated aggregations of Peyer's patches and in appendix.

What are the two functional categories of lymphoid organs?

Primary lymphoid organs and secondary lymphoid organs.

Primary lymphoid organs and their function

Red bone marrow and thymus; areas where T and B cells mature.

T and B cells originate and mature

Both originate in bone marrow; B cells mature in bone marrow, T cells mature in thymus.

Secondary lymphoid

Areas where mature lymphocytes first encounter their antigen and become activated

Secondary lymphoid organs

Lymph nodes, spleen, mucosa-associated lymphoid tissue (MALT), and diffuse lymphoid tissues.

Lymph nodes

Principal secondary lymphoid organs of body. Most embedded deep in connective tissue in clusters along lymphatic vessels. Some are nearer to body surface in inguinal, axillary, and cervical regions.

First function of lymph nodes

They act as lymph filters, cleansing the lymph by removing microorganisms and debris.

Second function of lymph nodes

Immune system activation: offer a place for lymphocytes to become activated and mount an attack against antigens.

Role of macrophages in lymph nodes

They remove and destroy microorganisms and debris that enter lymph.

Buboes

Inflamed, swollen, tender lymph nodes that indicate an overwhelming infection; often referred to as swollen 'glands'.

Lymph nodes affected by cancer

They can become secondary cancer sites if metastasizing cancer cells become trapped, leading to swollen but usually painless nodes.

Spleen located and size

The spleen is located on the left side of the abdominal cavity, just below the stomach, and is about the size of a fist.

Two main functions of the spleen

Site of lymphocyte proliferation and immune surveillance; cleanses blood of aged blood cells and platelets.

Two histological components of the spleen

White pulp and red pulp.

White pulp of the spleen

Immune function occurs, containing mostly lymphocytes on reticular fibers. Found around central arteries (islands of white in a sea of red pulp).

Red pulp in the spleen

Destruction of old blood cells and bloodborne pathogens; rich in RBCs and macrophages that engulf them.

Spleen's red pulp composition

They are composed of splenic cords (reticular tissue) that separates blood-filled splenic sinusoids (venous sinuses).

Role of the splenic artery and vein

They serve the spleen, entering and exiting at the hilum.

What happens to lymphocytes in lymph nodes?

They become activated and mount an attack against antigens.

What are the common locations of lymph nodes in the body?

Inguinal, axillary, and cervical regions where collecting vessels converge into trunks.

Clinical feature of bubonic plague related to lymph nodes

Buboes, which are swollen lymph nodes that can be pus-filled.

How do swollen lymph nodes due to infection differ from cancerous nodes?

Infected nodes are usually painful, while cancer-infiltrated nodes are swollen but not painful.

The largest lymphoid organ

The spleen.

Cause of the spleen to rupture

A direct blow or severe infection, causing spilling of blood into peritoneal cavity.

Splenectomy

Surgical removal of a ruptured spleen.

Why has the frequency of emergency splenectomies decreased?

It has been discovered that the spleen can often repair itself.

Organs that take over the functions of the spleen if it is removed

The liver and bone marrow.

Can the spleen regenerate in children?

Yes, if a small part is left, the spleen will regenerate in children younger than 12.

MALT stands for

Mucosa-associated lymphoid tissue (protects from pathogens trying to enter body)

MALT found in the body

In mucous membranes throughout the body, including the respiratory tract, genitourinary organs, and digestive tract

Largest collections of MALT

Tonsils, Peyer's patches, and appendix.

Tonsils

Simplest lymphoid organs: form ring of lymphatic tissue around pharynx (swellings of mucosa). It gathers and removes pathogens in food or air.

Tour types of tonsils?

Palatine tonsils, lingual tonsils, pharyngeal tonsils (adenoids), and tubal tonsils.

Palatine tonsils

Found at posterior end of oral cavity. Largest of tonsils and most often infected.

Lingual tonsil

Lumpy collection of follicles at base of tongue.

Pharyngeal tonsil

Located in posterior wall of nasopharynx

Tubal tonsils

Surround openings of auditory tubes into pharynx

Tonsillar crypts

Invaginations formed by overlying epithelium that trap bacteria or particulate matter. Risky but allows immune cells to become activated and build memory cells against potential pathogens.

Two main functions of Peyer's patches

To destroy bacteria and generate memory lymphocytes.

What are Peyer's patches?

Clusters of lymphoid follicles in the wall of the distal portion of the small intestine (aggregated lymphoid nodules).

Appendix

An offshoot of the first part of the large intestine containing a large number of lymphoid follicles.

Appendix's functions

To destroy bacteria and generate memory lymphocytes.

Thymus location

In the inferior neck, extending into the mediastinum and partially overlying the heart.

Thymus's Functions

To serve as a lymphoid organ where T cells mature.

Thymus during age

It's most active and largest during childhood. Then during adolescence, it stops growing and gradually atrophies.

Thymus differ from other lymphoid organs

It has no follicles (lacks B cells), does not directly fight antigens, and its stroma is made of epithelial cells.

Blood-thymus barrier

A barrier that keeps immature T lymphocytes isolated from any antigens to prevent premature activation.