Lymphatic System

What are the two parts of the lymphatic system?

• A network of lymphatic vessels

• Various lymphatic tissues and organs around the body

What are the lymphatic system functions?

• To transport fluids that have escaped from the blood vessel system back into the blood.

• Plays essential roles in body defense and resistance against disease.

What is edema? What causes of the formation of it?

Edema is leaked fluid from the blood plasma that accumulates in the capillary beds. As the blood circulates around the body, fluid goes in and out of the capillary beds. Some of the fluid stays in the tissue and leads to be brought back to the blood stream by the lymphatic system. If not it will accumulate producing edema.

Excessive edema accumulation will lead to what?

Impairment of the ability of tissue cells to make exchanges with the interstitial fluid and blood.

What is lymph?

The excess tissue fluid which is carried by lymphatic vessels and returned into the bloodstream.

Where are lymph capillaries located?

The form a network between the tissue cells and blood capillaries in the loose connective tissue of the body. They are anchored to the connective tissue by filaments.

How do lymph capillaries bring lymph back to the blood vessels?

They absorb the lymph, the endothelial cells of the walls form flap like one-way valves, the high fluid pressure opens the valves, the fluid goes into the capillaries, higher pressure on the inside closes the valves and keeps the fluid in.

Describe the anatomy of lymphatic vessels.

They have the same three tunics as blood vessels, they form a one-way system to the heart, the do not have a pump

How does lymph move to the heart?

• contraction and relaxation of skeletal muscle

• pressure change in thorax when breathing

• Rhythmic contraction of smooth muscle in vessel walls

Describe how lymphatic transport is.

Slow and sporadic,

What are the lymphatic collecting vessels?

Larger lymphatic vessels that collect lymph from lymphatic capillaries. The bring lymph to and take it away from the lymph nodes. They return fluid to circulatory veins in the heart.

Lymph enters the veins through what two ducts?

• Right lymphatic duct

• Thoracic duct

What does the right lymphatic duct do?

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

What does the thoracic duct do?

It receives lymph from the rest of the body. It arises as an enlarged sac called the cisterna chyli which is located anteriorly to the lumbar vertebrae and collects lymph from the lower limbs and intestinal trunk. Superiorly, it collects lymph from the left side of the head and thorax and left arm.

What are lacteals?

Lymph vessels in the intestines

How is lymph cleansed?

As lymph passes through the lymph nodes, it is cleansed of debris and examined by cells of the immune system.

Where are lymphocytes made?

in the red bone marrow

What do lymphocytes mature into?

Two immunocompetent cells: T-lymphocytes and B-lymphocytes

What is the function of t-lymphocytes?

Activated T-cells directly attack and destroy the infected cells

What is the function of b-lymphocytes?

They protect the body by producing plasma cells.

What do plasma cells do?

The secrete antibodies into the blood.

What do antibodies do?

They immobilize antigens until the can be destroyed by phagocytes.

What are macrophages?

Lymphatic system cells that phagocytize foreign substances and active the T-lymphocytes.

What are dendritic cells?

Spiny looking cells that found in the lymphoid tissue. They capture antigens and bring them back to the lymph nodes. They also play a role in T-lymphocyte activation.

What are reticular cells?

They are fibro-blast like cells that produce the reticular fiber stroma which is a network that supports other cells in the lymphoid tissue.

What is a lymph node?

A kidney shaped small structure. There are millions throughout the body. They filter lymph before it is brought back to the blood.

What is the anatomy of lymph nodes?

They are less than 1 inch long and kidney shaped. They are buried in the connective tissue around them. Each node is surrounded by a dense fibrous capsule from which strands called trabeculae extend and divide the node into several compartments.

What is the concave side of the lymph node called?

The hilum

What is the inside of the lymph node called?

The medulla

What is the outside of the lymph node called?

the cortex

What are the parts of the cortex?

• the follicles

• the germinal centers

• cortical sinusoids

Describe the three parts of the cortex.

• the follicles- collections of lymphocytes

• germinal centers- dark stained centers of the follicles. they enlarge when b-cells are producing plasma cells

• cortical sinusoids- contains in transit lymphocytes that are constantly circulating

What are the two parts of the medulla?

• medullary cords

• medullary sinuses

Describe the parts of the medulla.

• medullary cords- cords of lymphatic tissue and plasma cells and t-cells

• vessel likes spaces separating the medullary cords. these vessels are crisscrossed by reticular fibers

Describe the flow of lymph through nodes.

Enters the convex side via afferent lymph vessels → subscapular sinus → cortical sinusoids → medullary sinuses → exits the node through the hilum via efferent lymph vessels

What are the other lymphatic organs?

• spleen

• thymus

• tonsils

• Peyer’s patches

What is a function that only the lymph nodes do?

Filtering lymph

What tissue is predominant in lymph organs?

reticular connective tissue

Where is the spleen located?

Left side of the abdomen, anterior part of the stomach

What does the spleen do?

• filters and cleanses blood

• destroys worn out red blood cells'

• forms all blood cells in the fetus

• produces lymphocytes in the adult spleen

• stores platelets and acts as a blood reservoir

Describe the structure of the spleen.

Surrounded by a fibrous capsule with trabeculae extending inward. Contains lymphocytes, macrophages, and RBCs. Has two colored regions.

• white pulp: appears like islands in a red sea

  • mainly consists of lymphocytes on reticular fibers

  • involved in immune functions of the spleen

• Right pulp: all remaining splenic tissue

  • consists of blood sinusoids and macrophages

  • disposes worn out RBCs and blood-borne pathogens

What is a special characteristic of the spleen and how is it helpful?

The spleen’s capsule is thin so a direct blow can cause it to get ruptured.

The spleen can repair itself if left alone. If the spleen is removed, the liver and bone marrow will take over its functions. In children younger than 12, even if only a small part of the spleen is left, the spleen will regenerate itself.

When is the thymus most used?

It functions at peak levels during childhood and starts to atrophy after puberty. By old age it has been replaced almost entirely by fibrous fatty tissue.

Describe the medulla and cortex of the thymus.

cortex- mainly lymphocytes and a few macrophages

medulla- fewer lymphocytes, thymic corpuscles (made up of keratinized epithelial cells) which are the site of T-cell destruction,

What does the thymus do?

Site of t-cell destruction

produces thymosin to program t-lymphocytes

What are tonsils?

Small masses of lymphoid tissue in the mucosa around the throat.

How many tonsils are there are what are they?

There are four tonsils.

1. Paired palatine tonsils- either side of the posterior end of the oral cavity, largest and most easily infected

2. Lingual tonsil- at the base of the tongue

3. Pharyngeal tonsil- posterior wall of the nasopharynx

4. Tubal tonsils- surround the openings of the auditory tubes in the pharynx

What is the largest and most easily infected tonsil?

The paired palatine tonsils

What is the function of tonsils?

They trap and remove bacteria and other foreign materials entering the pharynx by food or air.

What is tonsilitis?

Inflammation of the tonsils when the become congested with bacteria.

What are Peyer’s patches?

Clusters of lymphoid follicles found in the wall of the small intestine and appendix.

What do Peyer’s patches do?

They are in the ideal position to:

1. destroy bacteria of the intestines and prevent pathogens from the intestinal wall

2. generate memory lymphocytes for long-term immunity

What is mucosa associated lymphatic tissue?

A collection of small lymphoid tissue that includes:

• peyer’s patches

• tonsils

• other accumulations of lymphoid tissue