I. Lymphatic Pathways

A. Lymphatic Capillaries

1. description--microscopic, closed-ended tubes that extend into the spaces of the tissue
2. composition--single layer of squamous epithelial cells
3. lymph--fluid inside a lymphatic capillary

B. Lymphatic Vessels

1. formation--formed by merging lymphatic capillaries
2. walls similar to veins--including having valves to prevent the backflow of lymph
3. lead to specialized organs called lymph nodes which then lead into large lymphatic trunks

C. Lymphatic Trunks

1. drain--lymph from large regions (lymph nodes) of the body
2. join--into one of two collecting ducts

a. thoracic duct--larger and longer of the collecting ducts; receives lymph from the lower body regions, left arm and left side of the head and neck, and left thorax; empties into the left subclavian vein near the junction of the left jugular vein

b. right lymphatic duct--receives lymph from the right side of the head and neck, right arm, and right thorax; empties into the right subclavian vein near the junction of the right jugular vein

3. lymph then enters the venous system and becomes part of the plasma just before the blood returns to the right atrium

Start with the vena cava and list the pathway for the blood.

At what point does the lymph leave the bloodstream?

Where does it go from there?

Follow the path until the lymph reenters the bloodstream. Where is that?

Review the lymph pathway from the main page of the immune system.

II. Lymph

A. Function--ooze into tissue spaces and looking for foreign particles to destroy

B. Movement--controlled by muscular activities

1. skeletal muscle contract and compress lymphatic vessels
2. breathing muscles aid the circulation of lymph
3. smooth muscles in the walls of larger lymphatic vessels contract and compress the lymph inside

IN ALL 3 CASES, LYMPH CAN NOT FLOW BACKWARDS BECAUSE OF THE VALVES.

III. Lymph Nodes

A. Structure--usually less than 2.5 cm in length and are somewhat bean-shaped

1. hilium--indented region in the node; area where lymph leaves the node

2. nodules--compartments that contain dense masses of lymphocytes

3. lymph sinuses--spaces within the nodules, provide channels for lymph circulation as it passes through the node

B. Location--generally occur in groups or chains along the larger lymphatic vessels

1. cervical nodes---in the neck

2. axillary nodes---the armpit

3. thoracic cavity---the chest

4. abdominal cavity nodes---the stomach

5. supratrochlear nodes---inside the elbow

6. pelvic nodes

7. inguinal nodes--the groin

Label the three parts of a lymph node.

.

Label where you would find each lymph node.

IV. Other Lymphatic Organs

A. Thymus

1. description--bi-lobed structure located in front of the aorta and behind the upper part of the sternum
2. lobules--subdivisions of the thymus that contain large numbers of lymphocytes
3. T-lymphocytes---develop here and leave the thymus to function in immunity
4. thymosin--a hormone secreted by the thymus to stimulate the activity of the lymphocytes after they leave the thymus

B. Spleen

1. size--the larger of the lymphatic organs
2. location--upper left portion of the abdominal cavity; just beneath the diaphragm and behind the stomach
3. description--resembles a large lymph node and is divided into lobules. However, unlike the lymph nodes, the spaces within the chambers of the spleen are filled with blood instead of lymph.
4. blood reservoir--during times of rest when circulation of blood is decreased some blood can be stored within the spleen; can be used during times of exercise
5. phagocytes--line the cavities of the spleen; can engulf and destroy foreign particles that may be carried in the blood as it flows through; can destroy damaged red blood cells also

V. Body Defenses Against Infections

A. Pathogens--disease-causing organisms; bacteria, fungi, viruses, protozoa, parasitic worms

B. Nonspecific immunity--protects against many types of pathogens

1. phagocytosis--neutrophils and monocytes that engulf particles similar to an amoeba. Some are fixed in an organ and others are free moving
2. mechanical barriers--skin and mucus membranes create barriers against the entrance of infectious agents
3. enzymatic actions--certain enzymes in our body fight invasion; gastric juice, lysozyme, hydrochloric acid
4. interferon--a group of proteins produced by cells in response to the presence of viruses; inhibit viral reproduction
5. inflammation and fever--a tissue's response to injury; localized redness, swelling, heat and pain; caused by white blood cells accumulation

C. Specific Immunity

1. definition--developing a protection from an infectious disease or particular foreign substance
2. antibodies--proteins (immunoglobulins) produced by lymphocytes, are carried by body fluids, and respond to or destroy antigens
3. antigens--large molecules not usually present in the body stimulate antibody production and combine with specific antibodies
4. primary immune response--the 1st time the body encounters a specific antigen
5. secondary immune response--the second time a body encounters an antigen; kills it or is killed by it

D. Lymphocytes

1. T-Lymphocytes--they mature in the thymus gland; do not secrete antibodies but must come in direct contact with an antigen to kill it
2. B-Lymphocytes--their site of processing is unknown, they secrete antibodies into the blood and lymph

E. Types of Immunities

1. humoral--result from exposure of B-lymphocytes to an antigen; antibodies are produced

a. naturally acquired active immunity--a person who has been exposed to a live pathogen, develops the disease and produces antibodies to the antigen
b. artificially acquired active immunity--a person is injected with a vaccine of a killed or weakened antigen; the person develops antibodies to the antigen
c. artificially acquired passive immunity--a person receives an injection of ready-made antibodies; used when a person does not have time to make their own antibodies

2. cell-mediated--T-lymphocytes must come in direct contact with the antigen

F. Allergies(hypersensitivity)---a person produces an abnormal immune reaction to a common antigen

1. definition

a. allergen--an antigen that stimulates an allergic reaction
b. histamine--a substance produced from allergies that cause dilated blood vessels causing weeping in the tissue; leads to sneezing, weeping eyes, runny nose

2. types of allergies

a. immediate hypersensitivity--the antibodies of B cells attach to a body cell causing it to release histamine
b. delayed hypersensitivity--requires a longer time before reaction; a cell mediated T cell response; usually treated with corticosteroids; examples--poison ivy, poison oak, sumac

G. Transplantation

1. tissue rejection reaction--when a person rejects a transplant because the immune system believes the new organ/tissue to be a foreign substance (antigen)

2. solutions to tissue rejection

a. tissues must be a close match to recipient
b. immunosuppressive drugs

How are specific and nonspecific immunities different?

Describe several nonspecific immunities. Why are they nonspecific?

What is the difference between primary and secondary immune responses?

What is the importance of an antibody?

What is the difference between an antigen and a pathogen?

What is the difference between the T and B lymphocytes? Be sure to include where they are produced, what they do, and how they do it.

Describe the difference between humoral and cellular immunity.

Give an example of a naturally acquired immunity.

Give an example of an artificially acquired active immunity.

Give an example of an artificially acquired passive immunity.

Give the difference between an allergen and an antigen.

What would be the use of an antihistamine compared to a decongestant?

Describe the differences between an immediate and a delayed reaction to an antigen.

Why do we reject some tissue or organ transplants? What can we do to minimize that possibility?