Ch 16 immunity system

3 functions of the lymphatic system

• transports excess intestinal fluid away from interstitial space and returns it to the blood stream

• Absorbs lipids from digestive system and transports them ti the bloodstream; accomplished by lymphatic capillaries called lacteals

• Defends the body against diseases, and allows humans to live in world with other organisms

Lymphatic capillaries

Thin walled

Walls formed from simple squamous epithelium

Merge into lymphatic vessels

lymph

Tissue (interstitial) fluid enters lymphatic capillaries; fluid is now called

Lymphatic Vessels:

Walls are similar to veins, but thinner

composed of 3 layers

Contain semilunar valves, which allow one-way flow

Larger vessels lead to lymph nodes and then to larger lymphatic trunks

Inner layer:

An endothelial lining

Middle layer:

Smooth muscle and elastic fibers

Outer layer

Connective tissue

Lymphatic collecting ducts:

Drain lymph from trunks

Two for the entire lymphatic system = Thoracic & right lymphatic

Thoracic duct:

Longer and wider of the two ducts

Drains majority of body

Begins as sac called cisterna chyli, empties into L. Subclavian Vein

Right lymphatic duct:

Much smaller than thoracic duct

Begins in left thorax, empties into R. Subclavian Vein

Drains upper left portion of body

head

Lymph Formation

Filtration from plasma normal exceeds reabsorption

increases the tissue fluid hydrostatic pressure

Edema

process prevents accumulation of excess tissue fluid

Contraction of skeletal muscles

compresses lymphatic vessels, moving the lymph

Respiratory process

creates low pressure in thorax, and high pressure in abdomen during inspiration; sends lymph from abdomen to thorax

Smooth muscle in the larger lymphatic vessels

contracts to aid in flow of lymph

Valves in

lymphatic vessels prevent backflow

Mucosa-associated lymphoid tissue (MALT):

Unencapsulated lymphatic tissue of the digestive, respiratory, urinary, and reproductive tracts

Tonsils and appendix are composed of lymphatic nodules (compact masses of lymphatic tissue)

Peyer’s patches are aggregates of lymphatic nodules found in ileum (distal part of small intestine)

Thymus

Lobules contain lymphocytes derived from progenitor cells in red bone marrow

Most cells are inactive; called thymocytes

T lymphocytes (T cells), which leave thymus to provide immunity

Spleen:

Largest lymphatic organ

Located in the upper left part of abdominal cavity

Resembles large lymph node

Contains venous sinuses filled with blood: White pulp and Red pulp

White pulp:

Lymphocytes

red Pulp

Red blood cells, lymphocytes, and macrophages

Innate (nonspecific) defenses:

General defenses

Protect against many types of pathogens

Adaptive (specific) defenses:

More specific and precise, targeting specific antigens

Carried out by lymphocytes that recognize certain foreign molecules

Enzymes

in body fluids provide a chemical barrier to pathogens; Examples: Pepsin in gastric juice and lysozyme in tears destroy microorganisms.

Interferons

block viral replication, act against growth of tumors, stimulate phagocytosis.

Complement

is a group of proteins in plasma and other body fluids that stimulates inflammation, attracts phagocytes, and enhances phagocytosis.

Natural Killer (NK) Cells:

Defend against viruses and cancer cells & Enhance inflammation

Phagocytosis

Removes foreign particles from the lymph

Phagocytes in the blood vessels and the tissues of the spleen, liver, or bone marrow remove particles from blood

endogenous pyrogen

IL-1 is also called (fire maker from within)

body temperature indirectly inhibits microbial growth; causes liver and spleen to take up iron, making it unavailable for bacteria and fungi to use in their normal metabolism

Antigens:

Non-self molecules that can evoke an immune response

T lymphocytes (T cells, thymus-derived lymphocytes):

Specialize in thymus

After release from thymus, make up 70 to 80% of circulating lymphocytes

Some T cells settle in lymphatic organs, such as lymph nodes, thoracic duct, white pulp of spleen

B lymphocytes (B cells, B = Bursa of Fabricius in chickens):

After release from bone marrow, make up 20 to 30% of lymphocytes in blood

Abundant in lymph nodes, spleen, bone marrow, intestinal lining

Helper T cells

Activate other cells; stimulates B cells to produce antibodies

Cytotoxic T cells:

Attack virally infected or cancerous cells

Memory T cells:

Provide future immune protection

Interferons

Block viral replication, stimulate macrophages to engulf viruses, stimulate B cells to produce antibodies, attack cancer cells

B cell actives

1. Antigen-bearing agents enter tissues.

2. B cell encounters an antigen that fits its antigen receptors.

3. Either alone or more often in conjunction with helper T cells, the B cell is activated. The B cell proliferates, enlarging its clone.

4. Some of the newly formed B cells differentiate further to become plasma cells.

5. Plasma cells synthesize and secrete antibodies whose molecular structure is similar to the activated B cell’s antigen receptors

T cell activites

1.Antigen-bearing agents enter tissues

2.An accessory cell, such as a macrophage, phagocytizes the antigen-bearing agent, and the macrophage’s lysosomes digest the agent.

3.Antigens from the digested antigen-bearing agents are displayed on the membrane of the accessory cell.

4.Helper T cell becomes activated when it encounters a displayed antigen that fits its antigen receptors.

5.Activated helper T cell releases cytokines when it encounters a B cell that has previously combined with an identical antigen-bearing agent.

6.Cytokines stimulate the B cell to proliferate, enlarging its clone.

7.Some of the newly formed B cells give rise to cells that differentiate into antibody-secreting plasma cells.

IgG

80% of antibodies; act on bacteria, viruses, toxins

Occurrence: Plasma and tissue fluid

IgE

<1% of antibodies; found in exocrine gland secretions

Exocrine gland secretions

Promotes inflammation and allergic responses

Agglutination

Clumping of antigens, making phagocytosis easier

Naturally acquired

Obtained by a natural process, such as getting and recovering from the disease, or given from mother to fetus or infant

Type I (immediate-reaction) hypersensitivity

Allergy; person produces many IgE antibodies against a specific allergen

Occurs minutes after contact with allergen; histamine is released

Symptoms include hives, hay fever, asthma, eczema, gastric disturbances, and anaphylactic shock (a life-threatening severe form)

Type III hypersensitivity (immune-complex reaction):

Antigen-antibody complexes form and deposit in certain tissues

Damages tissue via phagocytosis and complement-binding

Antibody complexes cannot be cleared from the body

Rheumatoid arthritis is an example

Type IV (delayed-reaction hypersensitivity):

May affect anyone

Results from repeated exposure of skin to allergen

Allergen activates T cells in skin, which release chemicals that cause eruptions and inflammation

Takes about 48 hours to occur

Graves disease

Restlessness, weight loss, irritability, increased heart rate and blood pressure

Thyroid gland antigens near thyroid-stimulating hormone receptor, causing overactivity

Type 1 diabetes mellitus

Thirst, hunger, weakness, emaciation

Pancreatic beta cells

Multiple sclerosis

Weakness, incoordination, speech disturbances, visual complaints

Myelin in peripheral nerves and in the white matter of the central nervous system