I. Functions

A. Maintenance of fluid balance

B. Immunity

II. Anatomy of the Lymphatic system

A. Lymph: clear watery fluid found in the lymphatic vessels

B. Lymphatic vessels

1. lymph capillaries are microscopic blind ended vessels originating in tissues (do not form a complete circle).

a. single layered wall of flattened endothelial cells.

b. lacteals: located in villi of small intestine.

2. Resemble veins, with some exceptions

a. thinner walls

b. more semilunar valves

c. lymph nodes

3. Function: allows molecules too large to be absorbed by blood capillaries to return to the blood stream.

C. Lymphatic ducts

1. formed by merging of smaller vessels

2. Right lymphatic duct

a. drains upper right quadrant.

b. empties into the right subclavian.

3. Thoracic duct

a. drains remainder of body

b. joins left subclavian vein.

D. Circulation of lymph

1. lymphatic pump

a. breathing movements

b. skeletal muscle contractions

E. Lymph nodes

1. Structure

a. shape: oval or bean

b. several afferent vessels enter. contain valves to keep lymph moving in proper direction.

c. one efferent vessel emerges. one way valves keep lymph moving in one direction.

2. Function

a. Defense

b. Hematopoeisis

3. Location

a. Submental and submaxillary groups

b. Superficial cervical lymph nodes

c. Superficial cubital (supratrochlear) lymph nodes.

d. Axillary lymph nodes

e. Inguinal lymph nodes

III. Lymphatic Organs

A. Tonsils

1. structure: masses of lymphoid tissue in a protective ring

2. location: palatine tonsils: on each side of the throat pharyngeal tonsils: near the posterior opening of the nasal cavity. lingual tonsils: near the base of the tongue.

3. function: help protect against bacteria

B. Thymus

1. structure: 2 pyramidal shaped lobes with delicate and finely lobulated surfaces.

2. location: in mediastinum.

3. function

a. lymphocyte development

b. secretes thymosin

C. Spleen

1. structure

a. ovoid shape.

b. fibrous capsule

c. largest lymphatic organ.

2. location: in left hypochondrium directly below the diaphragm, above the left kidney.

3. function

a. defense

b. hematopoeisis

c. RBC and platelet destruction

d. blood reservoir

IV. Immunity

A. Nonspecific Immunity

1. Species Resistance

2. Types of barriers

a. Mechanical barriers

i. skin

ii. mucous membrane

b. Chemical barriers

i. sebum

ii. mucus

iii. enzymes

iv. hydrochloric acid

3. Inflammation

a. Inflammatory response

i. tissue damage triggers release of mediators from cells such as mast cells.

ii. mediators (histamines, kinins, prostaglandins) attract WBCs to the area.

iii. produces characteristic signs of inflammation: heat, redness, pain, swelling.

b. Natural killer cells: lymphocytes that kill many types of tumor cells and cells infected by viruses.

c. Interferon: interferes with virus' ability to cause disease by preventing multiplication of viruses.

B. Specific Immunity

1. Antigens: surface proteins that induce an immune response.

2. Antibodies: immunoglobulins; chemicals that bind to foreign antigens. produce antibody-mediated response.

3. Clone: family of cells descending from one cell.

4. Complement: group of proteins that destroy foreign cells.

5. B cells

a. cells that produce antibodies that attack pathogens or direct phagocytes to attack them.

b. produce antibody-mediated immunity.

c. Activation of B cells

i. an antigen binds to antibodies of the surface of a B cell.

ii. rapid mitosis produce clones.

iii. some clones differentiate to become plasma cells to secrete antibodies.

iv. some clones remain as memory cells.

6. T cells

a. attack pathogens directly.

b. produce cell-mediated immunity, which is triggered when a T cell encounters a foreign cell.

c. function

i. search out, recognize, and bind to appropriate antigens located on the surfaces of cells.

ii. kills cells.

iii. usually work against virus-infected cells, cancer cells, transplanted tissues and organs.

7. Primary Response

a. T cells: attack antigens and can distinguish between self and invader.

b. B cells: produces antibodies that bind to and destroy antigens.

8. Secondary Response

a. response to subsequent infection by same pathogen.

b. memory T and B cells remain.

C. Inherited Immunity

1. specific or non-specific immune mechanisms in place by genetic mechanisms during the early stages of development. inborn immunity.

2. Acquired immunity: develops after birth.

a. active immunity: immunity developed as a result of an individual's own immune system responding to a harmful agent.

i. Naturally acquired active immunity: not deliberate exposure. occurs in the course of everyday living.

ii. Artificially acquired active immunity: deliberate immunization.

b. passive immunity: developed in another and then transferred to a previously unimmune person.

i. Naturally acquired passive immunity: antibodies received by fetus from mother.

ii. Artificially acquired passive immunity: antibodies received from injection.

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