The Lymphatic System

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Lymphatic System

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Network of :

Ducts

Vessels

Organs

Produces, screens and moves fluid called lymph from tissues to the bloodstream.

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4 Parts of Lymphatic System

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1. Lymph a fluid similar to plasma, identical to interstitial fluid. No Plasma proteins.

2. Lymphatic vessels (lymphatic's) - network that carries lymph from peripheral tissues to the venous system.

3. Lymphoid tissues and lymphoid organs- found throughout the body.

4. Lymphocytes, Phagocytes, and other immune system cells.

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Functions of the Lymphatic System

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1.Is to produce, maintain and distribute the lymphocytes.

2. Drain excess interstitial fluid

3. Transports dietary lipids

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Lymphocyte Production

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Produced in:

1. In lymphoid tissues (tonsils)

2. Lymphoid organs (spleen, thymus)

3.In Red bone marrow

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Lymphocyte Distribution

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Lymphocytes detect problems and travel into the site of injury or infection

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Lymphocyte Circulation

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1.From blood to interstitial fluid(lymph) through capillaries.

2. Return to venous blood through lymphatic vessels.

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Lymphatic Vessels

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Vessels that carry lymph.

Begins with smallest vessels:

1. lymphatic capillaries (terminal lymphatic's)

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Lymphatic Capillaries

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Differ from blood capillaries in 4 ways:

1.Start as pockets rather than tubes

2. Gave larger diameters

3. Thinner walls

4.Flat or irregular in section

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Lymphatic Capillaries ( continued)

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Absent from bones, teeth, bone marrow, and CNS

1.Very permeable (take up proteins, cell debris, pathogens and cancer cells.)

2.Endothelial cells loosely bound together with overlap.

3. Overlap acts as one way valve:

a. allows fluid, solutes, viruses, and bacteria to enter

b. prevents return to intercellular space

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Lacteals

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Are special lymphatic capillaries in small

intestine

Transport lipids from digestive tract

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Lymph Flow

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From lymphatic capillaries to larger lymphatic vessels containing one way valves. ( More numerous than veins)

1. Lymphatic vessels travel with veins

2. Due to Peristaltic Contractions of smooth muscle in lymphatic vessel walls.

3. Skeletal muscular contractions (like veins)

a. Important for lymph flow

b. Immobilizing a limb will slow lymph drainage

4. Arterial Pulsations

5. Respiratory pump

6. Rate of Lymph return is slow (120ml/hr)

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Lymphatic Ducts and the Venous System

The Lymphatic System

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Is similar to venous system:

Divided into :

1. Superficial lymphatics

2. Deep lymphatics

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Superficial Lymphatics

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Located in:

Skin, Mucus Membranes, Serous Membranes lining body cavities

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Deep Lymphatics

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Large vessels that accompany deep arteries and veins

They have smooth muscle in their walls

Are capable of peristalsis

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Superficial and Deep Lymphatics

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Join to form from large lymphatic trunks

Trunks empty into 2 major collecting vessels:

1. Thoracic duct

2. Right lymphatic duct

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Base of the Thoracic Duct

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Expands into cisterna chili

Cisterna chili receives lymph from:

right and left lumbar trunks

intestinal trunk

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Thoracic Duct

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Collects lymph from (3/4 of the body)

1. Left bronchiomediastinal trunk

2. Left Subclavian trunk

3. Left jugular trunk

Empties into left subclavian vein

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The Right Lymphatic Duct

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Collects lymph from (1/4 of the body)

1. Right jugular trunk

2. Right subclavian trunk

3. Right bronchiomediastinal trunk

Empties into right subclavian vein

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Lymphodema

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Blockage of lymph drainage from a limb

Cause severe swelling

Interferes with immune system function

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Lymphocytes

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Makes up 20-30% of circulating leukocytes

Most are stored, not circulating

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2 Main Classes of Circulating Lymphocytes

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1.T-Cells

a. thymus-dependent

2. B Cells:

b. bone-marrow derived.

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Other Supporting Cells

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Macrophages phogocytize foreign substances; help activate T-Cells

Dendritic cells capture antigens and deliver them to lymph nodes: activate T-cells

Reticular cells produce reticular fiber stroma that supports other cells in lymphoid organs

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T Cells

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Make up 80% of circulating lymphocytes

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3 Main Types of T-Cells

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1. Cytotoxic T Cells

2. Helper T Cells

3. Suppressor T Cells

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Cytotoxic T Cells

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Attack cells infected by viruses

Produce cell-mediated immunity

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Helper T Cells

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Stimulate Function of T cells and B cells

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Suppressor T Cells

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Inhibit function of T cells and B cells

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Regulatory T Cells

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Another name for helper and suppressor T cells

Control Sensitivity of Immune Response

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B Cells

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Make up 10-15% of circulating lymphocytes

Differentiate into plasma cells

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Plasma Cells

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Produce and secrete antibodies (immunoglobin proteins)

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Antigens

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Antibody generators

Act as targets which identify any pathogen or foreign compound

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Immunogobin Proteins

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Also called antibodies

The binding of a specific antibody to its specific target antigen initiates antibody-mediated

immunity

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Antibody-Mediated Immunity

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A chain of events which destroys the target compound or organism

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Lymphocyte Distribution

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Tissues maintain different T cell and B cell populations

Lymphocytes wander through tissues:

a. Enter blood vessels or lymphatic's for transport

b. can survive many years

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Production and Distribution of Lymphocytes

Lymphopoiesis

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Lymphocyte production involves:

1. Bone marrow

2. Thymus

3. Peripheral lymphoid tissues

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Hemocytoblasts

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In bone marrow, divide into 2 types of lymphoid stem cells

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Lymphoid Stem Cells

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Group 1:

1. Remain in bone marrow

2. Produce B cells and natural killer cells

Group 2:

1. Migrate to thymus

2. Produce T cells in environment isolated by blood-thymus barrier

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T Cells and B Cells

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Migrate throughout the body

a. to defend peripheral tissues

Retain their ability to divide:

a. is essential to immune system function

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Differentiation

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B cells differentiate :

a. with exposure to hormone interleukin-7

T cells differentiate :

a. with exposure to several thymic hormones

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Interleukin-7

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A cytokine produced by (structural) stroma cells in bone marrow

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Lymphoid Tissues

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1.Surveillance vantage point for lymphocytes and macrophages

2. Large reticular connective tissue-type of loose connective tissue

3.Two Types:

1.Diffuse lymphoid tissue of lymphoid cells and reticular fibers in every body organ.

2. Lymphoid follicles (nodules) are solid, spherical bodies of tightly packed lymphoid cells and reticular fibers

a. Germinal centers of proliferating B cells may form part of larger lymphoid organs

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Distribution of Lymphoid Nodules

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Lymph nodes

Spleen

Respiratory Tract (tonsils)

Along digestive and urinary tract

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Mucosa-Associated Lymphoid Tissue (MALT)

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1. Lymph Nodules - Large aggregations of naked (no capsule, trabeculae, or hilum.)

2. Found embedded in mucous membranes of systems that communicate with external environment.

3. Protects against outside pathogens in food or air

Include :

a. Gastrointestinal Tract

b. Genitourinary Tract

c. Upper Respiratory Tract

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Gut - Associated Lymphoid Tissue (GALT)

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Specifically in GI Tract.

Peyer's Patches - aggregated lymphoid nodules located throughout the small attaches

Appendix

Both destroy bacteria, generate "memory" lymphocytes

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The 5 Tonsils (GALT)

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In walls of Pharynx:

1. Left and Right Palatine Tonsils

2.Pharyx tonsil (adenoid)

3. 2 lingual tonsils

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Lymphoid Organs

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Are separated from surrounding tissues

by Fibrous Connective Tissue Capsule

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Lymph Nodes

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Range from 1-25mm in diameter

Act as filters for lymph fluid

Embedded in connective tissue, in clusters along lymphatic vessels

Near body surface in inguinal, axillary and cervical regions of body

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The Stroma (structural portion)

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structural latticework, primarily of reticular connective tissue

Trabeculae are Bundles of Collagen fibers

Extend from capsule into interior of lymph noe

Hilus- shallow indentation where blood vessels and nerves reach the lymph node.

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Lymph Node Vessels

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Afferent vessels carry lymph from peripheral tissue to lymph node

Fewer vessels leave lymph nodes at Hilus

Slow lymph flow through the node

allows lymphocytes and macrophages time to function.

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The Parenchyma (Functional Portion)

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Different types of lymph cells are located here

Lymph from Afferent lymphatics flow through lymph node in a network of sinuses from Subcapsular sinus through outer cortex

a. which contains germinal centers

b. contain many B cells

Through Deep Inner Cortex

a. Contain mainly T Cells in transit

b. T Cells circulate continuously among blood, lymph nodes, and lymph

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The Parenchyma (Functional Portion)

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Through Core (Medulla)

a. organized into medullary cords where lymph is stored.

b. Contain antibody producing B cells (plasma cells)

Into hilus and efferent lymphatics

Activated T cells and antibodies secreted by plasma cell leave through the efferent lymphatics

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Lymph Node Functions

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2 main functions

Filtering and Immune System Activation

(Antigen presentation)

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Lymph Node Functions

Filtering

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Purifies lymph before return to venous circulation

Removes:

debris

pathogens

99% of antigens

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Lymph Nodes Functions

Immunes System Activation (Antigen Presentation)

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Antigen Presentation

First Step in a immune response

Extracted antigens are presented to lymphocytes : or attached to dendritic cells to stimulate lymphocytes

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Lymphoid Functions

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Lymphoid tissues and lymph nodes:

Distributed to monitor peripheral infections

Respond before infections reach vital organs of trunk

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Lymph Glands

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Large lymph nodes at groin and base of neck

Swell in response to inflammation

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Lymphadenopathy ( Lymphadenitis)

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Chronic or Excessive enlargement of lymph nodes may indicate infections, endocrine disorders or cancer

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Lymphangitis

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1.Inflammation of lymphatic channels

2.Pathogens invaded lymphatic vessels through a wound or as a complication of infection

3.Red Streaks on the skin extending proximally toward regional lymph nodes

4.Treat with large dose of antibiotics

5. Immobilize the limb - slows fluid

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The Thymus

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Located in mediastinum

1. Deteriorates after puberty

a. diminishes after puberty

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Divisions of Thymus

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Divided into 2 thymic lobes

Septa divides lobes into smaller lobules

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Thymic Lobule

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Contains a dense outer cortex and pale central medulla

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Thymic Lobe ( Lymphocytes)

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Divide in cortex and T cells migrate into the medulla.

Mature T cells leave thymus by medullary blood vessels

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Reticular Epithelial Cells in the Cortex

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Dendritic Cells surround lymphocytes in cortex

Maintain blood thymus barrier (only in cortex)

Secrete thymic hormones that stimulate:

1. Stem Cell Divisions

2. T cell Differentiation

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The Medulla

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Contains fewer lymphocytes

No blood-thymus barrier

a. T cells can enter or leave bloodstream

Keratinized Epithelial Cells form layers (Hassall's or Thymic corpuscles)

Thymic corpuscles involved in regulatory T cell development (prevent autoimmunity)

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Thymus Hormones

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Thymosins

a. promote development of lymphocytes

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DiGeorge Syndrome

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Congenital absence of thymus

Marked by serious combined immune- deficiencies (SCIDS)

Life in a sterile bubble with death often resulting from opportunistic infection

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Functions of The Spleen

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1. Removal of abnormal blood cells and other blood components by phagocytosis

2. Storage of iron recycled from red blood cells

3. Initiation of immune response by B cells and T Cells:

a. in response to antigens in circulating blood

4. The stores blood platelets and monocytes

5. May be site of fetal erythrocyte productions (normally ceases before birth)

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Structures of the Spleen

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Attached to stomach by gastrosplenic ligament

Splenic veins, arteries and lymphatic vessels:

a. communicate with spleen at hilus

Inside fibrous capsule:

1. red pulp: which contains many red blood cells

2. white pulp: resembles lymphoid nodules

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Trabecular Arteries

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Branch and radiate toward capsule

Finer branches surrounded by white pulp

Capillaries discharge red blood cells into red pulp

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Red Pulp

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Contains elements of circulating blood:

a. plus fixed and free macrophages

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Splenic Circulation

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Blood passes through:

a. network of reticular fibers

Then enters large sinusoids ( lined by macrophages)

a. which empties into trabecular veins

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Spleen Function

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Phagocytes and other lymphocytes in spleen

a. identify and attack damaged and infected cells

b. in circulating blood

The spleen filters and cleans the blood

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Splenectomy

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Removal of spleen, usually due to damage

Difficult to repair surgically

Spleen will repair its self in time

People without spleen more susceptible to infection, specifically blood infection