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© 2012 Pearson Education, Inc.

Structures of Body Defenses

• Organization of the Lymphatic System

1. Lymph

• A fluid similar to plasma but does not have plasma proteins

2. Lymphatic vessels (lymphatics)

• Carry lymph from peripheral tissues to the venous system

3. Lymphoid tissues and lymphoid organs

4. Lymphocytes, phagocytes, and other immune system cells

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Structures of Body Defenses

• Function of the Lymphatic System

• To produce, maintain, and distribute lymphocytes

• Lymphocyte Production • Lymphocytes are produced

• In lymphoid tissues (e.g., tonsils)

• Lymphoid organs (e.g., spleen, thymus)

• In red bone marrow

• Lymphocyte distribution

• Detects problems

• Travels into site of injury or infection

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Structures of Body Defenses

• Lymphocyte Circulation

• From blood to interstitial fluid through capillaries

• Returns to venous blood through lymphatic vessels

• The Circulation of Fluids

• From blood plasma to lymph and back to the venous system

• Transports hormones, nutrients, and waste products

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Structures of Body Defenses

• Lymphatic Vessels

• Are vessels that carry lymph

• Lymphatic system begins with smallest vessels

• Lymphatic capillaries (terminal lymphatics)

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Structures of Body Defenses

• Lymphatic Capillaries

• Differ from blood capillaries in four ways

1. Start as pockets rather than tubes

2. Have larger diameters

3. Have thinner walls

4. Flat or irregular outline in sectional view

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Figure 22-2a Lymphatic Capillaries

Smoothmuscle

Arteriole Lymphaticcapillary

Venule Interstitialfluid

Blood capillaries Loose connective tissue

Lymphflow

Endothelialcells

The interwoven network formed by blood capillariesand lymphatic capillaries.

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Figure 22-2b Lymphatic Capillaries

Incompletebasementmembrane

Lymphflow

Lymphocyte

To largerlymphatics

Looseconnective

tissue

Interstitial fluid

Interstitial fluid

Bloodcapillary

Lymphaticcapillary

A sectional view indicating the movement of fluidfrom the plasma, through the tissues as interstitialfluid, and into the lymphatic system as lymph.

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Structures of Body Defenses

• Lymphatic Capillaries

• Endothelial cells loosely bound together with overlap

• Overlap acts as one-way valve

• Allows fluids, solutes, viruses, and bacteria to enter

• Prevents return to intercellular space

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Structures of Body Defenses

• Lymph Flow

• From lymphatic capillaries to larger lymphatic vessels

containing one-way valves

• Lymphatic vessels travel with veins

• Lacteals

• Are special lymphatic capillaries in small intestine

• Transport lipids from digestive tract

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Figure 22-3a Lymphatic Vessels and Valves

Vein

Artery

Lymphaticvessel

Lymphaticvalve

From lymphaticcapillaries

Vein

Artery

Lymphaticvessel

Towardvenoussystem

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Figure 22-3b Lymphatic Vessels and Valves

Lymphaticvessel

Lymphaticvalve

Like valves in veins, eachlymphatic valve consists ofa pair of flaps that permitmovement of fluid in onlyone direction.

Lymphatic vessel and valve LM 63

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Figure 22-4 The Relationship between the Lymphatic Ducts and the Venous System

Right internal jugular vein

Right jugular trunk

Right lymphatic duct

Right subclavian trunk

Right subclavian vein

Right bronchomediastinal trunk

Superiorvena cava (cut)

Azygos vein

Rib (cut)

Brachiocephalic veins

Drainageof right

lymphaticduct

Inferior vena cava (cut)

Drainageof thoracicduct

Right lumbar trunk

Left internal jugular vein

Left jugular trunk

Thoracic duct

Left subclavian trunk

Left bronchomediastinaltrunk

Left subclavianvein

First rib(cut)

Highestintercostalvein

Thoracicduct

Thoraciclymph nodes

Hemiazygosvein

Parietalpleura (cut)

Diaphragm

Cisterna chyli

Intestinal trunk

Left lumbar trunk

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Structures of Body Defenses

• Lymphoid Tissues

• Connective tissues dominated by lymphocytes

• Lymphoid Nodules

• Areolar tissue with densely packed lymphocytes

• Germinal center contains dividing lymphocytes

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Figure 22-7a Lymphoid Nodules (Part 1 of 2)

Intestinal lumen

Aggregatedlymphoid nodule

Underlyingconnective tissue

LM 40Aggregated lymphoid nodules in large intestine

Aggregated lymphoid nodules in section

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Figure 22-7a Lymphoid Nodules (Part 2 of 2)

Aggregated lymphoid nodules in section

Intestinal lumen

Mucousmembrane

Germinal center

Aggregatedlymphoid nodule

Underlyingconnective tissue

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Figure 22-7b Lymphoid Nodules

Pharyngealepithelium

Germinal centerswithin nodules

Pharyngeal tonsil

Palate

Palatine tonsil

Lingual tonsil

The positions of the tonsils and a tonsil in section. Notice the pale germinal centers, where lymphocyte cell divisions occur.

Pharyngeal tonsil LM 20

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Structures of Body Defenses

• Distribution of Lymphoid Nodules

• Lymph nodes

• Spleen

• Respiratory tract (tonsils)

• Along digestive, urinary, and reproductive tracts

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Structures of Body Defenses

• Mucosa-Associated Lymphoid Tissue (MALT)

• Lymphoid tissues associated with the digestive

system

• Aggregated Lymphoid Nodules

• Clustered deep to intestinal epithelial lining

• Appendix (Vermiform Appendix)

• Contains a mass of fused lymphoid nodules

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Structures of Body Defenses

• The Five Tonsils

• In wall of pharynx

• Left and right palatine tonsils

• Pharyngeal tonsil (adenoid)

• Two lingual tonsils

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Structures of Body Defenses

• Lymph Nodes

• Trabeculae

• Bundles of collagen fibers

• Extend from capsule into interior of lymph node

• Hilum

• A shallow indentation where blood vessels and nerves

reach the lymph node

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Structures of Body Defenses

• Lymph Nodes

• Afferent lymphatics

• Carry lymph

• From peripheral tissues to lymph node

• Efferent lymphatics

• Leave lymph node at hilum

• Carry lymph to venous circulation

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Figure 22-8 The Structure of a Lymph Node (Part 1 of 2)

Efferentvessel

Lymph nodeartery and vein

Hilum

Lymphvessel

Lymphnodes

Lymph nodes

Medullary sinus

Outer cortex (B cells)

Trabeculae

Medulla

Cortex

Subcapsularspace

Deep cortex(T cells)

Capsule Medullary cord(B cells and

plasma cells)

Afferentvessel

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Structures of Body Defenses

• Lymph Node Function

• A filter

• Purifies lymph before return to venous circulation

• Removes:

• Debris

• Pathogens

• 99% of antigens

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Structures of Body Defenses

• Lymphatic Functions

• Lymphoid tissues and lymph nodes

• Distributed to monitor peripheral infections

• Respond before infections reach vital organs of trunk

• Lymph nodes of gut, trachea, lungs, and thoracic duct

• Protect against pathogens in digestive and respiratory

systems

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22-2 Structures of Body Defenses

• Lymph Nodes (Glands)

• Large lymph nodes at groin and base of neck

• Swell in response to inflammation

• Lymphadenopathy

• Chronic or excessive enlargement of lymph nodes

• May indicate infections, endocrine disorders, or cancer

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22-2 Structures of Body Defenses

• The Thymus

• Located in mediastinum

• Atrophies after puberty

• Diminishing effectiveness of immune system

• Divisions of the Thymus

• Thymus is divided into two thymic lobes

• Septa divide lobes into smaller lobules

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Figure 22-9a The Thymus

Thyroid gland

Trachea

Right lobe

Diaphragm

Rightlung

THYMUS

The appearance and position of the thymus inrelation to other organs in the chest.

Leftlobe

Heart

Leftlung

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Figure 22-9b The Thymus

Rightlobe

Leftlobe

Lobule

Anatomicallandmarks onthe thymus.

Septa

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Figure 22-9c The Thymus CortexSeptaMedulla

Lobule

Lobule

The thymus gland LM 50

Fibrous septa divide the tissue of the thymus into lobulesresembling interconnected lymphoid nodules.

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22-2 Structures of Body Defenses

• Three Functions of the Spleen

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 responses by B cells and T cells

• In response to antigens in circulating blood

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Figure 22-10b The Spleen

SUPERIOR

Gastricarea

Hilum

Splenic vein

Splenic artery

Splenic lymphaticvessel

Renalarea

INFERIOR

A posterior view of the surface of an intactspleen, showing major anatomical landmarks.

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Figure 22-10c The Spleen

The histological appearance of the spleen. White pulp isdominated by lymphocytes; it appears purple becausethe nuclei of lymphocytes stain very darkly. Red pulpcontains a large number of red blood cells.

The spleen LM 50

White pulp ofsplenic nodule

Capsule

Red pulp

Trabecularartery

Central artery insplenic nodule