Chapter 19: The Lymphatic System - WOU

Chapter 19:

The Lymphatic System

Pathogens:

Microscopic organisms

that cause disease

Viruses

Bacteria

Fungi

Protists

Chapter 19: Lymphatic System

Lymphoid System:

? Defends body against external (e.g., pathogens)

and internal (e.g., cancer cells) threats

Composed of:

1) Lymph: Fluid portion (resembles plasma)

2) Lymphatic vessels: One-way flow; empty into veins

3) Lymphoid tissues / organs (e.g., spleen)

Functions:

? Produce / maintain / distribute lymphocytes

Lymphocytes:

? Recognize and respond to threats:

a) Pathogens

b) Abnormal body cells

c) Foreign proteins

? Return excess fluids to bloodstream

? Distributes hormones / nutrients / waste products

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Chapter 19: Lymphatic System

Similar to Marieb & Hoehn ¨C Figure 19.1

Flow of Lymph:

Lymphatic Capillaries

? Originate as pockets

? Large diameters / thin walls

? One-way valves (external)

Lymphatic Vessels

? Multi-layered walls

? Travel with blood vessels

? One-way valves (internal)

Collecting Vessels

Two Types:

? Superficial (e.g., skin)

? Deep (e.g., skeletal muscle)

Lymphatic Trunks

Lymphatic Ducts

Chapter 19: Lymphatic System

Flow of Lymph:

? Lymph from right side of

body above diaphragm

Similar to Marieb & Hoehn ¨C Figure 19.2

? Lymph from left side of

head, neck, and thorax

Thoracic Duct:

? Begins inferior to diaphragm

? Empties into left subclavian vein

Right Lymphatic Duct:

? Empties into right subclavian vein

Cisterna chyli

Lymphedema: Fluid build up in tissues due to

blockage of lymph drainage

? Lymph from abdomen,

pelvis, and lower limbs

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Chapter 19: Lymphatic System

Lymphocytes:

? 20 ¨C 30% of circulating white blood cells (leukocytes)

? Most lymphocytes not circulating (1012 = 2.2 lbs!)

Types:

Lifespan of lymphocytes

can reach 40+ years

1) T cells (Thymus-dependent)

? 80% of circulating lymphocytes in blood

? Sub-types:

a) Cytotoxic T cells: Attack foreign cells or body cells infected by viruses

b) Helper T cells: Stimulate the activation of other lymphocytes (i.e., cheerleaders)

c) Suppressor T cells: Inhibit the activation of other lymphocytes (i.e., bouncers)

(Regulatory T cells)

2) B cells (Bone marrow-derived)

? 10 - 15% of circulating lymphocytes in blood

? Responsible for producing / secreting antibodies (immunoglobulins)

3) NK cells (Natural Killer)

? 5 - 10% of circulating lymphocytes in blood

? Attack foreign cells, virus-infected body cells, & cancer cells (immunological surveillance)

Chapter 19: Lymphatic System

Lymphopoiesis (Lymphocyte production):

Red Bone

Marrow

Hemocytoblast

Blood ¨C Thymus Barrier

(migrate to thymus)

(remain in red bone marrow)

Lymphoid Stem Cell

T - Cell

Migrate to

peripheral tissues /

red bone marrow

B - Cell

T ¨C cells and B ¨C cells

retain the ability to

reproduce their own kind

Natural

Killer

Cell

Migrate to

peripheral tissues

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Chapter 19: Lymphatic System

Lymphoid Tissues:

? Connective tissues dominated by lymphocytes

Germinal

Center

? Lymph Nodule = Lymphocytes densely packed in areolar tissue

Mucosa-associated

Lymphoid Tissue (MALT)

Tonsils

? Linked with digestive system (e.g., appendix)

? Located in walls of pharynx (throat)

? Five (5) tonsils total (palatine / pharyngeal / lingual)

Tonsilitis = Infected and swollen tonsils

Martini ¨C Figure 22.6

Chapter 19: Lymphatic System

Large lymph nodes present

near connections to lymphatic trunks

Lymphoid Organs:

? Fibrous connective tissue capsule separates lymphoid tissue from

surrounding tissues.

Efferent

lymphatic

A) Lymph Nodes:

Hilum

Inter cortex

Antigen:

Foreign chemical

(T¨C cells)

Outer cortex

(B ¨C cells)

Trabecula

Functions:

1) Filters lymph (99% purified)

? Macrophages

2) ¡®Antigen¡¯ presentation

? B ¨C cells / Dendritic cells

? ¡®Early-warning¡¯ system

? Enlarge during local infection

? ? lymphocyte number

Capsule

Afferent

lymphatic

? Lymph node biopsy

Similar to Marieb & Hoehn ¨C Figure 19.4

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Chapter 19: Lymphatic System

Lymphoid Organs:

? Fibrous connective tissue capsule separates lymphoid tissue from

surrounding tissues.

B) Thymus:

? Located in mediastinum

? Largest at puberty (atrophies with age)

? Elderly more susceptible to disease

Function:

1) Maturation of T cells

2) Production of thymosins (hormones)

? Stimulate cell divisions

? Stimulate T ¨C cell differentiation

? Produced by Reticular epithelial cells

Blood ¨C Thymus Barrier:

Reticular cells wrapped tightly around

blood vessels in cortex

? 2 lobes

? Septal divisions (lobules)

? Cortex (T cell division)

? Medulla (T cell storage)

(medulla = no barrier)

Mature T cells exit thymus

via medullary blood vessels

Chapter 19: Lymphatic System

The spleen is very fragile;

often removed when damaged

(splenectomy)

Lymphoid Organs:

? Fibrous connective tissue capsule separates lymphoid tissue from

surrounding tissues.

C) Spleen:

? Located in abdominal cavity (left side)

? Largest aggregation of lymphoid tissue in body

Function:

Spleen

1) Removal of abnormal blood cells (phagocytosis)

2) Storage of iron (recycled from RBCs) / blood platelets

3) Initiation of immune response (T / B cells)

Capsule (collagen / elastic fibers)

Red Pulp (red blood cells / macrophages - sinusoids)

White Pulp (lymphocytes)

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