Lymphatic System and Body Defenses

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Lymphatic System and Body Defenses

• Chapter 12

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The Lymphatic System

• Two semi-independent parts
• Lymphatic vessels
• Lymphoid tissues and organs
• Function of lymphatic system
• Transport fluids back to the blood
• Essential role in body defense and disease
  resistance

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Lymphatic Vessels

• Function
• Pick up excess tissue fluid Lymph and return
  it to the blood stream
• Also known as lymphatics
• One way system flows only to the heart
• Characteristics
• Thin-walled
• Valved
• pumpless

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Lymph capillaries

• Web between tissue cells and blood capillaries
• Remarkably permeable
• Held by fine collagen fibres
• Act as one way doors
• Flap like mini valves close as high pressure
  builds up inside
• Keeps lymph from leaking back

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Lymphatic collecting vessels

• Collects lymph from lymph capillaries
• Carries lymph to and away from lymph node
• Returns fluid to the heart through two ducts
• Right lymphatic duct
• Drains lymph from right arm and right side of
  head and thorax
• Thoracic duct
• Receives lymph from rest of the body

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Lymphatic Vessels
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Lymph Nodes

• Function
• Remove foreign material from lymph
• Cluster along vessels in three main areas
• Inguinal
• Axillary
• Cervical
• Contain 2 types of cells
• Macrophages
• Engulf and destroy bacteria, viruses and foreign
  substances
• Lymphocytes (white blood cells)
• Respond to foreign substances

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Lymph Nodes (continued)

• Structure
• Kidney shaped, less than 1 long
• buried in connective tissue
• Cortex
• Outer part
• Contains follicles (collections of lymphocytes)
  and T-cells
• Medulla
• Inner part
• Contains phagocytic macrophages

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Flow of Lymph through Nodes

• Lymph enters through afferent lymph vessels
• Flows through sinuses
• Exits at indented region - hilus through
  efferent lymphatic vessels
• Slow process
• Allows time for lymphocytes and macrophages to
  perform

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Other Lymphoid Organs

• Spleen
• Thymus
• Tonsils
• Peyers patch
• Common features
• Predominance of reticular connective tissues and
  lymphocytes

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Other Lymphoid Organs

• Spleen
• Filters blood of bacteria, viruses
• Located on left side of abdominal cavity
• Destroys worn out red blood cells
• Acts as blood reservoire
• Produces lymphocytes
• Thymus
• Function peaks at youth
• Found low in throat over heart
• Produces hormones that program lymphocytes

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Other Lymphoid Organs

• Tonsils
• Small masses of lymphatic tissue around pharynx
• Trap and removes bacteria or pathogens entering
  throat
• So efficient can become congested
• tonsillitis
• Peyers patches
• Like tonsils but in small intestine
• Captures and destroys bacteria

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Mucosa-associated Lymphatic Tissue (MALT)

• Composed of
• Peyers patches
• Tonsils
• Other small collections of lymphatic tissue
• Protects respiratory and digestive tracts

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Body Defenses

• Two systems to fight off bacteria, viruses and
  fungi that your body comes in contact with
• Nonspecific body defenses
• Responds immediately to all foreign substances
• Provided by intact skin and mucous membranes, the
  inflammatory response and proteins
• Specific body defenses
• The Immune System
• Responds to particular foreign substances
  
  

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Nonspecific Body Defenses

• Some nonspecific resistance is inherited
• Refers to mechanical barriers that cover body
  surfaces and specialized cells
• Lines of defense
• Surface Membrane Barriers
• Cells and Chemicals

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Surface Membrane Barriers

• First line of defense
• The Skin-
• As long as unbroken, strong physical barrier
• Mucous membranes provide similar responses
• Both produce variety of chemicals
• Acid pH of skin prevents bacterial growth
• Stomach mucosa secretes hydrochloric acid and
  enzymes that kill pathogens
• Saliva and lacrimal fluid contain lysozume
• Mucus traps microorganisms that enter digestive
  and respiratory pathways.

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Surface Membrane Barriers continued

• Structural modifications fend off potential
  invaders
• When surface barriers broken, infection occurs
• Microorganisms invade deeper tissues and other
  mechanisms come into play

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Cells and Chemicals

• Second line of defense
• Rely on
• phagocytes and natural killer cells
• Inflammatory response
• Chemical substances
• Fever also a nonspecific protective response

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Phagocytes

• Located in nearly every body organ
• Engulf foreign particles, like amoebas
• Binds to particle then pulls it in
• Enclosed in vacuole
• Fused with enzymatic contents of lysosome
• Contents broken down or digested

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Events of Phagocytosis
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Natural Killer Cells

• police body in blood and lymph
• Can lyse and kill cancer and virus-infected body
  cells
• Act against any target by recognizing sugars on
  intruders surface

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Inflammatory Response

• Occurs whenever body tissues injured
• Four cardinal signs
• Redness
• Heat
• Swelling
• Pain
• Chain of events leading to protection and healing

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Inflammatory Response continued

• What does it do?
• Prevents spread of damaged agents to nearby
  tissues
• Disposes of cell debris and pathogens
• Sets stage for repair
• Other protected events are clotting
• Heat increases defensive actions and repair
  processes

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Third Line of Defense

• Immune response mediated by lymphocytes
• Respond to pathogens that have previously invaded
  the body

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The Inflammatory Response
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Antimicrobial Chemicals

• Two types
• Complement proteins
• Group of 20 plasma proteins
• Circulate in blood in inactive state
• Activated when fixed to pathogen
• Damage foreign cell surfaces
• Release vasodilators, chemotaxis chemicals and
  cause opsonixation
• Interferon
• Bind to near by cells when viruses are present
• Hinders ability of viruses to multiply within
  cells

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Fever

• Abnormally high body temperature
• Response to invading microorganisms
• Body thermostat can be reset in response to
  pyrogens
• High fevers are dangerous
• Mild/moderate fevers benefit the body
• Speeds up repair processes
• Liver and spleen gather iron and zinc during
  fevers preventing bacteria from multiplying

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Specific Body Defenses The Immune System
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