Lymphatic System and Body Defenses Chapter 12 The

Lymphatic System and Body Defenses Chapter 12

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

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

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

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

Lymphatic Vessels

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

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

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

Other Lymphoid Organs Spleen Thymus Tonsils Peyer’s patch Common features ◦ Predominance of reticular connective tissues and lymphocytes

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

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 �Peyer’s patches ◦ Like tonsils but in small intestine ◦ Captures and destroys bacteria

Mucosa-associated Lymphatic Tissue (MALT) �Composed of ◦ Peyer’s patches ◦ Tonsils ◦ Other small collections of lymphatic tissue �Protects tracts respiratory and digestive

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

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

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 p. H 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.

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

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

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

Events of Phagocytosis

Natural Killer Cells �“police” body in blood and lymph �Can lyse and kill cancer and virusinfected body cells �Act against any target by recognizing sugars on intruder’s surface

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

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

Third Line of Defense �Immune response mediated by lymphocytes ◦ Respond to pathogens that have previously invaded the body

The Inflammatory Response

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

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

Specific Body Defenses: The Immune System