Ch.12: The Lymphatic System and Body Defenses Flashcards
The lymphatic system consists of what two semi-independent parts?
- Lymphatic vessels
2. Lymphoid tissues and organs
What are the functions of the lymphatic system?
- Transports escaped fluids from the cardiovascular system back to the blood
- Plays essential roles in body defense and resistance to disease
Concept Link 1
Recall that the hydrostatic and osmotic pressures operating at capillary beds force fluid out of the blood at the arterial ends of the beds (“upstream”) and cause most of the expelled fluid to be reabsorbed at the venous ends (“downstream”) (Chapter 11, p. 388).
Lymph consists of _____ and _____ carried by lymphatic vessels.
- Excess tissue fluid
* Plasma proteins
If fluids are not picked up, _____ occurs as fluid accumulates in tissues.
Edema
_____ pick up excess fluid (lymph) and return it to the blood.
Lymphatic vessels (lymphatics)
What are lymphatic vessels (lymphatics)?
- Form a one-way system
* Lymph flows only toward the heart
What are lymph capillaries?
- Weave between tissue cells and blood capillaries
- Walls overlap to form flaplike minivalves
- Fluid leaks into lymph capillaries
- Capillaries are anchored to connective tissue by filaments
- Higher pressure on the inside closes minivalves
- Fluid is forced along the vessel
Concept Link 2
This is very similar to the way that valves in veins work to ensure blood returns to the heart, despite being under low pressure (Chapter 11, p. 372).
What is the function of lymphatic collecting vessels?
• Collect lymph from lymph capillaries
• Carry lymph to and away from lymph nodes
• Return fluid to circulatory veins near the heart
*Right lymphatic duct drains the lymph from the right arm and the right side of the head and thorax
*Thoracic duct drains lymph from rest of body
How are lymphatic vessels similar to veins of the cardiovascular system?
- Thin-walled
- Larger vessels have valves
- Low-pressure, pumpless system
Lymph transport is aided by:
- Milking action of skeletal muscles
- Pressure changes in thorax during breathing
- Smooth muscle in walls of lymphatics
Lymph nodes filter _____ before it is returned to the blood.
Lymph
Harmful materials that are filtered include:
- Bacteria
- Viruses
- Cancer cells
- Cell debris
What are defense cells within lymph nodes?
- Macrophages
* Lymphocytes
What is the function of macrophages?
Engulf and destroy bacteria, viruses, and other foreign substances in lymph
What is the function of lymphocytes?
Respond to foreign substances in lymph
Most lymph nodes are _____-shaped, less than _____ long, and buried in _____.
- Kidney
- 1 inch
- Connective tissue
- Surrounded by a capsule
- Divided into compartments by trabeculae
What is the cortex (outer part) of a lymph node?
- Contains follicles—collections of lymphocytes
* Germinal centers enlarge when antibodies are released by plasma cells
What is the medulla (inner part) of a lymph node?
Contains phagocytic macrophages
What is the flow of lymph through nodes?
- Lymph enters the convex side through afferent lymphatic vessels
- Lymph flows through a number of sinuses inside the node
- Lymph exits through efferent lymphatic vessels
- Because there are fewer efferent than afferent vessels, flow is slowed
What are other lymphoid organs contribute to lymphatic function (in addition to the lymph nodes)?
- Spleen
- Thymus
- Tonsils
- Peyer’s patches
- Appendix
What is the function of the spleen?
- Located on the left side of the abdomen
- Filters and cleans blood of bacteria, viruses, debris
- Provides a site for lymphocyte proliferation and immune surveillance
- Destroys worn-out blood cells
- Forms blood cells in the fetus
- Acts as a blood reservoir
The thymus functions at peak levels only during:
Youth
Concept Link 3
Remember that the thymus produces hormones, thymosin and others, that function in the programming of T lymphocytes so they can carry out their protective roles in the body (Chapter 9, p. 320).
What are tonsils and what are their function?
- Small masses of lymphoid tissue deep to the mucosa surrounding the pharynx (throat)
- Trap and remove bacteria and other foreign pathogens
- Tonsillitis results when the tonsils become congested with bacteria
What are Peyer’s patches?
- Found in the wall of the small intestine
- Similar lymphoid follicles are found in the appendix
- Macrophages capture and destroy bacteria in the intestine
What is mucosa-associated lymphoid tissue (MALT) and what is its function?
Includes: • Peyer’s patches • Tonsils • Appendix • Acts as a sentinel to protect respiratory and digestive tracts
What are two mechanisms that make up the immune system and defend us from foreign materials?
- Innate (nonspecific) defense system
* Adaptive (specific) defense system
What is immunity?
Specific resistance to disease
The immune system is a _____ system rather than an _____ system in an anatomical sense.
- Functional
* Organ
What is the first line of defense?
- Skin
- Mucous membranes
- Secretions of skin and mucous membranes
What is the second line of defense?
- Phagocytic cells
- Natural killer cells
- Antimicrobial proteins
- The inflammatory response
- Fever
What is the third line of defense?
- Lymphocytes
- Antibodies
- Macrophages and other antigen-presenting cells
What is the function of the innate (nonspecific) defense system?
- Mechanisms protect against a variety of invaders
* Responds immediately to protect body from foreign materials
What is the function of the adaptive (specific) defense system?
- Fights invaders that get past the innate system
- Specific defense is required for each type of invader
- The highly specific resistance to disease is immunity
Innate body defenses are mechanical barriers to pathogens (harmful or disease-causing microorganisms) and include:
• Body surface coverings *Intact skin *Mucous membranes • Specialized human cells • Chemicals produced by the body
Surface membrane barriers, such as the skin and mucous membranes, provide the _____ against the invasion of microorganisms.
• First line of defense
• Protective secretions produced by these membranes
*Acidic skin secretions inhibit bacterial growth
*Sebum is toxic to bacteria
*Mucus traps microorganisms
*Gastric juices are acidic and kill pathogens
*Saliva and tears contain lysozyme (enzyme that destroys bacteria)
Cells and chemicals provide a second line of defense, such as:
- Natural killer cells and phagocytes
- Inflammatory response
- Chemicals that kill pathogens
- Fever
What is the function of natural killer (NK) cells?
- Lyse (burst) and kill cancer cells, virus-infected cells
* Release chemicals called perforin and granzymes to degrade target cell contents
Inflammatory response is triggered when:
Body tissues are injured
What are the four most common indicators (cardinal signs) of acute inflammation?
- Redness
- Heat
- Pain
- Swelling (edema)
Damaged cells release inflammatory chemicals, such as:
- Histamine
* Kinin
Inflammatory chemicals cause:
- Blood vessels to dilate
- Capillaries to become leaky
- Phagocytes and white blood cells to move into the area (called positive chemotaxis)
What are the functions of the inflammatory response?
- Prevents spread of damaging agents
- Disposes of cell debris and pathogens through phagocytosis
- Sets the stage for repair
What is the process of the inflammatory response?
- Neutrophils migrate to the area of inflammation by rolling along the vessel wall (following the scent of chemicals from inflammation)
- Neutrophils squeeze through the capillary walls by diapedesis to sites of inflammation
- Neutrophils gather in the precise site of tissue injury (positive chemotaxis) and consume any foreign material present
What is the function of phagocytes?
- Cells such as neutrophils and macrophages engulf foreign material by phagocytosis
- The phagocytic vesicle is fused with a lysosome, and enzymes digest the cell’s contents
Antimicrobial proteins enhance innate defenses by:
- Attacking microorganisms directly
* Hindering reproduction of microorganisms