Anatomy - Lymphatic System and Body Defenses

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The lymphatic system consists of two parts, what are they?

The lymphatic system consists of two parts, what are they?

1. 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

Lymph consists of...

excess tissue fluid and plasma proteins carried by lymphatic vessels

What happens if fluids are not picked up?

edema occurs as fluid accumulates in tissues

What is the purpose of lymphatic vessels?

To pick up excess fluid (lymph) and return it to the blood.

Lymph flows only toward...

The heart

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

The right lymphatic duct

Drains the lymph from the right arm to the right side of the head and thorax

The thoracic duct

drains lymph from the rest of the body

How are lymphatic vessels similar to the veins of the cardiovascular system?

- thin-walled
- larger vessels have valves
- low-pressure, pumpless system

How is lymph transport aided?

- milking action of skeletal muscles
- pressure changes in thorax during breathing
- smooth muscle in walls of lymphatics

What is the purpose of lymph nodes?

To filter lymph before it is returned to the blood.

What are some harmful materials that the lymph nodes would filter?

- bacteria
- viruses
- cancer cells
- foreign substances

What kind of defense cells are present within the lymph nodes?

- macrophages that engulf and destroy bacteria, viruses, and other foreign substances in lymph
- lymphocytes that respond to foreign substances in lymph

Physical characteristics of the lymph nodes?

- kidney shaped
- less than 1 inch long
- buried in connective tissue
- surrounded by a capsule
- divided into compartments by trabeculae

What are the two compartments of a lymph node?

1. Cortex
2. Medulla

Cortex (outer part) of the lymph node

- contains follicles - collections of lymphocytes
- germinal centers enlarge when antibodies are released by plasma cells

Medulla (inner part) of a lymph node

contains phagocytic macrophages

Path of lymph through a lymph node

- enters the convex side through afferent lymphatic vessels
- flows through a number of sinuses inside the node
- exits through efferent lymphatic vessels

What contributes to the slow flow rate of lymph through the lymph node?

there are fewer efferent vessels than afferent.

Spleen

- located on the left side of the abdomen
- filters and cleans blood of bacteria, viruses, and debris
- provides a site for lymphocyte proliferation and immune surveillance
- destroys worn-out RBCs
- stores platelets and acts as a blood reservoir

Thymus

- found overlying the heart
- functions at peak levels only during youth
- 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

Tonsils

- small masses of lymphoid tissue deep to the mucosa surrounding the pharnyx (throat)
- trap and remove bacteria and other foreign pathogens entering the throat
- tonsillitis results when tonsils become congested with bacteria

What are Peyer's patches?

the numerous areas of lymphoid tissue in the wall of the small intestine they contain macrophages that capture and destroy bacteria in the intestine.

MALT (mucosa-associated lymphoid tissue)

found in and beneath the mucous membranes lining the digestive, respiratory, urinary, and reproductive tracts. Ex. Peyer's patches, Tonsils, and Appendix

What are the two mechanisms that make up the immune system to defend us from foreign materials?

1. Innate (nonspecific) defense system
2. Adaptive (specific) defense system

Immune system is a _____________ system rather than an ___________ system in an anatomical sense

functional, organ

Innate (nonspecific) defense mechanisms (first line of defense)

- skin
- mucous membranes
- secretions of skin and mucous membranes

Innate (nonspecific) defense mechanisms (second line of defense)

- phagocytic cells
- natural killer cells
- antimicrobial proteins
- the inflammatory response
- fever

Adaptive (specific) defense mechansisms (third line of defense)

- lymphocytes
- antibodies
- macrophages and other antigen presenting cells

When does innate immunity kick in?

Responds immediately to protect body from all foreign materials

When does the adaptive immune response kick in?

Once foreign invaders get past the innate immune system

What is the protective mechanism of the epidermis?

Forms mechanical barrier that prevents entry of pathogens and other harmful substances in the body

What is the protective mechanism of the acid mantle?

Skin secretions make epidermal surface acidic, which inhibits bacterial growth; sebum also contacts bacteria-killing chemicals

What is the protective mechanism of keratin?

provides resistance against acids, alkalis, and bacterial enzymes

What is the protective mechanism of intact mucous membranes?

form mechanical barrier that prevents entry of pathogens

What is the protective mechanism of mucus?

traps microorganisms in respiratory and digestive tracts

What is the protective mechanism of the nasal hairs?

filter and trap microorgansims and other airborne particles in nasal passages

What is the protective mechanism of cilia?

propel debris-laden mucus away from lower respiratory passages

What is the protective mechanism of gastric juice?

contains concentrated hydrochloric acid and protein-digesting enzymes that destroy pathogens in stomach

What is the protective mechanism of the acid mantle of the vagina?

inhibits growth of bacteria and fungi in female reproductive tract

What is the protective mechanism of lacrimal secretion (tears); saliva?

continuously lubricate and cleanse eyes (tears) and oral cavity (saliva); contain lysozyme, an enzyme that destroy microorganims.

What is the protective mechanism of phagocytes?

engulf and destroy pathogens that breach surface membrane barriers; macrophages also contribute to immune response.

What is the protective mechanism of natural killer cells?

promote cell lysis by direct cell attack against virus-infected or cancerous body cells; do not depend on specific antigen recognition

What is the protective mechanism of the inflammatory response?

prevents spread of injurious agents to adjacent tissues, disposes of pathogens and dead tissue cells, and promotes tissue repair; releases chemical mediators that attract phagocytes (and immune cells) to the area.

What is the protective mechanism of complement?

group of plasma proteins that lyses microorganisms, enhances phagocytosis by opsonization, and intensifies inflammatory response.

What is the protective mechanism of interferons?

proteins released by virus-infected cells that protect uninfected tissue cells from viral takeover; mobilize immune system

What is the protective mechanism of fluids with acid pH?

normally acid pH inhibits bacterial growth; urine cleanses the lower urinary tact as it flushes from the body.

What is the protective mechanism of a fever?

systemic response triggered by proteins; high body temperature inhibits multiplication of bacteria and enhances body repair processes.

Why are surface membrane barriers significant in the immune response?

they provide the first line of defence against the invasion of microorganisms

How do natural killer cells travel throughout the body?

they roam the body in blood and lymph

What are the 4 most common indicators of acute inflammation?

- redness
- heat
- pain
- swelling (edema)

What are the affects of histamine and kinin?

- blood vessel dilation
- the capillaries become leaky
- phagocytes and white blood cells move into the area (positive chemotaxis)

What are the goals of the inflammatory response?

- prevent spread of damaging agents to nearby areas
- dispose of cell debris and pathogens
- set stage for repair

Which white blood cell plays a major role in the inflammatory response?

Neutrophils

How do antimicrobial proteins enhance innate defenses?

- by attacking microorganisms directly
- by hindering reproduction of microorganisms

What are the two most important types of antimicrobial proteins?

Complement and interferon

Complement refers to

a group of at least 20 plasma proteins that circulate in the plasma

Complement is activated when

plasma proteins encounter and attach to cells (known as complement fixation)

membrane attack complex (MAC)

- result of complement fixation
- produce holes or pores in cells
- pores allow water to rush into the cell
- cell bursts (lysis)

Interferon

- small proteins secreted by virus-infected cells
- bind to membrane receptors on healthy cell surfaces to interfere with the ability of viruses to multiply

Interferon is not helpful in what kind(s) of infections?

bacterial or fungal infections

Which part of the brain regulates body temperature?

The hypothalamus

What is normal body temperature?

37 degrees Celsius
98.6 degrees Fahrenheit

What causes the hypothalamus to increase body temperature?

pyrogens

How does high body temperatures affect bacteria?

high temperatures inhibit the release of iron and zinc (which are needed by bacteria) from the liver and spleen

What does it mean that adaptive immunity is antigen specific?

the adaptive defense system recognizes and acts against particular foreign substances

The adaptive immune system is systemic, what does that mean?

immunity is not restricted to the initial infection site

The adaptive immune system has a good memory, what does this mean?

the adaptive defense system recognizes and mounts a stronger attack on previously encountered pathogens

Humoral immunity =

antibody mediated immunity, provided by antibodies present in body fluids

Cellular immunity =

cell mediated immunity, targets virus-infected cells, cancer cells, and cells of foreign grafts

What are antigens?

Any substance capable of exciting the immune system and provoking an immune response

Non-self antigens can be

- nucleic acids
- large carbohydrates
- some lipids
- pollen grains
- microorganisms

Self antigens do not trigger an immune response in us BUT

can be strongly antigenic to other people

Haptens

Incomplete antigens, not antigenic by themselves
When they link up with our proteins, the immune system may recognize the combination as foreign and respond with an attack

Where can you find haptens in everyday life?

poison ivy, animal dander, detergents, hair dyes, and cosmetics

Which cells are part of the adaptive defense system?

Lymphocytes (B and T) and Antigen presenting cells

Where are lymphocytes produced?

bone marrow, they arise from hemocytoblasts.

What determines whether a lymphocyte matures into a B or T cell?

It depends on where the lymphocyte becomes immunocompetent

What is immunocompetence?

The capability to respond to a specific antigen by binding to it with antigen-specific receptors that appear on the lymphocyte's surface

Where do T cells develop immunocompetence?

The thymus

T cells functions

- oversee cell-mediated immunity
- identify foriegn antigens
- those that bind self-antigens are destroyed
- self-tolerance is an important part of lymphocyte "education"

Where do B cells develop immunocompetence?

In the bone marrow

B cells provide _________ immunity

humoral

What determines which foreign substances our immune system recognizes and resists?

Genes

Where do immunocompetent T and B lymphocytes migrate?

the lymph nodes and spleen, where encounters with antigens occur

Differentiation from naive cells into mature lymphocytes is complete when

they bind with recognized antigens

Mature lymphocytes, especially __________ circulate continuously throughout the body

T cells

Antigen-presenting cells

Engulfs antigens and then presents fragments of them on their own surfaces where they can be recognized by T cells

Which 3 cell types behave as APCs?

Dendritic cells, Macrophages, B lymphocytes

What happens during the humoral immune response?

- B lymphocytes with specific receptors bind to a specific antigen and are stimulated to continue their development
- the binding eventually sensitizes, or activates, the lymphocyte to undergo clonal selection
- a large number of clones is produced (primary humoral response)

Most of the B cell clone members become

plasma cells
- produce antibodies to destroy antigens
- activity only lasts for 4 to 5 days
- peak antibody levels occur about 10 days after the response begins

Some B cells become

long-lived memory cells
- secondary humoral response
- provide immunological memory

Immunoglobulins (IG)

- constitute gamma globulin part of blood proteins
- soluble proteins secreted by activated B cells (plasma cells)
- formed in response to a huge number of different antigens

What are the 5 major immunoglobulin classes?

IgM, IgA, IgD, IgG, IgE

What is the function of IgM?

can fix complement

What is the function of IgA?

found mainly in secretions, such as mucus or tears

What is the function of IgD?

important in activation of B cell

What is the function of IgG?

can cross the placental barrier and fix complement; most abundant antibody in plasma

What is the function of IgE?

involved in allergic reactions