Lymphatic System

Question 1

What is lymph?

Answer 1

Excess fluid left behind by capillary exchange that drains from tissue spaces and is transported by lymphatic vessels back to the bloodstream.

Question 2

How are lymphatic vessels and veins similar?

Answer 2

They both are low-pressure vessels vested with a muscle layer and intraluminal valves.

Question 3

Describe lymphatic capillaries.

Answer 3

• tiny blind-ended tubes distributed in tissue spaces
• microscopic in size
• sheets consisting of one cell layer of simple squamous epithelium
• poor “fit” between adjacent cells results in porous walls
• called lacteals in the intestinal wall

Question 4

What are lacteals?

Answer 4

Lacteals are the central lymphatic vessels in the villi of the small intestine and perform nutrient absorption, especially dietary lipids, and the transportation of antigen and antigen-presenting cells.

Question 5

Name the two lymphatic ducts and the areas of the body each of them drain.

Answer 5

• Right lymphatic duct - drains lymph from the right upper extremity and right side of the head, neck, and upper torso
• Thoracic duct - largest lymphatic vessel; drains lymph from about 75% of the body

Question 6

What is the cisterna chyli?

Answer 6

The cisterna chyli is a lymphatic dilated sac (part of the thoracic duct) which collects lipid products that have formed in digestive organs.

Question 7

Describe the structure of the lymph node.

Answer 7

• Lymph nodes are small, round or bean-shaped clusters of cells along the pathway of lymphatic vessels.
• flow of lymph: to node via several afferent lymphatic vessels and drained from node by a single efferent lymphatic vessel.

Question 8

Explain the defense function of the lymph node.

Answer 8

The lymph nodes filter out harmful substances and waste products. They also contain immune cells called lymphocytes that destroy bacteria and cancer cells. The filtered fluid is then returned to your blood. If you have an infection or cancer, a lymph node may become swollen.

Question 9

Locate the thymus gland in the body and list its functions.

Answer 9

• lymphoid tissue organ located in the mediastinum
• plays a vital and central role in immunity
• develops T lymphocytes, or T-cells
• secretes hormones called thymosins, which influence T-cell development
• tissue eventually replaced by fat in the process called involution

Question 10

Name and locate three types of tonsils.

Answer 10

• palatine tonsils (“the tonsils”) - located in the lateral oropharynx
• pharyngeal tonsils (adenoids) - located in the posterosuperior surface of the nasopharynx
• lingual tonsils - located on the sides of the tongue at its base

Question 11

What are the three main functions of tonsils?

Answer 11

• filter out bacteria and viruses
• produce white blood cells and antibodies.
• prevent foreign objects from sliding into the lungs

Question 12

Give the location and function of the spleen.

Answer 12

• largest lymphoid organ
• located in the upper left quadrant of the abdomen
• functions include phagocytosis of bacteria and old RBCs; monocyte reservoir; acts as a blood reservoir

Question 13

What is innate immunity.

Answer 13

• called innate because we are born with it
• rapid first response; often triggers slower specific responses
• involves a variety of signaling chemicals called cytokines

Question 14

Explain the five types of innate immunity.

Answer 14

• Mechanical and chemical barriers (skin and mucous membranes prevent entry of pathogens; secretions such as sebum, mucus, acids, and enzymes chemically inhibit pathogens)
• Inflammation (isolates pathogens and stimulates the arrival of large numbers of immune cells; fever may enhance immune reactions)
• Phagocytosis (neutrophils first to arrive at site of inflammatory response; macrophages capable of consuming many pathogens)
• Complement (class of enzymes in blood plasma that can trigger a variety of immune responses; also involved in adaptive mechanisms)
• Interferon (protein produced by cells after they become infected by a virus; inhibits the spread of infection)

Question 15

What is adaptive immunity?

Answer 15

Adaptive because of its ability to recognize, respond to, and remember harmful substances or bacteria.
Also called specific immunity because it responds to particular antigens to which it has been exposed.

Question 16

Name and differentiate between the four types of adaptive immunity.

Answer 16

Natural immunity (exposure to causative agent is not deliberate)
- active (active disease produces immunity)
- passive (immunity passes from mother to fetus through placenta or breast milk)

Artificial immunity (exposure to causative agent is deliberate)
- active (vaccination results in activation of immune system and long-term protection)
- passive (protective material developed in another individual’s immune system and given to previously nonimmune individual giving short term protection. ex. anti-serum, anti-venom)

Question 17

What are cytokines?

Answer 17

Cytokines are molecules that communicate among cells, coordinating immune responses. (Interleukins are an example of cytokines)
Some cytokines stimulate the immune system and others slow it down.

Question 18

What are antibodies and how do they function?

Answer 18

• protein molecules with specific combining sites
• combining sites attach antibodies to specific antigens (foreign proteins) forming an antigen-antibody complex (this provides humoral, or antibody-mediated, immunity)
• antigen-antibody complexes may do the following: neutralize toxins, clump or agglutinate enemy cells, promote phagocytosis

Question 19

Explain the role of complement cascade in the immune system.

Answer 19

• Complement proteins normally present in blood in an inactive state
• Complement cascade is an important mechanism of action for antibodies
• Causes cell lysis, attracts immune cells to a site of infection, activates immune cells marking foreign cells for destruction, increases permeability of blood vessels (the inflammatory response)

Question 20

What is the difference between humoral (anti-body mediated) and cell-mediated immunity?

Answer 20

Humoral immunity produces antigen-specific antibodies and is primarily driven by B cells. Cell-mediated immunity on the other hand does not depend on antibodies for its adaptive immune functions and is primarily driven by mature T cells, macrophages and the release of cytokines in response to an antigen.

Question 21

What are the three types of phagocytes in the immune system, and their functions?

Answer 21

• Neutrophils - short-lived phagocytic cells; most abundant type of immune cell
• Monocytes - develop into phagocytic macrophages and migrate to tissues
• Dendritic cells (DCs) - often found at or near external surfaces

(macrophages and DCs act as antigen-presenting cells (APCs) by displaying ingested antigens on their outer surface to trigger specific immune cells.)

Question 22

Name the three types of lymphocytes.

Answer 22

Second most numerous immune system cells after neutrophils; include:
- Natural killer (NK) cells
- B cells
- T cells

Question 23

What are Natural Killer (NK) cells?

Answer 23

• agents of innate immunity
• can attach to any cell but kill only cells lacking normal self antigens
• usually kill by triggering apoptosis (programmed cell death)

Question 24

Describe the development of B cells.

Answer 24

• primitive stem cells migrate from bone marrow and go through two stages of development
• First stage - takes place in the liver and bone marrow before birth and in the bone marrow only in adults; small lymphocytes with antibody molecules in their plasma membranes; once mature, inactive B cells migrate chiefly to lymph nodes
• Second stage - inactive B cell develops into activated B cell; initiated by antigens and cytokines from T cells; activated B cell forms two clones of cells (plasma or effector cells and memory cells); plasma cells secrete antibodies into blood, memory cells are stored in lymph nodes; if subsequent exposure to specific antigen occurs, memory cells become plasma cells and secrete antibodies in large quantities

Question 25

Describe the function of B cells.

Answer 25

• Indirectly, B cells produce humoral immunity
• activated B cells develop into plasma cells
• plasma cells secrete antibodies into the blood, producing humoral immunity
• circulating antibodies produce humoral immunity

Question 26

Describe the development of T cells.

Answer 26

• agents of adaptive immunity
• stem cells from bone marrow migrate to thymus gland
• First stage - stem cells develop into T cells; T cells mature in the thymus during the few months before and after birth; mature T cells migrate chiefly to lymph nodes
• Second stage - T cells develop into activated T cells; occurs when and if antigen binds to T cell’s surface proteins and a cytokine (chemical signal) is received from another T cell; clones made up of effector cells and memory cells are formed

Question 27

Describe the types and functions of T cells.

Answer 27

• produce cell-mediated immunity
• Cytotoxic T cells - kill infected or tumor cells by releasing a substance that poisons infected or tumor cells
• Helper T cells - release cytokines that attract and activate macrophages to kill cells by phagocytosis; produce cytokines that help activate B cells
• Regulatory T cells - release cytokines to suppress immune responses

Question 28

Differentiate between humoral (antibody-mediated), and cell-mediated immunity.

Answer 28

Humoral immunity produces antigen-specific antibodies and is primarily driven by B cells. Cell-mediated immunity on the other hand does not depend on antibodies for its adaptive immune functions and is primarily driven by mature T cells, macrophages and the release of cytokines in response to an antigen.