The Lymphatic System Flashcards
1
Q
What are the functions of the lymphatic system?
A
- Transports fluids and helps fight infections
- Excess interstitial fluid that leaked out of blood capillaries enters lymph vessels
1. After entering vessels, the fluid is called lymph
2. Lymph vessels return the fluid to venous circulation
3. If not removed it would accumulate and cause edema - Lymph vessels transport dietary lipids
- Lymphatic organs aid in production and maturation of
lymphocytes - Lymphatic system generates immune response against antigens
2
Q
How do lymphocytes and macrophages monitor foreign substances?
A
- Some of the cells produce antibody proteins that bind the pathogen
- Other lymphatic cells attach the antigen directly
- Other lymphatic cells become memory cells to quickly attack the antigen if it appears again
3
Q
What are lymph vessels?
A
- The lymph vessel network transports excess fluid back to the blood
- As it flows through the network, lymph is carried through
progressively larger diameter vessels:
1. Lymphatic capillaries
2. Lymphatic vessels
3. Lymphatic trunks
4. Lymphatic ducts
4
Q
What are lymphatic capillaries?
A
- Closed-ended tubes interspersed among most blood capillary beds
- Not in red marrow or avascular tissues
- Recently found to be in dural venous sinuses of brain
- Resemble blood capillaries but have overlapping endothelial cells that act as one-way entry flaps
- Flaps are attached by anchoring filaments to nearby structures
- The gastrointestinal tract contains specialized lymph
capillaries called lacteals: collect interstitial fluid as well as lipids and lipid-soluble vitamins - Lymph collected from gastrointestinal system is called chyle
5
Q
What are lymphatic vessels?
A
- Lymphatic capillaries merge to form lymphatic vessels
- They resemble small veins in that they have components of all three vascular tunics and possess valves
- Afferent lymphatic vessels bring lymph to a lymph node
- Efferent lymphatic vessels transport filtered lymph away from the lymph node
6
Q
What are lymphatic trunks?
A
- Lymphatic trunks form from merging lymphatic vessels
- Each trunk drains lymph from a specific body region:
1. Jugular trunks: Head and neck
2. Subclavian trunks: Upper limbs, breasts and superficial thoracic wall
3. Bronchomediastinal trunks: Deep thoracic structures
4. Intestinal trunks: Most abdominal structures
5. Lumbar trunks: Lower limbs, abdominopelvic wall and pelvic organs
7
Q
What are lymphatic ducts?
A
- Lymphatic ducts form from the fusion of lymphatic trunks
1. The right lymphatic duct is deep to the clavicle and returns lymph at the junction of right subclavian and internal jugular veins - It returns lymph from the right side of the head and neck, right upper limb and the right side of the thorax
2. The thoracic duct is the largest lymphatic vessel
– It begins just inferior to the diaphragm as a rounded saclike structure called the cisterna chyli
– It collects lymph from most of the body (excluding the right lymphatic duct drainage)
– It passes through the diaphragm’s aortic opening and returns lymph into the junction between the left subclavian and internal jugular veins
8
Q
What are lymphatic cells?
A
- There are several types of lymphatic cells in the lymphatic and circulatory systems:
1. Macrophages: monocytes that have left blood - Engulf foreign substances; may present antigens to other lymphoid cells
2. Special epithelial cells (nurse cells): secretory cells in thymus
3. Dendritic cells: internalize antigens and present them to lymphocytes
4. Lymphocytes: most abundant lymphoid cells
9
Q
What are the types and functions of lymphocytes?
A
- 3 types:
1. T-lymphocytes (T-cells)
2. B-lymphocytes (B-cells)
3. Natural killer (NK cells) - All three migrate through the lymphatic system and search for harmful antigens
10
Q
What are T lymphocytes?
A
- T-cells make up about 70–85% of body lymphocytes
- They express a plasma membrane coreceptor (“CD” followed by a number) that can recognize a particular antigen
- There are several types of T-lymphocytes; two main groups:
1. Helper T-lymphocytes
2. Cytotoxic T-lymphocytes - Other types of T-lymphocytes include memory T-cells (mount rapid response to familiar antigen) and regulatory T-cells (prevent over-activity in immune response)
11
Q
What are helper T lymphocytes?
A
- Oversee immune response
- Primarily contain the CD4 coreceptor and are referred to as CD4+ cells or T4 cells
- Present antigens to other lymphatic cells
- Secrete cytokines - molecules that activate
other lymphatic cells
12
Q
What are cytotoxic T lymphocytes?
A
- Also called CD8+ cells or T8 cells, contain the CD8 coreceptor
- T8 cells come in direct contact with infected or tumor cells and kill them
- Cytotoxic T-cells respond to one type of antigen only
- Kill by secreting substances that cause unregulated entry into the cell
- Must be activated by a helper T-lymphocyte
13
Q
What are B lymphocytes?
A
- B-cells make up about 15–30% of body lymphocytes
- Contain antigen receptors to only one antigen
- Stimulate production of immunoglobulins or antibodies against that antigen
- There are five main classes of immunoglobulins
- B-lymphocytes are activated by helper T-lymphocytes
- B-cell then divides and becomes either a plasma cell or memory B-lymphocyte
- Most activated B-lymphocytes become plasma cells that
produce and secrete large amounts of antibodies - A few activated B-lymphocytes become memory B Lymphocytes and confer immunity to certain antigens for
many years or a lifetime
14
Q
What are NK cells?
A
- Also called large granular lymphocytes
- Relatively small percentage of all lymphocytes
- Express the CD16 receptors
- Unlike T-cells and B-cells, NK cells can kill a wide variety of infected cells and some cancerous cells
15
Q
What is lymphopoesis?
A
- The process of lymphocyte development
- Final result is that lymphocyte becomes immunocompetent, meaning it can participate in the immune response
- All lymphocyte types originate in red bone marrow but their maturation sites differ
