Lymphatic System Flashcards
What is lymph?
Lympth is interstitial fluid that has entered the lymphatic vessels. Lymph is a clear, pale-yellow fluid
Lympathic system consists of
lymphatic vessels, lymph, lymph nodes, thymus, spleen, GALT & MALT, red bone marrow
Lymphatic tissue is made of
Lymphatic tissue is made of a specialized form of reticular connective tissue. Lymphatic tissue contains large numbers of lymphocytes
Functions of Lymphatic System
- Drains excess interstitial fluid
- Transports dietary lipids
- Carries out immune responses
Lymphatic Vessels & Lymph Circulation
1, Begins as lymphatic capillaries
(tiny and closed at one end and located in spaces between cells)
2. Lymphatic capillaries unite to form larger lymphatic vessels (resemble veins but have thinner walls and more valves)
3. Lymph flows through lymph nodes
In skin:
Lymphatic vessels located in subcutaneous tissue, following the same route as veins
In viscera:
Lymphatic vessels follow same route as arteries, forming plexuses (networks) around viscera
Tissues that lack lymphatic vessels:
Avascular tissues, eg. cornea, lens, cartilage, CNS - brain and spinal cord
Structure of lymphatic capillaries
Larger in diameter than blood vessels
Have a one way structure - only permits in flow of interstitial fluid
Flow of Lymph
Blood capillaries (blood) > Interstitial spaces (interstitial fluid) > Lymphatic capillaries (lymph) > Lymphatic vessels (lymph) > Lymphatic ducts (lymph) > Junction of the internal jugular and subclavian veins (blood)
Lymphatic Ducts
Lymph passes from trunks into two main channels
- Thoracic duct (aka left lymphatic duct)
- Right lymphatic duct
Thoracic duct
The thoracic duct is the main duct for the return of lymph to blood
- 38-45cm long
- Main duct for the return of lymph to blood
- Drains lymph from most of the trunks: L & R Lumbar, Intestinal, L Jugular, L Subclavian, L Bronchomediastinal
- Then drains lymph into venous blood stream at junction of L internal jugular & L subclavian vein
Spleen
white pulp, red pulp
Lymph nodes
Act as a filter, cleaning the lymph
Same two pumps involved in venous return of blood to heart maintain flow of lymph
- Skeletal muscle pump – “milking action” of skeletal muscles compresses lymphatic vessels
- Respiratory pump – Pressure changes occuring during inhalation and exhalation
Primary Lymphatic Organs
Sites where stem cells divide and become immunocompetent (can mount an immune response)
- Red Bone Marrow – pluripotent stem cells give rise to:
- Immunocompetant B cells
- Pre-T cells - Thymus
- Pre-T cells migrate to thymus to finish their maturation > immunocompetent T cells
Secondary Lymphatic Organs
Sites where most immune responses occur
- Lymph nodes – organ (surrounded by a capsule)
- Spleen - organ
- Lymphatic nodules (follicles) – non organ (lacks a capsule)
What does the lymphatic system pick up, that is not reabsorbed?
Perhaps plasma proteins as molecules are too large
What do macrophages do in the thymus?
Thymic macrophages help clear debris of dead and dying cells
What is innate (non-specific) immunity?
External and internal physical and chemical defences which act in a non-specific way. Innate immunity is present from birth. Prevent access of microbes, or help eliminate microbes in the body.
What is the body’s first line of defence? Innate (non-specific) Immunity
Part of Innate (non-specific) Immunity, the body’s first line of defence is the skin and mucous membrane. Both provide physical and chemical barriers against pathogens entering to cause disease.
How does the skin (epidermis being the exterior) protect the body against pathogens, in Innate (non-specific) Immunity?
Innate (non-specific) Immunity & Skin (first line of defence)
- Keratin: many layers of closely packed keratinised cells
- Acid Mantle: sebaceous glands producing oily sebum
How does the epithelial layer of mucous membranes protect the body against pathogens, in Innate (non-specific) Immunity?
Innate (non-specific) Immunity & Mucous membranes (first line of defence). Mucous membranes line body cavities and secrete a mucous to trap microbes. Examples of how mucous membranes form the first line of defence: Mucous Gastric juice Nasal hairs Cilia Lacrimal secretions Saliva Urine Vaginal secretions Vomiting & Defecation
How does the second line of defence protect the body?
The second line of defence is used whenever first line has been penetrated. The second line of defence involves internal defenses such as:
- Antimicrobial Substances
- Natural Killer (NK) cells
- Phagocytes
- Inflammatory Response
- Fever
Natural Killer (NK) Cells
WBCs that circulate in the body, killing anything that looks abnormal to them (anything abnormal will be on the wall of the cell eg. plasma membrane proteins).
NK cells form 5-10% of lymphocytes in blood. NK cells are present in spleen, lymphnodes & red bone marrow
Phagocytes
- Phago= eat; cytes= cells
- Specialised cells that perform phagocytosis
- Ingestion of microbes & other particles
- Two types: Neutrophils & Macrophages
- Note: phagocytosis plays a role in innate & adaptive immunity
Five Phases of Phagocytosis
Five Phases of Phagocytosis
- Chemotaxis (movement of chemicals) – phagocyte will pick up on a released chemical (from the microbe) – will gobble it up. Or surrounding cells will release a chemical, warning the phagocyte that a microbe has come through / needs to be destroyed.
- Adherence: After sensing there is a microbe present, the phagocyte will surround the microbe. It will use its plasma membrane and wrap it around the microbe (engulfed).
- Ingestion / Digestion: Eats the microbe and brings it into the centre (in a vessiicels). Has really strong enzymes (lysosomes - vessicels) which fuse with the vessicel that has the microbe in it.
- It is killed and leftovers are referred to as the residual body (remains for the life of the phagocyte).
What are the four pillars of inflammation?
Pillars of inflammation
– redness (rubor): due to vasodilation
- heat (calor)
- swelling (tumor) - area of capillaries has increased due to blood flow – more fluid inside, due to vassodilation
- pain (dolor). All the chemicals that are produced can press upon your nerves.
* In serious inflammation there is also a loss of function – funcho lacea. This wont occur in all cases (whereas the first four will).
Three stages of an inflammatory response
- Vasodilation of arterioles & increased permeability of capillaries– histamine, kinin, LTs Vasodilation
- Emigration of phagocytes (process depends on chemotaxis)
- Tissue Repair
Adaptive (specific) immunity
Ability of body to defend itself against specific invading agents
Substances that provoke immune response are called antigens (Ags)
Two properties distinguish adaptive from innate immunity
Specificity
Memory
B cells and T cells (adaptive immunity)
Adaptive immunity involves
- Lymphocytes called B cells & T cells
both cells arise from stem cells in red bone marrow
- B-cells mature in red bone marrow
- T-cells (although from red bone marrow) mature in thymus gland
- Both cells develop immunocompetence
- Ability to carry out adaptive immune responses
- Insertion of Antigen receptors into their plasma membranes
What are CD4 and CD8?
CD4 are T-cells that act as helpers. CD8 are T-cells that act as killers (are cytotoxic).
CD4 help in both cell-mediated immune responses and antibody-mediated immune responses.
CD4 helper T-cells have the CD4 protein on their plasma membrane.
CD8 cytotoxic T-cells have the CD8 protein on their plasma membrane.
Cell-Mediated Immunity
Cell-Mediated Immunity
Cytotoxic T-cells directly attack invading antigens. Cell-mediated immunity is directed at intracellular pathogens, some cancer cells and tissue transplants.
Antibody-Mediated Immunity
Antibody-Mediated Immunity
B-cells transform into plasma cells that secrete antibodies. Antibody-mediated immunity is directed at extracellular pathogens.
Plasma cells are the effector cells in antibody mediated immunity and they secrete specific antibodies, which in turn circulate in the lymph and blood to reach the site of invasion.
Clonal selection
Clonal selection of lymphocytes occurs in the secondary lymphatic organs and tissues. The lympocutes proliferates and differentiates in response to a specific antigen. The result is a group of clones, that are able to recognise the same antigen (that the original could). Thus once clonal selection occurs there are thousands of lymphocytes (clones) that can respond to a specific antigen.
Effector cells
A lymphocyte that undergoes clonal selection gives rise to either memory cells or effector cells.
Effector cells include active helper T-cells, active cyotoxic T-cells and plasma cells (formally B-cells).
Effector cells take part on the immune response and then die.
Memory cells do not actively participate, they are the reserve army (able to respond to the same antigen, should it enter the body again).
Major Histocompatibility Complex (MHC) antigens
MHC are self antigens. Also called leukocyte antigens as first identified on WBCs. MHC antigens are unique (expect for twins) and the MHC molecules mark the surface of all cells except for RBCs. MHC are the reason why some transplants are rejected.
B cells
B cells produce antibodies (Ab)
Antigens
Antibody generators. Antigens are substances that are recognised as foreign and which provoke an immune response.
