The lymphatic system is responsible for: 1- returning tissue fluid to the blood 2- protecting the body against foreign material.

The lymphatic system is The lymphatic system is responsible for:responsible for:

1- returning tissue fluid to the 1- returning tissue fluid to the blood blood

2- protecting the body against 2- protecting the body against foreign material. foreign material.

The parts of the lymphatic systemThe parts of the lymphatic system

the lymphthe lymph the system of lymph vesselsthe system of lymph vessels lymphatic tissue, which includeslymphatic tissue, which includes

-lymph nodes-lymph nodes

-Nodules-Nodules

- the spleen- the spleen

- and the thymus gland.- and the thymus gland.

LYMPHLYMPH

Lymph Lymph is the name for tissue fluid that enters lymphis the name for tissue fluid that enters lymph capillaries. capillaries. Filtration in capillaries creates tissue fluid from bloodFiltration in capillaries creates tissue fluid from blood plasma, most of which returns almost immediately toplasma, most of which returns almost immediately to the blood in the capillaries by osmosis. the blood in the capillaries by osmosis. Some tissue fluid, however, remains in interstitial spacesSome tissue fluid, however, remains in interstitial spacesand must be returned to the blood by way of the lymphatic and must be returned to the blood by way of the lymphatic vessels.vessels. Without this return, blood volume and blood pressure Without this return, blood volume and blood pressure

would very soon decrease and edema developeswould very soon decrease and edema developes

LYMPH VESSELSLYMPH VESSELS The system of lymph vessels begins as dead-endThe system of lymph vessels begins as dead-end lymph capillaries lymph capillaries found in most tissue spacesfound in most tissue spaces Lymph capillaries are very permeable and collect tissue Lymph capillaries are very permeable and collect tissue

fluid and proteins.fluid and proteins. Lacteals Lacteals are specialized lymph capillaries in the villi of the are specialized lymph capillaries in the villi of the

small intestine; they:small intestine; they: absorb the fat-soluble end products of digestion, suchabsorb the fat-soluble end products of digestion, such as fatty acids and vitamins A, D, E, and K.as fatty acids and vitamins A, D, E, and K. -Lymph capillaries unite to form larger lymph vessels,-Lymph capillaries unite to form larger lymph vessels, whose structure is very much like that of veins.whose structure is very much like that of veins. There is no pump for lymph (as the heart is the pumpThere is no pump for lymph (as the heart is the pump for blood), for blood),

mechanisms that promote venous mechanisms that promote venous returnreturn

-The smooth muscle layer of the larger lymph-The smooth muscle layer of the larger lymph vessels constricts,vessels constricts,- and the one-way valves (just like those of veins) prevent and the one-way valves (just like those of veins) prevent

backflow of lymph. backflow of lymph. - the the skeletal muscle pumpskeletal muscle pump Lymph vessels in the extremities, especially the legs, are Lymph vessels in the extremities, especially the legs, are

compressed by the skeletal muscles that surround them;compressed by the skeletal muscles that surround them; this is. this is. The The respiratory pump respiratory pump negative intrathorasic pressurenegative intrathorasic pressure keeps the lymph moving towards the chest.keeps the lymph moving towards the chest.

LYMPHATIC TISSUELYMPHATIC TISSUE

*Lymphatic tissue consists mainly of lymphocytes in a*Lymphatic tissue consists mainly of lymphocytes in amesh-like framework of connective tissue.mesh-like framework of connective tissue.* Recall that most lymphocytes are produced from stem * Recall that most lymphocytes are produced from stem

cells in the red bone marrow, then migrate to the lymph cells in the red bone marrow, then migrate to the lymph nodes and nodules, to the spleen, and to the thymus.nodes and nodules, to the spleen, and to the thymus.

* In these structures, lymphocytes become activated and * In these structures, lymphocytes become activated and proliferate in response to infection (this is a function of allproliferate in response to infection (this is a function of all

lymphatic tissue).lymphatic tissue).* The thymus has stem cells that produce a significant * The thymus has stem cells that produce a significant

portion of the T lymphocytes.portion of the T lymphocytes.

LYMPH NODES AND NODULESLYMPH NODES AND NODULES

Lymph nodes Lymph nodes and and nodules nodules are masses of lymphaticare masses of lymphatic tissue. Nodes and nodules differ with respect to sizetissue. Nodes and nodules differ with respect to size

and location.and location.

NodesNodes are usually larger, 10 to 20 mm in length, and are are usually larger, 10 to 20 mm in length, and are encapsulated.encapsulated.

nodulesnodules range from a fraction of a millimeter to several range from a fraction of a millimeter to several millimeters in length and do not have capsules.millimeters in length and do not have capsules.

Lymph nodes Lymph nodes are found in groups along the pathwaysare found in groups along the pathways of lymph vessels to the subclavian veins. Lymph entersof lymph vessels to the subclavian veins. Lymph enters a node through several afferent lymph vessels anda node through several afferent lymph vessels and

leaves through one or two efferent vesselsleaves through one or two efferent vesselsAs lymph passes through a lymph node, bacteria As lymph passes through a lymph node, bacteria

andand other foreign materials are phagocytized by fixed other foreign materials are phagocytized by fixed

macrophagesmacrophages.. Plasma cells Plasma cells develop from lymphocytes exposed develop from lymphocytes exposed

to pathogens in the lymph and produce to pathogens in the lymph and produce antibodies.antibodies.

These antibodies will eventually reach the blood These antibodies will eventually reach the blood and circulate throughout the body.and circulate throughout the body.

Groups of lymph nodesGroups of lymph nodes

There are many groups of lymph nodes along all There are many groups of lymph nodes along all the lymph vessels, but three paired groups the lymph vessels, but three paired groups deserve mention because of their strategicdeserve mention because of their strategic

locations. These are the locations. These are the cervicalcervical, , axillaryaxillary, and , and inguinal inguinal lymph nodes. lymph nodes.

these are at the junctions of the head and these are at the junctions of the head and extremities with the trunk of the body.extremities with the trunk of the body.

If pathogens get to the lymph, they will be If pathogens get to the lymph, they will be destroyed by the lymph nodes before they get to destroyed by the lymph nodes before they get to the blood in the subclavian veinsthe blood in the subclavian veins

Lymph nodulesLymph nodules

Lymph nodules Lymph nodules are small masses of are small masses of lymphatic tissue found just beneath the lymphatic tissue found just beneath the epithelium of all epithelium of all mucous membranesmucous membranes. . because any natural body opening is a because any natural body opening is a possible portal of entry for pathogens. If possible portal of entry for pathogens. If bacteria in inhaled air get through the bacteria in inhaled air get through the epithelium of the trachea, lymph nodules epithelium of the trachea, lymph nodules with their macrophages are in position to with their macrophages are in position to destroy these bacteria before they get to the destroy these bacteria before they get to the blood.blood.

Lymph nodulesLymph nodules

Some of the lymph nodules have specific names.Some of the lymph nodules have specific names. Those of the small intestine are called Those of the small intestine are called Peyer’sPeyer’s patchespatches, , those of the pharynx are called those of the pharynx are called tonsilstonsils..*The palatine tonsils are on the lateral walls of the *The palatine tonsils are on the lateral walls of the

pharynx, pharynx, *the adenoid (pharyngeal tonsil) is on the posterior wall,*the adenoid (pharyngeal tonsil) is on the posterior wall, * the lingual tonsils are on the base of the tongue.* the lingual tonsils are on the base of the tongue.-The tonsils, therefore, form a ring of lymphatic-The tonsils, therefore, form a ring of lymphatic tissue around the pharynx, which is a commontissue around the pharynx, which is a common pathway for food and airpathway for food and air

SPLEENSPLEEN In the fetus, the spleen produces red blood cells,.In the fetus, the spleen produces red blood cells,. After birth the spleen is very much like a large After birth the spleen is very much like a large

lymph node, except that its functions affect the lymph node, except that its functions affect the blood that flows through it rather than lymph.blood that flows through it rather than lymph.

The functions of the spleen after birth are:The functions of the spleen after birth are: 1. Contains plasma cells that produce antibodies 1. Contains plasma cells that produce antibodies 2. Contains fixed macrophages that phagocytize2. Contains fixed macrophages that phagocytize pathogens and old red blood cells and form pathogens and old red blood cells and form

bilirubin.bilirubin.3. Stores platelets and destroys them when they are 3. Stores platelets and destroys them when they are

no longer useful. no longer useful.

THYMUSTHYMUS

The The thymus thymus is located inferior to the is located inferior to the thyroid gland.thyroid gland.

In the fetus and infant, the thymus is In the fetus and infant, the thymus is large and extends under the sternum.large and extends under the sternum.

With increasing age,the thymus With increasing age,the thymus shrinks, and relatively little thymus shrinks, and relatively little thymus tissue is found in adults, though it is tissue is found in adults, though it is still active.still active.

Functions of the thymusFunctions of the thymus

The stem cells of the thymus produce T The stem cells of the thymus produce T lymphocytes or lymphocytes or T cellsT cells

* Thymic hormones are necessary for what* Thymic hormones are necessary for what may be called “immunological competence.may be called “immunological competence.*The thymic hormones enable the T cells to *The thymic hormones enable the T cells to

participate in the recognition of foreign antigens participate in the recognition of foreign antigens and to provide immunity. and to provide immunity.

*This capability of T cells is established early in life *This capability of T cells is established early in life and then is perpetuated by the lymphocytesand then is perpetuated by the lymphocytes

newborn’s immune systemnewborn’s immune system

The newborn’s immune system is not yet The newborn’s immune system is not yet fully mature, and infants are more fully mature, and infants are more susceptible to certain infections than are susceptible to certain infections than are older children and adults.older children and adults.

* Usually by the age of 2 years, the immune * Usually by the age of 2 years, the immune system matures and becomes fully system matures and becomes fully functional. This is why some vaccines, functional. This is why some vaccines, such as the measles vaccine, are not such as the measles vaccine, are not recommended for infants younger than 15 recommended for infants younger than 15 to 18 months of age. to 18 months of age.

HODGKIN’S DISEASEHODGKIN’S DISEASE

Hodgkin’s disease Hodgkin’s disease is a malignant disorder ofis a malignant disorder ofthe lymph nodes; the cause is not known. Thethe lymph nodes; the cause is not known. Thefirst symptom is usually a swollen but painlessfirst symptom is usually a swollen but painlesslymph node, often in the cervical region. Thelymph node, often in the cervical region. Theindividual is prompted to seek medical attentionindividual is prompted to seek medical attentionbecause of other symptoms: chronic fever,because of other symptoms: chronic fever,fatigue, and weight loss. The diagnosis involvesfatigue, and weight loss. The diagnosis involvesbiopsy of the lymph node and the finding ofbiopsy of the lymph node and the finding ofcharacteristic cells.Treatment of Hodgkin’s disease characteristic cells.Treatment of Hodgkin’s disease

requires chemotherapy, radiation, or both. With early requires chemotherapy, radiation, or both. With early diagnosis and proper treatment, this malignancy is diagnosis and proper treatment, this malignancy is very often curable.very often curable.

IMMUNITYIMMUNITY

Immunity Immunity may be defined as the may be defined as the ability to destroy pathogens or other ability to destroy pathogens or other foreign material and to prevent further foreign material and to prevent further cases of certain infectious diseases.cases of certain infectious diseases.

This ability is of vital importance This ability is of vital importance because the body is exposed to because the body is exposed to pathogens from the moment of birth.pathogens from the moment of birth.

AntigensAntigens

Antigens Antigens are chemical markers that identify are chemical markers that identify cells.cells.

*Human cells have their own antigens that identify *Human cells have their own antigens that identify all the cells in an individual as “self ”.all the cells in an individual as “self ”.

*When antigens are foreign, or “non-self,” they *When antigens are foreign, or “non-self,” they may be recognized as such and destroyed.may be recognized as such and destroyed.

* Bacteria, viruses, fungi, and protozoa are all * Bacteria, viruses, fungi, and protozoa are all foreign antigens that activate immune rsponses, foreign antigens that activate immune rsponses, as are cell products such as bacterial toxins.as are cell products such as bacterial toxins.

Examples of antigensExamples of antigens Malignant cells, are recognized as foreign and are Malignant cells, are recognized as foreign and are

usually destroyed before they can establish usually destroyed before they can establish themselves and cause cancer. themselves and cause cancer.

Organ transplants are also foreign tissue, and the Organ transplants are also foreign tissue, and the immune system may reject (destroy) a transplanted immune system may reject (destroy) a transplanted kidney or heart.kidney or heart.

* Sometimes the immune system mistakenly reacts to * Sometimes the immune system mistakenly reacts to part of the body itself and causes an part of the body itself and causes an autoimmune autoimmune diseasedisease. .

Most often, however, the immune mechanisms Most often, however, the immune mechanisms function to protect the body from the microorganisms function to protect the body from the microorganisms around us and within us.around us and within us.

Components of immunityComponents of immunity

1-Innate immunity :1-Innate immunity : may be called nonspecific, may be called nonspecific, does not create memory, and its responses are does not create memory, and its responses are always the same regardless of the target. always the same regardless of the target.

2-Adaptive immunity:2-Adaptive immunity: is very specific, may is very specific, may involve antibodies, does create memory, and involve antibodies, does create memory, and may become more efficient.may become more efficient.

Both kinds of immunity work together to preventBoth kinds of immunity work together to prevent

damage and disease.damage and disease.

INNATE IMMUNITYINNATE IMMUNITY

The innate immune responses are alwaysThe innate immune responses are always the same, and their degree of efficiency does not the same, and their degree of efficiency does not

increase with repeated exposure, it includes:increase with repeated exposure, it includes:I-I-Barriers:Barriers:--The stratum corneum of the skinThe stratum corneum of the skin-The fatty acids in sebum-The fatty acids in sebum-The mucous membranes-The mucous membranes-ciliated epithelium of the upper respiratory tract-ciliated epithelium of the upper respiratory tract-The hydrochloric acid of the gastric juice-The hydrochloric acid of the gastric juice-Lysozyme found in saliva and tears-Lysozyme found in saliva and tears-WBC,s in subcutaneous tissue and connective T. -WBC,s in subcutaneous tissue and connective T.

II-Defensive CellsII-Defensive Cells

-white blood cells (neutrophills, eosinophills)-white blood cells (neutrophills, eosinophills)-Macrophages-Macrophages-Basophils and mast cells (a type of -Basophils and mast cells (a type of

connective tissue cell) are also defensive connective tissue cell) are also defensive cells that are found throughout areolar cells that are found throughout areolar connective tissue. They produce connective tissue. They produce histamine. Histamine causes vasodilation histamine. Histamine causes vasodilation and makes capillaries more permeable; and makes capillaries more permeable; these are aspects of inflammation.these are aspects of inflammation.

- - Natural killer cells Natural killer cells (NK cells)(NK cells)

Natural killer cells Natural killer cells (NK cells)(NK cells)

Natural killer cells Natural killer cells (NK cells) circulate in the (NK cells) circulate in the blood but are also found in the red bone blood but are also found in the red bone marrow, spleen, and lymph nodes. They marrow, spleen, and lymph nodes. They are a small portion (about 10%) of the total are a small portion (about 10%) of the total lymphocytes, but are able to destroy many lymphocytes, but are able to destroy many kinds of pathogens and tumor cells.kinds of pathogens and tumor cells.

NK cells make direct contact with foreign NK cells make direct contact with foreign cells, and kill them by rupturing their cell cells, and kill them by rupturing their cell membranes (with chemicals called membranes (with chemicals called perforins).perforins).

III-Chemical DefensesIII-Chemical Defenses

A-The A-The interferons interferons (alpha-beta-, and gamma-(alpha-beta-, and gamma-interferons) are proteins produced by cells interferons) are proteins produced by cells infected with viruses and by T cells. infected with viruses and by T cells.

*Viruses must be inside a living cell to reproduce, *Viruses must be inside a living cell to reproduce, interferon can block their reproduction so the interferon can block their reproduction so the viruses cannot infect new cells and cause viruses cannot infect new cells and cause disease.disease.

* Interferon is probably a factor in the self-limiting * Interferon is probably a factor in the self-limiting nature of many viral diseases (and is used in nature of many viral diseases (and is used in the treatment of some diseases, such as the treatment of some diseases, such as hepatitis Chepatitis C

Chemical defences ( cont.)Chemical defences ( cont.)

B-Complement B-Complement is a group of more than 20 is a group of more than 20 plasma proteins that circulate in the blood plasma proteins that circulate in the blood until activated.until activated.

-They are involved in the lysis of cellular -They are involved in the lysis of cellular antigens and the labeling of noncellular antigens and the labeling of noncellular antigens. antigens.

-Some stimulate the release of histamine in -Some stimulate the release of histamine in inflammation; inflammation;

-Others attract WBCs to the site.-Others attract WBCs to the site.

Chemical defences ( cont.)Chemical defences ( cont.)

C-Inflammation C-Inflammation is a general response to damage of is a general response to damage of any kind: microbial, chemical, or physical.any kind: microbial, chemical, or physical.

-Basophils and mast cells release histamine and -Basophils and mast cells release histamine and leukotrienes ,which leads to :leukotrienes ,which leads to :

-vasodilation increasing blood flow to the area.-vasodilation increasing blood flow to the area.-and capillaries become more permeable.-and capillaries become more permeable.-and tissue fluid and WBCs collect at the site. -and tissue fluid and WBCs collect at the site. *The purpose of inflammation*The purpose of inflammation-try to contain the damage, -try to contain the damage, -keep it from spreading, -keep it from spreading, -eliminate the cause. - and permit repair-eliminate the cause. - and permit repair

signs of inflammationsigns of inflammation

RednessRedness ,from greater blood flow ,from greater blood flow heatheat, from the blood and greater metabolic , from the blood and greater metabolic

activityactivity swellingswelling, from the accumulation of tissue fluid, from the accumulation of tissue fluid and painand pain: from the damage itself and perhaps : from the damage itself and perhaps

the swelling.the swelling.*inflammation is a positive feedback mechanism *inflammation is a positive feedback mechanism

that may become a vicious cycle of damage and that may become a vicious cycle of damage and more damage. more damage.

The hormone cortisol is one brake that prevents The hormone cortisol is one brake that prevents this, this,

BarriersBarriers

B-CellsB-Cells

ChemicalsChemicals