Chapter 22Chapter 22

The lymphatic systemThe lymphatic system

The lymphatic systemThe lymphatic system Consists of a network of tissues, vessels and Consists of a network of tissues, vessels and

organs that help maintain body fluid balance.organs that help maintain body fluid balance. Closely tied to the immune system in Closely tied to the immune system in

protecting the body against foreign organisms. protecting the body against foreign organisms. Organs and tissues of the lymphatic system:Organs and tissues of the lymphatic system:

LymphLymph Lymphatic vesselsLymphatic vessels Lymphatic cellsLymphatic cells Lymph nodesLymph nodes SpleenSpleen TonsilsTonsils Peyer’s patchesPeyer’s patches ThymusThymus

The lymphatic systemThe lymphatic system

Functions: Functions: (a). fluid recovery: reabsorbs 2-4 l/day; (a). fluid recovery: reabsorbs 2-4 l/day;

prevents edema.prevents edema. (b). Immunity: lymph nodes and lymph (b). Immunity: lymph nodes and lymph

organs monitor organs monitor lymph and blood for lymph and blood for pathogens and cancer cells. pathogens and cancer cells.

(c). lipid absorption through the lacteals in (c). lipid absorption through the lacteals in small intestine.small intestine.

Distribution of lymphDistribution of lymph

nodes in body.nodes in body.

Lymph flows toward Lymph flows toward

the heart with the aidthe heart with the aid

of small valvesof small valves

Lymphatic fluidLymphatic fluid How Formed: How Formed: produced by filtration of produced by filtration of

plasma through the capillaries and is plasma through the capillaries and is based on hydrostatic and osmotic based on hydrostatic and osmotic pressures in capillaries and interstitial pressures in capillaries and interstitial space.space.

Pathway of Lymph Flow: Pathway of Lymph Flow: Flow is Flow is always toward the heart. Begins in dead always toward the heart. Begins in dead ended lymphatic capillaries that occur ended lymphatic capillaries that occur everywhere capillaries exist (except: everywhere capillaries exist (except: brain, teeth, bones and bone marrow).brain, teeth, bones and bone marrow).

Lymphatic capillariesLymphatic capillaries

Lymphatic capillariesLymphatic capillaries

lymph capillarieslymph capillaries –smallest of lymph –smallest of lymph vessels; are permeable to lymph fluid vessels; are permeable to lymph fluid and proteins. Lymph capillaries drain and proteins. Lymph capillaries drain into lymph collecting vessels.into lymph collecting vessels.

lactealslacteals:: ‑ highly specialized lymphatic ‑ highly specialized lymphatic capillaries located in intestinal mucosa - capillaries located in intestinal mucosa - transport absorbed fat from intestines transport absorbed fat from intestines and empty into great thoracic duct and empty into great thoracic duct

Lymphatic collecting Lymphatic collecting vesselsvessels

Lymphatic collecting vessels contain Lymphatic collecting vessels contain valves that act as smooth muscle pumps valves that act as smooth muscle pumps to move lymph toward heart.to move lymph toward heart.

Travel with veins in superficial Travel with veins in superficial tissues/arteries in deeper tissues.tissues/arteries in deeper tissues.

Have the same three Have the same three tunicstunics as blood as blood vessels but walls are much thinner and vessels but walls are much thinner and lymph pressure is very low.lymph pressure is very low.

They also have lymph nodes scattered They also have lymph nodes scattered along their length to filter the lymph.along their length to filter the lymph.

Lymphatic cellsLymphatic cells

Natural killer cells (NK cells) large lymphocytes that Natural killer cells (NK cells) large lymphocytes that attack and lyse bacteria, foreign tissue cells and attack and lyse bacteria, foreign tissue cells and infected host cells.infected host cells.

T lymphocytes mature in the thymus (4 types Tc, Ts, T lymphocytes mature in the thymus (4 types Tc, Ts, Th, Tm).Th, Tm).

B lymphocytes mature in red bone marrow and B lymphocytes mature in red bone marrow and produce antibodies when activated.produce antibodies when activated.

Macrophages develop from monocytes and are Macrophages develop from monocytes and are phagocytic.phagocytic.

Dendritic cells (branched macrophages) found in Dendritic cells (branched macrophages) found in skin.skin.

Reticular cells branched cells in stroma of lymphatic Reticular cells branched cells in stroma of lymphatic organs.organs.

Lymph nodesLymph nodes Bean shaped organs that cleanse the lymph of Bean shaped organs that cleanse the lymph of

pathogenspathogens ~500 lymph nodes in the body ~ 1mm to ~500 lymph nodes in the body ~ 1mm to

25mm.25mm. Node is surrounded by a fibrous capsule from Node is surrounded by a fibrous capsule from

which trabeculae extend inward to split the which trabeculae extend inward to split the node into compartments called sinuses.node into compartments called sinuses.

Lymph enters node via afferent lymphatic Lymph enters node via afferent lymphatic vessel and exits through efferent lymphatic vessel and exits through efferent lymphatic vessel back into collecting vessels.vessel back into collecting vessels.

As lymph percolates thru the node As lymph percolates thru the node macrophages cleanse the lymph of all macrophages cleanse the lymph of all pathogens.pathogens.

Lymph nodesLymph nodes

Lymph TrunkLymph Trunk Formed by the convergence of several lymph Formed by the convergence of several lymph

collecting vessels that drain large areas of the collecting vessels that drain large areas of the body. body.

Six major trunks in body:Six major trunks in body:

1.1. Lumbar trunks- lymph from lower limb, pelvic Lumbar trunks- lymph from lower limb, pelvic region and anterior abdominal wall.region and anterior abdominal wall.

2.2. Intestinal trunk- lymph from stomach, intestines Intestinal trunk- lymph from stomach, intestines and other digestive organs (chyle).and other digestive organs (chyle).

3.3. Bronchomediastinal trunk- lymph from thoracic Bronchomediastinal trunk- lymph from thoracic visceraviscera

4.4. Subclavian trunks- lymph from upper limbs, Subclavian trunks- lymph from upper limbs, inferior neck and superior thoracic wall.inferior neck and superior thoracic wall.

5.5. Jugular trunks- lymph from head and neck.Jugular trunks- lymph from head and neck.

6.6. Intercostal trunk- lymph from intercostal regionIntercostal trunk- lymph from intercostal region

Lymphatic ductsLymphatic ducts The lymphatic trunks drain into the largest The lymphatic trunks drain into the largest

lymphatic vessels: the lymphatic ducts. Most lymphatic vessels: the lymphatic ducts. Most people (80%) have 2 lymphatic ducts: (1) people (80%) have 2 lymphatic ducts: (1) Thoracic duct (present in all people) and (2) Thoracic duct (present in all people) and (2) the Right lymphatic duct.the Right lymphatic duct.

The thoracic duct empties into the venous The thoracic duct empties into the venous circulation at the junction of the internal circulation at the junction of the internal jugular and left subclavian veins. Lymph is jugular and left subclavian veins. Lymph is then incorporated into the circulating blood, then incorporated into the circulating blood, eventually cleansed of foreign and dead eventually cleansed of foreign and dead matter and excreted via the liver.matter and excreted via the liver.

Thoracic duct andThoracic duct and

right lymphatic ductright lymphatic duct

Thoracic duct drainsThoracic duct drains

right side of face andright side of face and

most of left thorax most of left thorax andand

lower body.lower body.

Right lymphatic Right lymphatic drainsdrains

left side of head andleft side of head and

upper body.upper body.

Lymphoid tissueLymphoid tissue

The most important tissue of the immune system as The most important tissue of the immune system as it is responsible for the production and activation of it is responsible for the production and activation of the “B” and “T” lymphocytes. Found in two primary the “B” and “T” lymphocytes. Found in two primary sites:sites:

(1) In the infected mucous membranes of the (1) In the infected mucous membranes of the digestive, respiratory, urinary and reproductive digestive, respiratory, urinary and reproductive tracts. This tissue is called MALT (mucosa tracts. This tissue is called MALT (mucosa associated lymphoid tissue).associated lymphoid tissue).

(2) In all lymphoid organs except the thymus.(2) In all lymphoid organs except the thymus. Lymphoid tissue is a framework of reticular fibers and Lymphoid tissue is a framework of reticular fibers and

reticular cells in a network of “B” and “T” lymphocytes as reticular cells in a network of “B” and “T” lymphocytes as well as macrophages. This network consists of a network well as macrophages. This network consists of a network of lymphoid follicles with germinal centers of dividing of lymphoid follicles with germinal centers of dividing lymphocyteslymphocytes

Lymphoid organsLymphoid organs

Primary lymphoid organs are thymus and Primary lymphoid organs are thymus and bone marrowbone marrow

Secondary lymphoid organs include the Secondary lymphoid organs include the lymph nodes, spleen, tonsils, aggregated lymph nodes, spleen, tonsils, aggregated lymphoid nodules in the intestine and lymphoid nodules in the intestine and appendix. appendix. The thymus and bone marrow produce “T” The thymus and bone marrow produce “T”

and “B” lymphocytes and the secondary and “B” lymphocytes and the secondary organs serve to collect and destroy the organs serve to collect and destroy the infectious microorganisms where they are infectious microorganisms where they are removed by the liver and spleen.removed by the liver and spleen.

Red bone marrowRed bone marrow Second largest organ in the body next to skin.Second largest organ in the body next to skin. Two types red and yellow; red actively Two types red and yellow; red actively

produces all blood cells; yellow is dormant produces all blood cells; yellow is dormant and produces blood cells in extreme and produces blood cells in extreme emergencies. emergencies.

Composed of a network of reticular fibers Composed of a network of reticular fibers forming cave like structures with reticular forming cave like structures with reticular cells lining the walls. Within the caves are cells lining the walls. Within the caves are blood cells in various stages of development blood cells in various stages of development and fat cells. and fat cells.

Capillaries run throughout the network and Capillaries run throughout the network and carry the developed blood cells into the carry the developed blood cells into the circulation.circulation.

Red marrowRed marrow

SpleenSpleen

Located in the upper left quadrant of Located in the upper left quadrant of abdominal cavity with a gastric and renal area.abdominal cavity with a gastric and renal area.

Functions to remove blood borne antigens and Functions to remove blood borne antigens and aged or defective blood cells.aged or defective blood cells.

It is a site for hematopoiesis in fetus and It is a site for hematopoiesis in fetus and storage of blood throughout life.storage of blood throughout life.

Consists of red and white pulp. (seen in fresh Consists of red and white pulp. (seen in fresh tissue).tissue). Red pulp is sinuses engorged with rbc’s.Red pulp is sinuses engorged with rbc’s. White pulp is lymphocytes and macrophages White pulp is lymphocytes and macrophages

collected like sleeves along the splenic arterycollected like sleeves along the splenic artery

Spleen structureSpleen structure

Spleen anatomy & histologySpleen anatomy & histology

TonsilsTonsils

Located in the oropharynx, they trap Located in the oropharynx, they trap bacteria and foreign pathogens bacteria and foreign pathogens entering the mouth and nose.entering the mouth and nose.

Palatine tonsils – either side of and Palatine tonsils – either side of and posterior end of oral cavityposterior end of oral cavity

Lingual tonsils – base of tongueLingual tonsils – base of tongue Pharyngeal tonsils (adenoids)– posterior Pharyngeal tonsils (adenoids)– posterior

wall of nasopharynxwall of nasopharynx

TonsilsTonsils

Peyer’s patchesPeyer’s patches

Defined: large isolated clusters of Defined: large isolated clusters of lymphatic nodules found intermingled lymphatic nodules found intermingled around the ileum of the small intestines.around the ileum of the small intestines.

Function: destroy bacteria and generates Function: destroy bacteria and generates memory lymphocytes for long term memory lymphocytes for long term immunity against infection.immunity against infection.

ThymusThymus

Site where immature lymphocytes Site where immature lymphocytes develop into “T” lymphocytesdevelop into “T” lymphocytes

Secretes thymosin and thymopoietin Secretes thymosin and thymopoietin which stimulate “T” cells to become which stimulate “T” cells to become immunocompetent.immunocompetent.

Most prominent in childhood and by age Most prominent in childhood and by age 40 is ~ 5% active.40 is ~ 5% active.

Thymus structure & Thymus structure & histologyhistology