Lymphatic system

Dr. Delcambre

lymphatic system

•Open network of vessels, nodes, organs, tissues, and lymph that supports immunity and fluid balance

•Collects and returns excess interstitial fluid (ECF), removes waste and pathogens, produces and activates lymphocytes.

tertiary circulatory system member

lymphocenters

Areas where several lymphatics come together. major sites of Lymph B and T

• important for the proper functioning of immune system (like filter)

cisterna chyli

stopping point for all the fluid being returned to the heart

thoracic duct

last chance to dump (caudal to cranial to the heart). (dorsal to esophagus).

lymphadenopathy

enlarged, swollen, or changed lymph nodes

lymphedema

invrease in ECF in peripheral tissues (do not return and causes lymph buildup (edema)= lymphatic fluid stuck in peripheral tissue.

chyle

• fluid consisting of both fat and lymph, formed from small intestinal drainage into the lymphatic system – ex: in cisterna chyli and thoracic duct

• found mostly in cysterna chyli and thoracic duct.

• breed predisposition of spontaneous rupture of the thoracic duct (borzois).

• fluid is going in the potential space between lung and = chylothorax

spleen

•Filter and storage for blood

•Generation of antibodies

•Removal of old blood cells

•Recycling of iron

thymus

• maturation and differentiation of T-lymphocytes

• Involutes (shrinks) with age in dogs

tonsilar tissue

no afferent vessels going to it, efferent. Palatine, pharyngeal (aka adenoids),

MALT

Mucosal associated lymphoid tissue - BALT and GALT

BALT

Bronchiole associated lymphoid tissue.

GALT

Gut associated lymphoid tissue

hemal nodes

collection of lympoid tissues. serve as mini spleens, filtering blood.

popliteal ln

drains lateral and distal hind limb (green)

mandibular ln

drain the external head

retropharyngeal ln

drain oral and nasal passageways, pharenges

superficial cervical ln

drain brachial region and cervical region

axillary ln

medial thoracic, cranial pectoral region (includes cranial aspects of the mammary chain)

mesenteric/jejunal ln

drains small intestine and proximal large intestine

superficial inguinal ln

caudal mammary chain + adductor region

iliosacral/sublumbar ln

distal large intestine / pelvic cavity /reproductive tract issues.

lymphatic system

Groups of cells, tissues, and organs that monitor body surfaces and internal fluid compartments and react to the presence of potentially harmful substances.

circulating lymphocytes

in blood or lymph - 70%

non-circulating lymphocytes

destined specific tissues - 30%

•(e.g. CT under epithelium of respiratory, GI, and urogenital tracts)

antigens

• substances that can induce a specific immune response.

• broken into small peptides to get a sufficient response

mononuclear phagocytic system

most APCs belong to this system, macrophages. they interact with T lymphocytes to facilitate immune response.

Primary lymphatic organs

bone marrow and thymus

this is where lymphocytes differentiate into immunocompetent cells (training) and to distinguish self/non-self.

secondary lymphatic organs

• diffuse lymphatic tissue (GALT, BALT, MALT)

• lymphatic nodules, lymph nodes, tonsils and spleen

• where they activate

diffuse lymphatic tissue

• Special type of LCT found under epithelium (i.e., in the Lamina propria) of the GI, respiratory, and genitourinary tracts

• site of initial immune response

• includes fibroblasts, plasma cells, eosinophils

lymphatic nodule

•Found in structures associated with GI tract such as ileum, tonsils, appendix.

•Concentration of lymphocytes in meshwork of reticular cells.

primary nodule

small lymphocytes, no germinal center. dark lymphocytes.

secondary nodule

has a germinal center (pale) and a mantle zone (darker), additional activation

Peyer Patches

• aggregations of lymphatic nodules.

• located in ileum, lamina propria

• contain B and T lymphocytes

Tonsils

Immune surveillance of the mouth and nose.

•Stratified squamous epithelium (SSE) lines the tonsillar crypts= distinguishing feature of tonsils

palatine tonsil

located on either side of pharynx

pharyngeal tonsils

located at the roof of pharynx

lingual tonsils

located at the base of the tongue

lymph node

• small bean shaped, encapsulated. located along a pathway of lymphatic vessels.

• Filters lymph drained from peripheral tissues, screening it for pathogens.

•The principal site where T and B lymphocytes undergo antigen-dependent proliferation and differentiation into effector lymphocytes.

stroma of lymph node

• capsule and trabeculae (dense. CT)

• reticular tissue- fine mesh work

cortex of lymph node

secondary lymphoid nodules, composed mainly of B cells (proliferation and differentiation)

deep cortex

• no nodules

• mainly T cells (activation and differentiation)

• High endothelial Venule

High Endothelial Venule

• venules lined by cuboidal or low columnar endothelial cells

• concentrate lymph

• B and T ceclls leave blood through HEV and migrate into LN

lymph circulation

1. afferent lymph vessels

2. through the walls of post capillary (high endothelial) venules in deep cortex

3. lymph exits through the efferent lymph vessels

thymus

• educates the T lymphocytes

• Fully formed at birth, regresses after about 3-4 years in dogs (the lymphatic tissue is replaced by adipose tissue).

• T cells are produced in bone marrow and become immunocompetent in thymus (primary)

• no nodules

thymic lobules

subdivided into cortex and medulla.

• only efferent vessels

• surrounded by DICT

thymic cortex

dense population of small maturing T cells

•Macrophages reside in thymic cortex and are responsible for phagocytosis of T cells which do not fulfill thymic education requirement.

thymic medulla

•Mostly large lymphocytes (lighter staining).

•The center portion may be keratinized.

thymic corpuscles

isolated masses of closely packed, concentrically arranged epitheloreticular cells

blood thymic barrier

1.Capillary endothelium and its base membrane

2.Perivascular connective tissue space occupied by macrophages

3.Type I epithelioreticular cells

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•Barrier  between the T cells and the lumen of cortical blood vessels.

•Protects developing  lymphocytes in thymus  from antigens .

•Separates them from mature immuno-competent lymphocytes circulating in the blood stream.

spleen

largest lymphatic organ, filters blood and reacts to blood borne antigens

• hematopoietic and immune functions

immune function of spleen

•Antigen presentation by APCs and initiation of immune response

•Activation and proliferation of B and T lymphocytes

•Removal of macromolecular antigens from blood

hematopoietic function of spleen

•Removal and destruction of aged RBCs

•Retrieval of iron from RBCs

•Formation of RBCs in fetal life

•RBC and platelet storage in some species

structure of spleen

• encapsulated, trabeculae extend into parenchyma

•Parenchyma can be subdivided into: red pulp and White pulp

red pulp

vascular component (lots of RBCs)

consists of splenic sinuses separated by splenic cords

white pulp

lymphocyte aggregates, around central a, forming a PALS

• contain central artery derived from splenic a.

• nodules aooear as localizes expansions of PALS and displace a to the side (helps identify spleen)

splenic cords

loose meshwork of reticular cells and reticular fibers that contain large numbers of erythrocytes, macrophages, lympohocytes, plasma cells, and granulocytes.

splenic sinuses

special sinusoidal capillaries lined by rod-shaped endothelial cells (extremely long cells that run parallel to the direction of the vessel).

spaces allow blood cells to pass in and out, macrophages monitor lumen.

thymus

lymph node

spleen

tonsil

BALT

in lung