Lymphatic system  lymphoid tissue and

lymphatic vessels

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The lymphatic system is part of the immunesystem, made up of a network of conduits

that carry a clear fluid called lymphIt also includes the lymphoid tissue and lymphatic vessels through which the lymphtravels in a one-way system in which lymph flows only toward the heart.

Lymphoid tissue is found in many organs, including lymph nodes, and in the lymphoidfollicles associated with the digestive system such as the tonsils. The system alsoincludes all the structures dedicated to the circulation and production of lymphocytes,which includes the spleen, thymus, bone marrow and the lymphoid tissue associatedwith the digestive system, MALT (mucosal associated lymphoid tissue)

CLASSIFICATION

The lymphatic system functions:▪- to transport immune cells to and from the lymph nodes in to the bone- to transport (through the lymph) anGgen-­‐presenGng  cells  (APCs), such asdendritic cells, to the lymph nodes where an immune response is stimulated- to transport lymphocytes from the efferent lymphatics exiting the lymph nodes.-to transport cancer cells (cancer stem cells?) in the metastasis process- to remove interstitial fluid from tissues- to absorb and transport fats as chyle to the circulatory system

Where we are and where we go

Lymph node regions

The structure of a lymph node

mesenteries

Human lymph node

lymph node follicle

connective tissue

trabeculae

germinaltissue

subcapsular sinus

hilum

Human palatine tonsil

follicular dendritic cells

Human tonsil lymphonoid follicle

germinal centre (CD38+ B cells)naïve B cells (IgD+)transferrin receptor (CD 71+) positive cells

Note:Immature  Bcells,  whichhave  neverbeenexposed  toan  anGgen,are  knownas  naïve  Bcells  andexpress  IgM,IdD  isotypesin  a  cellsurfacebound  form

follicle of mucosa-associated lymphoid tissue (MALT)

germinal centre

Dendritic cells in the skin and lymphoid tissue

1. Adenoid (in posterior naris)2. Inferior concha (posterior view)The inferior nasal concha (Inferior Turbinated Bone) one of the turbinates 3. Posterior end of nasal septum

median recess (arrow);  the impression left by contact with the left Eustachian cushion is evident laterally (arrowhead).

Nasopharyngeal tonsil

The tonsillar bed, sagittal section

Arterial supply to the palatine tonsil

The neonatal thymus

The adult thymus

9 year-old 80 year-old

Thymic structure and cellular organization

Hassall’s corpuscole

Thymic stromallymphopoietinprotein (TSLP)

The microscopic organization

Phases of thymocyte maturation

Cells that pass both levels of selection are released into thebloodstream to perform vital immune functions

The medulla of neonatal thymus

Hassal’s corpuscles

The visceral surface of the spleen

The posterior relations of the spleen

Outline of the spleen

Origin of splenorenal ligamentPosterior peritoneal layer of lesser sac

Inferior diaphragmatic peritoneum

Phrenico-splenic ligamentSplenocolic ligamentPhrenicocolic ligamentPancreaticocolic ligament

Lateral colonic peritoneal fold

Anterior border of spleen

Gastrosplenic ligamentPeritoneal reflection at splenic hilum

POSTERIORCONNECTION

ANTERIORCONNECTION

SPLEENPERITONEALCONNECTIONS

Axial oblique computed tomography (CT) slice

A section through the spleen

white pulp (W)

trabeculae (T)

red pulp (R)

capsule (C)

Features of splenic structure

Transverse section through the spleen