Lymphatic SystemAamir Rauf Memon

6th Semester DPT

The lymphatic system comprises of a network of conduits called lymphatic vessels that carry a clear fluid called Lymph unidirectionally toward the heart.

It was first described by Olaus Rudbeck and Thomas Bartholin.

It includes all the structures dedicated to the circulation and production of lymphocytes i.e. spleen, thymus, bone marrow and the lymphoid tissue associated with the digestive system.

Lymphatic System

The lymphatic system has multiple interrelated functions:

1. Responsible for the removal of interstitial fluid from tissues.

2. Absorbs and transports fatty acids and fats as chyle from the digestive system.

3. Transports WBCs to and from the lymph nodes.4. The lymph transports antigen-presenting

cells (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated.

Functions of Lymphatic System

The study of lymphatic drainage of various organs is important in diagnosis, prognosis, and treatment of cancer.

The lymphatic system → responsible for carrying cancerous cells b/w various body parts in a process called metastasis.

The intervening lymph nodes can trap the cancer cells →if not successful in destroying the cancer cells → become sites of secondary tumors.

Clinical significance

Divisions of the lymphatic system:1. the conducting system and 2. the lymphoid tissue.

The conducting system carries the lymphconsists of tubular vessels i.e. the lymph

capillaries, the lymph vessels, and the right and left thoracic ducts.

The lymphoid tissue primarily involved in immune responses consists of lymphocytes and other  white blood cells  

Organization

1. Lymphedema is the swelling caused by the accumulation of lymph fluid, 

Cause→lymphatic system damage or malformations.

It usually affects the limbs, though face, neck and

abdomen may also be affected.

◦ Some common causes of swollen lymph nodes include:infections, infectious mononucleosis, and cancer→ Hodgkin's & non-Hodgkin lymphoma metastasis of cancerous cells via the lymphatic

system.

Diseases of the lymphatic system

1. Lymphangiomatosis is a disease involving multiple cysts or lesions formed from lymphatic vessels.

2. Elephantiasis, infection of the lymphatic vessels cause a thickening of the skin and enlargement of underlying tissues, especially in the legs and genitals. It is most commonly caused by a parasitic disease known

as lymphatic fi lariasis . 

3. Lymphangiosarcoma is a malignant soft tissue tumor.

4. Lymphangioma is a benign tumor occurring frequently in association with Turner syndrome.

5. Lymphangioleiomyomatosis is a benign tumor of the smooth muscles of the lymphatics that occurs in the lungs.

Diseases of the lymphatic system…

The spleen  has important roles in regard to RBCs  and the immune system. 

Functions:1. It removes old red blood cells and holds a reserve of blood in

 hemorrhagic shock while also recycling iron.

2. As a part of the mononuclear phagocyte system → metabolizes hemoglobin removed from  erythrocytes. 

3. It is one of the centers of activity of the reticuloendothelial system → analogous to a large lymph node → absence leads to a predisposition toward certain infections.

Red Pulp involved in the filtration of RBCsWhite Pulp involved in active immunity via hormonal & cell-

mediated pathways (antibodies) Composed of  Malpighian corpuscles :

o "lymphoid follicles" → B-lymphocyteso "periarteriolar lymphoid sheaths" (PALS) → T-lymphocytes

Spleen

It is secondarily involved in wide variety of systemic diseases & its response causes its enlargement (Splenomegaly).

The disorders are classified on the basis of the degree of the Splenomegaly characteristically produced & is given in the next slides:

Disorders of Spleen

1. Chronic myeloproliferative disorders:1. Chronic myeloid leukemia 2. Myeloid metaplasia with myofibrosis

2. Chronic lymphocytic leukemia3. Hairy cell leukemia

4. Lymphomas

5. Malaria

6. Gausher disease

7. Primary tumors of spleen(Rare)

1. Massive Splenomegaly (weight → 1kg)

1. Chronic Congestive Splenomegaly 1. Portal HTN or 2. Splenic Vein obstruction

2. Acute Leukemias (inconsistent)3. Hereditary Spherocytes4. Thalassemia major5. Autoimmune hemolytic anemia6. Amyloidosis7. Neimann-Pick disease8. Langerhans histiocytes9. Chronic splenitis10.Tuberculosis, Sarcoidosis,Typhoid11.Metastatic carcinoma or sarcoma

2. Moderate Splenomegaly (weight → 0.5-1 kg)

1. Acute splenitis

2. Acute splenic congestion

3. Infectious mononucleosis (EBV induced)

4. Miscellaneous Acute Febrile disorders Septicemia SLE Intra-abdominal infections

3. Mild Splenomegaly (weight → < 0.5 kg)

Hypersplenism → a state associated with many diseases affecting spleen

Characteristics → removal of excessive numbers of one or more of the formed elements (blood) resulting into → Anemia, Leukemia, or Thrombocytopenia.

Thrombocytopenia is more prevalent & severe.

The thymus is a central lymphoid organ of the immune system.

Functions

1. T cells that attack the body's own proteins are eliminated in the thymus through programmed cell death (apoptosis).

2. Provides an inductive environment for development of T-lymphocytes from hematopoietic progenitor cells(T-cell differentiation ). 

Thymus

Normal Thymus

Thymus is involved in Lymphomas (particularly those of T-cell lineage).

The most frequent thymic disorders are:1. Thymic hyperplasia2. Thymoma

Disorders of Thymus

Associated with the appearance of Lymphoid follicles/germinal centers(containing reactive B-cells) within the medulla.

Thymic follicular hyperplasia is present in those with Myasthenia gravis, SLE, RA.

Hyperplastic thymus removal is often beneficial early in the disease.

1. Thymic hyperplasia

Tumors in which the epithelial cells constitute the neoplastic elements.

Characteristics → Presence of abundant precursor T-cells(thyrocytes).

2. Thymoma

1. Benign or Encapsulated thymoma which is cytologically & biologically benign.

2. Malignant thymoma

Type-I:cytologically benign but biologically aggressive & capable

of local invasion.

Type-II (Thymic Carcinoma): cytologically malignant with all of the features of cancer &

comparable behavior.

Simple & clinically useful classification of Thymoma

Benign or Encapsulated_thymoma

Malignant more than the benign

Occur at any age but typically in Middle adult life

30% Asymptomatic

15-20 % with Myasthenia gravis have a thymoma Tumor removal often leads to the improvement in Neuromuscular

disorder

30-40% produce Local manifestations Mass demonstrable on CT Scan in the Anterosuperior mediastenum

associated with Cough, Dyspnea, & Superior Vana Caval Syndrome. The remainder were associated with some systemic disease

(Myasthenia gravis).

Associations with thymoma are:◦ Hypogammaglobulinemia, SLE, Pure red cell aplasia, & nonthymic cancers

Clinical Features

CT scan of the chest revealing a large necrotic mass in the left anterior mediastinum (indicated by the red line).

Usually fleshy, obviously invasive masses sometimes accompanied by metastases to sites as the lungs.

Most resmeble poorly/well-differentiated SCCs.

Next most common malignant pattern → Lymphoepithelium-like carcinoma

Composed of anaplastic cortical-type epithelial cells mixed with large numbers of benign lymphocytes.

Most common in Asian populations Sometimes contain EBV genome(member of Herpes virus

family) →B-cell polyclonal activation & proliferation

Gross appearance

Locally invasive circumscribed thymoma (Malignant Type-I)

Thymomas → lobulated, firm, gray white masses, 15-20cm longest in dimension

Most appear Encapsulated

20-25% with apparent penetration of the capsule & infiltration of perithymic tissues & structures

All thymomas made up of a mixture of epithelial cells & a variable infiltrate of non-neoplastic thymocyte

Microscopic appearance

Mediastenum Thymoma Type A Spindle Cell 6

Benign thymomas (medullary thymomas): spindled or elongated epithelial cells resemble those

that normally populate the medulla

Mixed thymomaan admixture of the plumper, rounded, cortical-type

epithelial cellsMedullary & Mixed patterns → 60-70% of all

thymomas.

Malignant thymoma type-II (Thymic Carcinoma)

Cytologically malignant accounting for 5% thymomas

Malignant thymoma type-I Cytologically bland but locally invasive tumor(Ocassionally

metastasize)

20-25% of all thymomas

Critical distinguishing feature → penetration of the capsule & the invasion of sorrounding structures

Neoplastic epithelial cells often from palisades around blood vessels → spindled epithelial cells present sometimes

Composed of varying proportions of the Epithelial cells & Reactive thymocytes

Epithelial cells resemble those found in the Cortex & are with abundant cytoplasm & rounded Vesicular nuclei.

The End……!!