General anatomy of lymphatic system

 

Lymphatic system

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Cells of lymphatic system: lymphocyte is the principal cells of lymphatic tissue which are responsible for functioning immune system

Cells of lymphatic or immune system:

1. Different types of lymphocyte:

a)     T lymphocyte: i) helper T cells (this lymphocyte stimulate the development of other lymphocytes so it is known as master lymphocyte, in HIV this cell is destroy by HIV virus, so other cells of immune system became inactive) ii) cytotoxic T cells iii) suppressor T cell  iv) memory T cell  

b)     B lymphocyte         c) natural killer cells

2. Antigen presenting cells:

a)Macrophages  b) Kupffer cells of the liver c)Langerhan’s cells in the epidermis d) Dendritic cells of spleen and lymph nodes

 

Lymphocyte	Origin	Maturation and differentiation occur in	Final destination
T lymphocyte	Bone marrow	Thymus	Mid & deep zone of lymph node, in peri-arterial lymphatic sheath of spleen, mucosa associate lymphatic tissue
B lymphocyte	Bone marrow	Bone marrow	superficial zone of lymph node, around the peri-arterial lymphatic sheath of white pulp of spleen, mucosa associate lymphatic tissue

Components of lymphatic system:

1. Lymph vessels: lymph capillaries, lymphatic vessels and terminal lymphatic duct
2. Lymphatic organs: primary and secondary lymphatic organs

                             Brief description of components of lymphatic system

Lymph: tissue fluid when enters in the lymphatic system is known as lymph. They conveys macromolecules like

protein, duct, carbon, cancer cells, bacteria etc.

Lymph vessels	Collect lymph	Drain lymph into the	Number
Lymph capillary: they begin blindly in the tissue space around the blood capillaries	Lymph Capillary  collects lymph from tissue space	Afferent lymph vessels	Many
Lymph vessels
Afferent lymph vessels	Collect lymph from lymph capillary	Adjacent lymph node	Many & located around the capsule  of lymph node
Efferent lymph vessels	Collect lymph from lymph node	Drain lymph into terminal lymphatic ducts	One in number, exit lymph node through in hilum
Terminal lymphatic duct : two in number
i) right lymphatic duct	Collect lymph from right side of head and neck, right upper limb & chest	Drain lymph into the venous system at the junction between right  internal jugular vein and rt subclavian vein
ii) thoracic duct	Collect lymph from whole body except right side of head and neck, right upper limb & chest	Drain lymph into the venous system at the junction between left internal jugular vein and left subclavian vein

Primary lymphatic organ:  1. Bone marrow  2. Thymus

Why bone marrow and thymus is primary lymphatic organ?

Ans: In these organs, the cells of immune system became mature and differentiate so they are known as primary lymphatic organ. After maturation and differentiation an immune cells (lymphocyte) can distinguish between self antigen and non-self antigen. So a mature lymphocyte destroy non-self antigen but not react with self antigen.

Secondary lymphatic organ: 1. Lymph node 2.Spleen 3.Tonsils 4. Mucosa associated lymphatic tissue: BALT (bronchus associate lymphatic tissue), GULT(gut associate lymphatic tissue)  

What is the function of secondary lymphatic organs?

Ans : They only proliferate the cells of immune system ( lymphocytes)  but maturation and differentiation is not possible in secondary lymphatic organ 

Thymus:

1. Type of organ: lympho-epithelial organ 2. Location:  in the superior mediastinum.  3. Parts: It has two lobes

4. Cells of thymus:  i) Developing T lymphocytes (which come from bone marrow lymphoid stem cells) 

     ii) epithelioreticular cells

5. Development:

           i) Lymphocyte: mesodermal in origin

           ii) Epithelium primordium : developed from the endoderm of 3rd and 4th pharyngeal pouches.

 

6. Thymus function: Maturation and differentiation of T lymphocytes so they can distinguish between self antigen and non-self antigen.

7. Histological features of thymus :

a) Capsule is present which penetrate and divides the thymus into incomplete lobules.

b) Each lobulus is divided into outer cortex and inner medulla

c) Outer cortex of each lobulus contain large number of developing T lymphocytes but contain no lymphatic nodule

d) Medullary tissue contain Hassall’s corpuscles which are formed by epithelioreticular cells

 

8. Blood thymic barrier

• Lining endothelium of the capillary  wall
•  Basal lamina of endothelial cells
•  Macrophages in the surrounding  perivascular connective tissue
•  Basal lamina of epithelioreticular    cells
•  Epithelioreticular cells

Important of blood thymic barrier: Prevent entering of antigen into the thymic cortex

 

9. Two important negative points of Thymus:

    i) It contains no lymphatic nodules and  ii) No B lymphocytes

 

 10. Thymic or Hassall’s corpuscles

•         Are distinguishing feature of thymic medulla. It is formed by epithelioreticular cells

•         The epithelioreticular cells are concentrically arranged and cytoplasm of the cells contain keratohyalin granules, lipid droplet and intermediate filaments

Involution of the thymus:  After puberty much of the parenchyma of the thymus, in particular cortical lymphoid tissue, is replaced by adipose tissue.

Lymph node

 

Lymph nodes are small encapsulated organs located along the pathway of lymphatic vessels   

Diameter: 1mm to 2 cm

Two types of lymphatic vessels are connected with lymph node: they are - the afferent and efferent lymph vessels

Afferent lymph vessels: convey lymph toward the L. node and penetrate the capsule at multiple sites

Efferent lymph vessels: convey lymph away from the lymph node and leave at the hilum. It is one in number.

Functions of lymph node:

1. Filter the lymph 2.Produce lymphocytes 3. Initiation of immune responses 4.phagocytosis

3. Histological features of Lymph node:

1. capsule is present
2. sub-capsular sinus is present
3. Outer cortex contains lymphatic nodules. Superficial part of cortex contain B lymphocytes and deeper zone of cortex contain T lymphocyte
4. inner medulla  contain medullary cord which composed of B lymphocyte and plasma cells  

5. What is lymph?

Ans: Tissue fluid, when enters into the lymphatic system is known as lymph

Lymph contains macromolecules of proteins and large particles – dust, carbon, bacteria, cancer cells etc. 

What is trabeculea? Ans: they are the part of capsule which enter in to the organ

What do you mean by sinuses of lymph node? Ans: these are empty spaces within a lymph node where lymph flows.

6. Lymph circulation: lymph enters into lymph capillaries then through afferent lymphatic vessels enters into subscapsular sinus of lymph nodes then trabecular sinuses of lymph node then medullary sinuses of lymph node then through efferent lymph vessel the lymph leave the lymph node and drain into the venous system

7. Cells present within the lymph nodes: T & B lymphocyte, dendritic cells, macrophages

 8. What is lymphatic nodule?

Ans: small collection of lymphocytes found in mucosa of different organs like ileum, appendix, bronchus etc.

Types of lymphatic nodule: primary and secondary lymphatic nodules

When a germinal center appears in a lymphatic nodule the lymphatic nodule known as secondary L nodule

9. What is germinal center: it is the site of lymphocyte production mainly B lymphocyte. It is a pale

Staining area situated within a lymphatic nodule contain immature lymphoblast. It is found in secondary lymphatic nodule.

Spleen: It is the largest accumulation of lymphoid tissue in the body.

Function: i) Removal of old red blood cells ii) Immune response iii) Reservoir of blood

iv) Formation of erythrocyte in fetal life

Histological features of spleen:

Capsule: a dense irregular connective tissue which is covered the spleen

Trabeculae: emerges from the capsule which divides the splenic pulp into incomplete compartments

Splenic pulp: functionally and morphologically it is divided into two compartments -white pulp & red pulp

White pulp: It is composed of periarterial lymphatic sheaths and lymphatic nodules with germinal centers.

Both periarterial lymphatic sheaths ( housing T –lymphocyte) & lymphatic nodules ( housing B- lymphocyte) surround the eccentrically located central artery, a distinguishing characteristic of the spleen.

Red pulp:It is formed by splenic cord and splenic sinusoid

Splenic cord contains T & B Lymphocytes,Reticular cells & fibers,Macrophages, Plasma cells,Many blood cells-Erythrocytes,Platelets, Granulocytes

Splenic sinusoids: is formed by Discontinuous endothelial cells & Incomplete basal lamina

Closed circulation:

Splenic artery →the trabecular artery →central artery →penicillar arteries→ terminal  arterial capillaries (TAC) →splenic sinusoids →splenic vein

Open circulation:

Splenic artery →the trabecular artery →central artery →penicillar arteries→terminal  arterial capillaries (TAC) →red pulp →splenic sinusoids →splenic vein

Cells of lymphatic system:

  (The principal cell of the lymphatic system is lymphocyte. They are two categories   T and B lymphocytes)

1.      T lymphocyte : helper T cell , cytotoxic T lymphocyte, suppressor T lymphocyte, memory cell

2.     B lymphocytes

3.     Natural killer cells

4.    Macrophages

5.      Dendritic cells of spleen and lymph nodes macrophages,

6.      Plasma cells

7.      Reticular cells & antigen presenting cells

Antigen presenting cells

•         Macrophages

•         Kupffer cells of the liver

•         Langerhan’s cells in the epidermis

•         Dendritic cells of spleen and lymph nodes

B lymphocytes

Tonsils 

 1.      Lining epithelium : non-keratinized stratified squamous epithelium

2.     Tonsillar crypts: invagination of lining epithelium

Lymphatic nodules with germinal centre