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:
- Lymph vessels: lymph capillaries, lymphatic vessels
and terminal lymphatic duct
- 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:
- Filter the lymph 2.Produce lymphocytes
3. Initiation of immune responses 4.phagocytosis
3. Histological
features of Lymph node:
- capsule is present
- sub-capsular sinus is present
- Outer cortex contains lymphatic
nodules. Superficial
part of cortex contain B lymphocytes and deeper zone of cortex contain T
lymphocyte
- 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
2.
Tonsillar
crypts: invagination of lining epithelium
