Download - Lymphoid organs
IMMUNE SYSTEM
AND
LYMPHOID ORGANS
IMMUNE SYSTEM
Has the ability to distinguish “self” (body’s own molecules) from “non-self”
(foreign substance)
This system has the ability to neutralize or inactivate foreign molecules
(virus, bacteria & parasites) and to destroy microorganisms or other cells
(e.g. virus infested cells, cancer cell, cells of transplanted organs)
Continued
The cells of the immune system are:
a) distributed throughout the body in blood, lymph, epithelial &
connective tissue
b) are arranged in small spherical nodules called ‘lymphoid
nodules’ which are isolated cells of immune system found in the
mucosa of GIT, respiratory system, reproductive & urinary system
c) are organized in larger lymphoid organs- lymph nodes, spleen,
thymus, bone marrow
ANTIGENS
A molecule recognized by the body as ‘foreign’ and is capable of eliciting a
response is called an ANTIGEN.
Antigen may consist of proteins, polysaccharides & nucleoproteins
It may be bacteria, protozoa, tumor cells or virus infested cells
ANTIBODIES
Are “glycoproteins” that interacts specifically with an antigen to destroy or
inactivate it.
B lymphocytes produce plasma cells which then produce antibodies
The antibodies:
a) may circulate in the plasma and reach tissues
b) present in secretions of glands i.e. salivary and mammary gland
c) integral membrane proteins of the surface of lymphocytes
CLASSES OF ANTIBODIES
Ig G 75-80%. Is only immunoglobulin to cross the placental barrier.
Ig A is found in secretions i.e. nasal, bronchial, intestinal, prostatic &
colostrum, saliva, vaginal fluid
Ig M 10%. Found on surface of B lymphocytes functions as its specific
receptor for antigen.
Ig E. Present on surface of mast cells & basophils
Ig D. Its functions not completely understood. Found on cell membrane
of lymphocytes
CELLS OF IMMUNE SYSTEM
Lymphocytes
Plasma cells
Mast cells
Neutrophils
Eosinophils
Cell of mononuclear phagocyte system
LYMPHOCYTES
T lymphocytes
B lymphocytes
NATURAL KILLER lymphocytes
PRECURSORS OF ALL LYMPHOCYTES TYPES ORIGINATE IN THE BONE MARROW
B LYMPHOCYTES
mature & become functional in the in the bone marrow
leave bone marrow & enter circulation
colonize C.T. epithelia, lymphoid nodule, lymphoid organ
After encountering an antigen, they redifferentiate into PLASMA CELLS
Activation of B lymphocytes require assistance of T helper cells
Some lymphocyte differentiate into B memory cells
T LYMPHOCYTES
leave bone marrow & enter circulation
reach thymus & undergo intense proliferation & differentiation / die
after maturation leave thymus
distributed in C.T. & lymphoid organs
constitute 65-70% of blood lymphocytes
SUBPOPULATIONS OF T LYMPHOCYTES:
- Helper T lymphocytes
- Cytotoxic T lymphocytes
- Regulatory T lymphocytes
PRIMARY /CENTRAL LYPHOID ORGANS:
- bone marrow
- thymus
SECONDARY / PERIPHERAL LYPHOID ORGANS:
- spleen
- lymph nodes
- solitary lymphoid nodules
- tonsils
- appendix
- peyer’s pathces of ileum
TYPES OF IMMUNE RESPONSES
INNATE RESPONSE
ADAPTIVE RESPONSE
INNATE RESPONSE
Include the action of complement system & cells such as neutrophils,
macrophages, mast cells & natural killer cells
Is fast
Is non- specific
Does not produce memory cells
ADAPTIVE RESPONSE
Depends on initial recognition of antigen by B & T lymphocytes
Is more complex
Is slower
Is specific
Produces memory cells
LEADS TO ELIMINATION OF ANTIGENS
HUMORAL RESPONSE
CELLLULAR RESPONSE
HUMORAL IMMUNITY:
- accomplished by antibodies produced by plasma cells
CELLULAR IMMUNITY:
- mediated by T lymphocytes
LYMPHOID TISSUE
is C.T. charecterized by rich supply of lymphocytes
lymphocytes are lying within rich network of reticular fibres (type III
collagen produced by reticular cells)
in thymus reticulum is formed by epithelial reticular cells
NODULAR LYMPHOID TISSUE
Groups of lymphocytes are arranged as spherical masses called
LYMPHOID NODULES
Lymphoid nodules contain B LYMPHOCYTES
Antigen arrives →B lymphocytes recognizes antigen → nodule becomes
activated →B lymphocytes proliferate in centre of nodule→ it stains lighter
& is called GERMINAL CENTRE
Lymphoid nodules are found in many C.T. and within lymph nodes, spleen
& tonsils. NOT IN THYMUS
THYMUS
bilobed organ
is central or primary lymphoid organ
dual embryological origin
surrounded by connective tissue capsule that sends septae into the
parenchyma and divides it into lobules
capsule consists of collagen &
elastic fibres, blood vessels
intra-lobular trabeculae
reticular frame work
each lobule has a cortex &
medulla
cortex richer in small
lymphocytes, stains darkly
medulla lighter staining
thymic cortex contains t
lymphocytes,
macrophages, epithelial
reticular cells
epithelial reticular cells are
stellate or squamous with long
processes
have large nucle
long procecesses form
cytoreticulum
thymic medulla also
contains cytoreticulum of
epthelial reticular cells
less densly packed T
lymphocytes
has structures called thymic
(Hassall’s) corpuscles
Hassall’s corpuscles
consists of epithelial
reticular cells arranged
concentrically
they are a charecteristic
feature of medulla
T LYMPHOCYTES PROLIFERATE & MATURE IN CORTEX. ONLY 2-3% MIGRATE TO MEDULLA WHERE THE ENTER THROUGH THE WALL OF VENULES INTO THE CIRCULATION. REST DIE
BLOOD THYMIC BARRIER
arterioles & capillaries in thymic cortex are sheathed by epithelial reticular
cells with tight junctions
capillary endothelium is continuous
basal lamina is thick
these features create a blood thymic barrier
it prevents most of circulating antigens from leaving the blood vessels and
entering the cortex
NO such barrier exists in the MEDULLA
THYMUS HAS NO AFFERENT LYMPHATIC VESSELS
THYMUS OF ELDERLY
TONSILS
are organs composed of aggrates of lymphoid tissue which is incompletely
encapsulated. they lie beneath & in contact with the epithelium of the initial
part of digestive tract
Types:
palatine
pharyngeal
lingual
tubal
PALATINE TONSILS
location
epithelium is stratified
squamous
epithelium rests on basal
lamina
thin fibrous connective tissue
layer deep to epithelium
epithelium in crypts intensly
infiltrated with lymphocytes
10-20 tonsillar crypts
lining of crypt same as
surface
secondary crypts
diffuse mass of lymphoid
tissue surround crypts
lymph nodules are embedded
in them
nodules may contain germinal
centres
CAPSULE
incomplete
Made of
dense C.T.
LINGUAL TONSIL:
covered by stratified squamous epithlium
- has single crypt
PHARYNGEAL TONSIL:
- lined by pseudostratified columnar ciliated epithelium
- no crypts
TUBAL TONSIL:
- ciliated columnar epithelium
LYMPH NODE
Are encapsulated kidney shaped
organs
Lye along the course of blood
vessels
Are inline filters
Have a convex side where
afferent vessels enter
and concave side (hilus) where
efferent vessels leave
Capsule sends in trabeculae
Framework is made of reticular
fibers and macrophages
Parenchyma divided into:
Outer cortex
Inner cortex
Medulla
Outer cortex
Subcapsular sinus formed by
macrophages, reticular cells &
fibres
Communicates with medullary sinus
through intermediate sinus
Outer cortex made of reticular fibres
Populated with B lymphocytes
Lymph nodules with germinal
center present
CORTEX
Inner cortex:
Contains few if any nodules
Many T lymphocytes
MEDULLA OF LYMPH NODE
Medullary cords
Branched extensions of inner
cortex
Contain B lymphocytes
Medullary sinuses
Are dilated, irregular spaces
containing lymph
Lined by reticular cells &
macrophages that form network
Afferent lymph vessels pour
lymph into subcapsular sinus
Lymph pass through intermediate
sinus into medulla
Subcapsular sinus slows flow of
lymph through node
Lymph collected by efferent
lymphatic vessels
As lymph flows through sinuses
99% or more antigens are
removed
SPLEEN
FUNCTIONS:
Filtration of blood
Destruction of aged RBC
Produces antibodies & activated lymphocytes
SPLEEN
Location
Surrounded by capsule
Trabeculae
Incomplete division of parenchyma or splenic pulp
Hilum
SPLEEN
Splenic pulp divided into:
White pulp
Red pulp
WHITE PULP
Lymphoid nodules
Periarteriolar lymphatic
sheath
RED PULP
Sinusoids
Splenic cords
WHITE PULP
Splenic artery divide to
trabecular artery
Enter parenchyma
Enveloped by sheath of T
lymphocytes (PALS)
Called ‘central arterioles’
PALS receive B lymphocytes &
form nodules
Penicillar arterioles
RED PULP
Splenic cords composed of
reticular fibres, T & B
lymphocytes, macrophages etc
They are seperated by irregular
shaped sinusoids
Sinusoid lined by elongated
endothelium called ‘stave cells’
Incomplete basal lamina
BLOOD FLOW IN RED PULP
CLOSED CIRCULATION:
Pencilar arterioles connect
directly to sinusoids
OPEN CIRCULATION:
Pencillar arterioles dump
blood into stroma
ESOPHAGUS
Is muscular tube
Extent
Wall has four layers:
Mucosa
Epithelium
Basement membrane
Lamina propria
Muscularis interna or muscularis mucosae
Submucosa
Muscularis externa
serosa
UPPER 1/3 OF ESOPHAGUS
MUCOSA Epumithelium: Stratified
squamous non-keratinized Lamina propria: scattered
lymphocytes, few lymphatic nodules, mucous glands, blood vessels
Muscularis mucosae: thick, striated muscles
SUB-MUCOSA Collagen & elastic fibres, mucous
glands, blood vessels, nerves
MUSCULARIS EXTERNA Skeletal /striated muscles
ADVENTITIA Collagen & elastic fibers, blood
vessels
MIDDLE 1/3 OF ESOPHAGUS
MUCOSA Epithelium: stratified squamous non-
keratinized Lamina prppria: : scattered lymphocytes,
few lymphatic nodules, mucous glands, blood vessels
Muscularis mucosae: thick, striated muscles
SUB-MUCOSA Collagen & elastic fibres, mucous glands,
blood vessels, nerves
MUSCULARIS EXTERNA Skeletal striated muscles, smooth muscles
ADVENTITIA Collagen & elastic fibers, blood & lymphatic
vessels
LOWER 1/3 OF ESOPHAGUS
MUCOSA Epithelium: Simple columnar
Lamina prppria: : scattered lymphocytes, few lymphatic nodules, mucous glands, blood vessels
Muscularis mucosae: thick, striated muscles
SUB-MUCOSA Collagen & elastic fibres, mucous glands,
blood vessels, nerves
MUSCULARIS EXTERNA smooth muscles
ADVENTITIA/ SEROSA Collagen & elastic fibers, blood & lymphatic
vessels
TRACHEA
Rigid tube
Extent
Patency maintained by C shaped cartilagenous rings
Between rings is fibroconnective tissue
MUCOSA
Epithelium: pseudo-stratified columnar ciliated with goblet cells
OTHER CELLS: Columnar non-ciliated cells Immature cells Basal cells Neuroendocrine (APUD)
Lamina propria: Collagen fibres, elastic fibres, lymphatic
nodules, mucous, serous glands
Muscularis mucosae: Smooth muscles
SUB-MUCOSA
Loose connective tissue Serous & musous glands Blood & lymph capillaries
CARTILAGE
Hyline cartilage covered with perichondrium
Trachealis (smooth) muscle
ADVENTITIA: Loose connective tissue Blood & lymph vessels