FUNCTIONS
-immune surveillance and defense against foreign substances
-Provides immune tolerance, distinguishing between “self” and “non-self”.
- Absorbs lipids into small lymphoid vessels (lacteals) in the intestinal villi for distribution of fatty lymph to the blood stream and liver.
* Maintains fluid balance by accumulating tissue fluid and white blood cells in lymph vessels and returning them to the blood.
PRIMARY LYMPHOID ORGANS
- SECONDARY LYMPHOID ORGANS
- PRIMARY LYMPHOID ORGANS- convert stem cells to the mature cells
- Bone marrow – lymphocyte stem cells
* T and B- lymphocytes originate; B- cells mature and go to secondary lymphoid organs ; T- cells move into the thymus. - Thymus - site of T-cell maturation.
- SECONDARY LYMPHOID ORGANS- activation and proliferation
- Tonsils – Lymphoid tissue with germinal centers that can produce lymphoid cells.
- Spleen – site where T & B lymphocytes interact with bloodborne antigens stimulation and cell division. cleanses the blood
Lymph nodes
Diffuse lymphoid tissues
– junction of major lymphatic vessels; sites where both T&B lymphocytes interact with blood-borne antigens – stimulation and & cell division.
- Diffuse lymphoid tissues
- MALTs – Mucosa associated
lymphocytic tissues. - GALTs – Gastrointestinal associated lymphocytic tissues
- BALTs – Bronchial associated
lymphocytic tissues.
MAJOR LYMPHOID CELLS TYPES:
- B-lymphocytes APC – differentiate into memory B cells and plasma
cells. - T-lymphocytes – differentiate into helper, memory, cytotoxic cells.
- Plasma cells - mount an immune response.
- Macrophages APC – phagocytose foreign matter.
- Dendritic cells APC – involved in initiation of immune response.
HIGH ENDOTHELIAL VENULES (HEVs):
- Location: Appendix, tonsils, Peyer’s patches and lymph nodes.
- Endothelium morphology: Simple cuboidal.
- transport of lymphocytes through the endothelium of the HEVs,
PARENCHYMA:
- STROMA:
- PARENCHYMA:
- The cells and tissues of an organ that perform the function of the organ.
- STROMA:
- The supporting framework of an organ, made of connective tissue.
- Free cells (mainly lymphocytes)
- Reticular cells – produce reticulin fibers
- Reticulin fibers –allows fluid (lymph) to pass through; also the CT support for the cells making up the parenchyma of the tissue.
what is LYMPH
- Lymph
- Clear, watery fluid in the lymphatic vessels.
- Interstitial fluid (IF)
- Fills the spaces between the cells.
Lymph vessel
Originate as lymphatic capillaries in the tissue.
* Carry lymphatic fluid to and from the lymph nodes, and towards the heart.
Accumulate tissue fluid, called lymph.
* Thin-walled vessels lined with endothelium
* Highly permeable
* Valves are present to ensure that the lymph will only flow one way – back to the bloodstream.
- Two main lymphatic trunks the empty into the subclavian vein
- Right lymphatic ducts
- Thoracic ducts
LYMPHATIC VESSEL AND VEIN
- Lymphatic and blood networks are close, but independent of each other
- Lymphatic vessels pickup fluid.
- The vein will have red blood cells in it
- Lymphatic vessels have more valves and lack pericytes.
LYMPHATIC PUMP
- Rate of flow 3L/day. travel at a slower speed
- Mechanisms that establish the pressure gradient for fluid flow:
- Breathing movements
- Skeletal muscle contractions.
CIRCULATION OF LYMPH
- Fluid exchange between capillaries and lymphatic vessels.
- Lymphatic vessels contain lymph nodes located at intervals
- Returns to venous circulation by way of subclavian veins.
THYMUS
- Flat, lymphoid organ in middle of upper chest up to neck
- composed of T-cells, reticular cells and some macrophages
- Produce hormones, thymosin that promotes maturation of T-lymphocytes.
- bigger when younger as you get older it is replaced by adipose.
- Presence of capsule
- Morphology: DICT
- Lobulated with CT septae
- Outer thymic cortex (C) basophilic:
- Nurse cells – support T-cell maturation (eosinophilic)
- Thymocytes, T-cells.
Inner thymic medulla (M) eosinophilic:
* Hassal’s corpuscles are keratinized dead epithelial cells migrating inwards from cortex.
* Self reactive T-cells are removed from here.
when youre young your thymus has * Lobules, cortex and medulla, septae
when you get old
* Fatty infiltration
* Lymphocyte depletion
LYMPH NODE
- Spherical or kidney-shaped lymphoid organ
- Aggregates along the lymphatic vessels.
- Location: Axilla, groin, neck, lung, hila, paraaortic area
- Main function: makes up a series of in-line filters
- Stimulate an immune response to antigens in the lymph.
- Defense against microorganisms.
- Prevent spread of tumour cells.
- STROMAL COMPARTMENT:
- Packed with lymphocytes and antigen presenting cells
(APCs). - LYMPHATIC OR SINUS COMPARTMENT:
- Act as a sieve/filter for antigens.
- VASCULAR COMPARTMENT:
- Sinusoids and blood vessels present.
- Delivers nutrients and lymphocytes to the nodes.
contains
* Capsule
* Cortex
* Medulla
* Hilum
* Afferent and efferent lymphatic vessels.
what is the path of the lymph flow through a lymph node
Afferent lymph carry lymph to peripheral tissues and penetrate lymph capsule
-Lymph sent to subcapsular space. Dendritic cells initiate immune system
-lymph flows to outer cortex that has B cells
-lymph flows through lymph sinus in deep cortex with T cells
-then to medullary sinus in lymph core with B cells and plasma cells
-efferent lymph leave the lymph at the hilum into venous circulation
what does the microanatomy of the lymph node look like
- has lymphocytes and reticulin CT.
- Follicles with germinal centers in the cortex.
- Capsule: Morphology: DICT
- Trabeculae:
- CT from the capsule extending into parenchyma.
- Afferent lymphatics.
- Subcapsular space.
- Hilum: Efferent lymphatics to the
lymphatic ducts. - the indentation of the node
what is the microanatomy of the lymph node cortex like
- Cortical sinuses: Where lymph will pass through towards the medulla.
- Cortical cords: B & T lymphocytes, macrophages and dendritic cells.
- Lymphoid follicles in outer
cortex with germinal centre
and mantle zone. - Paracortex (inner) : Only T-lymphocytes. No follicles.
what is the microanatomy of the Follicles in the cortex like
consists of the
Mantle zone
* Dark zone.
* Resting B- cells, helper T-cells, follicular dendritic cells, macrophages.
Germinal center
* Pale zone.
* Rich in plasma cells have more cytoplasm staining pink.
* Site of B-lymphocyte proliferation
* Active B-cells –turn plasma into AB
- T-lymphocytes in the periphery of the follicle and in areas between the follicles
what is the microanatomy of the medulla like
- Continuous with the cortex.
- Composed of medullary cords separated by medullary sinuses.
- Medullary cords
- Contains T-lymphocytes and
majority plasma cells.
what the lymph travels through
SPLEEN
*Largest lymphoid organ in the body; encapsulated.
* left upper part of the abdomen.
* part of the hepatic portal system Receives blood from the splenic artery and drains blood into the splenic vein back into the hepatic portal system which carried blood from the spleen and GIT
*(An antibody-forming organ).
* Site of destruction of aged rbcs and defective platelets.
* mononuclear phagocytic cells in red pulp, lymphoid cells in white pulp and platelets.
* Recycling iron in the bone marrow.
SPLEEN MICROANATOMY- can use a silver stain to identify the reticulin fibers in black and collagen in brown
- Capsule
- DICT
- invaginates as trabeculae in the spleen parenchyma.
- smooth muscles present.
White pulp
* contains lymphoid nodules.
* Basophilic darker staining.
* centriole arteriole with B & T lymphocytes around (peri-arteriole lymphoid sheath – PALS).
Red pulp/red matrix
*Highly vascular
* Forms the parenchyma; supported by reticulin CT.
* Composed of elongated structures called splenic cords (or Billroth’s cords) that are found between the splenic sinuses (sinusoids)
* Endothelium lines the surface of the sinusoids
* Sinuses drain in to the hepatic portal vein
-b lymp, t lymph, macrophage
TONSILS
- Solid organ - non encapsulated.
*Luminal surface epithelium SSNK.
*surface epithelial invaginates to form a blind-ended crypt. - Base has a hemi-capsule.
- Follicles in the parenchyma
* Germinal center- -lighter .
* Mantle zones.
MALT IN THE MUCOSA
DIFFUSE LYMPHOID TISSUES
Mucosa-associated lymphoid tissue
* Mucosal membrane (mucosa)
* lining cavities and organs - covering the surface of internal organs.
* Aggregations of lymphatic tissues found in many mucosal areas of the body.
* Consists of B and T lymphocytes, macrophages, plasma cells
BALT IN THE BRONCHUS
DIFFUSE LYMPHOID TISSUES
Bronchial-associated lymphoid tissue.
* Aggregate of lymphocytes and other immune response cells in submucosa of a bronchus.
* The intact surface epithelium is first line of defense.
* Cells of immune/ inflammatory response form second line of defense beneath the epithelium.
PEYER’s PATCHES IN THE ILEUM
MALT in the gastrointestinal tract is called GALT
- Collection of lymphoid tissue in the mucosa of the ileum (small intestine).
- Largest GALT
- Reactive follicles with germinal centres
- Proliferating B-cells.
- T-cells in between the follicles.
