Lymphoid System II Flashcards
MALT stands for…
Mucosa-Associated Lymphoid Tissue
Structureal organizatin of Lymphoid System
PIC
Major Lumphoid Tissues
(INCREASING COMPLEXITY)
- Circulating Lymphocytes
- Diffuse Lymphoid Tissues
- Solitary Nodules
- Aggregated Nodules (incompletely encapsulated)
- Specific Organs (encapsulated)
Aggregated Nodules
- Tonsils
- Peyers Patches
- Vermiform Appendix
Specific Organs
- Bone Marrow
- Thymus
- Lymph Nodes
- Spleen
Major Lymphoid Tissues: Circulating Lymphocytes
T Cells- 75%
B Cells- 10%
Natural Killer Cells- 15%
Major Lymphoid Tissues: Diffuse Lymphoid Tissues
(small intestine,GI Tract)
Key Points: Lamina Propria (LP) is connective tissue -Lymphocytes (mostly B) Secretes IgA -Eosinophils -Plasma Cells
*T Cells in the blood, B in connective tissue
IgA protexts mucoisal Epithelium infection
IgA (Secretory immunoglobulins) is secreted across surfaces such as…
- Gi tract- and transported across epithelium on the lumen of GI
- Respiratory tract
Function of IgA
- Produced by plasma cells
- Secretory piece.component (SC) added by epithelial cells, protects against lysosomal degradation, SC clipped at surface to release IgA dimer into lumen
Major Lymphoid Tissues: Solitary Nodules distinguishing factors
Nodules= same thing as Follicles
- Ring around it- mantle + Germinal center=Secondary Nodule (stains lighter)
- Primary Nodule= no activated germinal center
Major Lymphoid Tissues: Solitary Nodules
Gastrointestinal, respiratory tracts (mucosa and submucosa)
-Unencapsulated (lymph nodes- encapsulated)
1 Degree Nodule: Naive B cells
2 Degree Nodule:
-Cap or Mantle Naive B cells
-GerminalCenter
Activation of immune cells (B cells, T-Helper cell, Dendritic Cell)
Major Lymphoid Tissues: Aggregated Nodules- Tonsils
Surface- No connective tissue, just skin.
-Discontinuous ring of lymphatic tissue around oral cavity
Palatine Tonsils:
- Incompletely encapsulated
- Stratified squamous non-keratinized epithelium at the surface
Major Lymphoid Tissues: Aggregated Nodules- Peyers Patches
Occur in Ilium of GI tract (small intestine)
-Microfold cells transport antigen to macrophages for stimulation of B and T lymphocytes (immune response)
Major Lymphoid Tissues: Aggregated Nodules-Vermiform Appendix
Forms the termial narrowed tip of the cecum (MCBURNEYS POINT)
-uknown function
Major Lymphoid Tissues: Aggregated Nodules-Vermiform Appendix Lymphatic Tissue
In an older person, most of it is gone!
- amount of tissue as age goes on declines
- Gets replaced with adipose tissue
Major Lymphoid Tissues: Specific Organ- Bone Marrow (Central organ)
- Bone marrow is lined by endothelial cells
- PIC
Major Lymphoid Tissues: Thymus
- Where T Cells mature aka Thymocyte maturation
- Microframework of the thymus is formed by epithelial reticular cells
PIC
Major Lymphoid Tissues: Thymus Function
- Thymocyte Maturation
- Positive Selective forces
- Negative selective forces
- 95% of developing thymocytes are destroyed (NOT EFFICIENT)
- only 5% make it
Major Lymphoid Tissues: Blood Thymus Barrier
A blood thymus barrier prevents formed elements of the blood from redily contacting thymocytes in cortex of lobules– prevent an interaction which may cause immune response
Hassalls’ Corpuscle
Feature that allow us to identify thymus and not something else.
- derived from meddullary epithelial reticular cells
- Keratinized
- Secretes thymic epithelial cytokines
Histophysiology of the Thymus
PIC
Immunosinesence
As person gets older- components of immune ssytem occurs Immunosinesence
Seen in bone marrow: where red marrow is replaced with yellow marrow
Appendix:younger person has lymphocytes and older has fewer t cells
Thymus: mmuch of t cell component is replaced by adipose tissue
Major Lymphoid Tissues: Specific Organs-Lymph Nodes
Lympho nodes are a fiter of lymphatic vessels
-vessels drain connective tissue (uni directional) back to a large venous
-consenstrate in bundles in Axillary nodes, etc…
Bc these bumdles are pourus,
They are a route for tumor cells to circulate around body
-surgeons want to see NO spread cancer around nodes for longer/good prognosis
-Have >500 lymph nodes
Areas rich in nodes
- neck
- Mediastinum
- Retroperitonium
Function of Lymph Nodes
- Filter Lymph-fluid is drained from afferent to efferent lumphatic (PIC)
- Hold T and B cells
Postcapillary High Endothelial Venue (HEV) {Paracortex of Lymph Node}
-Lymphocytes make their way in through Lymph Nodes passing across HEV (PIC)
Spleen Function
- Filter blood
- Immune response to blood born Ag
- Platelet Storage
- Extra-medullary Hematopoiesis (referring to bone marrow- genetic memory of its 2nd trimester fetal life and if called upon it can reactivate and take over to undergo some hematopoeisis )
Spleen Structure
Red Pulp: Erithrocytes, no nuclei
White Pulp: abundant in ….
PIC
Blood circulation of Spleen
PIC
-Blood enters the central artery into the white pulp containing lymphocytes. Macrophages interact with pathogens and it may cause an immune response and may form a 2dary nodule
-around central artery theres a sheet of lymphocytes theres a periarterial
Major Lymphoid Tissues: Specific Organs-Lymph Nodes
Sinusoid (open circulation)- filtration slow 90%
Sinusoid (closed circulation)-filtration fast 10%
-When RBC pass sinusoid, they cas pass in/out of slits (PIC)
Splenic Sinusoids of Red Pulp
Blood cells flowing through the spleen must cross the sinusoidal wall to re-enter blood. Only healthy blood cells can survive this “right of passage” fully intact.
-If RBC are ,120 days old (flexible), they can squeeze back into lumen of sinousoid and exit thru veins BUT if old >120 days oR SICKLE CELL (inflexible) then macrophages are going to attack RBC and phagocytize them and destroy them.
