Lymphoid Tissue Histology II (Capsulated) Flashcards
Capsulated Lymphoid Tissue: with Lobules
Thymus
-Thymus:
- Produce only T-lymphocytes
- Decreases in size with age
- Largely replaced by fat and connective tissue
- Continues to make T-lymphocytes in adults
Big player in pre-puberty.
Structure: 2 lobes
- Has a connective tissue capsule
- Capsule associated w/ connective tissue septa that penetrate to the medulla
- Septa divide the Thymus into incomplete lobules
- The lobules possess a dark outer cortex(“bark/rind”-outside) and a light inner medulla (inside)
- Medulla contains “Hassal’s” Corpuscles
- No lymphoid nodules
- No germinal centers
Describe the Thymus cortex and cells
Thymus Cortex: dark
-Site of T-lymphocyte maturation
Cells:
- Subcapsular Thymic Epithelial Cells (line the space)
- Thymic Cortical Epithelial cells
- Maturing T-cells (developing Thymocytes)
(Macrophages present in both Cortex and Medulla)
Describe the Thymus Medulla
Thymus Medulla: lighter
-Site of mature lymphocytes
Cells:
- Hassal’s Corpuscles (easy to identify)
- Thymic Medullary Epithelial cells
- Dendritic Cells
Hassal’s (thymic) Corpuscles: (thymus)
- Only present in the Medulla
- Closely packed Epithelial cells
- Release a factor that stimulates Thymic Dendritic cells to complete maturation of T-cells
Describe the Thymus-Blood Barrier:
Thymus-Blood Barrier:
-Only exists in the Cortex (we can’t have blood mixing with maturing lymphocytes b/c antigens in blood will mess it up)
- Prevents most circulating antigens from reaching developing T-cells
- Epithelial-Reticular Cells bound to the capillaries
Capsulated Lymphoid Tissue: with No lobules
Spleen
Spleen:
-Left superior Quadrant
- Macrophages present destroyed old RBC’s
- Spleen traps antigens
- Reservoir for 1/3 of platelets
- Hematopoiesis takes place here as well (making blood stuff)
Organization of the Spleen (capsulated lymphoid tissue)
- Surrounded by a connective tissue capsule (collagen, elastic fibers, smooth muscle)
- Trabeculae extend from the capsule and divide the spleen into incomplete compartments
- No Cortex/Medulla
- Parenchyma is made up of reticular fibers supporting the two main components of the Spleen: the red and white pulp (both pink- red is more pink, white is more purple)
- White pulp: rich in lymphoid tissue
- Red pulp: rich in red blood cells
Organization of white pulp in spleen
- Germinal center
- Corona
- Central artery
- Periarteriolar lymphoid sheaths
White pulp:
- Germinal Center
- Corona (B cells and antigen presenting cells)
- Marginal zone (where red and white pulp interact)
- Periarteriolar lymphoid sheath (comprised of T cells)
- Central Arteriole
-If you cut through the spleen, the white pulp is like a ball and you might not go through the germinal center
Organization of the red pulp in spleen
Red pulp:
- Splenic cord formed by reticular cells (solid)
- Splenic sinusoid (space around cords-blood is in the space) (gaps w/ space in-between)
- Pennicillar arteries
- Macrophage sheathed capillaries
- Circulating blood cells
Blood supply to the spleen
- Splenic artery from the celiac trunk
- Splenic artery divides into trabecular arteries which follow the trabeculae into parenchyma of the Spleen
- Trabecular arteries divide into Central arteries which penetrate the White Pulp and are surrounded by Periarteriolar Lymphoid Sheaths
- Central arteries produce Raidal arteries (radiate outward) while in the White Pulp that feed into the Marginal Zone sinuses
- Central arteries leave the White Pulp and enter the Red Pulp as Penicillar arteries, which either end in the Splenic Sinusoids (fills w/ blood-closed circulation) or into the Red Pulp (open circulation)
- Penicillar arteries and the small capillaries that they produce are sheathed by Macrophages, that are responsible for removing damaged RBC’s and particles from the blood
Summary: splenic arteries splits into trabecular arteries→splits into central arteries, while central arteries in white pulp make radial arteries and central arteries in red pulp makes penicillar arteries, some of which empty into sinusoids and some do not
Lymph nodes
- Smallest, most numerous encapsulated Lymphoid Organs
- In line filters of lymph: removes antigens and cellular debris, make lymphocytes, add antibodies
Veins use valves to help it go in correct direction
True
Arteries push against veins and help squish blood into right direction
Lymph system works the same way
Lymph system uses valves
True
We dump the lymph into the veins
Lymph node general structure
- Surrounded by a connective tissue capsule
- Trabeculae extend into the parenchyma between cortical nodules
- Outer Cortex
- Inner Medulla
- Hilum (where enters via arteries, leaves via veins and lymph leaves via efferent lymph vessels)-where things go in and out
Describe the cortex of the lymph nodes
Outer cortex (B cell rich)
- Lymphatic Nodule (Germinal Center and Mantle)
- Subcapsular/Cortical Sinus
Inner Cortext (T cell rich) -Lymphatic Nodules
