Capsulated Lymphoid tissue Flashcards
- Thymus produces what kinds of cells?
2. The thymus____ in size with age and is replaced by what?
- T cells
2. decreases, replaced by fat and connective tissue but still continues to produce T cells in adults
What are the two main types of Capsulated lymphoid tissue? What organs fall under each type?
Capsulated lymphoid tissue can either have lobules or no lobules
The Thymus has lobules, but the spleen and lymph nodes do not
Thymus produces what types of cells?
What happens to size of thymus as we age?
T cells
Decreases in size and is replaced by fat and connective tissue but still continues to produce T lymphocytes in adults
Thymus has how many lobes?
What kind of capsule?
Septa or trabeculae?
2 lobes
Connective tissue capsule
Septa made of connective tissue that penetrates to medulla and divides thymus into incomplete lobules
Thymus lobules are darker where and lighter where?
Defining feature of thymus?
Lymph nodules?
Germinal centers?
Darker outer cortex, lighter inner medulla
Defining feature=Hassal’s corpuscle
NO lymph nodules!
NO germinal centers!!
Where does T lymphocyte maturation specifically occur in thymus?
What are the order of the types of cells starting from outer cortex to inner medulla?
Maturation occurs in cortex
Order from outer to inner:
Subcapsular thymic epithelial cells (right by capsule)
Thymic cortical epithelial cells (cortex)
Maturing T cells (developing thymocytes)–inner cortex
** T cells in the cortex are not completely mature!! THey are in the process of maturation!
Are macrophages in the cortex of the thymus or the medulla?
BOTH!
Where are MATURE T lymphocytes found within thymus? What other cells are found here?
In the medulla
Hassal’s corpuscles, thymic medullary epithelial cells and dendritic cells are also found in medulla
What is a Hassal’s corpuscle and what is its function?
Closely packed epithelial cells in thymic medulla only. It releases a factor that stimulates Thymic dendritic cells to complete maturation of T cells
Where in the thymus is the thymus blood barrier? What is the purpose of this barrier? What kind of cells make up this barrier?
ONLY in cortex
Prevents most circulating antigens from reaching developing T cells
Epithelial reticular cells bound to capillaries
Where is spleen located? What is a major function of the spleen? What other kinds of cells reside in spleen?
Left superior quadrant
Hematopoeisis takes place here and macrophages in spleen destroy old red blood cells; spleen also traps antigens
1/3 of platelets here
- Describe the capsule of the spleen
2. Does spleen have septa or trabeculae?
- Connective tissue capsule: collagen, elastic fibers, smooth muscle
- Trabeculae extend from capsule and divide spleen into incomplete compartments
Describe the cortex and Medulla of spleen
Trick question! Spleen doesn’t have cortex and medulla!
Describe the parenchyma of the spleen and its components
Parenchyma is made of reticular fibers supporting the red and white pulp
White pulp=rich in lymphoid tissue
Red pulp: rich in red blood cells
What are the key features of the white pulp of the spleen?
Germinal center
Corona (B cells and APCs)
Central artery
Periarteriolar lymphoid sheaths (PALS)–T cells
Marginal Zone (where red and white pulp interact)
Describe the organization of the Red pulp
Splenic cord formed by reticular cells Splenic Sinusoid Penicillar Arteries Macrophage sheathed capillaries Circulating blood cells
Describe the blood flow into the spleen
Splenic artery (from celiac trunk)–>Trabecular arteries into parynchema of spleen–>central arteries–>white pulp surrounded by periarteriolar lymphoid sheaths
*central arteries produce radial arteries while in white pulp which feed into marginal zone sinuses–>Enter red pulp as penicillar arteries which either end in splenic sinusoids (closed) or red pulp (open circulation)
How do are the damaged red blood cells removed once the central artery becomes penicillar arteries?
Penicillar arteries are sheathed by macrophages that reoved the damaged RBS from blood
Do lymph nodes have lobules?
What is a lymph node and what does it do?
NO lobules
Smallest, most numerous encapsulated lymphoid organs
Filters lymph–removes Ags and cellular debris, produce lymphocytes and add antibodies
Describe the capsule of lymph nodes
Do lymph nodes have septa or trabeculae?
Does it have cortex and medulla? What else does it have?
Connective tissue capsule
Trabeculae that extend into parenchyma between cortical nodules
Outer cortex, inner medulla=yes
Also has hilum where enters via arteries, leaves via veins and lymph leaves via efferent lymph vessels
Describe the outer and inner cortex of lymph nodes
Outer cortex: B cell rich, lymphatic nodule with germinal center, mantle and subcapsular/cortical sinus
Inner cortex: T cell rich, lymphatic nodules
Describe the medulla of lymph nodes
Has medullary cords composed of macrophages and plasma cells
Also has medullary sinuses which are spaces lined by endothelial cells surrounded by reticular cells and macrophages
What do the lymph node sinuses do?
Filter lymph and direct flow
Made of mesh of reticular cells and fibers, macrophages and follicular dendritic cells
It slows flow of lymph which facilitates Ag removal
Lymph is cleared of 90% of Ags and cellular debris
Which organs have a cortex and medulla?
Which organs have lymphoid nodules? Which ones do NOT?
Which organs have cords and sinuses?
Cortex and medulla: Thymus, lymph node
Lymph nodules: Lymph nodes, spleen and tonsils (Thymus does NOT!)
Cords and sinuses: Lymph nodes and spleen
Diagnostic feature of: Thymus: Lymph nodes: Spleen: Tonsils:
Thymus: Hassal’s Corpuscles
Lymph nodes: Cortical nodules, subcapsular sinus
Spleen: Central arteries
Tonsils: Epithelial covering
