Lymphoid system (Goyal) Flashcards
What are the main components of the lymphoid system?
- Lymphoid (lymphocytes + antigen presenting cells)
- Diffuse lymphoid tissue (aggregation of lymphoid cells in CT)
- Solitary lymph nodules (mucosa of digestive or resp. organs)
- Aggregation of lymph nodules (Peyer’s patch)
- Discrete lymphoid organs (LN, hemal nodes, tonsils, thymus, spleen)
What are the cells of the immune system?
B and T cells
Plasma cells
T helper cells (CD4+)
T cytotoxic cells (CD8+)
T suppressor cells (CD8+)
Natural Killer cells (nonspecific cytotoxicity)
Antigen presenting cells
Dendritic cell in LN
Langerhans in skin
Macrophages
B lymphocytes
What do all antigen presenting cells possess?
MHC class II molecules on their surface and exogenous antigens to T helper cells
IgA
Binds to epithelium covering or lining organs of the body
IgD
Binds to plasma membrane of B cells
IgE
Binds to plasma membrane of mast cells and basophils
IgG
80% of total serum Ig
IgM
First antibody produced in a primary immune response and in the neonate
Present in serum and on plasma membrane of B cells
_________ are the only leukocytes that recirculate between blood and CT
Lymphocytes
What is the role of Peyer’s patches in ruminants?
A source of B cell differentiation (in addition to the bone marrow)
Tonsils
Lymph nodule aggregation in CT under epithelium
3: lingual, palatine, pharyngeal
What are lingual and palatine tonsils covered by?
Stratified squamous epithelium
What are pharyngeal tonsils covered by?
Pseudostratified epithelium
T/F: Epithelial surface of palatine Tonsils of dogs and cats of may be smooth
TRUE
Which epithelial surface of tonsils have deep invaginations?
Lingual tonsils in horses
Palatine tonsils in horses and small ruminants
What do tonsils lack?
Afferent lymph vessels, so they can’t filter lymph but contain efferent lymph vessels
What do epithelial invaginations of a the palatine tonsil of a horse lead to?
Formation of a tonsillar crypt, which is the site for accumulation of food and organisms, then leading to tonsilitis
What are the structures of lymph nodes?
Stroma, outer cortex, inner cortex (paracortex) , circulating lymphocytes, medulla , sinusoids
Outer cortex
Lymph nodules
Germinal center
B lymphocytes mainly
Activation in response to foreign antigens
Stroma
Capsule (Dense CT, afferent lymph vessels enter)
Trabeculae
Reticular fibers
Inner cortex (paracortex)
Contains mainly T lymphocytes
Site where circulating lymphocytes gain access to LN via post- capillary venules (high endothelial- simple cuboidal)
Medulla
Medullary cords: composed of lymphocytes, plasma cells and macrophages
Sinusoids
Sub-capsular, trabecular or cortical and medullary
Surround medullary cords
What is the flow to lymph in LN?
Afferent lymph vessel –>
Sub-capsular sinusoids –>
Trabecular sinusoid –>
Medullary sinusoids –>
Efferent lymph vessel
What is the function of LN?
Filtration of lymph
Phagocytosis of foreign particles
Mounting an immune response
Retention of tumor cells
Porcine LN
Centrally located
Medullary cords absent
Lymph vessels exit @ periphery
Afferent vessels enter @ capsule and penetrate via the trabeculae to the nodules
Hemal Nodes
Present in ruminants
Lack lymph vessels and receive cells from blood
Diapedesis
Junction between cuboidal cells are loose
This enables lymphocytes to leave the blood and enter the LN
Thymus
Epithelio-lymphoid organs made of lobes and lobules (divided into cortex and medulla)
Thymus cortex
Aggregation of lymphocytes
Blood-thymus barrier in cortex enables T cell differentiation in the absence of external antigens
Thymus medulla
Compared to cortex, has fewer lymphocytes and more epithelial-reticular cells (with age degenerate and form Hassall’s corpuscles)
Thymus function
Priming of T cells tha migrate to rest of the body
Contains efferent lymph vessels
How is the thymus effected with age?
Atrophies with age, but small amount of tissue persists througout life
Effects of thymectomy @ neonatal age
Reduced # of lymphocytes
Atrophy of all lymphoid organs
No delayed hypersensitivity or graft rejection
Animals eventually become weak, lose weight and dies
What are the different parts of the spleen?
Capsule, Trabeculae, Red pulp, White pulp
Spleen trabeculae
Contains blood vessels. nerves, fibers and smooth muscle cells (especially developed in the horse)
Red pulp
Contains sinusoids and cords
Cords: between sinusoids and have RBCs. macrophages, lymphocytes, plasma cells and other leukocytes
Sinusoids in the spleen
Wide capillaries lined by endothelial cells with spaces between cells
Discontinuous BL
White pulp
Periateriolar lymphaic sheath (T cells surrounding central arteriole) and lymphaic nodules (B cells)
Lymph nodules of white pulp?
Germinal center: B cell proliferation
Mantle zone: B cell aggregation
Marginal zone: B and T cells, macrophages
Marginal zone of the spleen
Between white and red pulp
First site in the spleen where blood antigens get an access to immunocompetent cells
What are the functions of the spleen?
Filter blood
B and T cell proliferation
Phagocytosis of old RBC
Storage of blood and release
Prenatal hematopoiesis
What are the 3 types of spleen?
Defense, storage and intermediate
Defense spleen
Lymphatic tissue
Man, rabbits and hares
Storage spleen
Red tissue
Horses, dogs and cats
Intermediate spleen
Ruminants and swine
What gives capillaries to the white pulp?
Splenic, trabecular and central (arteriole) artery
Penicillus
Brush-like
Enters the red pulp as arteriole of the red pulp and continues as sheathed arterioles
Surrounded my macrophages
Pigs and cats
Closed circulation
Sheathed capillaries that open into sinusoids of the red pulp
Open cirucaltion
Sheathed capillaries that open into cords of the red pulp
Bursa Fabricus in cloaca of birds
An aggregation of lymph nodules under the cloacal epithelium
Site for B cell differentiation
Simple columnar and pseudostraitifed columnar
