Thymus Flashcards
What is the function of the thymus?
Immunity
Differentiate T lymphocytes and dissemination
Secrete hormones, etc..
During embryogenesis, where does the thymus develop?
epithelial portion
lymphocytes
3rd and 4th branchial (pharyngeal) pouches
bone marrow
What is the structure?
Lymphoepithelial
stroma: epithelial cells, macrophages, dendritic cells
thymocytes
Where does the thymus lie in most animals?
what animals does it lie elsewhere
cranial mediastinum
Pig-jugular groove along the ventro-lateral neck and NOT in the thoracic cavity
Avian- above jugular groove on either side and occupy almost the entire length of the neck.
What are the precursor cells that enter the thymus?
Prothymocytes
What is your portal of entry into the thymus?
Hematogenous
What are your responses to injury?
Atrophy
Enlargement
Inflammation
Lymphoid hyperplasia
Why would you have a small thymus?
C/S
Primary or acquired immunodeficiency
Congenital and Degenerative disorders
infections
Combined immunodeficiency disorders (CIDs)
Why would you have a large thymus?
C/S
Hemorrage, hematomas
Neoplasia
Thymic Cysts
Dyspnea
If you have CID how would your thymus look and why?
Small
Inadequate T and B lymphocyte function.
What CS would you see with CID?
Nasal discharge
Unthrifty haircoat
Loss of of condition
Pneumonia
Diarrhea
Lesions of CID in a horse?
Severe bronchopneumonia
Small thymus, spleen, LN
Thymus may be difficult to ID
Reduction in the white pulp of the spleen due to absence of germinal centers and PALS
Lymphocyte depletion in LN
Who does XSCID affect and what kind of cell?
Male pups
lack mature, functional T lymphocytes
*males are Xtra…
Lesions of XSCID in dogs?
Small thymus, obscured by medistinal fat
other lymphoid organs usually unidentifiable at necropsy
Small dysplastic lobules w/a variable number of Hassalls corpuscles
Who gets JLIDS and what cell does it affect? CS?
Juvenile Llamas
B-cell
Wasting and sysceptible to chronic dz that fail to respond to therapy. Mild nonreg anemia
*alpacas are A’s and Llamas are Bs? so think B cell?
What are some reasons for acquire immunodeficient thymus atrophy?
Lack of antigenic stimulation
toxins chemo radiation infection malnutrition age
What are some viruses that can cause thymus atrophy?
Parvo
distemper
adeno
BVDV,
EHV
FIV
What will you see in the thymus after atrophy?
lymphocytolysis
loss of architecture
decreased lymphocyte populations
What kind of toxins can cause atrophy?
metals
fungus
Why does chemo and radiation cause atrophy
Inhibition of cell division and activation of lymphocytes=
immunosuppression
What are some causes for thymic hemorrhage/hematomas?
Trauma:
Fall
HBC
pulling on the leash too hard
Rupture of dissecting aortic aneurysm
Rodenticides
Thymic lymphosarcoma is common in?
cats with FeLV
Calves with BLV
dogs
What are you gonna find in an aspirate of a thymic lymphosarcoma?
Medium to large lymphocytes with vacuolated cytoplasm
Will you see chylous with lymphosarcoma or thymoma?
sarcoma bc of lipid accumulation
Thymomas are a tumor of what cell type?
Epithelial cells
What life stage will you see a thymoma in a dog?
older
What can thymomas cause?
Myasthenia gravis
megaesophagus
What is the pathogenesis behind MG caused by a thymoma?
Thymic myoid cells express epitopes that are cross-reactive w/skeletal m proteins–ACh receptors.
Histo for thymoma
Round to spindle shaped epithelial cells
small lymphocytes with few medium and large lymphocytes
Thymic cysts
Lined by ciliated epithelium
usually no significance
Thymitis
Rare
infections from PMWS, salmon poisoning
