Thymus Flashcards

Study thymus anatomy, including its mediastinal location, lobular structure, embryological development, blood supply, T-cell maturation, and clinical significance.

Card 1 of 30Question

How is the thymus classified within the lymphatic system?

As a primary lymphatic organ.

In This Section

1. How is the thymus classified within the lymphatic system?

As a primary lymphatic organ.

2. What is the principal immunological function of the thymus?

To support the maturation and selection of T lymphocytes.

3. Where is the thymus located in the thorax?

Primarily in the anterior part of the superior mediastinum, extending into the anterior mediastinum.

4. Which bone lies anterior to the thymus?

The sternum, particularly the manubrium and upper body.

5. Which major cardiovascular structures lie posterior to the thymus?

The brachiocephalic veins, superior vena cava, great arteries, and pericardium.

6. Into which cervical region may the thymus extend, especially in children?

The lower anterior neck, near the inferior poles of the thyroid gland.

7. How many main lobes does the thymus typically possess?

Two lobes, right and left, joined by connective tissue.

8. What surrounds the thymus and sends septa into its substance?

A connective tissue capsule.

9. What anatomical subdivisions are formed by connective tissue septa within the thymus?

Numerous thymic lobules, which have distinct cortical regions and interconnected medullary tissue.

10. What are the two principal histological regions of a thymic lobule?

The outer cortex and inner medulla.

11. Why does the thymic cortex appear darker than the medulla in histological sections?

It contains a higher density of developing T lymphocytes.

12. Which specialized cells form the supporting framework of the thymus?

Thymic epithelial cells, also called epithelioreticular cells.

13. How does the supporting framework of the thymus differ from that of a typical lymph node?

The thymus has an epithelial stromal framework, whereas lymph nodes primarily have a reticular connective tissue framework.

14. What are Hassall's corpuscles?

Concentrically arranged thymic epithelial cells, often with central keratinization.

15. In which region of the thymus are Hassall's corpuscles found?

The thymic medulla.

16. Where do immature T-cell precursors originate before entering the thymus?

The bone marrow.

17. What is positive selection of developing T lymphocytes?

Selection of thymocytes capable of recognizing self-MHC molecules, mainly in the thymic cortex.

18. What is negative selection of developing T lymphocytes?

Elimination of thymocytes with excessive reactivity to self-antigens, particularly in the thymic medulla.

19. Which transcription factor in medullary thymic epithelial cells helps establish central immune tolerance?

AIRE, which promotes the expression of tissue-restricted self-antigens.

20. What is the blood-thymus barrier?

A specialized barrier in the thymic cortex that limits exposure of developing thymocytes to circulating antigens.

21. Which arteries primarily supply the thymus?

Thymic branches of the internal thoracic and inferior thyroid arteries.

22. Which major vein receives much of the venous drainage of the thymus?

The left brachiocephalic vein, with additional drainage to internal thoracic and inferior thyroid veins.

23. Which lymph node groups receive lymphatic drainage from the thymus?

Primarily the parasternal, brachiocephalic, and tracheobronchial lymph nodes.

24. Does the thymus normally possess afferent lymphatic vessels?

No, it has efferent lymphatic vessels but lacks conventional afferent lymphatic vessels.

25. From which embryological structure does the thymic epithelium develop?

The ventral portions of the third pharyngeal pouches.

26. Which parathyroid glands share a developmental origin with the thymus?

The inferior parathyroid glands, derived from the dorsal portions of the third pharyngeal pouches.

27. How does the thymus reach its definitive mediastinal position during embryological development?

It descends from the pharyngeal region into the anterior mediastinum.

28. What is an ectopic cervical thymus?

Thymic tissue remaining in the neck due to incomplete or abnormal embryological descent.

29. What is thymic involution?

The age-related reduction of functional thymic tissue with progressive replacement by adipose tissue, especially after puberty.

30. Which autoimmune neuromuscular disorder is strongly associated with thymic abnormalities?

Myasthenia gravis, which may be associated with thymic hyperplasia or thymoma.