Talk:Draft 2016

Spleen

Thymus Anatomy

adult thymus - bilobed, superior mediastinum, anterior to heart	infant thymus - large

Thymus Involution
	Overall Size Changes with age birth 10-15 g puberty 30-40 g after puberty - involution replaced by adipose tissue middle-aged 10 g

Thymus Functions
specialised thymus microenvironments allow the production of self-tolerant T-cells from immature precursors. release into circulation of these cells destruction of cells that recognise self antigens

Thymus Structure

Overview - red and white pulp	Overview - blood vessels	Red pulp

Reticular Fibers (type III collagen) act as supporting meshwork (can be seen in Silver stained preparations)

Adult Thymus

Fetal thymus anatomy

Gross Anatomy

Histology

Contains reticular cells but no fibers
Stem lymphocytes
- proliferate and differentiate
- forms long-lived T- lymphocytes
removes auto-reactive T-lymphocytes (negative selection)

‎‎Thymus 1

Reticular cells	Macrophages	Lymphocytes
Abundant, eosinophilic, large, ovoid and light nucleus 1-2 nucleoli sheathe cortical capillaries form an epitheloid layer maintain microenvironment for development of T-lymphocytes in cortex (thymic epitheliocytes)	cortex and medulla difficult to distinguish from reticular cells in (Stain - Haematoxylin Eosin) remove auto-reactive T-lymphocytes	located in cortex and medulla more numerous (denser) in cortex majority are developing T-lymphocytes (= thymic lymphocytes or thymocytes)

Histology

Cortical lymphoid tissue is replaced by adipose tissue (involution)
Increase in size of thymic corpuscles
Thymic corpuscle - (Hassall’s corpuscle) mass of concentric epithelioreticular cells.