Talk:Draft 2016: Difference between revisions

Revision as of 16:17, 26 February 2016

Spleen

Thymus Anatomy

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

Thymus Functions
specialised thymus microenvironments allow the production of self-tolerant T-cells (T lymphocytes) from immature precursors. immature precursors enter the thymus differentiate and undergo selection by thymic epithelial cell (TEC) subtypes mature release into circulation of these cells destruction of cells that recognise self antigens T-cells kill infected and oncogenic cells T Cells maturation within the thymus. T cell progenitors enter the thymus at the cortex/medulla border via post–capillary venules migrate toward the capsule in response to chemokine signalling. In the cortex, thymocytes undergo positive selection by cTECs then migrate to the medulla In the medulla, thymocytes are screened for reactivity to tissue-restricted self antigens expressed by mTECs. Mature T cells exit the thymus via blood or lymphatic vessels in response to a sphingosine-1-phosphate (S1P) gradient.			T and B lymphocytes

Thymus Structure

Thymus Structure

Thymus Histology

Capsule with trabeculae (dense connective tissue)

Infant thymus

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)

Thymus

Adult Thymus

Fetal thymus anatomy

Gross Anatomy

Superior mediastinum, anterior to heart
Bilobed lymphoepithelial organ

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

Page | Play

Thymus Cells

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

Fetal thymus
Young medulla
Young cortex

Adult Thymus

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.

@@ Line 26: / Line 26: @@
 ! colspan=2|Thymus Functions&nbsp;
 |-
-|
+| valogn=top|
-* specialised thymus microenvironments allow the production of self-tolerant T-cells from immature precursors.
+* specialised thymus microenvironments allow the production of self-tolerant T-cells (T lymphocytes) from immature precursors.
-* release into circulation of these cells
+** immature precursors enter the thymus
+** differentiate and undergo selection by thymic epithelial cell (TEC) subtypes
+** mature release into circulation of these cells
 * destruction of cells that recognise self antigens
+* T-cells kill infected and oncogenic cells
+T Cells  maturation within the thymus.
+# T cell progenitors enter the thymus at the cortex/medulla border via post–capillary venules
+# migrate toward the capsule in response to chemokine signalling.
+# In the cortex, thymocytes undergo positive selection by cTECs then migrate to the medulla
+# In the medulla, thymocytes are screened for reactivity to tissue-restricted self antigens expressed by mTECs.
+# Mature T cells exit the thymus via blood or lymphatic vessels in response to a sphingosine-1-phosphate (S1P) gradient.
 | [[File:Thymus structure and function cartoon01.jpg|600px]]
+|
+| [[File:T and B lymphocytes EM09.jpg]]
+T and B lymphocytes
 |}
@@ Line 38: / Line 54: @@
 ! Thymus Structure&nbsp;
 |-
-|  [[File:Spleen structure cartoon 01.jpg|800px]]
+|  [[File:Thymus histology 01.jpg|800px]]
 |}
@@ Line 50: / Line 65: @@
 * Capsule with trabeculae (dense connective tissue)
-[[File:Spleen histology 06.jpg|600px]]
+[[File:Thymus histology 01.jpg|600px]]
+Infant thymus
 {|