PRIMARY LYMPHOID ORGAN

1. Primary lymphoid organ
thymus
PRESENTEDTO
DR.S.SARANYA
ASST.PROF OF MICROBIOLOGY
SACRED HEART COLLEGE
TIRUPATTUR
PRESENTEDBY:
V.SALOMI(BP211509)
I M.SC MICROBIOLOGY
SACRED HEART COLLEGE
TIRUPATTUR

2.  The thymus is an organ that sits beneath the sternum in the upper
front part of the chest, stretching upwards towards the neck. In
children, the thymus is pinkish-gray, soft, and lobulated on its
surfaces.
 At birth it is about 4–6 cm long, 2.5–5 cm wide, and about 1 cm
thick.
 It increases in size until puberty, where it may have a size of about
40–50 g,following which it decreases in size in a process known
as involution.
Introduction

3. Thymus
 The thymus is the site of T cell development and maturation.
 It is a flat, bilobed organ situated above the heart.
 Each lobe is surrounded by a capsule and is divided into lobules which are
separated by strands of connective tissue called trabeculae.
 Each lobule is organized into two compartments-the outer compartment or
cortex is densely packed with immature T cells called thymocytes
whereas the inner compartment or medulla is sparsely populated with
thymocytes.

4.  Both the cortex and medulla of the thymus are criss-crossed by a three-
dimensional stromal cell network composed of epithelial cells, dendritic
cells and macrophages make up the framework of the organ and contribute
to the growth and maturation of thymocytes.
 Many stromal cells interact physically with the developing thymocytes.
Some thymic epithelial cells in the outer cortex called nurse cells have long
membrane extensions that surround as many as 50 thymocytes forming
large multicellular complexes.

5. STRUCTURE OF THYMUS

6. function of the thymus
 1. Release thymosin hormone that will stimulate the maturation of T cells.
 2. Thymus generate and select a repertoire of T cells that will protect the body from
infection.
 3. More than 95% of all thymocytes die by apoptosis(programmed cell death)in the
thymus without ever reaching maturity.
 4. Aging is accompanied by a decline in Thymic function

7.  Tumors in the thymus can press on nearby structures, causing symptoms
such as:
 Shortness of breath.
 Cough (which may bring up bloody sputum)
 Chest pain.
 Trouble swallowing.
 Loss of appetite.
 Weight loss.
symptoms

9. THANKYOU