1. Institute Of Health Science
School Of Biomedical Science
Department Of Medical Physiology
Submitted to: Mr Teshome G (Ass Prof.)
MAY 2023
JIMMA UNIVERSITY
5. Introduction
The name Thymus is from the Latin derivation of the
Greek word Thymos meaning warty excrescence due to
its resemblance to the flowers of the thyme plant .
The earliest known reference to the Thymus is attributed
to Rufus of Ephesus circa of 100 AD, a Greek anatomist
renowned for his investigations of the heart and eye .
Rufus attributed the discovery of the Thymus to the
Egyptians.
It was Galen, who first described the morphology of the
gland.
6. Definition
The term thymus is taken from Greek literature, where it
means ‘soul’ to indicate that the soul resides in the
thymus.
The thymus is one of the key organs in the lymphatic
system, which occurs in the mediastinum below the
sternum.
The thymus gland is distinct from other endocrine glands
in that it is active only before puberty.
In addition to the secretory cells of the thymus, it also
contains other immune cells
like macrophages, neutrophils, and dendritic cells.
7. Structure of Thymus Gland
• The thymus gland is a bilobed gland consisting of two
pyramid-shaped lobes, each with a lobulated surface
differentiated into the outer cortex and inner medulla.
• During embryonic development, the thymus originates
from the embryo’s third pair of pharyngeal pouches.
• Each lobe of the gland is surrounded by a dense capsule
of connective tissue and divided internally by a
connective tissue septum.
8. Cont,
• The size of the thymus is large in infants and young
children, with the largest size at puberty.
• The gland then slowly begins to coalesce after puberty to
be replaced by adipose tissue.
• The blood supply to the thymus gland is provided by the
inferior thyroid, internal thyroid, and intercostals arteries.
• The gland is attached to the sternum by sternohyoid and
sternothyroid muscles, both of which are bilateral.
11. Hormones of Thymus Gland
1. Thymosin
• Thymosin is produced by the epithelial cells of the cortex
and medulla, and it is the primary hormone secreted by
the gland.
• The most important function of thymosin is to induce T
cell differentiation and enhance the immunological
function of different immune cells.
12. Cont,
• Thymosin has also been associated with increasing the
phenotypic markers in lymphocytes.
• Thymosin is a protein that is heat stable up to 80°C
temperature and might contain a small amount of
carbohydrates.
13. Cont,
2. Thymopoietin
• Thymopoietin is a polypeptide hormone of the thymus
that has neuromuscular functions than immunological
ones.
• However, the increased levels of the hormone are known
to induce T cell activation and differentiation as well.
14. Cont,
• The thymus also makes hormones that are similar to the
hormones other glands in the body produce.
• They include:
• Melatonin: a sleep-regulating hormone that comes from
the pineal gland
15. Cont,
• Insulin: a blood sugar regulating hormone made by the
pancreas
• Growth hormone: a growth-regulating hormone from
the pituitary gland
• Prolactin: a breast-development hormone from the
pituitary gland
16. Functions of Thymus Gland
• The most important function of the thymus gland is to
induce the development, activation, and differentiation of
T cells so that they can perform their function as
mediators of cellular immunity.
17. Cont,
• The thymic hormones, thymosin, and thymopoietin
stimulate the prothymocytes to become thymocytes and
T lymphocytes.
• The gland also induces the release of cytokines that are
essential for controlling the development of T cells
through different stages.
18. Cont,
• The thymus is a part of fetal immunity by the 12th week
of pregnancy and remains active through fetal life as well
as childhood.
• As an endocrine gland, the thymus is known to produce
human growth hormone, which is essential for the
growth and development of the body.
19. Types of cells
T cells
Once fully mature, they help fightTrusted Source:
Tumors: Cancerous masses
Allergens: Substances that cause allergic reactions
Pathogens: Microbes, such as viruses and bacteria, that
can cause an infection
20. Cont,
B cells
The thymus also has a small population of B
lymphocytes, or B cells.
Evidence suggestsTrusted Source these B cells develop
in the thymus and are different from B cells elsewhere in
the body.
They are referred to as thymic B cells.
21. Cont,
Research shows that thymic B cells aid in negative
selection of lymphocytes.
This means they detect potentially harmful cells that
interact too strongly with antigens, which are toxins.
Although thymic B cells play an important role in
maintaining healthy cells, their function is not fully
understood.
23. Molecular mechanism
The present review addresses the signaling and
transcriptional functions of the thymus, including the
molecular mechanisms underlying the regulatory
functions of T cells and their role in the immune system.
24. Cont,
In addition, the levels of cytokines secreted in the
thymus have a significant effect on thymic functions,
including thymocyte migration and development, thymic
atrophy and thymic recovery.
25. Cont,
Furthermore, the regulation and molecular mechanisms
of stress-mediated thymic atrophy and involution were
investigated, with particular emphasis on thymic function
as a potential target for drug development and discovery
using proteomics.
27. Synthesis and secretion
Thymus hormones are hormones produced by the
thymus.
They are generally small proteins, which regulate the
development and selection of an immune-competent
repertoire of T cells, and stimulate antibody production
by B cells.
They are important for immune system development and
function and also the development of other tissues.
29. Associated conditions
Hyperactivity
• Various disorders can enlarge the thymus and cause it to
become hyperactive, or overly active.
• These may include:-tumors of the thymus,cancers of the
lymphatic system
• myasthenia gravis, an autoimmune disease involving
muscle weakness
30. Cont,
Small size or atrophy
• When people age, their thymus atrophies, or decreases
in size.
• This raises their likelihood of developing:- cancer, viral
and bacterial infections, autoimmune diseases.
31. Cont,
Thymus cancer
• The thymus may develop two typesTrusted Source of
cancer: thymoma and thymic carcinoma.
• Thymoma is a slow-growing cancer that rarely spreads
beyond the thymus.
• Thymic carcinoma is a faster-growing cancer that is
harder to treat.
32. Summary
• The thymus is an organ in the upper chest.
• It is largest in infants and young children, and it
decreases in size after puberty.
• It plays a critical role in immunity.
• Its primary functionTrusted Source involves T cell
maturation.
33. Cont,
• These cells help the body fight diseases, cancers,
allergens, and more.
• The thymus also contains B cells.
• They help the thymus select the best T cells while
disposing of potentially harmful ones.
• Conditions affecting the thymus include hyperactivity
from enlargement, cancer, and atrophy.
34. Reference
• Hall JE and Guyton AC. (2011) Textbook of Medical Physiology. Twelfth
Edition. Elsevier Saunders.
• Waugh A and Grant A. (2004) Anatomy and Physiology. Ninth Edition.
Churchill Livingstone.
• Marieb EN and Hoehn K. (2013) Human Anatomy and Physiology. Ninth
Edition. Pearson Education, Inc.
• Rastogi SC. (2007) Essentials of Human Physiology. Fourth Edition. New
Age International Limited
• Bach JF. Thymic hormones. J Immunopharmacol. 1979;1(3):277-310. doi:
10.3109/08923977909026377. PMID: 233313.
• Zdrojewicz Z, Pachura E, Pachura P. The Thymus: A Forgotten, But Very
Important Organ. Adv Clin Exp Med. 2016 Mar-Apr;25(2):369-75. doi:
10.17219/acem/58802. PMID: 27627572.
• Remien K, Jan A. Anatomy, Head and Neck, Thymus. [Updated 2021 Feb 9].
In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021
Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK539748/
35. If You have any query
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