Thymus Your thymus is a small gland in the lymphatic system that makes and trains special white blood cells called T-cells. The T-cells help your immune system fight disease and infection. Your thymus gland produces most of your T-cells before birth. The rest are made in childhood and you’ll have all the T-cells you need for life by the time you hit puberty. Advertisement Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy Care at Cleveland Clinic Endocrinology Care Endocrinology Care for Children Make an Appointment Advertisement Advertisement Advertisement Advertisement Contents Overview Function Anatomy Conditions and Disorders Additional Common Questions Overview What is the thymus? The thymus is a small gland that’s part of your lymphatic system. Your lymphatic system is made up of a network of tissues, vessels and organs such as your tonsils, spleen and appendix. Your lymphatic system is a part of your immune system. It helps defend against infection and disease. Function What does the thymus do? The primary function of the thymus gland is to train special white blood cells called T-lymphocytes or T-cells. White blood cells (lymphocytes) travel from your bone marrow to your thymus. The lymphocytes mature and become specialized T-cells in your thymus. After the T-cells have matured, they enter your bloodstream. They travel to your lymph nodes (groups of cells) and other organs in your lymphatic system, where they help your immune system fight disease and infection. Your thymus gland is also part of your endocrine system. Your endocrine system makes and releases hormones that control the functions of your body. Your thymus produces and releases several hormones including: Thymopoietin: fuels the production of T-cells and tells the pituitary gland to release hormones. Thymosin and thymulin: help make specialized types of T-cells. Thymic humoral factor: keeps your immune system working properly. During what age is the thymus gland most active? The thymus gland is most active during childhood. Your thymus actually starts making T-cells before you’re born. It keeps producing T-cells and you have all the T-cells you need by the time you reach puberty. After puberty, your thymus gland slowly starts to decrease in size and is replaced by fat. Anatomy Where is the thymus located? The location of your thymus gland is in your upper chest behind your breastbone (sternum). It sits between your lungs in a part of your chest called the mediastinum. Your thymus is just in front of and above your heart. What does the thymus gland look like? The thymus gland is pinkish-gray. It is made up of two irregularly shaped parts (lobes). The lobes have lots of small bumps called lobules on the surface. How big is the thymus gland? The thymus gland is quite big in babies and children. It reaches its biggest weight of about 1 oun

1. THYMUS,ADRENAL CORTEX,
PANCREAS

2. THE THYMUS
• Specialized primary lymphoid organ of the immune system
• Location: Anterior part of the upper mediastinum
• Wt: At birth-10-12gms
• Childhood & adolescence: 20-30gm
• Old age: 3-6gm

3. FUNCTIONS
• Initiates the development of immunologically competent T-
lymphocytes(early life)
• Maintenance (adult life)
Immunological role
Provides favorable environment for lymphocyte development
• Receives precursors from bone marrow –thymus-lymphnodes
Reticulo-epithelial tissue secretes THYMOSIN hormone , stimulates
formation of lymphocytes within thymus and in peripheral lymphoid
tissue

5. ADRENAL GLANDS
• Location: top of each kidney
• Wt: 4-5gm
• Parts: adrenal cortex ,
adrenal medulla

7. ADRENAL CORTEX
• Red to light brown in colour
• composed of three zones.
From the outer to inner
1. zonaglomerulosa- is narrow and the cells are in a whorled pattern.
2. zonafasciculata- wide and the cells lie in columns
3. zonareticularis- more randomly organised.
HORMONES OF THE ADRENAL CORTEX
1. Mineralocorticoids
2. Glucocorticoids
3. Adrenal androgens

8. MINERALOCORTICOIDS
• Produced in the zona glomerulosa.
• Primary mineralocorticoid is aldosterone. Its secretion is regulated by the
oligopeptide angiotensin II (angiotensin II is regulated by angiotensin I,
which in turn is regulated by renin).
• Help to control the water and electrolyte homeostasis, particularly the
concentration of Na+ and K+ ions.
• Aldosterone affects metabolism in different ways:
It increases urinary excretion of potassium ions.
 It increases interstitial levels of sodium ions.
 It increases water retention and blood volume.

9. GLUCOCORTICOIDS
• Produced in the zona fasciculata.
• Primary glucocorticoid :cortisol and corticosterone
• Secretion is regulated by the hormone ACTH from the anterior pituitary.
• cortisol enhances metabolism in several ways:
It stimulates the release of amino acids from the body
It stimulates lipolysis, the breakdown of fat
It stimulates gluconeogenesis, the production of glucose from newly-released amino acids and
lipids
 It increases blood glucose levels in response to stress, by inhibiting glucose uptake into muscle
and fat cells
It strengthens cardiac muscle contractions
 It increases water retention
It has anti-inflammatory and anti-allergic effects

11. ANDROGEN
• Also called androgenic hormones or testoids
• First discovered in 1936.
• Androgens are also the original anabolic steroids and the precursor of
all estrogens(Female sex hormones)
• Primary and most well-known androgen is testosterone.
• Stimulates or controls the development and maintenance of male
characteristics by binding to androgen receptors.
Activity of the accessory male sex organs and development of
male secondary sex characteristics.

12. Adrenal medulla
• Located at the center of the gland, being surrounded by the adrenal
cortex.
• Composed of hormone-producing chromaffin cells,is the principal site
of the conversion of the amino acid tyrosine into the catecholamines
adrenaline (epinephrine), noradrenaline (norepinephrine), and
dopamine in response to stimulation by sympathetic preganglionic
neurons.
• 80% of released catecholamines are epinephrine.
• Hormones are secreted and stored in the adrenal medulla and
released in response to appropriate stimuli.

14. Epinephrine (Also called adrenaline)
• Hormone and neurotransmitter.
• increases heart rate, contracts blood vessels, dilates air passages and
participates in the fight-or- flight response of the sympathetic nervous
system.
• increased blood pressure, blood vessel constriction in the skin and
gastrointestinal tract, blood vessel dilation in skeletal muscles, and
decreased metabolism

15. Norepinephrine (Also called noradrenaline.)
• catecholamine
• As a stress hormone, norepinephrine affects parts of the brain where
attention and responding actions are controlled.
• Along with epinephrine, norepinephrine also underlies the fight-or-
flight response, directly increasing heart rate, triggering the release of
glucose from energy stores, and increasing blood flow to skeletal
muscle.
• Also suppress neuroinflammation when released diffusely in the brain
from the locus coeruleus.

16. DOPAMINE

17. • Dopamine is a neurotransmitter.
• It is a chemical messenger that helps in the transmission of signals in
the brain and other vital areas.

21. DISEASES OF THE ADRENAL GLAND
• Cushing’s syndrome- the level of corticosteroids is excessive, usually
from overproduction by the adrenal glands.
• Addison's disease-adrenal glands are underactive, resulting in a
deficiency of adrenal hormones.