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Organ system histology
Arteriole, venule and capillary histology
Artery and vein histology
Cardiac muscle histology
Adrenal gland histology
Pituitary gland histology
Thyroid and parathyroid gland histology
Eye and ear histology
Nasal cavity and larynx histology
Small intestine histology
Lymph node histology
Skeletal muscle histology
Central nervous system histology
Peripheral nervous system histology
Ureter, bladder and urethra histology
Cervix and vagina histology
Fallopian tube and uterus histology
Mammary gland histology
Prostate gland histology
Testis, ductus deferens, and seminal vesicle histology
Bronchioles and alveoli histology
Trachea and bronchi histology
The lymphatic system is an essential part of the immune system and it consists of a network of lymphatic vessels, tissues, and organs.
The lymphatic vessels drain interstitial fluid or lymph from peripheral tissues back into the blood.
Lymphoid tissue and organs contain a lot of lymphocytes and other white blood cells.
The primary lymphoid organs include the thymus and bone marrow.
And the secondary lymphoid organs include the tonsils, lymph nodes, spleen, and mucosa-associated lymphoid tissue or MALT for short.
The thymus is a flat encapsulated lymphoid organ located in the anterior superior mediastinum, right behind the sternum.
During embryonic development, the thymus originates from the embryo’s third pair of pharyngeal pouches.
This organ is most active during childhood, reaching its largest size around puberty, with a weight of approximately 30 to 40 grams.
After puberty, the thymus will begin to slowly involute or decrease in size, with less lymphatic tissue and an increase in adipocytes.
The thymus plays an important role in the maturation of T cells, which includes negative selection or central tolerance.
This process, along with regulatory T cells help prevent autoimmunity.
This is a low power image of a neonatal thymus.
At this magnification, the thin collagenous capsule is a little hard to see, but if we zoom in a little further, we can see the capsule more clearly, as well as the connective tissue that extends inward from the capsule into the thymus, forming incomplete lobules.
The thymus is a flat encapsulated lymphoid organ located behind the sternum. It's most active during childhood and slowly involutes in adulthood, with fatty infiltrates and decreased thymic tissue. The thymus gland has two lobes, each of which has an outer cortex that's very basophilic and stains dark purple, whereas the inner medulla stains a lighter purple and pink color. The cortex consists of many basophilic T lymphoblasts that are supported by a meshwork of thymic epithelial cells (TECs), which have a pale cytoplasm with cytoplasmic processes. The inner medulla also has an abundance of TECs, but will also contain Hassall's corpuscles, which are the structures formed by closely packed and concentrically arranged TECs.
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