The thymus is the earliest immune organ. It appears in the 9th week of embryonic development and is roughly mature in structure by the 20th week.

Surface: a membrane composed of connective tissue

The thymus is located in front of the mediastinum and behind the sternum, and is divided into two lobes.

Efferent lymphatic vessels with rich blood supply and lymph node connections

The largest immune organ in the human body, located on the upper left side of the abdominal cavity, has hematopoietic, blood storage and filtering functions.

Embryonic hematopoietic organs

numerous sinusoids

Connective tissue is wrapped in membrane

White pulp – composed of lymphocytes

Red pith

fringe zone

Tonsils are the "gateway" to the respiratory tract and digestive tract - white blood cells and phagocytes

T lymphocytes (cell-mediated immunity) - mature in the thymus

B lymphocytes (humoral immunity) – mature in bone marrow

Natural killer cells (NK cells) – involved in innate immunity

Antigen presenting cells (APC)

Identify and eliminate foreign pathogenic microorganisms

Identify and remove aging and dead cells in the body to maintain internal environment stability

Recognize and eliminate cells with mutated surface antigens

The body's immune system, nervous system and endocrine system together constitute the neuroendocrine immune network regulatory system

Born with it, it has a defensive effect on a variety of pathogens

autoimmune

passive immunity

superficial cortex

Paracortex (deep cortex)

cortical lymphatic sinus

Medullary cord - mainly contains plasma cells, B cells, macrophages

medullary sinus

filter lymph fluid

Immunization