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    From Lymphatic System

    Lumbar Trunk
    Drains lower limbs and pelvic organs.
    Pectoral Axillary Nodes
    Located along the anterior chest wall.
    Intestinal Trunk
    Drains lymph from the intestines.
    Axillary Lymph Nodes
    Drain the upper limbs and chest wall.
    Apical Axillary Nodes
    Located at the apex of the axilla.
    Subscapular Axillary Nodes
    Located along the posterior chest wall.
    Tubal Tonsils
    Near openings of the auditory tubes.
    Mastoid Lymph Nodes
    Drain the posterior scalp and ear.
    Subclavian Trunk
    Drains lymph from the upper limbs.
    BALT
    Bronchus-associated lymphoid tissue.
    Lingual Tonsils
    Located at the base of the tongue.
    Inguinal Lymph Nodes
    Drain the lower limbs and external genitalia.
    Lateral Axillary Nodes
    Located along the humerus in the axilla.
    Lymph Nodes
    Small structures that filter lymph and store immune cells.
    Palatine Tonsils
    Located on each side of the oropharynx.
    Submandibular Lymph Nodes
    Drain the face, mouth, and pharynx.
    Lymphatic Capillaries
    Initial lymphatic vessels that collect interstitial fluid.
    Jugular Trunk
    Drains lymph from the head and neck.
    MALT
    Mucosa-associated lymphoid tissue.
    Deep Cervical Lymph Nodes
    Located along internal jugular vein; receive lymph from head and neck.
    Paratracheal Nodes
    Located lateral to the trachea.
    Peyer’s Patches
    Lymphoid nodules in the small intestine.
    Retroaortic Nodes
    Located behind the aorta.
    Cisterna Chyli
    Dilated sac at the start of the thoracic duct.
    Popliteal Lymph Nodes
    Drain the foot and leg.

    Spleen

    Reviewed by our medical team

    Filters blood and initiates immune response.

    1. Overview

    The spleen is the largest lymphatic organ in the human body, playing a dual role in both the immune and circulatory systems. It functions primarily as a blood filter, removing old and damaged red blood cells, and serves as a site for immune surveillance and response. Unlike lymph nodes, which filter lymph, the spleen filters blood directly. It is particularly rich in immune cells and is involved in the production and maturation of lymphocytes, making it a vital component of the body’s defense mechanisms.

    2. Location

    The spleen is located in the upper left quadrant of the abdomen, posterior to the stomach and protected by the 9th to 11th ribs. It lies beneath the left dome of the diaphragm and is anatomically related to the stomach (via the gastrosplenic ligament), left kidney (via the splenorenal ligament), colon (splenic flexure), and pancreas (tail of pancreas lies near the hilum). It is intraperitoneal and surrounded by a fibrous capsule.

    3. Structure

    The spleen is an ovoid, purplish organ typically weighing 150–200 grams in adults. Its surface is smooth and convex to match the contour of the diaphragm. Internally, the spleen is divided into two major regions:

    • White pulp: Lymphoid tissue surrounding central arterioles, containing lymphocytes (T and B cells), responsible for initiating immune responses to antigens present in the blood.

    • Red pulp: Composed of splenic sinusoids and cords (of Billroth), this region is responsible for filtering blood, destroying old erythrocytes, and storing platelets and iron.

    The spleen has a hilum on its medial surface, through which the splenic artery, splenic vein, lymphatic vessels, and nerves enter and exit. The organ is enclosed in a dense connective tissue capsule, with internal trabeculae supporting its parenchyma.

    4. Function

    The spleen performs several critical functions, both immunological and hematological:

    • Filtration of blood: Removes senescent red blood cells and platelets, as well as particulate matter and microorganisms.

    • Immune surveillance: Detects and mounts responses against blood-borne pathogens through antigen presentation and lymphocyte activation.

    • Reservoir function: Stores platelets and a small reserve of blood that can be mobilized during hemorrhage or hypovolemia.

    • Hematopoiesis (in fetal life): In the fetus, the spleen contributes to the formation of red and white blood cells before bone marrow becomes the primary hematopoietic organ.

    5. Physiological Role(s)

    In addition to its filtering and immune roles, the spleen is involved in several other physiological processes:

    • Erythrocyte quality control: Old or damaged red blood cells lose flexibility and are removed by splenic macrophages in the red pulp.

    • Iron recycling: The spleen breaks down hemoglobin from senescent RBCs, storing iron for reuse in erythropoiesis.

    • B-cell maturation and antibody production: Especially in the marginal zone of the white pulp, where B cells are exposed to antigens and can become activated to secrete antibodies.

    • Removal of opsonized microbes: The spleen clears circulating bacteria, particularly encapsulated organisms like Streptococcus pneumoniae and Haemophilus influenzae.

    6. Clinical Significance

    Hypersplenism

    Hypersplenism is a condition characterized by an overactive spleen, leading to excessive removal of blood cells, resulting in cytopenias (anemia, leukopenia, thrombocytopenia). It may occur in the setting of chronic liver disease (with splenomegaly), infections, or hematological malignancies.

    Splenomegaly

    An enlarged spleen can be caused by various conditions, including:

    • Infections (e.g., mononucleosis, malaria)

    • Hematologic diseases (e.g., leukemia, lymphoma)

    • Liver cirrhosis with portal hypertension

    • Autoimmune conditions (e.g., systemic lupus erythematosus)

    Massive splenomegaly may lead to abdominal discomfort, early satiety, or rupture from trauma.

    Splenic Rupture

    Due to its friable nature and position beneath the ribcage, the spleen is highly susceptible to injury from blunt abdominal trauma. A ruptured spleen can lead to life-threatening intraperitoneal hemorrhage. It may require emergency splenectomy (surgical removal).

    Asplenia and Postsplenectomy Syndrome

    Loss of splenic function (asplenia), whether congenital or acquired (e.g., post-splenectomy), increases susceptibility to life-threatening infections by encapsulated bacteria. This necessitates vaccination against organisms such as:

    • Streptococcus pneumoniae

    • Haemophilus influenzae type b (Hib)

    • Neisseria meningitidis

    Postsplenectomy patients may also require prophylactic antibiotics and long-term follow-up for infection risk management.

    Accessory Spleens

    Accessory spleens (splenunculi) are small nodules of splenic tissue found in about 10–30% of individuals. They are usually asymptomatic but can become clinically relevant if a splenectomy is performed for hematologic conditions, as the accessory spleen can sustain disease processes.

    Did you know? The lymphatic system is critical for regulating the body's defense mechanisms against harmful pathogens and infections.