Blood-forming Organs and Immune System

In the following, “Blood-forming organs and immune system” describes diseases that are assigned to this category according to ICD-10 (D50-D90). The ICD-10 is used for the International Statistical Classification of Diseases and Related Health Problems and is recognized worldwide.

Blood-forming organs and immune system

During the embryonic period, blood is formed primarily in the liver and spleen. After birth, blood formation (hematopoiesis) takes place in the bone marrow (medulla ossium), also called the “myelotic system.” If hematopoiesis in the bone marrow is impaired by chronic disease or direct damage to the bone marrow, the liver and spleen take over the task of hematopoiesis. This is called “extramedullary hematopoiesis.” The bone marrow is a soft tissue that fills the cavities of all bones. A distinction is made between red (blood-forming) bone marrow and yellow (fat-storing, non-blood-forming) bone marrow. After birth, initially only red bone marrow is present. From about the age of 5, this gradually withdraws from most bones and is replaced by yellow marrow. In an adult, red bone marrow is found only in the epiphyses (joint ends) of the long bones and in the bones of the axial skeleton (spinal column incl. small vertebral joints, sacroiliac joint (ISG; sacroiliac joint), pubic symphysis). Blood formation then takes place primarily in the bones of the spine, hip, shoulder, ribs, sternum, as well as in the bones of the skull. All blood cells originate from common cells, the stem cells. These are cells that are not yet differentiated (fully developed). The stem cells can either proliferate by cell division or become precursor cells for the two lines of blood cells (blood corpuscles), the myeloid cells and the lymphoid cells. These continue to divide and mature, that is, they differentiate into various types of mature blood cells, which then pass from the bone marrow into the blood. The myeloid progenitor cells are called pluripotent or multipotent. They give rise to the following blood cells:

  • Erythrocytes (red blood cells) → oxygen transport.
  • Platelets (blood platelets) → blood clotting.
  • Monocytes (belong to the white blood cells) – precursors of macrophages, which play an important role in the immune defense as “scavenger cells”.
  • Granulocytes (eosinophils, basophils, neutrophils → immune defense).

The lymphoid progenitor cells are called determinate because they differentiate into only one or two closely related cell types. They give rise to:

  • Lymphocytes – do not reach full maturity and thus functional capacity until they reach lymphoid tissue, which includes lymph nodes, tonsils, spleen, thymus, and intestine
    • B cells (B lymphocyte).
    • T cells (T lymphocyte)
    • Natural killer cells (NK cells)

Since most blood cells have a limited lifespan, they must be constantly replenished (several billion cells per day). Thus, the life span of erythrocytes (red blood cells) is 30-120 days and platelets (blood platelets) 3-12 days. The functions of the bone marrow also include the breakdown of aged erythrocytes. SpleenThe spleen (splen) is located in the left upper abdomen, below the diaphragm and behind the stomach. It weighs between 150 and 200 g. It can be divided into a red and white pulp, which have different functions. For example, the spleen is a filtering station of the blood: overaged and damaged erythrocytes and platelets are filtered and broken down by macrophages (phagocytes). This process, which takes place in the red pulp, is called blood cell molt (blood purification). In addition, the spleen has an immunological function (white pulp): B and T lymphocytes multiply and mature in it. The spleen is also the storage place of monocytes. Despite its important functions, the spleen is not a vital organ. LiverThe liver (hepar) is located in the right upper abdomen. It weighs between 1,400 and 1,800 g. It is the largest metabolic organ in humans. The main functions of the liver include:

In the fetus, the liver is involved in blood formation until the 7th month of pregnancy. After birth, it takes over this task only if the bone marrow is impaired in its hematopoietic function. Immune systemThe immune system (the body’s defense system) is divided into the lymphatic organs, which include the bone marrow, the lymphatic vascular system and the blood. The blood contains elements of the body’s defense system, namely the blood cells generated from stem cells in the bone marrow during hematopoiesis and matured in the lymphatic system. The lymphoid organs are classified as follows:

  • Primary lymphoid organs-differentiation of progenitor cells into immunocompetent T and B lymphocytes.
  • Secondary lymphoid organs – triggering a specific immune response.
    • Spleen
    • Lymph nodes
    • Tonsils (tonsils)
    • Appendix (appendix; vermiform appendix)
    • Lymphoid follicle (lymph nodule) – B lymphocytes
    • Peyer’s plaques – accumulation of 10-50 lymphoid follicles, which are found throughout the small intestine and are of importance in the intestinal defense against infection.

In the event of infection, the hematopoietic system produces more cells of the immune system. The body’s immune defense includes the following cells:

  • Granulocytes → rapid destruction or defense against bacteria.
  • Monocytes (become macrophages/”phagocytes”) → destruction of exogenous structures by phagocytosis (“eating the cell”).
  • Lymphocytes → defense against viruses and formation of antibodies.
    • B cells
    • T cells
    • Natural killer cells (NK cells)

Granulocytes, monocytes and lymphocytes are grouped under the term leukocytes (white blood cells). If the hematopoietic system is damaged or impaired in its function, this consequently also affects the immune defense, since the corresponding blood cells are not formed as required.

Common or important diseases of the hematopoietic organs and the immune system

  • Bleeding tendency
  • Iron deficiency anemia
  • Folic acid deficiency anemia
  • Hematuria (blood in the urine)
  • Hemophilia (hemophilia)
  • Immunodeficiency / immunodeficiencies
  • Diseases of the spleen – e.g. abscess or cyst of the spleen, rupture of the spleen (non-traumatic), asplenia (absence of the spleen due to splenectomy (removal of the spleen)).
  • Leukemias*
  • Purpura Schönlein-Henoch (PSH) – immunologically mediated vasculitis (vascular inflammation) of the capillaries and pre- and post-capillary vessels.
  • Purpura and petechiae (bleeding into the skin and mucous membranes).
  • Thrombocytopenia – the number of platelets (thrombocytes) in the blood is less than 150,000/μl (150 x 109/l)
  • Vitamin B12 deficiency anemia

* Leukemias = cancers of the hematopoietic system in the bone marrow. Based on their ICD-10 designation – C81-C96 – they are classified as “Malignant neoplasms of lymphoid, hematopoietic and related tissues, determined or suspected to be primary” under “neoplasms”, but are included here due to their pathogenesis (disease development).

Major risk factors for diseases of the hematopoietic organs and the immune system

Behavioral causes

  • Diet
    • Unbalanced diet
    • Vegetarian, vegan
  • Consumption of stimulants
    • Alcohol consumption
    • Smoking
  • Physical activity
    • Competitive sports
  • Overweight
  • Underweight

Causes due to disease

  • Anorexia nervosa (anorexia nervosa)
  • Blood clotting disorders
  • Bleeding (blood loss, especially in chronic gynecological or gastrointestinal bleeding)/bleeding anemia.
  • Chronic inflammatory bowel disease such as ulcerative colitis or Crohn’s disease/inflammatory anemia.
  • Chronic infections
  • Chronic renal failure
  • Chronic pancreatitis (inflammation of the pancreas)
  • Diabetes mellitus – diabetes mellitus type 1, diabetes mellitus type 2
  • Gastritis (inflammation of the gastric mucosa)
  • Helminthiasis (worm diseases)
  • Influenza A (flu/viral disease)
  • Gastric ulcers (stomach ulcers)
  • Parvovirus infections, e.g. ringworm (erythema infectiosum).
  • Streptococcal diseases (ß-hemolytic streptococci).
  • Tumor diseases of all kinds, especially of the lymphatic and hematopoietic systems.
  • Varicella (chickenpox)

Medication

Operations

  • Gastrectomy (stomach removal)
  • Small bowel resection (removal of the small bowel).

Environmental pollution – intoxications (poisoning).

  • Radiation exposure in early childhood

Please note that the enumeration is only an extract of the possible risk factors. Further causes can be found under the respective disease.

The main diagnostic measures for diseases of the hematopoietic organs and the immune system

  • Small blood count
  • Differential blood count
  • Coagulation parameters, coagulation factors
  • Inflammation parameters
  • Liver parameters
  • Thyroid parameters
  • Urine status
  • Sonography (ultrasound) of the affected body region
  • X-ray of the affected body region
  • Computed tomography (CT; sectional imaging procedure (X-ray images from different directions with computer-based evaluation)) of the affected body region.
  • Magnetic resonance imaging (MRI; computer-assisted sectional imaging procedure (using magnetic fields, that is, without X-rays)) of the affected body region.
  • Bone marrow biopsy
  • If ulcers (boils), tumors, or bleeding of other genesis (cause) are suspected.

Which doctor will help you?

For diseases of the hematopoietic organs and the immune system, the first point of contact is the family doctor, who is usually a general practitioner or internist. Depending on the disease or its severity, a presentation to an appropriate specialist, the hematologist, may be required.