Physiological role of the spleen
The spleen is a specialized lymphoreticular organ that serves as one of the main components of the human immune system. Its normal physiology includes a whole complex of vital tasks.
First, it ensures the formation of adequate cellular and humoral responses in response to antigen entry. Second, the organ functions as a powerful biological filter: it is responsible for eliminating microorganisms and certain antigens from the systemic bloodstream, as well as recognizing and subsequently removing aging or pathologically altered formed blood elements. In addition, the spleen takes an active part in regulating portal blood flow and is capable of assuming the function of extramedullary hematopoiesis (blood formation outside the bone marrow).
Splenomegaly: causes and focal changes
Splenomegaly (splenomegalia) is a pathological enlargement of the spleen. This condition is rarely an independent disease; most often it acts as an indicator of other serious pathological processes in the body.
The etiology of splenomegaly is extremely diverse and includes the following groups of causes:
- Infectious lesions: viral, bacterial, and protozoan infections.
- Immunopathological processes: including systemic amyloidosis.
- Local and systemic blood flow disorders: primarily venous congestion.
- Hematologic diseases and malignant tumors.
- Lysosomal storage diseases.
Upon macroscopic and microscopic examination, specific focal changes may be detected in the enlarged tissue. These are most characteristic of conditions such as sepsis, tuberculosis, and syphilis. A focal pattern is also observed in the formation of cystic changes, organ infarctions, hematomas, and malignant tumor metastases.
Hypersplenism: pathogenesis and classification
Hypersplenism is a severe clinical syndrome in which splenomegaly is accompanied by a pathological increase in organ function.
The pathogenesis of this condition is based on two interrelated mechanisms. On the one hand, massive destruction or excessive accumulation (sequestration) of formed blood elements occurs directly within the splenic tissue. On the other hand, there is a secondary suppression of bone marrow hematopoiesis. The clinical and laboratory manifestations of hypersplenism include pronounced bleeding and characteristic changes in the blood count: anemia, leukopenia, and thrombocytopenia.
In clinical practice, two forms of the syndrome are distinguished:
- Primary hypersplenism. Associated with prolonged "working hypertrophy" of the organ. It is often congenital in nature and accompanies such pathologies as congenital hemolytic anemia, thalassemia, and various hemoglobinopathies.
- Secondary hypersplenism. Develops as a complication of other diseases:
- Infections: malaria, typhoid fever, tuberculosis.
- Systemic diseases: Boeck's sarcoidosis, amyloidosis.
- Liver and vascular pathology: liver cirrhosis, portal or splenic vein thrombosis.
- Tumors and storage diseases: Hodgkin's lymphoma, Gaucher disease.
The clinical significance of hypersplenism lies in the fact that it is a direct manifestation of impaired blood-destroying function. This leads to a significant aggravation of the patients' general condition. In most cases, conservative therapy proves ineffective, and patients require surgical intervention — splenectomy (removal of the organ).
Hyposplenism
Hyposplenism is a condition characterized by reduced spleen function or its complete absence.
The causes of hyposplenism can include congenital organ agenesis, targeted surgical removal (splenectomy), or pathological occlusion of microcirculatory vessels leading to the death of functional tissue.
The manifestations of hyposplenism in the peripheral blood are the exact opposite of hypersplenism. Patients exhibit erythrocytosis, which very frequently occurs in combination with leukocytosis and thrombocytosis. The main consequences of this condition are associated with the loss of the organ's role as a biological filter. This leads to a sharp decrease in the body's non-specific resistance and a profound disruption of the immune status, making the patient extremely vulnerable to infectious agents.
Briefly: answers to topical questions
What macroscopic and microscopic changes occur in the spleen during sepsis?
In sepsis, the so-called "large septic spleen" is formed.
Macroscopic changes:
- The spleen is enlarged.
- The organ is flabby.
- The pulp yields an abundant scraping.
Microscopic changes:
- Pronounced leukocytosis.
- Neutrophilic infiltration of the splenic tissue.
What is the mechanism of splenomegaly development in liver cirrhosis?
The mechanism of splenomegaly development in liver cirrhosis is due to portal hypertension syndrome. The diffuse sclerotic process in the liver compresses the microvasculature, leading to impaired blood flow and increased pressure in the portal vein system.
The pathogenesis includes the following factors:
- Pronounced venous congestion.
- Diffuse hyperemia, distension of sinusoids with blood.
- Fibrosis (sclerosis) and hemosiderosis of the red pulp.
- Formation of arteriovenous shunts that further exacerbate portal hemodynamic disorders.
What does the spleen look like in Gaucher disease?
In Gaucher disease, splenomegaly develops in the spleen.
The microscopic picture is characterized by an increase in the absolute number of macrophages and the formation of specific storage cells — Gaucher cells. These are macrophages overloaded with lipids in their lysosomes. The accumulation of these cells is associated with chronic activation of the macrophage system and autocrine stimulation of monocytopoiesis due to a hereditary deficiency in β-D-glucocerebrosidase activity.
To memorize the hypersplenism triad in blood tests, use the "ALT" rule: Anemia, Leukopenia, Thrombocytopenia. All parameters drop due to excessive cell destruction in the spleen.
Class and exam questions
What is the difference between splenomegaly and hypersplenism?
Splenomegaly is the physical enlargement of the organ's size. Hypersplenism is a functional syndrome in which the enlarged spleen begins to destroy blood cells too actively.
How does hypersplenism affect the bone marrow?
It causes suppression of bone marrow hematopoiesis, which exacerbates the deficiency of formed elements in the peripheral blood.
What blood changes are characteristic of hyposplenism?
When spleen function is reduced or absent, erythrocytosis is observed, often accompanied by elevated white blood cell and platelet counts.
What else to study on this topic
- Mechanisms of extramedullary hematopoiesis
- Focal lesions of the spleen in tuberculosis and syphilis
- Congenital hemolytic anemias as a cause of primary hypersplenism
- Storage diseases (Gaucher disease) and their impact on lymphoreticular tissue
- Portal hypertension and venous congestion in liver cirrhosis
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