Pathologies of cellular components

Mitochondrial disorders

Mitochondria are traditionally viewed as the primary power plants of the cell. When their function is impaired, the entire body suffers, but most notably tissues with high energy demands. A typical example of such pathology is mitochondrial cytopathy.

This disease is rooted in a severe molecular defect affecting oxidative phosphorylation processes. As a result, the cell loses its ability to adequately synthesize energy.

• Morphological manifestations: attempting to compensate for the escalating energy deficit, muscle tissue responds with structural changes. Under the microscope, a marked increase in mitochondrial size, as well as a significant rise in their total number within the muscle fibers, can be detected.
• Clinical presentation: paradoxically, patients exhibit an extremely high overall metabolic rate. During differential diagnosis, it is crucial for the physician to consider that this hypermetabolism occurs completely without signs of hyperthyroidism, which rules out primary thyroid pathology.

Lysosomal storage diseases

Lysosomes function as the intracellular digestive system, containing hydrolytic enzymes necessary for clearing cellular debris. Molecular defects in these enzymes cause undigested substrates to fatally accumulate inside cells.

1. Metachromatic leukodystrophy. The disease is triggered by a deficiency of a specific enzyme—lysosomal sulfatase.
2. Morphology: due to the enzymatic block, massive accumulation of complex lipids, specifically cerebrosides, begins in the tissues.
3. Clinical presentation: the toxic effect of accumulated cerebrosides on the nervous system leads to severe consequences. Patients develop pronounced motor disorders, which are invariably accompanied by profound psychiatric disturbances.

1. Hurler syndrome. In this case, the molecular defect consists of a severe shortage of lysosomal α-L-iduronidase.
2. Morphology: the substrate that cannot be utilized and accumulates in tissues is dermatan sulfate.
3. Clinical presentation: the systemic accumulation of dermatan sulfate catastrophically affects organism development, causing severe physical growth retardation and profound intellectual disability in the patient.

Secretory granule pathologies

Secretory granules are responsible for the storage and subsequent exocytosis of cell-synthesized substances, including hormones. Disruption of their function can lead to major endocrine disorders. A striking example is proinsulin diabetes.

• Molecular defect: the disease arises due to a breakdown of the proinsulin-cleaving enzyme. Normally, this enzyme should convert the inactive precursor into the active hormone inside the granule.
• Morphology: a distinctive feature of this pathology is that visible morphological changes at the cellular and tissue levels are completely absent.
• Clinical presentation: due to the granules' inability to cleave the precursor, an abnormally high concentration of proinsulin is recorded in the patient's blood. Clinically, this condition manifests as classical diabetes.

Golgi complex disorders

The Golgi complex plays a key role in sorting, modifying, and packaging macromolecules. Failures in its operation disrupt the distribution of enzymes to other organelles, leading to intracellular chaos. Among such pathologies is I-cell disease.

• Molecular defect: the disease is based on a marked deficiency of the enzyme phosphotransferase.
• Morphology: impaired intracellular transport leads to the formation and massive accumulation of pathological inclusions within fibroblasts.
• Clinical presentation: the disease has a severe systemic course. Patients are diagnosed with pronounced psychomotor retardation, alongside the development of gross skeletal abnormalities.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Oxidative phosphorylation defect in mitochondrial cytopathy.
• The role of sulfatase and the consequences of cerebroside accumulation in nervous tissue.
• Dermatan sulfate metabolism and the functions of α-L-iduronidase in Hurler syndrome.
• The mechanism of action of the proinsulin-cleaving enzyme in secretory granules.
• Phosphotransferase deficiency and the pathogenesis of I-cell disease.

Other topics in the section "The Cell — The Elementary Unit of Life"

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