Vitamin A deficiency

Etiological forms and mechanisms of development

Retinol deficiency is divided into two main categories: genetically determined and acquired forms.

1. Genetically determined forms are characterized by a hereditarily increased body requirement for retinol. A striking example is Darier's disease (follicular dyskeratosis). Due to a genetic defect, patients require high doses of vitamin A. This disease is characterized by the following symptoms:
2. Skin: marked dryness, formation of thickened crusts.
3. Mucous membranes: dryness of the oral mucosa.
4. Skin appendages: longitudinal ridging and notches of the nail plates.
5. Neuropsychiatric status: tendency toward psychosis and decreased level of mental development.

1. Acquired forms are common and of high clinical significance. Their etiology includes:
2. Dietary deficiency: lack of $\beta$-carotene or retinol in the diet.
3. Malabsorption: gastrointestinal absorption disorders. Bile acids are critically required for the emulsification and assimilation of this fat-soluble vitamin.
4. Transport disorders: disruptions in the retinol delivery system to target cells.

Clinical manifestations of retinol deficiency

Vitamin A deficiency leads to damage to the visual organ, respiratory system, and skin:

• Nyctalopia ("night blindness"): decreased visual acuity at dusk. The pathogenesis is based on dystrophic changes in the retinal rods caused by impaired rhodopsin synthesis.
• Respiratory epithelial metaplasia: normal simple columnar epithelium is replaced by stratified squamous epithelium. This leads to a decline in the barrier function of the respiratory tract and frequent infectious diseases.
• Dermatological disorders: dryness and roughness of the skin develop (hyperkeratosis). Lesions are localized predominantly on the extensor surfaces of the elbow and knee joints.

Impact on systemic metabolism and bone tissue

At the general pathological level, retinol deficiency drives profound disorders in the structure of the osteocartilaginous system and proteins:

• The processes of protein synthesis (proteosynthesis) are slowed down.
• Inhibition of osteogenesis and chondrogenesis occurs.
• Destruction of bone and cartilage tissue progresses.
• Osteoporosis develops, accompanied by calcification of internal organs.

Chronic vitamin A toxicity

Excessive long-term intake of retinol causes hypervitaminosis affecting most body systems:

• Skin and hair: pigmentation, peeling, and skin cracks appear (especially pronounced on the palms and soles). Nails and hair become dry and brittle, and alopecia (hair loss) develops.
• Musculoskeletal system: joint and bone pain occurs, worsening with walking.
• Visceral organs: hepatomegaly and splenomegaly (enlargement of the liver and spleen), loss of appetite, weight loss, nausea, and vomiting are observed.
• Neurological status: increased irritability and insomnia are characteristic.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Pathogenesis of clinical manifestations in Darier's disease
• The role of bile acids in the emulsification and absorption of fat-soluble vitamins
• Mechanisms of metaplasia of columnar epithelium into stratified squamous epithelium
• Disorders of osteogenesis and chondrogenesis in retinol deficiency
• Differential diagnosis of hypovitaminosis A and chronic retinol toxicity

Other topics in "Chapter 14. Vitamin Metabolism Disorders"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.