Lecture 5: Disturbances of Growth

Questions:

1. What are the key factors involved in growth disturbances?

2. What are the types of disturbances of growth?

   1. What is agenesis, aplasia, and atresia?

   2. What is hypoplasia?

   3. What is atrophy?

   4. What is hypertrophy?

   5. What is hyperplasia?

   6. What is metaplasia?

   7. What is dysplasia?

3. What are other relevant terms related to growth disturbances?

4. What are regeneration and repair in the context of tissue response?

   1. What is regeneration?

   2. What is repair?

5. What are the notes on presentation sources?

SUMMARY:

🦠 Disturbances of Growth

In general, disturbances of growth usually involve:

• The number of cells in a tissue or organ

• The size of cells

• A combination of the number and size of cells

• A change from the normal in the relationship of cells or tissues to each other

👶 Agenesis, Aplasia, Atresia

• Agenesis

  Tissue or organ is not developed and is absent. For example, one kidney might be absent at birth.

• Aplasia

  Organ is present but markedly reduced in size, such as the absence of gonads or one horn of the uterus.

• Atresia

  Orifice or passage in the body is closed or not developed, for example, atresia ani.

📉 Hypoplasia

This disorder occurs during the period of growth, usually before birth, but also during postnatal growth. Genetic defects, certain infectious agents, and certain poisons can lead to hypoplasia.

萎 Atrophy

Atrophy can occur in two ways:

• Numerical

• Quantitative

Causes of Atrophy:

• Starvation and malnutrition: The lesion is most evident on the heart and around the kidneys, as well as in mesenteries.

• Lack of adequate blood supply: This brings a deficiency of oxygen.

• Disuse atrophy: This means uniformly reduced tissue.

• Pressure: This may also result in a slow localized loss of cells through degeneration and necrosis.

• Disturbances of endocrine glands

• Prolonged overwork

• Physiologic involution of the uterus and mammary glands following pregnancy and lactation, respectively

Atrophy Classification

• Simple atrophy

• Fatty atrophy

• Fibrous atrophy

• Pigment atrophy

• Mucoid atrophy

💪 Hypertrophy

Types of Hypertrophy:

1. Compensatory or adaptive hypertrophy: If part of an organ or one of a pair of organs is lost, compensatory hypertrophy may occur in the remaining part of the organ.

2. Hormonal hypertrophy: This most often is a physiologic phenomena but in some instances may be pathologic.

增 Hyperplasia

It can present in diffuse form or as nodular hyperplasia. Hyperplastic condition of the epidermis may take the form of:

• Increased thickness of the prickle – cell layer, which is known as acanthosis

• Increased thickness of the cornified layer, which is called hyperkeratosis

Hyperplasia, which accompanies many forms of chronic inflammation with its associated fibrosis, as in hepatic cirrhosis, may result in the formation of circumscribed, expanding nodules of proliferating cells.

Types of Hyperplasia:

• Compensatory or adaptive hyperplasia

• Hormonal hyperplasia

🔄 Metaplasia

The new adult cell types are derived from reserve cells, which are pluripotential for differentiation.

Examples:

• Squamous metaplasia

• Metastatic bone

• Myeloid metaplasia

Metaplasia is almost always reversible, but it may precede neoplastic transformation.

畸 Dysplasia

Dysplastic cells vary in size, shape, and staining characteristics. Within a multi-layered epithelial lining, the arrangement of cells to each other may vary, and the cells may develop an anaplastic appearance. This example of dysplasia may be a form of hyperplasia and hypertrophy and could, depending on the location, be a preneoplastic lesion. Dysplasia and hyperplasia may progress to a truly neoplastic appearance (carcinoma in situ).

➕ Other Terms Related to Growth

🧬 Regeneration

• Physiological regeneration examples: cover epithelium, adenomatous epithelium, erythrocytes, white blood cells

• Pathological regeneration: after a pathological process

Regeneration can be:

• Complete healing (per primam intentionem)

• Incomplete (per secundam intentionem)

• Superregeneration (caro luxurians – chronic inflammation)

🛠 Reparation

Process:

• Resorption: enzymatic digestion, phagocytosis

• Granulation tissue formation

Granulation tissue: not matured fibrous tissue with proliferating fibroblasts and growing capillaries in damaged tissue

Reparation Timeline:

• Fibroblasts, vascular proliferation: 48 – 72 hours

• Macrophages: 18 hours, lymphocytes: 26 hours, plasma cells: 7 days

• Fibrillary substances and argyrophilic fibers: 8 – 10 days, collagenous: 6 – 25 days, scar: 3 – 5 months