Lecture 5: Disturbances of Growth

What are the general aspects involved in disturbances of growth?

• 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

Define Agenesis.

Tissue or organ is not developed and is absent.

Example: One kidney might be absent at birth.

Define Atresia.

Orifice or passage in the body is closed or not developed. (atresia ani)

Define Aplasia.

Organ is present but markedly reduced in size.

Example: Absence of gonads or one horn of the uterus.

Define Hypoplasia.

Tissue or organ did not reach its normal size or structure

• occurs during the period of growth

• can be caused by genetic defects, infectious agents, and certain poisons

Define Atrophy.

A decrease in the amount of tissue after normal growth has been achieved. (tissue decreases in size after already reaching normal growth).

• Can occur numerically (fewer cells) or quantitatively (smaller cells)

List the causes of atrophy.

• Starvation and malnutrition

• Lack of adequate blood supply

• Disuse atrophy (use it or loose it, when a tissue is not used regularly → uniformly reduced tissue).

• Pressure (slow, localized cell loss by degeneration and necrosis)

• Disturbances of endocrine glands

• Prolonged overwork

• Physiologic involution of uterus and mammary glands

What are the different types of atrophy?

1. Simple atrophy

2. Fatty atrophy

3. Fibrous atrophy

4. Pigment atrophy

5. Mucoid atrophy

Define Hypertrophy.

An increase in tissue resulting from an increase in the size of individual cells.

What are the types of Hypertrophy?

1. Compensatory or adaptive hypertrophy: when a part of an organ is lost, the rest of the organ tries to pick up the slack and grows bigger.

2. Hormonal hypertrophy: usually normal, but can sometimes be pathological.

Define Hyperplasia.

An increase in the number of cells in a tissue or an organ; can be diffuse or nodular.

What forms can hyperplasia take in the epidermis?

Acanthosis: Increased thickness of the prickle – cell layer

Hyperkeratosis: Increased thickness of the cornified layer

What are the types of Hyperplasia?

Hyperplasia may occur in the context of chronic inflammation and fibrosis, such as hepatic cirrhosis (liver disease). In these situations, the hyperplasia can lead to formation of circumscribed, expanding nodules of proliferating cells.

1. Compensatory or adaptive hyperplasia: when part of organ is lost or damaged, remaining tissue proliferates to compensate the loss.

2. Hormonal hyperplasia: by hormones, physiological or pathological.

Define Metaplasia.

meaning when one type of mature cell is replaced by a different type of mature cell. These new cell types come from reserve cells that can differentiate into various cell types.

almost always reversible, but may also occur before a tissue or cells become cancerous (neoplastic).

What are some examples of Metaplasia?

Squamous metaplasia, Metastatic bone, Myeloid metaplasia

Define Dysplasia.

An abnormally developed tissue.

• cells vary in size, shape, and staining characteristics

• may be a form of hyperplasia and hypertrophy or it could be a preneoplastic lesion

Define Euplasia.

Normal growth.

Define Proplasia.

A slight increase or stimulation of growth.

Define Retroplasia.

Decreased growth activity through injury or aging.

Define Anaplasia.

Cells and tissues that are poorly differentiated.

Define Regeneration.

New tissue is completely the same as original damaged tissue, morphologically and functionally. Process of damaged tissue being replaced by new tissue.

Types:

1. By origin:

   • Physiological regeneration: happening naturally in tissues like cover epithelium, RBCs, WBCs

   • Pathological regeneration: Happening after a disease/injury.

What are the three types of Regeneration based on completeness?

1. Complete healing- tissue returns to original state

2. Incomplete - atypical healing, does not fully restore to original state

3. Superregeneration - excessive regeneration, linked with chronic inflammation

Reparation and process

Restoration of damaged tissue, which was not regenerated.

Process:

1. Resorption: enzymatic digestion and phagocytosis

2. Granulation tissue formation: development of immature fibrous tissue, proliferating fibroblasts, growing capillaries.

What is the Reparation Timeline?

• 48-72 hours: Fibroblasts appear and vascular proliferation begins

• 18 hours: Macrophages appear

• 26 hours: Lymphocytes appear

• 7 days: Plasma cells appear

• 8-10 days: Fibrillary substances and argyrophilic fibers form

• 6-25 days: Collagenous fibers develop

• 3-5 months: Complete scar formation