Section 14: Key Points
What We've Covered
This section made the following main points:
What We've Covered
This section made the following main points:
- To maintain homeostasis, cells and tissues undergo:
- Physiological adaptation, which is beneficial in nature — for example, increased skeletal muscle cells in athletes.
- Pathological adaptation, which is detrimental — for example, cellular changes in people who smoke cigarettes.
- Specific types of adaptation include:
- Atrophy — a decrease in the size of cells.
- Hypertrophy — an increase in the size of individual cells.
- Hyperplasia — an increase in the number of cells in a tissue.
- Metaplasia — the conversion from one type of mature cell to another type.
- Dysplasia — abnormal cell changes or deranged cell growth.
- Anaplasia — cells that are undifferentiated.
- Neoplasia — new growth of tissue.
- Most toxic effects, especially due to xenobiotics, are due to specific biochemical interactions without causing recognizable damage to a cell or its organelles. Cellular or biochemical toxicity leads to:
- The tissue being completely repaired and returned to normal.
- The tissue being incompletely repaired but capable of functioning with reduced capacity.
- Death of the organism or complete loss of a tissue or organ.
- Neoplasm or cancers.
- Tumors are either:
- Benign — similar to the cell of origin, slow-growing, and usually without systemic effects.
- Malignant — dissimilar from the cell of origin, rapid-growing, and commonly with systemic effects and life-threatening. Most malignant tumors are either:
- Carcinomas — arising in epithelium, the most common form of cancer, usually spread in the lymphatic system.
- Sarcomas — arising in connective or muscle tissue, usually spread by the blood stream.
- Carcinogenesis is a multi-step, multi-factorial genetic disease consisting of at least three main phases:
- Initiation — irreversible alteration of the DNA (mutation) of a normal cell.
- Promotion/Conversion — promoters enhance further development of the initiated cells, often influencing further expression of the mutated DNA such that the initiated cell proliferates and progresses further.
- Progression — development of the initiated cell into a biologically malignant cell population, often with metastasis to other areas of the body.
- Regulatory genes control the activity of structural genes and direct the proliferation process of the cell. Regulatory genes that play roles in carcinogenesis include:
- Proto-oncogenes — normal cellular genes that encode and instruct the production of regulatory proteins and growth factors within a cell or its membrane.
- Oncogenes — altered or misdirected proto-oncogenes with the ability to direct the production of proteins within the cell that change or transform the normal cell into a neoplastic cell.
- Tumor suppressor genes (anti-oncogenes) — present in normal cells and counteract and change the proto-oncogenes and altered proteins, preventing a cell with damaged DNA from proliferating and evolving into an uncontrolled growth.
- The p53 gene normally halts cell division, stimulates repair enzymes, and if necessary, commands the mutated cell to self-destruct
- p53 is the most frequently altered in human tumors and is incapable of its defense mechanisms
- Toxic damage to the nervous system is divided into three categories:
- Damage to sensory receptors and sensory neurons impacting the sensory functions.
- Damage to motor neurons causing muscular weakness and paralysis.
- Interneuronal damage causing learning deficiencies, memory loss, incoordination, and emotional conditions.