Morphology in biology is the study of the shape, size, and structure of organisms. Morphologic changes are alterations to this form and structure, occurring on a microscopic level within cells or on a macroscopic scale affecting entire organs. These changes are important for understanding how the body functions in both healthy and diseased states.
Foundations of Cellular Change
All major changes in a tissue or organ begin at the cellular level. When faced with stress or injury, cells can undergo structural alterations in size and shape. While healthy cells have a regular, predictable shape, damaged or cancerous cells may appear irregular. These shifts are visible under a microscope and serve as indicators of cellular health.
A cell’s internal components can also be modified. The nucleus may change in size, become misshapen, or show an altered pattern of chromatin. Within the cytoplasm, abnormal accumulations can occur, such as droplets of lipids, collections of proteins, or pigments like melanin or lipofuscin.
These microscopic alterations are the earliest detectable signs of a problem. Cellular swelling, or hydropic change, is one of the first results of cell injury. It is caused by a failure of membrane pumps that leads to an influx of water, allowing pathologists to identify disease processes early.
Adaptive Changes in Tissues
Tissues and organs can alter their structure in response to new or persistent stressors. These adaptive changes are organized, functional responses that allow the tissue to cope with a new environment. When the stress is removed, these changes are often reversible, allowing the tissue to return to its original state.
One adaptation is atrophy, a decrease in cell size that reduces an organ’s size, such as muscle wasting from disuse. Conversely, hypertrophy is an increase in cell size, resulting in an enlarged organ. The heart muscle of an athlete or a person with chronic high blood pressure undergoes hypertrophy to handle an increased workload.
Tissues also adapt by changing cell number. Hyperplasia is an increase in the number of cells, seen in the glandular tissue of the female breast during pregnancy. Another adaptation is metaplasia, where one mature cell type is replaced by another. For example, in response to chronic irritation from cigarette smoke, the cells lining the airways can be replaced by more resilient cells.
Disordered Growth and Disease
Sometimes, cellular growth becomes disordered and is no longer a controlled, adaptive response. These pathological changes represent a departure from normal function and can be a precursor to disease. The uncontrolled proliferation disrupts tissue function.
An example of disordered growth is dysplasia, an abnormality in cell maturation and organization within a tissue. The cells vary in size and shape, and their architectural orientation is disturbed. Cervical dysplasia, detected through a Pap smear, is a well-known example where these changes are considered a potential step toward cancer.
When disordered growth becomes autonomous, it is called neoplasia, or “new growth.” Neoplasms are tumors, which can be benign or malignant. Cancer cells exhibit distinct features, including large, irregular nuclei, a loss of resemblance to their tissue of origin, and a disorganized arrangement, reflecting their uncontrolled growth.
Methods of Observation
Scientists and medical professionals use several techniques to identify morphologic changes. The primary method for examining tissues is histology, which involves preparing a tissue sample, known as a biopsy, for examination under a microscope. The sample is preserved, sliced into thin sections, and treated with stains to highlight different cellular components.
For examining individual cells, a less invasive technique called cytology is used. It involves collecting cells that have been shed from a surface or are suspended in fluid. The Pap smear is a classic example, where cells are collected from the cervix to be examined for dysplastic changes.
Larger, organ-level alterations are visualized using medical imaging. Technologies like X-rays, CT scans, and MRI can detect changes such as organ enlargement or the presence of a tumor. These tools provide a non-invasive way to see structural changes within the body, guiding further diagnostic steps.