Abnormal morphology refers to deviations from the standard, expected shape, structure, or form of a biological entity, whether it is a whole organism, an organ, or a single cell. Morphology is concerned with the size, structure, and configuration of living things, from molecules to anatomy. Because the relationship between form and function is foundational in biology, any change in structure often directly impairs the ability of that cell or organism to perform its role.
A red blood cell, for example, is normally a biconcave disc designed to maximize oxygen transport; any alteration to that shape can compromise its function. Abnormal morphology is not merely a visual curiosity but frequently serves as a diagnostic indicator of underlying disease or dysfunction. This concept applies across all levels of life, from protein configuration to the entire body plan of an animal.
Understanding the Underlying Causes
The origins of abnormal morphology are generally categorized into three primary areas: genetic factors, acquired factors, and developmental errors. Genetic factors involve DNA mutations that alter the blueprint for proteins or regulatory elements, thereby changing the structure of cells and tissues. These mutations can be inherited or occur spontaneously, leading to conditions where the body produces structures with an incorrect form.
Acquired factors are external influences that damage or disrupt normally formed structures. These include environmental exposures such as toxins, certain drugs, or infectious agents that interfere with cell development or maintenance. Chronic diseases, including diabetes or autoimmune conditions, can also lead to morphological changes by creating a toxic or inflammatory environment.
Developmental errors arise during the complex process of embryonic growth. These errors can result from chromosomal abnormalities (too many or too few chromosomes) or from structural errors during cell division. These issues cause malformations when tissues and organs are first being formed, resulting in a shape that deviates from the normal pattern.
Morphological Deviations in Blood Cells
The analysis of blood cell morphology is a routine diagnostic tool in clinical medicine. Normal red blood cells (RBCs) are flexible, uniform biconcave discs, but changes in their shape, known as poikilocytosis, often signal specific pathologies. For instance, sickle-shaped cells result from a point mutation that causes hemoglobin to polymerize, deforming the cell and leading to sickle cell disease.
Another abnormal form is the spherocyte, a spherical red cell lacking the central pale area of a healthy disc, characteristic of hereditary spherocytosis or autoimmune hemolytic anemia. Fragmented RBCs, called schistocytes, are sharp-edged pieces indicating mechanical destruction, often caused by turbulent blood flow or microangiopathic conditions. Teardrop cells, or dacryocytes, are associated with bone marrow disorders like myelofibrosis, where the cells are squeezed out of damaged marrow.
White blood cells (WBCs) also exhibit morphological deviations that aid diagnosis. In conditions like leukemia, WBCs may display abnormal nuclear shapes or an excessive number of immature cells, known as blasts, which disrupt the normal differentiation process. WBCs can also show changes in size or stiffness in response to chronic conditions, such as increased rigidity observed in leukocytes from diabetic patients. Identifying these subtle changes on a peripheral blood smear provides immediate clues about systemic health.
Morphology and Male Reproductive Health
Sperm morphology, the assessment of sperm size and shape, is a significant component of male fertility testing. A morphologically normal sperm has a smooth, oval-shaped head, a distinct midpiece, and a single, uncoiled tail. The head contains the genetic material and must be properly formed to penetrate the egg, while the midpiece and tail are necessary for energy and propulsion.
Specialized testing, often using the strict Kruger criteria, defines normal morphology with high precision, requiring a minimum percentage of sperm to meet exact specifications. A sample only needs 4% or more normally shaped sperm to be considered to have fertility potential. This low threshold reflects the fact that all males produce a high percentage of abnormally shaped sperm.
Deviations from the normal shape can take many forms, including macrocephalic sperm (giant heads), microcephalic sperm (tiny heads), or sperm with multiple heads or tails. Head abnormalities, such as an amorphous or tapered shape, can impair the sperm’s ability to fertilize the egg. Defects in the tail, such as a coiled or stump tail, can severely compromise motility, preventing the sperm from reaching the egg.