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Types of Cell Shape

Although cells may share a host of characteristics, they, no less than dogs, exhibit astonishing variety in shape. In fact, the difference in shape between two cells might make the difference between a Saint Bernard and a Chihuahua look minor. This is because cells participate in biological functions ranging from respiration to reproduction. Cell shapes reflect the varied nature of those functions.

  1. Red Blood Cells

    • A red blood cell resembles a doughnut with a center depression on each side instead of a hole, observes the book "Human Physiology, 8th Ed.," by Arthur Vander et al. By imparting to the cell a high surface-to-volume ratio, the doughnut shape facilitates the diffusion of oxygen and carbon dioxide to and from the red blood cell's interior, note the authors. This maximizes the cell's ability to deliver oxygen to other cells while picking up the waste product carbon dioxide.

    White Blood Cells

    • Certain white blood cells, called neutrophils and macrophages, can change shape to enable them to engulf microbes that invade the body. Known as phagocytosis, this engulfing process starts with extensions of the white blood cell's cytoplasm, according to the book "Microbiology, 5th Ed.," by Jacquelyn G. Black. These extensions, known as pseudopodia because they resemble pairs of limbs, surround the invading microbe, then bring it into the cell where enzymes and other chemicals can digest it.

    Nerve and Muscle Cells

    • Nerve cells (neurons) range in length from less then 1 mm to long enough to span the distance from just above your waist to your toes, observes Gerard Tortora in his book "Principles of Human Anatomy, 9th Ed." The neuron's elongated shape facilitates the conduction of signals to muscles, telling the muscles when to contract or relax. Like neurons, skeletal muscle cells also have an elongated shape. Known as fibers, muscle cells form during embryonic development from the fusion of a hundred or more precursor cells, resulting in fibers that can shorten (contract) or lengthen (relax).

    Embryonic and Skin Cells

    • Some cells exhibit extensions. For example, seven days after fertilization, when the fertilized human egg reaches the uterus, its outer cellular layer, the trophoblast, extends fingerlike projections into the surrounding maternal tissue, according to the book "Biology, 5th Ed.," by Neil Campbell et al. These projections enable the fertilized egg to implant itself in the uterine wall. Also possessed of extensions are the skin cells known as melanocytes, which compose about 8 percent of the epidermis (the skin's outer layer), notes Tortora. To transfer melanin to other skin cells to protect them from ultraviolet rays, melanocytes have long, slender projections that interpenetrate other cells.

    Sperm Cells

    • The sperm cell resembles a snake with a pointed head, a powerhouse midsection and a long tail called a flagellum. The midsection contains numerous mitochondria, the cellular structures that convert energy into a form the cell can use, to power its flagellum, according to Tortora. Through undulating, the flagellum propels the sperm cell forward so that it might eventually reach the egg.

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