Overview
This lecture covers the main concepts of cellular form and function, focusing on cell shapes, basic cell theory, terminology roots, and the most useful measurements for cell size.
Major Types of Cell Receptors
- Intracellular receptors allow ligands to enter the cell directly to deliver a message.
- Membrane receptors allow ligands to attach to the cell membrane to send messages without entering the cell.
Cell Shapes and Examples
- Squamous cells are thin, flat, and scaly, like fried eggs; they line the esophagus and skin surface.
- Cuboidal cells are roughly square-shaped in frontal tissue sections; found in liver cells.
- Columnar cells are taller than they are wide; found in the inner lining of the stomach and intestines.
- Polygonal cells have irregular, angular shapes with several sides.
- Stellate cells have multiple pointed processes, giving a starlike appearance; seen in some nerve cell bodies.
- Spheroidal to ovoid cells are round to oval; seen in egg cells and white blood cells.
- Discoid cells are disc-shaped; characteristic of red blood cells.
- Fusiform cells are spindle-shaped, elongated with thick middles and tapered ends; seen in smooth muscle cells.
- Fibrous cells are long, slender, and threadlike; found in skeletal muscle and nerve fibers.
Principles of Cell Study and Measurement
- Cytology is the scientific study of cells.
- The micrometer (μm) is the most useful unit for measuring cell size; most human cells are 10–15 μm wide.
- The naked eye can typically see objects larger than 100 μm.
- The longest human cells are nerve and muscle cells.
Modern Cell Theory
- All organisms are made up of cells.
- Cells originate from preexisting cells.
- Cells have many structural similarities.
- An organism’s structure and function result from the activities of its cells.
Key Terms & Definitions
- Cytology — the study of cells.
- Squamous — thin, flat cell shape.
- Cuboidal — cube-shaped or square cell.
- Columnar — taller-than-wide cell shape.
- Polygonal — many-angled or irregularly shaped cell.
- Stellate — starlike cell shape.
- Spheroidal/Ovoid — round or oval cell shape.
- Discoid — disc-shaped cell.
- Fusiform — spindle-shaped cell.
- Fibrous — long and threadlike cell.
- Micrometer — one-millionth of a meter, used for cell measurement.
Action Items / Next Steps
- Review and memorize the different cell shapes and their examples.
- Learn the key root terms related to cell structure and biology.
- Study Modern Cell Theory for understanding foundational biology concepts.