Specialized absorptive cells increase effective surface area and transport capacity through microvilli, transport proteins, mitochondria, and short diffusion paths in epithelia.
Coverage 2016–2018 · Updated 15 Jul 2026
Cells can raise effective surface area-to-volume ratio by flattening, forming surface projections such as microvilli, or invaginating the plasma membrane.
Flattening adds exchange area and shortens diffusion distance. Microvilli and membrane invaginations add membrane area with little extra cytoplasmic volume, providing more space for channels, carriers and pumps.
Human erythrocytes are flattened into biconcave discs, increasing area and keeping haemoglobin close to the surface. Proximal convoluted tubule cells have apical microvilli for reabsorption and basal membrane invaginations that provide additional transport surface.
A proximal-tubule cell can accommodate many sodium-linked transport proteins on its microvilli, increasing the rate at which filtered solutes are reabsorbed without a proportional increase in cell volume.
More membrane area improves exchange only when suitable gradients, transport proteins and energy supplies are present. Microvilli are cell-surface projections, not multicellular villi.
This objective is assessed through multiple choice, commonly using Identify / State / Explain.
Identify / State / Explain / Describe
Build the answer around this relationship: Microvilli increase membrane surface area for absorption.
Naming microvilli without stating that they increase surface area for absorption.
Representative question
Where are microvilli located in the nephron?
Glomerulus
Proximal convoluted tubule
Loop of Henle
Collecting duct
A strong answer identifies the cell, names the structural adaptation, and states the function it improves. Erythrocytes and PCT cells show exchange and transport adaptations; pneumocytes show diffusion versus secretion; muscles show contraction coordination; gametes show fertilization roles.
