B2.3.7 Adaptations to increase surface area to volume ratios of cells

adaptations to increase SA:V ratio

• forming long, thin extensions

• having a thin, flat shape

• forming invaginations or microvilli

long and thin extensions of the cell membrane

significantly expand cell’s surface area while adding only a small amount to overall volume

• examples: phagocytic cell of mammal immune system, branches of cell of chordate nervous system, epidermis cells form root hairs in plants

thin and flat shape of cell

maximizes amount of surface area exposed relative to the volume it occupies more than a thicker/more rounded shape

• red blood cells (erythrocytes) exchange and transport O₂

• thinness of type 1 pneumocyte cells in lung alveoli reduces distances for diffusion of gases

• thin, flat epithelial cells form the tube of a capillary vessel for maximizing gas and nutrient exchange with tissue cell

invaginations

cavity formed when a surface folds inward to create an indentation

microvilli

small finger-like projections that are tiny invaginations of the cell membrane of a single cell; drastically increase overall surface area available without significantly increasing cell’s volume

• on the surface of cells in small intestine - increase surface area for absorbing nutrients from digested food

• on the surface of cells in kidney proximal convoluted tubule - increase surface area for reabsorbed useful substances before excretion in urine

alveolar epithelium

example of tissue where more than one cell type is present

• type I and II pneumocytes, blood capillary cells, erythrocytes

• different adaptations required for overall function of tissue

adaptation of type I pneumocytes

extreme thinness to reduce distance for diffusion

adaptation of type II pneumocytes

many secretory vesicles (lamellar bodies) in their cytoplasm, make and release surfactant to alveolar lumen

adaptation of blood capillary cells

thin to enable diffusion

adaptation of erythrocytes

• small size to allow them to flow in capillaries

• biconcave shape to increase surface area

• contain hemoglobin to carry oxygen as oxyhemoglobin