ANSC 3301 Lecture 4: 11 February
● Regulatory volume increases and decreases
○ Cells transport solutes in and out of the extracellular fluid to control cell volume
○ This regulates the composition of the ECF to provide cells with an external solution that
allows them to maintain an appropriate cell volume
■ Fluid will always follow solute movement!
○ Calcium is an important second messenger for muscle contraction
● Regulation of intracellular pH
○ pH is a measure of free proton concentration within a cell and there are buffers like
bicarbonate, phosphates and proteins that influence intracellular pH
■ Only free protons play a role in pH!
○ First intracellular pH is normally about 7.2
■ If it falls (more acidic) it increases the activity of the sodium proton exchanger
to remove protons to bring the pH back up to normal
● Uses sodium gradient to remove free protons (H+) out of the cell
■ If the pH increases (free proton levels are dropping)
● Cell will inhibit sodium proton exchanger and increase the chloride
bicarbonate exchanger which will decrease the pH by removing buffer
(HCO3-)
Epithelial Transport
● Epithelial tissues form the boundary between the animal and the environment
○ Line lungs, mouth, intestine
● These tissues also have physiological functions such as respiration, digestion and ion and osmoregulation
● Epithelial cell structures
○ Flat sheets- epidermis (skin)
○ Tubules- kidney
■ Have ability to modify fluid
○ Glands
■ Crypts: small intestine, colon
■ Acinar: salivary, mammary glands
■ Tubular: endometrial glands
● Exocrine gland: secrete fluid and substances to the external environment
○ pancreas
● Endocrine gland: secrete fluid into blood supply
● Types of junctions between cells
○ Tight junctions: does not allow for movement of electrolytes between cells
■ Can start to transport proteins to different sides
■ Transcellular: going through the cell
■ Paracellular: going in between the cell
■ Following the formation of tight junctions, epithelial cells become polarized
○ Septate junctions:
○ Desmosome: form stronger bond, bound to cytoskeletal elements
○ Gap junction: specialized protein complexes that create an aqueous pore between two adjacent
cells
■ communicating junction, hemichannels without moving into aqueous environment
■ Typically involves the movement of ions
■ Important in the heart as it allows the cells to beat in a coordinated fashion
● UTP stimulation of anion secretion
○ Promotes Chloride to move transcellular to attract positive ions (Na+) to follow
Document Summary
Cells transport solutes in and out of the extracellular fluid to control cell volume. This regulates the composition of the ecf to provide cells with an external solution that allows them to maintain an appropriate cell volume. Calcium is an important second messenger for muscle contraction. Ph is a measure of free proton concentration within a cell and there are buffers like bicarbonate, phosphates and proteins that influence intracellular ph. Only free protons play a role in ph! First intracellular ph is normally about 7. 2. If it falls (more acidic) it increases the activity of the sodium proton exchanger to remove protons to bring the ph back up to normal. Uses sodium gradient to remove free protons (h+) out of the cell. If the ph increases (free proton levels are dropping) Cell will inhibit sodium proton exchanger and increase the chloride bicarbonate exchanger which will decrease the ph by removing buffer (hco3-)
