Membrane Dynamics 5

The Body Is Mostly Water Distribution of water volume in the three body fluid compartments Figure 5-28

Osmosis and Osmotic Pressure Osmolarity describes the number of particles in solution Figure 5-29

Osmosis and Osmotic Pressure Figure 5-29 (1 of 3)

Osmosis and Osmotic Pressure Figure 5-29 (2 of 3)

Osmosis and Osmotic Pressure Figure 5-29 (3 of 3)

Osmolarity: Comparing Solutions Solution A = 1 OsM Glucose Solution B = 2 OsM Glucose B is hyperosmotic to A A is hyposmotic to B What would be the osmolarity of a solution which is isosmotic to A? to B?

Tonicity Tonicity describes the volume change of a cell placed in a solution

Tonicity Tonicity depends on the relative concentrations of nonpenetrating solutes Figure 5-30a

Tonicity Tonicity depends on nonpenetrating solutes only Figure 5-30b

Electricity Review Law of conservation of electrical charges Opposite charges attract; like charges repel each other Separating positive charges from negative charges requires energy Conductor versus insulator

Separation of Electrical Charges Resting membrane potential is the electrical gradient between ECF and ICF Figure 5-32b

Separation of Electrical Charges Resting membrane potential is the electrical gradient between ECF and ICF Figure 5-32c

Potassium Equilibrium Potential Figure 5-34a

Potassium Equilibrium Potential Figure 5-34b

Potassium Equilibrium Potential Resting membrane potential is due mostly to potassium Figure 5-34c

Sodium Equilibrium Potential Can be calculated using the Nernst Equation Figure 5-35

Changes in Membrane Potential Terminology associated with changes in membrane potential PLAY Animation: Nervous I: The Membrane Potential Figure 5-37

Insulin Secretion and Membrane Transport Processes Low glucose levels in blood No insulin secretion Metabolism slows. ATP decreases. Glucose Cell at resting membrane potential; no insulin is released. KATP channels open. Insulin in secretory vesicles K+ leaks out of cell Voltage-gated Ca2+ channel closed GLUT transporter (a) Beta cell at rest. The KATP channel is open and the cell is at its resting membrane potential. K+ 2 3 1 4 5 Figure 5-38a

Insulin Secretion and Membrane Transport Processes Low glucose levels in blood Glucose (a) Beta cell at rest. The KATP channel is open and the cell is at its resting membrane potential. 1 Figure 5-38a, step 1

Insulin Secretion and Membrane Transport Processes Low glucose levels in blood Metabolism slows. Glucose GLUT transporter (a) Beta cell at rest. The KATP channel is open and the cell is at its resting membrane potential. 2 1 Figure 5-38a, steps 1–2

Insulin Secretion and Membrane Transport Processes Low glucose levels in blood Metabolism slows. ATP decreases. Glucose GLUT transporter (a) Beta cell at rest. The KATP channel is open and the cell is at its resting membrane potential. 2 3 1 Figure 5-38a, steps 1–3

Insulin Secretion and Membrane Transport Processes Low glucose levels in blood Metabolism slows. ATP decreases. Glucose KATP channels open. K+ leaks out of cell GLUT transporter (a) Beta cell at rest. The KATP channel is open and the cell is at its resting membrane potential. K+ 2 3 1 4 Figure 5-38a, steps 1–4

Insulin Secretion and Membrane Transport Processes Low glucose levels in blood No insulin secretion Metabolism slows. ATP decreases. Glucose Cell at resting membrane potential; no insulin is released. KATP channels open. Insulin in secretory vesicles K+ leaks out of cell Voltage-gated Ca2+ channel closed GLUT transporter (a) Beta cell at rest. The KATP channel is open and the cell is at its resting membrane potential. K+ 2 3 1 4 5 Figure 5-38a, steps 1–5

Insulin Secretion and Membrane Transport Processes Glycolysis and citric acid cycle ATP Ca2+ signal triggers exocytosis, and insulin is secreted. Ca2+ (b) Beta cell secreting insulin. Closure of the KATP channel depolarizes the cell, triggering exocytosis of insulin. High glucose levels in blood Metabolism increases. Glucose Cell depolarizes and calcium channels open. KATP channels close. Ca2+ entry acts as an intracellular signal. GLUT transporter 2 3 1 4 5 6 7 Figure 5-38b

Insulin Secretion and Membrane Transport Processes Beta cell secreting insulin. Closure of the KATP channel depolarizes the cell, triggering exocytosis of insulin. High glucose levels in blood Glucose 1 Figure 5-38b, step 1

Insulin Secretion and Membrane Transport Processes Glycolysis and citric acid cycle (b) Beta cell secreting insulin. Closure of the KATP channel depolarizes the cell, triggering exocytosis of insulin. High glucose levels in blood Metabolism increases. Glucose GLUT transporter 2 1 Figure 5-38b, steps 1–2

Insulin Secretion and Membrane Transport Processes Glycolysis and citric acid cycle ATP (b) Beta cell secreting insulin. Closure of the KATP channel depolarizes the cell, triggering exocytosis of insulin. High glucose levels in blood Metabolism increases. Glucose GLUT transporter 2 3 1 Figure 5-38b, steps 1–3

Insulin Secretion and Membrane Transport Processes Glycolysis and citric acid cycle ATP (b) Beta cell secreting insulin. Closure of the KATP channel depolarizes the cell, triggering exocytosis of insulin. High glucose levels in blood Metabolism increases. Glucose KATP channels close. GLUT transporter 2 3 1 4 Figure 5-38b, steps 1–4

Insulin Secretion and Membrane Transport Processes Glycolysis and citric acid cycle ATP (b) Beta cell secreting insulin. Closure of the KATP channel depolarizes the cell, triggering exocytosis of insulin. High glucose levels in blood Metabolism increases. Glucose Cell depolarizes and calcium channels open. KATP channels close. GLUT transporter 2 3 1 4 5 Figure 5-38b, steps 1–5

Insulin Secretion and Membrane Transport Processes Glycolysis and citric acid cycle ATP Ca2+ (b) Beta cell secreting insulin. Closure of the KATP channel depolarizes the cell, triggering exocytosis of insulin. High glucose levels in blood Metabolism increases. Glucose Cell depolarizes and calcium channels open. KATP channels close. Ca2+ entry acts as an intracellular signal. GLUT transporter 2 3 1 4 5 6 Figure 5-38b, steps 1–6

Insulin Secretion and Membrane Transport Processes Glycolysis and citric acid cycle ATP Ca2+ signal triggers exocytosis, and insulin is secreted. Ca2+ (b) Beta cell secreting insulin. Closure of the KATP channel depolarizes the cell, triggering exocytosis of insulin. High glucose levels in blood Metabolism increases. Glucose Cell depolarizes and calcium channels open. KATP channels close. Ca2+ entry acts as an intracellular signal. GLUT transporter 2 3 1 4 5 6 7 Figure 5-38b, steps 1–7

Summary Mass balance and homeostasis Law of mass balance Excretion Metabolism Clearance Chemical disequilibrium Electrical disequilibrium Osmotic equilibrium

Summary Diffusion Protein-mediated transport Roles of membrane proteins Channel proteins Carrier proteins Active transport

Summary Vesicular transport Transepithelial transport Phagocytosis Endocytosis Exocytosis Transepithelial transport

Summary Osmosis and tonicity The resting membrane potential Osmolarity Nonpenetrating solutes Tonicity The resting membrane potential Insulin secretion