Osmosis, tonicity, and cell volume are regulated by the permeability of cell membranes to water and solutes. Water moves across membranes through aquaporin channels and by osmosis down its concentration gradient. The osmolarity of extracellular fluid is normally 300 mOsm, and cells maintain volume by moving water in or out depending if the extracellular fluid is hypo- or hypertonic. The kidneys help maintain electrolyte and acid-base balance by reabsorbing or secreting ions like sodium, potassium, hydrogen, and bicarbonate to keep fluid volumes and pH within normal ranges.

6. Effects of Tonicity on RBCs Hypotonic, isotonic and hypertonic solutions affect the fluid volume of a red blood cell. Notice the crenated and swollen cells.

12. Receptor Mediated Endocytosis

14. Phagocytosis or “Cell-Eating”

16. Vesicular Transport: Exocytosis

24. Permeable to water, Not permeable to solutes Presence of a membrane Impermeable to solute That leads to the volume Changes associated with Osmosis.

28. Water diffuses in Water diffuses out

31. Transport, the big picture fig 4-15

32. Facilitated diffusion (properties) Passive, carrier mediated Examples: glucose into most cells (not luminal membrane of kidney or intestine), urea, some amino acids Kinetics: shows: passive shows: carrier mediated

33. Non-mediated vs. mediated transport fig 4-9

34. Primary active transport (Na + /K + ATPase pump) 3 Na + ’s out, 2 K + ’s in, 1 ATP hydrolyzed fig 4-11

35. Primary active transport (Na + /K + ATPase pump) 3 Na + ’s out, 2 K + ’s in, 1 ATP hydrolyzed fig 4-11

36. Primary active transport kinetics shows active transport shows carrier mediated

37. Effect of Na + /K + ATPase pump fig 4-12

38. Secondary active transport fig 4-13

39. Secondary active transport properties Active (energy from ion gradient, usually Na + ) Carrier mediated Can be cotransport (symport) or countertransport (antiport) Examples (many): Na + /amino acids, Na + /glucose (luminal membrane kidney, GI tract), *Na + /H + kidney, *Ca ++ /3Na + muscle, *Cl - /HCO 3 - red cell. (* = countertransport) Kinetics see primary active transport graphs

45. Mechanism of Na + Selective Reabsorption in Collecting Duct Figure 20-12: Aldosterone action in principal cells

48. Artial Natruretic Peptide: Regulates Na + & H 2 O Excretion Figure 20-15: Atrial natriuretic peptide

50. Potassium Balance: Critical for Excitable Heart & Nervous Tissues Figure 20-4: Osmolarity changes as fluid flows through the nephron

51. Potassium Balance: Critical for Excitable Heart & Nervous Tissues Figure 20-12: Aldosterone action in principal cells

53. Response to Dehydration & Osmolarity Imbalance

62. Acid/Base Homeostasis: Overview Figure 20-18: Hydrogen balance in the body

64. Kidney Hydrogen Ion Balancing: Proximal Tubule Figure 20-21: Proximal tubule secretion and reabsorption of filtered HCO 3 -

66. Kidney Hydrogen Ion Balancing: Collecting Duct Figure 20-22: Role of the intercalated cell in acidosis and alkalosis