Lecture 20.docx

Lecture 20  What does the kidney do?  Maintains normal volume and composition of body fluid compartments  Excretes waste products from the body  Helps maintain blood pressure, hemoglobin levels and calcium levels through hormone secretion  How does the kidney do this  Filters a large volume of plasma water and solutes (at the glomerulus)  Filtered fluid enters tubules which add or remove water and solutes to form the final urine, which is excreted  Secretes hormones in response to changes in blood pressure, hemoglobin and calcium  Objectives  Know the body fluid compartments and what determines their volume and composition  Understand the factors which regulate glomerular filtration  Understand how tubules regulate the excretion of sodium, potassium, water and hydrogen ion  Understand the physiology of renin/angiotensin, erythropoietin and vitamin D  Case of the day: The seizing marathoner  A 45 year old women runs her first marathon after 6 months of training  Finished in 5 hours  Complained headache  Felt nauseated, vomited then had a grand mal seizure  Serum sodium was 122 mmol/L (Normal value being 140 mmol)  Some Definitions  Nephro = renal = kidney  Nephrologist, renal artery, kidney failure  Solutes = particle dissolved in a water solution  Sodium, Potassium, Glucose, etc.  Ions (electrolytes) = charged solutes – cations are + and anions are –  Osmolality = the total concentration of solutes in water which generates an osmotic force  Osmosis  The movement of water across a semi-permeable membrane in response to an osmotic gradient  The osmotic gradient  difference in the osmolality in the compartments separated by the membrane  Water moves from the compartment with low osmolarity to that of high osmolality  Hypotonic  refers to a solution which has a lower osmotic pressure (low concentration of solutes than other solutions)  Hypertonic  refers to a solution which has a higher osmotic pressure (higher concentration of solutes than other solution)  Osmosis can generate a pressure which is equivalent to that of hydrostatic pressure  Body Fluid Compartments  Humans are 50-60%  A simplified view of the body  Body water in two major compartments  Intracellular space  Extracellular space  About 2/3 is inside cells = =Intracellular fluid (ICF)  28 L  Intracellular Fluid  Bounded by cell membrane  About 1/3 is outside cells = Extracellular fluid (ECF)  14 L  Plasma 25%, Interstitial Fluid 75%  Plasma  Bounded by the capillaries  Interstitial fluid  Separated from blood stream by capillary wall and separated from the cell by cell membrane  What Factors Determine Body Water as a Fraction of Weight  Ratio of Fat/Muscle  Fat has very little water; muscle has a lot of water; muscle contains most water in the body  On average, there is more fat/muscle in:  Women compared to men (50% vs. 60%)  Older compared than younger  Chronic illness compared to healthy  Solutes in Body Fluids  Ions/Electrolytes  + Sodium, potassium, calcium, magnesium  - Chloride, bicarbonate, phosphate and protein  Fuels  Glucose, lactate, amino acids, ketoacids  Proteins  Albumin, globulin, hormones  Waste Products  Urea, creatinine, uric acid, etc.  Ions in the ICF and plasma (mEq/L)  Sodium  Charge [+], ICF [10], Plasma [140]  Potassium  Charge [+], ICF [150], Plasma [4]  Calcium  Charge [+], ICF [0.005], Plasma [3]  Chloride  Charge [-], ICF [4], Plasma [102]  Behaves like sodium  Bicarbonate  Charge [-], ICF [10], Plasma [24]  Protein/Phosphates  Charge [-], ICF [130], Plasma [14]  ICF vs. ECF  Osmolality (particles per volume)  ICF = ECF (because water will cross cell membranes through water channels (generally, except a few compartments in the kidney) when there is an osmotic gradient therefore there is no osmotic gradient between ICF and ECF  Charge  Cells have a negative charge compared to ECF  How are differences between ICF and ECF generated?  1) Sodium-Potassium ATPase  one of the most important pumps in the body  3 Na+ Out  2 K+ In  Hydrolyzes 1 ATP per exchange  Because of the unequal charge cross, this exchange leaves the cell negative. How do you maintain an electoral gradient? The vast bulk of ICF anions are macromolecules, proteins and organic solvents and cannot leak out because of their size.  2) Fixed intracellular polyanions – organic phosphate and proteins  3) Multiple Ion Channels  Why is the cell